Hydrogen evolution-enabled rhodaelectro-catalyzed [4+2] annulations of purines and 7-deazapurines with alkynes

Abstract

A rhodium-catalyzed electrochemical regioselective annulation of 6-phenylpurines and 6-phenyl-7-deazapurines with alkynes has been developed. Electricity is used to recycle the active rhodium-based catalyst, promote the evolution of H₂ and help in reducing the reaction temperature. This mild and green method enables a broad substrate scope and wide functional group tolerance, providing a new series of polycyclic purinium and 7-deazapurinium salts in high yields. Mechanistic studies show that the five-member rhodium(III) species and purinoisoquinolinium-coordinated rhodium(I) complex are the two key intermediates in this transformation.