# Patent

## Title
Brønsted acid-catalyzed asymmetric allylation and propargylation of aldehydes

## Abstract

A method synthesizing homoallylic or homopropargylic alcohols was developed to react aldehydes with allyl boronates, such as allylboronic acid pinacol ester, or allenylborates in the presence of a catalytic amount of a chiral binaphthyl-derived chiral phosphoric acid. The method showed enhanced enantiocontrol and chemical yield, which increased with lower temperatures. A large series of aldehydes were tested under these catalytic conditions and wide successful substrate scope was found, including aryl, heteroaryl, aromatic aldehydes, heteroaryl aldehydes, α,β-unsaturated aldehydes and aliphatic aldehydes, and alkyl aldehydes. Likewise, the use of crotyl boronates (E and Z) were successfully reacted with aryl aldehydes under the conditions to allow for highly enantio- and diasteo-selective crotylation.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application claims priority to U.S. Provisional Patent Application 61/350,611, entitled, “Bronsted Acid-Catalyzed Asymmetric Allylation of Aldehydes”, filed Jun. 2, 2010, the entire contents of which are hereby incorporated by reference.


GOVERNMENT SUPPORT
This invention was made with government support under Grant No. NIH GM-082935, awarded by the National Institutes of Health and Grant No. NSF-0847108, awarded by the National Science Foundation CAREER Program. The government has certain rights in the invention.


