# Patent

## Title
P-chiral phospholanes and phosphocyclic compounds and their use in asymmetric catalytic reactions

## Abstract

Chiral ligands and metal complexes based on such chiral ligands useful in asymmetric catalysis are disclosed. The metal complexes according to the present invention are useful as catalysts in asymmetric reactions, such as, hydrogenation, hydride transfer, allylic alkylation, hydrosilylation, hydroboration, hydrovinylation, hydroformylation, olefin metathesis, hydrocarboxylation, isomerization, cyclopropanation, Diels-Alder reaction, Heck reaction, isomerization, Aldol reaction, Michael addition; epoxidation, kinetic resolution and [m+n] cycloaddition. Processes for the preparation of the ligands are also described.

## Background
This application is a Divisional Application of and claims priority from U.S. application Ser. No. 10/856,014, filed on May 28, 2004, which is a Continuation-In-Part of and claims priority from U.S. application Ser. No. 10/291,232, filed on Nov. 8, 2002 and claims priority from U.S. Provisional Application Ser. No. 60/336,939, filed Nov. 9, 2001. All of the aforementioned applications are incorporated herein in their entirety.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to novel chiral ligands derived from P-chiral phospholanes and P-chiral phosphocyclic compounds and catalysts for applications in asymmetric catalysis. More particularly, the present invention relates to transition metal complexes of these chiral phosphine ligands, which are useful as catalysts in asymmetric reactions, such as, hydrogenation, hydride transfer, hydrocarboxylation, hydrosilylation, hydroboration, hydrovinylation, hydroformylation, allylic alkylation, olefin metathesis, isomerization, cyclopropanation, Diels-Alder reaction, Heck reaction, Aldol reaction, Michael addition, epoxidation, kinetic resolution and [m+n] cycloaddition.
2. Description of the Prior Art
Molecular chirality plays an important role in science and technology. The biological activities of many pharmaceuticals, fragrances, food additives and agrochemicals are often associated with their absolute molecular configuration. A growing demand in pharmaceutical and fine chemical industries is to develop cost-effective processes for the manufacture of single-enantiomeric products. To meet this challenge, chemists have explored many approaches for acquiring enantiomerically pure compounds ranging from optical resolution and structural modification of naturally occurring chiral substances to asymmetric catalysis using synthetic chiral catalysts and enzymes. Among these methods, asymmetric catalysis is perhaps the most efficient because a small amount of a chiral catalyst can be used to produce a large quantity of a chiral target molecule [Book, Ojima, I., Ed. Catalytic Asymmetric Synthesis, VCH, New York, 1993 and Noyori, R. Asymmetric Catalysis In Organic Synthesis, John Wiley & Sons, Inc., New York, 1994].
Asymmetric hydrogenation accounts for major part of all asymmetric synthesis on a commercial scale. Some dramatic examples of industrial applications of asymmetric synthesis include Monsanto's L-DOPA synthesis (asymmetric hydrogenation of a dehydroamino acid, 94% ee, 20,000 turnovers with a Rh-DIPAMP complex) [Knowles, W. S. Acc. Chem. Res. 1983, 16, 106], Takasago's L-menthol synthesis (asymmetric isomerization, 98% ee, 300,000 turnovers with a Rh-BINAP complex) [Noyori, R.; Takaya, H. Acc. Chem. Res. 1990, 23, 345] and Norvatis' (S)-Metolachlor synthesis (asymmetric hydrogenation of an imine, 80% ee, 1,000,000 turnovers with an Ir-ferrocenyl phosphine complex) [Spindler, F.; Pugin, B.; Jalett, H.-P., Buser, H.-P.; Pittelkow, U.; Blaser, H,-U., Altanta, 1996; Chem. Ind. (Dekker), 1996, 63 and Tongni, A. Angew. Chem. Int. Ed. Engl. 1996, 356, 14575].
Invention of chiral ligands for transition metal-catalyzed reactions plays a critical role in asymmetric catalysis. Not only the enantioselectivity depends on the framework of chiral ligands, reactivities can often be altered by changing the steric and electronic structure of the ligands.
Since small changes in the ligand can influence the (delta)(delta)G of the rate-determining step, it is very hard to predict which ligand can be effective for any particular reaction or substrate. Accordingly, discovery of new chiral ligands sets the foundation of highly enantioselective transition metal-catalyzed reactions.
In recent years, a large number of chiral ligands have been developed for use in asymmetric catalysis reactions. Despite this, only few chiral ligands have been found to be suitable for use in industry for the production of chiral molecules that require high selectivity.
One of the earliest P-chiral phosphine ligands is DIPAMP, which was developed by Knowles, J. Am. Chem. Soc., 99, 5946 (1977). The Rh(I)-DIPAMP complex has been used in the synthesis of L-DOPA.
There are continuing efforts from many groups to develop strategies for making P-chiral ligands for asymmetric catalysis, including, for example, the following: I. Ojima, Ed., Catalytic Asymmetric Synthesis, 2nd ed., VCH publishers, Wheinheim, 2000. Juge and Genet, Tetrahedron Left., 30, 6357 (1989), who have developed a method for making P-chiral phosphines. E. J. Corey, J. Am. Chem. Soc., 115, 11000 (1993), who has developed a method for preparing P-chiral phosphines and diphosphines. An enantioselective deprotonation as a method for the synthesis of P-chiral phosphines has been applied by Evans, J. Am. Chem. Soc., 117, 9075 (1995). Typically, phosphine-borane, phosphine sulfides have been used. Enantioselective deprotonation of these compounds and Cu-mediated coupling reactions can produce a number of diphosphines. A Cu-mediated coupling reaction was reported by Mislow, J. Am. Chem. Soc., 95, 5839 (1973). Formation of phosphine-borane and removal of borane have been reported by Imamoto, J. Am. Chem. Soc., 112, 5244 (1990), Yamago, J. Chem. Soc., Chem. Commun., 2093 (1994) and Livinghouse, Tetrahedron Lett., 35, 9319 (1994). Desulfurization of phosphine sulfides is reported by Mislow, J. Am. Chem., Soc., 91, 7023 (1969). More recently, Imamoto has successfully used these strategies to make a number of P-chiral phosphines such as BisP*, J. Am. Chem. Soc., 123, 5268 (2001), MiniPhos, J. Org. Chem., 64, 2988 (1999) and other mixed P-chiral ligands, Org. Lett., 3, 373 (2001).
These ligands have been used effectively in many asymmetric reactions, especially in asymmetric hydrogenation reactions, such as those described in Adv. Synth. Catal., 343, 118 (2001).
Some of these ligands are depicted below:




Despite the wide variation in the substituted groups in the above ligands, the majority of these ligands are derivatives of the DIPAMP ligand. A possible drawback of these ligands is that ligands having a DIPAMP structure are conformationally flexible and, as a result, enantioselectivity is difficult to optimize.
In contrast to the ligands of the prior art, the present invention provides a phospholane and phosphocyclic structure to restrict the conformational flexibility such that a high enantioselectivity can be achieved in the transition metal catalysts prepared from these ligands.
Thus, from a stereochemical point of view, additional stereogenic centers (e.g. four or more stereogenic centers) are typically created to make the novel ligands of the present invention substantially more selective in asymmetric catalytic reactions than, for example, the DIPAMP and BisP* ligands, which have only two stereogenic centers.
SUMMARY OF THE INVENTION
The present invention provides a chiral ligand represented by the following formula or its enantiomer:




wherein X is can be Z, Z-(CR4R5)n, (CR4R5)n-Z-(CR4R5)n, (CR4R5)n, CH2CH(OR′)CH(OR′), CH2CH(OH)CH(OH), CH2CH(OCR′2O)CH, CH2CH(OalkylO)CH, CH2CH(OCHR′O)CH, CH2(C6H4), CH2(Ar), CH2(hetereoaryl), CH2(alkenyl), arylene, substituted arylene, CH2(biaryl), CH2(ferrocene), divalent aryl, 1,2-divalent phenyl (ortho-phenylene), 2,2′-divalent-1,1′-biphenyl, 2,2′-divalent-1,1′-binaphthyl, divalent hetereoaryl, divalent ferrocene, SiR′2, PR′, NR6 and group represented by the formula:




wherein each n is independently an integer from 1 to 6;
wherein Z can be O, S, —COO—, —CO—, O—(CR4R5)n—O, CH2(C6H4), CH2(Ar), CH2(hetereoaryl), alkenyl, CH2(alkenyl), C5H3N, divalent aryl, 1,2-divalent phenyl (ortho-phenylene), 2,2′-divalent-1,1′-biphenyl, 2,2′-divalent-1,1′-binaphthyl, divalent hetereoaryl, divalent ferrocene, SiR′2, PR′ and NR6 wherein each of R′ and R6 is independently can be hydrogen, alkyl, substituted alkyl, aryl, substituted aryl, hydroxy, alkoxy, aryloxy, acyl and alkoxycarbonyl;
wherein E can be PR′2, PR′R′′, o-substituted pyridine, oxazoline, chiral oxazoline, CH2(chiral oxazoline), CR′2(chiral oxazoline), CH2PR′2, CH2(o-substituted pyridine), SiR′3, CR′2OH and a group represented by the formula:




wherein Y can be a bond, (CR4R5)m, Z, Z-(CR4R5)m and (CR4R5)m-Z-(CR4R5)m; wherein each m is independently an integer from 0 to 3;
wherein each R, R′, R′′ R′′′, R4 and R5 is independently hydrogen, linear, branched or cyclic alkyl, substituted alkyl, aryl, substituted aryl, hetereoaryl, ferrocenyl, halogen, hydroxy, alkoxy, aryloxy, alkylthio, arylthio and amido; and
wherein X and Z are have the same meaning as above.
More particularly, the present invention provides a chiral ligand represented by the formula and its enantiomer:




wherein R can be CH3, Et, i-Pr, t-Bu, Et3C, 2-ethylhexyl, 1-adamantyl, cyclopentyl, cyclohexyl, phenyl, naphthyl, ortho-anisyl, 3,5-dimethylphenyl, 3,5-di-t-butyl phenyl, p-tolyl and ferrocene.
The present invention further provides a catalyst prepared by a process including:
contacting a transition metal salt, or a complex thereof, and a chiral ligand according to the present invention as described herein above.
The present invention still further provides a process for preparation of an asymmetric compound including:
contacting a substrate capable of forming an asymmetric product by an asymmetric reaction and a catalyst prepared by a process including: contacting a transition metal salt, or a complex thereof, and a chiral ligand according to the present invention as described herein above.
The present invention still further provides a process for preparing (1R,1R′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl-1,1′-disulfide including the steps of:
asymmetrically deprotonating a 1-alkyl-phospholane-1-sulfide with n-butyllithium/(−)-sparteine in a solvent to produce an anion of the 1-alkyl-phospholane-1-sulfide; and
contacting the anion of the 1-alkyl-phospholane-1-sulfide and CuCl2 to oxidatively couple the anion of the 1-alkyl-phospholane-1-sulfide and produce a reaction mixture including the (1R,1R′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl-1,1′-disulfide.
Further still, the present invention provides a process for preparing (1S,1S′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl including the steps of:
asymmetrically deprotonating a 1-alkyl-phospholane-1-sulfide with n-butyllithium/(−)-sparteine in a solvent to produce an anion of the 1-alkyl-phospholane-1-sulfide;
contacting the anion of the 1-alkyl-phospholane-1-sulfide and CuCl2 to oxidatively couple the anion of the 1-alkyl-phospholane-1-sulfide and produce a reaction mixture including (1R,1R′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl-1,1′-disulfide;
recrystallizing the (1R,1R′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl-1,1′-disulfide from the reaction mixture; and
contacting the (1R,1R′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl-1,1′-disulfide and hexachlorodisilane in a solvent to produce (1S,1S′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl.
Additionally, the present invention provides processes for preparing a chiral cyclic phosphine oxide intermediate, represented by the formula:




The first process includes the steps of:
contacting an alkyl or aryl phosphine represented by the formula ArPH2 and an alkyl lithium to deprotonate said alkyl or aryl phosphine and produce a lithium salt thereof;
contacting said deprotonated alkyl or aryl phosphine and a cyclic sulfate represented by the formula:




to produce a cyclic phosphine represented by the formula:




and
contacting said cyclic phosphine and an oxidizing agent to produce the chiral phosphine oxide;
wherein each R, R′, R′′ can independently be hydrogen, linear, branched or cyclic alkyl, substituted alkyl, aryl, substituted aryl, alkoxy, aryloxy, alkylthio, and arylthio groups.
The second process includes the steps of:
contacting a 1,2-bis-(halomethyl)arene represented by the formula:




and an alkyl lithium or magnesium metal to produce a lithium salt or Grignard Reagent thereof;

contacting said lithium salt or Grignard Reagent and RP(W)2 to produce a cyclic phosphine represented by the formula:




and
contacting said cyclic phosphine and an oxidizing agent to produce the chiral phosphine oxide;
wherein W is a halogen; and
wherein each R, R′, R′′ can independently be hydrogen, linear, branched or cyclic alkyl, substituted alkyl, aryl, substituted aryl, alkoxy, aryloxy, alkylthio, and arylthio groups.
The presence of additional stereogenic centers (e.g. four or more stereogenic centers) in the novel ligands of the present invention makes them substantially more selective in asymmetric catalytic reactions than, for example, the DIPAMP and BisP* ligands, which have only two stereogenic centers.


DETAILED DESCRIPTION OF THE INVENTION
The present invention provides novel P-chiral phospholane and phosphocyclic compounds and described their use in asymmetric catalysis.
Introduction of cyclic structures can restrict the rotation of substituents adjacent to the phosphines and control of orientations of these groups around phosphine can lead effective chiral induction for asymmetric reactions. Metal complexes of these phosphines, and related none C2 symmetric ligands are useful for many asymmetric reactions.
Tunability of ligand chiral environment is crucial for achieving high enantioselectivity. The steric and electronic structure of the conformationally rigid cyclic phosphines can be fine-tuned by variation of ring size and substituents.
Several new chiral phosphines are developed for asymmetric catalytic reactions. A variety of asymmetric reactions, such as, hydrogenation, hydride transfer, allylic alkylation, hydrosilylation, hydroboration, hydrovinylation, hydroformylation, olefin metathesis, hydrocarboxylation, isomerization, cyclopropanation, Diels-Alder reaction, Heck reaction, isomerization, Aldol reaction, Michael addition, epoxidation, kinetic resolution and [m+n] cycloaddition were developed with these chiral ligands systems.
The ligands of the present invention can be a racemic mixture of enantiomers. Preferably, the ligand is a non-racemic mixture of enantiomers, and more preferably, the ligand is one of the enantiomers. Preferably, the ligand has an optical purity of at least 85% ee, and more preferably, the ligand has an optical purity of at least 95% ee.
Representative examples of chiral ligands of the current invention are shown below. A number of chiral ligands with desired structures according to the present invention can be made and used in the preparation of the catalysts described in the present invention.




