Reaction Steps
Under an argon atmosphere, to a mixture of (E)-5-[4-(tert-butyldimethylsilyloxy)phenyl]-3-styrylpyrazin-2-amine (7b) (500 mg, 1.24 mmol) and 4-(dimethylamino)pyridine (15.3 mg, 125 μmol) dissolved in anhydrous pyridine (20 mL) was added 2-[4-(tert-butyldimethylsilyloxy)phenyl]acetyl chloride (10) prepared above at 0° C. and the mixture was heated with stirring at 50° C. for 15 hours. After cooling to room temperature, to this was added water and the product was extracted with ethyl acetate (100 mL×3). The combined organic extract was washed successively with water (200 mL) and brine (200 mL), followed by drying over anhydrous sodium sulfate. After filtration and concentration under reduced pressure, the residue was purified by column chromatography (silica gel 50 g, n-hexane/ethyl acetate=3/1) to give Compound 11b (563 mg, 864 μmol, 69.7%) as a yellow solid. Rf=0.29 (n-hexane/ethyl acetate=3/1); 1H NMR (400 MHz, DMSO-d6) δ 0.17 (s, 6H), 0.24 (s, 6H), 0.96 (s, 9H), 0.97 (s, 9H), 3.66 (s, 2H), 6.81-6.91 (m, 3H, includes AA′BB′), 6.99-7.04 (AA′BB′, 2H), 7.28-7.40 (m, 7H, includes AA′BB′), 7.82 (d, 1H, J=16 Hz), 8.11-8.19 (AA′BB′, 2H), 8.91 (s, 1H), 10.66 (s, 1H); 13C NMR (75.5 MHz, DMSO-d6) δ −4.5 (2C), −4.6 (2C), 17.8, 17.9, 25.5 (6C), 42.0, 119.7 (2C), 120.3 (2C), 122.5, 127.1 (2C), 128.2 (2C), 128.5, 128.7 (2C), 128.9, 129.0, 130.3 (2C), 133.8, 136.0, 137.8, 142.8, 143.9, 148.0, 154.0, 156.7, 170.6; IR (KBr, cm−1) 471, 521, 638, 691, 746, 781, 806, 839, 914, 968, 1007, 1080, 1103, 1169, 1263, 1325, 1371, 1391, 1414, 1439, 1472, 1510, 1566, 1605, 1659, 2857, 2886, 2930, 2055, 3028, 3057, 3217; HRMS (ESI+) m/z 674.3203 ([M+Na]+, C28H49N3NaO3Si2+ requires 674.3205).
