α-Alkylidene-γ-butyrolactone Formation via Bi(OTf)<sub>3</sub>-Catalyzed, Dehydrative, Ring-Opening Cyclizations of Cyclopropyl Carbinols: Understanding Substituent Effects and Predicting <i>E</i>/<i>Z</i> Selectivity
作者:Matthew J. Sandridge、Brett D. McLarney、Corey W. Williams、Stefan France
DOI:10.1021/acs.joc.7b01706
日期:2017.10.20
A Bi(OTf)3-catalyzed ring-opening cyclization of (hetero)aryl cyclopropyl carbinols to form α-alkylidene-γ-butyrolactones (ABLs) is reported. This transformation represents different chemoselectivity from previous reports that demonstrated formation of (hetero)aryl-fused cyclohexa-1,3-dienes upon acid-promoted cyclopropyl carbinol ring opening. ABLs are obtained in up to 89% yield with a general preference
据报道,Bi(OTf)3催化(杂)芳基环丙基甲醇的开环环化反应,形成α-亚烷基-γ-丁内酯(ABL)。这种转化代表了与以前的报道不同的化学选择性,以前的报道表明在酸促进的环丙基甲醇开环后会形成(杂)芳基稠合的环己-1,3-二烯。通常以E-异构体为佳,以高达89%的产率获得ABL 。从机械上讲,Bi(OTf)3用作稳定且易于处理的TfOH的前体。然后,TfOH催化环丙基羰基阳离子的形成,该环丙基经历开环,分子内被相邻酯基的捕集,随后的水解以及甲醇的损失,从而导致了ABL的形成。甲醇和环丙烷上取代基的性质和相对位置决定了化学和立体选择性的结果。甲醇取代基决定了环丙基羰基阳离子形成的程度。环丙烷供体取代基决定了整个反应的化学选择性。弱稳定或电子贫乏的供体基团可提供更高的ABL产品收率。相反,观察到大量具有高度稳定的环丙烷供体取代基的竞争产物。最后,一个预测模型E / Z选择性是通过DFT计算得出的。