Compounds of formula I: ##STR00001## where R.sub.1, R.sub.2 and R.sub.3 are the same or different and signify hydrogens, halogens, alkyl, alkylaryl, alkyloxy, hydroxy, nitro, amino, alkylcarbonylamino, alkylamino or dialkylamino group; R.sub.4 signifies hydrogen, alkyl or alkylaryl group; X is CH.sub.2, O or S, and n is 1, 2 or 3, with the proviso that if X is CH.sub.2, n is not 1, and a method for their preparation. The compounds have potentially valuable pharmaceutical properties for the treatment of cardiovascular disorders such as hypertension and chronic heart failure.