Alkenylbenzenes reactions

The reaction of diolefins with aromatics is similar to that of styrenes with aromatics. Hoffman and Michael (44) reported that toluene and various conjugated diolefins could be reacted at 60-90 in the presence of sodium to yield alkenylbenzenes [Reaction (25)]. 

Most of the reactions of alkenes that were discussed in Chapter 6 find a parallel in the reactions of alkenylbenzenes... 

Section 11 16 Addition reactions to alkenylbenzenes occur at the double bond of the alkenyl substituent and the regioselectivity of electrophilic addition is governed by carbocation formation at the benzylic carbon See Table 11 2... 

Reactions involving benzylic cations, benzylic radicals, and alkenylbenzenes will be discussed in Sections 11.12 through 11.17. 

Problem 16.21 Styrene, the simplest alkenylbenzene, is prepared commercially for use in plastics manufacture by catalytic dehydrogenation of ethylbenzene. How might you prepare styrene from benzene using reactions you ve studied ... 

The primary allylic carbanion apparently predominates and reacts with aromatic to yield the alkenylbenzene and regenerate the benzylic carbanion [Reaction (27)]. 

Only a few examples of alkenylbenzene hydroformylation are available. Styrene and a-methylstyrene were reported to lead to hydrogenation as the main reaction when Co2(CO)8 was used. 

An overview of the reactions over zeolites and related materials employed in the fields of refining, petrochemistry, and commodity chemicals reviewed the role of carbocations in these reactions.15 An overview appeared of the discovery of reactive intermediates, including carbocations, and associated concepts in physical organic chemistry.16 The mechanisms of action of two families of carcinogens of botanical origin were reviewed.17 The flavanoids are converted to DNA-reactive species via an o-quinone, with subsequent isomerization to a quinone methide. Alkenylbenzenes such as safrole are activated to a-sulfatoxy esters, whose SnI ionization produces benzylic cations that alkylate DNA. A number of substrates (trifluoroacetates, mesylates, and triflates) known to undergo the SnI reaction in typical solvolysis solvents were studied in ionic liquids several lines of evidence indicate that they also react here via ionization to give carbocationic intermediates.18... 

In a similar way, alkenyl benzenes undergo the other addition reactions characteristic of the carbon-carbon double bond. Let us look further at the reactions of conjugated alkenylbenzenes, and the way in which the ring affects orientation and reactivity,... 

Addition of an unsymmetrical reagent to a double bond may in general yield two different products. In our discussion of alkenes (Secs. 6.11 and 6.17), we found that usually one of the products predominates, and that we can predict which it will be in a fairly simple way in either electrophilic or free-radical addition, the first step takes place in the way that yields the more stable particle, carbonium ion in one kind of reaction, free radical in the other kind. Does this rule apply to reactions of alkenylbenzenes ... 

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