Iodonium triflates

The arylation of the i-tributyistannyl glycai 717 offers a synthetic route to chaetiacandin[585,586]. The Pd-catalyzed reactions of the 3-stannylcyclobute-nedione 718 with iodobenzene, and benzoyl chloride[S87], and alkenylation with alkenyl(phenyl)iodonium triflates proceed smoothly by the co-catalysis by Cul[588,589],... 

In contrast to the previous method (equation 70), reaction 72 made possible the preparation of iodonium triflates from functionalized acetylenes bearing an electron-withdrawing group such as tosyl, cyano, or carbonyl [138]. Of special interest is the application of this method to the synthesis of the bisiodonium acetylenic salt [139, 140] (equation 73). 

Alkynyl iodonium triflates prepared by the above reactions (equations 70,72, and 73) have become valuable reagents m organic chemistry, serving as premier... 

Diarylmethylenecyclopropa[6]naphthalenes 14, unlike their benzene parent counterparts which give cycloaddition reactions at the cyclopropene bridge bond [10a], react on the exo double bond in Diels-Alder cycloadditions (see Sect. 2.1.1) [10b]. The reactions of 14 with the highly electron-deficient acetylenic(phenyl)iodonium triflate 584 give products 586a and 587, which are believed to derive from unstable primary [2 + 2] cycloadducts 585 (Scheme 82) [10b],... 

Tributylstannyl)-3-cyclobutene-1,2-diones and 4-methyl-3-(tributylstan-nyl)-3-cyclobutene-l,2-dione 2-ethylene acetals undergo the palladium/copper-catalyzed cross coupling with acyl halides, and palladium-catalyzed carbon-ylative cross coupling with aryl/heteroaryl iodides [45]. The coupling reaction of alkenyl (phenyl )iodonium triflates is also performed by a palladium/copper catalyst [46],... 

The use of alkynyliodonium salts in the synthesis of 2,3-disubstituted 4,5-dihydrofurans was reported by Feldman. In this conversion, the addition of p-toluenesulfinate to ethers of 1-hydroxybut-3-ynyl(phenyl)iodonium triflates 79 induces a series of reactions that afford eventually 2-substituted 3-p-toIuenesulfonyl-4,5-dihydrofurans 80 . 

A study of the regioselectivity of the 1,3-dipolar cycloaddition of aliphatic nitrile oxides with cinnamic acid esters has been published. AMI MO studies on the gas-phase 1,3-dipolar cycloaddition of 1,2,4-triazepine and formonitrile oxide show that the mechanism leading to the most stable adduct is concerted. An ab initio study of the regiochemistry of 1,3-dipolar cycloadditions of diazomethane and formonitrile oxide with ethene, propene, and methyl vinyl ether has been presented. The 1,3-dipolar cycloaddition of mesitonitrile oxide with 4,7-phenanthroline yields both mono-and bis-adducts. Alkynyl(phenyl)iodonium triflates undergo 2 - - 3-cycloaddition with ethyl diazoacetate, Ai-f-butyl-a-phenyl nitrone and f-butyl nitrile oxide to produce substituted pyrroles, dihydroisoxazoles, and isoxazoles respectively." 2/3-Vinyl-franwoctahydro-l,3-benzoxazine (43) undergoes 1,3-dipolar cycloaddition with nitrile oxides with high diastereoselectivity (90% de) (Scheme IS)." " ... 

The reaction of lithium or sodium arylteUurolate with alkynyl phenyl iodonium triflates or tosylates. ... 

Alkynylphenyl tellurides from arylteUurolates and alkynyliodonium salts (general procedure) To a stirred solution of PhLi in Et20/cyclohexane at room temperature under N2, tellurium powder was added and the solution was stirred for 1 h. The appropriate iodonium triflate was added and the solution was stirred for 2 h. The product was eluted through a small portion of silica gel with CHjCN and the volume was reduced in vacuo followed by purification via radial chromatography. 

Cyano)(trifluoromethanesulfonoxy)-iodojbenzene or cyano(phenyl)-iodonium triflate... 

The unique reactivity pattern of alkynyl iodonium salts discussed in Sections II,A.2 and II,D,la can also serve as two-carbon conjunctive reagents in the synthesis of pyrroles, dihydropyrroles, and indoles. Feldman et al. found that combination of alkyl or aralkyl tosylamide anions 101 with phenyl(propynyl)iodonium triflate (102) furnishes the corresponding dihydropyrroles 103 (95JOC7722) (Scheme 28). 

