Sodium hydride → (R)-tert-butyl 4-(5-fluoro-4-(methoxycarbonyl)-2-nitrophenyl)-2-isopropyl-3-oxopiperazine-1-carboxylate

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Reaction Conditions

Reaction Steps

Under N2 atmosphere, NaH (8.8 g, 0.22 mol, 60% in mineral oil, 1.1 eq.) was added in portions at −10° C. to a 1 L three-neck flask containing (R)-tert-butyl 2-isopropyl-3-oxopiperazine-1-carboxylate (26.66 g, 0.11 mol) in DMF (300 mL). The mixture was stirred at −10° C. for 30 min. Then the mixture was added dropwise to a 1 L three-neck flask containing methyl 2,4-difluoro-5-nitrobenzoate (26.3 g, 0.121 mol, 1.1 eq.) in DMF (200 mL) at −20° C. over 10 min After addition, the resulting mixture was stirred between −20° C. and −30° C. for another 10 min. The reaction was quenched with sat. aq. NH4Cl (200 mL) and then water (800 mL). The aqueous layer was extracted with EtOAc (3×1 L). The combined organic layers were washed with water (3×1 L) and brine, and dried over anhydrous Na2SO4. The mixture was filtered and the filtrate was evaporated under vacuum. The residue was purified by column chromatography on silica gel eluting with petroleum ether: EtOAc 8:1˜4:1 to give (R)-tert-butyl 4-(5-fluoro-4-(methoxycarbonyl)-2-nitrophenyl)-2-isopropyl-3-oxopiperazine-1-carboxylate (32 g, 66.3% yield) as a yellow solid. LC-MS MS (ESI) m/z 384.1 [M−56+H]+, 462.1 [M+Na]+. 1H NMR (CDCl3 300 MHz): δ 8.63 (d, J=6.9 Hz, 1H), 7.16 (d, J=10.2 Hz, 1H), 4.61-4.30 (m, 2H), 3.97-3.89 (m, 4H), 3.62-3.48 (m, 2H), 2.40-2.34 (m, 1H), 1.49 (s, 9H), 1.08 (d, J=6.9 Hz, 3H), 1.01 (d, J=6.9 Hz, 3H).

Provenance & Evidence