A suspension of methyl 8-bromo-1-propyl-1,2,3,4-tetrahydro-1-benzazocine-5-carboxylate (700 mg), 4-(2-butoxyethoxy)phenylboric acid (640 g), and potassium carbonate (744 mg) in toluene (15 ml), ethanol (1.5 ml) and water (1.5 ml) was stirred for 30 minutes under an argon atmosphere. After addition of tetrakis(triphenyl)phosphine palladium (120 mg), the solution was heated at 100° C. for 3 hours under an argon atmosphere. The solution was allowed to cool, followed by addition of water and 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=10:1) to obtain yellow oil of methyl 8-[4-(2-butoxyethoxy)phenyl]-1-propyl-1,2,3,4-tetrahydro-1-benzazocine-5-carboxylate (294 mg). The oil was redissolved in THF (21 ml) and methanol (21 ml), and after addition of 1N sodium hydroxide (7 ml), the mixture was heated at 70° C. for 2 hours. The mixture was cooled to 0° C., followed by addition of water, neutralized with 1N hydrochloric acid, and then 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 recrystallized from hexane-ethyl acetate to yield yellow crystals of 8-[4-(2-butoxyethoxy)phenyl]-1-propyl-1,2,3,4-tetrahydro-1-benzazocine-5-carboxylic acid (200 mg).
