[Br:1][C:2]1[CH:20]=[CH:19][C:5]([N:6]([CH2:10][CH2:11][CH2:12][CH2:13][C:14]([O:16][CH2:17]C)=[O:15])[CH2:7][CH2:8][CH3:9])=[C:4]([CH:21]=O)[CH:3]=1.CO.C[O-].[Na+].Cl>COC(=O)OC.O>[Br:1][C:2]1[CH:20]=[CH:19][C:5]2[N:6]([CH2:7][CH2:8][CH3:9])[CH2:10][CH2:11][CH2:12][C:13]([C:14]([O:16][CH3:17])=[O:15])=[CH:21][C:4]=2[CH:3]=1
To a solution of ethyl 5-(4-bromo-2-formyl-N-propylanilino)pentanoate (5.0 g) in dimethylcarbonate (100 ml) was added a methanol solution of 28% sodium methoxide (3.5 g), and the mixture was heated at 50° C. for 2 hours under a nitrogen atmosphere. After cooling to 0° C. and neutralization with 1N hydrochloric acid, to the solution was added water, followed by extraction with ethyl acetate. The organic layer was washed with saturated saline, and dried over magnesium sulfate. After distilling off the solvent under reduced pressure, the residue was purified by silica gel column chromatography (hexane:ethyl acetate=5:1) to obtain yellow oil of methyl 8-bromo-1-propyl-1,2,3,4-tetrahydro-1-benzazocine-5-carboxylate (3.5 g).
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