Copper diaryliodonium salts

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. 

Arylboronic acids, (ArB(OH)2, react with thiols and copper(II) acetate to give the corresponding alkyl aryl sulfide. " Arylboronic acids also react with N-methylthiosuccinimide, with a copper catalyst, to give the aryl methyl sulfide. " " In the presence of a palladium catalyst, thiophenols react with diaryliodonium salts. 

The remainder of the mechanistic information presented in this review draws from the investigations and proposals by Lockhardt391 and Barton and coworkers343 on the intermediacy of hypervalent copper(III) species during the reactions of diaryliodonium salts and pentavalent bismuth reagents. Most of the reactions utilize Cu(I) or Cu(II) salts as the starting copper source. Radical mechanisms are ruled out because the reactions are not inhibited when radical scavengers (such as 1,1-diphenylethylene) are added. It appears that Cu(H) is not the major catalytic species in the reaction. 

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... 

The arylation of nucleophiles by reaction with diaryliodonium salts can be greatly facilitated by copper catalysis. This effect was observed by Beringer et al in the thermal decomposition of diaryliodonium halides as well as by Caserio et al in the hydrolysis of diaryliodonium salts. 2 jhe thermal decomposition of diphenyliodonium chloride shows a reduced activation energy upon copper catalysis Ea = 19 kcal/mole in Methylene glycol in the presence of CuCl instead of 31 kcal/mole in the absence of catalyst.From the synthetic point of view, the copper-catalysed arylation with diaryliodonium salts has been particularly useful in the case of a number of reactions involving heteroatomic nucleophiles, in particular for 5-, 5e-, O- and N-arylation reactions. 

The 5-arylation of sulfides is greatly improved by copper catalysis. The uncatalysed reaction requires heating under reflux to afford modest to moderate yields of the 5-aryl sulfonium derivatives. By contrast, upon copper catalysis, the reaction proceeds at room temperature to afford good to high yields of the 5-aryl sulfonium derivatives. 2-146,151 Moreover, the reaction was extended to the double arylation of the more readily available aiylthiols.l Similarly, the reaction of areneselenolates with diaryliodonium salts led to diarylselenides and triarylselenonium salts were easily obtained by copper catalysed arylation of diarylselenides. 2... 

McMillan and Allen have accomplished the enantioselective a-arylation of aldehydes using diaryliodonium salts and a combination of copper and organic amine catalysts. This asymmetric protocol has been applied to the rapid synthesis of (5 -ketoprofen, a commercially successful oral and topical analgesic [920],... 

Strong Bronsted acids form when diaryliodonium salts, like BF4, AsFe , PFe and SbFg are reduced with compounds like ascorbic acid in the presence of copper salts, such acids also initiate the polymerizations of tetrahydrofuran, cyclohexene, and s-trioxane [54]. 

DMSO solvent, requires the presence of a weak acid such as acetic or trifluorobenzoic and involves a significant kinetic isotope effect indicating that C-H bond cleavage is, at least partially, rate determining. " The trifiuoromethylation of iodoheteroaromatics, such as 4-iodopyridine, by copper-catalysed reaction with trifluoromethyldiphenylsul-fonium salts is likely to involve the intermediacy of trifiuoromethylcopper. " Copper catalysis has also been used in the synthesis of Ai-arylpurines, (59), by reaction of purines with diaryliodonium salts. 

Bhong BY, Shelke AV, Karade NN (2013) Nano copper oxide mediated ligand-free C-S cross-coupling and concomitant oxidative aromatization of 4-aryl-3,4-dihydropyrimi-din-2(l 7/)-thione with diaryliodonium salts. Tet Lett 54 739-743... 

Although diaryliodonium salts are generally synthesized under transition metal-free conditions, an interesting rhodium- and copper-catalyzed synthesis was recently published. Arenes with N-containing directing groups were reacted with DIB/TsOH to provide aryl(phenyl) tosylates (Scheme 4b) which were chemoselectively applied in various metal-catalyzed transformations [86]. Salts with an oxime ether substituent could be obtained under rhodium- and silver-catalyzed conditions (see Sect. 3.1.2) [86]. 

