2-(4-Nitrophenyl)propionic acid → (R)-2-(4-Nitrophenyl)propanoic acid

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A 2 liter three necked flask equipped with a mechanical stirrer is charged with racemic 2-(4-nitrophenyl)propionic acid (40.55 grams, 0.208 mol) and ethyl acetate (1600.0 mL). To this solution at 30° C. was then added S(−)-α-methylbenzylamine (13.49 mL, 0.104 mol) all at once. Reaction exothermed to 38° C. with massive formation of a white precipitate in less than 15.0 minutes. The reaction mixture was then heated at ethyl acetate reflux for 10.0 minutes and allowed to equilibrate to room temperature with stirring overnight. The precipitate was then filtered to give a semi-dried white product, (2R)-2-(4-nitrophenyl)propanoic acid, S(−)-α-methylbenzylamine (wet cake=25.43 grams). Reslurried the wet cake in ethyl acetate (1600.0 mL) at reflux for 10.0 minutes, stirred to room temperature overnight, and filtered the white precipitate, (2R)-2-(4-nitrophenyl)propanoic acid, S(−)-α-methylbenzylamine, (wet cake=21.02 grams, ee=91.4%). Repeated the later again and dried the precipitate at 40° C. in a vacuum oven for 24.0 hours, (2R)-2-(4-nitrophenyl)propanoic acid, S(−)-α-methylbenzylamine, (18.02 g, 55%, ee=95%); 1H nmr (DMSO, 300 MHz) δ 1.31-1.32 (d, 3H), 1.37-1.38 (d, 3H), 3.56-3.60 (m, 1H), 4.18-4.20 (m, 1H), 7.27-7.53 (aromatic, 7H), 8.09-8.12 (aromatic, 2H);

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