    X=(CH2)n, n=1, 2, 3, 4, 5, 6. CH2OCH2, CH2NHCH2, CH2CH(R′)CH(R′), CH2CH(OR′)CH(OR′), CH2CH(OH)CH(OH), CH2CH(OCR′2O)CH, CH2CH(OalkylO)CH, CH2CH(OCHR′O)CH, CH2NR′CH2, CH2CH2NR′CH2, CH2CH2OCH2, CH2(C6H4), CH2(Ar), CH2(hetereoaryl), CH2(alkenyl), alkyl, substituted alkyl, aryl, substituted aryl, CH2(biaryl), CH2(ferrocene).
    R=alkyl, aryl, substituted alkyl, substituted alkyl, hetereoaryl, ferrocene
    E=PR′2, PR′R′′, o-substituted pyridine, oxazoline, chiral oxazoline, CH2(chiral oxazoline), CR′2(chiral oxazoline), CH2PR′2, CH2(o-substituted pyridine), SiR′3, CR′2OH






then ligands are:





    Y=(CH2)n, n=0, 1, 2, 3, CH2NHCH2, CR′2, CO, SiR′2, C5H3N, C6H4, alkyl, substituted alkyl, divalent aryl, 2,2′divalent-1,1′biphenyl, substitued aryl, hetereoaryl, ferrocene
    R′=alkyl, aryl, substituted alkyl, aryl, alkylaryl, H.


In these ligands, the bridge group X for the phosphocyclic compounds are (CH2)n, n=1, 2, 3, 4, 5, 6. CH2OCH2, CH2NHCH2, CH2CH(R′)CH(R′), CH2CH(OR′)CH(OR′), CH2CH(OH)CH(OH), CH2CH(OCR′2O)CH, CH2CH(OalkylO)CH, CH2CH(OCHR′O)CH, CH2NR′CH2, CH2CH2NR′CH2, CH2CH2OCH2, CH2(C6H4), CH2(Ar), CH2(hetereoaryl), CH2(alkenyl), alkyl, substituted alkyl, aryl, substituted aryl, CH2(biaryl), CH2(ferrocene). R is alkyl, aryl, substituted alkyl, substituted aryl, hetereoaryl, ferrocene. E is PR′2, PR′R′′, o-substituted pyridine, oxazoline, chiral oxazoline, CH2(chiral oxazoline), CR′2(chiral oxazoline), CH2PR′2, CH2(o-substituted pyridine), SiR′3, CR′2OH.




then ligands are:





Y can be (CH2)n, n=0, 1, 2, 3, CH2NHCH2, CH2SCH2, CH2PR′CH2, CR′2, CO, SiR′2, C5H3N, C6H4, alkyl, substituted alkyl, divalent aryl, 2,2′divalent-1,1′biphenyl, substituted aryl, hetereoaryl, ferrocene. R′=alkyl, aryl, substituted alkyl, aryl, alkylaryl, H.
In a preferred embodiment, the ligand of the present invention includes compounds represented by the formulas wherein:
X can be (CH2)n wherein n is from 1 to 6, CH2OCH2, CH2NHCH2, CH2CH(R′)CH(R′), CH2CH(OR′)CH(OR′), CH2NR′CH2, CH2CH(OH)CH(OH), CH2CH2NR′CH2, CH2CH2OCH2 and a group represented by the formula:




wherein each R4 and R5 can independently be hydrogen, alkyl, aryl, substituted alkyl and substituted aryl; and wherein:
Y can be (CH2)n wherein n is from 0 to 3, CH2NHCH2, CH2SCH2, CH2PR′CH2, CR′2, CO, SiR′2, C5H3N, C6H4, alkylene, substituted alkylene, 1,2-divalent arylene, 2,2′-divalent-1,1′-biphenyl, substituted aryl, hetereoaryl and ferrocene.
More particularly, the chiral ligand can be represented by the formula and its enantiomer:




wherein R can be alkyl, aryl, substituted alkyl, substituted aryl, hetereoaryl, ferrocenyl, alkoxy and aryloxy; and
wherein n is from 0 to 2;
R can be CH3, Et, iPr, t-Bu, 1-adamantyl, Et3C, cyclo-C5H9, cyclo-C6H11, phenyl, p-tolyl, 3,5-dimethylphenyl, 3,5-di-t-butyl phenyl, ortho-anisyl and naphthyl.
Examples of such ligands include a ligand represented by the formula and its enantiomer:




and a ligand represented by the formula and its enantiomer:





Other preferred ligands include:
(1) chiral ligands represented by the formula:




wherein X is CH2(C6H4) to produce a five-membered ring wherein the CH2 group of the CH2(C6H4) is attached to the phosphorus atom and the aromatic carbon ortho- to the CH2 group of the CH2(C6H4) is attached to the chiralcarbon atom bonded to P, H, and the group E; and
(2) chiral ligand of claim 1, represented by the formula:




wherein X is CH2(C6H4) to produce a five-membered ring wherein wherein the CH2 group of the CH2(C6H4) is attached to the chiral carbon atom that is bonded to P, H, and the group E, and the aromatic carbon ortho- to the CH2 group of the CH2(C6H4) is attached to the phosphorus atom.
In these two classes of ligands, R is preferably, CH3, Et, i-Pr, t-Bu, Et3C, 2-ethylhexyl, 1-adamantyl, cyclopentyl, cyclohexyl, phenyl, naphthyl, ortho-anisyl, 3,5-dimethylphenyl, 3,5-di-t-butyl phenyl, p-tolyl or ferrocene.
The above two classes of ligands illustrate that when group X is unsymmetric, two different ring compounds can be formed depending on the points of attachment of an unsymmetric, such as, CH2(C6H4) represented by the formula:




to the group:





Accordingly, whenever two different compounds can result from combining the component groups in a chemical formula of the ligands, for example, by reversing the points of attachments of one of the component groups, the present application contemplates ligands that result from both approaches.
Other preferred chiral ligands include ligands represented by the following formulas or their enantiomers:




wherein R can be CH3, Et, i-Pr, t-Bu, Et3C, 2-ethylhexyl, 1-adamantyl, cyclopentyl, cyclohexyl, phenyl, naphthyl, ortho-anisyl, 3,5-dimethylphenyl, 3,5-di-t-butyl phenyl, p-tolyl and ferrocene;
(2) ligand represented by formula L9 or its enantiomer:




(3) ligand is represented by formula L16 or its enantiomer:




(4) a ligand represented by the formula or its enantiomer:




wherein the R group on the phosphorus is cis- or trans-isomer with respect to the group PR′R′′; and
(5) a ligand represented by the formula or its enantiomer:




and
(6) a ligand is represented by the formula or its enantiomer:




wherein R can be CH3, Et, i-Pr, t-Bu, Et3C, 2-ethylhexyl, 1-adamantyl, cyclopentyl, cyclohexyl, phenyl, naphthyl, ortho-anisyl, 3,5-dimethylphenyl, 3,5-di-t-butyl phenyl, p-tolyl and ferrocene; and
wherein X is a divalent group selected from CH2(C6H4), CH2(Ar), CH2(hetereoaryl), C5H3N, arylene, substituted arylene, CH2(biaryl), CH2(ferrocene), divalent aryl, 1,2-divalent phenyl (ortho-phenylene), 2,2′-divalent-1,1′-biphenyl, and 2,2′-divalent-1,1′-binaphthyl.
Selective examples of specific chiral ligands are listed below to illustrate the new P-chiral phospholanes and P-chiral phosphocyclic compounds (L1 to L35).
For each ligand, the corresponding enantiomer is also contemplated. These compounds can be prepared from corresponding phosphine-boranes, phosphine sulfides and phosphine oxides.



















Since Ir-catalyzed asymmetric hydrogenation is still highly substrate-dependent, development of new efficient chiral ligands for Ir-catalyzed hydrogenation is a continuing challenge.
After development of phosphinooxazoline ligands for Ir-catalyzed asymmetric hydrogenation, Pfaltz and others have continued their efforts for the search of new efficient P, N ligands (A. Lightfoot, P. Schnider, A. Pfaltz, Angew. Chem. Int Ed. 1998, 37, 2897–2899).
Various P, N ligands such as TADDOL-phosphite-oxazoline, PyrPHOX, and phosphinite-oxazoline were subsequently developed by Pfaltz and coworkers (J. Blankenstein, A. Pfaltz, Angew. Chem. Int. Ed. 2001, 40, 4445–4447). Burgess also reported JM-Phos and imidazolylidene-oxazoline (D.-R. Hou, J. H. Reibenspies, K. Burgess, J. Org. Chem. 2001, 66, 206–215; M. T. Powell, D.-R. Hou, M. C. Perry, X. Cui, K. Burgess, J. Am. Chem. Soc. 2001, 123, 8878–8879).
In this invention, we also report a new class of chiral P, N ligands, the phospholane-oxazolines, for Ir-catalyzed asymmetric hydrogenation. Excellent enantioselecitivities have been obtained in hydrogenation of methylstilbenes and methylcinammic esters.
After the discovery of TangPhos (1) as a highly electron-donating P-chiral 1,2-bisphosphine ligand, our efforts continued to identify other members of this general class of compounds which have similarly superior enantioselectivity and reactivity profile.
TangPhos (1) has superior enantioselectivity and reactivity profile particularly in the Rh-catalyzed hydrogenation of a wide variety of olefins to produce chiral α, or β amino acids, amines, alcohols and carboxylic acid derivatives ((a) Tang, W.; Zhang, X. Angew. Chem., Int. Ed. 2002, 41, 1612. (b) Tang, W.; Zhang, X. Org. Lett. 2002, 4, 4159. (c) Tang, W.; Liu, D.; Zhang, X. Org. Lett. 2003, 5, 205).
However, one of the difficulties encountered in the synthesis of TangPhos (1) was that only one enantiomer of 1, (1S,1S′,2R,2R′-TangPhos (see below) was readily accessible using (−)-sparteine, which is available as a chiral induction base only in one enantiomeric form.
Separation of the racemic sulfide-protected TangPhos precursor by preparative HPLC is the only current way to obtain the other enantiomer of TangPhos. An attempt to resolve the corresponding phosphine oxide intermediate of racemic TangPhos did not offer much promise because of the highly hygroscopic nature of that intermediate. As a result, the high cost of the other enantiomer has so far limited the potential applications of TangPhos in asymmetric syntheses.
Herein, we also report a concise synthesis of a new P-chiral bisphosphine ligand 20, named DuanPhos (see below) in both enantiomeric forms and the highly enantioselective hydrogenation of a series of functionalized olefins using a Rh-20 complex as the catalyst.
The superior results obtained using DuanPhos in a variety applications makes it a new benchmark ligand in asymmetric catalytic reactions.




The synthetic route to both enantiomers of DuanPhos (20) is shown herein below as Scheme 1 in which resolution of a bisphosphine oxide intermediate is a key step.




From commercially available diol 30, cyclic sulfate 40 was formed in high yield according to the literature procedure ((a) Gao, Y.; Sharpless, K. B. J. Am. Chem. Soc. 1988, 110, 7538. (b) Kim, B. M.; Sharpless, K. B. Tetrohydron Lett. 1989, 30, 655).
Treatment of 40 with tert-butylphosphine (tert-Butylphosphine was prepared on lab scale by reduction of commercially available tert-butyldichlorophosphine with LAH. It can also be prepared on industrial scale from phosphine and isobutene) in the presence of n-BuLi, followed by in situ oxidation with H2O2, provided phosphine oxide 50 in excellent yield. CuCl2 mediated homo-coupling of 50 in the presence of LDA gave racemic bisphosphine oxide 60.
It is noteworthy that the meso diastereomer of 60 was not formed in an appreciable amount, probably due to steric hindrance in the coupling step.
Racemic 60 can be easily resolved with inexpensive (L)-DBT.H2O (DBT=dibenzoyl tartaric acid) to afford enantiomerically pure (+)-60 (>99% ee with one resolution, no further recrystallization needed) in 15% yield.
The remainder of 60 was treated with (D)-DBT.H2O to give (−)-60 (>99% ee) in 17% yield. Thus, the overall yield of the coupling and is resolution steps was 32%.
The absolute configurations of both enantiomers of 20 were determined by comparison with the single crystal X-ray crystallography of the complex of (−)-60 and (D)-DBT.
In order to examine the catalytic properties of DuanPhos (20), complex {Rh(NBD)[(1R,1R′,2S,2S′)-20]}SbF6 70 (NBD=norbornadiene) was prepared and used as the catalyst precursor in the hydrogenation of various prochiral olefins.
Some preliminary results are summarized in Table 1 below.







TABLE 1







Asymmetric Hydrogenation of Olefins with Rh-DuanPhos Complex 70












Entrya

Substrate
Conversion
ee (%)b
confgc





 1d 2




80a R = H80b R = Ph
100%100%
>99>99
RR


 


 3 4 5 6




90a R = Me, R′ = Et(E)90b R = Me, R′ = Et(Z)90c R = p-MeO—Ph, R′ = Me(Z)90d R = p-Cl—Ph, R′ = Me(Z)
100%100%100%100%
>99  97  92  92
RRSS


 


 7 8 910




100a Ar = Ph, R = H100b Ar = Ph, R = i-Pr100c Ar = p-MeO—Ph, R = Me100d Ar = p-CF3—Ph, R = Me
100%100%100%100%
>99  97  99  99
RRRR


 


111213 14




110a Ar = Ph110b Ar = p-MeO—Ph110c Ar = p-F—Ph110d Ar = 2-naphthyl
100%100%100%100%
  97  96  97  98
RRRR


 


1516 




120a R = H120b R = i-Pr (E/Z mixture)
100%100%
>99>99
SS





aThe hydrogenations were carried out at room temperature in solvent (MeOH for substrates 80, 90 and 100 or THF for substrates 110 and 120) under 20 psi of hydrogen pressure with 7 (1 mol %) as the catalyst precursor.


bThe ee values were determined by chiral GC or chiral HPLC. For separation conditions, see ref. 7.


cThe absolute configurations of the products were determined by comparing the retension times of two enantiomers with reported data.


dThis reaction was run with S/C = 10,000:1.






