R11???C(H)(X)???CO2R12, R11???C(CH3)(X)???CO2R12, R11???C(H)(X)???C(O)R12, R11???C(CH3)(X)???C(O)R12 (in which R11 and R12 each is a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, aryl group or aralkyl group and X is chlorine, bromine or iodine); and