Objectives After completing this section, you should be able to write an equation to illustrate an internal Claisen condensation, that is, a Dieckmann cyclization. identify the product formed when a 1,6‑ or 1,7‑diester undergoes an internal Claisen condensation. identify the diester needed to prepare a given cyclic β ‑keto ester by an internal Claisen condensation. identify the structural features present in a diester that lead to the formation of more than one product in an internal Claisen condensation. Key Terms Dieckmann cyclization Study Notes Essentially no new material is introduced in this section; Dieckmann cyclizations are intramolecular Claisen condensations. These reactions occur for 1,6‑ and 1,7‑diesters, as these substances result in the formation of compounds containing five‑ and six‑membered rings, respectively. You may recall that the formation of such ring systems is favoured because they are relatively free of strain. Dieckmann Condensation A diester can undergo an intramolecular reaction called a Dieckmann condensation. Example 23.9.1: Dieckman Condensation Mechanism Dieckmann, W. Ber. Dtsch. Chem. Ges. 1894 , 27 , 102–103. Exercises Exercise 23.9.1 Draw the expected product for the following reaction: Answer Exercise 23.9.2 The Dieckmann cyclization of the following molecule is expected to give a mixture of two cyclized products. Draw the structure of the two products and briefly explain why a mixture is formed. Answer