4-Methoxypiperidine-4-carboxylic acid methyl ester hydrochloride (0.50 g, 2.38 mmol) was dissolved in methanol (10 mL) and treated with K2CO3 (0.328 g, 2.38 mmol) in a minimum of water to de-salt. Reaction mixture was concentrated in vacuo and azeotroped to dryness with toluene. The residue and 4-oxoazepane-1-carboxylic acid ethyl ester (0.441 g, 2.38 mmol) were dissolved in methanol (20 mL) at rt and treated with zinc chloride (0.975 g, 7.15 mmol). The reaction mixture was stirred at 50° C. for 2 h. The solution was cooled to room temperature, sodium cyanoborohydride (0.299 g, 4.77 mmol) was added and the reaction mixture was stirred at 50° C. overnight under nitrogen. The solvents were removed in vacuo, and the residue was suspended between DCM and sat. NaHCO3 sol. The turbid mixture, was passed through a pad of celite which was washed with DCM. The organics layers were combined, washed with sat. NaCl sol. and dried by passing through a Biotage Phase Separator cartridge. The solvents were removed in vacuo and the residue was purified by column chromatography (normal phase, [Biotage SNAP cartridge KP-sil 25 g, 40-63 μm, 60 Å, 50 mL per min, gradient 1% to 6% MeOH in DCM]) to give ethyl 4-[4-methoxy-4-(methoxycarbonyl)piperidin-1-yl]azepane-1-carboxylate (0.136 g, 16.4%) as a colourless oil.
