Vinyl iodonium triflate

The introduction of acetylene, terminal alkynes or internal alkynes into methylene chloride solutions of iodosylbenzene and triflic acid [1 1, in situ generation of PhI(OH)OTf] results in the production of [j3-(trifluoromethanesulfonyloxy)vinyl]iodonium triflates (equation 172)78,133. Since the -configuration has been determined for selected members of this series (R1, R2 = n-Pr, H n-Bu, H), these reactions appear to proceed via stereoselective anti-additions of PhI(OH)OTf to the alkynes. 

In conclusion, vinyl iodonium salts are excellent pregenitors for vinylic cations due to high nucleofugality of the iodonio group (about 106-fold of triflate), although they are in equilibrium with the less reactive hypervalent... 

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)." " ... 

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. 

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

Similar Pd(II)/Cu(I) cocatalyzed couplings of (/ ,/ -dialkylvinyl)iodonium triflates with alkynylstannanes afford conjugated enynes, again with retention of configuration in the vinyl ligands (equation 260)157. 

A very general and mild procedure for the stereospecific synthesis of aIkenyl(aryl)iodonium triflates 309 involves aryl(cyano)iodonium triflates 308 as iodonium transfer reagents in reactions with stannylated alkenes 307 (Scheme 2.89) [367,443,444], This method was also applied to the preparation of the parent vinyliodonium triflate from tributyl(vinyl)tin [445],... 

Synthesis of 3,3-disubstituted oxindoles from arylation- and vinylation-carbocycUzation of electron-deficient alkenes with diaryliodonium salts catalyzed by CuCl catalyst was reported by Zhou, Li, and coworkers. A wide range of diaryl and vinyl(aryl)iodonium triflates and various substitutions on phenylacrylamides are compatible for this reaction. Both ( )-physostigmine and ( )-physovenine have been synthesized successfully in 41 and 36% overall yield using this vinyl addition/cyclization method [71]. Fu and coworkers developed a Cul-catalyzed synthesis of oxindole derivatives from readily available Af-alkyl-Af-phenylacrylamides and diaryliodonium triflates [72] (Scheme 8.34). 

Furthermore, arylthiophenes have been prepared using the Stille coupling of hypervalent iodonium salts [96] or organolead compounds [97, 98] as electrophiles in place of aryl or vinyl halides and triflates. Hypervalent iodonium salts are sufficiently reactive to undergo coupling at room temperature. 

The exceptional nucleofugality of the phenyliodonio group has been determined in an alkenyl salt and it is about 106 times greater than that of triflate [30]. This remarkable property makes alkenyl iodonium salts excellent vinyl cation equivalents in nucleophilic substitutions. The chemistry of alkenyl iodonium salts is dominated by the transfer of their aliphatic moiety to a variety of nucleophiles other important reactions involve Michael-type addition and alkylidenecarbene generation, along with elimination to alkynes which is actually an undesirable side-reaction. 

The reactions of vinyl(tri-n-butyl)stannanes with the appropriate [cyano(sulfonyloxy)-iodo]benzenes in dichloromethane constitute a facile stereoselective approach to / ,/ -disubstituted vinyl(phenyl)iodonium tosylates and triflates (equation 168)130,131. Although this method has not yet been used for the preparation of a,/ -disubstituted and a,/ ,/ -trisub-stituted analogs, it has been applied to the synthesis of ethenyl(phenyl)iodonium triflate131. The efficiency of this approach may be contrasted with the early work on chlorostannanes and chloroiodanes. 

When (Z)-(j5-fluoro-j5-trifluoromethylvinyl)phenyliodonium triflate is mixed with sodium phenoxide or sodium 2-phenylethoxide in dichloromethane, substitution is directed to the jft-carbon atom of the vinyl ligand, while the iodonium function remains intact (equation 200)136. With the 4-ter/-butylbenzenethiolate ion, however, substitution occurs at both vinyl carbon atoms (equation 201)136. 

Palladium(II)-copper(I) cocatalyzed couplings of several (/ ,/ -dialkylvinyl)phenyliodo-nium triflates with 4-isopropoxy-3-tri- -butylstannyl-3-cyclobutene-l,2-dione (71) in DMF at room temperature have recently been described (equation 259)157. As observed in earlier studies of Cu(I)- or Pd(II)-promoted reactions of vinyliodonium salts, the vinyl ligands are introduced with retention of configuration. Since iodobenzene is a byproduct of ligand coupling, the production of 3-phenyl-4-isopropoxy-3-cyclobutene-1,2-dione might also be expected. However, the (/ ,/ -dialkylvinyl)iodonium ions are much more reactive... 

The original procedure involved the coupling of aryl bromides with secondary amines. However, since then the scope has been expanded to include substrates such as aryl iodides, chlorides, fluorides, triflates, tosylates, nonaflates, iodonium salts, and even boronic acids. While the reaction has not been extensively utilized with vinyl or alkynyl substrates, it can be performed with various heteroaryl halides. Similarly, numerous types of nitrogen-containing coupling partners, including primary amines, imines, various azoles, lactams, and simple amides, can now be used in this reaction. 

The selective formation of the arylated or vinylated allylalcohol was rationalized by assuming a cationic four-manbered intermediate, in which the hydrogen atom (H ) on the hydroxyl-bearing carbon is located unfavorably for a syn palladium hydride elimination. The cationic intermediates were generated from organic triflates, iodonium salts,or organic iodide/thallium or silver salt combinations (Scheme 28). 

Heck-type reactions with enol carboxylates (e.g., vinyl acetate) are generally complex. Most common are reactions in which vinyl acetate is employed as an ethylene equivalent (see Scheme 24). However, an example of a preparatively useful reaction with an intact acetate function is given in entry 44.The reaction of vinyl triflates with vinyl phosphonates affords the corresponding conjugate dienylphosphonates (entry 45).f A new access to reactive nonaflates via a one-pot nonaflation-Heck reaction was recently reported (entry 46). " This reaction sequence starts from silyl enol ethers and provides functionalized 1,3-dienes in a simple manner, lodonium salts can be used as RPd precursors (entry 47). It is notable that the palladium(O) insertion preferentially occurs inbetween the iodonium ion and the vinylic, rather than the arylic sp -hybridized carbon (entry 47). Some years ago, Jeffery used acetylenic halides to achieve (JiJ-enynoates and (Ji)-enynones in fair yields at room temperature (entry 48). ... 

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