[CH3:1][CH:2]1[CH2:6][CH:5]([C:7]([O:9]C)=O)[C:4](=O)[CH2:3]1.S(O)(O)(=O)=O.[CH3:17][S:18][C:19](=[NH:21])[NH2:20].[OH-].[K+]>O>[CH3:1][CH:2]1[CH2:3][C:4]2[N:20]=[C:19]([S:18][CH3:17])[NH:21][C:7](=[O:9])[C:5]=2[CH2:6]1A solution of methyl 4-methyl-2-oxocyclopentanecarboxylate (0.42 g, 2.69 mmol), 2-methyl-2-thiopseudourea sulfate (1.10 g, 7.9 mmol) and potassium hydroxide (0.50 g, 8.9 mmol) in water (12 mL) was stirred at 25° C. for 30 minutes, and then heated to reflux for 4 hours. The reaction was cooled to 0° C. by adding ice and a precipitate was formed. The solid product was removed by filtration and the filter cake dried to give 6-methyl-2-(methylthio)-6,7-dihydro-3H-cyclopenta[d]pyrimidin-4(5H)-one (0.19 g, 43% yield) as a white solid. 1H NMR (400 MHz, d6-DMSO): 2.87 (m, 2H), 2.53 (s, 3H), 2.37 (m, 2H), 2.28 (s, 3H), 1.49 (m, 1H), 1.02 (d, 3H).
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