Compounds of the formulae Iv1 and Iv2 ##STR58## are prepared by reacting compounds of the formula Ie with compounds of the formulae M--O--N???C(R1)R2 or M--O--N???C(CN)CONH--R5 in inert solvents and, in the event that M is hydrogen, in the presence of a base, for example alkali metal carbonate, sodium hydride or a tert-amine, for example pyridine, at -20??? to 140??? C.; where M is hydrogen or an