bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation of Chiral Building Blocks for Starburst Dendrimer Synthesis
Authors: Lapierre Jean‐Marc , Skobridis Konstantinos , Seebach Dieter 
Published: December 2004

AbstractDouble aldols, formally derived from acetic acid and two different aldehydes, as obtained by addition of the enolate of (R,R)‐2‐(tert‐butyl)‐6‐methyl‐1,3‐dioxan‐4‐one (A) to various aldehydes, are reduced to triols which are actually substituted chiral ‘tris(hydroxymethyl)methanes’ (see B and 3–8). Etherifications of the three OH groups of these triols with functionalized halides (allyl, 4‐(silyloxy)but‐2‐en‐l‐yl, 4‐substituted benzyl) and esterifications with pent‐4‐enoic and 3,5‐dinitrobenzyl chlorides, followed by functional group manipulations, lead to the potential center pieces 14–30 for the construction of chiral dendrimers: the building blocks prepared contain the required ‘spacers’ between the core unit, as well as three vinyl groups, three aryl bromide groups, three alcoholic or phenolic OH groups, three mesylate groups, three ester groups, or six arylamino groups at the terminus of their branches. The new compounds are all obtained on a preparative scale and are fully characterized (including elemental analysis).
Biosynthesis of the Irregular C12‐Terpenoid Dehydrogeosmin in Flower Heads of Rebutia marsoneri WERD. (Cactaceae)
Authors: Feng Zhuofu , Huber Udo , Boland Wilhelm 
Published: December 2004

AbstractFarnesol (3a) is the precursor to the irregular C12 terpenoid (4S, 4aS, 8aS)‐1,2,3,4,4a,5,8,8a‐octahydro‐4,8a‐dimethylnaphthalen‐4a‐ol (= dehydrogeosmin; 1). The irregular C‐backbone originates from the oxidative removal of a C3 side chain from a C15 eudesmane‐type intermediate (Scheme 2). The bicyclic C‐framework is assembled by a formal addition of H2O across the endocyclic double bonds of a monocyclic germacradiene‐type precursor. The biosynthetic pathway follows from administration of the deuteriated farnesols 3b–e to flower heads of the cactaceae Rebutia marsoneri Werd. and mass‐spectroscopic analysis of the collected volatiles.
Complexes of the Triolide from (R)‐3‐Hydroxybutanoic Acid with Sodium, Potassium, and Barium Salts: Crystal Structures, Ester Chelates and Ester Crowns, Crystal Packing, Bonding, and Electron‐Localization Functions
Authors: Seebach Dieter , Bürger H. Michael , Plattner Dietmer A. , Nesper Reinhard , Fässler Thomas 
Published: December 2004

