Reaction Steps
To a mixture of phosphonium salt 6 (4.7 g, 6.5 mmol) and tetrahydrofuran (25 ml, cooled to −78° C.) was added n-BuLi (2.6 mL, 2.5 M, 6.5 mmol, over 5 minutes), followed by stirring for one hour. Next, 3-fluoro-4,5-dimethoxybenzaldehyde (1g, 5.4 mmol) in tetrahydrofuran (10 ml) was added (dropwise) over 30 minutes. The mixture was allowed to warm to room temperature, and stirring continued for 16 hours. The reaction was terminated by the addition of water (50 mL), the product was extracted with ethyl acetate, solvents were removed in vacuo, and the residue (1:1 E/Z, 75% yield) obtained was subjected to flash chromatography on silica gel using hexane-ethyl acetate (9:1) as eluent to afford Z-stilbene 7a (1 g, 34%) as a clear oil; 1H-NMR (300 MHz, CDCl3) δ 1.07 (s, 9H), 3.46 (s, 3H), 3.65 (s, 3H), 3.90 (s, 3H), 6.24 (d, 1H, J=12 Hz), 6.33 (d, 1H, J=12 Hz), 6.56 (m, 2H), 6.72 (m, 3H), 7.35 (m, 6H), 7.70 (m, 4H); and 12C NMR (75 MHz, CDCl3) δ 19.75, 26.65, 55.07, 55.99, 61.43, 108.26, 108.28, 109.40, 109.55, 111.74, 120.83, 122.42, 127.36, 127.46, 127.48, 127.70, 129.37, 129.50, 129.63, 130.32, 132.59, 132.66, 133.57, 134.77, 135.27, 135.83, 135.95, 144.74, 149.88, 152.91, 152.95, 154.59, 156.53; HRMS (calcd for C33H36FO4Si) [M+H]+ 543.2368, found 543.2372.
