Diaryliodonium salts, reaction with

Diaryliodonium salts react with sodium benzoate to give the aryl benzoates in moderate to good yields (40-85%). Treatment of biphenyleneiodonium sulfate (29) with sodium methoxide failed to give 2-iodo-2 -methoxybiphenyl. However, this product was obtained by an indirect sequence involving the formation of 2-iodo-2 -acetoxybiphenyl (30) by reaction of the biphenyleneiodonium sulfate with sodium acetate in boiling glacial acetic acid. Nearly quantitative yields were obtained when the reaction was catalysed by copper salts. 102... 

Complex heteroaryl ketones (169) have been prepared from heteroaldehydes (170) by exploiting the electrophilicity of diaryliodonium salts (171), with catalysis by a commercially available NHC. The reaction works in DCM, at 0 C or lower, in less than a day, using DMAP to generate the carbene and a protic additive (water or alcohol). 

As part of a later investigation into palladium-catalyzed reactions of diaryliodonium salts 220, Chen and Zhou found that reaction with amidoximes in the presence of carbon monoxide also gave 1,2,4-oxadiazoles (Equation 41) <2002SC887>. 

Photosensitization of diaryliodonium salts by anthracene occurs by a photoredox reaction in which an electron is transferred from an excited singlet or triplet state of the anthracene to the diaryliodonium initiator.13"15,17 The lifetimes of the anthracene singlet and triplet states are on the order of nanoseconds and microseconds respectively, and the bimolecular electron transfer reactions between the anthracene and the initiator are limited by the rate of diffusion of reactants, which in turn depends upon the system viscosity. In this contribution, we have studied the effects of viscosity on the rate of the photosensitization reaction of diaryliodonium salts by anthracene. Using steady-state fluorescence spectroscopy, we have characterized the photosensitization rate in propanol/glycerol solutions of varying viscosities. The results were analyzed using numerical solutions of the photophysical kinetic equations in conjunction with the mathematical relationships provided by the Smoluchowski16 theory for the rate constants of the diffusion-controlled bimolecular reactions. 

In a modified version of the Suzuki reaction arylboronates or boranes are utilized instead of arylboronic acid. Under the action of phosphine-free palladium catalysts NaBPh4 and tra(l-naphtyl)borane were found suitable phenyl-sources for arylation of haloaromatics in fully or partially aqueous solutions at 20-80 °C with good to excellent yields (Scheme 6.12) [32-34]. Aryl halides can be replaced by water-soluble diaryliodonium salts, At2IX (X = HSO4, BF4, CF3COO) in the presence of a base both Ar groups take part in the coupling [35]. 

Arenediazonium salts reacted with tetramethyltin under very mild conditions in acetonitrile yielding the corresponding toluenes [63] and this reaction could be carried out in aqueous media, as well [64] (Scheme 6.29). Similar to the Heck reactions discussed in 6.1.1, a one-pot procedure could be devised starting from anilines, with no need for the isolation of the intermediate diazonium salts. The pH of the solutions should always be kept below 7 in order to avoid side reactions of the diazonium salts, however, unlike with the Heck reactions, HCl or H2SO4 can also be used. Since organotin compounds are easily hydrolysed in acidic solutions, a careful choice of the actual pH is required to ensure fast and clean reactions. Diaryliodonium salts are hydrolytically stable and also react smoothly with various organotin compounds (Scheme 6.29) [65]. 

As mentioned above, condensed 1,2,3-triazine derivatives can be arylated by treatment with nitro-activated aryl halides. The only other report of direct arylation of the 1,2,3-triazine system is due to McKillop and Kobylecki, who studied the reaction of l,2,3-benzotriazin-4-one (10, R = H) with diaryliodonium salts in the presence of base. Treatment of 10, R = H, with diphenyl- and di-p-bromophenyliodonium chloride results in exclusive arylation at N2 and gives the corresponding triazinium betaines (77, R = Ph, p-BrCjH4) in good yield. When di-p-tolyliodonium chloride is used, a mixture of the Nj-, Nj-, and 0-arylated... 

The synthetic potential of palladium-mediated cross-coupling reactions (Heck, Suzuki, Stille, Sonogashira, Buchwald-Hartwig) led to the search for a practical synthesis of p-[ F]fluoroiodo- and p-[ F]fluorobromobenzene. p-[ F]Fluoroio-dobenzene (G, X = iodine) can be obtained in poor yield from p F]fluoride and a trimethylammonium precursor (P7). p-p F]Fluorobromobenzene can be prepared in a more reproducible way from 5-bromo-2-nitrobenzaldehyde (radiochemical yields > 70%). The synthesis involves a two-step procedure radiofluorination (F for NO2 substitution), then a catalysed decarbonylation [190,191]. Also very efficient is the one-step reaction of p F]fluoride with a suitable diaryliodonium salt (P6) giving >70% radiochemical yield [192-194]. 

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. 

Reaction of some / -trifyloxy-vinyl(phenyl)iodonium triflates with aryllithi-ums can lead to the synthesis of diaryliodonium salts in a manner analogous to... 

