A smooth rearrangement of N-p-toluenesulfonyl 2-tert-butyldiphenylsilylmethyl-substituted azetidines into N-p-toluenesulfonyl 3-tert-butyldiphenylsilyl-substituted pyrrolidines
作者:Bharat D. Narhe、Vardhineedi Sriramurthy、Veejendra K. Yadav
DOI:10.1039/c2ob07140a
日期:——
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 σC–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 SN2 opening by the internal nitrogen nucleophile. Oxidative cleavage of σC–Si bond leads to the formation of 3-hydroxypyrrolidines.
在二氯甲烷的刘易斯酸条件下,N-对甲苯磺酰基2-叔丁基二苯基硅甲基取代的氮杂环丁烷被重新排列为3-叔丁基二苯基硅基取代的吡咯烷,其中硅通过硅化铵离子发生1,2-迁移。通过对3-和4-取代-2-叔丁基二苯基硅甲基氮杂环丁烷形成的吡咯烷产物进行立体化学分析,以及通过对N-对甲苯磺酰基2(R)-叔丁基二苯基硅甲基氮杂环丁烷形成的吡咯烷产物进行旋光数据和手性高效液相色谱分析,发现硅化铵离子的形成与σC-N断裂并不一致。空间位阻较小的硅化铵离子形成后,内部氮亲核试剂会对其进行SN2开环。σC-Si键的氧化断裂会导致3-羟基吡咯烷的形成。