(wherein R8 represents a lower alkyl group such as methyl, n-propyl or isopropyl, and X is a halogen atom such as chlorine, bromine or iodine) in the presence of a metal or metallic compound under the conditions of Reformatsky reaction to give a compound of formula (IV): ##STR4## (wherein A, R3, R4, R5, R7 and R8 are the same as defined above) and