AbstractThe triolide of (R)‐3‐hydroxybutanoic acid ((R,R,R,))‐3,7,11‐trimethyl‐2,6,10‐trioxadodecane‐1,5,9‐trione; (1), readily available from the corresponding biopolymer P(3‐HB) in one step, forms crystalline complexes with alkali and alkaline earth salts. The X‐ray crystal structures of three such complexes, (3 NaSCN)·4 1 (2), (2 KSCN)·2 1 · H2O (3), and (2) Ba(SCN)2 · 2 1 · 2 H2O · THF (4), have been determined and are compared. The triolide is found in these structures (i) as a free molecule, making no contacts with a cation (clathrate‐type inclusion), (ii) as a monodentate ligand coordinated to a single ion with one carbonyl O‐atom only, (iii) as a chelator, forming an eight‐membered ring, with two carbonyl O‐atoms attached to the same ion, (iv) as a linker, using two carbonyl O‐atoms to bind to the two metals of an ion‐X‐ion unit (ten‐membered ring), and (v), in a crown‐ester complex, in which an ion is sitting on the three unidirectional CO groups of a triolide molecule (Figs. 1–3). The crystal packing is such that there are columns along certain axes in the centers of which the cations are surrounded by counterions and triolide molecules, with the non‐polar parts of 1 on the outside (Fig. 4). In the complexes 2–4, the triolide assumes conformations which are slightly distorted, with the carbonyl O‐atoms moved closer together, as compared to the ‘free’ triolide 1 (Fig. 5). These observed features are compatible with the view that oligo (3‐HB) may be involved in the formation of Ca polyphosphate ion channels through cell membranes. A comparison is also made between the triolide structure in 1–4 and in enterobactin, a super Fe chelator (Fig. 5). To better understand the binding between the Na ion and the triolide carbonyl O‐atoms in the crown‐ester complex, we have applied electron‐localization function (ELF) calculations with the data set of structure 2, and we have produced ELF representations of ethane, ethene, and methyl acetate (Figs. 6–9). It turns out that this theoretical method leads to electron‐localization patterns which are in astounding agreement with qualitative bonding models of organic chemists, such as the ‘double bond character of the COOR single bond’ or the ‘hyperconjugative n → σ* interactions between lone pairs on the O‐atoms and neighbouring σ‐bonds’ in ester groups (Fig. 8). The noncovalent, dipole/pole‐type character of bonding between Na+ and the triolide carbonyl O‐atoms in the crown‐ester complex (the NaOC plane is roughly perpendicular to the OCO plane) is confirmed by the ELF calculation; other bonding features such as the CN bond in the NaSCN complex 2 are also included in the discussion (Fig. 9).
Catalytic Enantioselective Hydrosilylation of Aromatic Ketones Using Rhodium Complexes of TADDOL‐Derived Cyclic Phosphonites and Phosphites
Authors: Sakaki Jun‐ichi , Schweizer W. Bernd , Seebach Dieter 
Published: December 2004

AbstractCyclic phosphonites and phosphites2–4are readily available from Cl2PR and (R,R)‐ or (S,S)‐α,α,α′,α′‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanols (= TADDOLs1, which, in turn, are only two steps away from tartrate); the X‐ray crystal structure of one representative, the phenyl phosphonite2b, was determined. Five previously described and six new ones of the chiral P derivatives were tested as ligands for RhI‐ and PdO‐catalyzed reactions such as hydrocarbonylations, hydroborations, and hydrosilylations of CC bonds; while the resulting catalysts were highly active and regioselective, they did not lead to useful enantiomer enrichment in the products (Scheme 1). In contrast, hydrosilylation of phenyl and 2‐naphthyl methyl or ethyl ketone by Ph2SiH2(1.2 equiv.) gave, after desilylation, the corresponding secondary alcohols of (R)‐configuration with up to 87% ee in the presence of 0.1 equiv. of the penta(2‐naphthyl)‐substituted phosphonite3dand 0.02 mol‐equiv. of Rh (Table 1).
A Novel Synthesis of 2,2‐Disubstituted 3‐Amino‐2H‐azirines Based on the Reaction between Amide Enolates and Diphenyl Phosphorochloridate
Authors: Villalgordo José M. , Heimgartner Heinz 
Published: December 2004

AbstractA novel synthesis of 2,2‐disubstituted 3‐amino‐2H‐azirines based on the reaction between amide enolates and diphenyl phosphorochloridate (DPPCl), followed by treatment with NaN3 is presented. The yields obtained in general are excellent, and the method is suitable for laboratory‐scale preparations as well as for larger amounts.
Determination of the Absolute Configuration of Dimethyl (2S,3S)‐2‐Allyl‐3‐hydroxyglutarate: A Chiral Building Block for Preparing Branched‐Chain Nucleoside Analogues
Authors: Arslan Tuncer , Herradon Bernardo , Schweizer Bernd W. , Benner Steven A. 
Published: December 2004

AbstractA yeast‐catalyzed reduction of dimethyl (2S,3S)‐2‐allyl‐3‐hydroxyglutarate is the key step in the preparation of bis‐homo, branched‐chain nucleoside analogues. To establish unambiguously the stereochemical course of the microbial reaction, the product has been converted to a derivative esterified with camphanoyl chloride, and a crystal structure of the derivative solved.
Oceanapins A–F, Unique Branched Ceramides Isolated from the Haplosclerid Sponge Oceanapia cf. tenuis of the Coral Sea
Authors: Mancini Ines , Guella Graziano , Pietra Francesco , Debitus Cécile 
Published: December 2004