Methyl α-acetaminoacrylate 80a and Methyl α-(acetamino)-2-phenylacrylate 80b, two widely studied α-dehydroamino acid substrates in literature (an attempt to resolve the corresponding phosphine oxide intermediate of racemic TangPhos failed due to the highly hygroscopic nature of that intermediate) were hydrogenated with 70 under very mild conditions (methanol as solvent, room temperature, 20 psi of H2 pressure) in 100% conversions and above 99% enantioselectivities.
It is noteworthy that high turnover numbers (10,000) were achieved with substrate 80a, which indicate the high catalytic activity of 70. β-Amino acids are of great importance as building blocks in combinatorial chemistry and drug discovery ((a) Hoekstra, W. J., Ed. The Chemistry and Biology of β-Amino Acids. Curr. Med. Chem. 1999, 6, 905. (b) Enantioselective Synthesis of β-Amino Acids; Juaristi, E., Ed.; Wiley-VCH: New York, 1997. (c) Guenard, D.; Guritte-Voegelein, R.; Potier, P. Acc. Chem. Res. 1993, 26, 160). However, asymmetric hydrogenation of β-dehydroamino acid derivatives, one of the simplest and most efficient ways to obtain chiral β-amino acids, remains much less successful compared to hydrogenation of their α-analogues.
Few catalysts can provide high enantioselectivities for both E and Z isomers of β-(acylamino)acrylate derivatives ((a) Drexler, H.-J.; You, J.; Zhang, S.; Fischer, C.; Baumann, W.; Spannenberg, A.; Heller, D. Org. Process Res. Dev. 2003, 7, 355 and references cited therein), which are formed simultaneously in most synthetic protocols. As shown in entries 3 and 4, both (E) and (Z)-ethyl-3-acetamino-2-butenoate (90a and 90b) were hydrogenated with 70 in very high enantioselectivities.
For more challenging β-aryl substituted substrates 90c and 90d, high ee values were also obtained (entry 5 and 6). Enantioselective hydrogenation of α-arylenamides 100 has also been investigated with many phosphine ligands (an attempt to resolve the corresponding phosphine oxide intermediate of racemic TangPhos failed due to the highly hygroscopic nature of that intermediate).
As shown in entries 7–10, Rh-DuanPhos complex 70 provided excellent enantioselectivities for the hydrogenation of enamides 100 regardless of the E/Z mixture of tri-substituted substrates or the substituents on the phenyl ring. These results are comparable to the best reported to date.
To demonstrate further the versatile utility of Rh-DuanPhos in asymmetric hydrogenation, another two types of functionalized olefins, enol acetates 110 and itanonic acid derivatives 120, were briefly explored with complex 70 as the catalyst precursor. The ee values were excellent and compared favorably to those obtained with Rh-TangPhos.
The present invention further provides a catalyst prepared by a process including:
contacting a transition metal salt, or a complex thereof, and a chiral ligand according to the present invention as described herein above.
Suitable transition metals for the preparation of the catalyst include Ag, Pt, Pd, Rh, Ru, Ir, Cu, Ni, Mo, Ti, V, Re and Mn.
As mentioned above, the catalyst can be prepared by contacting a transition metal salt or its complex and a ligand according to the present invention.
Suitable transition metal salts or complexes include the following:
AgX; Ag(OTf); Ag(OTf)2; AgOAc; PtCl2; H2PtCl4; Pd2(DBA)3; Pd(OAc)2; PdCl2(RCN)2; (Pd(allyl)Cl)2; Pd(PR3)4; (Rh(NBD)2)X; (Rh(NBD)Cl)2; (Rh(COD)Cl)2; (Rh(COD)2)X; Rh(acac)(CO)2; Rh(ethylene)2(acac); (Rh(ethylene)2Cl)2; RhCl(PPh3)3; Rh(CO)2Cl2; RuHX(L)2(diphosphine); RuX2(L)2(diphosphine); Ru(aryl group)X2; Ru(arene)X2(diphosphine); Ru(RCOO)2(diphosphine); Ru(COD)(COT); Ru(methallyl)2(diphosphine); Ru(aryl group)X2(PPh3)3; Ru(COD)(COT)X; RuX2(cymen); Ru(COD)n; RuCl2(COD); (Ru(COD)2)X; Ru(aryl group)X2(diphosphine); RuX2(diphosphine); RuCl2(═CHR)(PR′3)2; Ru(ArH)Cl2; Ru(COD)(methallyl)2; (Ir(NBD)2Cl)2; (Ir(NBD)2)X; (Ir(COD)2Cl)2; (Ir(COD)2)X; CuX(NCCH3)4; Cu(OTf); Cu(OTf)2; Cu(Ar)X; CuX; Ni(acac)2; NiX2; (Ni(allyl)X)2; Ni(COD)2; MoO2(acac)2; Ti(OiPr)4; VO(acac)2; MeReO3; MnX2 and Mn(acac)2. Each R and R′ in these is independently selected from alkyl or aryl; Ar is an aryl group; and X is a counteranion. In the above transition metal salts and complexes, L is a solvent and the counteranion X can be halogen, BF4, B(Ar)4 wherein Ar is fluorophenyl or 3,5-di-trifluoromethyl-1-phenyl, ClO4, SbF6, PF6, CF3SO3, RCOO or a mixture thereof.
In another aspect, the present invention includes a process for preparation of an asymmetric compound using the catalysts described above. The process includes the step of contacting a substrate capable of forming an asymmetric product by an asymmetric reaction and a catalyst according to the present invention prepared by contacting a transition metal salt, or a complex thereof, and a ligand according to the present invention.
Suitable asymmetric reactions include asymmetric hydrogenation, hydride transfer, allylic alkylation, hydrosilylation, hydroboration, hydrovinylation, hydroformylation, olefin metathesis, hydrocarboxylation, isomerization, cyclopropanation, Diels-Alder reaction, Heck reaction, isomerization, Aldol reaction, Michael addition; epoxidation, kinetic resolution and [m+n] cycloaddition wherein m=3 to 6 and n=2.
Preferably, the asymmetric reaction is hydrogenation and the substrate to be hydrogenated is an ethylenically unsaturated compound, imine, ketone, enamine, enamide, and vinyl ester.
The present invention still further includes a process for preparation of an asymmetric compound including:
contacting a substrate capable of forming an asymmetric product by an asymmetric reaction and a catalyst prepared by a process including: contacting a transition metal salt, or a complex thereof, and a chiral ligand according to the present invention as described herein above.
The present invention still further includes a process for preparing (1R,1R′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl-1,1′-disulfide including the steps of:
asymmetrically deprotonating a 1-alkyl-phospholane-1-sulfide with n-butyllithium/(−)-sparteine in a solvent to produce an anion of the 1-alkyl-phospholane-1-sulfide; and
contacting the anion of the 1-alkyl-phospholane-1-sulfide and CuCl2 to oxidatively couple the anion of the 1-alkyl-phospholane-1-sulfide and produce a reaction mixture including the (1R,1R′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl-1,1′-disulfide.
Further still, the present invention includes a process for preparing (1S,1S′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl.
The process includes the steps of:
asymmetrically deprotonating a 1-alkyl-phospholane-1-sulfide with n-butyllithium/(−)-sparteine in a solvent to produce an anion of the 1-alkyl-phospholane-1-sulfide;
contacting the anion of the 1-alkyl-phospholane-1-sulfide and CuCl2 to oxidatively couple the anion of the 1-alkyl-phospholane-1-sulfide and produce a reaction mixture including (1R,1R′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl-1,1′-disulfide;
recrystallizing the (1R,1R′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl-1,1′-disulfide from the reaction mixture; and
contacting the (1R,1R′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl-1,1′-disulfide and hexachlorodisilane in a solvent to produce (1S,1S′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl.
Preferably, (1S,1S′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl is (1S,1S′,2R,2R′)-1,1′-di-tert-butyl-[2,2′]-diphospholanyl, which is prepared from suitable tert-butyl group containing starting materials.
The present invention also provides a process for making chiral phosphine oxide intermediates using the following methods:




(1) The di-lithium salt of an alkyl or aryl phosphine such as RPH2 is allowed to react with a cyclic sulfate having an aromatic backbone, such as, the cyclic sulfate derived from an ortho-arylenedimethanol or the cyclic sulfate derived from a diol such as HOCH2XCH2OH, to produce a cyclic phosphine. Upon oxidation of the cyclic phosphine, the corresponding phosphine oxide is obtained. An example of the ortho-arylenedimethanol is ortho-phenylenedimethanol. However, any ortho-arylenedimethanol can be used.




(2) a bis-Grignard or a di-lithium reagent derived from an ortho-bis-dichloromethylarylene or a bis-Grignard or a di-lithium reagent derived from ClCH2XCH2Cl, i.e., ClMgCH2XCH2MgCl and LiCH2XCH2Li, respectively, is allowed to react with an aryldichlorophosphine (ArPCl2) to produce a cyclic phosphine. Upon oxidation of the cyclic phosphine, the corresponding phosphine oxide is obtained. An example of the ortho-bis-dichloromethylarylene is ortho-bis-dichloromethylbenzene. However, any ortho-bis-dichloromethylarylene can be used.
In the above starting materials, X can be a divalent group, such as, an alkylene, arylene, CH2(C6H4), CH2(Ar), CH2(hetereoaryl), CH2(alkenyl), arylene, substituted arylene, CH2(biaryl), CH2(ferrocene), divalent aryl, 1,2-divalent phenyl (ortho-phenylene), 2,2′-divalent-1,1′-biphenyl, 2,2′-divalent-1,1′-binaphthyl, divalent hetereoaryl, divalent ferrocene, and the like.
The R group can be hydrogen, linear, branched or cyclic alkyl, substituted alkyl, aryl, substituted aryl, hetereoaryl, ferrocenyl, and the like. Preferably, the R group is can be CH3, Et, i-Pr, t-Bu, Et3C, 2-ethylhexyl, 1-adamantyl, cyclopentyl, cyclohexyl, phenyl, naphthyl, ortho-anisyl, 3,5-dimethylphenyl, 3,5-di-t-butyl phenyl, p-tolyl and ferrocene.
Several suitable procedures to prepare the chiral ligands according to the present invention are described herein below.
(a) Synthesis of TangPhos Using Asymmetric Deprotonation




(b) Synthesis of TangPhos through Chiral Separation




(c) Synthesis of TangPhos Ligands through Utilization of Backbone Chirality




(d) Synthesis of TangPhos Ligands through a Chiral Pool Method




(e) Synthesis of PN Ligands for Asymmetric Catalysis




(a) nBuLi, Sparteine, CO2; (b) amino alcohol, EDC, HOBT, DMF, then MsCl; (c) Raney Ni

General Procedures
All reactions and manipulations were performed in a nitrogen-filled glovebox or using standard Schlenk techniques. THF and toluene were dried and distilled from sodium-benzophenone ketyl under nitrogen. Methylene chloride was distilled from CaH2. Methanol was distilled from Mg under nitrogen. (R, R)-BDNPB was made a solution of 10 mg/ml in toluene before use. Column chromatography was performed using EM silica gel 60 (230 ̃400 mesh). 1H, 13C and 31P NMR were recorded on Bruker WP-200, AM-300, and AMX-360 spectrometers. Chemical shifts were reported in ppm down field from tetramethylsilane with the solvent resonance as the internal standard. Optical rotation was obtained on a Perkin-Elmer 241 polarimeter. MS spectra were recorded on a KRATOS mass spectrometer MS 9/50 for LR-EI and HR-EI. GC analysis was carried on Helwett-Packard 6890 gas chromatography using chiral capillary columns. HPLC analysis was carried on WatersTM 600 chromatography.
EXAMPLE 1
Synthesis of TangPhos (1)
An efficient three-step synthetic of chiral C2 symmetric P-chiral bisphospholane route has been developed.
Preparation of 1-tert-butyl-phospholane 1-sulfide




Preparation of BrMgCH2(CH2)2CH2MgBr. To a dry Schlenk flask held with magnesium turning (7.92 g, 0.33 mol) in 300 ml dry THF was added dropwise 1,4-dibromobutane (23.7 g, 0.11 mol) in 50 mL of THF at room temperature. The reaction was very exothermic during the addition. After the addition was complete (within 1 h), the resulting dark solution was kept at r.t. for 2 more hours. The whole solution was used directly for the following reaction.
To a solution of phosphorous trichloride (13.7 g, 0.10 mol) in THF (300 mL) was added dropwise a solution of t-BuMgCl in THF (100 mL, 1.0M) at −78° C. The addition was complete within 2 hrs. After the mixture was stand at −78° C. for 1 h, a solution of BrMgCH2(CH)2CH2MgBr in THF (made above) was added dropwise. The addition was complete within 2 hrs. The mixture was then allowed to warm to r.t over 2 h and stirred overnight.
At room temperature, to the reaction mixture was added sulfur powder (4.8 g, 0.15 mol) through one portion. The resulting solution was further stirred at r.t. for 2 h. Water (300 mL) was then added. To the THF layer was added 500 mL EtOAc. The organic layer was washed with water (300 mL) followed by brine (300 mL), dried over Na2SO4, and concentrated. The resulting oil was passed through a silica gel column followed by recrystallization to give colorless crystalline product 1-tert-butyl-phospholane 1-sulfide 8 g (45% yield).
Synthesis of (1R,1R′,2R,2R′)-1,1′-di-tert-butyl-[2,2′]-diphospholanyl  1,1′-disulfide




At −78° C., to a solution of (−)-sparteine (7.83 mL, 34 mmol) in ether (200 mL) was added n-butyllithium (21.3 mL, 34 mmol, 1.6M in hexane) dropwise. The resulting solution was kept at −78° C. for 30 min. Then at this temperature, to the solution was added dropwise a solution of 1-tert-butyl-phospholane 1-sulfide (5.0 g, 28.4 mmol in ether (100 mL). The addition was complete within 1 hr.
The resulting mixture was kept at −78° C. and stirred for 8 more hrs. Then dry CuCl2 (5.73 g, 42.6 mmol) was added into the solution through one portion. The resulting suspension was vigorously stirred and allowed to warm to r.t. over 4 hrs. 150 ml of concentrated ammonia was added. The water layer was washed twice with EtOAc (2×100 mL). The combined organic phase was further washed in a sequence with 5% ammonia (100 mL), 1N HCl (100 mL), water (100 mL), and brine (100 mL).
After drying over Na2SO4, the solution was concentrated under reduced pressure to give an oily solid, which was subsequently purified by passing a silica gel column to give a solid mixture (4 g) of (1R,1R′,2R,2R′)-1,1′-di-tert-butyl-[2,2′]-diphospholanyl 1,1′-disulfide (72% ee, 83%) and meso compound (1R,1R′,2S,2S′)-1,1′-di-tert-butyl-[2,2′]-diphospholanyl 1,1′-disulfide (17%).
The mixture was recrystallized from ethyl acetate and ethanol to give 700 mg of pure product (1R,1R′,2R,2R′)-1,1′-di-tert-butyl-[2,2′]-diphospholanyl 1,1′-disulfide (ee: >99% according to HPLC, total yield: 14%).
Synthesis of (1S,1S′,2R,2R′)-1,1′-di-tert-butyl-[2,2′]-diphospholanyl TangPhos (1)




To a solution of (1R,1R′,2R,2R′)-1,1′-di-tert-butyl-[2,2′]-diphospholanyl 1,1′-disulfide (440 mg, 1.26 mmol) in 25 ml benzene was added hexachlorodisilane (3.25 mL, 5.08 g, 18.9 mmol). The mixture was stirred at reflux for 4 h. After the solution was cooled to r.t., 50 mL of degassed 30% (w/w) NaOH solution was carefully added to the reaction mixture with an ice-water bath.
The resulting mixture was then stirred at 60° C. until the aqueous layer became clear. The two phases were separated. The water phase was washed twice with degassed benzene (2×30 mL). The combined benzene was dried over Na2SO4 and concentrated.
The solid residue was re-dissolved in a minimum amount of degassed dichloromethane, which was subsequently passed through a basic Al2O3 plug (eluent: Et2O:hexane=1:10) to give pure white product (1) 320 mg (88% yield).
EXAMPLE 2
Asymmetric Hydrogenation of Dehydroamino Acids General Procedure for Asymmetric Hydrogenation
To a solution of [Rh(COD)2]BF4 (5.0 mg, 0.012 mmol) in THF (10 mL) in a glovebox was added a chiral phosphine ligand (TangPhos 0.15 mL of 0.1 M solution in toluene, 0.015 mmol). After stirring the mixture for 30 min, the dehydroamino acid (1.2 mmol) was added.
The hydrogenation was performed at rt under 20 psi of hydrogen for 24 h. The reaction mixture was treated with CH2N2, then concentrated in Vacuo. The residue was passed through a short silica gel column to remove the catalyst. The enantiomeric excesses were measured by GC using a Chirasil-VAL III FSOT column.
The absolute configuration of products was determined by comparing the observed rotation with the reported value. All reactions went in quantitative yield with no by-products found by GC.
Asymmetric hydorgenation for making alpha amino acid derivatives using TangPhos (1) as the ligand is shown in the Table below:










Asymmetric Hydrogenation of Dehydroamino Acid Derivativesa


















 








 









Entry
Substrate
eec(%)












1
Ar = Ph, R = H
>99d


2
Ar = Ph, R = CH3
>99


3
Ar = p-F—Ph, R = H
  99d


4
Ar = p-F—Ph, R = CH3
>99


5
Ar = p-MeO—Ph, R = H
>99d,e


6
Ar = p-MeO—Ph, R = CH3
>99


7
Ar = m-Br—Ph, R = H
>99d


8
Ar = m-Br—Ph, R = CH3
>99


9
Ar = o-Cl—Ph, R = H
>99d


10
Ap = o-Cl—Ph, R = CH3
>99


11
Ar = 2-thienyl, R = H
>99d


12
Ar = 2-thienyl, R = CH3
>99


13
Ar = 2-naphthyl, R = H
>99d


14
Ar = 2-naphthyl, R = CH3
>99


15
Ar = Ph, R = H, N-benzoyl
>99d


16
Ar = Ph, R = CH3, N-benzoyl
>99





aThe reaction eas carried out at rt under 20 psi of H2 for 24 h. THe catalyst was made in situ by sitirring a solution of [Rh(NBD)2]SbF6 and TangPhos in methanol (2 mL) [substrate:[Rh]:TangPhos = 1:0.01:0.011]. The reaction went with 100% conversion.


bThe R absolute configuration was assigned by comparison of optical rotation with reported data.


cEnantiomeric excesses were determined by chiral GC using a Chrialsil- VAL III FSOT column.


dDetermined on corresponding methyl ester.


eThe % ee was determined by HPLC using a Daicel Chiralcel OJ column.






