[CH2:1]([O:3][C:4]([CH:6]1[CH2:11][CH2:10][NH:9][CH2:8][CH2:7]1)=[O:5])[CH3:2].[CH3:12][C:13]([CH3:15])=O.C(O)(=O)C.C([BH3-])#N.[Na+]>CO>[CH2:1]([O:3][C:4]([CH:6]1[CH2:11][CH2:10][N:9]([CH:13]([CH3:15])[CH3:12])[CH2:8][CH2:7]1)=[O:5])[CH3:2]To ethylpiperidine-4-carboxylate (1 eq) in methanol was added acetone (1 eq) and acetic acid (5%) and the resulting mixture was stirred for 2 h at ambient temperature. To it was then added sodium cyanoborohydride (1 eq) and continued stirring for 16 h. The mixture was then concentrated and to it was added sodium bicarbonate and was partitioned between ethyl acetate and water. The organic layer was dried with sodium sulfate and concentrated to yield ethyl-1-(methylethyl)piperidine-4-carboxylate. To this was then added concentrated hydrochloric acid and water (2:1) and the mixture was refluxed for 5 h. The resulting 1-(methylethyl)piperidine-4-carboxylic acid was then azeotroped with toluene. MS: MH+=172.
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