AbstractA series of ceramides, called oceanapins A–F (2–7), which are unique for branching at both the sphingosine and fatty‐acid chains, have been isolated as pure compounds from the haplosclerid sponge Oceanapia cf. tenuis of the Coral Sea. Following acid hydrolysis, both the fatty‐acid and the sphingosine portions were obtained separately, which allowed their unequivocal structural definition. The absolute configuration was secured via protection of C(1′)–OH and Mosher's esterification at C(3′)–OH of the oceanapins.
Radical Cations of Tetrazinodi(heteroarenes): An ESR and ENDOR Study
Authors: Gerson Fabian , Lamprecht Axel 
Published: December 2004

Abstract14N‐ and 1H‐Coupling constants, determined by ESR, ENDOR, and general‐TRIPLE‐resonance spectroscopy, are reported for the radical cations of tetrazinodi(heteroarenes) 1–8. The results comply with the expectation that donor properties of these compounds are mainly due to the electron‐rich dihydrotetrazine ring.
Die Synthese von Azaisomeren des Triesters von PQQ: 3H‐Pyrrolo[3,2‐f]‐, 1H‐Pyrrolo[3,2‐h]‐ und 7H‐Pyrrolo[2,3‐h]chinolinchinon‐Derivate
Authors: Martin Pierre , Winkler Tammo 
Published: December 2004

The Synthesis of Azaisomers of the Triester of PQQ: 3H‐Pyrrolo[3,2‐f]‐, 1H‐Pyrrolo[3,2‐h]‐, and 7H‐Pyrrolo[2,3‐h]quinolinequinone DerivativesWe describe here the synthesis of the title compounds 3–5, starting from highly substituted aminoindoles. The annelated pyridine rings were built up in each case with dimethyl 4‐oxoglutaconate according to Corey's procedure. All three o‐quinone derivatives 3–5 are stable compounds, comparable to PQQ‐triester. The azaisomers vary in biological activity from practically inactive to strong inhibition of the α‐amidating enzyme or the ornithin decarboxylase.
FT‐IR Investigation of Rare‐Earth and Metal‐Ion Solvation. Part 14. Interaction between uranyl perchlorate and dimethyl sulfoxide in anhydrous acetonitrile
Authors: Bünzli Jean‐Claude G. , Metabanzoulou Jean‐Pierre 
Published: December 2004

AbstractThe interaction between the uranyl ion and perchlorate in anhydrous acetonitrile has been investigated by FT‐IR and Raman spectroscopy. Vibrations assigned to uncoordinated (u), monodentate (m), and bidentate (b) perchlorate anions were identified in 0.075M solutions. Quantitative data indicate that perchlorate is distributed as follows: 37 ± 2% are uncoordinated, 36 ± 7% are monodentate, and 27 ± 7% are bidentate. This is in agreement with the conductivity of the solutions which is at the lower end of the range accepted for 1:1 electrolytes. The splittings v4–v1(m) and v8–v1(b) of 147 and 246 cm−1, respectively, point to a large inner‐sphere interaction. An equilibrium occurs between two differently coordinated species. Various amounts of DMSO were added to 0.05M perchlorate solutions (R′ = [DMSO]t/[UO]t = 1–10). The v7 (SO) and v22 (CS) vibrations of DMSO were used to determine the average number of coordinated DMSO molecules per uranyl ion, which is close to 4. Some bidentate perchlorate ions are still present in these solutions, but all the MeCN molecules (2.6 on average) are expelled out of the inner coordination sphere. The data can again be interpreted in terms of an equilibrium between differently coordinated species. The average coordination number of the uranyl ion is 4.4, as the perchlorate salt in MeCN solution, and may be somewhat smaller in the presence of DMSO. The possible presence of dimeric species is also discussed.
Short Optimally Capped Duplex DNA as Conformationally Restricted Analogue of B‐DNA
Authors: Bannwarth Willi , Dorn Arnulf , Iaiza Patrick , Pannekouke Xavier 
Published: December 2004

