To a solution of carboxylic acid 16 (207 mg, 0.753 mmol) in anhydrous THF (10 mL) was added 1,1′-carbonyldiimidazole (128 mg, 0.790 mmol) at rt, and the mixture was stirred overnight. To the resulting solution was added 1,2-phenylenediamine (570 mg, 5.27 mmol), followed by trifluoroacetic acid (52 μl ), and the reaction mixture was stirred for 16 h at rt. The reaction mixture was diluted with ethyl acetate (30 mL), washed with saturated NaHCO3 solution (5 mL) and then water (10 mL), dried (MgSO4), and concentrated. Purification by flash silica gel chromatography (50% ethyl acetate in toluene) afforded the title compound 20 (115 mg, 42% yield): 1H NMR (300 MHz, CDCl3) δ 7.44 (br. s, 1H), 7.01-7.29 (m, 5H), 6.70-6.78 (m, 4H), 6.09 (m, 2H), 5.90 (d, J=15.0 Hz, 1H), 4.10 (br. t, J=6.6 Hz, 1H), 3.89 (br. s, 2H), 3.18 (s, 3H), 2.95 (s, 3H), 2.66 (m, 1H), 2.50 (m, 1H); 13C NMR (75.4 MHz, CDCl3) δ 40.5, 41.6, 82.8, 112.3, 118.1, 119.4, 121.7, 124.4, 125.1, 127.0, 127.6, 128.6, 130.0, 140.0, 140.8, 142.5, 150.2, 164.7.
