Abstract o-Phenylenediamine, 4-nitro-1, 2-phenylenediamine, 3, 4-diaminobenzophenone, 3, 4-diaminotoluene, 4, 5-dimethylphenylenediamine and 3, 4-diaminobenzoic acid (1a–f) react with 4-isothiocyanatobutan-2-one to give the pyrimidobenzimidazole derivatives (2a–f) respectively. Condensation of 4-nitro-1, 2-phenylenediamine with 4-isothiocyanatobutan-2- one at room temperature gave the thiourea derivative (3). o-Nitroaniline, on condensation ...