To a solution of 92 (166 g, 0.3 mol) in Ac2O (1 L) and AcOH (100 mL) was added anhydrous ZnCl2 (353 g, 2.6 mol) at 0° C. After kept additional 2 hours at room temperature, the reaction was poured into ice-cold H2O (1.5 kg) slowly and extracted with dichloromethane (3×500 mL). The organic layers combined, washed with brine (3×200 mL) and dried over anhydrous sodium sulfate. After filtration, volatiles were distilled out by high vacuum to give crude 93 (160 g, (ES, m/z) [M+H]+ 471.0) as a brown oil. A solution of the above crude 93 in methanol (1 L) was treated with K2CO3 (18 g, 0.13 mol) at 30° C. for 8 hours, after filtration, the solvent was distilled out under vacuum to give a residue, which was purified by a silica gel column with 20%-30% ethyl acetate in petroleum ether to afford the title compound (94) (108 g, 79% 2 steps) as a yellow syrup; (ES, m/z) [M+H]+ 429.0; 1H NMR (300 MHz, CDCl3) δ 7.26-7.43 (m, 10H), 6.29 (d, J=6.6 Hz, 1H), 4.54-4.81 (m, 4H), 4.41 (d, J=4.8 Hz, 1H), 4.17-4.18 (m, 1H), 3.57-3.79 (m, 4H), 3.02 (s, 6H).
