Reaction Steps
To a stirred solution of 4-bromomandelic acid (832 mg, 3.6 mmol), 2-phenylpyrrolidine (530 mg, 3.6 mmol), BOP reagent (benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphonate, 1.53 g, 3.6 mmol) in 25 mL of anhydrous acetonitrile was added triethylamine (1.06 mL, 7.2 mmol) at room temperature under an argon atmosphere. The reaction mixture was stirred at room temperature for 4 h, concentrated under reduced pressure, then dissolved in methylene chloride (50 mL). The methylene chloride solution was washed with 1N HCl solution, water, saturated sodium bicarbonate solution, water, brine, and dried over anhydrous MgSO4, concentrated under reduced pressure to afford a syrup in a flask. PPA (polyphosphoric acid, 10 g) was added to the flask. The reaction mixture was heated on a rotavap in boiling water bath for 1 h, cooled to room temperature, solublized in ice water, extracted with methylene chloride (4×15 mL). The methylene chloride extract was washed with saturated sodium bicarbonate solution, water, brine, and dried over anhydrous MgSO4, concentrated under reduced pressure to afford a crude product mixture. Flash chromatography (silica gel, 0.5% MeOH, 0.01% Et3N in methylene chloride) to afford 860 mg of 4 (70% yield for two steps) as a mixture of trans and cis isomers with trans to cis ratio 2:1 (estimated by 1H NMR integration). Recrystallization with THF isolated trans isomer as a yellow solid, mp 204-206° C. 1H NMR (CDCl3) δ 1.96-2.22 (m, 3H, C2H2 & C1H), 2.66-2.78 (m, 1H, C1H), 3.48-3.58 (m, 1H, C3H), 3.732 (dd, 1H, J=7.5, 11.7 Hz, C3H), 4.610 (s, 1H, C6H), 4.64-4.70 (m, 1H, C10bH), 6.591 (d, 1H, J=7.8 Hz, aryl), 7.104 (d, 2H, J=8.1 Hz, C6 phenyl aryl), 7.12-7.28 (m, 3H, 8, 9, aryl), 7.520 (d, 2H, J=8.4 Hz, C6 phenyl aryl); 13C NMR (CDCl3) δ 23.06 (C2), 31.21 (C1), 45.07 (C3), 52.99 (C10b), 58.62 (C6), 121.10 (C4'), 123.58 (aromatic), 126.74 (aromatic), 127.38 (aromatic), 131.38 (aromatic), 132.60 (aromatic), 136.15 (aromatic), 136.55 (aromatic), 136.79 (aromatic), 167.36 (C5). HRMS calculated 341.0415 (for C18H16NOBr), measured 341.0427 (relative error 3.4 ppm).
