A Study of Baker's Yeast Reduction of Piperidone-carboxylates.
摘要:
The stereoselective baker's yeast reduction of various N-protected piperidone-carboxylic acids have been studied, and the enantioselectivity was found to be widely dependent on whether fermenting or non-fermenting conditions were employed. Thus reaction of N-tert-butoxycarbonyl-4-oxopiperidine-3-carboxylic acid ethyl ester (6) with fermenting baker's yeast gave almost racemic N-tert-butoxycarbonyl-4-hydroxypiperidine-3-carboxylic acid ethyl ester (7), however, with complete diastereoselectivity. Reduction of 6 with non-fermenting yeast gave 7 with a 24-41% enantiomeric excess. Similarly, reduction of N-tert-butoxycarbonyl-3-oxopiperidine-4-carboxylic acid ethyl ester (17) with fermenting baker's yeast gave racemic N-tert-butoxycarbonyl-3-hydroxypiperidine-4-carboxylic acid ethyl ester [(+/-)-18] diastereoselectively. A convenient method for determining the enantiomeric excess of the hydroxypiperidine carboxylic acids derivatives was found in the reaction with Sanger's reagent followed by HPLC on a chiral column.
the latter obtained from bakers yeast reduction of the corresponding piperidone, were coupled in solid-phasesynthesis to form simplified oligosaccharide analogues. A split-and-mix synthesis approach was used to create small combinatorial libraries which were characterised by LC-MS and screened as inhibitors of glycosidases.
Nickel Catalysis via S<sub>H</sub>2 Homolytic Substitution: The Double Decarboxylative Cross-Coupling of Aliphatic Acids
作者:Artem V. Tsymbal、Lorenzo Delarue Bizzini、David W. C. MacMillan
DOI:10.1021/jacs.2c08989
日期:2022.11.23
generation, radical sorting via selective binding to a Ni(II) center, and bimolecularhomolyticsubstitution (SH2) at a high-valent nickel–alkyl complex. This catalytic manifold enables the hitherto elusive cross-coupling of diverse aliphatic carboxylic acids to generate valuable C(sp3)–C(sp3)-products. Notably, the powerful SH2 mechanism provides general access to sterically encumbered quaternary carbon
交叉偶联平台传统上是围绕一系列闭壳步骤构建的,例如氧化加成、金属转移和还原消除。在此,我们描述了一种双光/镍催化歧管,它通过互补序列进行交叉偶联,涉及自由基生成、通过选择性结合到 Ni(II) 中心的自由基分选以及高催化下的双分子均解取代 (S H 2)。 -价镍-烷基络合物。这种催化歧管能够实现迄今为止难以捉摸的不同脂肪族羧酸的交叉偶联,生成有价值的 C(sp 3 )–C(sp 3 )-产物。值得注意的是,强大的 S H 2 机制提供了对空间阻碍的季碳中心的普遍访问,解决了片段偶联化学中长期存在的挑战。