Synthesis of (−)-Aphanorphine Using Aryl Radical Cyclization

The synthesis of (−)-aphanorphine was achieved by using Bu<sub>3</sub>SnH-mediated aryl radical cyclization of 1-benzyloxycarbonyl-2-(2-bromo-4-methoxyphenylmethyl)-2-methoxycarbonyl-4-(phenylthiomethylene)pyrrolidine, leading to exclusive formation of the 6-<i>exo</i> cyclization product.