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0 °C

To a solution of diisopropylamine (77 mL, 0.54 mol) in anhydrous THF (500 mL) was added n-butyl lithium (210 mL, 0.53 mol, 2.5 M solution in hexane) over 20 min at −78° C. Then the mixture was stirred at 0° C. under nitrogen for 30 min. To a mixture of dimethyl 1-(2-chloroethyl)cyclohexane-1,4-dicarboxylate (116 g, 0.44 mol) and hexamethylphosphoramide (317 ml, 1.7 mol) in anhydrous THF (800 mL) was added lithium diisopropylamine (freshly prepared above) over 30 min at −40° C. The mixture was stirred for 2 h at −78° C. and then stirred overnight allowing warming to room temperature. To the reaction mixture was added saturated aqueous ammonium chloride (200 mL) and the mixture was stirred for 10 min. The solvent was removed by evaporation under reduced pressure. The aqueous layer was extracted with ethyl acetate (3×200 mL). The combined extracts were washed with brine (2×300 mL) and dried over sodium sulfate. Concentration under reduced pressure gave crude product, which was purified by silica gel column chromatography (10% ethyl acetate in petroleum ether) to afford the title compound (58 g, 0.25 mol, 50% yield in two steps). 1H NMR (400 MHz, CDCl3) δ ppm 3.65 (s, 6H), 1.81 (s, 12H).

1. customfreshly prepared above) over 30 min at −40° C
2. stirringThe mixture was stirred for 2 h at −78° C.
3. stirringstirred overnight
4. temperatureallowing warming to room temperature
5. stirringthe mixture was stirred for 10 min
6. customThe solvent was removed by evaporation under reduced pressure
7. extractionThe aqueous layer was extracted with ethyl acetate (3×200 mL)
8. washThe combined extracts were washed with brine (2×300 mL)
9. dry with materialdried over sodium sulfate
10. concentrationConcentration under reduced pressure
11. customgave crude product, which
12. customwas purified by silica gel column chromatography (10% ethyl acetate in petroleum ether)