Potassium Carbonate → 8-(3-Sulfamoyl-phenylamino)-4,5-dihydro-thiazolo[4,5-h]quinazoline-2-carboxylic acid ethyl ester

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To 7-oxo-4,5,6,7-tetrahydro-benzothiazole-2-carboxylic acid ethyl ester (0.1128 g, 0.50 mmol) was added DMF/DMA solution (3 mL) and the mixture was refluxed under nitrogen for 1 hour. The reaction mixture was concentrated in vacuo and the resulting crude product (6-dimethylaminomethylene-7-oxo-4,5,6,7-tetrahydro-benzothiazole-2-carboxylic acid ethyl ester) was taken through to the next step without further purification. The above was dissolved in anhydrous DMA (3 mL) and treated with 3-guanidino-benzenesulfonamide hydrogen chloride (128 mg, 0.51 mmol) and powdered potassium carbonate (35 mg, 0.26 mmol). The mixture was heated to 120° C. with vigorous stirring for 12 hours. The mixture was cooled down to room temperature, and diluted with water. The resulting solid was filtered, rinsed with more water, a little bit of iPrOH and Et2O. The crude solid was purified by silica gel to give the title compound as a brown solid in 24% yield (52 mg). MS (ES+) 432, (ES−) 430. δH (d6 DMSO) 1.36 (3H, t), 3.05 (2H, t), 3.17 (2H, t), 4.42 (2H, q), 7.33 (2H, s), 7.41 (1H, d), 7.50 (1H, t), 7.89 (1H, d), 8.43 (1H, t), 8.52 (1H, s), 10.04 (1H, s).

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