Rhodium-Catalyzed [4+2] Cascade Annulation to Easy Access N-Substituted Indenoisoquinolinones

An efficient approach for the synthesis of N substituted indenoisoquinolinones via rhodium(III)-catalyzed C- H bond activation/subsequent [4 + 2] cyclization starting from easily available 2-phenyloxazolines and 2-diazo-1,3-indandiones has been developed. A series of indeno[1,2-c]isoquinolinones were obtained in up to 93% yield through C-H functionalization, followed by intramolecular annulation, elimination, and ring opening in a "one pot manner" under mild reaction conditions. This protocol features excellent atom-and step-economy and provides a novel strategy for the synthesis of N-substituted indenoisoquinolinones and a chance to study their biological activities.