Alkylation of the dianion of .beta.-keto esters
01 Nov 1970-Journal of the American Chemical Society (American Chemical Society)-Vol. 92, Iss: 22, pp 6702-6704
About: This article is published in Journal of the American Chemical Society.The article was published on 1970-11-01. It has received 91 citations till now. The article focuses on the topics: Alkylation & Beta (finance).
Citations
More filters
123 citations
TL;DR: Permutation of the reduction methods yielded all four stereoisomers of the crystalline target compound 6a (> or = 99.3% ee, dr > or = 205:1), which is a versatile 1,3-diol building block.
Abstract: A stereoselective chemoenzymatic synthesis of all four stereoisomers of tert-butyl 6-chloro-3,5-dihydroxy-hexanoate (6a) is presented. The key step of the sequence is a highly regio- and enantioselective single-site reduction of tert-butyl 6-chloro-3,5-dioxohexanoate (1a) by two enantiocomplementary biocatalysts. Alcohol dehydrogenase from Lactobacillus brevis (recLBADH) afforded a 72% yield of enantiopure tert-butyl (S)-6-chloro-5-hydroxy-3-oxohexanoate [(S)-2a]. The enantiomer (R)-2a was prepared with 90-94% ee by Baker's yeast reduction in a biphasic system (50% yield). Both biotransformations were performed on a gram scale. The beta-keto group of the enantiomeric delta-hydroxy-beta-keto esters 2a thus obtained was reduced by syn- and anti-selective borohydride reductions. Permutation of the reduction methods yielded all four stereoisomers of the crystalline target compound 6a (> or = 99.3% ee, dr > or = 205:1), which is a versatile 1,3-diol building block. recLBADH accepts a variety of beta,delta-diketo esters as was determined in a photometric assay. tert-Butyl 3,5-dioxo-hexanoate (1b) and tert-butyl 3,5-dioxo-heptanoate (1c) were reduced on a preparative scale as well to afford the corresponding delta-hydroxy-beta-keto esters (R)-2b and (R)-2c with 99.4% ee and 98.1% ee, respectively.
84 citations
72 citations
72 citations
TL;DR: In this paper, the capability of sponges to convert Δ 5 - into Δ 5,7 -sterols, which was as efficient as the conversion of Δ 7 -to Δ 5,7 -structure common to plant and yeast sterols, was demonstrated by double labelling experiments.
66 citations