Abstract: An unexpectedly high yield of carbon monooxide as a deoxygenationproduct of carbonyl compound was obtained in the reaction of tetraphenyl-cyclopentadienone with dibromocarbene using phenyl tribromomethyl mercury asthe carbene precursor.This unique phenomenon is rationalized in terms of thepush-pull stabilization gained from the interaction between the partially aromaticcyclopentadienide moiety and the positively charged dibromomethylene moiety inthe dihalocarbonyl Ylide-like transition state.

Key words: Carbonyl ylide, Dihalocarbene, Push-pull stabilization, Reaction mech-anism