Regioselective Reductive Coupling of o-Haloaromatic Ketones with Terminal Alkynes via Photoredox/Cobalt Dual Catalysis.

The regioselective reductive coupling of o-haloaromatic ketones with alkynes to access indenols still poses a challenge, as existing methods typically rely on stoichiometric metal reductants and elevated temperatures. Herein, we describe a photoredox/cobalt catalytic system that enables selective reductive coupling of o-iodo, o-bromo, and o-chloroaromatic ketones as well as o-bromoaromatic aldehydes, with terminal alkynes to afford 2-substituted indenols. This protocol uses a tertiary amine as the terminal reductant, proceeds at room temperature, and features mild conditions, excellent regioselectivity, and broad substrate scope.