- Pummerer rearrangement
The Pummerer rearrangement is an
organic reaction whereby analkyl sulfoxide rearranges to an α-acyloxy -thioether in the presence ofacetic anhydride .Ref|Pummerer1909 Ref|Pummerer1910 In this reaction,sulfur is reduced while adjacent carbon is oxidized.Several reviews have been published.Ref|DeLucchi1991 Ref|Padwa1997 Ref|Padwa2002
The usage of α-acyl sulfoxides and
Lewis acid s, such as TiCl4 and SnCl4, allow the reaction to proceed at lower temperatures (0 °C).Ref|Stamos1986Mechanism
The mechanism of the Pummerer rearrangement begins with the
acylation of thesulfoxide (1 and 2). Compound 3 undergoes elimation to produce thesulfonium ion 4. Acetate adds to the sulfonium ion to give the final product 5.Other
anhydride s and acyl halides can give similar products. Inorganic acids can also give this reaction.This product can be converted toaldehyde orketone byhydrolysis .Ref|Meffre1999Variations
The sulfonium ion can be trapped by both intramolecular and intermolecular
nucleophile s formingcarbon -carbon bonds and carbon-heteroatom bonds. For example,thionyl chloride can be used to generate and trap the sulfonium ion:Ref|Kosugi1989Likewise, nucleophiles (such as
veratrole Ref|Ishibashi) can also be used.Pummerer fragmentation
When the α-organic residue can form a very good
leaving group this group and not the α-hydrogen atom will eliminate in the intermediate step in a Pummerer fragmentation Ref|Laleu2006. This reaction type is demonstrated below with a set of sulfoxides and theanhydride oftrifluoroacetic acid (TFAA):The organic group on the right is the moderately
methyl violet carbocation with pKR+ = 9.4 leading to a classical Pummerer rearrangement. The reaction on the left is a fragmentation because the leaving group with pKR+ = 9.4 is particularly stable.ee also
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Organosulfur chemistry References
# Pummerer, R. "
Ber. " 1909, "42", 2282.
# Pummerer, R. "Ber. " 1910, "43", 1401.
# De Lucchi, O.; Miotti, U.; Modena, G. "Org. React." 1991, "40", 157-184. (Review)
# Padwa, A.; Gunn, D. E., Jr.; Osterhout, M. H. "Synthesis" 1997, 1353-1377. (Review)
# Padwa, A.; Rur, S. K.; Danca, M. d.; Ginn, J. D.; Lynch, S. M. "Synlett" 2002, 851-862. (Review)
# Stamos, I. K. "Tetrahedron Lett. " 1986, "27", 6261.
# Meffre, P.; Durand, P.; Le Goffic, F. "Organic Syntheses ", Coll. Vol. 10, p.562 (2004); Vol. 76, p.123 (1999). ( [http://www.orgsyn.org/orgsyn/prep.asp?prep=v76p0123 Article] )
# Kosugi, H.; Watanabe, Y.; Uda, H. "Chem. Lett." 1989, 1865.
# Ishibashi, H. "et al." "Chem. Pharm. Bull." 1989, "37", 3396.
# "Pummerer fragmentation vs. Pummerer rearrangement: a mechanistic analysis" Benoît Laleu, Marco Santarem Machado and Jérôme LacourChem. Commun. , 2006, 2786 - 2788, DOI| 10.1039/b605187a
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