X3-Iodanes

The reactions involved are unimolecular, and the cyclohexenyl derivative 3 undergoes solely the spontaneous heterolysis while both spontaneous heterolysis and ligand coupling occur with the iodane 14. The relative contributions of the two reactions of 14 depend on the solvent polarity. The results summarized in Table I show that the iodonium ion and the counteranion are in equilibrium with the hypervalent adduct, X3-iodane. The equilibrium constants depend on the identity of the anion and the solvent employed, and the iodane is less reactive than the free iodonium ion as the k /k2 raios demonstrate. Spontaneous heterolysis of 3 occurs more than 100 times as fast as th t of the adduct 14 as observed in methanol the leaving ability of the iodonid group is lowered by association by more than 100 times. 

Structure 1 1 10-1-3 chloro(diphenyl)-X3-iodane 2 8-I-2 diphenyliodonium chloride... 

Vinyliodonium ions, 35 and 36, are hypervalent iodine species in which one or two alkenyl ligands are bound to a positively charged iodine(III) atom. Although they are reactive with nucleophilic reagents, they are less labile than alkynyliodonium ions, and stable halide salts of vinyliodonium ions can be prepared. The first vinyliodonium compounds [i.e. (a, / -dichlorovinyl)iodonium salts] were synthesized by the treatment of silver acetylide-silver chloride complexes with (dichloroiodo)arenes or l-(dichloroiodo)-2-chloroethene in the presence of water (equation 152). The early work was summarized by Willgerodt in 1914115. This is, of course, a limited and rather impractical synthetic method, and some time elapsed before the chemistry of vinyliodonium salts was developed. Contemporary synthetic approaches to vinyliodonium compounds include the treatment of (1) vinylsilanes and vinylstannanes with 23-iodanes, (2) terminal alkynes with x3-iodanes, (3) alkynyliodonium salts with nucleophilic reagents and (4) alkynyliodonium salts with dienes. 

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