Vinyl iodonium salts solvolysis

The focus of Chapters 3 and 4 is on vinyl cations. In Chapter 3, T. Muller et al. discuss the preparation, isolation, and characterization of unusually stable vinyl cations whereas Chapter 4 by T. Okuyama and M. Fujita describes the generation and reactions of vinyl cations formed via solvolysis of vinyl iodonium salts. 

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... 

Previously, we have discussed that the inversion of the stereoehemistry in the solvolysis product of vinyl iodonium salt 2 could be explained by an in-plane S 2 vinylic substitution. The same arguments can be employed now to explain how the minor isomer 6Z is formed (Scheme 35.6). Direct attack of acetic acid to the a-carbon should lead to the observed reaction product in a one-step proeess through transition state 9. The position of the deuterium atom should not change (no scrambling), only the stereochemistry of the product has been reversed during the reaction. 

Although formation of primary vinyl cation was disproved by the chirality probe approach, a vinyl cationic intermediate can be generated from a primary substrate via participation if a more stable cation could result. Unsymmetrically substituted 2,2-dialkylvinyl iodonium salt 24 gave mainly rearranged products on solvolysis.15 The products involve those of the 1,2-shift of either of the alkyl groups on the p position (Scheme 4). Those formed from migration of the alkyl... 

Photosolvolysis of ( )-styryl iodonium salt 26 also gave product distributions quite different from those obtained in thermal solvolysis.16,23 Quantum yields for the formation of photoproducts formed via heterolytic cleavage of the vinylic C-I bond of 26 in methanol and TFE at 20 °C are given in eq 20.23... 

As discussed in the previous sections, the thermal solvolysis reactions of alkenyl iodonium salts usually occur via trans j8-phenyl- or trans j8-alkyl-assisted departure of the iodobenzene leaving group, by in-plane vinylic Sn2 substitution or by ligand... 

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). 

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