Diisopropylethylamine → tert-Butyl {4-[({4-[4-(3-chlorophenyl)-5-oxo-4,5-dihydro-1,2,4-oxadiazol-3-yl]-1,2,5-oxadiazol-3-yl}amino)carbonyl]benzyl}carbamate

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A solution of 3-(4-amino-1,2,5-oxadiazol-3-yl)-4-(3-chlorophenyl)-1,2,4-oxadiazol-5(4H)-one (0.5 g, 1.8 mmol) and 4-{[(tert-butoxycarbonyl)amino]methyl}benzoic acid (0.67 g, 2.7 mmol) in dichloromethane (35 mL) was treated with 4-dimethylaminopyridine (0.13 g, 1.1 mmol) and N,N-diisopropylethylamine (0.93 mL, 5.4 mmol) followed by bromotris(pyrrolydino)phosphonium hexafluorophosphate (1.3 g, 2.7 mmol) and additional N,N-diisopropylethylamine (0.93 mL, 5.4 mmol). The reaction mixture was stirred for 16 h, diluted with ethyl acetate (˜200 mL) and washed with 0.1 M HCl (2×100 mL) and brine (25 mL), dried with sodium sulfate, filtered, and concentrated. Purification of the crude reaction mixture on silica gel gave the intermediate tert-butyl {4-[({4-[4-(3-chlorophenyl)-5-oxo-4,5-dihydro-1,2,4-oxadiazol-3-yl]-1,2,5-oxadiazol-3-yl}amino)carbonyl]benzyl}carbamate. This material was diluted with dichloromethane (30 mL), treated with 4.0 M HCl in 1,4-dioxane (4.5 mL), and stirred for 1 h. The reaction mixture was concentrated and purified by preparative LCMS to give the desired product (542 mg, 58%). LCMS for C18H14ClN6O4 (M+H)+: m/z=413.0.

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