One-Pot Synthesis of Unsymmetric Diaryliodonium Salts from Iodine and Arenes

Abstract

The first synthesis of unsymmetric diaryliodonium salts directly from iodine and arenes is presented. The methodology provides diaryliodonium salts with the trimethoxyphenyl (TMP) moiety as dummy group. The protocol avoids the customary use of iodoarenes, which can be both expensive and toxic. Excess reagents are not required, and the reactions are performed under mild conditions. O-Arylations with these TMP salts were demonstrated to be highly chemoselective. D iaryliodonium salts (diaryl-λ 3 -iodanes) have become exceedingly popular electrophilic arylating reagents for a wide range of nucleophiles under both metal-free and metalcatalyzed conditions in the past decade.1 The interest in applications with these hypervalent iodine reagents was accelerated by the development of novel synthetic routes to diaryliodonium salts, making these easily available at low cost. Our first contribution to this field was the development of a general one-pot route to diaryliodonium salts from iodoarenes using the reagent system mCPBA/triflic acid (TfOH) in dichloromethane, which delivered diaryliodonium triflates in high yields within short reaction times.2 The reaction was extended to the direct synthesis of symmetric diaryliodonium salts from arenes and iodine, a cascade reaction involving iodination, oxidation, and electrophilic aromatic substitution between the arene and the formed iodine(III) intermediate. 2The triflic acid system proved to be too reactive for the synthesis of iodonium salts with both aryl moieties substituted with electron-donating groups. Such diaryliodonium salts have previously been synthesized from [hydroxy(tosyloxy)iodo]-benzene (HTIB, Koser's reagent) derivatives.3 HTIB can be synthesized from the corresponding iodoarene using mCPBA/ tosic acid, 4 and we recently improved the synthesis of HTIB derivatives 1 by two interconnected routes. They can either be obtained by mCPBA-oxidation of iodoarenes (Scheme 1a) or from iodine and arenes by initial oxidative iodination, followed by oxidation to yield 1 (Scheme 1b). 5 The iodination was found to be the most difficult step in this sequence, limiting the substrate scope to arenes with electron-donating (EDG) substituents, and trifluoroethanol (TFE) 6 was employed as cosolvent to increase the reaction rates.To overcome the scope limitations in our mCPBA/triflic acid system, we developed a one-pot synthesis of electron-rich diaryliodonium salts 2 from iodoarenes, which likely proceeds via in situ formation of iodine(III) compounds 1 (Scheme 2a).That transformation could also be extended to the use of iodine and arenes as starting materials (Scheme 2b). 7 The latter route tolerated only arenes with EDG substituents, and the synthesis of unsymmetric diaryliodonium salts (R 1 ≠ R 2 ) was unsuccessful due to product mixtures, further limiting the scope. 8Stuart and co-workers later modified our mCPBA/TsOH conditions into a sequential one-pot reaction with iodoarenes and trimethoxybenzene (TMP-H) to obtain unsymmetric

Diaryliodoniums Salts as Coupling Partners for Transition-Metal Catalyzed C- and N-Arylation of Heteroarenes

“…Diaryliodonium salts are air-and moisture-stable, non-toxic, easy to handle and commercially available or easy to prepare [1][2][3][4][5][6][7][8]. During the last decade, noteworthy improvement in the synthesis and use of diaryliodonium salts has been reported [9][10][11][12][13][14][15][16][17][18][19][20][21]. Owing to their electron-deficient nature at the iodine center and to the excellent leaving-group ability of the iodoarene, diaryliodonium salts are frequently employed as aromatic electrophiles in aryl transfer processes [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38].…”

Visible‐Light‐Induced 3‐Component Synthesis of Sulfonylated Oxindoles by Fixation of Sulfur Dioxide

“…The reaction of phenyl(2,4,6‐trimethoxyphenyl)iodonium tosylate 4b afforded the sulfonylated oxindole 3a in 63 % yield with a selective transfer of the phenyl group over the electron‐rich 2,4,6‐trimethoxyphenyl moiety (TMP). Aryl(2,4,6‐trimethoxyphenyl)iodonium salts have been recently introduced as an attractive new class of chemoselective, iodonium salt‐derived aryl transfer reagents , , . In order to demonstrate the utility of such unsymmetrical salts in our 3‐component transformation, an additional reaction with the iodonium salt 4c was performed.…”

“…Aryl(2,4,6-trimethoxyphenyl)iodonium salts have been recently introduced as an attractive new class of chemoselective, iodonium salt-derived aryl transfer reagents. [39,41,42] In order to demonstrate the utility of such unsymmetrical salts in our 3-component transformation, an additional reaction with the iodonium salt 4c was performed. Also in this case a selective transfer of the desired aryl moiety was observed.…”

Hypervalent Iodine Reagents by Anodic Oxidation: A Powerful Green Synthesis

“…The acid‐catalyzed coupling of arenes with preformed hypervalent iodine reagents represents the general two‐step approach for the synthesis of symmetrical and unsymmetrical diaryliodonium salts . Recently, flow and one‐pot procedures for the synthesis of unsymmetrical diaryliodonium salts have been reported …”

“…[42] Recently,f low and one-pot procedures for the synthesis of unsymmetricald iaryliodonium salts have been reported. [43,44] The electrochemical anodic oxidation of iodoarenes in the presence of arenes is as ustainable, single-step approach for the generation of diaryliodoniums alts. This transformationw as first described by Miller and Hoffmann in 1966.…”