Reduction of carbonyl compounds via hydrosilylation: V. Synthesis of optically active allylic alcohols via regioselective asymmetric hydrosilylation

Regioselective asymmetric reduction of prochiral α,β-unsaturated ketones to optically active allylic alcohols was performed via hydrosilylation catalyzed by a rhodium(I) complex with (+)-BMPP, (+)-DIOP and (?)-DIOP as chiral ligands. The allylic alcohols with optical purity up to 69% e.e. were obtained in good yields. The extent of asymmetric induction was found to depend on the stereo-electronic matching of the chiral ligand, ketone and hydrosilane employed. In the asymmetric reduction of (R)-carvone, leading to carveol, the extent of asymmetric induction was found to depend markedly on the ligand/rhodium ratio. Either trans-(5R,1S)-carveol or cis-(5R,1R)-carveol was obtained with good stereoselectivity by using (?)-DIOP or (+)-DIOP as chiral ligand, and it turned out that the chiral center present in carvone had only a slight influence on the asymmetric induction by the chiral catalysts.     

Modular synthesis of optically active lactones by Ru-catalyzed asymmetric allylic carboxylation and ring-closing metathesis reaction

A new synthetic route to optically active unsaturated γ- and δ-lactones has been demonstrated via asymmetric allylic carboxylation with a planar-chiral Cp'Ru catalyst and ring-closing metathesis reaction with a Grubbs II catalyst, and successfully applied to the enantioselective synthesis of (R)-(-)-massoialactone.     

Asymmetric Catalysis by Vitamin B12. The isomerization of achiral epoxides to optically active allylic alcohols

Achiral epoxides are isomerized to optically active allylic alcohols under the influence of catalytical amounts of cob(I) alamin in protic polar solvents.     

Reactions of 2,3-epoxyhalides. Synthesis of optically active allylic alcohols and homoallylic epoxides

Mild and efficient reactions for the conversion of optically active 2,3-epoxy-halides to optically active allylic alcohols and optically active epoxides are described.     

Homogeneously catalysed isomerisation of allylic alcohols to carbonyl compounds

Isomerisation of allylic alcohols forms an elegant shortcut to carbonyl compounds in a completely atom-economical process that offers several useful applications in natural-product synthesis and in bulk chemical processes. This review focuses on the heart of isomerisation catalysis: the catalyst. Combinations of transition metals (from Group 4 to 10), ligands and reaction conditions are compared with respect to yield, turnovers, rate and selectivity. A selected number of clever solutions to synthetic problems are highlighted, such as the synthesis of enols and enolates, chiral carbonyl compounds and silyl substituted ketones. Furthermore, a general overview of the mechanisms proposed for the isomerisation of allylic alcohols is given while some catalyst systems are singled out to discuss mechanistic research.     

Modification of optically active ferrocenylphosphine ligands for palladium-catalyzed asymmetric allylic alkylation

Optically active ferrocenylphosphines containing a functional group on the side chain were effective as ligands for the palladium—catalyzed asymmetric allylic alkylation of 1,3-disubstituted allyl acetates such as l,3-diphenyl-3-acetoxy-l-propene with sodium acetylacetonate and related soft carbon nucleophiles to give the alkylation products of up to 92% ee.     

Practical synthesis of optically active amino alcohols via asymmetric transfer hydrogenation of functionalized aromatic ketones

2-Substituted acetophenones such as 2-cyano-, 2-azido-, or 2-nitroacetophenones were effectively reduced with a mixture of HCOOH/N(C(2)H(5))(3) containing a chiral Ru(II) catalyst, RuCl[(S,S)-N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine](p-cymene), giving the corresponding optically active alcohols, which can be converted to optically active amino alcohols with excellent ee's. Similarly, the reaction of 2-benzoylacetophenone with the same Ru catalyst gave a quantitative yield of the corresponding optically active 1,3-diol with 99% ee.     

Direct conversion of benzylic and allylic alcohols to phosphonates

Benzyl phosphonate esters often serve as reagents in Horner-Wadsworth-Emmons reactions. In most cases, they can be prepared from benzylic alcohols via formation of the corresponding halide followed by an Arbuzov reaction. To identify a more direct synthesis of phosphonate esters, we have developed a one-flask procedure for conversion of benzylic and allylic alcohols to the corresponding phosphonates through treatment with triethyl phosphite and ZnI(2).     

