Diethyl methylmalonate → 2-[(2Z)-3-Chloro-2-butenyl]-2-methylmalonic Acid Diethyl Ester

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11.5 g of sodium cut into small pieces was introduced into a three-necked flask equipped with agitator, reflux condenser, and dropping funnel. To this charge was added dropwise 250 ml of absolute ethanol so quickly that the solution was boiling vigorously. Then 87 g of distilled diethyl methylmalonate was added dropwise to the hot alcoholate solution. After allowing the mixture to cool to about 75° C., the reaction solution was combined with 66 g of 1,3-dichloro-2-butene dropwise; the solution turned yellow during this step. After 2 hours of agitation under heating, the suspension, at this point having pH 5-6 and being almost completely decolorized, was freed of precipitated sodium chloride by filtration. The filtrate was concentrated and combined with the methylene chloride obtained by washing the precipitate. The organic solution was thereafter shaken with saturated sodium chloride solution, dried over magnesium sulfate, concentrated on a forced circulation evaporator, and fractionated under vacuum. Yield: 105 g of the desired diester, bp2.5 110° C.

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