Sodium hydride → tert-butyl{1-[2-(7-fluoro-2-oxoquinoxalin-1(2H)-yl)ethyl]piperidin-4-yl}carbamate

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A suspension of a 1:1 mixture of 7-fluoroquinoxalin-2(1H)-one (Intermediate 143) and 6-fluoroquinoxalin-2(1H)-one (Intermediate 144) (1.5 g total, 9.1 mmol) was treated with sodium hydride (60% in oil, 0.44 g, 11.0 mmol) at 0° C. The reaction was allowed to stir at room temperature for 2 hours. The reaction mixture was cooled to 0° C. and 2-{4-[(tert-butoxycarbonyl)amino]piperidin-1-yl}ethyl methanesulfonate (Intermediate 6, 1.33 mmol/mL, 11.0 mmol), dissolved in dry DMF (5 mL) was added and it was stirred at room temperature overnight. The reaction mixture was diluted with water and with diethyl ether (5×50 mL). The combined organic phases were dried over sodium sulfate and concentrated to dryness under reduced pressure. Chromatography with hexanes/acetone (5:1 to 3:1). The higher Rf material was isolated as a mixture of Intermediate 141 with an O-alkylated isomer, which was rechromatographed on silica gel with hexanes/ethyl acetate (1:3) to give pure Intermediate 141 as a colorless solid, 0.24 g, 14%. Isolation of the lower Rf material from the first column gave 0.38 g (21%) of pure Intermediate 142 as a colorless solid.

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