[CH2:1]([O:3][C:4]([C:6]1[N:11]=[C:10]([C:12]2[CH2:13][CH2:14][N:15]([C:18]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])=[O:19])[CH2:16][CH:17]=2)[CH:9]=[CH:8][CH:7]=1)=[O:5])[CH3:2]>C(O)C.[Pd]>[CH2:1]([O:3][C:4]([C:6]1[N:11]=[C:10]([CH:12]2[CH2:13][CH2:14][N:15]([C:18]([O:20][C:21]([CH3:22])([CH3:24])[CH3:23])=[O:19])[CH2:16][CH2:17]2)[CH:9]=[CH:8][CH:7]=1)=[O:5])[CH3:2]A solution of 3′,6′-dihydro-2′H-[2,4′]bipyridinyl-6,1′-dicarboxylic acid 1′-tert-butyl ester 6-ethyl ester (1.12 g, 3.37 mmol) in ethanol (67 mL) was pumped through Pd/C cartridge using H-Cube apparatus (20° C., 10 bar, 2 mL/min.). The solvent was then evaporated under reduce pressure to give 3′,4′,5′,6′-tetrahydro-2′H-[2,4′]bipyridinyl-6,1′-dicarboxylic acid 1′-tert-butyl ester 6-ethyl ester (1.001 g, 89%), which can be used in the next step without further purification. 1H-NMR (400 MHz, d6-DMSO): δ=1.31-1.38 (t, 3H), 1.47 (s, 9H), 1.55-1.65 (m, 2H), 1.79-1.88 (m, 2H), 2.91-2.99 (m, 2H), 3.42-3.48 (m, 1H), 4.05-4.12 (m, 2H), 4.31-4.37 (q, 2H), 7.55 (d, 1H), 7.84-7.92 (m, 2H). MS: m/z=333 (M+1. MS: m/z=335 (M+1).
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