- Stetter reaction
The Stetter reaction is an
organic reaction involving thenucleophile catalyzedconjugate addition of analdehyde to aMichael acceptor such as anenone Ref|Stetter. The reaction product is a 1,4-dicarbonyl compound. The activecatalyst can be a combination of athiazolium salt and a base orcyanide ] .Reaction mechanism
Key in the
reaction mechanism is the conversion of the aldehyde carbonyl group from anelectrophile to anucleophile in anumpolung process. This is accomplished bydeprotonation of the quaternary thiazolium salt 1 by base to the thiazoliumylide 2 which reacts in anucleophilic 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 resultingcarbanion 5 is able to react withenone 6 in aMichael 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 thecatalytic cycle .The Stetter reaction is related to the
Benzoin condensation where the nucleophilic catalyst is acyanide ion and the electrophile a carbonyl.cope
An example of the Stetter reaction is the preparation of 2,5-undecanedione from
heptanal and 3-buten-2-one as shown below. Ref|Stetter2.Just as with benzoin condensations the reaction can be carried out as an
intramolecular asymmetric synthesis using persistent carbenic triazolium salts, exemplified by the synthesis of a hydrobenzofuranone shown below.Ref|Liu. The base in this reaction is KHMDS Ref|cre.References
# "Review. Catalyzed Addition of Aldehydes to Activated Double Bonds - A New Synthetic Approach" Stetter, H.
Angewandte Chemie International Edition Volume 15, Issue 11 , Pages 639 - 647 1976 [http://www3.interscience.wiley.com/cgi-bin/abstract/106580616/ABSTRACT Abstract]
# H. Stetter, H. Kuhlmann, and W. HaeseOrganic Syntheses , Coll. Vol. 8, p.620; Vol. 65, p.26 [http://www.orgsynth.org/orgsyn/pdfs/CV8P0620.pdf Article]
# "Asymmetric Synthesis of Hydrobenzofuranones viaDesymmetrization of Cyclohexadienones Using the Intramolecular Stetter Reaction"Qin Liu and Tomislav RovisJ. Am. Chem. Soc. ; 2006; 128(8) pp 2552 - 2553; [http://dx.doi.org/10.1021/ja058337u Abstract]
# The first step in this sequence is theoxidation ofp-cresol byiodosobenzene diacetate in presence of 30 equivalents ofethanol , the second step another oxidation this time of thehydroxyl group byDess-Martin periodinane . "ee" stands forenantiomeric excess
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