[CH3:1][C@@H:2]1[CH2:6][CH2:5][C:4](=O)[CH:3]1[C:8]([O:10]CC)=O.[NH2:13][C:14]([NH2:16])=[S:15].[OH-].[K+]>C(O)C.O>[SH:15][C:14]1[N:13]=[C:8]([OH:10])[C:3]2[C@H:2]([CH3:1])[CH2:6][CH2:5][C:4]=2[N:16]=1To a solution of a mixture of (2R)-ethyl 2-methyl-5-oxocyclopentanecarboxylate (20 g, 117.5 mmol) and thiourea (9.2 g, 120.9 mmol) in ethanol (100 mL) was added KOH (8.3 g, 147.9 mmol) in water (60 mL). The mixture was refluxed for 10 hours. After cooling, the solvent was removed and the residue was neutralized with concentrated HCl (12 mL) at 0° C. and then extracted with DCM (3×150 mL). The solvent was removed and the residue was purified by silica gel chromatography, eluting with Hexane/ethyl acetate (2:1) to give (R)-2-mercapto-5-methyl-6,7-dihydro-5H-cyclopenta[d]pyrimidin-4-ol (12 g, 56%). MS (APCI+) [M+H]+183.
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