Synthesis of (−)-Aphanorphine Using Aryl Radical Cyclization

The synthesis of (−)-aphanorphine was achieved by using Bu3SnH-mediated aryl radical cyclization of 1-benzyloxycarbonyl-2-(2-bromo-4-methoxyphenylmethyl)-2-methoxycarbonyl-4-(phenylthiomethylene)pyrrolidine, leading to exclusive formation of the 6-exo cyclization product.