Reaction Steps
A mixture of (S)-6-(2-hydroxy-2-methylpropyl)-3-((S)-1-(4-(2-oxo-1,2-dihydropyridin-4-yl)phenyl)ethyl)-6-phenyl-1,3-oxazinan-2-one (1.683 g, 3.77 mmol, 1.0 equiv), Cu(OAc)2 (0.692 g, 3.81 mmol, 1.01 equiv), bipyridine (0.599 g, 3.83 mmol, 1.02 equiv), cyclopropylboronic acid (0.681 g, 7.93 mmol, 2.10 equiv) and Na2CO3 (0.890 g, 8.40 mmol, 2.23 equiv) in dichloroethane (40 mL) was stirred at 70° C. for 22 h under air. The reaction mixture was quenched with satd aq NH4Cl, diluted with CH2Cl2, dried over Na2SO4. After the solvent was removed under reduced pressure, the residue was purified by chromatography on silica gel eluted with MeOH/CH2Cl2 to afford 1.560 g (85%) of (S)-3-((S)-1-(4-(1-cyclopropyl-2-oxo-1,2-dihydropyridin-4-yl)phenyl)ethyl)-6-(2-hydroxy-2-methylpropyl)-6-phenyl-1,3-oxazinan-2-one. LC-MS tR=1.41 min in 3 min chromatography, m/z 429, 487 (MH+); 1H NMR (400 MHz, CD3OD) δ 7.52 (d, J=7.0 Hz, 1H), 7.29-7.18 (m, 7H), 6.92 (d, J=8.2 Hz, 2H), 6.54 (d, J=1.8 Hz, 1H), 6.47 (dd, J=7.3, 1.8 Hz, 1H), 5.47 (q, J=7.0 Hz, 1H), 3.27-3.21 (m, 1H), 2.95-2.91 (m, 1H), 2.48-2.33 (m, 2H), 2.15-2.08 (m, 1H), 2.07 (s, 2H), 1.42 (d, J=7.0 Hz, 3H), 1.20 (s, 3H), 1.05-1.00 (m, 2H), 0.87 (s, 3H), 0.83-0.79 (m, 2H); 13C NMR (100 MHz, CD3OD) δ 166.17, 155.63, 152.88, 144.03, 142.27, 138.90, 136.91, 129.71, 128.70, 128.58, 127.67, 126.09, 116.08, 107.10, 85.19, 71.49, 55.13, 54.62, 37.44, 33.24, 32.71, 31.86, 30.03, 15.60, 7.27. (S)-3-((S)-1-(4-(1-cyclopropyl-2-oxo-1,2-dihydropyridin-4-yl)phenyl)ethyl)-6-(2-hydroxy-2-methylpropyl)-6-phenyl-1,3-oxazinan-2-one (ca. 1.5 g) and isopropyl acetate (30 mL) was heated in a 120° C. oil bath, affording a homogeneous solution. Heating was discontinued and the resulting solution was slowly stirred while slowly cooling to rt in the oil bath overnight. The solids were filtered and washed with isopropyl acetate, dried at room temperature under high vacuum affording crystalline solid Mp 91-94° C.
