An efficient ultrasonic-assisted synthesis of the thiazolo[2,3-b] quinazoline and thiazolo[3,2-a] pyrimidine derivatives

Treatment of cyclohexanone or cyclopentanone (2) with aromatic aldehyde (1) and thiourea (3) in the presence of modified montmorinollite nanostructure or HCl as a catalyst under heating and solvent-free conditions produced 7-benzylidene-4-aryl-3,4,6,7-tetrahydro-1H cyclopenta[d]pyrimidine-2(5H)-thione or 8-benzylidene-4-aryl-3,4,5,6,7,8 hexahydroquinazoline-2(1H)-thione (4). Compound 4 was utilized as a key intermediate for the synthesis of new thiazolo[2,3-b]quinazoline and thiazolo[3,2-a]pyrimidine derivatives (5a-5o) via the reaction with diethyl and dimethyl acetylene dicarboxylate by two different methods: (a) in methanol as a solvent under ultrasonic irradiation at ambient temperature; (b) in methanol as a solvent at ambient temperature (conventional magnetic stirring). Ultrasound-assisted synthesis provides excellent yields (87-95 %) in short reaction times (30-50 min) at room temperature. The chemical structures of the newly synthesized compounds were characterized by UV-Vis, IR and NMR spectral and elemental analysis.