"The compounds of formula (Idd), that is, the compounds of formula (Id) in which R2 is a hydrogen atom, can be alkylated in the 4-position according to the scheme: ##STR18## wherein X represents a chlorine, bromine or iodine atom, and the other substituents are defined as before except that R2 is other than H, in an organic solvent in the presence of base." . . . .