EXAMPLE 3
Asymmetric Synthesis of Beta-Amino Acid Derivatives Synthesis of Starting Material 3-Acetamido-3-Aryl-2-Propenoates and 3-Acetamido-3-hetero-Aryl-2-Propenoates
Typical procedure: The starting material methyl 3-acetamido-3-phenyl-2-propenoate can be conveniently synthesized from cheap acetophenone in three steps according to known literature procedure in good yields. The literatures are Zhu, G.; Zhen, Z.; Zhang, X. J. Org. Chem. 1999, 64, 6907–6910; Krapcho, A. P.; Diamanti, J. Org. Synth. 1973, 5, 198–201. 1H-NMR (CDCl3, 360 MHz) δ (Z isomer) 2.17 (s, 3H), 3.77 (s, 3H), 5.29 (s, 1H), 7.37–7.45 (m, 5H); (E isomer) 2.38 (s, 3H), 3.77 (s, 3H), 6.65 (s, 1H), 7.37–7.45 (m, 5H).
Hydrogenation for Making Beta Amino Acid Derivatives with the Rh-TangPhos (1) System
















 












entrya
R1
R2
geom.c
eeb(%)
config.















1
Me
Et
E
99.5
R


2
Me
Et
Z
97.3
R


3
Me
i-Pr
E
99.3
R


4
Et
Me
E
99.6
R


5
n-Pr
Et
E
99.6
R


6
i-Bu
Me
E
98.5
R


7
Ph
Me
E/Z
93.8
S


8
p-F-Ph
Me
E/Z
95.0
S


9
p-Cl-Ph
Me
E/Z
92.3
S


10
p-Br-Ph
Me
E/Z
95.1
S


11
p-Me-Ph
Me
E/Z
94.0
S


12
p-MeO-Ph
Me
E/Z
98.5d
S


13
p-BnO-Ph
Me
E/Z
98.5
S


14
o-Me-Ph
Me
E/Z
74.3
S


15
o-MeO-Ph
Me
E/Z
83.1
S





aThe reactions were carried out under 20 psi of H2 in THF at rt for 24 h. Substrate/[Rh(TangPhos)nbd]SbF6 = 200:1. The absolute configurations were determined by comparing the optical rotations with reported values.


bThe ee (%) values were determined by chiral GC using a Chiralselect 1000 column.


cFor the E/Z ratios of E/Z mixtures.


dThe ee was determined by chiral HPLC using (s, s)-whelk-01 column






For general synthetic procedures of β-aryl β-acetamidoacrylate esters, see Zhou, Y.-G.; Tang, W.; Wang, W.-B.; Li, W.; Zhang, X. J. Am. Chem. Soc. 2002, 124, 4952–4953. For general synthetic procedure of β-alkyl β-acetamidoacrylate esters, see Zhu, G.; Chen, Z.; Zhang, X. J. Org. Chem. 1999, 64, 6907–6910. For analytical data of known substrates and products, please also refer to the two aforementioned papers.
Methyl 3-Acetamido-3-(4-benzyloxyphenyl)-2-propenoate:
Z/E=9:1; 1H NMR (360 MHz, CDCl3) δ (Z isomer) 2.06 (s, 3H), 3.65 (s, 3H), 4.98 (s, 2H), 5.18 (s, 1H), 6.86 (d, J=6.8 Hz, 2H), 7.28 (m, 7H), 10.46 (s, 1H); (E isomer) 2.27 (s, 3H), 3.65 (s, 3H), 4.98 (s, 2H), 6.44 (s, 1H), 6.86 (d, J=6.8 Hz, 2H), 7.28 (m, 7H).
General Procedure for Asymmetric Hydrogenation of β-alkyl or β-aryl β-acetamidoacrylic Esters
To a solution of β-acetamidoacrylic ester (0.5 mmol) in 4 mL of degassed THF Rh[(TangPhos)nbd]SbF6 (2.5 μmol) was added in a glovebox filled with nitrogen. The whole solution was transferred into an autoclave.
The autoclave was then purged three times with hydrogen and filled with hydrogen with 20 psi pressure. The resulting reactor was stirred at room temperature for 24 hr. After release of the hydrogen, the autoclave was opened and the reaction mixture was evaporated.
The residue was passed through a short silica gel plug to give hydrogenation product β-amino acid derivatives. A small amount of sample was subjected to chiral GC or HPLC analysis.
Methyl 3-acetamido-3-(4-benzyloxyphenyl)-propanoate:
98.5% ee, [α]25D=−79.5°; 1H NMR (300 MHz, CDCl3) δ 2.00 (s, 3H), 2.83 (dd, J=15.7, 6.2 Hz, 1H), 2.93 (dd, J=15.6, 6.0 Hz, 1H), 3.63 (s, 3H), 5.05 (s, 2H), 5.40 (m, 1H), 6.93 (d, 1H), 6.94 (dd, J=6.7, 2.0 Hz, 2H), 7.23 (dd, J=6.8, 1.8 Hz, 2H), 6.72 (m, 5H); 13C NMR (75 MHz, CDCl3) δ 23.8, 40.2, 49.5, 52.2, 115.4, 127.9, 128.0, 128.4, 129.0, 133.3, 137.3, 158.6, 169.7, 172.1; MS (ESI) m/z 328 (M++1); HRMS calculated for C19H22 4 3281549. found 328.1553. Chiral HPLC conditions ((s, s)-whelk-01): solvent hexane:isopropanol (1:1); flow rate 1 mL/min; retention time 8.2 min (R), 13.1 min (S).
EXAMPLE 4
Asymmetric Hydrogenation of Enamides







TABLE







Rh-Catalyzed Asymmetric Hydrogenation of α-Arylenamides


using TangPhos (1).








 













Entry
Substrate
Ar
R
ee[%][b]

















1

Ph
H
>99



2

m-Me—Ph
H
>99



3

p-CF3—Ph
H
>99



4

p-Cy—Ph
H
>99



5

p-Ph—Ph
H
  99



6

2-naphthyl
H
>99



7

Ph
CH3
  98



8

p-CF3—Ph
CH3
  98



9

p-MeO—Ph
CH3
  98



10

2-naphthyl
CH3
  99



11

Ph
CH(CH3)2
  98



12

Ph
CH2Ph
  99



 











13




  97







[a]Conditions: see Experimental Section for details. Enamides were prepared according to the literature method.



[b]The R absolute configuration was assigned by comparison of optical rotation with reported data. ee's were determined by chiral GC using Supelco Chiral Select 1000 column or by chiral HPLC with a (R, R)-Poly Whelk-01 column.






EXAMPLE 5
High Turnovers for Asymmetric Hydrogenation of Enamides Using Rh(TangPhos (1) Catalyst
Asymmetric hydrogenation with [Rh(NBD)TangPhos(1)]+SbF6− as the catalyst:




Procedure for Hydrogenation of α-Dehydro Amino Acid:

To a solution of methyl α-(acetylamino)-2-phenylacrylate (2.19 g, 10 mol) in 20 mL of degassed methanol in glovebox was added [RH(nbd)(1)]SbF6 (1 ml of 0.001M solution in methanol, 0.001 mmol). The hydrogenation was performed at room temperature under 40 psi of H2 for 8 h. After carefully releasing the hydrogen, the reaction mixture was passed through a short silica gel column to remove the catalyst. The enantiomeric excesses of (R)-methyl 2-acetylamino-3-phenylpropionate were measured by chiral GC directly. (Conversion: 100%, ee: 99.8%, TON: 10,000)
EXAMPLE 6
Asymmetric Hydrogenation of Itaconic Acid Derivatives with Rh(TangPhos) (1) Catalyst





















 








 












entry
R1
R2[b]
ee(%)[c]







1
H
H
99



2
CH3
CH(CH3)2
96



3
CH3
Ph
93



4
CH3
p-MeO—Ph
97



5
CH3
p-Me—Ph
97



6
CH3
p-Cl—Ph
>99  



7
CH3
m-Cl—Ph
99



8
CH3
1-naphthyl
99



9
CH3
2-naphthyl
99







[a]Conditions: catalyst precursor = [Rh(TangPhos)(nbd)]SbF6 (1 mol %), room temperature, 20 psi H2, THF. The absolute configuration of product was determined by comparison with reported data.



[b]Most substrates (except entry 1) employed as crude E/Z mixtures ranging from 2/1 to >10/1.



[c]Determined on chiral GC or HPLC column after conversion of the hydrogenation product into dimethyl ester.






EXAMPLE 7
Asymmetric Hydrogenation of Arylenol Acetates with the [Rh(TangPhos (1)] Catalyst
















 











entry
Ar
ee(%)[b]







1
2-naphthyl
97



2
Ph
96



3
p-F—Ph
92



4
p-Cl—Ph
97



5
2-furyl
93



6
p-NO2—Ph
99







[a]Conditions: catalyst precursor = [Rh(TangPhos)(nbd)]SbF6 (1 mol %), room temperature, 20 psi H2, EtOAc. The absolute configuration of product was determined by comparison with reported data.



[c]Determined on a chiral GC column (chiral select 1000).






EXAMPLE 8
Synthesis of Chiral PN Ligands for Asymmetric Catalysis
Since Ir-catalyzed asymmetric hydrogenation is still highly substrate-dependent, development of new efficient chiral ligands for Ir-catalyzed hydrogenation is a continuing challenge. A new class of chiral P, N ligands, the phospholane-oxazolines have been developed as follows:




At −78° C., to a solution of (−)-sparteine (14.4 mL, 62.5 mmol) in ether (100 mL) was added dropwise n-BuLi (1.6M in hexane, 39 mL, 62.5 mmol). The mixture was stirred at −78° C. for 30 min. A solution of 2 (10 g, 56.8 mmol) in ether (150 mL) was added dropwise. The addition was complete in 1 h. The resulting reaction mixture was allowed to warm to rt and stirred overnight. The mixture was re-cooled to −78° C. Through the suspension was bubbled CO2 for 2 h. Then it was quenched with the addition of 1N HCl (200 mL) followed by EtOAc (200 mL). The organic layer was washed sequentially with 1N HCl (200 mL), H2O (200 mL), and brine (100 mL). The solution was dried over Na2SO4 and evaporated. The residue was treated with 2 N NaOH solution (300 mL). The resulting clear solution was neutralized by the addition of 2 N HCl. The precipitate was collected through vacuum filtration to give the product (8.0 g, 72% ee, 64% yield). The ee was determined by converting the product into its corresponding methyl ester by treatment with TMSCHN2 in THF/CH3OH solution (HPLC conditions for the methyl ester: Chiralpak AD column; hex:ipr=95:5; 8.8 min, 11.3 min.) A sample of product (7.5 g) was recrystallized twice from ethanol to give 4.5 g of enantiomerically pure product 3 (>99.9% ee, 40% total yield).
3: [α]D20=16.9° (c=0.9, CHCl3); 1H NMR (360 MHz, CDCl3) δ 1.35 (d, 3JHP=17.0 Hz, 9H), 1.71 (m, 1H), 2.18 (m, 3H), 2.47 (m, 2H), 3.34 (m, 1H); 13C NMR (90 MHz, CD3OD) δ 25.4 (d, 2JCP=1.7 Hz), 26.0 (d, 2JCP=2.2 Hz), 31.3 (d, 2JCP=7.3 Hz), 32.8 (d, JCP=48.8 Hz), 36.1 (d, JCP=44.1 Hz), 46.4 (d, JCP=36.0), 172.9; 31P NMR (145 MHz, CD3OD) δ 89.3 (s); APCI MS 121 (M++H); HRMS calculated for C9H18PSO2 221.0765. found 221.0762.
The methyl ester of 3: [α]D20=42.6° (c=1, CHCl3); 1H NMR (360 MHz, CDCl3) δ 1.21 (d, 3JHP=16.8 Hz, 9H), 1.69 (m, 1H), 1.92 (m, 2H), 2.30 (m, 3H), 3.23 (m, 1H), 3.66 (s, 3H); 13C NMR (90 MHz, CDCl3) δ 25.2 (d, 2.7 Hz), 25.4 (d, 2JCP=1.8 Hz), 29.9 (d, 2JCP=7.4 Hz), 31.7 (d, JCP=47.9 Hz), 35.3 (d, JCP=43.5 Hz), 45.4 (d, JCP=35.5 Hz), 52.7, 170.0; 31P NMR (145 MHz, CDCl3) δ 87.8; APCI MS 235 (M++H); HRMS calculated for C10H20PSO2 235.0922. found 235.0909.