Chemoenzymatic synthesis of optically active heterocyclic homoallylic and homopropargylic alcohols

A chemoenzymatic methodology has been developed using indium-mediated allylation of heterocyclic aldehydes under aqueous conditions followed by Pseudomonas cepacia lipase-catalyzed enantioselective acylation of racemic homoallylic and homopropargylic alcohols in organic media. It is observed that the lipase immobilized on ceramic particles (PS-C Amano II) catalyzes the resolution in a highly enantioselective manner in less time as compared to the native enzyme (PS Amano). The approach provides new functionalized chiral synthons useful in the synthesis of natural and pseudonatural products.     

Copper-catalyzed asymmetric addition of Et2Zn to 2-cyclohexen-1-one and 2-carbamoyloxy-2-cyclohexen-1-one with phosphoramidite,phosphite, and bidentate phosphite–oxazoline ligands

New biphenol-backboned phosphite–oxazoline bidentate ligands were synthesized and applied in the copper-catalyzed asymmetric conjugate additions on 2-cyclohexen-1-one with Et₂Zn. In these reactions, the non-chiral oxazoline unit has demonstrated significant impact on the enantioselectivity. 2-Carbamoyloxy-2-cyclohexen-1-one is a new α-oxygenated cyclic enone substrate and was synthesized and applied to the aforementioned addition with certain phosphoramidite, phosphite, and the new bidentate ligands. Good ee has been obtained on this substrate.     

Preparation of optically active allylic hydroperoxy alcohols and 1, 3-diols by enzyme-catalyzed kinetic resolution and photooxygenation of chiral homoallylic alcohols

All four possible enantiomers of the 3-hydroperoxy-4-penten-1-ols 2a, b and their corresponding 4-pentene-1,3-diols 4a,b have been prepared for the first time in high enantiomeric purity (up to 98% ee) and in preparative amounts according to two distinct ways: First the photooxygenation of the racemic homoallylic alcohols 1 gave the racemic hydroperoxy alcohols 2, which have subsequently been kinetically resolved by horseradish peroxidase (HRP); alternatively, first the lipase-catalyzed resolution afforded the optically active homoallylic alcohols 1 and subsequent photooxygenation led to the enantiomerically enriched hydroperoxy alcohols 2.     

Organocatalytic asymmetric vinylogous addition to quinones - formation of optically active alpha-aryl ketones

The first organocatalytic addition of dicyanoalkylidenes to quinones catalyzed by Cinchona alkaloids leading to formation of 1,4-diketone derivatives with high diastereomeric ratios (up to >98 : <2 dr) and enantioselectivities (up to 99% ee) has been developed; the optically active compounds obtained are useful for a number of transformations, e.g. the synthesis of optically active alpha-aryl ketones.     

A highly enantioselective synthesis of chiral allylic alcohols by asymmetric addition of novel mixed reagents of trialkenylbismuthines/dialkylzincs to aldehydes

A novel mixture of reagents of trialkenylbismuthines/dialkylzincs was developed and applied toward the synthesis of chiral allylic alcohols. The chiral β-amino alcohols catalyzed addition of the mixed reagents of trialkenylbismuthines/dialkylzincs to aldehydes gave enantiomerically enriched allylic alcohols with up to 97% ee.     

(S)-2-芳基丙酸不对称合成研究进展

对(S)-2-芳基丙酸类非甾体抗炎药光学纯品的不对称合成方法进行了总结和概述，从中反映近年不对称合成中新概念、新方法和新技术的应用。     

Synthesis and bioactivity of optically active forms of 1-methyl-2-cyclohexen-1-ol. An aggregation pheromone of dendroctonus pseudotsugae

Both the enantiomers of 1-methyl-2-cyclohexen-1-ol, an aggregation pheromone of the female Douglas-fir beetle, were synthesized from the enantiomers of seudenol (3-methyl-2-cyclohexen-1-ol). The enantiomers were less active than the racemate of 1-methyl-2-cyclohexen- 1-ol as an aggregation pheromone.     

Enzymatic synthesis of optically active 1- and 2-aminoalkanephosphonates

A number of 1- and 2-aminoalkanephosphonates were resolved with high enantioselectivity by Candida antarctica lipase B-catalyzed acetylation. By this method, optically pure aminoalkanephosphonates and amidoalkanephosphonates, the precursors of the corresponding aminoalkanephosphonic acids, were synthesized.