Borane;tetrahydrofuran → 1-Cyclopropyl-1,2,3,4-tetrahydroquinoxaline

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To a stirred suspension of 1-cyclopropyl-1,4-dihydro-quinoxaline-2,3-dione (10.0 g, 49.45 mmol, 1.0 equiv) in tetrahydrofuran (500 mL) was added dropwise a 1 M solution of borane-tetrahydrofuran complex (108.8 mL, 108.8 mmol, 2.2 equiv; [CAS RN 14044-65-6]) and the reaction mixture stirred at room temperature over night. The solvent was removed by evaporation under reduced pressure and the crude reaction mixture extracted from a saturated aqueous solution of sodium bicarbonate (100 mL) with ethyl acetate (three times 100 mL). The combined organic phases were dried over sodium sulfate and purified by silica gel column chromatography using a MPLC system (CombiFlash Companion, Isco Inc.) eluting with a gradient of n-heptane:ethyl acetate to give 4.2 g (49%) of the title compound as a light yellow solid. MS (ISP): m/z=175.4 [M+H]+.

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