Redox-neutral C–H acylation of indole with ketene by manganese catalysis

A low-cost manganese-catalyzed oxidant-free selective C–H acylation of indole with ketene is reported. This protocol features mild reaction conditions and good functional group tolerance. The yield is from middle to excellent. The acylation products can be further converted to diverse useful compounds. Mechanism study reveals the acylation transformation possibly undergoes a cyclomanganated complex species as reactive intermediate.