Visible light-mediated gold-catalyzed alkynylative cyclization of allenoates with iodoalkynes for the synthesis of β-alkynyl-γ-butenolides

A method for the tandem cyclization/alkynylation of allenoates with iodoalkynes via gold catalysis under light irradiation is described. This transformation features a broad substrate scope, good functional group tolerance, and compatibility with heterocyclic substrates. The reaction proceeds smoothly at room temperature by using cheap, readily available acriflavine (ACF) as a photocatalyst, and offers β-alkynyl-γ-butenolides derivatives in moderate to good yields. Initial mechanistic studies suggest that a vinylgold(i) complex acts as a key intermediate, which would undergo photosensitization from the ACF singlet excited state. The corresponding energy transfer would promote the oxidative addition of the iodoalkyne partner to deliver C(sp²)-C(sp) coupling products after reductive elimination.