General procedure for the synthesis of benzophenone, (S)-2-amino-3-(4-fluorophenyl)propanoic acid and (R)-2-amino-3-(4-fluorophenyl)propanoic acid from 4-fluorophenylpyruvic acid and 2,2-diphenylglycine: To a 5 mL reaction vial fitted with a magnetic stirring bar was added 3-cyclohexyl-2-oxypropanoic acid (1j) (0.0510 g, 0.30 mmol ), 2,2-diphenylglycine (2) (0.0681 g, 0.30 mmol), chiral pyridoxamine 6 g (0.0195 g, 0.030 mmol), and MeOH-H2O (8:2, 3.0 mL). The reaction mixture was stirred at 20 °C for 3 days. Subsequently, the reaction mixture was transferred to a 25 mL round-bottomed flask and MeOH was added until all solids were completely dissolved. Next, silica gel (0.50 g) was added. After removal of the solvent by reduced pressure distillation at 20 °C, the resulting residue was separated by silica gel column chromatography (eluent ratio EtOH/ethyl acetate/25-28% ammonia = 100:58:16) to afford compound 3j (0.0401 g, 78% yield, 52% ee) as a white solid. To determine the enantiomeric excess of 3b-k, the compounds were first converted to N-benzoylmethyl esters by treatment with thionyl chloride in methanol followed by reaction with benzoyl chloride and then analyzed by HPLC. For the determination of the enantiomeric excess of 3a, it was analyzed by HPLC after conversion to methyl ester by treatment with CH2N2 in methanol.
