One-Pot Synthesis of Diaryliodonium Salts Using Toluenesulfonic Acid: A Fast Entry to Electron-Rich Diaryliodonium Tosylates and Triflates

Abstract

A direct synthesis of symmetric and unsymmetric electron-rich diaryliodonium salts is described. The use of MCPBA and toluenesulfonic acid delivers diaryliodonium tosylates in high yields. An in situ anion exchange has also been developed, giving access to the corresponding triflate salts.

hypervalent iodine - diaryliodonium salts - oxidations - arenes - electrophilic aromatic substitution

References and Notes

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New, commercially available cans of MCPBA were found to contain large and variable amounts of H₂O. The MCPBA needs to be dried under vacuum at r.t. for 1 h to obtain reproducible results.

<A NAME="RG40207ST-11">11</A>

Unpublished results from our laboratory.

For syntheses of diaryliodonium tosylates, see ref. 7b, 7f and:

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<A NAME="RG40207ST-12E">12e</A>

Prof. Tsugio Kitamura presented some unpublished results on the synthesis of these compounds at the SIS Conference at Chiba University in November 2007.

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<A NAME="RG40207ST-15">15</A> The sulfonic acid moiety of TsOH is expected to form sulfuric acid upon formation of this byproduct. In order to confirm that, the reaction mixture described in Scheme 3 was diluted with MeOH and a few drops of aq BaCl₂ solution was added. White precipitates were formed, indicating the presence of SO₄ ^2-. In a parallel reaction, toluene was used instead of fluorobenzene, which resulted in no precipitates in the test with BaCl₂. See: Jackson DD. J. Am. Chem. Soc.  1901,  23:  799 

<A NAME="RG40207ST-16">16</A> The reactions were carried out in sealed tubes to allow for reaction temperatures above the boiling point of CH₂Cl₂, and were run without precaution to avoid moisture or air, i.e. without inert gas or dried solvent. TfOH (³99%) was stored under argon atmosphere. The percentage of active oxidizing agent in MCPBA was determined by iodometric titration, see: Vogel AI. Furniss BS. Hannaford AJ. Rogers V. Smith PWG. Tatchell AR. Vogel’s Textbook of Practical Organic Chemistry   Longman; London / New York: 1978.  p.1280