Diaryliodonium ion

Cyclic diaryliodonium ions may be prepared from appropriate diazonium salts. Biphenyl-eneiodonium iodide (4 X = I) and its analogues, for example, are prepared from 2,2 -diaminobiphenyl (08G619, 41JA1187, 58JCS2658). Bromonium and chloronium salts are obtained from 2-halo-2 -aminobiphenyl (3) (52JA274). 

Diarylhalonium Ions. In contrast to dialkylhalonium ions and alkylarylhalonium ions, diarylhalonium ions are considerably more stable. This is particularly the case for diaryliodonium ions, which have been known for 110 years.328a It is interesting,... 

The catalytic influence of 18-crown-6 on the production of fluorobenzene from diphenyliodonium tetrafluoroborate and KF in dichloroethane was documented some years ago [123]. More recently, diaryliodonium salts have been used for direct syntheses of [18F]-fluoroarenes [124,125]. After an initial study in which various counterions were surveyed, this was finally accomplished by the treatment of diaryliodonium triflates and trifluoroacetates with 18F K+-APE 2.2.2 (i.e., the aminopolyether 4,7,13,16,21,24,27-hexaoxa-l,10-diazabicyclo-[8.8.8]hexacosane) or Cs 18F in acetonitrile (Scheme 44). An added feature of these studies is rather extensive confirmation that nucleophiles are preferentially directed to the more deactivated ring of unsymmetrical diaryliodonium ions, unless one of the rings possesses ortho-substituents [125]. 

In a rare example of the use of iodonium salts for heteroatom-heteroatom bond formation, diaryliodonium halides were employed with sodium 0,0-diethyl phosphoroselenolate for a one-pot synthesis of diaryl diselenides (Scheme 9) [27]. These transformations probably occur via arylation of the phosphoroselenolate salt with the diaryliodonium ions, hydrolysis of the resulting aryl phosphoroselenolates with sodium hydroxide, and air oxidation of the arene-selenide ions thus produced. 

Diaryliodonium ions are also reducible, and their cathodic reduction using an Hg cathode affords Ar Hg [Eq. (8)] [48]. Benzylsulfonium ion is also effective as a substrate [49]. 

In recent years, a variety of hypervalent iodine reagents have been available. The versatility of these hypervalent organoiodine reagents in organic synthesis has been well recognized. Diaryliodonium salts constitute an important reagent class for the transfer of aryl groups. These iodonium ion salts have been used effectively in C-arylation of a variety of nucleopohiles.112 The arylation of the anion of nitroalkanes with diaryliodonium salts was already reported in 1963.113... 

A. Shah, V.W. Pike, D.A. Widdowson, The synthesis of [F-18]fluoroarenes from the reaction of cyclotron-produced [F-18]fluoride ion with diaryliodonium salts, J. Chem. Soc. Perkin Trans. I Organic and Bio-Organic Chemistry 13 (1998) 2043-2046. 

In view of the propensity of alkynyliodonium ions for Michael reactions with a wide range of nucleophiles, such displacements at iodine represent an unusual mode of reactivity. However, carbon ligand exchanges of this type at polyvalent iodine do find precedent in the literature106 and probably proceed via the tetrasubstituted iodate ions shown in equation 130. A similar mechanism was first proposed by Beringer and Chang to account for interconversions of diaryliodonium salts with aryllithium reagents (equation 131)106. 

Apart from copper(I)-mediated reactions, few studies of the treatment of vinyliodonium salts with carbanions have appeared. The vinylations of the 2-phenyl- and 2- -hexyl-l,3-indandionate ions shown in equations 222 and 223 are the only reported examples of vinyliodonium-enolate reactions known to this author26,126. ( ,)-l-Dichloroiodo-2-chloroethene has been employed with aryl- and heteroarvllithium reagents for the synthesis of symmetrical diaryliodonium salts (equation 224)149,150. These transformations are thought to occur via the sequential displacement of both chloride ions with ArLi to give diaryl (/ -chlorovinyl)iodanes which then decompose with loss of acetylene (equation 225). That aryl(/ -chlorovinyl)iodonium chlorides are viable intermediates in such reactions has been shown by the conversion of ( )-(/ chlorovinyl)phenyliodonium chloride to diaryliodonium salts with 2-naphthyl- and 2-thienyllithium (equation 226)149,150. 

The nucleophilic attack by [18F]fluoride ion on the diaryliodonium salt occurs preferably at the more electron-deficient ring [42], Therefore, a more electron-rich ring such as... 

Figure 14,4 Reaction of [18F]fluoride ion with diaryliodonium salts. Proportions of the four possible products ([18F]fluoroarenes vs. iodoarenes) is dependent on the ring substituents.

Later, in 1995, Pike and Aigbirhio applied for the first time diaryliodonium salts for the preparation of F-labeled aryl fluorides using potassium [ F]-fluoride in the presence of the diaza-crown ether Kryptofix (K2.2.2 structure 24 in Scheme 7.7) in acetonitrile at 85 °C or 110 "C [67]. Under these conditions, the reaction of diphenyliodonium chloride provided [ F]-fluorobenzene in 31-78% radiochemical yield. The use of Kryptofix is required for phase transfer of the [ F]-fluoride ion obtained by the nuclear reaction in the cyclotron as a solution in water enriched with oxygen-18. 

Chun and Pike described the rapid, single-step radiosynthesis of azido- or azidomethyl-bearing [ Fjfluoroarenes 48 and 50 from the reactions of diaryliodonium salts 47 or 49, respectively, with nocarrier-added [ F]fluoride ion within a microfluidic apparatus to obtain these previously poorly accessible F-labeled click synthons in good radiochemical yields (Scheme 7.17) [83]. The radiosynthesis of synthons 50 was also possible with wet cyclotron-produced NCA [ F]fluoride ion, in the presence of about 70 vol.% water and thus obviating the need to dry the cyclotron-produced [ F]fluoride ion and greatly enhancing the practicality of the method [83]. 

The photo-initiated production of catalytic amounts of HBF4, ITPFfi, or HAsF most commonly derives from irradiation of diaryliodonium salts, where the counter ion... 

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