Compounds of the formula I ##STR1## where R is alkyl of 1 to 10, preferably 1 to 4, carbon atoms, X is O or S, Y is hydrogen or nitrophenyl which is unsubstituted or substituted by chlorine, bromine, methoxy or methyl, when n is 1, and is C.sub.2 -C.sub.6 -alkylene when n is 2, and Z is cyano or 2-benzimidazolyl, are prepared by a process in which an iminoether of the formula II ##STR2## is reacted with a compound of the formula III ##STR3## where A.sup..crclbar. is an anion. The compounds prepared according to the invention are useful intermediates, for example for the preparation of diazo components.