Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India.
Org Biomol Chem. 2012 Jun 14;10(22):4390-9. doi: 10.1039/c2ob07140a. Epub 2012 May 4.
The rearrangement of N-p-toluenesulfonyl 2-tert-butyldiphenylsilylmethyl-substituted azetidines into 3-tert-butyldiphenylsilyl-substituted pyrrolidines under Lewis acid conditions in dichloromethane involves 1,2-migration of silicon through a siliranium ion. The formation of siliranium ion was discovered not to be in concert with σ(C-N) cleavage from stereochemical analysis of the pyrrolidine products formed from 3- and 4-substituted-2-tert-butyldiphenylsilylmethyl azetidines and also from the optical rotation data and chiral HPLC analysis of the pyrrolidine product formed from N-p-toluenesulfonyl 2(R)-tert-butyldiphenylsilylmethyl azetidine. The formation of sterically less hindered siliranium ion is followed by its S(N)2 opening by the internal nitrogen nucleophile. Oxidative cleavage of σ(C-Si) bond leads to the formation of 3-hydroxypyrrolidines.
在路易斯酸条件下，将 N-p-甲苯磺酰基 2-叔丁基二苯基甲硅烷基取代的氮杂环丁烷重排成 3-叔丁基二苯基甲硅烷基取代的吡咯烷，涉及硅通过硅鎓离子的 1,2-迁移。通过立体化学分析从 3-和 4-取代的 2-叔丁基二苯基甲硅烷基氮杂环丁烷以及从 N-p-甲苯磺酰基 2(R)-叔丁基二苯基甲硅烷基氮杂环丁烷形成的吡咯烷产物的旋光度数据和手性 HPLC 分析，发现硅鎓离子的形成与 σ(C-N) 断裂不一致。形成空间位阻较小的硅鎓离子后，其由内部氮亲核试剂进行 S(N)2 开环。σ(C-Si)键的氧化断裂导致 3-羟基吡咯烷的形成。
