Dimethyl malonate → 2-benzylsulfanyl-7-hydroxy-1H-[1,2,4]triazolo[1,5-a]pyrimidin-5-one

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A solution of 125 g (0.58 mol) of a 25% solution of sodium methoxide in methanol dissolved in 100 ml of absolute ethanol was treated with 66.3 ml (0.29 mol) of dimethyl malonate followed by 60.0 g (0.20 mol) of 3-amino-5-benzylthio-1,2,4-triazole. The resulting solution was heated at reflux for 5 days. On cooling to room temperature the solid which had separated was collected by filtration, washed with cold ethanol and dissolved in 1000 ml of water. The resulting yellow solution was acidified with concentrated HCl to precipitate a solid. The solid was collected by filtration and dried to yield 70.1 g (82%) of the desired product as a white solid, m.p. 199°-210° C. (decomposition). IR and 1H NMR spectra were in agreement with the assigned structure.

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