Iodanes diaryl

Diaryliodonium salts (diaryl-A3-iodanes) are widely used as arylating agents. There are a number of methods available for their synthesis typically involving two or three steps.378,379 A recent one-pot approach, however, offers a simple and high-yielding access to unsymmetrical diaryliodonium triflates using meto-chloroperbenzoic acid (mCPBA) as the oxidant380 [Eq. (4.111)]. Moreover, symmetrical diaryliodonium salts can directly be prepared from iodine and arenes without the use of expensive aryl iodides [Eq. (4.112)]. 

Reaction of diarylhalo-A3-iodanes with sodium AT,AT-dialkyldithiocarbamates results in the formation of yellow or orange dialkylcarbamoyl(diaryl)-A3-iodanes, which are stable in the dark but decompose to aryl iodides and aryl dialkyldithiocarbamates in daylight via light-promoted homolytic pathway [29]. For ligand exchange of A3-iodanes with sulfides, see Section 3.2.5.4. 

Ligand exchange on iodine(III) with carbon nucleophiles provides a useful method for synthesis of A3-iodanes with two carbon ligands. Koser and coworkers found that exposure of aryltrimethylsilanes to [hydroxyltosyloxy)-iodo]benzene 17 in refluxing acetonitrile allows the directed synthesis of diaryl-A3-iodanes [31]. The reaction involves silicon-directed ipso carbon attack on the positively charged iodine and, therefore, is regiospecific. 

We propose a mechanism of carbon-halogen bond-forming ligand coupling of diaryl(halo)-A3-iodanes, which involves a highly polarized apical-equatorial transition state. Ligand coupling mechanism of p-chlorophenyl(p-methyl-phenyl)bromo-A3-iodane 77, which exists as an equilibrium mixture of 77a and... 

Recently, Widdowson and coworkers reported the ab initio MO calculations for the ligand coupling of diaryl(fluoro)-A3-iodanes [125]. 

Studies on the solution structure of A3-iodanes are relatively limited. In polar solvents, cryoscopic and conductance measurements have shown extensive dissociation of diaryl-A3-iodanes (Ar2IL L = BF4, Cl, Br, OAc) into the solvated iodo-nium ions (Ar2I+S S = polar solvents such as H20, MeOH, and DMSO) [3,210]. Even in dichloromethane, bis(4-methylphenyl)-A3-iodane (Ar2IBF4 Ar=p-MeC6H4) dissociates into the solvated iodonium ions with dissociation constant Kdissoc=4.7xlO-6M[211]. 

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. 

Ligand exchange of monoaryl-A -iodanes with an arylsilane or arylstannane leads to analogous diaryl reagents, which have unique uses. For example, diaryl-A -iodanes bring about a-arylation of enolates, as shown below ... 

Abstract This chapter focuses on recent developments in metal-free and metal-catalyzed arylations with diaryliodonium salts (diaryl-X -iodanes). Synthetic routes to diaryliodonium salts are briefly described, and chemoselectivity trends with unsymmetric iodonium salts are discussed. 

Diaryl-A, -iodanes are well-known iodine(lll) compounds and can work as excellent electrophilic arylating agents because of the remarkable electron deficiency at iodine. Because of their relatively low cost and toxicity, they are promising substitutes for transition metal-based reagents [61]. 

Diaryl-A, -iodanes (often referred to as diaryliodonium salts) such as [PhjIJOTf or derivatives can couple the phenyl group with another aromatic ring to form a... 

Table 2 Comparison of Pd-catalyzed alkene arylations using diaryl-k iodanes 1...

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