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Stetter reactionThe Stetter reaction is an organic reaction involving the nucleophile catalyzed conjugate addition of an aldehyde to a Michael acceptor such as an enone . The reaction product is a 1,4-dicarbonyl compound. The active catalyst can be a combination of a thiazolium salt and a base or cyanide]. Additional recommended knowledgeReaction mechanismKey in the reaction mechanism is the conversion of the aldehyde carbonyl group from an electrophile to a nucleophile in an umpolung process. This is accomplished by deprotonation of the quaternary thiazolium salt 1 by base to the thiazolium ylide 2 which reacts in a nucleophilic addition with the aldehyde 3 to the tetrahedral intermediate 4. After a 1,2-rearrangement reaction of the methylene proton in 4 to oxygen the resulting carbanion 5 is able to react with enone 6 in a Michael reaction to adduct 7. A hydrogen migration takes place to 8 after which the thiazolium group is expelled generating the 1,4-diketone 9 and completing the catalytic cycle. The Stetter reaction is related to the Benzoin condensation where the nucleophilic catalyst is a cyanide ion and the electrophile a carbonyl. ScopeAn example of the Stetter reaction is the preparation of 2,5-undecanedione from heptanal and 3-buten-2-one in scheme 3 .Just as with benzoin condensations the reaction can be carried out as an intramolecular asymmetric synthesis and with persistent carbenic triazolium salts exemplified by the synthesis of a hydrobenzofuranone in scheme 4 . The base in this reaction is KHMDS . References
Categories: Addition reactions | Carbon-carbon bond forming reactions |
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Stetter_reaction". A list of authors is available in Wikipedia. |