A mixture of methyl 2-tert-butoxy-2-(4-(4-fluorophenyl)-2-isopropyl-8,8-dimethyl-5,6,7,8-tetrahydro-1,6-naphthyridin-3-yl)acetate (intermediate 5) (20 mg, 0.045 mmol) and 4-fluorobenzaldehyde (0.048 mL, 0.452 mmol) was stirred in CH2Cl2 (1 mL) at 0° C. for 45 min. AcOH (2.59 μl, 0.045 mmol) was added followed by NaBH(OAc)3 (9.58 mg, 0.045 mmol). After stirring at 0° C. for an additional 5 min, the reaction mixture was stirred at room temperature for 22 h. Additional NaBH(OAc)3 (9.58 mg, 0.045 mmol) and AcOH (2.59 μl, 0.045 mmol) were added and the mixture was stirred for an additional 1 h. The mixture was quenched with satd NaHCO3 and the product was extracted with CH2Cl2, dried (Na2SO4), filtered and adsorbed onto silica gel. The product was purified by flash chromatography (Biotage; 0%-50% EtOAc/hexane) to give methyl 2-tert-butoxy-2-(6-(4-fluorobenzyl)-4-(4-fluorophenyl)-2-isopropyl-8,8-dimethyl-5,6,7,8-tetrahydro-1,6-naphthyridin-3-yl)acetate (14.7 mg, 47% yield) as a colorless oil. 1H NMR (500 MHz, CDCl3) δ ppm 7.34 (ddd, J=2.14, 5.72, 8.32 Hz, 1H), 7.24-7.28 (m, 2H), 7.14-7.20 (m, 2H), 7.06-7.14 (m, 1H), 6.99 (t, J=8.70 Hz, 2H), 4.83 (s, 1H), 3.71 (s, 3H), 3.45-3.60 (m, 2H), 3.40 (d, J=13.43 Hz, 1H), 3.23 (d, J=15.26 Hz, 1H), 3.06 (d, J=15.26 Hz, 1H), 2.50 (d, J=10.99 Hz, 1H), 2.34 (d, J=11.29 Hz, 1H), 1.33 (d, J=2.44 Hz, 6H), 1.28 (s, 3H), 1.11 (d, J=6.71 Hz, 3H), 0.98 (s, 9H). 19F NMR (500 MHz, CDCl3) δ ppm −114.17, −116.52. LCMS (M+H) calcd for C33H41F2N2O3: 551.30. found: 551.4. By NMR.