Stang etal. (94JA93) have developed another alkynyliodonium salt mediated approach for the synthesis of y-lactams including bicyclic systems containing the pyrrole moiety. This method is based on the formation of 2-cyclopentenones 114 via intramolecular 1,5-carbon-hydrogen insertion reactions of [/3-(p-toluenesulfonyl)alkylidene]carbenes 113 derived from Michael addition of sodium p-toluenesulfinate to /3-ketoethynyl(phenyl) iodonium triflates 112 (Scheme 32). Replacing 112 by j8-amidoethynyl (phenyl)iodonium triflates 115-119 provides various y-lactams as outlined in Eqs. (26)-(30). 

Cycloaddition of benzyne intermediates with aminothiazadienes provide access to substituted 2,4-diamino-4//-l,3-benzothiazines 196 in high yields. The benzynes are prepared by the treatment of (phenyl)[o-(trimethylsilyl)aryl]-iodonium triflates with 1.5 equiv of tetrabutylammonium fluoride (Scheme 20). Interestingly, 3-substituted-l,2-benzisothiazoles 197 are obtained when 4 equiv of tetrabutylammonium fluoride is used <2005H(65)1615>. 

Long-lived vinyl cations have been reviewed.114 Vinyl cations (67) can be prepared by the fragmentation of alkenyl(aryl)iodonium triflates, giving triflate capture products, some of which may be rearranged.115 Otherwise vinyl cation research has been quiet this year. 

The pareitropone project began quite by accident after an unexpected observation expanded our thinking about potentially accessible targets for alkynyliodonium salt/alkylidenecarbene chemistry (Scheme 18). Treatment of the tosylamide iodonium salt 125 with base under standard conditions was designed to provide no more than routine confirmation of the aryl C-H insertion capabilities, which were first exposed in indoleforming reactions using tosylanilide anion nucleophiles and propynyl(phenyl)iodonium triflate,5b of the intermediate carbene 126. However, this substrate did not perform as expected, since only trace amounts of the 1,5 C-H insertion product 127 was detected. One major product was formed, and analysis of its spectral data provided yet another surprising lesson in alkynyliodonium salt chemistry for us. The data was only consistent with the unusual cycloheptatriene structure 129. 

The AuCl-catalysed 4 + 2-cycloaddition of benzyne with o-alkynyl(oxo)benzenes produced anthracene derivatives having a ketone in the 9-position, in good to high yields under mild conditions.118 Hypervalent iodine compounds, [5-acyl-2-(trimethyl-silyl)]iodonium triflates, readily yielded acylbenzynes which could be trapped with furan.119 Both DMAD and benzyne reacted with borabenzene to yield substituted borabarrelenes and borabenzobarrelenes, respectively.120... 

A similar electrophile, iodosyl triflate, CF3S020I0, was employed with arylsi-lanes [98]. The same reagent upon reaction with Me3SiCN formed (CN)2I+ TfO" which was coupled with tributyltin substituted arenes or heterocycles to afford bis(heteroaryl)iodonium triflates, e.g. dithienyl and difuryl derivatives [99]. However, this method gave poor results with nitrogen heterocycles. For them another approach was developed based on the reaction of the appropriate lithium compound with / -(dichloroiodo)chloroethylene (Scheme 33). Pyridine and quinoline compounds were formed in this way in moderate yield (23-71 %) [100]. 

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

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]. 

Other similar approaches have used alkenylsilanes and PhI0/Et30+ BF4 and also alkenylstannanes and PhI+CN TfO [123,124]. The reactions proceed also stereoselectively. The parent ethenyl(phenyl)iodonium triflate as well as several trisubstituted alkenyl members were obtained in this way. In an analogous manner E-alkenylzirconium compounds upon reaction with (diacetoxyiodo)ben-zene afforded -alkenyl(phenyl)iodonium salts stereoselectively [125]. 

In a similar manner, lLf,lH-perfluoroalkyl(aryl)iodonium triflates 44 are best prepared by the reaction of triflates 43 with trimethylsilylarenes under mild conditions (Scheme 19) [39]. 

Perfluoroalkyl(phenyl)iodonium sulfonates 42 (also known as FITS reagents), as well as lFf,lff-perfluoroalkyl(aryl)iodonium triflates 44, have found practical application as electrophilic fluoro alkylating reagents toward a... 

The stable (arylsulfonylmethyl)iodonium salts 49 and 50 can be conveniently prepared in two steps starting from the readily available iodomethyl sulfones 47 (Scheme 23) [41]. Iodonium salts 49 and 50 are not moisture sensitive, can be purified by crystallization from acetonitrile, and can be stored for several months in a refrigerator. The structure of iodonium triflate 50 was unambiguously established by a single crystal X-ray analysis [41]. 

The palladium/copper-cocatalyzed coupling of the readily available trisubsti-tuted alkenyl(phenyl)iodonium triflates 77 with alkynyl- and alkenylstannanes proceeds under exceedingly mild conditions with retention of geometry of the alkenyl ligand of the iodonium salt (Scheme 35) [60]. 

