Many variations of the basic Pummerer rearrangement have been described:[5]
additive Pummerer reactions
domino Pummerer reaction, whereby the C-S bond is cleaved often
asymmetric Pummerer reactions, which exploits the chirality of most sulfoxides
interrupted Pummerer reactions
The usage of α-acyl sulfoxides andLewis acids, such asTiCl4 andSnCl4, allow the reaction to proceed at lower temperatures (0 °C).[6]
Thionyl chloride can be used in place of acetic anhydride to trigger the elimination for forming the electrophilic intermediate and supplying chloride as the nucleophile to give an α-chloro-thioether:[7]
Example of the Pummerer rearrangement using thionyl chloride
Otheranhydrides and acyl halides can give similar products. Inorganic acids can also give this reaction. This product can be converted toaldehyde orketone byhydrolysis.[8]
The activated thialelectrophile can be trapped by various intramolecular and intermolecularnucleophiles to formcarbon–carbon bonds and carbon–heteroatom bonds.
When a substituent on the α position can form a stablecarbocation, this group rather than the α-hydrogen atom will eliminate in the intermediate step. This variation is called aPummerer fragmentation.[11] This reaction type is demonstrated below with a set of sulfoxides andtrifluoroacetic anhydride (TFAA):
Pummerer fragmentation
The organic group "R2" shown in the diagram above on the bottom right is themethyl violet carbocation, whose pKR+ of 9.4 is not sufficient to out-compete loss of H+ and therefore a classical Pummerer rearrangement occurs. The reaction on the left is a fragmentation because the leaving group with pKR+ = 23.7 is particularly stable.
^Padwa, Albert; Gunn, David E. Jr.; Osterhout, Martin H. (1997). "Application of the Pummerer Reaction Toward the Synthesis of Complex Carbocycles and Heterocycles".Synthesis.1997 (12):1353–1377.doi:10.1055/s-1997-1384.
^Padwa, Albert; Bur, Scott K.; Danca, Diana M.; Ginn, John D.; Lynch, Stephen M. (2002). "Linked Pummerer-Mannich Ion Cyclizations for Heterocyclic Chemistry".Synlett.2002 (6):851–862.doi:10.1055/s-2002-31891.
^Akai, Shuji; Kita, Yasuyuki (2007). "Recent Advances in Pummerer Reactions".Sulfur-Mediated Rearrangements I. Topics in Current Chemistry. Vol. 274. pp. 35–76.doi:10.1007/128_073.ISBN978-3-540-68097-0.
^Stamos, Ioannis K. (1986). "Arylation of α-phosphoryl sulfides via their pummerer rearrangement intermediates generated from the corresponding sulfoxides".Tetrahedron Letters.27 (51):6261–6262.doi:10.1016/S0040-4039(00)85447-7.
^Kosugi, Hiroshi; Watanabe, Yasuyuki; Uda, Hisashi (1989). "Lewis Acid-Mediated Carbon-Carbon bond forming reaction using the Pummerer Rearrangement Products from Chiral beta-Hydroxy Sulfoxides".Chemistry Letters.18 (10):1865–1868.doi:10.1246/cl.1989.1865.
