Dimethylformamide diethylacetal → 3,4-dihydro-6,7-dimethoxy-2-(dimethylaminomethylene)-1(2H)-naphthalenone

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Reaction Steps

From 3,4,5-trimethoxyphenylguanidinium nitrate (1.14 g, 4.0 mmol), 3,4-dihydro-6,7-dimethoxy-2-(dimethylaminomethylene)-1(2H)-naphthalenone (1.04 g, 4,0 mmol) and sodium hydroxide (176 mg, 4.4 mmol). The crude product was purified by chromatography on silica (3% methanol in dichloromethane) and recrystallised from ethyl acetate-hexane to give the title compound as pale yellow crystals (354 mg) m.p. 179-182°. δH (CDCl3) 8.22 (1H, s), 7.83 (1H, s), 7.12 (1H, br s), 6.99 (2H, s), 6.75 (1H, s), 3.96 (3H, s), 3.94 (3H, s), 3.88 (6H, s), 3.83 (3H, s) and 2.89-2.81 (4H, m). MS (ES+) 424 (MH+, 100%). The 3,4-dihydro-6,7-dimethoxy-2-(dimethylaminomethylene)-1(2H)-naphthalenone starting material was prepared from 6,7-dimethoxy-1-tetralone (4.12 g, 20 mmol) and N,N-dimethyl formamide diethyl acetal (10.3 ml, 60 mmol) to give the product as red-brown crystals (3.26 g) m.p. 138-140°. MS (ES+) 284 (MNa+, 12%), 262 (MH+, 100%), 189 (28%).

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