Hydroxy iodo arenes

R. M. Moriarty, R. K. Vaid, G. F. Koser [ Hydroxy(organosulfonyloxy)iodo] arenes in Organic Synthesis [16]... 

Recent developments in this area include the use of poly[hydroxy(tosyloxy)-iodo]styrenes [80], chiral 2-(a-alkoxyalkyl) analogs of [hydroxy(tosyloxy)-iodo]benzene [81 - 83], and iodine(III)-phosphonate and -phosphinate reagents [84] for C-oxygen bond formation at a-carbon. Oxysulfonylations at the a-carbon atoms of carboxylic anhydrides with [hydroxy(sulfonyloxy)iodo]arenes have also been documented [85]. 

Bis(acyloxy)iodo]arenes. (Difluoroiodo)- and (dichloroiodo)arenes. Iodosylarenes. [Hydroxy(iosyloxy)iodo]benzene and its Analogues. Reagents of Iodine (V). 

The synthesis of the first alkynyliodonium tosylates was achieved by the treatment of terminal alkynes with [hydroxy(tosyloxy)iodo]benzene (HTIB) (equation 8)8,10,11. Such reactions are generally conducted with an excess of alkyne in chloroform at reflux, although they can be carried out at room temperature, and dichloromethane can be employed as solvent. This procedure is, however, restricted to terminal alkynes in which R is either an aryl group or a bulky alkyl group. With linear alkyl groups (i.e. R = n-Pr, n-Bu, fl-C5Hn), phenyl(/ -tosyloxyvinyl)iodonium tosylates are obtained instead (equation 9)8. In some cases (R = /-Pr, /-Bu), mixtures of alkynyl- and (/ -tosyloxyvinyl)iodonium tosylates are produced8. ter -Butylacetylene appears to be the optimum substrate for this approach and has been employed with a series of [hydroxy(tosyloxy)iodo]arenes for the synthesis of various aryl(ter/-butylethynyl)iodonium tosylates (equation 10)9. 

Chromones and flavones 16 are formed by Pd(0)-catalyzed carbonylative cyclization of o-hydroxy- or o-acetoxy iodo arenes with terminal alkynes in the presence of Et2NH. Intermediates are the corresponding or /zo-functionalyzed aryl alkynyl ketones 15, which can be synthesized separately and cyclized by Et2NH [37]. 

Table 2.6 Preparation of [hydroxy(organosulfonyloxy)iodo]arenes.

Various [hydroxy(tosyloxy)iodo]arenes 64 can be conveniently prepared by a ligand-exchange reaction of (diacetoxyiodo)arenes with p-toluenesulfonic acid monohydrate in acetonitrile (Scheme 2.26). This method has been apphed to the synthesis of derivatives with various substituted aromatic groups [150,166,186,209, 210], [hydroxy(tosyloxy)iodo]heteroarenes [206] and the recyclable hypervalent iodine reagents 65-68 (also see Chapter 5) [154,155,158]. Similarly, numerous polylluoroalkyl derivatives of the types C F2 +iI(OH)OTs [135,176,211] andC F2 +iCH2l(OH)OTs [176,212] can be prepared from the respective bis(trifluoroacetates) and p-toluenesulfonic acid. 

Wirth and coworkers have reported the preparation of a series of ortho-substituted chiral [hydroxy(tosyloxy)iodo]arenes 69 starting from the corresponding aryl halides (Scheme 2.27) [166,191]. 

A convenient modified procedure for the preparation of various [hydroxy(organosulfonyloxy)iodo]arenes 70 consists of the one-pot reaction of iodoarenes and mCPBA (m-chloroperoxybenzoic acid) in the presence of organosulfonic acids in a small amount of chloroform at room temperature (Scheme 2.28) [203]. 

Further modification of this procedure, developed by Olofsson and coworkers, involves a one-pot oxidative iodination/oxidation/ligand exchange sequence of reactions leading to the synthesis of [hydroxy(organosulfonyloxy)iodo]arenes 72 from arenes 71, iodine, mCPBA and the respective sulfonic acids (Scheme 2.29) [204]. 

Numerous methods for the preparation of symmetrical and unsymmetrical diaryl- and hetaryliodo-nium organosulfonates have been developed. A common synthetic approach to unsymmetric diaryl-and hetaryl(aryl)iodonium tosylates (e.g 262, 264, 266 and 268) is based on the reactions of [hydroxy(tosyloxy)iodo]arenes with aryltrimethylsilanes 261 [198], aryltributylstannanes 263 [376], aryl-boronic acids 265 [377], or the appropriate heteroaromatic precursors 267 (Scheme 2.75) [378,379]. The reaction of HTIB with arylstannanes proceeds under milder conditions compared to arylsilanes and is applicable to a wide range of arenes with electron-withdrawing substituents. Arylboronic acids in general have some advantage over arylstannanes in the case of the electron-rich heterocyclic precursors [377]. 

The aza analogues of 417, iodine-nitrogen zwitterions 419, have been prepared by the reaction of 2-amino-1,4-naphthoquinone (418) with [hydroxy(tosyloxy)iodo]arenes (Scheme 2.122) [205,562,563]. Ylides 419 show interesting reactivity upon heating, aryl migration from iodine to nitrogen occurs, giving product 420,... 

The functionalization of carbonyl compounds at the a-carbon is the most typical reaction of [hydroxy(organosulfonyloxy)iodo]arenes 139 (Scheme 3.58) [184],... 

