) may also be prepared by the following Process [F]. (In the formula, R1 is as defined in the general formula (1???), each of R17, R18 and R19 is independently selected from hydrogen, a hydrocarbon group and a silicon-containing hydrocarbon group, and may be the same or different from each other, and L is an alkali metal.) Also in this process, since an isomer of (24) wherein R1 and R3 are adjacen