Abstract: To synthesize molecules with antiulcer action, specifically ranitidine, niperotidine and cimetidine, having the formula: ##STR1## wherein R.sub.1 is hydrogen or together with R.sub.2 represents the rest of a cycloaliphatic or heterocyclic optionally substituted ring with 5 or 6 carbon atoms, R.sub.2 represents H, alkyl, alkyl substituted with a simple or substituted aromatic ring or with a single or substituted heterocyclic ring, Ar represents a simple or substituted phenyl group, a simple or substituted heterocyclic aromatic group, N=1, 2, 3, 4, 5 or 6 and X represents CH--NO.sub.2, S, N--C.tbd.N, the compound (II) is prepared through the following process sequence: ##STR2## wherein Z=H, NO.sub.2, halogen and R.sub.3 =--(CH.sub.2).sub.n Ar, --(CH.sub.2).sub.n --SH, --(CH.sub.2).sub.n --S--S--(CH.sub.2).sub.n, --(CH.sub.2).sub.n --S--CH.sub.2 Ar Y being halogen.