Vinyliodonium halides formation

Anion exchange between (E)-1 -decenyl(phenyl)iodonium tetrafluoroborate and TB AC1 occurs instantaneously in CDC13 at room temperature, while addition of the authentic chloride salt to dichloromethane (rt) affords a 45 55 mixture of (Z)-l-chlorodecene and 1-decyne146. Thus, the reactions shown in equations 206-208 are thought to involve the initial formation of vinyliodonium halides which then give rise to the observed products. 

Substitution. Because haloalkene formation (equation 206) proceeds with inversion instead of retention, these reactions are deemed inconsistent with the Ad-E manifold146. A bimolecular S -like process between the vinyliodonium halides and TBAX, facilitated by the exceptional leaving ability of iodobenzene, has been proposed (equation 210)84,146. 

In order to strengthen evidence in favour of the proposition that concerted inplane 5n2 displacement reactions can occur at vinylic carbon the kinetics of reactions of some /3-alkyl-substituted vinyliodonium salts (17) with chloride ion have been studied. Substitution and elimination reactions with formation of (21) and (22), respectively, compete following initial formation of a chloro-A, -iodane reaction intermediate (18). Both (17) and (18) undergo bimolecular substitution by chloride ion while (18) also undergoes a unimolecular (intramolecular) jS-elimination of iodoben-zene and HCl. The [21]/[22] ratios for reactions of (18a-b) increase with halide ion concentration, and there is no evidence for formation of the -isomer of (Z)-alkene (21) iodonium ion (17d) forms only the products of elimination, (22d) and (23). 

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