"In the cyclization of the compound [31] or [32], if the starting material is a compound in which R3' is a (lower) alkyl having 1 to 3 substituents selected from a halogen atom, hydroxy or a (lower) alkoxy, and the solvent is an acid anhydride, the (lower) alkyl may be acylated to give a compound in which R3' is a (lower) alkyl having at least one (lower) alkanoyloxy in such reaction." . . . .