(c) Synthesis of tert-butyl 4-hydroxyazepane-1-carboxylate: Ammonium formate (900 mg) and 10% palladium/carbon catalyst (200 mg) were added to an ethanol solution (10 mL) of 1-benzyl-4-azepane (450 mg, 2.19 mmol), and the reaction mixture was heated and refluxed for 1 hour. Upon completion of the reaction, the mixture was filtered through a diatomaceous earth pad and the filtrate was concentrated. The resulting residue was dissolved in dichloromethane (10 mL) and di-tert-butyl dicarbonate (0.504 mL, 2.19 mmol) was added at room temperature with continuous stirring for 19 hours. At the end of the reaction, saturated aqueous sodium bicarbonate solution was added to the mixture, followed by water and extraction with chloroform. The organic layers were combined, dried with anhydrous magnesium sulfate and the solvent was removed by distillation under reduced pressure. The resulting crude product was purified by silica gel column chromatography (eluent: hexane/ethyl acetate=2/1) to afford the target compound tert-butyl 4-hydroxyazepane-1-carboxylate (333 mg, 70% yield).