Aryl and heteroaryl (furyl, thienyl) boronic acids are especially suitable for the preparation of their iodonium salts, having the added advantage of better yields and lack of toxicity [108]. Tetraarylborates (sodium or potassium) reacted with (diacetoxyiodo)arenes in acetic acid to afford diaryliodonium salts in excellent yield (Scheme 37). It appears that triarylboranes formed upon reaction of the borates with acetic acid serve actually as the real arylating agents [109]. 

The self-condensation of iodosylbenzene was the first reported synthesis of a diaryliodonium salt back in 1892. The mechanism of the reaction was delineated only recently. This approach served for the synthesis of p-(phenylene)bis-(aryliodonium) salts [47], as well as some oligomers from (diacetoxyiodo)ben-zene and triflic acid [117], followed by coupling with an arene (Scheme 39). Under suitable conditions the same reaction can lead to simple phenyl(aryl)-iodonium triflates [118]. 

Aryl-, as well as heteroaryliodonium salts, belong to the most common, stable, and well investigated class of polyvalent iodine compounds. The preparation and chemistry of aryliodonium salts was extensively covered in several reviews [5,7,9,10]. Diaryliodonium salts have found synthetic application as arylating reagents in reactions with various organic substrates. 

Compounds containing an active methylene group, or the respective carbanions formed in situ, react smoothly with diaryliodonium salts to yield a-arylated products [1]. A recent example of arylation of carbanions under polar, non-cat-alytic conditions is represented by the reaction of diaryliodonium salts with malonates 90 (Scheme 41) [69]. 

Diaryliodonium salts 98 react with aldehydes 99 in the presence of chromium dichloride and nickel dichloride with the formation of benzyl alcohols 100 (Scheme 44) [74]. The mechanism of this reaction involves the generation of organochromium(III) species via reaction of iodonium salts with chromium dichloride, followed by their nucleophilic addition to aldehydes to yield alcohols. 

Recent progress on the use of hypervalent iodine reagents for the construction of heteroatom-heteroatom bonds is reviewed. Reactions of aryl-A3-iodanes with heteroatom substrates derived from third-row elements and beyond are considered first, and an unusual example of heteroatom-heteroatom bond formation with diaryliodonium salts is then discussed. Finally, the use of sulfonylimino(aryl)iodanes for imidations of phosphorus, sulfur, selenium, and arsenic compounds, including enantioselective transformations (S,Se), and alternate hypervalent iodine approaches to N-sulfonylsulfilimines and N-sulfonylarsinimines are summarized. 

In summary, recent investigations of reactions of aryl-A3-iodanes,ArIL1L2,with heteroatom substrates, derived from third-row elements and beyond, provide examples of P-O, S-O, Se-O, Se-P, Se-S, Te-O, Bi-O and Sb-0 bond formation. Sulfonylimino(aryl)iodanes, ArI = NS02R, are especially useful as imidation reagents, and have been utilized for the construction of P-N, S-N, Se-N, and As-N bonds. Diaryliodonium salts have been employed indirectly for formation of the Se-Se bond. 

It is well-known that nucleophilic substitution reactions of diaryliodonium salts (74), prepared by the reaction of substituted arenes (73) with iodine(III) reagents such as PIDA, PIFA, Phl=0, and I(OCOCF3)3, smoothly proceed to yield various functionalized arenes (75) [49] [Eq. (15)]. 

Diaryliodonium salts, with few exceptions, are stable compounds towards heat, oxygen and humidity they are mildly light-sensitive and should be stored in the dark, without refrigeration. Generally, their reactivity is less pronounced than that of other hypervalent iodine compounds. Indeed, in several of their reactions relatively drastic conditions may be necessary, especially for the least reactive heterocyclic iodonium salts. The search for optimum conditions is often desirable even for well-established reactions, by applying new findings concerning the use of specific... 

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. 

A mechanism with similar propagation steps to the usual S l has been proposed in the reaction of diaryliodonium salts with triphenylphospliine in this case, both the nucleophile and leaving group are neutral. This reaction is catalysed by light or by the thermal decomposition of di- -butyl peroxalate. The propagation steps that have been proposed in... 

The caged species may escape geminate recombination and produce various species that can initiate cationic polymerization. Solvent (RH) often participates in these reactions producing protonic acids. As shown in Eq. (44), protonic acids are also formed by reaction of radical cations with aryl radicals or by Friedel-Crafts arylation. Up to 70% of the protonic acid is formed upon photolysis of diaryliodonium salts [205]. In addition to initiation by protons, arenium cations and haloarene radical cations can react directly with monomer. The efficiency of these salts as cationic initiators depends strongly on the counterions. Those with complex anions such as hexafluoroantimonate, hexafluorophosphate, and triflate are the most efficient. 

Many different photoinitiators based on onium -type compounds with anions of low nucleophilicity also have been described in the literature as effective catalysts for the polymerization of epoxides Thus, diaryliodonium salts diaryliodosyl salts triarylsulfonium salts and related compoundstri-phenylsulfoxonium saltsdialkylphenacylsulfonium salts and dialkyl-4-hydroxyphenylsulfonium salts seem to be most suitable as photoinitiators for epoxy curing. Some of the principles of the reaction mechanism involving these initiators are discussed in detail in the following Sections. Various other onium photoinitiators such as diarylchloronium and diarylbromonium salts , thiopyrylium salts 3), triarylselenonium salts and onium salts of group Va elements >... 

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