AbstractWe describe the synthesis of short double‐stranded DNA fragments (see 4 and 13) which are capped on both ends by an optimally designed linker molecule. The new structures are stable with respect to hybrid dissociation and should have implications in physical studies involving double‐stranded DNA as well as in the antisense area for the specific modulation of gene expressions.
Synthesis of 2′‐Deoxyisoinosine and Related 2′‐Deoxyribonucleosides
Authors: Seela Frank , Chen Yaoming , Bindig Uwe , Kazimierczuk Zygmunt 
Published: December 2004

AbstractVarious 2‐substituted purine and pyrrolo[2,3‐d]pyrimidine 2′‐deoxyribonucleosides with methylthio (13a), chloro (13b), methoxy (9b), and oxo (2, 3) substituents at C(2) are prepared. They are obtained eitherviastereoselective nucleobase‐anion glycosylation or by base transformation. A three‐step synthesis of the unknown 2′‐deoxyisoinosine (2) from 2′‐deoxyguanosine (15) is described. Compound2as well as its 7‐deazapurine derivative3exhibit strong fluorescence.
Synthesis of (R)‐ and (S)‐5‐(Hydroxymethyl)‐3‐isopropyloxazolidin‐2‐one, intermediates in the preparation of optically active β‐blockers
Authors: Warmerdam Erwin G. J. C. , Brussee Johannes , van der Gen Arne , Kruse Chris G. 
Published: December 2004

AbstractThe (R)‐ and (S)‐5‐(hydroxymethyl)‐3‐isopropyloxazolidin‐2‐ones, ((R)‐ and (S)‐2, resp.), pivotal intermediates in the preparation of optically active β‐blockers, were synthesized using (R,E)‐2‐hydroxypent‐3‐enenitrile (1) as the chiral starting material. In the synthesis of (R)‐2, a known cyclization/inversion step was applied.
Glycosylidene Carbenes. Part 14. Glycosidation of partially protected galactopyranose‐, glucopyranose‐, and mannopyranose‐derived vicinal diols
Authors: Muddasani Pulla Reddy , Bozó Eva , Bernet Bruno , Vasella Andrea 
Published: December 2004

AbstractThe relation between H‐bonding in diequatorial trans‐1,2 and axial, equatorial cis‐1,2‐diols and the regioselectivity of glycosidation by the diazirine 1 was examined. H‐Bonds were assigned on the basis of FT‐IR and 1H‐NMR spectra (Fig. 1). Glycosidation by 1 of the gluco‐configurated diequatorial trans‐2,3‐diols 4–7 yielded the mono‐glucosylated products 16/17/20/21 (69–89%); 1,2‐/1,3‐linked products (37–46:63–54), 24/25/28/29 (60–63%; 1,2‐/1,3‐linked products 46–51:54–49), 32–35 (69–94%; 1,2‐/1,3‐linked products 45–52:55–48), and 36/37/40/41 (59–63%; 1,2‐/1,3‐linked products 52–59:48–41), respectively (Scheme 1, Table 3). The disaccharides derived from 4, 5, and 7 were characterized as their acetates 18/19/22/23, 26/27/30/31, and 38/39/42/43, respectively. Glycosidation of the galacto‐configurated diequatorial 2,3‐diols 8 and 9 and the manno‐configurated diequatorial 3,4‐diol 10 by 1 (Scheme 2, Table 3) also proceeded in fair yields to give the disaccharides 44–47 (69–80%;1,2‐/1,3‐linked products ca. 1:1), 48–51 (51–61%;1,2/‐1,3‐linked products 54–56:56–54), and 56/57/60/61 (71–80%; 1,3‐/1,4‐linked products 49–54:51–46), respectively. The 1,3‐linked disaccharides 56/57 derived from the diol 10 were characterized as the acetates 58/59. The regio‐ and stereoselectivities of the glycosidation by 1 were much better for the α‐D‐manno‐configurated axial, equatorial cis‐2,3‐diol 11 and the galacto‐configurated axial, equatorial cis‐3,4‐diol 13 (1,2‐/1,3‐linked disaccharides ca. 3:7 for 11 and 1,3‐/1,4‐linked disaccharides ca. 4:1 for 13; Scheme 3, Table 4). The regio‐ and stereoselectivity for the β‐D‐manno‐configurated cis‐2,3‐diol 12 were, however, rather poor (1,2‐/1,3‐linked products 48:52). The 1,2‐linked disaccharides 66/67 derived from 12 were characterized as the acetates 70/71. Koenigs‐Knorr‐type glycosidation of the cis‐diols 11–13 by 2 or 3 proceeded with a similar regio‐ and a higher stereoselectivity (α‐D > β‐D with the donor 2 and α‐D < β‐D with the donor 3) than with 1, with the exception of 12 which did not react with 2. The regioselectivity of the glycosidations by 1 agrees fully with the H‐bonding scheme of the diols and with the hypothesis that the intermediate carbene is preferentially protonated by the most weakly H‐bonded OH group. The regioselectivity of the glycosidation by 2 and by 3 is determined by a higher reactivity of the equatorial OH groups and by H‐bonding. Several H‐bonded and equilibrating isomers of a given diol may intervene in the glycosidation by 1, or by 2 and 3, resulting in the same regioselectivity. The low nucleophilicity of 12 and the low degree of regioselectivity in its reaction with 3 show that stereoelectronic effects may also profoundly influence the nucleophilicity of OH groups.
Glycosylidene Carbenes. Part 15. Synthesis of disaccharides from allopyranose‐derived vicinal 1,2‐diols. Evidence for the protonation by a H‐bonded hydroxy group in the σ‐plane of the intermediate carbene, followed by attack on the oxycarbenium ion in the π‐plane
Authors: Muddasani Pulla Reddy , Bernet Bruno , Vasella Andrea 
Published: December 2004

