Vinyl iodonium salts tetrafluoroborate

Cyclohexenyl and cyclopentenyl iodonium tetrafluoroborates were also photolyzed in methanol. Ring-strained five-membered cyclic vinyl cation could be generated photochemically as well as the six-membered cyclic vinyl cation. In conclusion, vinyl iodonium salts are excellent pregenitors for vinylic cations due to high nucleofiigality of the iodonio group (about 10 -fold of triflate), although they are in equilibrium with the less reactive hypervalent... 

The situation is quite different for the photochemical solvolysis reactions of vinyl iodonium salts. In all cases studied thus far these reactions involve direct, unassisted heterolytic cleavage of the vinylic C-I bond, yielding primary and endocyclic secondary vinyl cations. For example, photosolvolysis of ( )-styryl(phenyl)iodo-nium tetrafluoroborate (37) very efficiently yields the products resulting from heterolytic cleavage of the vinylic C-I bond, depicted in Scheme (Also... 

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... 

Finally, vinyl(tri-rc-butyl)stannanes have also been utilized with iodosylbenzene and Meerwein s reagent126 for the synthesis of the ( rr-butylcyclohexenyl)iodonium tetrafluoroborate shown in equation 162 and with iodosylbenzene/BF3-etherate to give the (ketovinyl)iodonium salt shown in equation 169128. 

The nitrite ion behaves as a nitrogen nucleophile with vinyliodonium ions. Thus, admixture of the vinyliodonium tetrafluoroborates shown in equations 188 and 189 with sodium nitrite results in the production of nitroalkenes119,125,126. Cupric sulfate is apparently necessary for the success of the latter reaction, although its role has not been clarified. The (cyclohexenyl)iodonium salt also reacts with sodium thiophenoxide to give the corresponding vinyl phenyl sulfide125,126. 

It has been shown that selective a-vinylation of enolate anions derived from 1,3-dicarbonyl compounds can be achieved by reaction with 4-/-butyl-1 -cyclohcxcnyl-(aryl)iodonium and 1 -cyclopentenyl(aryl)iodonium tetrafluoroborates without competing a-arylation, provided that the alkenyliodonium salt used bears a / -mcthoxyphcnyl, rather than phenyl, group.24... 

In a recent series of studies focused on the synthetic utility of alkenyliodo-nium salts, ( )-/J-phenylethenyl(phenyl)- and ( )-l-hexenyl(phenyl)iodonium tetrafluoroborates, 22 and 23, were utilized for alkenylations of a range of soft, anionic nucleophiles (Scheme 45) [128-135]. In all cases but one, alkenylations with 22 occurred with retention of configuration, while alkenylations with 23 occurred with inversion of configuration. Only the dialkyl phosphoroselenolate salts gave mixtures of (Z)- and (fj)-products with 22 [132]. Furthermore, although cuprous iodide was used to catalyze the reactions of 22 and 23 with the phosphorothioate and -dithioate salts, the stereochemical results were the same [131,133]. It was generally assumed that retention was an outcome of the ligandcoupling or addition-elimination pathways, while stereochemical inversion was attributed to the vinylic... 

Cyclohexenyliodonium salts are moderately stable due to a compromise between the stability of the secondary vinyl cation and the ring strain of the cyclic structure. Solvolysis of 4- -butyl-l-cyclohexenyl(phenyl)iodonium tetrafluoroborate (30) was investigated in various alcoholic and aqueous solutions. The main products are those expected for a cyclohexenyl cation intermediate (31), the enol ether (32) and/or cyclohexanone as well as iodobenzene (Scheme 25). 

DialkyIvinyliodonium salts have a better chance to afford primary vinyl cations than their /3-phenyl counterparts due to the stabilizing effect of j8-alkyl substituents discussed above. Solvolyis of (E)- and (Z)-2-methy 1-5-phenyl-1-pentenyl(phenyl)-iodonium tetrafluoroborate (50) gave a variety of extensively rearranged products, as illustrated in Scheme 32 and summarized in Table 12. ... 

---