[Cl:1][C:2]1[CH:3]=[C:4]([C:9]2[CH2:14][CH:13]([CH3:15])[N:12]([C:16]([O:18][C:19]([CH3:22])([CH3:21])[CH3:20])=[O:17])[CH2:11][C:10]=2[C:23](OCC)=[O:24])[CH:5]=[CH:6][C:7]=1[Cl:8].ClC1C=C(C2CCN(C(OC(C)(C)C)=O)C(C)C=2C(OCC)=O)C=CC=1Cl.[H-].[Al+3].[Li+].[H-].[H-].[H-]>C1(C)C=CC=CC=1.C1COCC1>[Cl:1][C:2]1[CH:3]=[C:4]([C:9]2[CH2:14][CH:13]([CH3:15])[N:12]([C:16]([O:18][C:19]([CH3:22])([CH3:21])[CH3:20])=[O:17])[CH2:11][C:10]=2[CH2:23][OH:24])[CH:5]=[CH:6][C:7]=1[Cl:8]A mixture of regioisomers 1-(1,1-dimethylethyl) 3-ethyl 4-(3,4-dichlorophenyl)-6-methyl-5,6-dihydro-1,3(2H)-pyridinedicarboxylate and 1-(1,1-dimethylethyl) 3-ethyl 4-(3,4-dichlorophenyl)-2-methyl-5,6-dihydro-1,3(2H)-pyridinedicarboxylate (P21, 0.45 g) was dissolved in toluene (15 mL) and cooled to −20° C. Lithium aluminium hydride 1.0M in THF (0.869 mL) was added dropwise at −20° C. and the mixture was stirred at this temperature for 2 h. The reaction was then quenched with a saturated solution of NH4Cl (10 mL) and diluted with ethyl acetate (20 mL); the organic layer was separated, washed with water (20 mL), dried and concentrated in vacuo. Purification by chromatography on silica gel eluting with a gradient 100% cyclohexane-50% cyclohexane/ethyl acetate afforded 240 mg of title compound as colourless oil. The structure of the major regioisomer was confirmed by nOe NMR experiments.
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