Reaction of Simple Arenes with FSO3H*SbF5/SO2: One-Pot Synthesis of Aromatic Sulfoxides. Mechanistic Aspects and Synthetic Utility

Article abstract of DOI:10.1021/jo00005a037

In a simple one-pot reaction, mono-, di-, tri-, and polyalkylbenzenes, isomeric alkylhalobenzenes, and fluoro-, (trifluoromethyl)-, and 1,3,5-trifluorobenzene were converted to their corresponding diaryl sulfoxides with FSO3H*SbF5 (1:1) (magic acid)/SO2.Dependency of the yields on the acidity (H₀) and the arene structure was demonstrated.Reduction of the formed sulfoxide was also observed as a minor pathway to give diaryl sulfide.The reduction is superacid-catalyzed, and protonated sulfoxides are the key intermediates en route to sulfides.Protonation of several functionalized diaryl sulfoxides was also studied in magic acid/SO2 under stable ion conditions.Unlike the parent diphenyl sulfoxide, which is S-protonated, alkyl-, fluoro-, and trifluoromethyl-substituted diaryl sulfoxides O-protonate to give long-lived sulfoxonium ions.The proposed mechanism for the arene/superacid/SO2 system involves sulfination of the arenium ions, O-protonation of the resulting sulfinic acid, dehydration of the oxonium ion "ArSO⁺" and arylation.In the absence of SO2, the fluorosulfonation, ionization, arylation path becomes dominant.The scope of the reaction is sufficiently broad to be synthetically useful.The methodology is also applicable to unsymmetrical (mixed) diaryl sulfoxides.