Cyclopentenones from a Novel [4+1]Cocyclization of Methylenecyclopropanes with Fischer Carbenechromium Complexes

Fischer carbenechromium complexes react with methylenecyclopropanes and bicyclopropylidene in an unprecedented manner. All four carbon atoms of the methylenecyclopropane moiety along with carbon monoxide are incorporated with the formation of three new C-C (sigma)-bonds to give substituted cyclopentenone derivatives in moderate (33-58% for methylenecyclopropanes) to good yields (65-72% for bicyclopropylidene).