Ammonium Chloride → 2-(Benzhydrylidene-amino)-3-(1-fluoro-cyclopentyl)-propionic acid ethyl ester

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To a solution of N-(diphenylmethylene)glycine ethyl ester (1.94 g, 7.26 mmol) in N,N-dimethylformamide (10 mL) at 0° C. was added solid potassium t-butoxide (0.89 g, 7.93 mmol) over 10 min and the resulting solution stirred for an additional 15 min. A trifluoro-methanesulfonic acid 1-fluoro-cyclopentylmethyl ester (2 g, 7.99 mmol) solution in N,N-dimethylformamide (2 mL) was added and the resulting mixture allowed to warm to room temperature over 2 h. The resulting mixture was poured into saturated ammonium chloride and extracted with dichloromethane (200 mL). The organic phase was separated, washed with saturated sodium chloride solution and dried over magnesium sulfate. The mixture was filtered and evaporated and the residue purified by AnaLogix flash chromatography (AnaLogix SuperFlash Flash Column 120 g, 10% to 20% ethyl acetate/hexanes) which afforded 2-(benzhydrylidene-amino)-3-(1-fluoro-cyclopentyl)-propionic acid ethyl ester (1.36 g, 58%) as a yellow oil: 1H NMR (300 MHz, CDCl3) δ ppm 1.26 (t, J=7.1 Hz, 3H), 1.39-1.97 (m, 8H), 2.11-2.41 (m, 1H), 2.45-2.76 (m, 1H), 4.01-4.27 (m, 2H), 4.37 (dd, J=7.5, 4.5 Hz, 1H), 7.16-7.25 (m, 2H), 7.29-7.41 (m, 3H), 7.41-7.56 (m, 3H), 7.64 (d, J=7.8 Hz, 2H).

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