Dichloromethane → (3S)-3-amino-1-hydroxy-5-methoxy-3,4-dihydroquinolin-2(1H)-one, hydrochloride salt

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tert-Butyl N-(diphenylmethylene)-2-methoxy-6-nitro-L-phenylalaninate (58) To a solution of tert-butyl N-(diphenylmethylene)glycinate (56) (1.2 g, 4.2 mmol), 2-(bromomethyl)-1-methoxy-3-nitrobenzene (57) (0.86 g, 3.3 mmol) and O-allyl-N-(9-anthracenylmethyl)cinchonidinium bromide (0.21 g, 0.33 mmol) in DCM (10 mL) cooled at −30° C., was added CsOH (0.84 g, 5.0 mmol). (See E. J. Corey et al., Journal of the American Chemical Society 1997, 119, 12414-12415.) The reaction was stirred at −30° C. overnight. The mixture was warmed to 0° C., quenched with saturated aqueous ammonium chloride solution (5 mL) and diluted with DCM (5 mL). The aqueous layer was extracted with DCM (3×5 mL), and the combined organic layers were washed with water, dried over Na2SO4, filtered and concentrated under reduced pressure. The residue was purified by chromatography on silica gel (Gradient: 0% to 20% EtOAc in heptane) to give the title compound as a yellow solid (1.32 g, 87%). APCI m/z 461.2 (M+1). 1H NMR (400 MHz, CDCl3) δ 1.41 (s, 9H), 3.49 (dd, J=13.5, 4.3 Hz, 1H), 3.55 (s, 3H), 3.63 (dd, J=13.6, 9.6 Hz, 1H), 4.29 (dd, J=9.6, 4.3 Hz, 1H), 6.64 (br d, J=6.4 Hz, 2H), 6.88 (m, 1H), 7.20-7.34 (m, 8H), 7.51-7.54 (m, 2H).

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