Compounds of the tautomeric formula ##STR1## wherein R, R.sub.1 and R.sub.2, which may be identical to or different from each other, are each hydrogen or alkyl of 1 to 4 carbon atoms;R.sub.3 is straight or branched alkyl, optionally interrupted by heteroatoms such as oxygen, sulfur or nitrogen; straight or branched alkenyl; alkynyl; cyano; cycloalkyl or cycloaliphatic alkyl; a bicyclic group; aryl; or a heterocyclic group; orR.sub.2 and R.sub.3, together with each other and the nitrogen atoms to which they are attached, form a heterocyclic group;R.sub.4 is hydrogen, halogen, alkyl of 1 to 4 carbon atoms or alkoxy of 1 to 4 carbon atoms; andHet is a substituted or unsubstituted heterocycle containing two or three heteroatoms; tautomers thereof, and non-toxic, pharmacologically acceptable acid addition salts thereof. The compounds as well as their salts are useful as anti-ulcerogenics.