NHC-mediated enantioselective formal [4 + 2] cycloadditions of alkylarylketenes and β,γ-unsaturated α-ketocarboxylic esters and amides
作者:Stuart M. Leckie、T. Bruce Brown、David Pryde、Tomas Lebl、Alexandra M. Z. Slawin、Andrew D. Smith
DOI:10.1039/c3ob40424b
日期:——
Chiral N-heterocyclic carbenes (NHCs) promote the asymmetric formal [4 + 2] cycloaddition of alkylarylketenes with β,γ-unsaturated α-ketocarboxylic esters and amides. Divergent diastereoselectivity is observed in this process, with γ-aryl-β,γ-unsaturated α-ketocarboxylic esters and amides giving preferentially syn-dihydropyranones (up to 68 : 32 dr syn : anti, up to 98% ee), while γ-alkyl-derivatives generate
手性N-杂环卡宾(NHC)促进烷基芳基烯酮与β,γ-不饱和α-酮羧酸酯和酰胺的不对称形式[4 + 2]环加成。在此过程中观察到不同的非对映选择性,其中γ-芳基-β,γ-不饱和α-酮羧酸酯和酰胺优先提供顺-二氢吡喃酮(高达68:32 dr syn : anti,高达98%ee),而γ-烷基衍生物生成抗二氢吡喃酮(高达18:82 dr syn : anti,高达75%ee)。