Intramolecular reaction mixed Claisen condensation

The Claisen reaction is a carbonyl condensation that occurs between two ester components and gives a /3-keto ester product. Mixed Claisen condensations between two different esters are successful only when one of the two partners has no acidic a hydrogens (ethyl benzoate and ethyl formate, for instance) and thus can function only as the acceptor partner. Intramolecular Claisen condensations, called Dieckmann cyclization reactions, provide excellent syntheses of five- and six-membered cyclic /3-keto esters starting from 1,6- and 1,7-diesters. 

In Summary Claisen condensations are endothermic and therefore would not take place without a stoichiometric amount of base strong enough to deprotonate the resulting 3-ketoester. Mixed Claisen condensations between two esters are nonselective, unless they are intramolecular (Dieckmann condensation) or one of the components is devoid of a-hydrogens. Ketones also participate in selective mixed Claisen reactions because they are more acidic than esters. 

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