A mixture of 3 (2.27 mmol), EDC.HCl (1.3 g, 6.82 mmol), HOBT.H2O (0.52 g, 3.41 mmol), chiral amino alcohol (3.41 mmol), triethylamine (1.9 mL, 13.6 mmol) in 10 mL of DMF was stirred at 70° C. overnight. To the cooled mixture was added 30 mL of 2 N HCl solution. The resulting mixture was then extracted with ethyl acetate. The organic layer was washed with water and brine, dried over Na2SO4. After removal of the solvent, the residue was purified by column chromatography to give condensation product in 70–80% yield.
To a mixture of condensation product (1.67 mmol), diisopropyl-ethylamine (1.98 mL, 6.68 mmol) and triethylamine (1.38 mL, 16.7 mmol) in 10 mL of CH2Cl2 was added 258 μL (3.34 mmol) of methanesulfonyl chloride at 0° C. After addition, the resulting mixture was allowed to warm to room temperature and stirred overnight. The solvent was removed. The residue was redissolved in ethyl acetate, washed with water and brine, and dried over Na2SO4. After removal of solvent, the crude product was purified by column chromatography to give pure 4a–f in 70–80% yield.
4a: [α]20D=−75.1° (c=0.9, CHCl3), 1H NMR (360 MHz, CDCl3) δ 0.81 (d, 6.8 Hz, 3H), 0.89 (d, 6.8 Hz, 3H), 1.24 (d, 3JHP=16.5 Hz, 9H), 1.58 (m, 1H), 1.71 (m, 1H), 1.90 (m, 1H), 2.11 (m, 2H), 2.37 (m, 2H), 3.19 (m, 1H), 3.86 (m, 1H), 3.94 (t, 7.9 Hz, 1H), 4.21 (t, 8.1 Hz, 1H); 13C NMR (90 MHz, CDCl3) δ 18.7, 19.4, 25.4 (m), 30.6 (d, 2JCP=7.9 Hz), 31.8 (d, JCP=47.5 Hz), 32.0, 33.1, 35.2 (d, JCP=43.4 Hz), 38.8 (d, JCP=39.5 Hz), 70.6, 72.4, 163.9; 31P NMR (145 MHz, CDCl3) δ 88.0; APCI MS 288 (M++H); HRMS calculated for C14H27NOPS 288.1551. found 288.1549.
4b: [α]20D=−75.9° (c=0.9, CHCl3), 1H NMR (360 MHz, CDCl3) δ 0.83 (S, 9H), 1.25 (d, 3JHP=16.4 Hz, 9H), 1.56 (m, 1H), 1.87 (m, 1H), 2.14 (m, 2H), 2.38 (m, 2H), 3.21 (m, 1H), 3.83 (m, 1H), 4.01 (t, 8.4 Hz, 1H), 4.16 (t, 8.5 Hz, 1H); 13C NMR (90 MHz, CDCl3) δ 25.6 (d, 2JCP=1.6 Hz), 26.5, 30.6 (d, 2JCP=7.9 Hz), 31.9 (d, JCP=47.2 Hz), 32.0, 33.8, 35.3 (d, JCP=43.6 Hz), 38.9 (d, JCP=40.0 Hz), 69.1, 75.9, 163.9; 31P NMR (145 MHz, CDCl3) δ 87.3; ESI MS 302 (M++H); HRMS calculated for C15H29NOPS 302.1707. found 302.1716.
4c: [α]20D=−98.9° (c=1, CHCl3), 1H NMR (360 MHz, CDCl3) δ 1.24 (d, 3JHP=16.6 Hz, 9H), 1.58 (m, 1H), 1.91 (m, 1H), 2.16 (m, 2H), 2.39 (m, 2H), 3.28 (m, 2H), 3.19 (t, 8.3 Hz, 1H), 4.58 (t, 8.3 Hz, 1H), 5.14 (m, 1H), 7.19 (m, 5H); 13C NMR (90 MHz, CDCl3) δ 25.0 (d, 2JCP=1.1 Hz), 30.2 (d, 2JCP=7.7 Hz), 31.3 (d, JCP=47.3 Hz), 31.5, 34.8 (d, JCP=43.4 Hz), 38.6 (d, JCP=39.2 Hz), 69.6, 74.9, 127.3 (m), 142.3, 165.2 (d, 2JCP=4.6 Hz); 31P NMR (145 MHz, CDCl3) δ 88.8; APCI MS 322 (M++H); HRMS calculated for C17H25NOPS 322.1395. found 322.1409.
4d: [α]20D=−54.2° (c=1, CHCl3), 1H NMR (360 MHz, CDCl3) δ 1.17 (d, 3JHP=16.5 Hz, 9H), 1.52 (m, 1H), 1.84 (m, 1H), 2.07 (m, 2H), 2.32 (m, 2H), 2.58 (dd, 8.2 Hz, 13.6 Hz, 1H), 2.98 (dd, 5.5 Hz, 13.6 Hz, 1H), 3.06 (dd, 9.6 Hz, 17.3 Hz, 1H), 3.88 (t, 7.3 Hz, 1H), 4.09 (t, 8.5 Hz), 4.3 (m, 1H), 7.13 (m, 5H); 13C NMR (90 MHz, CDCl3) δ 24.4, 24.6 (d, 2JCP=1.2 Hz), 29.8 (d, 2JCP=8.0 Hz), 30.9 (d, JCP=47.4 Hz), 34.3 (d, JCP=43.4 Hz), 37.8 (d, JCP=39.1 Hz), 41.5, 66.8, 71.3, 125.8, 127.9, 128.8 (m), 163.7 (d, 2JCP=4.7 Hz); 31P NMR (145 MHz, CDCl3) δ 88.5; APCI MS 336 (M++H); HRMS calculated for C18H27NOPS 336.1551. found 336.1542.
4e: [α]20D=−83.90 (c=1, CHCl3), 1H NMR (360 MHz, CDCl3) δ 0.67 (t, 6.4 Hz, 6H), 1.04 (d, 3JHP=16.4 Hz, 9H), 1.43 (m, 3H), 1.67 (m, 1H), 1.94 (m, 2H), 2.19 (m, 2H), 3.00 (m, 1H), 3.60 (t, 7.4 Hz, 1H), 3.91 (m, 1H), 4.08 (m, 8.5 Hz, 1H); 13C NMR (90 MHz, CDCl3) δ 22.3, 22.5, 24.4, 24.6, 24.9, 29.8 (d, 2JCP=7.9 Hz), 30.9 (d, JCP=47.4 Hz), 31.4 Hz, 34.3 (d, JCP=43.4 Hz), 37.9 (d, JCP=39.4 Hz), 45.3, 64.1, 72.6, 162.9 (d, 2JCP=4.6 Hz); 31P NMR (145 MHz, CDCl3) δ 88.0; ESI MS 302 (M++H); HRMS calculated for C15H28NOPS 302.1708. found 302.1715.
4f: [α]20D=+28.6° (c=0.9, CHCl3), 1H NMR (360 MHz, CDCl3) δ 0.82 (d, 6.7 Hz, 3H), 0.94 (d, 6.7 Hz, 3H), 0.95 (d, 3JHP=16.4 Hz, 9H), 1.58 (m, 1H), 1.75 (m, 1H), 1.89 (m, 1H), 2.13 (m, 2H), 2.39 (m, 2H), 3.11 (m, 1H), 3.81 (m, 1H), 3.95 (t, 8.2 Hz, 1H), 4.20 (t, 8.2 Hz); 13C NMR (90 MHz, CDCl3) δ 18.6, 20.0, 25.2, 25.4 (d, 2JCP=1.4 Hz), 30.7 (d, 2JCP=7.8 Hz), 32.8 (d, JCP=47.6 Hz), 32.0, 33.2, 35.1 (d, JCP=43.6 Hz), 38.7 (d, JCP=39.8 Hz), 70.6, 72.8, 163.7 (d, 2JCP=4.5 Hz); 31P NMR (145 MHz, CDCl3) δ 87.9; ESI MS 288 (M++H); HRMS calculated for C14H27NOPS 288.1551. found 288.1545.




General Procedure:

To a N2-flushed Schlenk flask was loaded 5.0 g of Raney Ni 2800 slurry. The Raney Ni was washed sequentially with methanol (10 mL×3), ether (10 mL×3), and dried degassed CH3CN (10 mL×3). To this flask was then transferred a solution of 4a–f (1.5 mmol) in CH3CN (20 mL) via cannula. The resulting mixture was stirred under N2 for 2 d. The mixture was then filtered under N2. The Raney Ni solid was washed with CH3CN (10 mL×5). The combined CH3CN with filtrate was evaporated under N2 to give an oily residue. The residue was passed through an Al2O3 (basic) plug under N2 to give pure oily product 5a–f (80–95%).
5a: 1H NMR (400 MHz, CD2Cl2) δ 0.88 (d, 6.8 Hz, 3H), 0.94 (d, 6.8 Hz, 6.8 Hz), 1.08 (d, 3JHP=11.9 Hz, 9H), 1.72 (m, 4H), 2.01 (b, 3H), 2.81 (b, 1H), 3.85 (b, 1H), 3.95 (t, 7.6 Hz, 1H), 4.20 (t, 7.6 Hz, 1H); 13C NMR (100 MHz, CD2Cl2) δ 18.3, 18.8, 23.3 (d, 2JCP=17.5 Hz), 27.6 (d, 2JCP=14.5 Hz), 29.0, 29.1 (d, JCP=18.4 Hz), 33.2 (d, JCP=19.9 Hz), 36.9 (d, JCP=20.2 Hz), 70.2, 72.4, 169.1 (d, 2JCP=15.9 Hz); 31P NMR (145 MHz, CD2Cl2) δ 26.0; ESI MS 256 (M++H); HRMS calculated for C14H27NOP 256.1830. found 256.1820.
5b: 1H NMR (360 MHz, CDCl3) δ 0.71 (s, 9H), 0.90 (d, 3JHP=11.9 Hz, 9H), 1.56 (m, 3H), 1.83 (m, 3H), 2.73 (b, 1H), 3.65 (m), 3.92 (t, 7.6 Hz, 1H), 3.99 (t, 9.3 Hz, 1H); 13C NMR (90 MHz, CDCl3) δ 21.9 (d, 2JCP=17.6 Hz), 24.8, 26.4 (d, 2JCP=14.2 Hz), 27.7 (d, 2.84 Hz), 28.9 (d, JCP=18.0 Hz), 32.4 (d, JCP=70.0 Hz), 35.8 (d, JCP=19.8 Hz), 67.7, 74.4, 168.9 (d, 2JCP=15.9 Hz); 31P NMR (145 MHz, CDCl3) δ 25.2; ESI MS 270 (M++H); HRMS calculated for C15H29NOP 270.1987. found 270.1972.
5c: 1H NMR (360 MHz, CD2Cl2) δ 0.98 (d, 3JHP=12.0 Hz, 9H), 1.66 (m, 3H), 1.92 (m, 3H), 2.80 (m, 1H), 3.91 (t, 7.9 Hz, 1H), 4.46 (dd, 8.3 Hz, 10.0 Hz, 1H), 5.01 (m, 1H), 7.17 (m, 5H); 13C NMR (90 MHz, CD2Cl2) δ 23.5 (d, 2JCP=17.6 Hz), 27.9 (d, 2JCP=14.4 Hz), 29.2 (d, 2JCP=2.1 Hz), 29.4 (d, JCP=18.7 Hz), 33.4, 37.1 (d, JCP=20.1 Hz), 70.1, 75.3, 127.0–129.1 (m), 144.0, 172.0 (d, 2JCP=15.8 Hz); 31P NMR (145 MHz, CD2Cl2) δ 27.4; ESI MS 290 (M++H); HRMS calculated for C17H24NOP 290.1674. found 290.1663.
5d: 1H NMR (360 MHz, CD2Cl2) δ 1.06 (d, 3JHP=11.9 Hz, 9H), 1.74 (m, 3H), 2.01 (m, 3H), 2.67 (dd, 7.5 Hz, 13.6 Hz, 1H), 2.74 (m, 1H), 2.96 (dd, 6.1 Hz, 13.6 Hz, 1H), 3.92 (dd, 7.0 Hz, 8.2 Hz, 1H), 4.17 (t, 9.0 Hz, 1H), 4.30 (m, 1H), 7.28 (m, 5H); 13C NMR (90 MHz, CD2Cl2) δ 23.4 (d, JCP=17.9 Hz), 27.8 (d, 2JCP=14.4 Hz), 29.1 (d, 2JCP=2.2 Hz), 29.3 (d, JCP=18.7 HZ), 33.4 (d, 2JCP=1.2 Hz), 37.1 (d, JCP=20.0 Hz), 42.5, 68.0, 72.2, 126.8, 128.9, 130.0, 139.2, 170.9 (d, 2JCP=15.8 Hz); 31P NMR (145 MHz, CD2Cl2) δ 26.7; ESI MS 304 (M++H); HRMS calculated for C18H27NOP 304.1830. found 304.1836.
5e: 1H NMR (360 MHz, CD2Cl2) δ 0.86 (d, 4.3 Hz, 3H), 0.92 (d, 4.3 Hz, 3H), 1.03 (d, 3JHP=11.9 Hz, 9H), 1.25 (m, 1H), 1.49 (m, 1H), 1.73 (m, 4H), 1.95 (m, 3H), 2.74 (m, 1H), 3.75 (t, 7.7 Hz, 1H), 4.03 (m, 1H), 4.25 (dd, 8.0 Hz, 9.1 Hz, 1H); 13C NMR (90 MHz, CD2Cl2) δ 23.1, 23.3 (d, 2JCP=17.7 Hz), 26.0, 27.8 (d, 2JCP=14.4 Hz), 29.1 (d, 2JCP=2.4 Hz), 29.2 (d, JCP=18.7 Hz), 33.3 (d, 1.6 Hz), 37.1 (d, JCP=19.9 Hz), 46.3, 65.2, 73.4, 169.9 (d, 2JCP=15.8 Hz); 31P NMR (145 MHz, CD2Cl2) δ 26.1; ESI MS 270 (M++H); HRMS calculated for C15H28NOP 270.1987. found 270.2042.
5f: 1H NMR (360 MHz, CDCl3) δ 0.73 (d, 6.8 Hz, 3H), 0.80 (d, 6.8 Hz, 3H), 0.93 (d, 3JHP=12.0 Hz, 9H), 1.49 (m, 1H), 1.66 (m, 3H), 1.89 (m, 3H), 2.66 (m, 1H), 3.76 (m, 1H), 3.84 (t, 7.6 Hz, 1H), 4.07 (t, 8.8 Hz, 1H); 13C NMR (90 MHz, CDCl3) δ 16.6, 17.9, 21.8 (d, 2JCP=17.4 Hz), 26.5 (d, 2JCP=14.3 Hz), 27.5 (d, 2JCP=2.4 Hz), 27.8 (d, JCP=18.0 Hz), 31.3, 31.9 (d, 1.1 Hz), 35.5 (d, JCP=19.8 Hz), 68.5, 70.6, 169.0 (d, 2JCP=15.5 Hz); 31P NMR (145 MHz, CDCl3) δ 25.9; ESI MS 256 (M++H); HRMS calculated for C14H27NOP 256.1830. found 256.1805.
EXAMPLE 9
Preparation of Ir-PN Compounds




General Procedure:

