Microwave-Assisted Synthesis of Novel Imidazo- and Pyrimidopyrido[4’,3’:4,5]thieno[2,3-d]pyrimidines

Bronchial asthma is a chronic debilitating disease, which in its severe forms can even threaten life. It is, in general, characterized by both broncho-constriction and airway inflammation which leads to bronchial hyper responsiveness [1]. Although different classes of drugs have been employed, methylxanthines continue to enjoy significant status as drugs of choice in asthma therapy, despite a narrow therapeutic index. Currently, new tricyclic heterocyclic compounds designed on the basis of the xanthine skeleton are being investigated as possible bronchodilators with a wider margin of safety. While reviewing the recent perspectives in the design of anti-asthmatic agents [2] we observed that different angularly fused heterocyclic ring systems like imidazoquinolines [3] imidazonaphthyridines [4] benzimidazolo-quinazolines, [5, 6] imidazoquinazolines [7] and benzimidazolopyridopyrimidines [8] have been identified as potentially useful compounds. The encouraging broncho-dilatory activity of these compounds led us to attempt the isosteric replacement of benzene by thiophene [9]. The source of regulation of energy has not normally received proper recognition in synthetic organic chemistry. Microwaves have the capacity to alter that, because of the fact that the energy is directly transferred and concentrated in the reaction mixture and also because of the convenience in performing organic transformation with microwave apparatus [10]. In recent years, reagents impregnated on mineral solid support and assisted by microwaves have gained popularity in the synthesis of various heterocyclic com-