[BH4-].[Na+].C([O:5][C:6]([C:8]1[CH:21]=[C:11]2[C:12](=[O:20])[N:13]([CH2:16][CH:17]3[CH2:19][CH2:18]3)[CH2:14][CH2:15][N:10]2[N:9]=1)=O)C>C1COCC1.CO.O>[CH:17]1([CH2:16][N:13]2[CH2:14][CH2:15][N:10]3[N:9]=[C:8]([CH2:6][OH:5])[CH:21]=[C:11]3[C:12]2=[O:20])[CH2:18][CH2:19]1
Sodium borohydride (0.23 mL, 6.1 mmol) was added dropwise to a stirred solution of 5-cyclopropylmethyl-4-oxo-4,5,6,7-tetrahydro-pyrazolo[1,5-a]pyrazine-2-carboxylic acid ethyl ester (0.32 g, 1.2 mmol) in a mixture of THF (4 mL) and MeOH (1 mL) under N2 at 0° C. The reaction mixture was stirred at 80° C. for 30 minutes and then diluted with water and extracted with DCM. The aqueous layer was acidified with a 1N solution of HCl and extracted with DCM. The organic layers were combined, dried (NaSO4), filtered and the solvents evaporated in vacuo. The crude product was purified by flash column chromatography (silica; 7 M solution of ammonia in methanol in DCM 0/100 to 10/90). The desired fractions were collected and the solvents evaporated in vacuo to yield 5-cyclopropylmethyl-2-hydroxymethyl-6,7-dihydro-5H-pyrazolo[1,5-a]pyrazin-4-one (0.21 g, 78% yield) as a colorless oil.
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