Compounds of the general formula: ##STR1## wherein the radicals R.sub.1 and R.sub.2 are the same or different and represent hydrogen or C.sub.1 -C.sub.6 -alkyl, the radicals R.sub.3 and R.sub.4 are the same or different and represent hydrogen, C.sub.1 -C.sub.6 -alkyl, hydroxy, C.sub.1 -C.sub.6 -alkoxy, C.sub.2 -C.sub.6 -alkanoyloxy, halogen or C.sub.2 -C.sub.6 -alkanoyl, X is oxygen, sulphur or the group --NR.sub.5 and R.sub.5 is hydrogen, C.sub.1 -C.sub.6 -alkyl, C.sub.2 -C.sub.6 -alkanoyl or benzoyl, m and n in each case may represent the integers 1, 2 or 3 and the phenyl radical A is unsubsituted or is substituted by halogen, nitro, C.sub.1 -C.sub.6 -alkyl, trifluoromethyl, C.sub.3 -C.sub.7 -cycloalkyl, hydroxy, C.sub.1 -C.sub.6 -alkoxy, C.sub.2 -C.sub.6 -alkanoyloxy, amino, C.sub.1 -C.sub.6 -alkylamino, di-C.sub.1 -C.sub.6 -alkylamino, C.sub.2 -C.sub.6 -alkanoylamino, CN, carboxy, C.sub.1 -C.sub.6 -alkoxycarbonyl, phenyl, C.sub.1 -C.sub.6 -alkylphenyl or trifluoromethylphenyl, their pyridine-N-oxides and physiologically acceptable salts thereof, processes for their preparation and medicines containing such compounds as active ingredients.