AbstractThe α‐D‐allo‐diol 9 possesses an intramolecular H‐bond (HOC(3) to OC(1)) in solution and in the solid state (Fig. 2). In solution, it exists as a mixture of the tautomers 9a and 9b (Fig. 3), which possess a bifurcated H‐bond, connecting HOC(2) with both OC(1) and OC(3). In addition, 9a possesses the same intramolecular H‐bond as in the solid state, while 9b is characterized by an intramolecular H‐bond between HOC(3) and OC(4). In solution, the β‐D‐anomer 12 is also a mixture of tautomers, 12a and presumably a dimer. The H‐bonding in 9 and 12 is evidenced by their IR and 1H‐NMR spectra and by a comparison with those of 3–8, 10, and 11. The expected regioselectivity of glycosidation of 9 and 12 by the diazirine 1 or the trichloroacetimidate 2 is discussed on the basis of the relative degree of acidity/nucleophilicity of individual OH groups, as governed by H‐bonding. Additional factors determining the regioselectivity of glycosidation by 1 are the direction of carbene approach/proton transfer by H‐bonded OH groups, and the stereoelectronic control of both the proton transfer to the alkoxy‐alkyl carbene (in the σ‐plane) and the combination of the thereby formed ions (π‐plane of the oxycarbenium ion). Glycosidation of 9 by the diazirine 1 or the trichloroacetimidate 2 proceeded in good yields (75–94%) and with high regioselectivity. Glycosidation of 9 and 12 by 1 or 2 gave mixtures of the disaccharides 14–17 and 18–21, respectively (Scheme 2). As expected, glycosidation of 12 by 1 or by 2 gave a nearly 1:1 mixture of regioisomers and a slight preference for the β‐D‐anomers (Table 4). Glycosidation of the α‐D‐anomer 9 gave mostly the 1,3‐linked disaccharides 16 and 17 (α‐D β‐D) along with the 1,2‐linked disaccharides 14 and 15 (α‐D < β‐D, 1,2‐/1,3‐linked glycosides ca. 1:4), except in THF and at low temperature, where the β‐D‐configurated 1,2‐linked disaccharide 15 is predominantly formed. Similarly, glycosidation of 9 with 2 yielded mainly the 1,3‐linked disaccharides (1,2‐/1,3‐linked products ca. 1:3 and α‐D/β‐D ca. 1:4). Yields and selectivity depend upon the solvent and the temperature. The regioselectivity and the unexpected stereoselectivity of the glycosidation of 9 by 1 evidences the combined effect of the above mentioned factors, which also explain the lack of regio‐complementarity in the glycosidation of 9 by 1 and by 2 (Scheme 3). THF solvates the intermediate oxycarbenium ion, as evidenced by the strong influence of this solvent on the regio‐ and stereoselectivity, particularly at low temperatures, where kinetic control leads to a stereoelectronically preferred axial attack of THF on the oxycarbenium ion.
An ‘Umpolung’ Route to Peptide Mimetics of Thyrotropin‐Releasing Hormone based on a cyclohexane framework
Authors: Bös Michael , Olson Gary L. , Vincent George P. 
Published: December 2004

