[F:1][C:2]1[CH:9]=[CH:8][C:5]([CH:6]=O)=[CH:4][C:3]=1[N+:10]([O-:12])=[O:11].C(O)(=O)C.[NH:17]1[CH2:22][CH2:21][CH2:20][CH2:19][CH2:18]1.C(O[BH-](OC(=O)C)OC(=O)C)(=O)C.[Na+].Cl>C(Cl)Cl>[F:1][C:2]1[CH:9]=[CH:8][C:5]([CH2:6][N:17]2[CH2:22][CH2:21][CH2:20][CH2:19][CH2:18]2)=[CH:4][C:3]=1[N+:10]([O-:12])=[O:11]4-Fluoro-3-nitro-benzaldehyde (3.39 g, 0.0200 mol) was dissolved in methylene chloride (100 mL) and acetic acid (3.50 mL, 0.0616 mol) and the mixture was cooled to −10° C. Piperidine (2.4 mL, 0.024 mol) was then added to the cooled mixture over 10 minutes. Sodium triacetoxyborohydride (17.0 g, 0.0802 mol) was added in one portion. After stirring at 0° C. for 18 hours, the reaction was poured into a mixture of 1N aqueous HCl and ice. The organic phase was removed, and the aqueous layer was made basic by the addition of NaOH pellets. The aqueous layer was extracted twice with methylene chloride, dried over magnesium sulfate, filtered and concentrated. The residue was taken up in methylene chloride and purified by silica gel chromatography (ethyl acetate/hexanes as eluent) followed by further purification by preparative HPLC to yield 2.69 g of 1-(4-fluoro-3-nitro-benzyl)-piperidine as a TFA salt.
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