FIELD OF THE INVENTION
This invention relates to the synthesis of homoallyl alcohols. Specifically, the invention relates to the reaction of aldehydes with allyl boronates in the presence of a catalytic amount of a chiral phosphoric acid to produce chiral allylic alcohols with high enantiocontrol and chemical yield.
BACKGROUND OF THE INVENTION
Asymmetric allylboration of aldehydes has been an invaluable tool for the formation of carbon-carbon bonds with control over relative and absolute stereochemistry (Lachance, H.; Hall, D. G. Org. React. 2008, 73, 1; Denmark, S. E.; Fu, J. Chem. ReV. 2003, 103, 2763; Denmark, S. E.; Almstead, N. G. In Modern Carbonyl Chemistry; Otera, J., Ed.; Wiley-VCH: Weinheim, Germany, 2000; Chapter 10, p 299; Chemler, S. R.; Roush, W. R. In Modern Carbonyl Chemistry; Otera, J., Ed.; Wiley-VCH: Weinheim, Germany, 2000; p 403; Yamamoto, Y.; Asao, N. Chem. ReV. 1993, 93, 2207; Roush, W. R. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Pergamon Press: Oxford, U.K., 1991; Vol. 2, p 1). The foundation of this reaction was provided by Hoffmann's recognition of the diastereospecificity of the reaction when both (E)- and (Z)-crotylboronates are used (Hoffmann, R. W.; Ladner, W. Tetrahedron Lett. 1979, 20, 4653; Hoffmann, R. W.; Zeiss, H. J. Angew. Chem., Int. Ed. Engl. 1979, 18, 306; Hoffmann, R. W.; Zeiss, H. J. J. Org. Chem. 1981, 46, 1309) and Brown's highly stereoselective allylborations using pinene-derived chiral reagents (Brown, H. C.; Jadhav, P. K. J. Am. Chem. Soc. 1983, 105, 2092.; Brown, H. C.; Bhat, K. S. J. Am. Chem. Soc. 1986, 108, 293. (f) Ramachandran, P. V. Aldrichimica Acta 2002, 35, 23). Over the past three decades, additional methodologies that have relied upon stoichiometric chiral reagents or mediators have included work by Roush (Roush, W. R.; Walts, A. E.; Hoong, L. K. J. Am. Chem. Soc. 1985, 107, 8186; Chen, M.; Handa, M.; Roush, W. R. J. Am. Chem. Soc. 2009, 131, 14602; Kister, J.; DeBaillie, A. C.; Lira, R.; Roush, W. R. J. Am. Chem. Soc. 2009, 131, 14175), Masamune (Short, R. P.; Masamune, S. J. Am. Chem. Soc. 1989, 111, 1892), Corey (Corey, E. J.; Yu, C. M.; Kim, S. S. J. Am. Chem. Soc. 1989, 111, 5495), Seebach (Seebach, D.; Beck, A. K.; Imwinkelzied, R.; Roggo, S.; Wonnacott, A. Helv. Chim. Acta 1987, 70, 954), Duthaler (Riediker, M.; Duthaler, R. O. Angew. Chem., Int. Ed. Engl. 1989, 28, 494), Panek (Panek, J. S.; Yang, M. J. Am. Chem. Soc. 1991, 113, 6594), Leighton (Kinnaird, I. W. A.; Ng, P. Y.; Kubota, K.; Wang, X.; Leighton, J. L. J. Am. Chem. Soc. 2002, 124, 7920; Hackman, B. M.; Lombardi, P. J.; Leighton, J. L. Org. Lett. 2004, 6, 4375.), Chong (Wu, T. R.; Shen, L.; Chong, J. M. Org. Lett. 2004, 6, 2701), Soderquist (Burgos, C. H.; Canales, E.; Matos, K.; Soderquist, J. A. J. Am. Chem. Soc. 2005, 127, 8044. (m) Gonzalez, A. Z.; Roman, I. G.; Alicea, E.; Canales, E.; Soderquist, J. A. J. Am. Chem. Soc. 2009, 131, 1269), and Aggarwal (Althaus, M.; Mahmood, A.; Suarez, J. R.; Thomas, S. P.; Aggarwal, V. K. J. Am. Chem. Soc. 2010, 132, 4025).
Catalytic methods that avoid the use of stoichiometric chiral reagents have also emerged, and include work by Yamamoto (Furuta, K.; Mouri, M.; Yamamoto, H. Synlett 1991, 561), Umani-Ronchi (Costa, A. L.; Piazza, M. G.; Tagliavini, E.; Trombini, C.; Umani-Ronchi, A. J. Am. Chem. Soc. 1993, 115, 7001), Keck (Keck, G. E.; Tarbet, K. H.; Geraci, L. S. J. Am. Chem. Soc. 1993, 115, 8467), Denmark (Denmark, S. E.; Fu, J. Chem. ReV. 2003, 103, 2763; Denmark, S. E.; Fu, J. J. Am. Chem. Soc. 2001, 123, 9488) and others (Malkov, A.; Orsini, M.; Pernazza, D.; Muir, K. W.; Langer, V.; Meghani, P.; Kocovsky, P. Org. Lett. 2002, 4, 1047; Kim, I. S.; Ngai, M.; Krische, M. J. J. Am. Chem. Soc. 2008, 130, 14891). Also, recent catalytic allylborations by Hall (Kennedy, J. W. J.; Hall, D. G. J. Am. Chem. Soc. 2002, 124, 11586; Rauniyar, V.; Hall, D. G. J. Am. Chem. Soc. 2004, 126, 4518; Yu, S. H.; Ferguson, M. J.; McDonald, R.; Hall, D. G. J. Am. Chem. Soc. 2005, 127, 12808; Rauniyar, V.; Hall, D. G. Angew. Chem., Int. Ed. 2006, 45, 2426; Hall, D. G. Synlett 2007, 1644; Rauniyar, V.; Zhai, H.; Hall, D. G. J. Am. Chem. Soc. 2008, 130, 8481; Rauniyar, V.; Hall, D. G. J. Org. Chem. 2009, 74, 4236), Miyaura (Ishiyama, T.; Ahiko, T.-A.; Miyaura, N. J. Am. Chem. Soc. 2002, 124, 12414), Shibasaki (Wada, R.; Oisaki, K.; Kanai, M.; Shibasaki, M. J. Am. Chem. Soc. 2004, 126, 8910), and Schaus (Lou, S.; Moquist, P. N.; Schaus, S. E. J. Am. Chem. Soc. 2006, 128, 12660; Barnett, D. S.; Moquist, P. N.; Schaus, S. E. Angew. Chem., Int. Ed. 2009, 48, 8679) have opened new doors for the synthesis of homoallylic alcohols. Most of the current methods for enantioselective propargylations involve the use of chiral reagents (Ikeda, N.; Arai, I.; Yamamoto, H. J. Am. Chem. Soc. 1986, 108, 483-486; Haruta, R.; Ishiguro, M.; Ikeda, N.; Yamamoto, H. J. Am. Chem. Soc. 1982, 104, 7667-7669; Corey, E. J.; Yu, C.-M.; Lee, D.-H. J. Am. Chem. Soc. 1990, 112, 878-879; Lee, K.-C.; Lin, M,-J.; Loh, T.-P. Chem. Commun. 2004, 2456-2457; Lai, C.; Soderquist, J. A. Org. Lett. 2005, 7, 799-802). Alternatives to propargylation involving stoichiometric chiral reagents have also been developed and are limited to use of allenylic or propargylic metal reagents or intermediates (Denmark, S. E.; Fu, J. Chem. Rev. 2003, 103, 2763; Boldrini, G. P.; Tagliavini, E.; Trombini, C.; Umani-Ronchi, A. J. Chem. Soc., Chem. Commun. 1986, 685-686; Minowa, N.; Mukaiyama, T. Bull. Chem. Soc. Jpn. 1987, 60, 3697-3704; Keck, G. E.; Krishnamurthy, D.; Chen, X. Tetrahedron Lett. 1994, 35, 8323-8324; Yu, C.-M.; Yoon, S.-K.; Choi, H.-S.; Baek, K. Chem. Commun. 1997, 763-764; Yu, C.-M.; Yoon, S.-K.; Baek, K.; Lee, J.-Y. Angew. Chem. Int. Ed. 1998, 37, 2392-2395; Iseki, K.; Kuroki, Y.; Kobayashi, Y. Tetrahedron: Asymmetry, 1998, 9, 2889-2894; Denmark, S. E.; Wynn, T. J. Am. Chem. Soc. 2001, 123, 6199-6200; Evans, D. A.; Sweeney, Z. K.; Rovis, T.; Tedrow, J. S. J. Am. Chem. Soc. 2001, 123, 12095-12096; Hanawa, H.; Uraguchi, D.; Konishi, S.; Hashimoto, T.; Maruoka, K. Chem.-Eur. J. 2003, 9, 4405-4413; Inoue, M.; Nakada, M. Org. Lett. 2004, 6, 2977-2980; Naodovic, M.; Xia, G.; Yamamoto, H. Org. Lett. 2008, 10, 4053-4055; Fandrick, D. R.; Fandrick, K. R.; Reeves, J. T.; Tan, Z.; Tang, W.; Capacci, A. G.; Rodriguez, S.; Song, J. J.; Lee, H.; Lee, H.; Yee, N. K.; Senanayake, C. H. J. Am. Chem. Soc. 2010, 132, 7600-7601; Usanov, D. L.; Yamamoto, H. Angew. Chem. Int. Ed. 2010, 49, 8169-8172; Shi, S.-L.; Xu L.-W.; Oisaki, K.; Shibasaki, M. J. Am. Chem. Soc. 2010, 132, 6638-6639).
Enantiomerically pure homopropargylic alcohols are highly useful intermediates and have shown a broad synthetic utility. The terminal alkyne functionality serves as a synthetic handle for coupling reactions, metathesis and heterocycle synthesis (Trost, B. M.; Dumas, J.; VIIIa, M. J. Am. Chem. Soc. 1992, 114, 9836-9845; McDonald, F. E.; Gleason, M. M. J. Am. Chem. Soc. 1996, 118, 6648; Schmidt, D. R.; O'Malley, S. J.; Leighton, J. L. J. Am. Chem. Soc. 2003, 125, 1190-1191; O'Sullivan, P. T.; Buhr, W.; Fuhry, M. A. M.; Harrison, J. R.; Davies, J. E.; Feeder, N.; Marshall, D. R.; Burton, J. W.; Holmes, A. B. J. Am. Chem. Soc. 2004, 126, 2194-2207; Trost, B. M.; Dong, G. Nature, 2008, 456, 485-488; Francais, A.; Leyva, A.; Etxebarria-Jardi, G. Ley, S. V. Org. Lett. 2010, 12, 340-343). The addition of allenic or propargylic reagents to carbonyl compounds is mechanistically similar to the corresponding reaction with the allylic reagents. However, though many useful and innovative methods exist for the synthesis of homoallylic alcohols (Denmark, S. E.; Fu, J. Chem. Rev. 2003, 103, 2763; Brown, H. C.; Jadhav, P. K. J. Am. Chem. Soc. 1983, 105, 2092; Corey, E. J.; Yu, C. M.; Kim, S. S. J. Am. Chem. Soc. 1989, 111, 5495; Keck, G. E.; Tarbet, K. H.; Geraci, L. S. J. Am. Chem. Soc. 1993, 115, 8461; Burgos, C. H.; Canales, E.; Matos, K.; Soderquist, J. A. J. Am. Chem. Soc. 2005, 127, 8044.; Lachance, H.; Hall, D. G. Org. React. 2008, 73, 1; Chen, M.; Handa, M.; Roush, W. R. J. Am. Chem. Soc. 2009, 131, 14602; Althaus, M.; Mahmood, A.; Suarez, J. R.; Thomas, S. P.; Aggarwal, V. K. J. Am. Chem. Soc. 2010, 132, 4025), the enantioselective synthesis of homopropargylic alcohols still remains a challenge. There are two main issues: the lower reactivity of the allenylic and propargylic substrates in comparison to allylic reagents, and the difficulties associated with controlling the regioselectivity (H. Yamamoto, in Comprehensive Organic Synthesis: Propargyl and Allenyl Organometallics, ed. C. H. Heathcock, Pergamon, Oxford, 1991, vol. 2, pp. 81-98).
However, most stereoselective methods are limited by one or more drawbacks. These include the use of stoichiometric chiral inductors, allylation reagents that are difficult to prepare or are air/moisture-sensitive, the use of undesirable metal-based catalysts such as tin, or substrates leading to toxic byproducts. Therefore, what is needed is a competent, catalytic, and practical solution for the direct enantioselective synthesis of homoallylic alcohols, an important class of versatile intermediates used in the synthesis of pharmaceuticals and natural products.
SUMMARY OF THE INVENTION
Recent developments in Brønsted acid catalyzed allylborations of aldehydes, ketones and imines has fascinated synthetic chemists (Yu, S. H.; Ferguson, M. J.; McDonald, R.; Hall, D. G. J. Am. Chem. Soc. 2005, 127, 12808-12809; Rauniyar, V.; Hall, D. G. Angew. Chem., Int. Ed. 2006, 45, 2426; Rauniyar, V.; Zhai, H.; Hall, D. G. J. Am. Chem. Soc. 2008, 130, 8481; Lou, S.; Moquist, P. N.; Schaus, S. E. J. Am. Chem. Soc. 2006, 128, 12660; Lou, S.; Moquist, P. N.; Schaus, S. E. J. Am. Chem. Soc. 2007, 129, 15398-15404; Barnett, D. S.; Moquist, P. N.; Schaus, S. E. Angew. Chem., Int. Ed. 2009, 48, 8679; Jain. P.; Antilla. J. C. J. Am. Chem. Soc. 2010, 132, 11884-11886), however, to there are no reports concerning the effects of a Brønsted acid on allenylboration of these compounds.
A method of synthesizing homoallyl alcohols or homopropargyl alcohols is described whereby aldehydes can be reacted with allyl boronates, such as allylboronic acid pinacol ester or allenylboronates, in the presence of a catalytic amount of a chiral phosphoric acid to produce chiral allylic or propargylic alcohols with extremely high enantiocontrol and chemical yield. The method was optimized in terms of the chiral Brønsted acid, having the formula




