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26.10.2.1.7.1 Variation 1: Dieckmann Condensation

DOI: 10.1055/sos-SD-026-01067

Chataigner, I.; Harrison-Marchand, A.; Maddaluno, J.Science of Synthesis, (2005261178.

Several reviews have been devoted to the Dieckmann condensation.[‌94‌] Typically, this reaction consists of the cyclization of a dicarboxylic ester (or related function) to a 3-oxo ester under basic conditions (with bases such as alkaline alkoxides) and can thus be regarded as the intramolecular version of the Claisen condensation (see Section 26.10.2.1.2.2). Four-membered to large oxo-substituted rings can be accessed by this method, but cyclopentanones and cyclohexanones represent the core domain of its application. The 3-oxo ester pattern undergoes ready decarboxylation after cyclization, so the Dieckmann route is a useful source of cyclic ketones. Because the reaction is completely reversible, the retro-Dieckmann is a useful synthetic tool. The driving force of the condensation appears to be the ready deprotonation of the resulting 3-oxo ester, obtained in its enolate form in the basic medium. Kinetic and isotopic effects show that the rate-limiting step is the cyclizing addition of the primary enolate to the second ester. The competition between the inter- and intramolecular condensations explains why the Dieckmann reaction is often conducted under high-dilution conditions, especially when preparing medium to large ring ketones. The control of the regioselectivity represents one of the major difficulties associated with this reaction (this is also encountered in the Claisen condensation) when it is applied to dissymmetric diesters (or esteramides). This point, as well the incompatibility of normal experimental conditions with base-labile groups, explains the continuing development of this reaction.

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