2,3-Dimethyl-1,3-butadiene → 2H-Pyran-2,2-dicarboxylic acid, 3,6-dihydro-4,5-dimethyl-, diethyl ester

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Reaction Steps

Part A. The method of Bonjouklian and Ruden, J. Org. Chem., v. 42, p. 4095 (1977), was used here. Thus, a solution of diethylketomalonate (10.0 mL, 65.6 mmol) and 2,3-dimethyl-1,3-butadiene (16.3 mmol, 144 mmol) in acetonitrile (22 mL) was heated in a sealed tube at 140° C. for 6 hours. The contents of the tube was cooled, extracted with methylene chloride washing, evaporated and separated by flash chromatography (1:9 ethyl acetate-hexane) to afford diethyl 3,6-dihydro-4,5-dimethyl-2H-pyran-2,2-dicarboxylate as an oil (13.6 g, 53.1 mmol, 81%). 1H NMR (CDCl3): δ 4.26 (4H, q, J=7.0 Hz); 4.15 (2H, br s); 2.57 (2H, br s); 1.69 (3H, s); 1.51 (3H, s); 1.28 (6H, t, J=7.0 Hz). Mass spectrum (NH3 -CI/DDIP): m/z 275 (14%); 274 (100%); 257 (23%); 183 (1%).

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