Synthesis of the Pyrrolidine Ring System by Radical Cyclization

Article abstract of DOI:10.1021/jo00350a038

A series of bromo-substituted allyl- and diallyl-substituted sulfonamides have been found to undergo free radical cyclization when treated with tri-n-butyltin hydride in the presence of AIBN.The regiochemical course of the cyclization depends on the nature of the substituent groups attached to the ?-bond.The stereoelectronic factors governing the cyclization reaction of these N-allylsulfonamides are even more stringent than those which occur with the simple 5-hexenyl system.This is probably related to the shorter C-N bond distance which promotes the 5-exo trigcyclization pathway.The present method provides an attractive entry to the preparation of pyrrolidines from easily available N-(2-bromoethyl)-N-allyl- and N-(2-bromopropenyl)-N-allylsulfonamides.The method represents a clear-cut example of the use of hetero-substituted radicals in C-C bond-forming processes.