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. The reaction mixture was concentrated in vacuo and azeotroped to dryness with toluene. The residue and 4-oxoazepane-1-carboxylic acid tert-butyl ester (0.745 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 3 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 partitioned between DCM and sat. NaHCO3 sol. The aqueous phase was extracted with DCM (2×20 mL). The organics 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 10% MeOH in DCM]) to give tert-butyl 4-[4-methoxy-4-(methoxycarbonyl)piperidin-1-yl]azepane-1-carboxylate (0.163 g, 15.5%) as a colourless oil.
