Olefination of arenes

Myers AG, Tanaka D, Mannion MR (2002) Development of a decarboxylative palladation reaction and its use in a Heck-type olefination of arene carboxylates. J Am Chem Soc 124 11250-11251... 

Tanaka D, Romeril ASP, Myers AG (2005) On the mechanism of the palladium(II)-catalyzed decarboxylative olefination of arene carboxylic acids. Crystallographic characterization of non-phosphine palladium(II) intermediates and observation of their stepwise transformation in Heck-like processes. J Am Chem Soc 127 10323-10333... 

Even though not (yet) among the typically employed reactions for the production of materials, C-H olefinations of arenes are a valuable, more sustainable alternative for the synthesis of olefin-substituted arenes. C-H olefinations are among the first C-H functionalizations ever reported [65], and the originally stoichiometric modifications of simple arenes with olefins in the presence of Pd" have initiated broad research efforts. To this day, C-H alkenylations are more common using aromatic substrates without directing groups [18], and these reactions will be addressed in the next chapter of this book. However, several examples of chelate-assisted C-H olefinations are known [30, 66-74], which exhibit excellent ortho-selectivity. 

The utility of the Heck reaction in its many forms has been extensively studied for the construction of useful synthons and complex molecules. Advances in C—H functionalization have enabled the synthesis of Heck products directly from unactivated arenes via Pd(II) catalysis. Olefination of electron-rich and -deficient arenes has been reported. Approaches to olefination of arenes have included directed olefination with haloolefins. ... 

Mechanism proposed by Mural for the ortho-directed olefination of arenes... 

The Fujiwara-Moritani reaction enables the coupling of alkenes with arenes under oxidative conditions—also named oxidative Heck reaction (for the mechanism, see Ref [ 29]) Garcia-Rubia et al. used this Pd"-catalyzed oxidative direct C-H alkenylation to produce /rans-stilbene derivatives.As exemplified by their synthesis of pterostilene (Scheme 5-45), a partially methylated resveratrol derivative, a 2-pyridyl sulfinyl group efficiently promotes the Pd"-catalyzed ortho C-H olefination of arenes and can be readily removed or transformed into a thiol group. 

The remarkable generality of FERET to predict the behavior of Br2 in aromatic bromination as well as in olefin addition is established by the single linear correlation in Fig. 21b when the solvation difference (see equation (103)) between the cation radicals of arene and olefin donors is taken into account.263... 

The synthetic applications 440) and mechanistic aspects 4411 of intermolecular photocycloaddition reactions of arenes to olefins have been reviewed recently. Intramolecular cycloadditions442a,b) have been studied in the context of the photochemical behaviour of bichromophoric molecules, as to investigate interchromophoric interactions in polyfunctional molecules. Three types of addition products can be formed in the photocycloaddition of benzene to an alkene (4.37)441. ... 

The uniqueness of the intramolecular 1,3-photocycloaddition of arenes to olefins with the developement of three new rings and up to six stereocentres has been efficiently demonstrated in the synthesis of (+)-a-cedrene from the... 

The first systematic investigations of the catalytic Friedel-Crafts-type reaction with alcohols and olefines were performed by Yamamoto and colleagues. After reporting the development of a Pd-catalyzed method for the allylation of different naphthol derivatives [24], the authors used Mo(CO)g for the Friedel-Crafts-type alkylation of electron-rich arenes with allyl acetates [25], The same molybdenum catalyst was additionally used for a Friedel-Crafts-type alkylation of arenes using 1-phenylethanol and styrene as alkylating reagents [26], However, Mo(CO)g is toxic and must be handled under strictly inert conditions. Thus, more stable Lewis acids were necessary. 

When an alkene is used in the alkylation of arenes, metal halides with hydrogen halide or water as cocatalyst, protic acids, and acidic oxides can be used as catalysts. Both linear and cyclic alkenes are used in alkylations. Alkylation with alkenes is usually preferred in industry because the processes are simpler and olefins are readily and cheaply available in pure form from petroleum refining processes. 

Some of the reagents used in olefin epoxidation can be applied in the direct oxidation of arenes to arene oxides. Benzene oxide, however, like other arene oxides, exists in equilibrium with oxepin, its valence tautomer, and has not been isolated. Existence of benzene oxides as intermediates can be concluded from observations like the NIH shift discussed above.752,753... 

Burke discussed recently that for easily oxidizable substances, such as alcohols and amines, the redox potentials of Table II might be irrelevant, as incipient formation of oxidic layers at lower oxidation potentials and not the bulk oxide may already cause the observed oxidative conversion (189). Nonetheless, for substances that are less easily oxidized for instance, olefines or arenes, the given redox potentials are certainly relevant with respect to the rate of their mediated oxidation. 

The most simple combination of arene and alkene, benzene + ethene, was studied by Mirbach et al. [114], Their experiments were carried out in a UV autoclave fitted with a low-pressure mercury lamp under elevated olefin pressure in various solvents. The major product was the meta photocycloadduct, tricyclo[3.3.0.02,8]oct-3-ene. After short irradiation times, the major side products... 

Study of the reactivity of aromatic C-H bonds in the presence of transition metal compounds began in the 1960s despite the quite early discovery of Friedel-Crafts alkylation and acylation reactions with Lewis acid catalysts. In 1967, we reported Pd(II)-mediated coupling of arenes with olefins in acetic acid under reflux [1], The reaction involves the electrophilic substitution of aromatic C-H bonds by a Pd(II) species, as shown in Scheme 2, and this is one of the earliest examples of aromatic C-H bond activation by transition metal compounds. Al-... 

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