Ethanol → 7-Benzyl-5,6,7,8-tetrahydro-[2,7]naphthyridine-4-carboxylic acid methyl ester

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Reaction Steps

In a 1 L copper flask was placed 7-benzyl-5,6,7,8-tetrahydro-[2,7]-naphthyridine-4-carbonitrile (44.8 g, 0.18 mol) in ethanol (200 mL). A solution of sodium hydroxide (36 g, 0.9 mol) in water (200 mL) was added and the resulting mixture was refluxed for 8 hr. The reaction mixture was concentrated under reduced pressure. To the residue was added ethanol (150 mL) and toluene (150 mL) and concentrated under reduced pressure. This process was repeated three times. Finally methanol (150 mL) and toluene (150 mL) were added and concentrated under reduced pressure. The solid residue was further dried under high vacuum line overnight. To the residue was added a solution of 30% sulfuric acid in methanol (w/w, 800 mL) and refluxed for 24 hr. The reaction mixture was cooled to room temperature and filtered to remove white solid (inorganic salt). The solid on filter paper was washed with methanol (100 mL) and the filtrate was concentrated under reduced pressure. To the residue was added ice (300 g) and basified with ammonium hydroxide (175 mL. 28-38% ammonia). The mixture was extracted with dichloromethane (2×250 mL). The combined organic layers were washed with brine (150 mL), filtered through 1 PS filter paper and concentrated to give a brown oil. The oil was purified by flash chromatography on silica gel (500 g) with anhydrous sodium sulfate (50 g) on top packed with hexane. The column was eluted with 200 mL portions of 25% ethyl acetate in hexane followed by 50% ethyl acetate in hexane. The eluent containing product was concentrated to give the title compound (39.1 g, 77%) as an oil which solidified on standing. 1H NMR 60 MHz, (CDCl3), δ 8.8 (s, 1H), 8.2 (s, 1H), 7.3 (s, 5H), 3.8 (s, 3H), 3.6 (s, 2H), 3.5 (s, 2H), 3.2 (m, 2H), 2.6 (m, 2H).

Provenance & Evidence