Dieckmann condensation

The Dieckmann condensation is the intramolecular chemical reaction of diesters with base to give β-keto esters.^[1] It is named after the German chemist Walter Dieckmann (1869–1925).^[2][3] The equivalent intermolecular reaction is the Claisen condensation. Dieckmann condensations are highly effective routes to 5-, 6-, and 7-member rings, but poor for larger rings.^[4]

The Dieckmann condensation

Dieckmann condensation
Named after	Walter Dieckmann
Reaction type	Ring forming reaction
Identifiers
Organic Chemistry Portal	dieckmann-condensation
RSC ontology ID	RXNO:0000065

Reaction mechanism

Deprotonation of an ester at the α-position generates an enolate ion which then undergoes a 5-exo-trig nucleophilic attack to give a cyclic enol. Protonation with a Brønsted–Lowry acid (H₃O⁺ for example) re-forms the β-keto ester.^[5]

Dieckmann condensation reaction mechanism for the example given

Due to the steric stability of five- and six-membered rings, these structures will preferentially be formed. 1,6 diesters will form five-membered cyclic β-keto esters, while 1,7 diesters will form six-membered β-keto esters.^[6]

Animation of the reaction mechanism

Further reading

• Dieckmann, W. Ber. 1894, 27, 102 & 965
• Dieckmann, W. Ber. 1900, 33, 595 & 2670
• Dieckmann, W. Ann. 1901, 317, 51 & 93

See also

• Claisen condensation
• Gabriel–Colman rearrangement
• Thorpe reaction