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

A MnI‐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 MnI‐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. Magic manganese! The title reaction allows simple access to a broad range of 2‐allenylindoles with efficient chirality transfer, and for the first time also allows the direct preparation of ketones by MnI‐catalyzed C−H activation. The coordination of the carbonate oxygen atom to the Mn catalyst and the congested tertiary carbon atom play crucial roles in the reaction mechanism.