osmium-catalyzed dihydroxylation has uncovered that electron-deficient olefins are converted into the corresponding diols much more efficiently when the pH of the reaction medium is maintained on the acidic side. Further studies have identified citric acid as the additive of choice, for it allows preparation of very pure diols in yields generally exceeding 90%. As described here, a much wider range of olefin classes
The nature of the O-protecting group is crucial to obtain, in terms of diastereoselectivity and chemical yields, the best results. An abinitiomolecularorbitalstudy on 2-silyloxy propanal and MM2 studies on 2-alkoxy propanal show the existence of stable cyclic and acyclic conformers, which are presumably responsible for the high syn diastereoselectivity observed in the addition of non-metal carrying
Enantioselective synthesis of threo-α,β-dihydroxyphosphonates by asymmetric dihydroxylation of vinylphosphonates. An application to the stereocontrolled synthesis of (4S,5S)-4-diethylphosphono-5-hydroxymethyl-2,2-dimethyl-1,3-dioxolane
The asymmetricdihydroxylation (AD) reaction of vinylphosphonates with AD-mix-α and -β reagents was successfully applied to the enantioselective synthesis of threo-α, β-dihydroxyphosphonates. β-Aryl substituents on the vinyl phosphonates were found to be good directors for the reaction with respect to the yield and enantioselectivity. The utility of chiral α, β-dihydroxyphosphonate 2c was illustrated
Quinine as chiral discriminator for determination of enantiomeric excess of diethyl 1,2-dihydroxyalkanephosphonates
作者:Alina Maly、Barbara Lejczak、Pawel Kafarski
DOI:10.1016/s0957-4166(03)00177-0
日期:2003.4
2-dihydroxyethanephosphonates obtained either by chemical or biocatalytic synthesis. Sharpless asymmetric dihydroxylation of diethyl trans-vinylphosphonates enabled differentiation of threo and erythro isomers of 1,2-dihydroxyphosphonates, and provided standards for the determination of the absolute configuration of each of enantiomeric pair of threo isomers.
Asymmetric dihydroxylation (AD) of 1(E)-alkenylphosphonates with an AD-mix -alpha or -beta reagent was examined to give a series of optically active threo-alpha,beta-dihydroxyphosphonates. Good enantioselectivity (>88% eel was observed in the AD reaction of 1(E)-alkenylphosphonates with conjugated aromatic substituents. The steric effects of the ester functionality in the course of the dihydroxylation were also evaluated. Enantioselectivity and yield were significantly improved when the AD reaction was carried out with dimethyl phosphonate instead of diethyl phosphonate. (C) 1997 Elsevier Science Ltd. All rights reserved.