Lecture28outline-1

Lecture28outline-1 - I. Review Ester enolates can be formed...

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I. Review • Ester enolates can be formed in small quantities by alkoxide bases • The alkoxide should be the same group as is present in the ester to avoid complications from transesterification • When enolates are formed in the presence of esters, condensation reactions occur to form a β -keto ester (Claisen condensation) through the formation of a tetrahedral intermediate followed by alkoxide extrusion • This reaction is driven by deprotonation of the carbon between the carbonyl groups • The reaction stops at one addition because the enolate product is not highly electrohilic or nucleophilic • The pKa's of 1,3-dicarbonyl compounds are much lower than monocarbonyl compounds, ranging between 9 (diketones) and 13 (diesters) • All steps in the Claisen condensation are reversible except for the final deprotonation step because of the high acidity of the hydrogens between the two carbonyl groups • The stability of the anions of 1,3-dicarbonyl compounds makes alkylation chemistry
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This note was uploaded on 05/17/2010 for the course CHEM 0740 taught by Professor Professor during the Spring '10 term at Pittsburgh.

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Lecture28outline-1 - I. Review Ester enolates can be formed...

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