Reaction Steps
Under an argon atmosphere, to a suspension of methyltriphenylphosphonium bromide (1.29 g, 3.61 mmol) in anhydrous THF (5 mL) was gradually dropwise added n-butyl lithium (1.65 M in n-hexane) (1.70 mL, 2.81 mmol) at 0° C. The mixture was stirred at 0° C. for 15 minutes as it was. To the mixture was added 2-(5-amino-6-benzyl-3-vinylpyrazin-2-yl)-5-methoxybenzaldehyde (8) (871 mg, 2.52 mmol) at 0° C. After elevating to room temperature, stirring was continued for 1.5 hours. After to this was added water, the product was extracted with ethyl acetate (×3). The combined organic extract was washed successively with water (×1) and brine (×1), followed by drying over anhydrous sodium sulfate. After filtration and concentration under reduced pressure, the residue was purified by silica gel flash column chromatography (n-hexane/ethyl acetate=3/1) to give 2-amino-3-benzyl-5-(4-methoxy-2-vinylphenyl)-6-vinylpyrazine (9) (570 mg, 1.66 mmol, 65.8%) as a white solid. TLC Rf=0.37 (n-hexane/ethyl acetate=3/1); 1H NMR (500 MHz, CDCl3) δ 3.88 (s, 3H), 4.16 (s, 2H), 4.39 (s, 2H), 5.18 (dd, 1H, J=1.0, 10.5 Hz), 5.30 (dd, 1H, J=2.0, 10.5 Hz), 5.67 (dd, 1H, J=1.0, 17.5 Hz), 6.25 (dd, 1H, J=2.0, 17.5 Hz), 6.47 (dd, 1H, J=10.5, 17.5 Hz), 6.50 (dd, 1H, J=10.5, 17.5 Hz), 6.90 (dd, 1H, J=2.5, 8.0 Hz), 7.20-7.26 (m, 5H), 7.29-7.35 (m, 2H); 13C MR. (126 MHz, CDCl3) δ 41.2, 55.6, 110.5, 113.8, 115.4, 119.3, 127.2, 128.7 (2C), 129.2 (2C), 129.8, 132.1, 133.0, 135.1, 137.0, 138.3, 140.3, 141.9, 144.8, 151.4, 159.8.
