Manganese(I)-Catalyzed Regioselective C-H Allenylation: Direct Access to 2-Allenylindoles

A Mn-I-catalyzed regioselective C-H allenylation is reported that allows a broad range of 2-allenylindoles to be synthesized regioselectively on a gram scale under simple conditions. Notably, a highly efficient chirality transfer was observed (up to 93% ee) in this transformation. This procedure was further found to allow, for the first time, the direct preparation of ketones by Mn-I-catalyzed C-H activation. Mechanistic investigations revealed that the precoordination of the oxygen atom to the manganese center as well as the congested tertiary carbon atom in the propargylic carbonates play a crucial role.