Aryl Transfer Selectivity in Metal‐Free Reactions of Unsymmetrical Diaryliodonium Salts

Abstract

Aromatic rings are found in a wide variety of products, including pharmaceuticals, agrochemicals, and functional materials. Diaryliodonium salts are new reagents used to transfer aryl groups under both metal-free and metal-catalyzed reactions and thereby synthesize arene-containing compounds. This minireview focuses on recent studies in selective aryl transfer reactions from unsymmetrical diaryliodonium salts under metal-free conditions. Reactions reported from 2007 to 2017, which represents a period of significant growth in diaryliodonium salt chemistry, are presented and organized by the type of reactive intermediate formed in the reaction. Specifically, reactions involving λ -iodane, λ -iodane radical anions, aryl radicals, and arynes are discussed. Chemoselectivity trends in aryl transfer are compared and contrasted across reaction intermediates and translation to potential auxiliaries are posited.

Trimethoxyphenyl (TMP) as a Useful Auxiliary for in situ Formation and Reaction of Aryl(TMP)iodonium Salts: Synthesis of Diaryl Ethers

“…Aryl electrophiles bearing leaving groups feature prominently and both metal-free [1] and metal-catalyzed [2] reactions of aryl (pseudo)halides with nucleophiles are well established (Scheme 1a). [5] Of note, in 2013, Olofsson and co-workers reported a chemoselectivity study of aryl transfer to C-, O-, and N-nucleophiles and found that the 2,4,6-trimethoxyphenyl (TMP) group is a useful dummy ligand for aryl transfer from aryl(TMP) iodonium salts; [6] use of these reagents has continued to emerge over a range of mechanistically distinct reactions. [3] However, despite these advantages, the need to synthesize diaryliodonium salts is often viewed as a drawback.…”

Iodonium Salts as Benzyne Precursors

“…In particular, Okuyama and Ochiai have reported that the leaving group ability (nucleofugality) of the iodobenzene group is about million times greater than the triflate group . Owing to the high nucleofugality of ArI, diaryliodonium salts Ar 2 IX are powerful arylating reagents acting as a formal source of Ar + and efficient benzyne precursors (Scheme ) . As shown in Scheme , diaryliodonium compounds 1 can generate benzyne 2 via elimination of iodoarene ArI and substituent Z under appropriate conditions.…”

Metal-free formal synthesis of phenoxazine

“…The synthesis of diaryl ether 3 is the key step of the sequence, proceeding via arylation of phenols with diaryliodonium salts using our reported methodology [23–25]. In reactions with unsymmetrical iodonium salts, this type of O -arylation is known to have an ortho -effect, i.e., chemoselective transfer of the ortho -substituted aryl moiety [29–30]. The use of unsymmetrical iodonium salts facilitates the synthesis of the reagents and avoids waste of an expensive iodoarene, and we hence envisioned chemoselective transfer of the desired aryl moiety from an unsymmetrical salt with a suitable “dummy” aryl group.…”