Reaction Steps
The acid chloride (4-fluoro-3-trifluoromethyl-phenyl)acetyl chloride was prepared by addition of several drops of DMF to an ice-cold solution of 2.06 g (4-fluoro-3-trifluoromethyl-phenyl)acetic acid (9.27 mmol, 1.70 equiv.) and 0.81 mL oxalyl chloride (9.27 mmol, 1.70 equiv.) dissolved in 15 mL dichloromethane. Gas evolution ensued and the reaction was equilibrated to room temperature and stirred for 2 h until gas evolution ceased. This solution was added dropwise over 15 min. to a solution of 2.6 g A2 (5.37 mmol, 1.00 equiv.) and 2.24 mL triethylamine (16.1 mmol, 3.00 equiv.) dissolved in 20 mL dichloromethane cooled by an acetone-dry ice bath. The resulting mixture was stirred at low temperature for 20 min. then poured into saturated aqueous sodium bicarbonate. The organic separation was washed with brine, dried over magnesium sulfate, filtered, and concentrated in vacuo to afford a glassy solid. The product was purified by chromatography on silica gel, eluting with a gradient of 50% ethyl acetate in hexane to 100% ethyl acetate. The chromatographed product was then recrystallized from methyl tert-butyl ether to afford A3 as colorless crystals, m.p.=157-159° C. 1H NMR (400 MHz; CDCl3; T=300 K) {mixture of S-cis:S-trans amide rotamers in ca. 2.3:1 ratio} δ1.20 (t, J=7.6 Hz, 3H), 1.46 (t, J=7.2 Hz, 6.5H), 1.46 (d, J=7.2 Hz, 6.5H), 2.48 (d, J=16 Hz, 1H), 2.92 (ddd, J=2.8, 7.6, 16.0 Hz, 2H), 2.94 (d, J=16 Hz, 1H), 3.13 (ddd, J=3.6, 7.2, 14.8 Hz, 4.6H), 3.22 (dd, J=6.8, 6.8 Hz, 2H), 3.50 (ddd, J=5.2, 10.6, 13.3 Hz, 2.3H), 3.67 (ddd, J=8.0, 8.0, 13.3 Hz, 1H), 3.84 (s, 4.6H), 3.90 (ddd, J=4.8, 10, 14.8 Hz, 2.3H), 4.02 (ddd, J=8.0, 8.0, 13.3 Hz, 1H), 4.06-4.27 (m, 4.6H), 4.42 (qt, J=8 Hz, 6.6H), 5.01 (qt, J=6.8 Hz, 1H), 5.16 (qt, J=7.2 Hz, 2.3H), 7.09-7.19 (m, 10H), 7.21-7.28 (m, 5H), 7.33-7.50 (m, 8.9H), 7.53 (dd, J=4.6, 9.1 Hz, 1H), 7.63-7.68 (m, 2.3H), 8.58 (dd, J=2.0, 8.0 Hz, 2.3H), 8.61 (dd, J=2.0, 8.0 Hz, 1H), 8.96 (dd, J=2.0, 4.4 Hz, 2.3H), 9.06 (dd, J=2.0, 4.8 Hz, 1H) ppm. MS(ESI+) m/z=688.9 [M+H]+. Analytical calculated: 52.33% C, 3.95% H, 19.31% F, 8.14% N. Found: 52.29% C, 3.97% H, 19.40% F, 8.12% N.
