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An optimization of Grimmel's method under microwave irradiation is reported here for the first time to synthesize 4-amino-N-(4-oxo-2-substituted-4H-quinazolin-3-yl)benzenesulfonamide derivatives. The method was successfully applied for the synthesis of 2-alkyl and 2-aryl substituted derivatives. However, unexpected results were obtained when the same protocol was applied for 2-styryl-substituted quinazolinones. 2-Styrylquinazolinone derivatives were then synthesized via benzoxazinones under microwave irradiation. Subsequently, the effect of various bases (e.g. Et3N, NMM, DMAP, DIPEA) on the efficiency of cyclization to quinazolinone was investigated. The use of microwave irradiation allows significant rate enhancements and better yields compared to conventional conditions.

An optimization of the reaction conditions in solvent free and solution phase microwave assisted synthesis of 2-styryl-4(3H)-quinazolinone derivatives having substituted benzothiazole/5-tertbutylisoxazole at the 3 rd position is discussed. In solvent free reactions acidic alumina was used as a solid support, while a mixture of DMF and pyridine was used in solution phase synthesis. A comparative study of yield and reaction time for both the optimized method revealed that the solution phase microwave irradiation gave better results than solvent free method.