Statement of a methodology for the microwave-induced preparation of biologically important benzothiazolo [2, 3-b] quinazolines and its comparison with ultrasonic and classical heating

Synthesis of substituted 3,3- dimethyl trihydro benzothiazolo[2,3-b]quinazoline-2Hones a class of well established medicinally important compound is developed by the multicomponent condensation reaction of 2-amino-6-chloro-benzothiazole (1), substituted benzaldehydes (2) and 5,5-dimethylcyclohexane-1,3-dione (dimedone, 3) under different reactions conditions and energy sources, e.g. microwave irradiation, sonication and classical heating for comparison purposes. The use of a monomode oven allowed an accurate consideration of the temperature distribution in the microwave reaction vessel, which revealed a very strong and unexpected thermal heterogeneity. The reaction was facilitated by the presence of a trace of DMF, the catalytic role of which is demonstrated.