Urea → Thieno(3,2-d)pyrimidine-2,4(1H,3H)-dione

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A mixture of methyl 3-amino-2-thiophenecarboxylate 1 (13.48 g, 85.85 mmol) and urea (29.75 g, 5 eq.) was heated at 190° C. for 2 hours. The hot reaction mixture was poured onto sodium hydroxide solution and any insoluble material was removed by filtration. The mixture was then acidified (HCl, 2N) to yield 1H-thieno[3,2-d]pyrimidine-2,4-dione 2 as a white precipitate, which was collected by filtration and air dried (9.49 g, 66%). 1H NMR 400 MHz, d6-DMSO) 6.90 (1H, d, J=5.2 Hz), 8.10 (1H, d, J=5.2 Hz), 11.60-11.10 (2H, br s).

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