This reaction of ketones with [hydroxy(organosulfonyloxy)iodo]arenes followed by treatment with an appropriate nucleophile in situ offers a convenient entry into various other a-substituted ketones, or can lead to various heterocycles via cyclization of the initially formed a-tosyloxyketones [176,177, 184, 190, 191], For example, the reaction of various ketones with [hydroxy(p-nitrobenzenesulfonyloxy)iodo]benzene (HNIB) and subsequent treatment with the appropriate nucleophile has been used for a one-pot preparation of secondary a-alkoxy or a-acetoxy ketones 142 [192], a-iodoketones 143 [118] and a-azidoketones 144 [193] in generally high yields (Scheme 3.60). 

Carboxylic anhydrides can be functionalized at the a-carbon using [hydroxy(organosulfonyloxy)-iodo]arenes. Treatment of carboxylic anhydrides 149 with reagents 150 at about 100 °C followed by esterification of the reaction mixture with methanol affords 2-sulfonyloxycarboxylate esters 151 in moderate to good yields (Scheme 3.62) [207]. 

The reactions of HTIB with alkenes (Scheme 3.73) can be rationalized by a polar addition-substitution mechanism similar to the one shown in Scheme 3.70. The first step in this mechanism involves electrophilic flnfi-addition of the reagent to the double bond and the second step is nucleophilic substitution of the iodonium fragment by tosylate anion with inversion of configuration. Such a polar mechanism also explains the skeletal rearrangements in the reactions of HTIB with polycyclic alkenes [227], the participation of external nucleophiles [228] and the intramolecular participation of a nucleophilic functional group with the formation of lactones and other cyclic products [229-231]. An analogous reactivity pattern is also typical of [hydroxy(methanesulfonyloxy)iodo]benzene [232] and other [hydroxy(organosulfonyloxy)iodo]arenes. 

Togo and coworkers have found that alkyl aryl ketones and dialkyl ketones could be converted into the corresponding a-tosyloxyketones in generally low yields by the reaction with mCPBA and p-toluenesulfonic acid monohydrate in the presence of a catalytic amount of molecular iodine in a mixture of acetonitrile and 2,2,2-trifluoroethanol (method A, Scheme 4.5) [23]. The same conversion of ketones into the corresponding a-tosyloxyketones could be smoothly carried out by the reaction with mCPBA and TSOH H2O in the presence of catalytic amounts of iodine and fert-butylbenzene in a mixture of acetonitrile and 2,2,2-trifluoroethanol (method B). In these reactions, p-iodotoluene 8 (method A) and 4-fcrr-butyl-l-iodobenzene 9 (method B) are formed at first and are then converted into the corresponding [hydroxy(tosyloxy)iodo]arenes, ArI(OH)OTs,... 

Togo and coworkers have reported the preparation of a recyclable, polystyrene-supported [hydroxy(tosyloxy)iodo]arene (25) from the respective poly[(diacetoxyiodo)styrene] (4) and p-toluenesulfonic acid monohydrate in chloroform at room temperature (Scheme 5.13) [24,25]. According... 

The reactivity pattern of recyclable hypervalent iodine reagents 65-67,69-71,73,74 and 76 is similar to the common iodobenzene-based reagents [34], For example, the recyclable (diacetoxyiodo)arenes 65,69,73 and 76 can be used instead of (diacetoxyiodo)benzene in the KBr or TEMPO-catalyzed oxidations of alcohols [74-78], while [hydroxy(tosyloxy)iodo]arenes 67, 71 and 74 are excellent reagents for tosyloxylation of ketones (Scheme 5.28) [76]. 

Likewise, the a-tosyloxylation of ketones with ion-supported [hydroxy(tosyloxy)iodo]arenes 101 proceeds smoothly in acetonitrile even at 0 °C (Scheme 5.34) [95]. These reactions are faster than those with... 

Solvent-free reactions have many advantages such as reduced pollution, lower costs and the simplicity of the processes involved [60]. The solvent-free preparation of several important hypervalent iodine reagents has been reported [61,62], [Hydroxy(sulfonyloxy)iodo]arenes (42) have been prepared in excellent yields by the solid-state reaction simply by grinding (diacetoxyiodo)arenes and appropriate sulfonic acids for several minutes in an agate mortar [61]. Tosyloxy- and mesyloxy benziodoxoles 44 can be prepared by a similar solvent-free procedure starting from 2-iodosylbenzoic acid (43) [61], Likewise, [hydroxy(phosphoryloxy)iodo]arenes 46 have been conveniently prepared by a solvent-free method from (diacetoxyiodo)arenes and phosphate esters 45 (Scheme 6.17) [62],... 

The reaction of polycyclic aromatic hydrocarbons with [hydroxy(tosyloxy)iodo]benzene in the presence of trimethylsilyl isothiocyanate leads to the regioselective thiocyanation of an arene nucleus, as illustrated by the reaction of anthracene shown in Scheme 3.213 [274],... 

Kita and coworkers developed an efficient synthesis of aiyl(phenyl)iodonium tosylates from HTIB and arenes in TFE at room temperature [29, 30]. This type of iodonium salt is chemoselectively employed in metal-free syntheses of biaryls (see Sect. 4.2.1). The synthetic strategy has been employed, for example, in the synthesis of polyfluorinated At21X [81] and acid-labile boron-substituted diaryliodonium salts firom aryl boronates with HTIB or the reagent combination PIFA/AcOH (Scheme 4a) [82]. Suna and coworkers have recently described the synthesis of heteroaryl(aryl)iodonium salts from heteroarenes and [hydroxy(tosyloxy)iodo] mesitylene or DIB combined with TsOH or AcOH. The salts were either isolated or used in situ (see Sects. 3.1.2 and 3.2.2) because of their relative instability [83, 84]. (Diacetoxyiodo)arenes were recently combined with electron-donating arenes and trimethylsilyl triflate (TMSOTf) to provide unsymmetric iodonium trifiates without the need for acid addition [85]. 

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