[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][C:11]([C:17]2[CH:22]=[CH:21][N:20]=[C:19]([Cl:23])[CH:18]=2)(C(O)=O)[CH2:10][CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2]>C1(C)C=CC=CC=1>[Cl:23][C:19]1[CH:18]=[C:17]([CH:11]2[CH2:12][CH2:13][N:8]([C:6]([O:5][C:1]([CH3:4])([CH3:3])[CH3:2])=[O:7])[CH2:9][CH2:10]2)[CH:22]=[CH:21][N:20]=1The pure compound 1-(tert-butoxycarbonyl)-4-(2-chloropyridin-4-yl)piperidine-4-carboxylic acid (42 g, 0.12 mols, 1 equiv.) from Step B was dissolved in toluene (250 mL) and heated at 110° for 4 hours. The reaction was monitored by TLC (ethyl acetate/petroleum ether; 1/5). Once complete, the mixture was concentrated and purified by flash chromatography using silica gel (ethyl acetate/petroleum ether; 1/20) to give tert-butyl 4-(2-chloropyridin-4-yl)piperidine-1-carboxylate (31 g, 87%)
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