To a Schlenk tube was added 5a–f (0.346 mmol), [Ir(COD)Cl]2 (116 mg, 0.173 mmol), and dried degassed CH2Cl2 (4 mL). The deep red mixture was heated under N2 to reflux for 1 h, until in situ 31P NMR indicated that the starting material was consumed. After the reaction mixture was cooled to rt, Na[BARF] (453 mg, 0.519 mmol) was added followed by degassed H2O (5 mL), and the resulting two-phase mixture was stirred vigorously for 30 min. The two layers were separated, and the water layer was further washed with CH2Cl2. The combined CH2Cl2 solution was evaporated to give a brown residue, which was subsequently passed through an Al2O3 plug (eluent: hexane:CH2Cl2=1:2) to give pure orange product 6a–f in 50–70% yield.
6a: 1H NMR (360 MHz, CD2Cl2) δ 0.74 (d, 6.8 Hz, 3H), 0.91 (d, 7.0 Hz, 3H), 1.17 (d, 3JHP=15.4 Hz, 9H), 1.58 (m, 2H), 1.83–2.40 (m, 13H), 3.09 (m, 1H), 4.13 (m, 3H), 4.51 (t, 9.4 Hz, 1H), 4.65 (dd, 3.8 Hz, 9.4 Hz, 1H), 4.94 (m, 2H), 7.59 (s, 4H), 7.73 (s, 8H); 13C NMR (90 MHz, CD2Cl2) δ 14.0, 19.0, 24.0 (d, 2JCP=25.6 Hz), 27.1 (d, 2JCP=3.5 Hz), 27.8, 30.1 (d, 1.9 Hz), 31.1, 32.2 (d, 1.9 Hz), 32.5 (d, JCP=23.4 Hz), 33.9 (d, 2.1 Hz), 36.2 (d, 3.7 Hz), 37.8 (d, JCP=30.0 Hz), 60.6, 63.1, 70.0, 73.0, 90.3 (d, 11.8 Hz), 93.5 (d, 10.9 Hz), 118.0 (t), 120.7, 123.7, 126.7, 129.3 (dd, 28.4 Hz, 58.6 Hz), 135.4 (t, 92.9 Hz), 162.3 (q, 49.6 Hz), 190.1 (d, 2JCP=19.7 Hz); 31P NMR (145 MHz, CD2Cl2) δ 51.9; ESI+MS: 556 (cation+1); ESI−MS: 863 (anion); HRMS calculated for IrC22H39NOP 556.2320. found 556.2318; HRMS calculated for C32H12F24B 863.0649. found 863.0650.
6b: 1H NMR (360 MHz, CD2Cl2) δ 0.88 (s, 9H), 1.15 (d, JHP=15.4 Hz, 9H), 1.43 (b, 2H), 1.60–2.40 (m, 11H), 2.87 (d, 7.6 Hz, 1H), 3.55 (m, 1H), 3.80 (b, 1H), 4.38 (m, 2H), 4.54 (m, 1H), 4.73 (dd, 1.8 Hz, 9.8 Hz), 5.02 (b, 1H), 7.48 (s, 4H), 7.64 (s, 8H); 13C NMR (90 MHz, CD2Cl2) δ 23.7, 24.0, 25.5, 26.0, 25.5, 27.3 (d, 2JCP=3.4 Hz), 29.4, 31.5 (d, JCP=25.5 Hz), 34.0, 34.8, 35.7, 37.2 (d, JCP=30.3 Hz), 37.7, 56.5, 65.2, 71.1, 75.2, 86.0 (d, 16.5 Hz), 96.0 (d, 8.1 Hz), 111.8 (t), 120.7, 123.7, 126.7, 129.4 (dd, 28.5 Hz, 62.7 Hz), 135.4 (t), 162.3 (q, 49.4 Hz), 188.4 (d, 2JCP=17.9 Hz); 31P NMR (145 MHz, CD2Cl2) δ 42.4; ESI+MS: 570 (cation+1); HRMS calculated for IrC23H41NOP 570.2477. found 570.2437; HRMS calculated for C32H12F24B 863.0649. found 863.0633.
6c: 1H NMR (360 MHz, CD2Cl2) δ 1.09 (d, 3JHP=15.5 Hz, 9H), 1.25 (m, 1H), 1.46 (m, 2H), 1.80–2.40 (m, 11H), 3.19 (m, 1H), 3.78 (m, 2H), 4.00 (m, 1H), 4.46 (dd, 5.2 Hz, 9.2 Hz, 1H), 4.81 (m, 1H), 4.93 (dd, 9.4 Hz, 10.0 Hz, 1H), 5.23 (m, 1H), 7.01 (m, 2H), 7.34 (m, 3H), 7.48 (s, 4H), 6.65 (s, 8H); 13C NMR (100 MHz, CD2Cl2) δ 23.1 (d, 2JCP=26.5 Hz), 27.3, 27.6, 28.0, 28.5, 30.9, 31.4, 33.0 (d, JCP=23.6 Hz), 33.9, 35.4, 37.1 (d, JCP=29.9 Hz), 61.7, 62.6, 69.4, 81.3, 93.3 (d, 11.6 Hz), 94.2 (d, 13.9 Hz), 118.3, 121.3, 124.0, 126.5, 126.7, 129.6 (dd, 25.2 Hz, 67.1 Hz), 130.5 (m), 135.6, 139.2, 162.5 (q, 49.5 Hz), 191.3 (d, 2JCP=19.8 Hz); 31P NMR (145 MHz, CD2Cl2) δ 53.7; ESI+MS: 590 (cation+1); HRMS calculated for IrC25H37NOP 590.2164. found 570.2120.
6d: 1H NMR (360 MHz, CD2Cl2) δ 1.18 (d, 3JHP=15.5 Hz, 9H), 1.64 (m, 3H), 1.80–2.50 (m, 11H), 2.61 (dd, 9.8 Hz, 14.1 Hz, 1H), 3.06 (m, 2H), 4.08 (m, 1H), 4.29 (m, 2H), 4.49 (t, 9.0 Hz, 1H), 4.69 (dd, 2.7 Hz, 9.4 Hz), 4.98 (m, 1H), 5.12 (b, 1H), 7.20 (m, 2H), 7.35 (m, 3H), 7.57 (s, 4H), 7.73 (s, 8H); 13C NMR (100 MHz, CD2Cl2) δ 23.7 (d, 2JCP=24.6 Hz), 26.6, 27.0 (d, 2JCP=3.7 Hz), 27.2, 30.0 (d, JCP=15.4 Hz), 32.1, 32.3 (d, 6.3 Hz), 33.4, 36.3 (d, 3.7 Hz), 36.7 (d, JCP=30.1 Hz), 41.4, 60.4, 64.0, 65.2, 76.6, 88.9 (d, 12.6 Hz), 94.3 (d, 10.3 Hz), 117.8, 120.9, 123.6, 126.3, 128.3, 129.1 (m), 129.6, 134.5, 135.2, 162.0 (q, 49.5 Hz), 190.1 (d, 2JCP=19.2 Hz); 31P NMR (145 MHz, CD2Cl2) δ 52.0; ESI+MS: 604 (cation+1); HRMS calculated for IrC26H39NOP 604.2320. found 604.2322.
6e: 1H NMR (360 MHz, CD2Cl2) δ 0.93 (d, 6.5 Hz, 3H), 0.97 (d, 6.5 Hz), 1.18 (d, 3JHP=15.5 Hz, 9H), 1.39 (m, 2H), 1.60 (m, 4H), 1.80–2.50 (m, 11H), 3.06 (d, 7.6 Hz), 3.98 (m, 2H), 4.21 (m, 1H), 4.56 (m, 2H), 4.77 (m, 1H), 5.01 (m, 1H), 7.57 (s, 4H), 7.73 (s, 8H); 13C NMR (90 MHz, CD2Cl2) δ 21.6, 23.8, 23.9 (d, 2JCP=24.6 Hz), 25.8, 26.5, 27.1 (d, 2JCP=3.7 Hz), 27.4, 30.2, 32.3 (d, JCP=24.1 Hz), 32.5, 33.8, 36.4 (d, 3.8 Hz), 37.0 (d, JCP=30.2 Hz), 45.0, 60.4, 63.3, 64.0, 77.6, 89.2 (d, 12.4 Hz), 64.6 (d, 40.9 Hz), 118.1 (t), 120.7, 123.7, 126.7, 129.5 (dd, 37.7 Hz, 76.2 Hz), 135.4 (t, 103.7 Hz), 162.4 (q, 49.7 Hz), 189.5 (d, 2JCP=24.6 Hz); 31P NMR (145 MHz, CD2Cl2) δ 51.3; ESI+MS: 570 (cation+1); HRMS calculated for IrC23H41NOP 570.2477. found 570.2423.
6f: 1H NMR (400 MHz, CD2Cl2) δ 0.79 (d, 6.8 Hz, 3H), 1.00 (d, 7.1 Hz, 3H), 1.18 (d, 3JHP=15.5 Hz, 9H), 1.80–2.30 (m, 12H), 2.40 (m, 2H), 3.55 (m, 1H), 4.18 (m, 1H), 3.93 (m, 1H), 4.46 (m, 1H), 4.52 (t, 9.4 Hz, 1H), 4.58 (m, 1H), 4.75 (dd, 3.6 Hz, 9.7 Hz, 1H), 5.02 (m, 1H), 7.61 (s, 4H), 7.77 (s, 8H); 13C NMR (100 MHz, CD2Cl2) δ 14.3 (d, 9.6 Hz), 18.6 (d, 3.5 Hz), 22.6 (d, 2JCP=29.7 Hz), 27.1 (d, 2JCP=4.6 Hz), 27.6, 27.7, 31.5, 31.8, 32.5, 33.5 (d, JCP=21.2 Hz), 35.1, 36.4 (d, JCP=30.4 Hz), 62.5 (d, 7.5 Hz), 65.4, 68.9, 73.3, 85.6 (d, 14.2 Hz), 94.9 (d, 8.7 Hz), 117.7, 120.9, 123.6, 126.3, 129.2 (dd, 37.2 Hz, 68.5 Hz), 135.2, 162.1 (q, 49.7 Hz), 187.0 (d, 2JCP=20.9 Hz); 31P NMR (145 MHz, CD2Cl2) δ 60.0; ESI+MS: 556 (cation+1); ESI−MS: 863 (anion); HRMS calculated for IrC22H39NOP 556.2320. found 556.2309; HRMS calculated for C32H′2F24B 863.0649. found 863.0650.
EXAMPLE 10
Asymmetric Reduction of Unfunctionalized Alkenes
General Hydrogenation Procedure:
To a solution of an olefin substrate (0.2 mmol) in CH2Cl2 (2 mL) was added Ir complex 6 (2 μmol, 1 mol %) under nitrogen. The solution was then transferred into an autoclave. The hydrogenation was performed at room temperature under 50 bar of H2 for 12–48 h. After carefully releasing the hydrogen, the reaction mixture was evaporated. The residue was re-dissolved with ethyl acetate, which was subsequently passed through a short silica gel plug to remove the catalyst.
The resulting solution was directly used for chiral GC or HPLC to measure the enantiomeric excess.
Ir-Catalyzed Asymmetric Hydrogenation of Methylstilbenes





















 








 












Entry[a]
Substrate
R
Catalyst
ee %[b]
Config.[c]





1

H
6a
91
R


2

H
6b
81
R


3

H
6c
95
R


4

H
6d
89
R


5

H
6e
75
R


6

H
6f
77
S


7

OMe
6c
91
R


8

Cl
6c
90
R





[a]See Experimental Section for detailed conditions.


[b]ee's were determined by Chiral HPLC (Chiralcel OJH).


[c]The absolute configuration was assigned by comparison of rotation with reported data.






Ir-Catalyzed Asymmetric Hydrogenation of β-Methylcinnamic Esters

















 












Entry[a]
Substrate
R
Catalyst
ee %[b]
Config.[c]















1
 7
Ph
6a
94
R


2
 7
Ph
6b
91
R


3
 7
Ph
6c
98
R


4
 7
Ph
6d
92
R


5
 7
Ph
6e
95
R


6
 7
Ph
6f
93
S


7
 8
p-F—Ph
6c
95
R


8
 9
p-Cl—Ph
6c
98
R


9
10
p-CH3—Ph
6c
97
R


10
11
p-OCF3—Ph
6c
97
R


11
12
p-OCH3—Ph
6c
97
R


12
13
m-CH3—Ph
6c
99
R


13
14
1-naphthyl
6c
98
R


14
15
2-naphthyl
6c
95
R


15
(Z)-9
p-Cl-Ph
6c
80
S





[a]See Experimental Section for detailed conditions.


[b]ee's were determined by chiral HPLC (Chiralcel OJH) or Chiral GC (Chiralselect 1000).


[c]The absolute configuration was assigned by comparison of optical rotation with reported data or by analogy.






