Enantioselective Synthesis of (+)‐Monobromophakellin and (+)‐Phakellin: A Concise Phakellin Annulation Strategy Applicable to Palau'amine

A unique oxidative cyclization of a tricycle bearing a guanidine aminal provides a concise route to the enantioselective synthesis of (+)-phakellin and (+)-monobromophakellin in nine and ten steps, respectively, starting from L-proline (see scheme). This sequence provides a simple annulation strategy applicable to the preparation of more complex members of this family of marine sponge-derived alkaloids including palau'amine.