Arylalkenes, electrophilic

Palladium salts will attack C-H bonds in functionalised aromatics such as acetoaniline to form palladium-carbon bonds that subsequently undergo insertion of alkenes [31], (3-Hydride elimination gave styryl derivatives and palladium hydride, which requires re-oxidation of palladium by benzoquinone. The reaction can be regarded as a combined Murai reaction (C-H activation, if electrophilic) and a Heck reaction (arylalkene formation), notably without the production of salts as the cross-coupling reactions do. An example is shown in Figure 19.15. 

With arylalkenes, only the coupled alkenes were obtained as ( /Z)-mixtures (Equation 103). If a CHjOAc group was present at the other end of the arylalkene, the reaction took a totally different course, leading to an arylation (Equation 104). These results have been interpreted in terms of the generation of an electrophilic radical on homolysis of the C-I bond. 

Yukawa-Tsuno correlations for electrophilic addition of alkenes 322 Hydration of arylalkenes 322 Bromination of arylalkenes 326... 

Electrophilic addition reactions are some of the most important processes (21) involving a cationic transition state or intermediate. The acid-catalysed hydration of arylalkenes such as styrene [32] is typical of such processes... 

Arylalkene bromination is a typical electrophilic addition to form an a-carbocation, but markedly non-linear structure-reactivity relationships were observed for brominations of styrene [32], trans-stilbene [37] and a-methylstilbene [38] (Ruasse and Dubois, 1972, 1974 Ruasse et al., 1978 Ruasse and Argile, 1983). Some of these curvatures could not be interpreted directly by the Y-T equation but some were related to a mechanistic changeover based on a multipathway scheme (Ruasse, 1990). Three pathways leading to the and carbocations and to the bromonium ion in the bromination of trans-stilbene (Ruasse and Dubois, 1972, 1974) are shown in Scheme 10. 

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