Photochemical Reaction of Diphenylcyclobutenedione Derivatives. Formation and Reaction of Conjugated Bisketene and ItsN-Analog

The photolysis of diphenylcyclobutenedione derivatives (Va, b) under N2 and that in the presence of substrate, O2 or isocyanide, have been studied. The former resulted in the recovery of a large amount of V and the fragmentation; the latter gave the insertion products into V, diphenylmaleic anhydrides and iminocyclopentenones in good yield. The intermediates, bisketene and ketene-ketenimine as primary photo products were confirmed by the photolysis of Va in methanol to give succinates and by low-temperature IR-technique. Structural aspects of bisketene intermediate were discussed.