AbstractPeptide mimetics of thyrotropin‐releasing hormone (TRH) in which the peptide backbone is replaced by cyclohexane were synthesized from the cyclohexenone precursor 7. The aromatic side chains of the mimetics were derived from the corresponding aldehydes which were attached to the cyclohexenone via the Wittig reagent 8. The TRH mimetics are active in a mouse model of cognitive performance.
Variable‐Temperature and ‐Pressure 31P‐NMR Study of the Intramolecular PPh3 Migration in the Cluster Compound [Ir2Rh2(CO)11PPh3]
Authors: Laurenczy Gábor , Bondietti Giacomo , Merbach André E. , Moullet Bertrand , Roulet Raymond 
Published: December 2004

AbstractThe reaction of [Ir2Rh2(CO)12] with 1 mol‐equiv. of PPh3 yields [Ir2Rh2(CO)11PPh3] (1) as a mixture of two isomers with the phosphine ligand axially bound either to one basal Rh‐atom in the kinetically preferred isomer 1 R or to one basal Ir‐atom in the thermodynamically preferred isomer 11. Both isomers are fluxional on the 13C‐NMR time scale at low temperature due to CO scrambling. Around room temperature, a new type of fluxional process starts to operate which is responsible for the isomerisation 1R⇄11, i.e. the intramolecular migration of the reputedly inert PPh3 ligand from one metal centre to another. The activation volumes of conversions 1R → 11 and 11 → 1R are both positive, indicating that the migration of PPh3 is dissociative in character. This article reports the first application of variable pressure 31P‐NMR to mechanistic studies.
Stable Quinone Methides: Regioselective para‐Oxidation of a 2,4‐bis[(alkylthio)methyl]phenol and addition reactions to quinonemethides
Authors: Meier Hansrudolf , Kuenzi Hanspeter , Fuhrer Hermann , Rist Günther 
Published: December 2004

AbstractThe 2,4‐bis‐functionalized phenol 1 is dehydrogenated regioselectivity with potassium ferricyanide, affording the corresponding p‐quinonemethide 2. Hydrolysis of 2 affords a mixture of dithioacetal 5a and benzaldehyde 6; 1,6‐addition of thiols to 2 gives the dithioacetals 5 of benzaldehyde 6; reaction of 2 with 2,2′‐azobis(isobutyronitrile) (= 2,2′‐dimethyl‐2,2′‐azobis(propanenitrile)) leads to 9a, 9b, and 10, addition products of the 1‐cyano‐1‐methylethyl radical. The structures of all products are confirmed mainly by 1H‐ and 13C‐NMR spectroscopy, and the mode of their formation is discussed.
Aldehyde Intermediates in the Synthesis of Tacamine‐Type Indole Alkaloids: Preparation of (±)‐apotacamine
Authors: Tolvanen Arto , Belle David Din , Lounasmaa Mauri 
Published: December 2004

AbstractThe synthesis of aldehyde intermediates suitable for the preparation of indole alkaloids of the tacamine (1) type is described. The four possible aldehydes 4–7 were prepared from methyl 5‐ethylnicotinate (8) in a few simple steps using a base‐catalyzed epimerization as the final step (Schemes 1 and 2). The key aldehyde 4, which is an analogue of the important vincamine intermediate 3 (‘Oppolzer's aldehyde’), was finally converted into the indole alkaloid (±)‐apotacamine (21).