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 oxoniumion syn to the angular hydrogen. The results are rationalized in terms of the predilection of the associated oxoniumions 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。
A New Method for the Synthesis of Medium- and Large-Sized Carbocycles
作者:Keiichi Masuya、Keiji Tanino、Isao Kuwajima
DOI:10.1055/s-1999-2696
日期:1999.5
A new synthetic method for medium and large-sized carbocycles has been developed. An acyclic compound having an olefin moiety and a 3-(methylthio)allyl acetate moiety at each of the terminal positions was designed as a cyclization precursor. The corresponding allyl cation intermediate, which was generated by treatment with EtAlCl2, underwent cyclization via an intramolecular addition reaction. The ring size of the product, which depends on the reaction site of the allyl cation, can be controlled by changing the nucleophilicity of the terminal olefin moiety.