Dimethyl malonate → 1,1-Dimethyl 2-ethenylcyclopropane-1,1-dicarboxylate

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To a solution of 36.6 g (1.6 g-atom) of sodium in 500 ml of anhydrous ethanol was added 105.5 g (0.80 mol) of dimethyl malonate. After several minutes, while maintaining the temperature at 60° C., 250 ml anhydrous methanol was added to solubilize the precipated sodium malonate salt. The freshly prepared disodiomalonate methanol solution was added to 100.0 g (0.80 mol) trans 1,4-dichlorobutene-2 heated to 60°-70° C. at a rate to allow a gentle reflux in the condenser. When the addition was completed, the reaction mixture was refluxed with stirring for an additional 4 hours. The reaction mixture was then cooled to ambient temperature, filtered and the resulting filtrate concentrated. Distillation of the crude product under reduced pressure afforded 82 g (44.5%) of the desired product dimethyl 2-vinylcyclopropane-1,1-dicarboxylate. B.p. 73°-78° at 1.25 mm Hg; nD24 1.4612; [lit. B.p. 71°- 73° (1 mm); nD25 1.4602].

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