Hydrochloric Acid → 6-Methoxy-1,2,3,4-tetrahydronaphthalen-2-one

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Reaction Steps

A suspension of 2,6-dimethoxynaphthalene (20.0 g, Aldrich) in 200 mL of anhydrous EtOH was heated to reflux under a stream of nitrogen. Sodium spheres (18 g, Aldrich) were added gradually to the hot suspension over a period of 2 hours. Additional ETOH (50 ml) was added and the reaction was heated until all of the sodium had dissolved. The solution was cooled to room temperature and placed in an ice bath. The addition of 6 N HCl brought the solution to pH 6, and additional HCl (10 mL) was added. The solution was heated to reflux for 0.5 h. The golden mixture was cooled to room temperature, H2O (200 mL) was added, and the solution was extracted with ET2O. The combined ET2O extracts were dried (Na2SO4), filtered, and concentrated to afford 6-methoxy-2-tetra-lone as a red oil (23.5 g). Triethyl phosphono-acetate (29 mL, Aldrich) was added dropwise to a suspension of hexane-washed sodium hydride (5.8 g of 60% dispersion) in benzene (80 mL) cooled in an ice bath. The phos-phonate solution was stirred at room temperature for 0.5 h, and the ice bath was replaced. A solution of 6-methoxy-2-tetralone (23.5 g) in benzene (20 mL) was added to the phosphonate solution over 10 minutes, and the reaction was allowed to stir at room temperature overnight. The reaction was poured into H2O and extracted with EtOAc (3×150 mL). The combined extracts were dried (Na2SO4), filtered, and concentrated to afford a brown oil which was purified using silica gel chromatography. Elution with 10% EtOAc/hexane afforded the title compound (27 g) as a yellow oil. NMR (300 MHz, CDCl3) δ6.98 (d, J=9.03 Hz, 1 H), 6.79-6.70 (m, 2H), 6.35 (s, 1H), 3.94 (q, J=7.11 Hz, 2H), 3.58 (s, 3H), 2.99 (s, 2H), 2.61 (t, J 8.11 Hz, 2H), 2.14 (t, J=8.07 Hz, 2H), 1.08 (t, J 7.14 Hz, 3H).

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