Organotin compounds can be effectively used as substrates in the palladium-catalyzed cross-coupling reactions of alkenyliodonium salts [66,67]. For example, the reaction of alkenyliodonium triflate 84 with 5-stannylated uracil 83 proceeds smoothly to provide cross-coupled products 87 in moderate yield. The same products 87 are obtained in almost quantitative yield in the palladium-catalyzed cross-coupling of uracil iodonium triflate 85 and vinyltin 86 (Scheme 39) [67]. 

Benzyne is an important reactive intermediate especially useful for the construction of polycyclic compounds via cycloaddition reactions with various dienes. Several benzyne precursors, including diphenyliodonium-2-carboxylate [ 1 ], have been previously used for the generation of benzyne by thermal decomposition. More recently, several new precursors that generate benzyne quantitatively under very mild conditions have been developed [105 -108]. An efficient benzyne precursor, iodonium triflate 109, can be readily prepared by the reaction of l,2-bis(trimethylsilyl)benzene 108 with [(diacetoxy)iodo]benzene in the presence of trifluoromethanesulfonic acid (Scheme 47) [105]. 

Under similar conditions, (2-oxoazetidinyl)malonates 129 can be alkynylated by (trimethylsilyl)ethynyl iodonium triflate (Scheme 53). In contrast to the previous reaction (Scheme 52), this alkynylation directly affords the desilylated terminal alkynes 130 as the final isolated products [112]. This reaction (Scheme 53) allows ethynylation of malonates under milder conditions compared to the reaction shown in Scheme 51. 

Likewise, alkynyliodonium tosylates can be coupled with dialkyl- and diphenyl cuprates 136 to afford the respective alkyl- and phenyl-substituted alkynes 137 (Scheme 56) [114]. An interesting example of this reaction involves the coupling of (trimethylsilyl)ethynyl iodonium triflate with cubyl cuprate generated in situ from iodocubane 138 [116]. 

A variety of five-membered nitrogen heterocycles can be prepared efficiently by inter- or intramolecular addition/cyclizations of sulfonamide anions with alkynyliodonium salts. The intermolecular variant employs the combination of the amides 172 or anilides 174 with propynyl(phenyl)iodonium triflate (Scheme 65) [131,132]. The yield of dihydropyrroles 173 in this cyclization is extremely sensitive to the nature of the protective group P the tosyl group in 172 proved... 

A similar intermolecular cyclization was recently utilized in the synthesis of highly substituted dihydropyrrole derivatives [133 -135]. In a specific example, the addition of pentadienyltosylamide derivatives 177 to propynyl(phenyl)iodo-nium triflate initiates a sequence of transformations that furnishes the complex, highly functionalized cyclopentene-annelated dihydropyrrole products 178 in moderate yields with complete stereoselection (Scheme 66). Under similar reaction conditions, the isomeric isoprene-derived tosylamide 179 reacts with propynyl(phenyl)iodonium triflate to give azabicyclo[3.1.0]hexane 180 as the final product [134]. 

Anions of secondary-sulfonamides, especially N-substituted tosylamidate ions, have emerged as premier partners for C-N bond forming reactions with alkynyliodonium salts. To a much lesser extent secondary-carboxamidate ions have also been used for this purpose. For example, the sequential treatment of -substituted tosylamides with n-butyllithium and phenyl(trimethylsi-lylethynyl)iodonium triflate (26) affords the corresponding N-trimethylsi-lylethynyl-p-toluenesulfonamides, which can be desilylated with tetrabutylam-monium fluoride in wet THF (Scheme 51) [ 151 ]. It is noteworthy that the presence of such groups as n-Bu and CH2 = CH(CH2)2- in the tosylamidate ions did... 

This approach to N-alkynylsulfonamides has been applied to the synthesis of enantiomerically pure derivatives 27 of N-(ethynyl)allylglycine (Scheme 52) [152]. In this case, deprotonated sulfonamide derivatives of (S)-allylglycine were treated with ethynyl(phenyl)iodonium triflate (28), since the trimethylsi-lylethynyl salt 26 was not very effective for this purpose. 

Reactions of phenyl(propynyl)iodonium triflate (30) with tosylamidate ions possessing N-alkyl chains of two or more carbon atoms follow the carbene insertion pathway leading to AT-tosyldihydropyrroles 31 (Scheme 54) [154,155]. The N-cyclohexyl tosylamidate ion leads stereospecifically to the ds-fused bicyclic dihydropyrrole under these conditions. 

Reactions of silyl, pyranyl, furanyl, and 1,3-dioxanyl ethers, 37, of 4-hydroxy-l-butynyl(phenyl)iodonium triflate with sodium p-toluenesulfinate in THF afford... 

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