Vinyliodonium halides reactions

The production of the (Z)-haloalkenes is thought to proceed via initial exchange of the tetrafluoroborate and halide ions and collapse of the resulting vinyliodonium halides by the addition-elimination (Ad-E) mechanism (equations 203 and 204)84. As with Ad-E reactions of moderately activated vinyl halides (X = Cl, Br), which typically occur with configurational retention (> 95%)143 145, the intermediate carbanions apparently prefer a least motion rotation of 60° prior to the expulsion of iodobenzene. It has been demonstrated by an NMR study that anion exchange between (Z)-(2)-phenylsulfonyl-l-decenyl)-phenyliodonium tetrafluoroborate and tetrabutylammonium chloride occurs instantaneously in deuteriochloroform84. Furthermore, when authentic halide salts of the... 

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). 

Two examples of Pd(II)-catalyzed carbomethoxylations of vinyl(phenyl)iodonium salts have been reported (equations 251 and 252)125,126. The mild reaction conditions and stereospecificity of carbonylation recommend further applications of vinyliodonium compounds for the synthesis of a,/ -unsaturated carboxylate esters. By way of comparison, similar carbobutoxylations of vinyl halides (Br, I) typically require higher temperatures (60-100 °C) and longer reaction times, and they sometimes proceed with low stereospecificity151. 

Thermal decomposition of vinyliodonium salts (39) leads to the halide derivatives (40). jn the case of substituted vinyliodonium salts such as propenyliodonium salts (41), thermolysis gave the product of inversion of configuration (42). However, reaction with copper chloride at room temperature afforded by contrast the chloroalkene (43) with retention of configuration. 

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