Stereocontrolled Preparation of Spirocyclic Ethers by Intramolecular Trapping of Oxonium Ions with Allylsilanes
作者:Leo A. Paquette、Jinsung Tae
DOI:10.1021/jo961306k
日期:1996.1.1
6-dimethyl derivative, the substituents act in a reinforcing manner and direct cyclization uniquely in one direction. Both the cis and trans bicyclic ethers ring close on that pi-surface of the intermediate oxonium ion syn to the angular hydrogen. The results are rationalized in terms of the predilection of the associated oxonium ions for nucleophilic capture via a chairlike or twist-boat transition state
已经研究了在各个环位置被烷基取代的2-(苯磺酰基)-2-(4-(((三甲基甲硅烷基)甲基)-4-戊烯基)四氢吡喃自发分子内环化的立体选择性。对于4-和6-甲基衍生物,螺环中心的形成仅与甲基相反。5-甲基实例的结果是3.7:1 syn / anti拆分。对于反式4,6-二甲基衍生物,取代基以增强方式起作用,并且在一个方向上唯一地直接环化。顺式和反式双环醚均在中间体氧鎓离子的pi表面上与角氢同位而闭合。根据相关联的氧鎓离子的偏爱,可以通过椅子状或扭曲舟状过渡态进行亲核捕获,从而使结果合理化。