Rh(III)-Catalyzed One-Pot Three-Component Diannulation of Benzils, Ammonium Acetate, and Alkynes to Build 1,1′-Biisoquinolines

An efficient one-pot synthesis of 1,1′-biisoquinolines by a three-component reaction of commercially available raw materials (benzils, NH4OAc, and alkynes) is disclosed. This complicated reaction involves in situ diimine formation via benzil-NH4OAc condensation, Rh(III)-catalyzed 2-fold imine-directed C–H activation, and annulation with alkynes. Both symmetric and unsymmetric 1,1′-biisoquinolines could be assembled in moderate to high yields. The reaction mechanism is supported through ESI-MS, in which Cp*ClRh+, Cp*(OAc)Rh+, Cp*(OPiv)Rh+, and two rhodacycle intermediates are successfully detected to explain the evolution of rhodium species.