Vinylation of aromatics

The reaction sequence in the vinylation of aromatic halides and vinyl halides, i.e. the Heck reaction, is oxidative addition of the alkyl halide to a zerovalent palladium complex, then insertion of an alkene and completed by /3-hydride elimination and HX elimination. Initially though, C-H activation of a C-H alkene bond had also been taken into consideration. Although the Heck reaction reduces the formation of salt by-products by half compared with cross-coupling reactions, salts are still formed in stoichiometric amounts. Further reduction of salt production by a proper choice of aryl precursors has been reported (Chapter III.2.1) [1]. In these examples aromatic carboxylic anhydrides were used instead of halides and the co-produced acid can be recycled and one molecule of carbon monoxide is sacrificed. Catalytic activation of aromatic C-H bonds and subsequent insertion of alkenes leads to new C-C bond formation without production of halide salt byproducts, as shown in Scheme 1. When the hydroarylation reaction is performed with alkynes one obtains arylalkenes, the products of the Heck reaction, which now are synthesized without the co-production of salts. No reoxidation of the metal is required, because palladium(II) is regenerated. 

Some intermediates to fine chemicals are prepared industrially by vinylation of aromatics. We have selected three well-known products as representative cases, namely an intermediate to Naproxen, a non-steroidal antirheumatic drug (Albermarle) (Equation 11) an intermediate to Prosulfuron, a potent herbicide (Ciba Geigy-Novartis) (Equation 12) and a monomer for polymerization to Cyclotene electronic resins (Dow Chemicals) (Equation 13). 

This method permits vinylation of aromatic compounds. In the isoflavanone synthesis, 4-chromanone (44) is converted to the enol ester 45, which is reacted with phenylpalladium acetate, formed in situ from phenylmercury chloride and Pd(OAc)2, to give — after hydrolysis - isoflavanone (46) (Schema 15). A simple synthesis of... 

The Rh-catalyzed reaction of aryl- and vinylsilanediols with internal alkynes in aqueous solvent gives hydroarylation and hydrovinylation products, respectively (Scheme 10.216) [561]. It has been proposed that this reaction occurs via carborho-dation of an aryl- or vinylrhodium intermediate to an alkyne then protonation with the silanediol. Arylation and vinylation of aromatic aldehydes with organosilicon reagents can also be achieved in Rh-catalyzed systems (Scheme 10.216) [560, 562]. 

Sims, V.A. 1962. Vinylation of aromatic heterocyclic nitrogen compounds. US Patent... 

Thallation of aromatic compounds with thallium tris(trifluoroacetate) proceeds more easily than mercuration. Transmetallation of organothallium compounds with Pd(II) is used for synthetic purposes. The reaction of alkenes with arylthallium compounds in the presence of Pd(Il) salt gives styrene derivatives (433). The reaction can be made catalytic by use of CuCl7[393,394], The aryla-tion of methyl vinyl ketone was carried out with the arylthallium compound 434[395]. The /9-alkoxythallium compound 435, obtained by oxythallation of styrene, is converted into acetophenone by the treatment with PdCh[396]. 

Similarly, the addition of low quantities of vinyl or polyvinylthiazoles in the synthesis of aromatic polyesters increases the rate of polymerization (315). 

When aiomatics aie present, they can capture the intermediate vinyl cation to give P-aryl-a,P-unsatutated ketones (182). Thus acylation of alkyl or aryl acetylenes with acyhum salts in the presence of aromatics gives a,P-unsaturated ketones with a trisubstituted double bond. The mild reaction conditions employed do not cause direct acylation of aromatics. 

In order to increase the solubiUty parameter of CPD-based resins, vinyl aromatic compounds, as well as other polar monomers, have been copolymerized with CPD. Indene and styrene are two common aromatic streams used to modify cyclodiene-based resins. They may be used as pure monomers or contained in aromatic steam cracked petroleum fractions. Addition of indene at the expense of DCPD in a thermal polymerization has been found to lower the yield and softening point of the resin (55). CompatibiUty of a resin with ethylene—vinyl acetate (EVA) copolymers, which are used in hot melt adhesive appHcations, may be improved by the copolymerization of aromatic monomers with CPD. As with other thermally polymerized CPD-based resins, aromatic modified thermal resins may be hydrogenated. 

Hydrogen bromide adds to acetylene to form vinyl bromide or ethyHdene bromide, depending on stoichiometry. The acid cleaves acycHc and cycHc ethers. It adds to the cyclopropane group by ring-opening. Additions to quinones afford bromohydroquinones. Hydrobromic acid and aldehydes can be used to introduce bromoalkyl groups into various molecules. For example, reaction with formaldehyde and an alcohol produces a bromomethyl ether. Bromomethylation of aromatic nuclei can be carried out with formaldehyde and hydrobromic acid (6). 

