Sulfur-controlled 6-exo aryl radical cyclisation of N-ethenyl-2-(2-bromophenyl)acetamides: synthesis of (±)-tetrahydropalmatine and saulatine

Abstract

Bu₃SnH-mediated aryl radical cyclisation of 2-(2-bromophenyl)-N-[2,2-bis(phenylsulfanyl)ethenyl]acetamide 7 takes place in a 6-exo-trig manner to give the isoquinolinone 9. The method has been applied to the synthesis of (±)-tetrahydropalmatine 16 and saulatine 24.