[C:1](O[BH-](OC(=O)C)OC(=O)C)(=O)C.[Na+].[N+:15]([C:18]1[CH:25]=[CH:24][C:21]([CH:22]=O)=[CH:20][CH:19]=1)([O-:17])=[O:16].[CH:26]12[CH2:32][CH:29]([CH2:30][CH2:31]1)[CH2:28][C@@H:27]2[NH2:33].C=O.[OH-].[Na+]>C(O)(=O)C.C(Cl)Cl>[CH:26]12[CH2:32][CH:29]([CH2:30][CH2:31]1)[CH2:28][C@@H:27]2[N:33]([CH3:1])[CH2:22][C:21]1[CH:24]=[CH:25][C:18]([N+:15]([O-:17])=[O:16])=[CH:19][CH:20]=1Sodium triacetoxyborohydride (3.5 mmol, 0.75 g) was added to a mixture of 4-nitro-benzaldehyde Compound 4a (2.8 mmol, 0.42 g), (2S)-bicyclo[2.2.1]hept-2-ylamine Compound 15d (3.0 mmol, 0.33 g) and glacial acetic acid (3 drops) in CH2Cl2 (40 mL). The resulting suspension was allowed to stir at room temperature for 12 hrs. An aliquot of the reaction mixture showed the formation of product (MS m/e 247, 100%). An aqueous solution of formaldehyde (37% solution, 9.6 mmol, 0.8 mL) was added to the reaction mixture followed by sodium triacetoxyborohydride (3.5 mmol, 0.75 g) and the mixture was allowed to stir at r.t. for 2 hrs. The reaction mixture was basified with 2N NaOH solution and was extracted with CH2Cl2. The organic layer was washed with brine, separated and dried over Na2SO4. The drying agent was filtered and the solvent was removed in vacuo to obtain (2S)-bicyclo[2.2.1]hept-2-yl-methyl-(4-nitro-benzyl)-amine Compound 15e (0.72 g, 98%) as an orange oil. MS m/e 261 (M+H, 100%), which was used in the next step without further purification.
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