A rapid method for the preparation of N-aryl-2-methylthio-4-oxo-1,4-dihydro quinoline-3-carbonitriles (2a–e) and N-aryl-3-methylthio-4H-1,4-benzothiazine-2-carbonitrile 1,1-dioxides (2f–o) is reported. The cyclization is accelerated by microwave irradiation under solvent free conditions in the presence of K2CO3.
An improved procedure for the preparation of the title compounds 1-3 has been developed. Direct condensation of methyl 3-mercaptopropionate with methyl acrylate using sodium hydride as a base gave compound 1 in good yield. The reaction of methyl thioglycolate and methyl acrylate at 0 °C gave compound 2 as the major product whereas at lower temperature (−40 °C) isomer 3 was found as the major product. The condensation reactions of methyl thioglycolate with methyl methacrylate and crotonate were also carried out.
