[NH2:1][C:2]1[C:3]2[CH:15]=[CH:14][CH:13]=[CH:12][C:4]=2[S:5][C:6]=1[C:7](OCC)=[O:8].[CH:16]([NH2:18])=O>>[N:1]1[C:2]2[C:3]3[CH:15]=[CH:14][CH:13]=[CH:12][C:4]=3[S:5][C:6]=2[C:7](=[O:8])[NH:18][CH:16]=1A 100 mL RBF was charged with ethyl 3-aminobenzo[b]thiophene-2-carboxylate (17.7 g, 80 mmol), treated with formamide (60.6 mL, 1520 mmol) and heated to 190° C. for 2 hrs. Precipitate formed upon cooling. The solid precipitate was collected by filtration and washed with ether, then recrystallized from ethanol/tetrahydrofuran. Benzo[4,5]thieno[3,2-d]pyrimidin-4(3H)-one (9.9 g, 61% yield) was obtained.
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