CO2(CO)8-catalyzed intramolecular hetero-Pauson-Khand reaction of alkynecarbodiimide:: Synthesis of (±)-physostigmine

Herein we describe a novel CO2(CO)(8)-catalyzed intramolecular aza-Pauson-Khand-type reaction of alkynecarbodiimide derivatives affords pyrrolo[2,3-b]indol-2-one ring systems in reasonable yields. This is the first reported CO2(CO)(8) Successfully applied in the hetero-Pauson-Khand reaction. Significantly, the transformation of one of our pyrrolo[2,3-b]indol-2-one derivatives into the indole alkaloid, (+/-)-physostigmine, was completed in a highly stereoselective manner.