A new and general one-pot transformation of aromatic aldehydes to fluorinated olefins containing–CH C (Cl) CF3 or–CH C (F) CClF2 moieties is described. Freons CCl3CF3 and CCl2FCClF2 were used as trifluoromethyl and difluoromethyl C2-building blocks respectively. A proposed mechanism for the reaction is discussed.