Cross-coupling reactions of aromatic or vinylic halides and olefins catalyzed by palladium. 

With each succeeding year in the 1950s and 1960s there was a swing away from coal and vegetable sources of raw materials towards petroleum. Today such products as terephthalic acid, styrene, benzene, formaldehyde, vinyl acetate and acrylonitrile are produced from petroleum sources. Large industrial concerns that had been built on acetylene chemistry became based on petrochemicals whilst coal tar is no longer an indispensable source of aromatics. 

Carboxylic acids react with xenon difluoride to produce unstable xenon esters The esters decarboxylate to produce free radical intermediates, which undergo fluonnation or reaction with the solvent system Thus aliphatic acids decarboxylate to produce mainly fluoroalkanes or products from abstraction of hydrogen from the solvent Perfluoro acids decarboxylate in the presence of aromatic substrates to give perfluoroalkyl aromatics Aromatic and vinylic acids do not decarboxylate [91] (equation 51)... 

An interesting class ot covalent Inflates are vin l and ar>/ or heteroaryl Inflates Vinyl inflates are used for the direct solvolytic generation of vinyl cations and for the generation of unsaturated carbenes via the a-elimination process [66] A triflate ester of 2-hydroxypyridine can be used as a catalyst for the acylation of aromatic compounds with carboxylic acids [109] (equation 55)... 

Much of the difference in chemical shift between aromatic protons (6.5-8.0 8) and vinylic protons (4.5-6.5 5) is clue to a property of aromatic... 

The value of CM has been determined by a number of groups as 6x 10 5 (Table 6.14.1. " However, the mechanism of transfer has not been firmly established. A mechanism involving direct hydrogen abstraction seems unlikely given the high strength of vinylic and aromatic C-M bonds. The observed value of Cy is only slightly lower than Ctr for ethylbenzene ( 7x 10"5). w... 

This section will describe the Friedel-Crafts alkylation reactions of aromatic hydrocarbons with alkenylchlorosilanes containing short chain alkenyl groups such as allyl and vinyl. The reaction will be discussed in terms of the substituent effect on silicon and the arene rings. 

A layer of poly (vinyl alcohol) forms a gel when treated with aqueous alkaline solutions of acylacetamides of aromatic amines which have an unsubstituted methylene group between the two carbonyl groups 29). Several examples are illustrated in Figure 5. 

Bfx, Fx, and related compoimds are the subject of a great munber of invention patents especially related to its uses in material sciences. For example, they were included in the formiflation as rubber additives [245,246], as inhibitors in the polymerization of aromatic vinyl monomers [247], as components in the igniting composition for inflation of airbags [248,249], as explosives [250-253], as soHd propellants [254], as burn-rate modifiers [255], and as liquid-crystalHne materials [256]. 

The asymmetric Baylis-Hillman reaction of sugar-derived aldehydes as chiral electrophiles with an activated olefin in dioxane water (1 1) proceeded with 36-86% de and in good yields of the corresponding glycosides (Eq. 10.47).104 The use of chiral /V-mcthylprolinol as a chiral base catalyst for the Baylis-Hillman reaction of aromatic aldehydes with ethyl acrylate or methyl vinyl ketone gave the adducts in good yields with moderate-to-good enantioselectivities in l,4-dioxane water (1 1, vol/vol) under ambient conditions.105... 

Addition of Vinyl and Aryl Groups. The reaction of aromatic radicals, generated by decomposition of diazonium salts, with iminium salts in the presence of TiCE in aqueous media produces secondary amines (Eq. 11.53).91 The iminium salts are formed in situ from aromatic amines and aldehydes. 

Another important click reaction is the cycloaddition of azides. The addition of sodium azide to nitriles to give l//-tetrazoles is shown to proceed readily in water with zinc salts as catalysts (Eq. 11.71).122 The scope of the reaction is quite broad a variety of aromatic nitriles, activated and nonactivated alkyl nitriles, substituted vinyl nitriles, thiocyanates, and cyanamides have all been shown to be viable substrates for this reaction. The reaction of an arylacetylene with an azide in hot water gave 1,4-disubstituted 1,2,3-triazoles in high yields,123 while a similar reaction between a terminal aliphatic alkyne and an azide (except 111 - nitroazidobenzcnc) afforded a mixture of regioisomers with... 

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