5655-01-6

Step C: Pyrrolo[3,2-D]pyrimidin-4-one (23 g) prepared in Step B was dissolved in ethanol (210 ml) followed by addition of formamidine acetate (23.3 g). The reaction mixture was placed in an oil bath at 100-105°C and heated to reflux for 16 hours. After completion of the reaction, the mixture was cooled to room temperature and the precipitate precipitated was collected by filtration. The precipitate was washed repeatedly with ethanol until the washings were colorless. Finally, the precipitate was dried under high vacuum (HV) conditions to give a gray solid product (15.3 g, 75% yield, molecular ion peak MH+ = 136 by mass spectrometry).

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