反应详情

温度

23 °C

To a solution of CBZ-L-tert-leucine (20.53 g, 77.4 mmol, 1 equiv) in THF (150 mL) was added 1,1′-carbonyldiimidazole (13.81 g, 85.14 mmol, 1.1 equiv) at 23° C. The resulting solution was stirred at 23° C. for 1 h. In a separate flask, n-butyllithium (101.59 mL of a 1.6 M solution in hexanes, 162.54 mmol, 2.1 equiv) was added to a solution of diisopropylamine (22.78 mL, 162.54 mmol, 2.1 equiv) in THF (100 mL) at −78° C. The reaction mixture was stirred for 15 min at −78° C., warmed to 0° C. for 5 min, then cooled back to −78° C. A solution of tert-butyl acetate (21.9 mL, 162.54 mmol, 2.1 equiv) in THF (10 mL) was added via cannula, and the resulting mixture was stirred at −78° C. for 10 min. The above imidazole solution was then added dropwise to the lithium enolate at −78° C. The resulting mixture was stirred at −78° C. for 1 h, quenched with 1 M HCl (100 mL), and extracted with EtOAc (2×100 mL). The combined organic layers were washed with brine (150 mL), dried over Na2SO4, and concentrated. The residue was purified by flash chromatography on silica gel (10% EtOAc in hexanes) to afford 4-benzyloxycarbonylamino-5,5-dimethyl-3-oxo-hexanoic acid tert-butyl ester as a pale yellow oil (12.06 g, 44%): IR (cm−1) 1717, 1508, 1265, 739; 1H NMR (CDCl3) δ 1.09 (s, 9H), 1.44 (s, 9H), 3.50 (s, 2H 4.29 (d, 1H, J=9.3), 5.03 (s, 2H), 5.35-5.42 (m, 1H), 7.34 (s, 5H).

1. stirringThe reaction mixture was stirred for 15 min at −78° C.
2. temperaturewarmed to 0° C. for 5 min
3. temperaturecooled back to −78° C
4. stirringthe resulting mixture was stirred at −78° C. for 10 min
5. stirringThe resulting mixture was stirred at −78° C. for 1 h
6. customquenched with 1 M HCl (100 mL)
7. extractionextracted with EtOAc (2×100 mL)
8. washThe combined organic layers were washed with brine (150 mL)
9. dry with materialdried over Na2SO4
10. concentrationconcentrated
11. customThe residue was purified by flash chromatography on silica gel (10% EtOAc in hexanes)