droxide, 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 IV above with a compound of general formula: ##STR54## in which X has the same meaning as above and preferably represents chlorine or a benzenesulphonyl or p-toluenesulphonyl radical, A represents an alkylene radical and R3 and R4