Thionyl chloride (10 mL) was added slowly to a suspension of cis 10 (0.75 g, 1.8 mmol) and trans 10 (1.35 g, 3.3 mmol) in methanol (100 mL) at 0° C. The resulting mixture was stirred for 6 h at 0° C. After completion of the reaction (TLC), the reaction mixture was poured slowly into a mixture of ice (200 g) and a saturated solution of sodium bicarbonate (100 mL). The resulting mixture was extracted with chloroform (3×150 mL), and the combined extracts were dried with sodium sulfate, filtered though a thin pad of silica gel, and evaporated to dryness to obtain 11 as amorphous glassy solid (2.1 g, 96%). IR (film) 1733, 1637 cm−1; 1H NMR (500 MHz, CDCl3) δ 7.67 (s, 1 H), 7.52 (d, J=7.7 Hz, 1 H), 7.25 (t, J=7.0 Hz, 1 H), 7.03 (t, J=7.5 Hz, 1 H), 6.83 (d, J=7.8 Hz, 1 H), 6.73 (s, 1 H), 6.54 (s, 1 H), 5.45 (s, 1 H), 3.95 (s, 3 H), 3.89 (s, 1 H), 3.82 (s, 3 H), 3.72 (s, 3 H), 3.63 (s, 1 H), 3.03 (s, 3 H); 13C NMR (126 MHz, CDCl3) δ 172.06, 164.17, 155.49, 152.15, 149.18, 134.39, 132.53, 129.10, 126.67, 126.53, 125.93, 125.14, 121.60, 111.86, 110.17, 59.32, 56.29, 56.20, 53.27, 53.06, 48.66, 34.57; ESIMS m/z (rel intensity) 429 (MH+, 100), 451 (56); ESIHRMS m/z MH+ calcd. for C22H24N2O7, 429,1662; found, 429.1665.