where R═SiPh3, 4-(b-Nath)-Ph, 9-anthryl, 4-a-Naph)-Ph, (2,4,6-i-Pr)-Ph, or (2,5-CF3)-Ph. Ideally, the catalyst is a a triisopropylphenyl substituted BINOL based phosphoric acid, such as (R)-TRIP-PA. The catalyst is optionally added at about 5 mol %, and about 1 mol %, including 5 mol %, 2.5 mol %, or 1 mol %. A large series of aldehydes were tested under these catalytic conditions and wide successful substrate scope was found, including aryl, heteroaryl, aromatic aldehydes, heteroaryl aldehydes, α,β-unsaturated aldehydes and aliphatic aldehydes, and alkyl aldehydes. Likewise, the use of crotyl boronates (E and Z) were successfully reacted with aryl aldehydes under the conditions to allow for highly enantio- and diasteo-selective crotylation. The reaction optionally is performed in a solvent, such as toluene, m-xylene, benzene, methylene chloride, ether, or DCM.
Further testing of the reactions showed that lowering the temperature of the reactants to between about 0° C. and about −30° C., including 0° C., −5° C., −10° C., −15° C., −20° C., −25° C., or −30° C., improved enantioselectivity. Likewise, optionally adding 4 ÅMS with at least 20 mol % improved enantioselectivity.
The discovery and development of new catalytic methods for efficient synthesis of chiral homoallylic and homopropargylic alcohols will enhance the use of these versatile intermediates in natural product synthesis.



BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which:
FIG. 1 is an image of the chemical structure of (R) TRIP-PA.
FIG. 2 is a structural diagram of catalysts evaluated for the allylboration of compounds in Table 3.
FIG. 3 is an image of the proposed transition-state assembly for chiral phosphoric acid-catalyzed allylation of aldehydes.
FIG. 4 is a structural diagram of catalysts evaluated for the propargylation of compounds in Tables 5 and 6.
FIG. 5 is a structural diagram of starting reactants used in Table 6.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Binaphthyl-derived chiral phosphoric acids (PAs) have been shown to be versatile and efficient catalysts that promote a variety of enantioselective transformations. Chiral PA catalysts have found success in a large number of carbon-carbon and carbon-heteroatom bond-forming processes as well as a variety of oxidation and reduction reactions (Akiyama, T. Chem. Rev. 2007, 107, 5744; Doyle, A. G.; Jacobsen, E. N. Chem. ReV. 2007, 107, 5173; Terada, M. Chem. Commun. 2008, 4097). The present invention uses a new catalytic enantioselective allylation and crotylation of aldehydes with a non-metal based catalyst and is an easy to use asymmetric allylation. The allylation and crotylation uses commercially available allyl and crotyl pinacol boronate esters in a controlled, stereoselective manner utilizing an organocatalyst. Although chiral PA-catalyzed reactions involving aldehydes are very rare, (Terada, M.; Soga, K.; Momiyama, N. Angew. Chem., Int. Ed. 2008, 47, 4122; Momiyama, N.; Tabuse, H.; Terada, M. J. Am. Chem. Soc. 2009, 131, 12882.; Sun, F.-L.; Zeng, M.; Gu, Q.; You, S.-L. Chems. Eur. J. 2009, 15, 8709; Huang, Y.; Unni, A. K.; Thadani, A. N.; Rawal, V. H. Nature 2003, 424, 146; Nakashima, D.; Yamamoto, H. J. Am. Chem. Soc. 2006, 128, 9626; Rueping, M.; Nachtsheim, B. J.; Moreth, S. A.; Bolte, M. Angew. Chem., Int. Ed 2008, 47, 593. (d) Rueping, M.; Ieawsuwan, W.; Antonchick, A. P.; Nachtsheim, B. J. Angew. Chem., Int. Ed. 2007, 46, 2097) the enantioselective synthesis of homoallylic alcohols was investigated by reacting aldehydes with allylboronic acid pinacol ester 2 using chiral acid-catalyzed conditions. Boronate 2 is a relatively stable, nontoxic, commercially available reagent, so it was an ideal choice for our evaluation of the chemistry. The substrate scope on the aldehyde is vast thus allowing for aryl, heteroaryl, alkyl and α,β-unsaturated aldehydes.
Unless otherwise noted, the terms used herein are to be understood according to conventional usage by those of ordinary skill in the relevant art. It is to be understood that as used in the specification and in the claims, “a” or “an” can mean one or more, depending upon the context in which it is used. Thus, for example, reference to “a solvent” can mean that at least one solvent can be used.
As used herein, “about” means approximately or nearly and in the context of a numerical value or range set forth means±15% of the numerical.
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and within which are shown by way of illustration specific embodiments by which the invention may be practiced. It is to be understood that there are other embodiments by which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention.
Allylboration of Aldehydes
A screw-cap reaction tube with a stir bar was evacuated, flame-dried, and back-filled with argon. To this tube was added the (R)-TRIP-PA catalyst 4 (3.77 mg, 0.005 mmol 5 mol %), freshly distilled aldehyde (0.1 mmol, 10.1 μL), such as benzaldehyde, and 1.5 ml of dry toluene. The reaction mixture was then cooled to −30° C. followed by the addition of allylboronic acid pinacol ester 2 (23.1 μL, 0.123 mmol), dropwise over 30 seconds. The mixture was stirred overnight at this temperature under argon and then directly loaded on silica gel column, the product was separated by flash chromatography using ethyl acetate and hexanes (1:9). The product was obtained as colorless oil in 99% yield and 98% enantiomeric excess (ee) as judged by separation using a chiral HPLC (Chiralcel OD-H column using hexanes: i-PrOH=99:1).
Merck TLC plates (silica gel 60 F254) were run under the following conditions: Ethyl acetate:Hexanes (1:4). Visualization was accomplished UV light (256 nm), with the combination of ceric ammonium molybdate as indicator. Flash column chromatography was performed with Merck silica gel (230-400 mesh). Enantiomeric excess (ee) was determined using a Varian Prostar HPLC with a 210 binary pump and a 335 diode array detector. Optical rotations were performed on a Rudolph Research Analytical Autopol IV polarimeter (λ 589) using a 700-μL cell with a path length of 1-dm. 1HNMR and 13C NMR were recorded on a Varian Inova-400 spectrometer with chemical shifts reported relative to tetramethylsilane (TMS). All the compounds were known compounds and were characterized by comparing their 1H NMR and 13C NMR values to the reported values.
During the initial investigations leading to a catalytic reaction between benzaldehyde and 2, (R)-TRIP-PA (4), seen in FIG. 1, was found to be a very effective promoter (Hoffmann, S.; Seayad, A.; List, B. Angew. Chem., Int. Ed. 2005, 44, 7424). Both isomers of this catalyst (R and S) are commercially available and easily prepared from BINOL (Hoffmann, S.; Seayad, A.; List, B. Angew. Chem., Int. Ed. 2005, 44, 7424). Upon solvent screening, toluene, m-xylene, benzene, and methylene chloride were found effective for the asymmetric synthesis of alcohol 3a, as seen in Table 1. It was determined that toluene was the most suitable solvent, allowing for a 93% ee of 3a at room temperature in a reaction time of 1 h (entry 8). The enantioselectivity was further improved by reducing the temperature to 0° C. (96% ee; entry 9) and −30° C. (98% ee; entry 10) in the presence of 5 mol % catalyst. Unexpectedly, lowering the catalyst loading to 2.5 mol % allowed for a 97% ee (entry 11), and further lowering to 1 mol % (entry 12) still allowed for an impressive 95% enantioselectivity.







