. . "wherein R7 is as defined above with respect to the formula (I), and X is a halogen atom or a p-toluenesulfonate group, or with a dialkyl sulfate such as dimethyl sulfate or diethyl sulfate in an organic solvent inert to the reaction, such as toluene, xylene, nitrobenzene, tetrahydrofuran, dioxane, N,N-dimethylformamide, N-methylpyrrolidone or dimethylsulfoxide, in the presence of an acid binding a" . . .