"hydroxide, an alkali metal hydride such as sodium hydride or an alkali metal alcoholate, for example sodium methylate or ethylate, a 4-hydroxyphenyl derivative of formula (4) above with a compound of general formula: ##STR68## in which X has the same meaning as above and preferably represents chlorine or a benzenesulphonyoxy or p-toluenesulphonyloxy radical, A represents an alkylene radical and R3" . . . . . .