22288-78-4

623-49-4

319442-19-8

Step A: Methyl 3-amino-2-thiophenecarboxylate (3.0 g, 19 mmol) was dissolved in acetic acid (24 mL), followed by the sequential addition of concentrated hydrochloric acid (2.4 mL) and ethyl cyanoformate (3.78 g, 38 mmol). The resulting inhomogeneous mixture was heated and stirred at 70 °C for 3 h. After completion of the reaction, it was cooled to room temperature. The solid generated in the reaction was collected by filtration and washed with deionized water. The filtrate was adjusted to a pH of about 5 with 1N NaOH solution, at which point a solid precipitated, and the precipitate was collected by filtration and again washed with deionized water. The two collected solids were combined and dried overnight in a vacuum drying oven to give the final ethyl 4-oxo-3,4-dihydrothieno[3,2-d]pyrimidine-2-carboxylate (2.69 g, 63% yield).