Synthesis of 3‐Methyleneisoindolin‐1‐ones via Rhodium(III)‐Catalyzed C−H/N−H Activation and Annulation of <i>N</i>‐Methoxybenzamides with Potassium Vinyltrifluoroborate

Isoindolinones are vital heterocyclic compounds in medicinal chemistry, notable for their diverse bioactivities. Significant attention has been devoted to their preparation; however, existing methods are unsuitable for constructing unsubstituted 3-methyleneisoindolin-1-ones. Herein, we present a rhodium(III)-catalyzed method for synthesizing unsubstituted 3-methyleneisoindolin-1-ones via C-H/N-H activation and annulation of N-methoxybenzamides with potassium (ethenyl)trifluoroborate. This approach offers mild reaction conditions, high regioselectivity, and efficient yields. Interestingly, sterically demanding or heterocyclic N-methoxyaromaticamides resulted in the formation of 2-vinyl(hetero)aromatic amides instead of 3-methyleneisoindolin-1-ones. Mechanistic insights suggest a rhodacycle intermediate pathway, highlighting the method's potential for developing new bioactive isoindolinone derivatives.