Visible-Light-Promoted Generation of α-Ketoradicals from Vinyl-bromides and Molecular Oxygen: Synthesis of Indenones and Dihydroindeno[1,2-c]chromenes.

Ortho-alkynylated α-bromocinnamates can be converted by a visible-light-mediated photocascade reaction with molecular oxygen into either indenones or dihydroindeno[1,2-c]chromenes. The one-step process features key photochemical steps, that is, the initial activation of vinyl bromides through energy transfer to give α-ketoradicals in a reaction with molecular oxygen, followed by α-oxidation of an arene moiety by 6-π electrocyclization, and subsequent hydroxylation by an electron-transfer process from the same photocatalyst leads to the dihydroindeno[1,2-c]chromenes.