Compounds of formula III: ##STR1## wherein R.sup.1 is a 5- or 6-membered aromatic heterocyclic group; and R.sup.4 and R.sup.5 each idependently signify hydrogen, halogen, trifluoromethyl, cyano, nitro, amino or lower alkyl; are useful intermediates in a novel process for the preparation of a class of pharmacologically active compounds of formula I: ##STR2## wherein R.sup.1, R.sup.4 and R.sup.5 are as defined above; and R.sup.3 represents hydrogen or lower alkyl.