Vinylidene-iodonium ylides

The treatment of alkynyliodonium salts not amenable to cyclopentene formation with sodium azide in methanol affords vinyliodonium salts and/or enol ethers (equation 107)". Enol ether formation also occurs when glyme is employed as the solvent (equation 108)". Finally, regeneration of the vinylidene-iodonium ylide, PhC (N3)=C—IPh, from (Z)-(/ -azido-/ -phenylvinyl)phenyliodonium tosylate with potassium J-butoxide in glyme likewise affords an enol ether (equation 109). 

In view of their capacity for Michael reactions with nucleophiles to give intermediate vinylidene-iodonium ylides, alkynyliodonium ions might be expected to behave as 1,3-dipolarophiles. Cycloadducts in which the nucleophilic end of the dipole is bound to the / -carbon atom of the starting alkynyliodonium ion (i.e. the / -adduct) might also be anticipated (equation 136). 

As discussed in Section II.D, the ability of alkynyliodonium salts to undergo Michael additions with nucleophilic reagents provides access to / -functionalized vinyliodonium salts (equation 177). However, this approach will not succeed unless the intermediate vinylidene-iodonium ylides can be captured by protonation. Thus, the best results are obtained when the nucleophile bears an acidic hydrogen or when the reactions are conducted in an acidic medium. 

The a-carbon-hydrogen bonds of vinyl(phenyl)iodonium ions are relatively acidic, two examples of base catalyzed hydrogen-deuterium exchange in -oxavinyliodonium salts having been reported (equations 227 and 228)79,95. Although vinylidene-iodonium ylides... 

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