1,5-Diazabicyclo(4.3.0)non-5-ene → Cyclopropanecarboxylic acid, 3-(2,2-dichloroethenyl)-2,2-dimethyl-, ethyl ester

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13 g of diethyl 2,2-dimethyl-3-(2',2'-dichlorovinyl)-cyclopropane-1,1-dicarboxylate were dissolved in 50 g of o-xylene and 20 g of 1,5-diaza-bicyclo[4.3.0]non-5-ene were added. The mixture was then heated to the boil for 8 hours. After cooling, ice-cold dilute hydrochloric acid was added, so that a neutral or weakly acid pH value resulted. The organic phase was separated off and dried with Na2SO4 and the xylene was distilled off in vacuo (boiling point = 35° - 40° C./12 mm Hg). The residue weighed 12.5 g. Fractional distillation gave 4.7 g of 2,2-dimethyl-3-(2',2'-dichlorovinyl)-cyclopropane-1-carboxylic acid ethyl ester, of which 30% was in the cis form and 70% was in the trans form. The boiling point was 65° - 72° C./0.3 mm Hg. The nuclear magnetic resonance spectrum agreed with that given in the literature. 6.5 g of the starting material were recovered. The yield was thus 92%.

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