Reaction Steps
To a solution of Compound 20b (18.6 mg, 6.50×10−2 mmol), DCC (13.4 mg, 6.50×1031 2 mmol), and DMAP (15.8 mg, 0.13 mmol) in dry CH2Cl2 (4 mL) cooled in an ice-water bath was added 2,5-dimethoxybenzoic acid (17.8 mg, 9.76×10−2 mmol) followed by stirring at room temperature for 24 hours. The reaction mixture was filtered through a short plug of Celite with rinsing by EtOAc. The filtrate was concentrated under reduced pressure and the residue was purified by flash column chromatography (silica gel, 20 percent EtOAc in hexane) to give 21.7 mg (74 percent) of Compound 40: pale yellow oil; Rf32 0.33 (20 percent EtOAc in hexane); IR (neat) 2958, 2235, 1721, 1640, 1189, 1064 cm−1; 1H NMR (300 MHz, CDCl3) δ8.32 (d, J=7.26 Hz, 1H), 8.08-8.04 (m, 1H), 7.88-7.78 (m, 2H), 7.60 (s, 1H), 7.54-7.42 (m, 4H), 7.03 (dd, J=9.03 and 3.39 Hz, 1H), 6.92 (d, J=9.03 Hz, 1H), 6.45 (s, 1 H), 3.84 (s, 3H), 3.80 (s, 3H), 2.46-2.25 (m, 4H), 1.95-1.70 (m, 4H); 13C NMR (75 MHz, CDCl3) δ169.9, 154.5, 153.7, 134.2, 133.3, 132.2, 129.5, 129.2, 127.0, 126.9, 126.4, 126.0, 124.3, 123.7, 120.3, 117.1, 114.6, 103.1, 93.5, 81.0, 79.5, 69.6, 57.6, 56.6, 28.3, 28.1, 22.6, 21.5; MS (+CI) m/z (relative intensity) 451 (M+, 3), 164 (100).
