Cyclopropyl carbanions derived from esters of 2-phenylcyclopropylcarboxylic acids: Configurational stability and reaction with electrophiles |
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Authors: | B A Feit R Elser U Melamed I Goldberg |
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Institution: | Department of Chemistry, Tel-Aviv University, Tel-Aviv 69978 Israel |
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Abstract: | The base-catalyzed cis-trans isomerization of cis and trans-alkyl 2-phenylcyclopropylcarboxylates was studied in several aprotic solvents. It was found that contact ion-pain of the derived carbanion lithium salts were configurationally more stable than the solvent-separated ones. Reaction of either the cis or the trans esters with MeI, and the reaction of the cis ester with Ph2C = O, resulted in the corresponding I-substituted derivatives having cis geometry only. This was explained as due to steric hindrance to elctrophilic attack exerted by the 2-phenyl group in the case of the trans substrate. The trans esters did not react with Ph2C=O. Inhibition of the trans-to-cis isomerization of the carbanion salt of the trans substrate in presence of Ph2C=O could lead to this result. |
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