Reaction Steps
n-Butyllithium (10.2 mL, 1.6 M solution in hexanes, 16.5 mmol) was injected into a solution of (3R)-3-isopropyl-2,5-diethoxy-3,6-dihydropyrazine (3.5 g, 16.5 mmol) in THF (70 mL) at −78° C. After 30 min of further stirring, 4-allyldimethylsilylbenzyl bromide (1 Scheme 2, 4.4 g, 16.5 mmol) in dry THF (30 mL) was added to the reaction mixture over a period of 1 h. After 1 h, saturated NH4Cl (1 mL) was added and the reaction mixture was allowed to warm to room temperature. The reaction mixture was concentrated, diluted with ethyl acetate (100 mL), and extracted with brine (20 mL×2). The organic layer was concentrated and the residue was purified by column chromatography (1:25 ethyl acetate/hexanes) to afford a colorless oil (4.7 g, 71%); 1H NMR (300 MHz, CDCl3) δ 0.28 (s; 6 H), 0.65 (d, J=6.75 Hz, 3 H), 0.96 (d, J=6.75 Hz, 3 H), 1.29 (t, J=7.05 Hz, 3 H), 1.35 (t) J=7.09 Hz, 3 H), 1.74 (d, J=8.05 Hz, 2 H), 2.19 (quintet of d, J=6.87, 3.21 Hz, 1 H), 3.10 (d, J=4.92 Hz, 2 H), 3.28 (m, 1 H), 4.07-4.24 (4 H), 4.31 (app q, J=4.50 Hz, 1 H), 4.83 (s, 1 H), 4.87 (m, 1 H), 5.77 (ddt, J=15.87, 11.13, 8.08 Hz, 1 H), 7.14 (d, J=7.98 Hz, 2 H), 7.38 (d, J=7.98 Hz, 2 H); 13C NMR (75 MHz, CDCl3) −3.4 −3.3, 14.5, 16.6, 19.1, 23.9, 31.3, 40.2, 56.7, 60.2, 60.4, 60.5, 113.3, 129.5 (2C), 133.2 (2C), 134.7, 135.9, 138.5, 162.2, 163.5; HRMS calcd for C23H36N2O2Si 400.2546, found 400.2543.
