Solvolysis reactions tetrafluoroborate

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... 

Reactions of 3 in alcoholic and aqueous solvents result in a normal solvolysis product 8 (and cyclohexanone 9) as well as the recombination product 6 (eq 4).5 This is again rationalized by an ion-pair mechanism. 2-Methylcyclohex-l-enyl(phenyl)iodonium tetrafluoroborate (10) undergoes solvolysis about 250 times as fast as 3, and gives some rearranged product 12 in accord with the SnI solvolysis mechanism (Scheme 1). 

Photosolvolysis of some vinyl iodonium substrates can be compared with thermal solvolysis of the same substrates. Photochemical reaction of (E)- and (Z)-2-phenylprop-l-enyl(phenyl)iodonium tetrafluoroborate (31) in methanol and TFE gave products of heterolytic cleavage of vinylic C-I bond as summarized in Table III (for the product structures see eq 14.17 In contrast to... 

In the case of nonsymmetrical epoxides, the regioselectivity is determined by the particular reaction conditions. Thus, styrene oxide (6) undergoes methanolysis in the presence of the Lewis acid catalyst copper(II) tetrafluoroborate to give the hydroxy ether 60, derived from attack of the nucleophile at the more substituted oxiranyl carbon. Similar outcomes have been observed in the solvolysis of 6 with the assistance of aminopropyl silica gel (APSG) supported iodine in catalytic quantities <02SL1251>. This selectivity appears to be much less decisive, however, in the case of monoalkyl epoxides, as illustrated in the corresponding reaction of 1-octene oxide (61), which yields an almost 1 1-mixture of isomers under the same conditions <02OL2817>. 

The mechanism of solvolysis of methoxy-substituted diaryliodonium tetrafluoroborates, Arl+Ph Bp4, in methanoi and 2,2,2-trifluoroethanol has been investigated [893]. The solvolysis products include alkox-ide substitution products (ArOR and PhOR) as well as iodoarenes (Phi and Arl). The ratios of products, ArOR/PhOR, range from 8 2 to 4 6. The results of this study provide experimental evidence against the formation of aryl cation under these conditions and support the pathways via ligand coupling or 5nAt2 mechanisms involving a solvent molecule as a nucleophile in the transition state [893]. If the reaction is performed in inert (not nucleophilic) solvent, various nucleophiles may be involved in the reaction with iodonium salt. 

To understand the results obtained in the acetolysis of ii-styryl(phenyl)iodo-nium tetrafluoroborate 1 is a bit more complicated. As we can see in Scheme 35.1, the reaction affords a mixture of retained (3E) and inverted (3Z) solvolysis (substitution) products, together with iodobencene (the leaving group) and phenylace-tylene (clearly an elimination product). It is almost impossible to formulate a single mechanism that could explain the formation of all the reaction products. In consequence, several mechanistic pathways should be considered in this case. 

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