Intramolecular cascade annulation triggered by C-H activation via rhodium hydride intermediate

A novel intramolecular cascade annulation of O-substituted N-hydroxybenzamides for the synthesis of indolizinones triggered by rhodium(III)-catalyzed sequential C(sp(2))-H activation and C(sp(3))-H amination is developed. This method features air as the oxidant, a broad substrate scope and excellent functional-group tolerance, including various heterocyclic substrates. The applicaton of indolizinone products with aminal functionality is demonstrated by further derivatization. Mechanistic studies and DFT calculations indicate that two pathways are involved in the formation of indolizinones via rhodium hydride intermediate.