Triethylamine → tert-butyl (5-bromo-3-(3-phenylisoxazol-5-yl)pyrazin-2-yl)-N-tert-butoxycarbonyl-carbamate

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NCS (12.19 g, 91.26 mmol) was added to a solution of benzaldehyde oxime (10.05 g, 82.96 mmol) in DMF (40.20 mL) and the mixture heated at 55° C. for 15 minutes. The reaction mixture was cooled to ambient temperature and tert-butyl N-(5-bromo-3-ethynyl-pyrazin-2-yl)-N-tert-butoxycarbonyl-carbamate (36.34 g, 91.26 mmol) and DMF (30.15 mL) were added followed by the dropwise addition of Et3N (10.07 g, 13.87 mL, 99.55 mmol). The reaction mixture was stirred at ambient temperature for 45 minutes and then heated to 65° C. for 1 hour. The reaction mixture was cooled to ambient temperature and the solvent removed under high vacuum. The residue was taken up in ethyl acetate (50 ml). Remaining solid was filtered off and the filtrate concentrated in vacuo and then purified by column chromatography on silica using the ISCO column companion system, eluting with ethyl acetate/petroleum ether (0-40% EtOAc). Product fractions were combined and concentrated in vacuo to give tert-butyl (5-bromo-3-(3-phenylisoxazol-5-yl)pyrazin-2-yl)-N-tert-butoxycarbonyl-carbamate as a pale yellow solid (19 g, 46%). LC/MS m/z 419 [M−100+1]+.

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