Catalytic Propargylation of Aldehydes with Alkynes via C(sp³)-H Activation

Carbonyl propargylation through activation of native propargylic C(sp³)-H bonds represents an attractive yet underdeveloped approach to homopropargylic alcohols. Herein, we report a catalytic addition of readily available alkynes to aldehydes enabled by visible-light-induced ligand-to-metal charge transfer (LMCT). Using commercially available CrBr₃•6H₂O, the transformation proceeds under operationally simple, redox-neutral conditions using only minimal reaction components and without substrate prefunctionalization. Structurally diverse homopropargylic alcohols are obtained from a broad range of alkynes and aliphatic or aromatic aldehydes with excellent regioselectivity.