TABLE 1







Optimization of the Catalytic Allylboration of Aldehydesa








 











entry
solvent
time (h)
yield (%)b
ee (%)c














1
ether
16
99
35


2
DCM
16
99
88


3
THF
48
51
6


4
m-xylene
48
99
89


5
EtOAc
24
76
29


6
CH2CN
48
55
33


7
benzamine
2
99
92


8
toluene
1
99
93


9
toluened
4
99
96


10
toluenee
16
99
98


11
toluenee,f
16
99
97


12
toluenee,g
16
99
95





aReaction conditions: 1 (0.10 mmol), 2 (0.12 mmol), 5 mol % (R)-TRIP-PA, unless otherwise specified.


bIsolated yield.


cDetermined by chiral HPLC analysis.


dReaction conducted at 0° C.


eReaction conducted at −30° C.


fUsing 2.5 mol % catalyst.


gUsing 1 mol % catalyst.






The optimized reaction conditions were effective in promoting the asymmetric allylboration of a wide range of aldehydes, allowing for an extremely efficient reaction, seen in Table 2. The substrate scope extended to electron-rich and electron-poor aromatic aldehydes (entries 1-11). An ester functional group was tolerated in the chemistry (entry 8), and several hindered aldehydes also were effectively allylated (entries 7, 9, and 10). Unexpectedly, heteroaryl (entry 12), α,β-unsaturated (entries 13 and 14), and aliphatic (entries 15 and 16) aldehydes were found to be allylated efficiently with high enantioselectivity. The only limits were a lowering of enantioselectivity in the reaction with some of the aliphatic aldehyde substrates, (entries 17 and 18).







TABLE 2







Asymmetric Allylboration of Aldehydesa








 











entry
R
product
yield (%)b
ee (%)c














1
Ph
3a
99
 98d


2
4-ClC6H4
3b
98
99


3
4-BrC6H4
3c
99
99


4
4-NO2C6H4
3d
98
98


5
4-MeOC6H4
3e
95
98


6
3-MeOC6H4
3f
96
97


7
2-MeC6H4
3g
97
93


8
4-CO2MeC6H4
3h
96
96


9
1-napththyl
3i
93
98


10
9-anthryl
3j
94
91


11
piperonyl
3k
98
98


12
2-thienyl
3l
91
 96e


 


13




3m
94
96


 


14




3n
93
93


 


15
Bn
3o
98
90


16
PhCH2CH2
3p
96
 87e


17
BnOCH2
3q
92
 79e


18
c-C6H11
3r
98
73





aReaction conditions: 1 (0.10 mmol), 2 (0.12 mmol), 5 mol % (R)-TRIP-PA.


bIsolated yield.


cThe products were determined to be R by chiral HPLC analysis and optical rotation data in the literature.


dWith (S)-TRIP-PA the opposite (S) enantiomer of 3a was also obtained in 98% yield and 97% ee under otherwise identical conditions.


eIn three cases, the opposite (S) enantiomer was produced in excess using the (R)-TRIP-PA catalyst.






These examples represent a novel situation where a chiral Brønsted acid activates allylboronate esters, in the absence of a Lewis acid, in a highly enantioselective catalytic process (Yu, S. H.; Ferguson, M. J.; McDonald, R.; Hall, D. G. J. Am. Chem. Soc. 2005, 127, 12808. (d) Rauniyar, V.; Hall, D. G. Angew. Chem., Int. Ed. 2006, 45, 2426. (e) Hall, D. G. Synlett 2007, 1644. (f) Rauniyar, V.; Zhai, H.; Hall, D. G. J. Am. Chem. Soc. 2008, 130, 8481. (g) Rauniyar, V.; Hall, D. G. J. Org. Chem. 2009, 74, 4236).
Crotylboration of Aldehydes
A screw-cap reaction tube with a stir bar was evacuated, flame-dried, and back-filled with argon. To this tube was added different catalysts, seen in FIG. 2, freshly distilled benzaldehyde (0.10 mmol) and 1.5 ml of dry toluene, shown in Table 3. The reaction mixture was then cooled to required temperature followed by the addition of crotyl boronic acid pinacol ester 5 (0.12 mmol), dropwise over 30 seconds. The mixture was stirred overnight at this temperature. Next day 1 ml of 1M HCl was added and the reaction was stirred for 15 minutes. Proton NMR of the crude mixture was collected and then the product was purified by flash chromatography using ethyl acetate and hexanes (1:9).







TABLE 3







Catalyst screening for the allylboration of aldehydes:








 












entry
catalyst
% conversion
ee (%)















1
4a
100
4



2
4b
100
5



3
4c
100
4



4
4d
100
6



5
4e
100
93



5
4f
100
8



6
4g
100
6



7
4h
100
88









(R)-TRIP-PA was found to promote the crotylboration of benzaldehyde with high diastereo- and enantioselectivity, seen in Table 4. Use of (E)-crotylboronate 5a provided the anti isomer 6a exclusively with 96% ee at room temperature (entry 1) and >99% ee at 0° C. (entry 2) using the general reaction conditions. When (Z)-crotylboronate 5b was employed, the syn isomer 6b was obtained exclusively with 94% ee at −30° C.







TABLE 4







Asymmetric Crotylboration of Benzaldehydea








 













entry
R1
R2
temp
6a/6bb
yield (%)c
ee (%)d





1
CH3
H
rt
2:98
96
96


2
CH3
H
 0° C.
2:98
96
99


3
H
CH3
−30° C.
98:2
95
94





aReaction conditions: 1 (0.10 mmol), 2 (0.12 mmol), 5 mol % (R)-TRIP-PA.


bDetermined by 1H NMR analysis.


cIsolated yield.


dDetermined by chiral HPLC analysis.






