Enantioselective NHC-Catalysed Formal [4+2] Cycloaddition of Alkylarylketenes with β,γ-Unsaturated α-Ketophosphonates
作者:Andrew Smith、Stuart Leckie、Charlene Fallan、James Taylor、T. Brown、David Pryde、Tomáš Lébl、Alexandra Slawin
DOI:10.1055/s-0033-1338851
日期:——
NHC-mediated enantioselective formal [4+2] cycloadditions of alkylarylketenes with γ-substituted-β,γ-unsaturated α-ketophosphonates is described. A substrate-dependent switch in diastereoselectivity was observed, with γ-aryl α-ketophosphonates providing preferentially the syn-dihydropyranone-phosphonates and γ-methyl α-ketophosphonates favouring the anti-dihydropyranone-phosphonate. In addition, ketene generation
描述了 NHC 介导的对映选择性形式 [4+2] 烷芳基烯酮与 γ-取代-β,γ-不饱和 α-酮膦酸酯的环加成反应。观察到非对映选择性的底物依赖性转换,γ-芳基α-酮膦酸酯优先提供顺式二氢吡喃酮膦酸酯和γ-甲基α-酮膦酸酯,有利于抗二氢吡喃酮膦酸酯。此外,与相应的两步法相比,原位生成乙烯酮保留了高水平的立体选择性并提高了产品收率。