Direct evidence for the existence of an intermediate bisketene (Phi = 0.14, epsilon(575) = 2300 M-1 cm(-1)), generated from pyracyloquinone, was obtained by laser flash photolysis with UV/VIS and IR detection. The bisketene was found to react with DMSO to give acenaphthylene-5,6-dicarboxylic anhydride and dimethyl sulfide, quantitatively.