Phosphorus oxychloride → Tert-butyl 4-[({4-[4-(3-bromo-4-fluorophenyl)-5-oxo-4,5-dihydro-1,2,4-oxadiazol-3-yl]-1,2,5-oxadiazol-3-yl}amino)carbonyl]-4-phenylpiperidine-1-carboxylate

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A solution of 3-(4-amino-1,2,5-oxadiazol-3-yl)-4-(3-bromo-4-fluorophenyl)-1,2,4-oxadiazol-5(4H)-one (0.15 g, 0.44 mmol), 1-(tert-butoxycarbonyl)-4-phenylpiperidine-4-carboxylic acid (0.4 g, 1.3 mmol), and 4-dimethylaminopyridine (32 mg, 0.26 mmol) in acetonitrile (2 mL) was treated with phosphoryl chloride (0.13 mL, 1.4 mmol) and heated in the microwave at 100° C. for 10 min. The reaction mixture was concentrated and the residue was diluted with ethyl acetate (25 mL) and washed with water (25 mL) and brine (25 mL), dried with sodium sulfate, filtered, and concentrated to a crude residue which was purified by silica gel to give the coupled product, tert-butyl 4-[({4-[4-(3-bromo-4-fluorophenyl)-5-oxo-4,5-dihydro-1,2,4-oxadiazol-3-yl]-1,2,5-oxadiazol-3-yl}amino)carbonyl]-4-phenylpiperidine-1-carboxylate. This material was diluted with dichloromethane (5 mL) and treated with 4.0 M HCl in 1,4-dioxane (3 mL) and stirred for 45 min. The reaction mixture was concentrated and the crude residue was purified by preparative LCMS to give the desired product (10 mg, 4%). LCMS for C22H19BrFN6O4 (M+H)+: m/z=529.0, 531.0.

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