Although the reaction mechanism for this interesting activation has yet to be elucidated, the observed diastereoselectivity in the crotylation strongly suggests that the allylboration proceeds via a type-I mechanism involving a chair-like six-membered cyclic transition state, similar to previous uncatalyzed reactions involving allylboronates (Yang, J. E. Six-Membered Transition States in Organic Synthesis; Wiley: Hoboken, N.J., 2008; Chapter 3, pp 97-146. (b) Li, Y.; Houk, K. N. J. Am. Chem. Soc. 1989, 111, 1236). Recent work by Hall (Rauniyar, V.; Zhai, H.; Hall, D. G. J. Am. Chem. Soc. 2008, 130, 8481; Rauniyar, V.; Hall, D. G. J. Org. Chem. 2009, 74, 4236) and Schaus (Barnett, D. S.; Moquist, P. N.; Schaus, S. E. Angew. Chem., Int. Ed. 2009, 48, 8679) suggested that activation by protonation of the boronate oxygen could be involved. Similarly, Lewis acid-promoted boronate activation has also been invoked previously (Rauniyar, V.; Hall, D. G. J. Am. Chem. Soc. 2004, 126, 4518). Without being bound to a specific theory, the reaction likely occurs via protonation of the boronate oxygen by the chiral phosphoric acid catalyst, as seen in FIG. 3.
Allenylboration of Aldehydes
Based on the development of phosphoric acid catalyzed allylboration, allenylboration was used to synthesize non-racemic homopropargyl alcohols. Benzaldehyde was reacted with boronate 2, a relatively stable, non-toxic and commercially available reagent. The C—C bond formation proceeded smoothly in presence of various chiral acid-catalysts (Akiyama, T. Chem. Rev. 2007, 107, 5744; Doyle, A. G.; Jacobsen, E. N. Chem. Rev. 2007, 107, 5173; Terada, M. Chem. Commun. 2008, 4097) with complete regioselectivity, as seen in Table 5. PA5 (Hoffmann, S.; Seayad, A.; List, B. Angew. Chem., Int. Ed. 2005, 44, 7424), seen in FIG. 4, gave the best enantioselectivity along with toluene as the solvent. Superior selectivity was attained with higher catalyst loading in presence of 4 ÅMS (entry 13). Slight improvement in enantioselectivity was observed with the lowering of temperature to 0° C. (entry 14) and −20° C. (entry 15), albeit with longer reaction times.







TABLE 5







Catalyst screening and optimization of the catalytic propargylation of


aldehydesa








 












entry
catalystb
solvent
time (h)
yield (%)c
ee (%)d















1
PA1
toluene
40
94
0


2
PA2
toluene
40
93
7


3
PA3
toluene
40
92
20


4
PA4
toluene
40
95
9


5
PA5
toluene
40
91
74


6
PA6
toluene
40
93
4


7
PA7
toluene
40
94
16


8
PA5
benzene
40
89
62


9
PA5
DCM
40
87
43


10
PA5
PhCF3
40
94
68


11
PA5
p-xylene
40
92
75


12
PA5
toluenee
40
92
77


13
PA5
toluenee,f
24
93
87


14
PA5
toluenee,f,g
64
96
90


15
PA5
toluenee,f,h
72
94
91





aReaction conditions: 1 (0.10 mmol), 2 (0.15 mmol), 5 mol % catalyst, unless otherwise specified.


bCatalysts were washed with 6M HCl after purification by column chromatography.


cIsolated yield.


dDetermined by chiral HPLC analysis.


eReaction conducted in presence of 4 Å MS.


f20 mol % chiral acid catalyst used.


gReaction conducted at 0° C.


hReaction conducted at −20° C.






Having optimized the conditions, a range of various aldehydes were tested to study the scope and limitation of the developed methodology, as seen in Table 6. Though benzaldehyde showed >90% conversion in 48 hours, the reaction time was not further optimized and all the substrates were allowed to react for 96 hours to ensure complete conversion. The catalyst system showed tolerance to electron density effect (1b-1d for electron-withdrawing and 1e-1g electron-donating groups in comparison to 1a) giving excellent yields and selectivity (92-96% ee). An ester (1h, 91% ee), an ether (1i, 94% ee) tethered on the aromatic ring and a sterically hindered substrate (1j, 91% ee), seen in FIG. 5, were also well tolerated.







TABLE 6





Enantioselective propargylation of aldehydesa



















 








 








 








 








 








 








 








 








 








 








 








 








 








 











aReaction conditions: 1 (0.10 mmol), 2 (0.12 mmol), 20 mol % PA5. All yields are isolated yields. Enantioselectivity was determined by chiral HPLC. The products were determined to be (R) by chiral HPLC analysis and optical rotation data in the literature.


bEnantioselectivity was determined by 1H NMR after conversion to the corresponding Mosher ester.






The procedure was also extended to aliphatic aldehydes with enantioselectivities of 77-83% ee, seen with compounds 1k-1m. The allenylboration proceeds via a six-membered cyclic transition state where the catalyst powers the reaction by protonation of the boronate oxygen.
A simple and highly efficient chiral phosphoric acid-catalyzed allylboration of aldehydes has been developed. The protocol provides a highly enantioselective method for the synthesis of homoallylic alcohols from simple starting materials. The reaction is simple and highly efficient with a broad scope in synthetic chemistry. The usefulness of this organocatalytic reaction is highlighted by the stability and commercial availability of the substrates and the catalyst.
EXAMPLES
The following reactions were carried out in flame-dried screw-cap test tubes and were allowed to proceed under a dry argon atmosphere with magnetic stirring. Toluene was purified by passing through a column of activated alumina under a dry argon atmosphere. A screw-cap reaction tube with a stir bar was evacuated, flame-dried, and back-filled with argon. Aldehydes were purchased from commercial sources and were distilled prior to use. TRIP catalyst was prepared from chiral BINOL according to the known literature procedure (Hoffmann, S.; Seayad, A.; List, B. Angew. Chem., Int. Ed. 2005, 44, 7424). To this tube was added the (R)-TRIP-PA catalyst 4 (5 mol %), freshly distilled aldehyde (0.1 mmol) and 1.5 ml of dry toluene. The reaction mixture was then cooled to −30° C. followed by the addition of allylboronic acid pinacol ester 2 (0.12 mmol), dropwise over 30 seconds. The mixture was stirred overnight at this temperature and then directly loaded on a silica gel column, the crude product was purified by flash chromatography using ethyl acetate and hexanes (1:9).
Thin layer chromatography was performed on Merck TLC plates (silica gel 60 F254). Visualization was accomplished UV light (256 nm), with the combination of ceric ammonium molybdate as indicator. Flash column chromatography was performed with Merck silica gel (230-400 mesh). Enantiomeric excess (ee) was determined using a Varian Prostar HPLC with a 210 binary pump and a 335 diode array detector. Optical rotations were performed on a Rudolph Research Analytical Autopol IV polarimeter (λ 589) using a 700-μL cell with a path length of 1-dm. 1H NMR and 13C NMR were recorded on a Varian Inova-400 spectrometer with chemical shifts reported relative to tetramethylsilane (TMS). All the compounds were known compounds and were characterized by comparing their 1H NMR and 13C NMR values to the reported values.




(R)-1-Phenyl-but-3-en-1-ol (3a)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 99% yield with spectral properties reported in literature (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601). Enantiomeric excess was determined by HPLC with a chiralcel OD-H column (hexane/iPrOH=99/1, 0.7 mL/min), tmajor=29.27 min, tminor 34.44 min; ee=98%. [α]24D=+55.74 (c=0.98, CHCl3). The reported value (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601) for the R-enantiomer (95% ee) is [α]D=+56.5 (c=1.0, CHCl3). 1H NMR (400 MHz, CDCl3): δ 7.35-7.20 (m, 5H), 5.85-5.71 (m, 1H), 5.16-5.10 (m, 2H), 4.72 (dd, J=7.6, 5.6 Hz, 1H), 2.54-2.43 (m, 2H), 2.00 (br s, 1H).




