Radical-Mediated 5-Exo-Trig Cyclizations of 3-Silylhepta-1,6-dienes

摘要

Regioselectivity of the sulfonyl radical mediated 5-exo-trig cyclization of 3-silylheptadienyl systems 3a-d has been studied.At low temperature,the reaction of the sulfonyl radical occurs regioselectively at the allylsilane terminus,while a reversal of regioselectivity is observed at 80 deg C.This general trend has been rationalized on the basis of polar effects and radical stabilization.Thiyl-mediated radical cyclization of dienes 3a,3c-d,7 with subsequent sulfur atom transfer was also studied,providing thiabicyclo[3.3.0] skeleton in one step with excellent stereocontrol.