Methanol → 1-(4-Methoxybenzyl)piperidine-4-carboxaldehyde

A 1.5 M solution of diisobutylaluminium hydride in toluene (3.12 ml, 4.68 mmol) was added dropwise to a solution of methyl 1-(4-methoxybenzyl)piperidine-4-carboxylate (1.23 g, 4.68 mmol) in toluene (30 ml) under argon at −78° C. in the course of 30 min and the mixture was then stirred at this temperature for 30 min. Thereafter, methanol (15 ml) was added dropwise such that the internal temperature remained at −78° C., before the mixture was then slowly warmed to room temperature. Saturated sodium chloride solution (20 ml) was added to the reaction mixture and the suspension was filtered through sea sand. The organic phase was dried with sodium sulfate and concentrated i. vac. The residue was purified by flash chromatography with cyclohexane/ethyl acetate (1:3).