Kang and coworkers developed a number of metal-catalyzed arylations with diaryliodonium salts under mUd reaction conditions at the turn of the century, including the Pd-catalyzed arylation of secondary amines at room temperature and the Cu-catalyzed arylation of amines, anilines, amides, imidazoles, and triazoles at room temperature to 50 °C [98, 99]. The copper-catalyzed N-arylation of indoles, on the other hand, required heating to 150 °C in DMF [100], and makes an interesting comparison with the recently developed C-arylation of the same substrates (see Sect. 4.2.2). 

The groups of Wen and Nachtsheim developed one-pot syntheses of carbazoles from cyclic diaryliodonium salts and amines using copper- and palladium-catalyzed reaction conditions, respectively. This double arylation strategy made... 

The copper-catalyzed cascade annulation of nitriles, diaryliodonium salts, and alkynes was recently described by Chen and coworkers. N-Arylation of the nitrile resulted in an V-arylnitrilium intermediate, which was trapped by the aUcyne and subsequently underwent electrophilic annulation to yield substituted quinolines (Scheme 6d) [107]. The concept was later varied to reach polycyclic quinolines, quinazolines, quinazolinimine, and acridine scaffolds [108—110], A similar cascade reaction delivered iminobenzoxazines by N-aiylation of ort/io-cyanoanilides followed by C-O cyclization [111], and the reactimi of nitriles with [1,1-biphenyl]-derived iodonium salts resulted in phenanthiidines [112]. The corresponding C-arylation cascade reactions are discussed in Sect. 4.3. 

The vast majority of fluoridations of diaryliodonium salts have been performed tmder metal-free conditions, but Sanford and coworkers recently developed copper-catalyzed conditions for efficient fluoridation with KF (Scheme 11a). The method has a wide scope, and imsymmetric mesityl salts could be chemoselectively employed, giving easy access to a range of fluoro(hetero)arenes. The methodology was subsequently modified to suit radiofluorination and applied to the synthesis of the radiotracers 4-[ F]fluorophenylalanine and 6-[ F]fluoroDOPA [152, 153]. 

This section describes selected arylations of phosphorus, sulfur, and halide nucleophiles under metal-free and metal-catalyzed conditions. Arylations of other nucleophiles, e.g., selenium and tellurium, have been reviewed previously [4]. Aryl phosphonates [ArPO(OR)2] can be synthesized by arylation of phosphite anions with diaryliodonium salts and NaH in DMF at 70-80 °C [158]. A copper-catalyzed arylation of various phosphorous nucleophiles, e.g., diarylphosphine oxides and //-phosphonates, was recently reported to proceed at room temperature. The observed chemoselectivity with unsymmetric salts was opposite to the general trend in metal-catalyzed reactions (see Sect. 2.1), which was explained by a radical mechanism [159]. 

Scheme 8 a-Arylation of aldehydes using diaryliodonium salts with copper catalysts... 

With Copper In 2009, Gaunt s group [30] reported a wieta-selective Cu-catalyzed direct arylation of anilides with diaryliodonium salts, which was expected from a S Ar mechanism (Scheme 4.6). This was achievable by the coordination of the amide carbonyl group with the metal that managed to override the natural selectivity of these S Ar reactions. [31] This proposal was backed up by computational studies. In Scheme 4.6, we compare the selectivity of the Cu-catalyzed pathway with the Pd-catalyzed pathway. 

Scheme 8,71 Enantioselective a-arylation of W-acyloxazolidinones with copper(ll)-bisoxazoline catalysts and diaryliodonium salts, as described by Gaunt and coworkers [122].

Arylboronic acid is the most versatile organometalloid due to its efficiency and ready commercial availability. Other organometalloids that can also participate in this copper-promoted cross-coupling reaction are aryltrialkylsiloxanes [51b, 54], aryltrime-thylstannanes [55], triarylbismuths [5,56], arylleads [57], diaryliodonium salts [58a], diethylzinc [58b] and dialkylaluminum chlorides [58c]. 

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