(R)-1-(4-Chloro-phenyl)-but-3-en-1-ol (3b)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 98% yield with spectral properties reported in literature (Wu. T. R.; Shen, L.; Chong, M. Org. Lett. 2004, 6, 2701-2704). Enantiomeric excess was determined by HPLC with a chiralcel AD-H column (hexane/iPrOH=99/1, 1.0 mL/min), tmajor=26.59 min, tminor=28.55 min; ee=99%. [α]24D=+ 63.3 (c=1.14, CHCl3). The reported value (Wu. T. R.; Shen, L.; Chong, M. Org. Lett. 2004, 6, 2701-2704) for the R-enantiomer (94% ee) is [α]D=+61.4 (c=1.17, CHCl3). 1H NMR (400 MHz, CDCl3): δ 2.04 (s, 1H), 2.39-2.52 (m, 2H), 4.66-4.73 (m, 1H), 4.96-5.20 (m, 2H), 5.69-5.83 (m, 1H), 7.18-7.35 (m, 4H).




(R)-1-(4-Bromo-phenyl)-but-3-en-1-ol (3c)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 99% yield with spectral properties reported in literature (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-560). Enantiomeric excess was determined by HPLC with a chiralcel OJ-H column (hexane/iPrOH=95/5, 0.4 mL/min), tminor=25.61 min, tmajor=28.16 min; ee=99%. [α]24D=+ 25.82 (c=0.91, Benzene). The reported value (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601) for the R-enantiomer (96% ee) is α]D=+23.2 (c=1.17, Benzene). 1H NMR (400 MHz, CDCl3): δ 7.47 (d, J=8.4 Hz, 2H), 7.23 (d, J=8.4 Hz, 2H), 5.83-5.71 (m, 1H), 5.18-5.13 (m, 2H), 4.69 (dd, J=7.6, 4.8 Hz, 1H), 2.52-2.39 (m, 2H), 2.06 (br s, 1H).




(R)-1-(4-Nitro-phenyl)-but-3-en-1-ol (3d)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 98% yield with spectral properties reported in literature (Burgos, C. H.; Canales, E.; Matos, K.; Soderquiest, J. A. J. Am. Chem. Soc. 2005, 127, 8044). Enantiomeric excess was determined by HPLC with a chiralcel AS-H column (hexane/iPrOH=97/3, 0.7 mL/min), tmajor=52.09 min, tminor=54.52 min; ee=98%. [α]24D=+65.87 (c=1.07, CHCl3). The reported value (Burgos, C. H.; Canales, E.; Matos, K.; Soderquiest, J. A. J. Am. Chem. Soc. 2005, 127, 8044) for the R-enantiomer (97% ee) is [α]D=+64.2 (c=0.8, CHCl3). 1H NMR (400 MHz, CDCl3): δ 8.23 (d, J=8.8 Hz, 2H), 7.56 (d, J=8.8 Hz, 2H), 5.86-5.72 (m, 1H), 5.24-5.17 (m, 2H), 4.89 (m, 1H), 2.61-2.55 (m, 1H), 2.52-2.44 (m, 1H) 2.31 (br s, 1H).




(R)-1-(4-Methoxy-phenyl)-but-3-en-1-ol (3e)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 95% yield with spectral properties reported in literature (Wu. T. R.; Shen, L.; Chong, M. Org. Lett. 2004, 6, 2701-2704). Enantiomeric excess was determined by HPLC with a chiralcel OD-H column (hexane/iPrOH=98/2, 1.0 mL/min), tmajor=18.64 min, tminor=22.87 min; ee=98%. [α]24D=+30.84 (c=1.01, Benzene). The reported value (Wu. T. R.; Shen, L.; Chong, M. Org. Lett. 2004, 6, 2701-2704) for the R-enantiomer (95% ee) is [α]D=+30.5 (c=1.0, Benzene). 1H NMR (400 MHz, CDCl3): δ 7.25 (d, J=8.0 Hz, 2H), 6.86 (d, J=8.0 Hz, 2H), 5.83-5.72 (m, 1H), 5.16-5.09 (m, 2H), 4.69 (m, 1H), 3.78 (s, 3H), 2.50 (m, 2H), 1.95 (br s, 1H).




(R)-1-(3-Methoxy-phenyl)-but-3-en-1-ol (3f)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 96% yield with spectral properties reported in literature (Zheng, Y.; Zhou, J.; Loh. T. Org. Lett. 1999, 11, 1855-1857). Enantiomeric excess was determined by HPLC with a chiralcel OJ-H column (hexane/iPrOH=98/2, 0.8 mL/min), tminor=28.63 min, tmajor=30.17 min; ee=97%. [α]24D=+53.81 (c=0.89, Benzene). The reported value (Zheng, Y.; Zhou, J.; Loh. T. Org. Lett. 1999, 11, 1855-1857) for the R-enantiomer (73% ee) is [α]D=+41.0 (c=2.22, Benzene). 1H NMR (400 MHz, CDCl3): δ 7.27-7.22 (m, 1H) 6.94-6.89 (m, 2H), 6.82-6.78 (m, 1H), 5.85-5.47 (m, 1H), 5.19-5.10 (m, 2H), 4.67-4.72 (m, 1H), 3.80 (s, 3H), 2.56-2.42 (m, 2H), 1.95 (br s, 1H).




(R)-1-o-Tolyl-but-3-en-1-ol (3g)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 97% yield with spectral properties reported in literature (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601). Enantiomeric excess was determined by HPLC with a chiralcel AD-H column (hexane/iPrOH=95/5, 0.5 mL/min), tmajor=13.89 min, tminor=16.32 min; ee=93%. [α]24D=+68.8 (c=1.11, Benzene). The reported value (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601) for the R-enantiomer (97% ee) is [α]D=+75.5 (c=1.0, Benzene). 1H NMR (400 MHz, CDCl3): δ 7.49 (d, J=7.8 Hz, 1H), 7.28-7.12 (m, 3H) 5.22-5.14 (m, 2H), 4.97 (dd, J=8.0, 4.8 Hz, 1H), 2.54-2.40 (m, 2H), 2.35 (s, 3H), 2.02 (br s, 1H).




(R)-Methyl 4-(1-hydroxybut-3enyl)benzoate (3h)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 96% yield with spectral properties reported in literature (Kim, I. S.; Ngai, M.; Krische, M. J. J. Am. Chem. Soc. 2008, 130, 14891). Enantiomeric excess was determined by HPLC with a chiralcel AD-H column (hexane/iPrOH=95/5, 0.6 mL/min), tmajor=23.67 min, tminor=26.84 min; ee=96%. [α]24D=27.84 (c=1.31, Benzene). 1H NMR (400 MHz, CDCl3): δ 8.00 (d, J=8.0 Hz, 2H), 7.42 (d, J=8.0 Hz, 2H), 5.83-5.72 (m, 1H), 5.17-5.12 (m, 2H), 4.79 (dd, J=8.0, 4.8 Hz, 1H), 3.90 (s, 3H), 2.56-2.41 (m, 2H), 2.24 (br s, 1H).




