Epimerization of 2‘-Carbonylalkyl-<i>C</i>-Glycosides via Enolation, β-Elimination and Intramolecular Cycloaddition
作者:Zerong Wang、Huawu Shao、Edith Lacroix、Shih-Hsiung Wu、Harold J. Jennings、Wei Zou
DOI:10.1021/jo034446k
日期:2003.10.1
as an intermediate. When 2'-aldehyde (36) and 2'-ketone (41) of 2,3-di-O-benzyl-alpha/beta-l-C-arabinofuranoside were used as substrates we were able to obtain the respective equatorial alpha-C-arabinopyranosides (37 and 42). These observations confirmed that the epimerization involves an acyclic alpha,beta-unsaturated aldehyde or ketone, which is formed by the enolation of 2'-carbonyl-alpha-C-glycoside
用4%NaOMe处理葡萄糖,半乳糖,甘露糖,2-脱氧和2-叠氮基糖的2'-羰基-α-C-糖吡喃糖苷导致端基异构体异构化,使其各自的β-端基异构体具有良好或优异的收率。α-C-吡喃半乳糖苷(10)的2'-醛在氘代甲醇中的差向异构化作用使β-端基异构体在1'-位具有唯一的氘代取代作用,排除了外糖参与的可能性中间体。当使用2,3-二-O-苄基-α/β-1C-阿拉伯呋喃糖苷的2'-醛(36)和2'-酮(41)作为底物时,我们能够获得各自的赤道α-C-阿拉伯吡喃糖苷(37和42)。这些观察结果证实,差向异构体涉及无环的α,β-不饱和醛或酮,它是由2'-羰基-α-C-糖苷的烯醇化和随后的β-消除形成的。此后发生分子内杂-迈克尔环加成反应,导致形成热力学控制的稳定产物,该产物仅是赤道的C-糖吡喃糖苷,但2'-羰基-C-呋喃糖苷除外,其中获得了两种端基异构体的混合物。