Green Synthesis of 3,4-Unsubstituted Isoquinolones through Rhodium(III)-Catalyzed C-H Activation and Annulation in Ethanol

A mild and convenient synthesis of 3,4-unsubstituted isoquinolones has been achieved from N-methoxybenzamides and vinylene carbonate as an acetylene surrogate with a versatile rhodium(III) catalyst. The reaction proceeded at room temperature in biomass derived ethanol solvent. This protocol avoids the use of stoichiometric external oxidant, as the vinylene carbonate served as the internal oxidant. The C-H/N-H activation and annulation manifold proceeded with broad substrate scope and excellent levels of regioselectivities. The preliminary mechanistic studies suggest facile and reversible chelation-assisted C-H rhodation. Diversification of 3,4-unsubstituted isoquinolones provide access to 4-substituted isoquinolones and 3,4-unsubstituted isoquinolines, which are complementary to the previously reported protocols. An efficient method for synthesizing 3,4-unsubstituted isoquinolines has been developed via rhodium(III)-catalyzed C-H activation and annulation under mild reaction conditions.image