(R)-1-Naphthalen-1-yl-but-3-en-1-ol (31)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 93% yield with spectral properties reported in literature (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601). Enantiomeric excess was determined by HPLC with a chiralcel OD-H column (hexane/iPrOH=90/10, 0.5 mL/min), tminor=16.44 min, tmajor=26.73 min; ee=98%. [α]24D=+98.63 (c=1.06, Benzene). The reported value (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601) for the R-enantiomer (92% ee) is [α]D=+97.3 (c=1.0, Benzene). 1H NMR (400 MHz, CDCl3): δ 8.09 (d, J=8.2 Hz, 1H), 7.88 (d, J=7.8 Hz, 1H), 7.79 (d, J=8.2 Hz, 1H), 7.68 (d, J=7.1 Hz, 1H), 7.55-7.45 (m, 3H), 6.00-5.87 (m, 1H), 5.58-5.52 (m, 1H), 5.28-5.16 (m, 2H), 2.80-2.56 (m, 2H), 2.14 (br s, 1H).




(R)-1(anthrcen-9-yl)but-3-en-1-ol (3j)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 93% yield with spectral properties reported in literature (Bold, G.; Duthaler, R. D.; Riediker, M. Angew. Chem. 1989, 101, 491-493). Enantiomeric excess was determined by HPLC with a chiralcel AD-H column (hexane/iPrOH=95/5, 1.0 mL/min), tmajor=17.60 min, tminor=21.29 min; ee=91%. [α]24D=+17.38 (c=1.85, CHCl3). 1H NMR (400 MHz, CDCl3): δ 8.72-8.60 (m, 2H), 8.39 (s, 1H), 8.02-7.97 (m, 2H), 7.51-7.42 (m, 4H), 6.29 (dd, J=6.3 Hz, 1H), 6.01-5.90 (m, 1H), 5.29-5.10 (m, 2H), 3.24-3.15 (m, 1H), 2.89-2.81 (m, 1H), 2.25 (br s, 1H).




(R)-1-(Benzo[d][1,3]dioxol-5-yl)but-3-en-1-ol (3k)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 98% yield with spectral properties reported in literature (Kim, I. S.; Ngai, M.; Krische, M. J. J. Am. Chem. Soc. 2008, 130, 14891). Enantiomeric excess was determined by HPLC with a chiralcel OD-H column (hexane/iPrOH=98/2, 1.0 mL/min), tmajor=22.37 min, tminor=27.64 min; ee=98%. [α]24D=+35.53 (c=0.95, CHCl3). 1H NMR (400 MHz, CDCl3): δ 6.86 (m, 1H), 6.81-6.75 (m, 2H), 5.95 (s, 2H), 5.84-5.72 (m, 1H), 5.18-5.11 (m, 2H), 4.65 (t, J=6.8 Hz, 1H), 2.46 (t, J=6.4 Hz, 2H), 1.96 (br s, 1H).




(S)-1-Thiophen-2-yl-but-3-en-1-ol (3l)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 91% yield with spectral properties reported in literature (Singh, S.; Kumar, S.; Chimni, S. S. Tetrahedron Asym. 2002, 13, 2679-2687). Enantiomeric excess was determined by HPLC with a chiralcel OJ-H column (hexane/iPrOH=93/7, 0.5 mL/min), tminor=21.37 min, tmajor=24.59 min; ee=96%. [α]24D=−12.33 (c=1.07, CHCl3). The reported value (Xia, G; Yamamoto, H. J. Am. Chem. Soc. 2006, 128, 2554-2555) for the R-enantiomer (95% ee) is [α]D=+9.7 (c=1.0, EtOH). 1H NMR (400 MHz, CDCl3): δ 7.27-7.24 (m, 1H), 6.98-6.94 (m, 2H), 5.87-5.76 (m, 1H), 5.20-5.14 (m, 2H), 4.96-5.00 (m, 1H), 2.63-2.59 (m, 2H), 2.10-2.11 (m, 1H).




(R),(E)-1-Phenyl-hexa-1,5-dien-3-ol (3m)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 94% yield with spectral properties reported in literature (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601). Enantiomeric excess was determined by HPLC with a chiralcel AS-H column (hexane/iPrOH=95/5, 1.0 mL/min), tmajor=8.00 min, tminor=9.04 min; ee=96%. [α]24D=−9.76 (c=1.12, Et2O). The reported value (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601) for the R-enantiomer (97% ee) is [α]D=−12.3 (c=1.0, Et2O). 1H NMR (400 MHz, CDCl3): δ 7.39-7.21 (m, 5H), 6.60 (d, J=16.0 Hz, 1H), 6.23 (dd, J=16.0, 6.4 Hz, 1H), 5.90-5.80 (m, 1H), 5.20-5.14 (m, 2H), 4.35 (ddd, J=6.8, 6.0, 6.0 Hz, 1H), 2.45-2.33 (m, 2H), 1.80 (br s, 1H).




(R),(E)-2-Methyl-1-phenyl-hexa-1,5-dien-3-ol (3n)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 93% yield with spectral properties reported in literature (Malkov, A.; Dufkova, L.; Farrugia, L.; Kocovsky, P. Angew. Chem. Int. Ed. 2003, 42, 3674-3677). Enantiomeric excess was determined by HPLC with a chiralcel OD-H column (hexane/iPrOH=97/3, 1.0 mL/min), tmajor=10.85 min, tminor=12.64 min; ee=93%. [α]24D=+2.37 (c=0.79, CHCl3). The reported value 10 for the R-enantiomer (50% ee) is [α]D=+1.1 (c=1.15, CHCl3). 1H NMR (400 MHz, CDCl3): δ 1.82-1.84 (m, 1H), 1.87-1.88 (m, 3H), 2.34-2.48 (m, 2H), 4.17-4.25 (m, 1H), 5.11-5.21 (m, 2H), 5.77-5.88 (m, 1H), 6.52 (s, 1H), 7.18-7.35 (m, 5H).




(R)-1-Phenylpent-4-en-2-ol (3o)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 98% yield with spectral properties reported in literature (Rauniyar, V.; Zhai, H.; Hall, D. G. J. Am. Chem. Soc. 2008, 130, 8481). Enantiomeric excess was determined by HPLC with a chiralcel OD-H column (hexane/iPrOH=97/3, 0.5 mL/min), tminor=15.51 min, tmajor=19.65 min; ee=90%. [α]24D=−12.20 (c=1.01). The reported value (Rauniyar, V.; Zhai, H.; Hall, D. G. J. Am. Chem. Soc. 2008, 130, 8481) for the R-enantiomer (97% ee) is [α]D=−14.24 (c=0.65, CHCl3). 1H NMR (400 MHz, CDCl3): δ 7.35-7.20 (m, 5H), 5.94-5.80 (m, 1H), 5.20-5.12 (m, 2H), 3.93-3.84 (m, 1H), 2.86-2.70 (m, 2H), 2.38-2.18 (m, 2H), 1.7 (br s, 1H).




(S)-1-Phenylpent-4-en-2-ol (3p)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 96% yield with spectral properties reported in literature (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601). Enantiomeric excess was determined by HPLC with a chiralcel OD-H column (hexane/iPrOH=95/5, 1.0 mL/min), tmajor=8.76 min, tminor=13.29 min; ee=87%. [α]24D=−25.4 (c=0.97, Benzene). The reported value (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601) for the S-enantiomer (86% ee) is [α]D=−26.4 (c=1.0, Benzene). 1H NMR (400 MHz, CDCl3): δ 1.76-1.84 (m, 2H), 2.14-2.37 (m, 2H), 2.64-2.86 (m, 2H), 3.62-3.72 (m, 1H), 5.08-5.19 (m, 2H), 5.72-5.98 (m, 1H), 7.13-7.32 (m, 5H).




