Lithium bis(trimethylsilyl)amide (1.0 mol/L in tetrahydrofuran; 11.00 mL) is added dropwise to 5-bromo-2-chloro-4-picoline (0.95 g) dissolved in tetrahydrofuran (15 mL) at −40° C. under argon atmosphere. The mixture is stirred for 2 h at −35 to −45° C. prior to addition of piperidine-1,4-dicarboxylic acid 1-tert-butyl ester 4-ethyl ester (1.33 g) dissolved in tetrahydrofuran (15 mL). The reaction mixture is allowed to warm to room temperature over a period of 1 h. Ice-cold water is added and the mixture is extracted with ethyl acetate. The combined extracts are washed with brine, dried (MgSO4), and concentrated. The residue is chromatographed on silica gel (cyclohexane/ethyl acetate 75:25→60:40) to give the title compound. Mass spectrum (ESI+): m/z=417/419/421 (Cl+Br) [M+H]+.
