A general synthesis of bicyclo [3.2. 0] heptenones from 4-allylcyclobutenones is described. The rearrangement is envisaged to involve an electrocyclic ring opening of the cyclobutenone and subsequent intramolecular 2+ 2 cycloaddition of the resulting vinylketene to the nonconjugated allylic alkene moiety. This method is particularly suitable for the synthesis of highly substituted derivatives since the regiochemistry of the ...