6-Methoxy-3,4-dihydronaphthalene-2-carboxylic acid → 6-methoxy-1,2,3,4-tetrahydronaphthalene-2-carboxylic Acid

A mixture of 7-methoxy-1,2-dihydro-3-naphthoic acid (0.22 g), 5% palladium-carbon (0.1 g) and methanol (20 ml) is subjected to catalytic reduction at room temperature under atmospheric pressure of H2. After hydrogen absorption has ceased, the catalyst is filtered off, and the filtrate is evaporated to dryness under reduced pressure to give 6-methoxy-1,2,3,4-tetrahydro-2-naphthoic acid as colorless powder. To this product are added 1-(3,4,5-trimethoxybenzyl)piperazine dihydrochloride (0.4 g), triethylamine (0.5 g) and N,N-dimethylformamide (10 ml), and the mixture is stirred. To this solution is added dropwise at room temperature diethyl phosphorocyanidate (1 ml). The mixture is stirred for one hour. After addition of water (100 ml), the reaction mixture is extracted with ethyl acetate. The organic layer is washed with water, dried and concentrated under reduced pressure. The residue is purified by silica gel column chromatography (hexane:acetone=1:1). The resulting oily product is dissolved in ethanol and the solution is treated with 5N ethanolic hydrogen chloride (1 ml). The mixture is diluted with ethyl ether, and then resulting precipitates are collected by filtration to give 1-(6-methoxy-1,2,3,4-tetrahydro-2-naphthoyl)-4-(3,4,5-trimethoxybenzyl) piperazine hydrochloride (0.35 g) as colorless prisms, m.p. 220°-225° C. (decomp.).