Asymmetric Weitz−Scheffer Epoxidation of Isoflavones with Hydroperoxides Mediated by Optically Active Phase-Transfer Catalysts
作者:Waldemar Adam、Paraselli Bheema Rao、Hans-Georg Degen、Albert Levai、Tamás Patonay、Chantu R. Saha-Möller
DOI:10.1021/jo0162078
日期:2002.1.1
isoflavone epoxidation as illustrated for the substrate 3c. This fact indicates the pivotal role of the hydroxy group for enantioselective control, which is rationalized in terms of a hydrogen-bonded aggregate between the ether-oxygen atom of isoflavone 3 and the phase-transfer catalyst 1. The present attractive and convenient method should be useful for the preparation of optically active epoxides of
异黄酮3的不对称Weitz-Scheffer环氧化反应是由辛可宁和辛可尼定衍生的相转移催化剂(PTCs)1介导的,提供的对映异构体富集的异黄酮环氧化物4的ee值几乎定量,产率高达98%。使用适当配置的PTC 1,可以通过使用市售的枯基氢过氧化物2b作为氧化剂来获得异黄酮环氧化物的两种对映异构体。最有效的PTC(1b)中羟基官能团的甲基化会大大降低异黄酮环氧化的对映选择性,如底物3c所示。这一事实表明了羟基在对映选择性控制中的关键作用,这通过异黄酮3的醚-氧原子与相转移催化剂1之间的氢键结合的聚集体得以合理化。