Reaction Steps
Under an argon atmosphere, to a mixture of 5-[4-(tert-butyldimethylsilyloxy)phenyl]-3-(naphthalen-1-yl)pyrazin-2-amine (7d) (500 mg, 1.17 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) at 0° C. and the mixture was heated with stirring at 50° C. for 16 hours. After cooling to room temperature, to this was added water and the product was extracted with ethyl acetate (200 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 11d (442 mg, 653 μmol, 55.9%) as a yellow foamy solid. Rf=0.26 (n-hexane/diethyl ether=2/3); 1H NMR (400 MHz, DMSO-d6) δ 0.13 (s, 6H), 0.19 (s, 6H), 0.91 (s, 9H), 0.92 (s, 9H), 3.24 (s, 2H), 6.54-6.60 (AA′BB′, 2H), 6.65-6.72 (AA′BB′, 2H), 6.91-6.98 (AA′BB′, 2H), 7.36-7.54 (m, 4H), 7.61-7.69 (m, 1H), 7.87-8.08 (m, 4H, includes AA′BB′), 9.09 (s, 1H), 10.27 (s, 1H); 13C NMR (75.5 MHz, DMSO-d6) δ −4.6 (4C), 17.90, 17.94, 25.48 (3C), 25.55 (3C), 119.4 (2C), 120.4 (2C), 125.0, 125.4, 125.7, 126.2, 126.8, 128.0, 128.15, 128.21 (2C), 128.6, 128.9 (2C), 129.9, 130.7, 133.4, 134.8, 138.2, 144.4, 147.9, 148.3, 153.5, 156.7, 169.3 (one carbon at the benzyl position was unobservable due to overlapping with the septet peak of DMSO); IR (KBr, cm−1) 492, 538, 675, 718, 779, 806, 839, 914, 1007, 1080, 1115, 1169, 1260, 1362, 1420, 1441, 1472, 1510, 1605, 1670, 2857, 2886, 2930, 2955, 3046, 3223; HRMS (ESI+) m/z 698.3205 ([M+Na]+, C40H49N3NaO3Si2+ requires 698.3205).
