Ethyl chloroformate → 1-tert-Butyl 4-ethyl 4-cyanopiperidine-1,4-dicarboxylate

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A solution of LDA (107 ml, 214.01 mmol) was added to a stirred solution of tert-butyl 4-cyanopiperidine-1-carboxylate (30 g, 143 mmol) in THF (250 ml) at −78° C., under nitrogen. The resulting solution was stirred at −78° C. for 30 minutes. Ethyl chloroformate (16.37 ml, 171.2 mmol) was added. The resulting solution was stirred and allowed to warm to room temperature. The reaction mixture was quenched with saturated NaHCO3 (250 ml), extracted with DCM, and the organic layer was washed with saturated brine (100 ml) then dried over MgSO4, filtered and evaporated to afford the crude material as a orange oil. This material was purified by flash silica chromatography, elution gradient 10% EtOAc in isohexane. Pure fractions were evaporated to dryness to afford 1-tert-butyl 4-ethyl 4-cyanopiperidine-1,4-dicarboxylate (20.8 g, 51.6%) as a yellow oil.

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