Total Synthesis of Spirotryprostatins through Organomediated Intramolecular Umpolung Cyclization.

Cyclodipeptide 2,5-diketopiperazines (DKP) are privileged structural units present in drugs and natural alkaloids. This work reports a new method for the synthesis of biologically important DKP scaffolds based on an intramolecular nucleophilic α-addition of general amides towards an alkynamide system. The utility of this umpolung cyclization mediated by trimethyl phosphine and l-glutamic acid is highlighted by its application to the concise total syntheses of 6-methoxyspirotryprostatin B (the first total synthesis), spirotryprostatin A, and spirotryprostatin B.