Vinyl iodonium salts, with

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... 

Reactions of (ii)-l-decenyl(phenyl)iodonium salt (6a) with halide ions have been examined under various conditions. The products are those of substitution and elimination, usually (Z)-l-halodec-l-ene (6b) and dec-l-yne (6c), as well as iodobenzene (6d), but F gives exclusively elimination. In kinetic studies of secondary kinetic isotope effects, leaving-group substituent effects, and pressure effects on the rate, the results are compatible with the in-plane vinylic mechanism for substitution with inversion. The reactions of four ( )-jS-alkylvinyl(phenyl)iodonium salts with CP in MeCN and other solvents at 25 °C have been examined. Substitution with inversion is usually in competition with elimination to form the alk-l-yne. 

The SyN2 reactions of vinylic compounds have been reviewed.23 An. S NVo- (an in-plane attack at the cr orbital giving inversion of configuration) and an S Nn mechanism (an out-of-plane attack on the tt orbital giving retention of configuration) have been found with vinyl iodonium salts. 

The treatment of /J, /J-dialkylvinyl(phenyl)iodonium salts with an appropriate base leads to alkylidenecarbenes. When such carbenes are generated in the presence of neutral heteroatom nucleophiles, vinyl onium salts can be obtained... 

The reaction of vinylic phenyliodium salts (57) with cyanide anions could be mistaken for a simple substitution reaction.59 However, the presence of both allylic (58) and vinylic (59) nitrile products suggests a more complex picture. Deuterium labelling experiments show that the allylic product is formed via the Michael addition of cyanide to the vinylic iodonium salt, followed by elimination of iodobenzene and a 1,2-hydrogen shift in the 2-cyanocycloalkylidene intermediate (60). H-shift occurs from the methylene carbon in preference to the methine carbon. The effects of substitution and different nucleophiles were examined. 

Vinyl(aryl)iodonium salts with cyclic vinyl ligands... 

As evidenced by the treatment of three (Z)-(/l-arylsulfonyl-l-decenyl)phenyliodonium fluoroborates with triethylamine, the presence of electronically diverse substituents (H,p-N02, / -MeO) in the arylsulfonyl groups appears to have little impact on their migratory aptitudes (equation 239)32. Indeed, among six [(/1-alkyl-/l-arylsulfonyl)vinyl]iodonium salts that have been investigated, the cyclopentene/alkyne ratios show little variability (i.e. 70 30 to 80 20)32. Finally, the presence of an appropriately placed alcohol function in the side chain of a (/l-sulfonylvinyl)iodonium salt has been shown to completely suppress migration in favor of insertion (equation 240)32. 

Palladium(II)-catalyzed couplings of vinyl(phenyl)iodonium salts with mono-substituted alkenes to give conjugated dienes have also been explored132. Such reactions proceed readily at room temperature and generally occur with retention of configuration in the vinyliodonium component and rnam-stereoselectivity in the olefinic substrate (equations 253-256). 

In some cases, it is possible to oxygenated a nonaromatic carbon atom using various reagents, where the product is an O- ester rather than an alcohol. In one example, a vinyl iodonium salt was heated with DMF to product the corresponding formate ester. 

Vinyl iodonium salts, prepared by reaction of vinylsilanes with iodosylbenzene and triethyloxonium tetrafluoroborate, have been found to be excellent educts for nucleophilic substitution by a variety of nucleophiles. Reaction with KCu(CN)p in DMF was thus possible and acrylonitrile derivatives prepared accordingly. 

Vinyl iodonium salt 40, which is highly effective as an activated species of vinyl iodide, could be synthesized from vinyl silanes 39 by the reaction with iodosyl benzene and triethyloxonium tetrafluoroborate. Thus, from vinyl silane, a,/3-unsaturated ester 41 could be synthesized by Pd-catalyzed carbonylation (Eq. 12). Alkynylphenyliodo-nium tosylates 42 were easily prepared from 1-alkynes with Phl(OH)OTs or by reaction... 

In conclusion The products obtained in the acetolysis of vinyl iodonium salt 1 are formed by three different meehanisms a) direct in-plane Sn2 vinylic substitution, b) substitution with neighboring group participation of the phenyl group and c) solvent-assisted a-elimination. 

Evidence for a Michael addition of a nucleophile to alkenyl(phenyl)iodonium salts at the Cp atom has now been reported for the first time. Nucleophilic vinylic substitutions of (Z)-(/3-bromoalkenyl)iodonium tetrafiuoroborates (161) and its (Z)-(/3-chloroalkenyl) analogue with sodium benzenesulfinate in THE afforded stereoselectively (Z)-l,2-bis(benzenesulfonyl)alkene (163) with retention of configuration. Intermediate formation of (Z)-[/3-(benzenesulfonyl)alkenyl]iodonium salt (162) in these reactions was established by NMR experiments in CDCI3. The formation of (Z)-(162) involves a hitherto unobserved Michael addition of benzenesulfinate anion to the alkenyliodonium salts at the Cp atom, followed by halogen extrusion. ... 

The styryl iodonium salt (7 a) reacts slowly with acetic acid to give the E and Z isomeric products (8a) and (9a) in the ratio 85 15.3 The decenyl system (7b) is much more reactive and gives only the inversion product, the Z isomer (9b). It was suggested that the styryl system reacts in a two-step mechanism via the vinylene phenonium ion (10), whereas the decenyl system follows a one-step vinylic. S n2 mechanism, hi contrast, 2-bromo-l-decenyliodonium salt reacts with bromide ion in MeCN with complete retention.4 The observed rate constants show an unexpected dependence on [Br ], in accordance with a mechanism involving ligand coupling within a bromoiodane intermediate. 

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

Alkenyl(phenyl)iodonium salts are highly reactive in vinylic nucleophilic substitution reactions because of the excellent leaving group ability of the phenyliodonium moiety. Only a few examples of non-catalytic alkenylation of carbon nucleophiles are known [50,51]. In most cases these reactions proceed with predominant retention of configuration via the addition-elimination mechanism or ligand coupling on the iodine [42,50]. 

Enolate anions derived from various 1,3-dicarbonyl compounds can be viny-lated with cyclohexenyl- and cyclopentenyl- iodonium salts (Scheme 27) [50]. The vinylation of enolate anions 58 in these reactions is frequently accompanied by the formation of the phenylated dicarbonyl compounds however, the selectivity of these vinylations can be improved by using alkenyl(p-methoxyphenyl)-iodonium salts instead of 57. 

Alkynyl(phenyl)iodonium salts can be efficiently coupled with various organo-copper reagents. Direct coupling of alkynyliodonium tosylates 132 with vinyl-... 

Alkenylations of heteroatom nucleophiles with alkenyl(aryl)iodonium salts occur by a variety of mechanisms, including SN1, SN2, alkylidenecarbene, and addition-elimination pathways [ 126,127]. Reactions that occur with retention of configuration at vinylic carbon are sometimes attributed to a ligand-coupling... 

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. 

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