Synthesis of tetrahydro-1-benzazocin-2(1H)-ones using 8-endo-trig radical cyclization of 2,2-bis(phenylthio)-N-[o-(prop-2-enyl)phenyl]acetamides?

The effects of N-substituents upon the 8-endo-trig radical cyclization of 2,2-bis(phenylthio)-N-[o-(prop-2-enyl)phenyl]acetamides (4) were examined. The N-(p-methoxybenzyl) (4a) and N-tosyl derivatives (4b), when treated with tributyltin hydride in the presence of a small amount of azoisobutyronitrile, gave regioselectively the corresponding 3,4,5,6-tetrahydro-3-phenylthio-1-benzazocin-2(1H)-ones (5a,b) (8-endo cyclization products) in 40 and 47% yields, respectively, while the N-unsubstituted derivative (4c) afforded the reduction products (6c) and (8) as the major products, Some chemical transformation reactions of 5a are also described.