To a suspension of sodium hydride (60% dispersion in oil, 1.55 g, 38.7 mmol) in anhydrous acetonitrile (200 mL) was added to tert-butyl 2,6-dihydropyrrolo[3,4-c]pyrazole-5(4H)-carboxylate (5.3 g, 25.5 mmol) in one portion under nitrogen at room temperature. The reaction mixture was stirred at room temperature for 2 h. To the resulting white suspension was slowly added cyclopropanesulfonyl chloride (6.9 g, 49.1 mmol) and the mixture was stirred at room temperature for 18 h, quenched with water (120 mL) and the layers were separated. The aqueous layer was then extracted with dichloromethane (2×100 mL). The combined organic layers were dried over anhydrous sodium sulfate and concentrated under reduced pressure. The crude material was purified on silica chromatography (300 g Biotage™ column) and eluted with 15-80% ethyl acetate in hexanes to yield the title compound and tert-butyl 1-(cyclopentylsulfonyl)-2,6-dihydropyrrolo[3,4-c]pyrazole-5(4H)-carboxylate as a white solid. LC/MS: 314.2 (M+1).
