Photocycloaddition of ketones 1a–c with tetramethylethylene 2 furnishes tetrasubstituted furans 3a–c in isolated yields of≈ 85%; a suggested mechanism for formation of 3a involves [3+ 2] cycloaddition by way of an initial biradical 5 to form an intermediate carbene 6, followed by cyclization to the furan.
