The intermediacy of oxycyclobutenes in the synthesis and reactions of cyclobutenones and cyclobutenols

Vinylcyclobutenol 7, generated via the singlet oxygenation of alkylidenecyclobutene 5, rearranges at room temperature to a solvent dependent mixture of isomeric dienones 10 and 11. Alkylidenecyclobutene 5 was prepared in turn via an inverse Wittig addition of the isopropyl ylide to cyclobutenone 4; in a normal addition of ketone to ylide, vinylallene 12 is also obtained. Finally, the corresponding Wittig reaction of 4,4- dichlorocyclobutenone 3 yields only the 2,4-dichloro isomer 13. When this reaction is carried in the presence of n-butoxide, dienone 32 is generated.