(S)-1-Benzyloxy-pent-4-en-2-ol (3q)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 92% yield with spectral properties reported in literature (Lee, J.; Miller, J. J.; Hamilton, S. S.; Sigman, S. S. Org. Lett. 2005, 7, 1837-1839). Enantiomeric excess was determined by HPLC with a chiralcel AS-H column (hexane/iPrOH=97/3, 0.5 mL/min), tminor=20.91 min, tmajor=25.09 min; ee=79%. [α]24D=−1.26 (c=1.27, CHCl3). The reported value (Lee, J.; Miller, J. J.; Hamilton, S. S.; Sigman, S. S. Org. Lett. 2005, 7, 1837-1839) for the R-enantiomer (53% ee) is [α]D=+0.9 (c=2.5, CHCl3). 1H NMR (400 MHz, CDCl3): δ 7.37-7.24 (m, 5H), 5.87-5.75 (m, 1H), 5.13-5.06 (m, 2H), 4.54 (s, 2H), 3.92-3.84 (m, 1H), 3.50 (dd, J=9.2, 3.6 Hz, 1H), 3.36 (dd, J=9.6, 7.6 Hz, 1H), 2.35 (br s, 1H), 2.25 (t, J=6.8 Hz, 2H).




(R)-1-Cyclohexyl-but-3-en-1-ol (3r)
Following the general procedure for the allylation of aldehydes, the title compound was obtained in 98% yield with spectral properties reported in literature (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601). Enantiomeric excess was determined by formation of 3,5 dinitrobenzoate ester of the title compound followed by HLPC with a chiralcel OD-H column (hexane/iPrOH=95/5, 1.0 mL/min), tmajor=10.97 min, tminor=11.76 min; ee=73%. [α]24D=+ 5.24 (c=1.0, EtOH). The reported value (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601) for the R-enantiomer (93% ee) is [α]D=+13.7 (c=1.0, EtOH). 1H NMR (400 MHz, CDCl3): δ 0.91-1.32 (m, 4H), 1.55-1.87 (m, 7H), 2.16-2.08 (m, 1H), 2.30-2.37 (m, 1H), 3.42-3.35 (m, 1H), 5.16-5.10 (m, 2H), 5.90-5.78 (m, 1H).




1-Methyl-1-phenyl-but-3-en-1-ol (6a)
Following the general procedure for the crotylboration of aldehydes, the syn product was obtained when cis-crotylboronic acid pinacol ester was used at −30° C., in 95% yield with spectral properties reported in literature (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601). Enantiomeric excess was determined by HPLC with a chiralcel OD-H column (hexane/iPrOH=95/5, 1.0 mL/min), tminor=7.17 min, tmajor=8.32 min; ee=93%. [α]24D=+19.27 (c=2.27, CHCl3). The absolute configuration of the syn isomer was found to be (1R,2S) by comparing with the literature (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601). 1H NMR (400 MHz, CDCl3): δ 0.99 (d, J=6.8 Hz, 3H), 1.94-1.96 (m, 1H), 2.52-2.62 (m, 1H), 4.60 (dd, J=5.5 Hz, 1H), 5.01-5.07 (m, 2H), 5.70-5.80 (m, 1H), 7.22-7.35 (m, 5H).
Crude proton NMR spectrum (after quench with 1M HCl) showing the syn-product when (Z)-crotyl boronate 5b was used.




1-Methyl-1-phenyl-but-3-en-1-ol (6b)
Following the general procedure for the crotylboration of aldehydes, the anti product was obtained when trans-crotylboronic acid pinacol ester was used at −0° C., in 96% yield with spectral properties reported in literature (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601). Enantiomeric excess was determined by HPLC with a chiralcel AD-H column (hexane/iPrOH=98/2, 1.0 mL/min)) tminor=12.73 min, tmajor=13.77 min; ee=99%. [α]24D=98.97 (c=2.27, CHCl3). The absolute configuration of the anti isomer was found to be (1R,2R) by comparing with the literature (Wadamoto, M.; Ozasa, N.; Yanagigawa, A.; Yamamoto, H. J. Org. Chem. 2003, 68, 5593-5601). 1H NMR (400 MHz, CDCl3): δ 0.88 (d, J=6.8 Hz, 3H), 2.13 (br s, 1H), 2.41-2.60 (m, 1H), 4.36 (d, J=7.8 Hz, 1H), 5.12-5.26 (m, 2H), 5.66-5.86 (m, 1H), 7.20-7.37 (m, 5H).
Crude proton NMR spectrum (after quench with 1M HCl) showing the anti-product when (E)-crotyl boronate 5b was used.
In the preceding specification, all documents, acts, or information disclosed does not constitute an admission that the document, act, or information of any combination thereof was publicly available, known to the public, part of the general knowledge in the art, or was known to be relevant to solve any problem at the time of priority.
The disclosures of all publications cited above are expressly incorporated herein by reference, each in its entirety, to the same extent as if each were incorporated by reference individually.
While there has been described and illustrated specific embodiments of a method for preparing homoallyl alcohols, it will be apparent to those skilled in the art that variations and modifications are possible without deviating from the broad spirit and principle of the present invention. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

## Claims

1. A method of synthesizing homoallyl or homopropargyl alcohols, comprising the steps of:
obtaining an aldehyde, where the aldehyde does not possess a protecting group;
obtaining an allylboronate or allenylboronate, where the allylboronate or allenylboronate does not possess a protecting group;
lowering the temperature of the aldehyde and the allylboronate or allenylboronate to between about 0° C. and about −30° C.;
reacting the aldehyde with the allylboronate or allenylborate in the presence of a chiral acid catalyst, wherein the chiral acid catalyst has the formula





where R═SiPh3, 4-(b-Nath)-Ph, 9-anthryl, 4-(a-Naph)-Ph, (2,4,6-i-Pr)-Ph, or (2,5-CF3)-Ph; and

wherein the reaction forms a homoallyl alcohol.

2. The method of claim 1, wherein the aldehyde is selected from the group consisting of aromatic aldehydes, heteroaryl aldehydes, α,β-unsaturated aldehydes and aliphatic aldehydes.

3. The method of claim 1, further comprising reacting the aldehyde and allylboronate in a solvent, wherein the solvent is toluene, m-xylene, benzene, methylene chloride, ether, or DCM.

4. The method of claim 3, wherein the solvent is toluene.

5. The method of claim 1, wherein the chiral acid catalyst is (R)-3,3′-Bis(2,4,6-triisopropylphenyl)-1,1′-binaphthyl-2,2′-diyl hydrogenphosphate.

6. The method of claim 1, wherein the temperature of the reactants is 0° C. or −30° C.

7. The method of claim 1, wherein the chiral acid catalyst is at a catalyst loading amount of between about 5 mol %, and about 1 mol %.

8. The method of claim 7, wherein the chiral acid catalyst is at a catalyst loading amount of 5 mol %, 2.5 mol %, or 1 mol %.

9. The method of claim 1, further comprising adding a 4 Å molecular sieve and at a catalyst loading amount of 20 mol %.

10. The method of claim 9, further comprising lowering the temperature of the reactants to between about 0° C. and about −20° C.

11. The method of claim 9, wherein the temperature of the reactants is 0° C. or −20° C.

12. The method of claim 2, wherein the aldehydes are heteroaryl, α,β-unsaturated, or aliphatic.

13. The method of claim 7, wherein the chiral acid catalyst is at a catalyst loading amount of 2.5 mol % or 1 mol %.