A series of (E)-α,β-unsaturated esters were prepared via a Heck reaction according to a known procedure: Littke, A. F.; Fu, G. C. J. Am. Chem. Soc., 2001, 123, 6989–7000. To a Schlenk flask was added aryl halide (6.6 mmol), methyl crotonate (1.40 mL, 13.2 mmol), Pd2(dba)2 (151 mg, 165 μmol), Cy2NMe (1.55 mL, 7.26 mmol), degassed dried dioxane (20 mL), and then tBu3P (67 mg, 0.33 mmol). The whole mixture was stirred under N2 at rt overnight. At the conclusion of the reaction, the mixture was diluted with Et2O, filtered through a pad of silica gel with copious washing, concentrated, and purified through column chromatography to give product in 70–80% yield.
7: 1H NMR (300 MHz, CDCl3) δ 2.62 (d, 1.3 Hz, 3H), 3.78 (s, 3H), 6.17 (d, 1.2 Hz, 1H), 7.40 (m, 3H), 7.51 (m, 2H); 13C NMR (90 MHz, CDCl3) δ 18.4, 51.5, 117.1, 126.7, 128.9, 129.5, 142.6, 156.3, 167.7; APCI MS: 177 (M++1); HRMS calculated for C11H13O2 177.0916. found 177.0906.
8: 1H NMR (360 MHz, CDCl3) δ 2.55 (d, 1.2 Hz, 3H), 3.74 (s, 3H), 6.09 (d, 1.2 Hz, 1H), 7.05 (m, 2H), 7.45 (m, 2H); 13C NMR (90 MHz, CDCl3) δ 18.2, 51.3, 115.6 (d, 21.6 Hz), 116.8, 128.8 (d, 32.0 Hz), 138.4, 154.7, 162.1, 164.8, 167.3; APCI MS: 195 (M++1); HRMS calculated for C11H12O2F 195.0821. found 195.0824.
9: 1H NMR (300 MHz, CDCl3) δ 2.58 (d, 1.3 Hz, 3H), 3.78 (s, 3H), 6.14 (dd, 1.2 Hz, 2.4 Hz, 1H), 7.38 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 18.3, 51.6, 117.5, 128.0, 129.1, 135.5, 140.9, 154.8, 167.5; APCI MS: 211 (M++1); HRMS calculated for C11H12O2Cl 211.0526. found 211.0519.
10: 1H NMR (300 MHz, CDCl3) δ 2.40 (s, 3H), 2.61 (d, 1.2 Hz, 3H), 3.79 (s, 3H), 6.17 (d, 1.2 Hz, 1H), 7.21 (d, 8.0 Hz, 2H), 7.42 (d, 8.0 Hz, 2H); 13C NMR (75 MHz, CDCl3) δ 18.3, 21.6, 51.5, 116.2, 126.7, 129.6, 139.6, 156.2, 167.8; APCI MS: 191 (M++1); HRMS calculated for C12H15O2 191.1072. found 191.1058.
11: 1H NMR (360 MHz, CDCl3) δ 2.59 (d, 1.2 Hz, 3H), 3.79 (s, 3H), 6.15 (d, 1.2 Hz, 1H), 7.24 (d, 8.1 Hz, 2H), 2.55 (dd, 2.0 Hz, 7.9 Hz); 13C NMR (90 MHz, CDCl3) δ 18.1, 51.3, 117.7, 119.2, 121.0, 121.1, 128.0, 140.9, 149.9, 154.3, 167.1;
12: 1H NMR (300 MHz, CDCl3) δ 2.58 (d, 1.2 Hz, 3H), 3.74 (s, 3H), 3.81 (s, 3H), 6.13 (dd, 1.1 Hz, 2.4 Hz, 1H), 6.89 (dd, 2.1 Hz, 6.8 Hz, 2H), 7.45 (dd, 2.1 Hz, 6.8 Hz, 2H); 13C NMR (75 MHz, CDCl3) δ 18.0, 51.4, 55.7, 114.2, 115.2, 134.5, 155.6, 160.9, 167.8; APCI MS: 207 (M++1); HRMS calculated for C12H15O3 207.1021. found 207.1023.
13: 1H NMR (360 MHz, CDCl3) δ 2.40 (s, 3H), 2.60 (d, 1.0 Hz, 3H), 3.78 (s, 3H), 6.16 (d, 1.0 Hz, 1H), 7.21 (m, 1H), 7.29 (m, 3H); 13C NMR (90 MHz, CDCl3) δ 18.2, 21.6, 51.2, 116.8, 123.6, 127.2, 128.6, 130.0, 138.3, 142.4, 156.3, 167.5; ESI MS: 191 (M++1); HRMS calculated for C12H15O2 191.1072. found 191.1091.
14: 1H NMR (360 MHz, CDCl3) δ 2.68 (s, 3H), 3.83 (s, 3H), 6.04 (s, 1H), 7.32 (m, 1H), 7.53 (m, 3H), 7.90 (m, 3H); 13C NMR (90 MHz, CDCl3) δ 21.9, 51.3, 120.4, 124.4, 125.4, 126.2, 126.5, 128.4, 128.7, 130.3, 133.9, 142.2, 157.6, 167.2; ESI MS: 227 (M++1); HRMS calculated for C15H15O2 227.1072. found 227.1066.
15: 1H NMR (300 MHz, CDCl3) δ 2.74 (s, 3H), 3.82 (s, 3H), 6.33 (s, 1H), 7.56 (m, 3H), 7.90 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 18.4, 51.6, 117.5, 124.4, 126.4, 127.0, 127.2, 128.0, 128.6, 128.9, 133.5, 133.9, 139.6, 156.1, 167.7; APCI MS: 227 (M++1); HRMS calculated for C15H15O2 227.1072. found 227.1064.
Analytical Data and GC or HPLC Conditions for New Hydrogenation Products
Hydrogenation Product of 7:
98% ee; [α]20D=−15.5° (c=0.7, CHCl3); chiral HPLC: Chiralcel OJH, hex: iPr=95:5, tR=7.9 min (R), 9.0 min (S); 1H NMR (300 MHz, CDCl3) δ 1.33 (d, 7.0 Hz, 3H), 2.58 (dd, 8.2 Hz, 15.1 Hz, 1H), 2.66 (dd, 6.9 Hz, 15.1 Hz, 1H), 3.30 (s, 3H), 7.31 (m, 5H); 13C NMR (75 MHz, CDCl3) δ 22.2, 36.9, 43.2, 51.9, 126.8, 127.1, 128.9, 146.1, 173.3; APCI MS: 196 (M++NH4+); HRMS calculated for C11H18NO2 196.1338. found 196.1335.
Hydrogenation Product of 8:
95% ee; [α]20D=−1.9° (c=0.5, CHCl3); chiral GC: Chiralselect 1000, 140° C., tR=19.3 min (S), 19.9 (R); 1H NMR (400 MHz, CDCl3) δ 1.31 (d, 7.0 Hz, 3H), 2.60 (m, 2H), 3.30 (m, 1H), 3.64 (s, 3H), 7.16 (d, 8.0 Hz, 2H), 7.27 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 22.2, 36.2, 43.0, 51.9, 121.4, 128.4, 144.7, 148.1, 172.9; APCI MS: 214 (M++NH4+); HRMS calculated for C11H17FNO2 214.1243. found 214.1248.
Hydrogenation Product of 9:
98% ee; [α]20D=−32.4° (c=1.1, CHCl3); chiral GC: Chiralselect 1000, 140° C., tR=53.7 min (S), 55.5 min (R); 1H NMR (300 MHz, CDCl3) δ 1.29 (d, 7.0 Hz, 3H), 2.58 (m, 2H), 3.29 (m, 1H), 3.63 (s, 3H), 7.17 (m, 2H), 7.27 (m, 2H); 13C NMR (75 MHz, CDCl3) δ 22.2, 36.3, 43.0, 52.0, 128.5, 129.0, 132.4, 144.5, 173.0; APCI MS: 230 (M++NH4+); HRMS calculated for C11H17FNO2 230.0948. found 230.0942.
Hydorgenation Product of 10:
97% ee; [α]20D=−2.4° (c=0.3, CHCl3); chiral GC: Chiralselect 1000, 140° C., tR=27.1 min (S), 27.7 min (R); 1H NMR (400 MHz, CDCl3) δ 1.31 (d, 7.0 Hz, 3H), 2.35 (s,3H), 2.56 (dd, 8.2 Hz, 15.1 Hz, 1H), 2.64 (dd, 7.0 Hz, 15.1 Hz, 1H), 3.29 (m, 1H), 3.66 (s, 3H), 7.14 (s, 4H); 13C NMR (100 MHz, CDCl3) δ 21.4, 22.3, 36.4, 43.2, 51.9, 127.0, 129.6, 136.3, 143.1, 173.3; ESI MS: 210 (M++NH4+); HRMS calculated for C12H20NO2210.1494. found 210.1479.
Hydrogenation Product of 11:
97% ee; [α]20D=−23.4° (c=0.3, CHCl3); chiral GC: Chiralselect 1000, 140° C., tR=20.0 min (S), 20.5 min (R); 1H NMR (400 MHz, CDCl3) δ 1.30 (d, 7.0 Hz, 3H), 2.58 (m, 2H), 3.29 (m, 1H), 3.66 (s, 3H), 6.99 (m, 2H), 7.20 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 22.4, 36.2, 43.2, 51.9, 115.5, 128.5, 141.7, 160.6, 163.1, 173.1; ESI MS: 280 (M++NH4+); HRMS calculated for C12H17F3NO3 280.1161. found 280.1173.
Hydrogenation Product of 12:
97% ee; [α]20D=−23.8° (c=0.7, CHCl3); chiral HPLC: Chiralcel OJH, hex: iPr=95:5, tR=12.1 min (R), 13.9 min (S); 1H NMR (360 MHz, CDCl3) δ 1.27 (d, 7.5 Hz, 3H), 2.52 (dd, 8.0 Hz, 15.0 Hz, 1H), 2.59 (dd, 7.1 Hz, 15.0 Hz, 1H), 3.61 (s, 3H), 3.78 (s, 3H), 6.83 (m, 2H), 7.15 (m, 2H); 13C NMR (90 MHz, CDCl3) δ 22.1, 35.9, 43.2, 51.6, 55.4, 114.1, 127.8, 138.1, 158.3, 173.1; ESI MS: 226 (M++NH4+); HRMS calculated for C12H20NO3 226.1443. found 226.1425.
Hydrogenation Product of 13:
99% ee; [α]20D=−20.2° (c=0.5, CHCl3); chiral GC: Chiralselect 1000, 140° C., tR=47.0 min (S), 48.0 min (R); 1H NMR (360 MHz, CDCl3) δ 1.31 (d, 7.0 Hz, 3H), 2.35 (s, 3H), 2.52 (dd, 8.4 Hz, 15.2 Hz, 1H), 2.64 (dd, 6.7 Hz, 15.1 Hz, 1H), 3.25 (m, 1H), 3.65 (s, 3H), 7.04 (m, 3H), 7.21 (m, 1H); 13C NMR (90 MHz, CDCl3) δ 21.6, 22.0, 35.5, 36.5, 42.9, 51.6, 123.9, 127.4, 127.7, 128.6, 138.2, 145.9, 173.1; ESI MS: 210 (M++NH4+); HRMS calculated for C12H20NO2 210.1494. found 210.1479.
Hydrogenation Product of 14:
98% ee; [α]20D=+1.8° (c=0.72, CHCl3); chiral HPLC: Chiralcel OJH, hex: iPr=99:1, tR=32.2 min (R), 36.5 min (S); 1H NMR (400 MHz, CDCl3) δ 1.48 (d, 6.9 Hz, 3H), 2.67 (dd, 9.3 Hz, 15.3 Hz, 1H), 2.89 (dd, 5.3 Hz, 15.3 Hz, 1H), 3.70 (s, 3H), 4.21 (m, 1H), 7.50 (m, 4H), 7.77 (d, 8.0 Hz, 1H), 7.90 (d, 8.0 Hz, 1H), 8.22 (d, 8.4 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 21.6, 31.2, 42.7, 51.9, 122.7, 123.4, 125.9, 126.5, 127.4, 129.4, 131.5, 134.4, 142.1, 173.5; ESI MS: 246 (M++NH4+); HRMS calculated for C15H20NO2 246.1494. found 246.1497.
Hydrogenation Product of 15:
95% ee; [α]20D=−40.2° (c=1.2, CHCl3); chiral HPLC: Chiralcel OJH, hex: iPr=99:1, tR=65.2 min (R), 70.9 min (S); 1H NMR (300 MHz, CDCl3) δ 1.43 (d, 7.0 Hz, 3H), 2.68 (dd, 8.1 Hz, 15.2 Hz, 1H), 2.78 (dd, 7.0 Hz, 15.2 Hz, 1H), 3.49 (m, 1H), 3.65 (s, 3H), 7.46 (m, 3H), 7.69 (s, 1H), 7.83 (m, 2H); 13C NMR (75 MHz, CDCl3) δ 22.2, 37.0, 43.1, 52.0, 125.4, 125.8, 125.9, 126.4, 128.0, 128.1, 128.6, 132.8, 134.0, 143.6, 173.3; ESI MS: 246 (M++NH4+); HRMS calculated for C15H20NO2 246.1494. found 246.1481.
EXAMPLE 10
Synthesis and Structure of the Following Bisphosphine
Synthesis and Application of TangPhos Type Ligands




A chiral bisphosphine with the following structure was prepared by the procedure outlined above:




The X-ray structure of the corresponding bisphosphine sulfide was obtained and is shown below:




Further Applications

Rh-compound with this ligand is an effective catalyst for hydrogenation of enamides (e.g., E/Z mixture of PhCH(NHAc)CHCOOEt) to make beta amino acids (up to 99% ee has been achieved).







General Procedures:

All reactions and manipulations that follow were performed in a nitrogen-filled glovebox or using standard Schlenk techniques. THF was dried and distilled from sodium-benzophenone ketyl under nitrogen. Methylene chloride was dried over CaH2 and flushed with nitrogen. Methanol was distilled from Mg under nitrogen. Column chromatography was performed using EM silica gel 60 (230 ̃400 mesh). 1H, 13C, and 31P were recorded on Bruker AM-300, AMX-360, and APX-400 spectrometers. Chemical shifts were reported in ppm up field to tetramethylsilane with the solvent resonance as the internal standard. MS spectra were recorded on a KRATOS mass spectrometer MS 9/50 for LR-ESI and HR-ESI or LR-APCI and HR-APCI. GC analysis was carried on Helwett-Packard 6890 gas chromatography using chiral capillary columns. HPLC analysis was carried on WatersTM 600 chromatography.
1,5-Dihydro-benzo[e][1,3,2]dioxathiepine 3,3-dioxide (40).
To a solution of 1,2-benzenedimethanol (2.00 g, 14.5 mmol) and triethylamine (8.08 mL, 58.0 mmol) in 50 mL of CH2Cl2 was added thionyl chloride (1.59 mL, 21.7 mmol) dropwise at 0° C. The resulting dark brown solution was stirred at 0° C. for 1 h. Then 30 mL of brine was added. The organic layer was separated and the aqueous layer was extracted with CH2Cl2 (20 mL) once. The combined organic layers were dried with Na2SO4 and evaporated. The residue was further dried on vacuum pump for 2 h to afford crude cyclic sulfite (2.48 g. 13.5 mmol). This crude cyclic sulfite was dissolved in a mixture of acetonenitrile, chloroform and water (20, 20, 30 mL respectively). NaIO4 (4.33 g, 20.3 mmol) and RuCl2.xH2O (60 mg) were added at 0° C. The resulting reaction mixture was vigorously stirred at 0° C. for 1 h. 30 mL of brine was added, followed by 60 mL of Et2O. The aqueous layer was extracted with Et2O (30 mL×2). The combined organic layers were dried with Na2SO4 and evaporated. The resulting solid residue was purified by passing through a short silica gel plug (CH2Cl2 as eluent) to give 40 as a white solid (2.55 g, 88%).
1H NMR (CDCl3, 360 MHz) δ 7.47–7.44 (m, 2H), 7.39–7.36 (m, 2H), 5.43 (s, 4H); 13C NMR (CDCl3, 90 MHz) δ 134.0, 130.1, 129.6, 73.7; HRMS (M++1) m/z calcd. for C8H9O4S 201.02161. found 201.02002.
2-tert-Butyl-1,3-dihydro-isophosphindole 2-oxide (50).
To a solution of tert-butyl phosphine (1.40 mL, 11.5 mmol) in THF (40 mL) was added dropwise n-BuLi (11.5 mmol) at −78° C. The resulting yellow solution was allowed to warm to rt and stirred at rt for 1 h. A solution of 40 (2.29 g, 11.5 mmol) in THF (20 mL) was added at −78° C. via cannula. The resulting solution was allowed to warm to rt and stirred at rt for 5 h. After being cooled to −78° C. again, n-BuLi (11.5 mmol) was added dropwise. The reaction mixture was warmed to rt and stirred overnight. 2.5 mL H2O2 (30% aq.) was added at 0° C. After being stirred at 0° C. for 1 h, the reaction was quenched with saturated Na2SO3 solution (10 mL) at 0° C. for 1 h. After usual workup, the crude product was purified by recrystallization (CH2Cl2 and hexane) to give 50 as white crystals (2.26 g, 94%).
1H NMR (CDCl3, 360 MHz) δ 7.13–7.07 (m, 4H), 3.23–3.02 (m, 4H), 1.07 (d, J=14.7 Hz, 9H); 13C NMR (CDCl3, 90 MHz) δ 136.3 (d, J=8.6 Hz), 127.5, 127.1 (d, J=13.7 Hz), 32.1 (d, J=64.9 Hz), 30.3 (d, J=60.5 Hz), 23.9; 31P NMR (CDCl3, 145 Hz) δ 77.11; HRMS (M++1) m/z calcd. for C12H18OP 209.10898. found 209.10703.
(±)-2,2′-Di-tert-butyl-1,3,1′,3′-tetrahydro-[1,1′]biisophosphindolyl 2,2′-dioxide (60).
To a suspension of 50 (2.95 g, 23.8 mmol) in THF (160 mL) was added dropwise LDA (26.2 mmol) at −78° C. The resulting red solution was allowed to warm to rt and stirred at rt for 2 h. After being cooled to −78° C., CuCl2 was added in one portion. The resulting brown suspension was slowly warmed to rt under vigorous stirring overnight. 50 mL of concentrated NH3.H2O was added. After 10 min, the dark blue aqueous layer was separated and extracted with CH2Cl2 (30 mL×3). The combined organic layers were dried with Na2SO4 and evaporated. The residue was passed through a silica gel plug to give crude product 60 as a pale yellow solid (2.45 g), which was directly subject to resolution. 31P-NMR showed that this crude product involved starting material and some unidentified byproducts.
Resolution of (±)-2,2′-Di-tert-butyl-1,3,1′,3′-tetrahydro-[1,1′]biisophosphindolyl 2,2′-dioxide (60).
To a solution of the above crude 60 (2.45 g) in 25 mL of MeOH was added (L)-DBT.H2O (2.34 g). The resulting suspension was heated under refluxing for 4 h. After being cooled to rt, the white precipitate was filtered and washed with small amount of MeOH. The precipitate was then treated with 4N NaOH solution (10 mL), extracted with CH2Cl2, dried with Na2SO4 and evaporated to afford pure (+)-60 (>99% ee) as a white solid (0.73 g, 30%).
[α]20D=59.0 (c=1.1, CHCl3); 1H NMR (CDCl3, 360 MHz) δ 7.83–7.81 (m, 2H), 7.04–6.92 (m, 6H), 4.26 (d, J=3.5 Hz, 2H), 3.21–3.03 (m, 4H), 1.12 (d, J=14.4 Hz, 18H); 13C NMR (CDCl3, 90 MHz) δ 138.4 (t, J=6.5 Hz), 136.1 (t, J=5.1 Hz), 129.0 (t, J=6.4 Hz), 128.1, 127.5, 126.4 (t, J=7.1 Hz), 38.9 (m), 32.7 (m), 30.0 (m), 23.9; 31P NMR (CDCl3, 145 Hz) δ 75.31; HRMS (M++1) m/z calcd. for C24H33O2P2 415.19503. found 415.19285. The filtration was also evaporated. After being washed with 2N NaOH solution, extracted with CH2Cl2 and concentrated, the residue was treated with (D)-DBT.H2O in a similar way to afford the other enantiomer (−)-60 (>99% ee) as a white solid (0.81 g, 33%). [α]20D=−59.8 (c=1.0, CHCl3).
The X-ray structure of (−)-60 in its complex with (D)-DBT was obtained and is shown below:




