Hydrochloric Acid → 2-Di-n-propylamino-8-chloro-1,2,3,4-tetrahydronaphthalene

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Reaction Steps

To a solution of 8-chloro-2-tetralone (3.0 gm, 16.6 mMol) in benzene (25 mL) were added dipropylamine (3.35 mL, 33.2 mMol) and p-toluenesulfonic acid (100 mg), and the reaction mixture was heated at reflux for 4 hours with constant water removal (Dean-Stark trap). The reaction mixture was then cooled to room temperature, and the volatiles were removed in vacuo to give a dark viscous residue. To a solution of this crude material in methanol (30 mL) were added acetic acid (3 mL) followed by the dropwise addition of sodium borohydride (1.5 gm) in ethanol (60 mL) with cooling. The reaction mixture was stirred for 18 hours at room temperature. To this was then added hydrochloric acid (6M, 20 mL) and the mixture stirred 4 hours at room temperature. The volatiles were then removed in vacuo and the residue triturated with water. The aqueous phase was extracted once with diethyl ether, and the organic phase was discarded. The remaining aqueous phase was made basic with concentrated ammonium hydroxide and was then extracted well with dichloromethane. The organic extracts were combined, washed with saturated aqueous sodium chloride, dried over sodium sulfate and concentrated in vacuo to give an orange liquid. Purification by chromatography on basic alumina (Activity I, dichloromethane) gave a colorless liquid (1.75 gm, 40%). The hydrochloride salt was formed and recrystallized (ethanol/diethyl ether) to give a colorless, crystalline-solid (m.p.=159°-160° C.).

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