N-(Diphenylmethylene)glycine tert-butyl ester → tert-butyl 3-(1-benzyl-3-nitro-1H-pyrazol-4-yl)-N-(diphenylmethylene)-L-alaninate

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To a −30° C. solution of tert-butyl N-(diphenylmethylene)glycinate (98% 1.16 g, 3.85 mmol), C4 (951 mg, 3.21 mmol) and O-allyl-N-(9-anthracenylmethyl)cinchonidinium bromide (95%, 0.205 g, 0.322 mmol) in dichloromethane (25 mL) was added cesium hydroxide monohydrate (0.647 g, 3.85 mmol). (See E. J. Corey et al., J. Am. Chem. Soc. 1997, 119, 12414-12415.) The reaction was stirred at −30° C. for 18 hours, then washed with water, dried over magnesium sulfate, filtered and concentrated under reduced pressure. The residue was purified by chromatography on silica gel (Eluants: dichloromethane, then EtOAc) to give C5 as a gum. Yield: 1.63 g, 3.19 mmol, 99%. LCMS m/z 511.3 (M+1). 1H NMR (400 MHz, CDCl3) δ 1.39 (s, 9H), 3.24 (dd, half of ABX pattern, J=14.3, 8.2 Hz, 1H), 3.38 (br dd, half of ABX pattern, J=14.3, 4.6 Hz, 1H), 4.22 (dd, J=8.3, 4.6 Hz, 1H), 5.25 (AB quartet, JAB=14.6 Hz, ΔνAB=18.3 Hz, 2H), 6.72 (br d, J=7 Hz, 2H), 7.16-7.22 (m, 4H), 7.25-7.44 (m, 8H), 7.50-7.54 (m, 2H).

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