X-ray structure of (−)-60 in its complex with (D)-DBT (D)-DBT has been omitted for clarity
(1R,1R′,2S,2S′)-2,2′-Di-tert-butyl-2,3,2′,3′-tetrahydro-1H,1′H-[1,1′]biisophosph-indolyl (20) (DuanPhos).
To a suspension of (+)-60 (207 mg, 0.5 mmol) in dried toluene (8 mL) under N2 was added triethylamine (0.694 mL, 5.0 mmol) and HSiCl3 (0.303 mL, 3.0 mmol). The resulting mixture was heated at 70° C. for 16 h. 5 mL of degassed NaOH solution (30% aq.) was added at 0° C., the mixture was then heated at 60° C. for 1 h. The two layers were separated and the aqueous layer was extracted with Et2O (10 mL×3). The combined organic layers were evaporated under vacuum. The solid residue was passed through a short silica gel plug under N2 (hexane:Et2O=90:10 as eluent) to give (1R,1R′,2S,2S′)-20 as a white solid (170 mg, 89%). The other enantiomer (1S,1S′,2R,2R′)-20 was obtained from (−)-60 in a similar yield following the same procedure. 1H NMR (CDCl3, 300 MHz) δ 7.35–7.32 (m, 2H), 7.19–7.05 (m, 6H), 3.71–3.62 (m, 2H), 3.31–3.18 (m, 2H), 2.73 (d, J=17.6 Hz, 2H), 0.59 (t, J=6.0 Hz, 18H); 13C NMR (CDCl3, 75 MHz) δ 146.0, 144.2, 126.7, 126.6, 126.2, 126.1, 52.7 (t, J=4.8 Hz), 29.4 (t, J=6.1 Hz), 27.9 (t, J=5.4 Hz), 26.9 (t, J=7.3 Hz); 31P NMR (CDCl3, 145 Hz) δ 4.70; HRMS (M++1) m/z calcd. for C24H33P2 383.20520. found 383.20528.
Preparation of {Rh(NBD)[(1R,1R′,2S,2S′)-2]}SbF6 (70).
To a solution of [Rh(NBD)2]SbF6 (91.3 mg, 0.175 mmol) in THF (1 mL) at −20° C. was added a suspension of (1R,1R′,2S,2S′)-20 (DuanPhos) (70 mg, 0.183 mmol) in THF (3 mL). The resulting red solution was allowed to warm to rt and stirred at rt for 15 min. The solution was concentrated to about 3 mL. Then 12 mL of Et2O was added under vigorous stirring, during which orange precipitate was formed. The precipitate was filtered and redissolved in 2 mL of THF. 10 mL of Et2O was then added under vigorous stirring. The precipitate was filtered and washed with Et2O (4 mL×2) to afford 70 as an orange solid (90 mg, 61%). 1H NMR (CDCl3, 360 MHz) δ 7.48–7.46 (m, 2H), 7.41–7.33 (m, 6H), 5.78 (d, J=1.4 Hz, 4H), 4.27 (s, 3H), 4.19 (s, 1H), 3.83 (s, 1H), 3.78 (s, 1H), 3.45–3.37 (dd, J=10.5 Hz, J=17.6 Hz, 2H), 1.90 (s, 2H), 0.81 (d, J=14.6 Hz, 18H); 31P NMR (CDCl3, 145 Hz) δ 103.46; HRMS (cation) m/z calcd. for C31H40P2Rh 577.16548. found 577.16577. HRMS (anion) m/z calcd. for SbF6 234.89370. found 234.89467.
General Procedure for Asymmetric Hydrogenation
To a solution of substrate (0.123 mmol) in 1 mL of degassed solvent (MeOH or THF) in glove-box was added {Rh(NBD)[(1R,1R′,2S,2S′)-20]}SbF6 70 (1 mg, 0.00123 mmol). This resulting solution was then transferred into an autoclave and charged with 20 psi of hydrogen. The hydrogenation was performed at room temperature for 12 h. After carefully releasing the hydrogen, the reaction mixture was passed through a short silica gel column to remove the catalyst. The enantiomeric excesses were measured by chiral GC or HPLC directly.
The present invention has been described with particular reference to the preferred embodiments. It should be understood that the foregoing descriptions and examples are only illustrative of the invention. Various alternatives and modifications thereof can be devised by those skilled in the art without departing from the spirit and scope of the present invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications, and variations that fall within the scope of the appended claims.

## Claims

1. A catalyst prepared by a process comprising:
contacting a transition metal, a salt thereof, or a complex thereof, and a chiral ligand represented by the following formula or its enantiomer:




wherein X is a divalent group selected from the group consisting of: Z, Z-(CR4R5)n, (CR4R5)n-Z-(CR4R5)n, (CR4R5)n, CH2CH(OR′)CH(OR′), CH2CH(OH)CH(OH), CH2CH(OCR′2O)CH, CH2CH(OalkylO)CH, CH2CH(OCHR′O)CH, CH2(C6H4), CH2(Ar), CH2(hetereoaryl), arylene, substituted arylene, CH2(biaryl), CH2(ferrocene), divalent aryl, 1,2-divalent phenyl (ortho-phenylene), 2,2′-divalent-1,1′-biphenyl, 2,2′-divalent-1,1′-binaphthyl, divalent hetereoaryl, divalent ferrocene, SiR′2, PR′, NR6 and group represented by the formula:




wherein each n is independently an integer from 1 to 6;
wherein Z is selected from the group consisting of: O, S, —COO—, —CO—, O—(CR4R5)n—O, CH2(C6H4), CH2 (Ar), CH2(hetereoaryl), C5H3N, divalent aryl, 1,2-divalent phenyl (ortho-phenylene), 2,2′-divalent-1,1′-biphenyl, 2,2′-divalent-1,1′-binaphthyl, divalent hetereoaryl, divalent ferrocene, SiR′2, PR′ and NR6 wherein each of R′ and R6 is independently selected from the group consisting of: hydrogen, alkyl, substituted alkyl, aryl, substituted aryl, hydroxy, alkoxy, aryloxy, acyl and alkoxycarbonyl;
wherein E is selected from the group consisting of: PR′2, PR′R′′, o-substituted pyridine, oxazoline, chiral oxazoline, CH2(chiral oxazoline), CR′2(chiral oxazoline), CH2PR′2, CH2(o-substituted pyridine), SiR′3, CR′2OH and a group represented by the formula:




wherein Y is selected from the group consisting of: a bond, (CR4R5)m, Z, Z-(CR4R5)m and (CR4R5)m-Z-(CR4R5)m; wherein each m is independently an integer from 0 to 3;
wherein each R, R′, R′′, R4 and R5 is independently selected from the group consisting of: hydrogen, linear, branched or cyclic alkyl, substituted alkyl, aryl, substituted aryl, hetereoaryl, ferrocenyl, halogen, hydroxy, alkoxy, aryloxy, alkylthio, arylthio and amido; and
wherein X and Z are have the same meaning as above.

2. The catalyst of claim 1, wherein said catalyst is a racemic mixture of enantiomers.

3. The catalyst of claim 1, wherein said catalyst is a non-racemic mixture of enantiomers.

4. The catalyst of claim 1, wherein said catalyst is one of the enantiomers.

5. The catalyst of claim 1, wherein said transition metal is selected from the group consisting of: Ag, Pt, Pd, Rh, Ru, Ir, Cu, Ni, Mo, Ti, V, Re and Mn.

6. The catalyst of claim 5, wherein said transition metal is selected from the group consisting of: Cu, Ag, Ni, Pt, Pd, Rh, Ru and Ir.

7. The catalyst of claim 1, wherein said transition metal salt, or complex thereof, is selected from the group consisting of: AgX; Ag(OTf); Ag(OTf)2; AgOAc; PtCl2; H2PtCl4; Pd2(DBA)3; Pd(OAc)2; PdCl2(RCN)2; (Pd(allyl)Cl)2; Pd(PR3)4; (Rh(NBD)2)X; (Rh (NBD)Cl)2; (Rh(COD)Cl)2; (Rh(COD)2)X; Rh(acac)(CO)2; Rh(ethylene)2(acac); (Rh(ethylene)2Cl)2; RhCl(PPh3)3; Rh(CO)2Cl2; RuHX(L)2(diphosphine), RuX2(L)2(diphosphine), Ru(arene)X2(diphosphine), Ru(aryl group)X2; Ru(RCOO)2(diphosphine); Ru(methallyl)2(diphosphine); Ru(aryl group)X2(PPh3)3; Ru(COD)(COT); Ru(COD)(COT)X; RuX2(cymen); Ru(COD)n; Ru(aryl group)X2(diphosphine); RuCl2(COD); (Ru(COD)2)X; RuX2(diphosphine); RuCl2(═CHR)(PR′3)2; Ru(ArH)Cl2; Ru(COD)(methallyl)2; (Ir(NBD)2Cl)2; (Ir(NBD)2)X; (Ir(COD)2Cl)2; (Ir(COD)2)X; CuX (NCCH3)4; Cu(OTf); Cu(OTf)2; Cu(Ar)X; CuX; Ni(acac)2; NiX2; (Ni(allyl)X)2; Ni(COD)2; MoO2(acac)2; Ti(OiPr)4; VO(acac)2; MeReO3; MnX2 and Mn(acac)2;
wherein each R and R′ is independently selected from the group consisting of: alkyl or aryl; Ar is an aryl group; and X is a counteranion.

8. The catalyst of claim 7, wherein L is a ligand derived from a solvent and wherein said counteranion X is selected from the group consisting of: halogen, BF4, B(Ar)4 wherein Ar is fluorophenyl or 3,5-di-trifluoromethyl-1-phenyl, ClO4, SbF6, PF6, CF3SO3, RCOO and a mixture thereof.

9. The catalyst of claim 1, prepared in situ or as an isolated compound.

10. A process for preparing (1S,1S′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl chiral ligand represented by the following formula or its enantiomer:



wherein X is a divalent group selected from the group consisting of: Z, Z-(CR4R5)n, (CR4R5)n-Z-(CR4R5)n, (CR4R5) n, CH2CH(OR′)CH(OR′), CH2CH(OH)CH(OH), CH2CH(OCR′2O)CH, CH2CH(OalkylO)CH, CH2CH(OCHR′O)CH, CH2(C6H4), CH2(Ar), CH2(hetereoaryl), arylene, substituted arylene, CH2(biaryl), CH2(ferrocene), divalent aryl, 1,2-divalent phenyl (ortho-phenylene), 2,2′-divalent-1,1′-biphenyl, 2,2′-divalent-1,1′-binaphthyl, divalent hetereoaryl, divalent ferrocene, SiR′2, PR′, NR6 and group represented by the formula:




wherein each n is independently an integer from 1 to 6;
wherein Z is selected from the group consisting of: O, S, —COO—, —CO—, O—(CR4R5)n—O, CH2(C6H4), CH2 (Ar), CH2(hetereoaryl), C5H3N, divalent aryl, 1,2-divalent phenyl (ortho-phenylene), 2,2′-divalent-1,1′-biphenyl, 2,2′-divalent-1,1′-binaphthyl, divalent hetereoaryl, divalent ferrocene, SiR′2, PR′ and NR6 wherein each of R′ and R6 is independently selected from the group consisting of: hydrogen, alkyl, substituted alkyl, aryl, substituted aryl, hydroxy, alkoxy, aryloxy, acyl and alkoxycarbonyl;
wherein E is selected from the group consisting of: PR′2, PR′R′′, o-substituted pyridine, oxazoline, chiral oxazoline, CH2(chiral oxazoline), CR′2(chiral oxazoline), CH2PR′2, CH2(o-substituted pyridine), SiR′3, CR′2OH and a group represented by the formula:




wherein Y is selected from the group consisting of: a bond, (CR4R5)m, Z, Z-(CR4R5)m and (CR4R5)m-Z-(CR4R5)m; wherein each m is independently an integer from 0 to 3;
wherein each R, R′, R′′, R4 and R5 is independently selected from the group consisting of: hydrogen, linear, branched or cyclic alkyl, substituted alkyl, aryl, substituted aryl, hetereoaryl, ferrocenyl, halogen, hydroxy, alkoxy, aryloxy, alkylthio, arylthio and amido; and
wherein X and Z have the same meaning as above; said process comprising the steps of:
asymmetrically deprotonating the sulfide of a 1-alkyl-phospholane represented by the formula:




wherein E is hydrogen with n-butyllithium/(−)-sparteine in a solvent to produce an anion of said 1-alkyl-phospholane-1-sulfide wherein E is a lithium cation;
contacting said anion of said 1-alkyl-phospholane-1-sulfide and CuCl2 to oxidatively couple said anion of said 1-alkyl-phospholane-1-sulfide and produce a reaction mixture comprising (1R,1R′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl-1,1′-disulfide corresponding to the disulfide of said chiral ligand;
recrystallizing said (1R,1R′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl-1,1′-disulfide corresponding to the disulfide of said chiral ligand from said reaction mixture; and
contacting said (1R,1R′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl-1,1′-disulfide corresponding to the disulfide of said chiral ligand and hexachlorodisilane in a solvent to produce said (1S,1S′,2R,2R′)-1,1′-di-alkyl-[2,2′]-diphospholanyl chiral ligand.

11. The process of claim 10, wherein said alkyl is tert-butyl.

12. The catalyst of claim 1, wherein said ligand is selected from the group consisting of compounds represented by the formula or their enantiomers: