Hydroquinone → 4-[2-(3,4-Dihydro-2H-pyran-2-yl)ethenyl]-3,5-dimethyl-1,2-oxazole

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Reaction Steps

8.75 G. (0.20 mole) of 55 percent sodium hydride dispersion was washed under nitrogen with dry pentane to remove the mineral oil. To the flask was added 600 ml. of dimethylsulfoxide (dried over Linde 3A molecular sieves). The resulting suspension was carefully degassed, placed under nitrogen, and heated at 70°-75° for 1 hour. The gray-green solution was cooled to approximately 15° and 91.6 g. (0.20 mole) of (3,5-dimethyl-4-isoxazolylmethyl)triphenylphosphonium chloride, prepared as described in Example 4 above, was added in one portion. After approximately 5 minutes, a bright orange precipitate formed in the initially dark red solution. This suspension was stirred at room temperature for 45 minutes. To the mixture was then added, drop-wise via syringe, 25.0 g. (0.223 mole) of acrolein dimer (freshly distilled from and into hydroquinone) at such a rate that the temperature remained less than 30° (10-15 minutes with water bath cooling). The light orange-brown solution was stirred at room temperature for 20 minutes, and then at 60°-65° for 3 hours. (In some experiments, the mixture became very black during the heating period). The reaction mixture was cooled, poured onto ice, and slurried until all of the dark oil solidified. The suspension was filtered and the filter cake was washed well with pentane. The filtrates were extracted with pentane and the pentane solutions were washed with water and brine and dried over anhydrous sodium sulfate. Solvent removal gave a slightly orange oil which was distilled from a small quantity of anhydrous potassium carbonate to give the desired product as a colorless liquid, b.p. 83°-85°/0.1 mm. A similarly prepared sample of b.p. 77°-80°/0.5 mm. was submitted for analysis.

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