Aromatic compounds, addition benzylic

The reaction has been applied to nonheterocyclic aromatic compounds Benzene, naphthalene, and phenanthrene have been alkylated with alkyllithium reagents, though the usual reaction with these reagents is 12-20, and Grignard reagents have been used to alkylate naphthalene. The addition-elimination mechanism apparently applies in these cases too. A protected form of benzaldehyde (protected as the benzyl imine) has been similarly alkylated at the ortho position with butyl-lithium. ... 

Recently, Behiman and coworkers discussed the mechanism of the Elbs oxidation reaction and explained why the para product predominates over the ortho product in this oxidation. According to the authors, semiempirical calculations show that the intermediate formed by the reaction between peroxydisulfate anion and the phenolate ion is the species resulting from reaction of the tautomeric carbanion of the latter rather than by the one resulting from the attack by the oxyanion. This is confirmed by the synthesis of the latter intermediate by the reaction between Caro s acid dianion and some nitro-substituted fluorobenzenes. An example of oxidative functionalization of an aromatic compound is the conversion of alkylated aromatic compound 17 to benzyl alcohols 20. The initial step in the mechanism of this reaction is the formation of a radical cation 18, which subsequently undergoes deprotonation. The fate of the resulting benzylic radical 19 depends on the conditions and additives. In aqueous solution, for example, further oxidation and trapping of the cationic intermediate by water lead to the formation of the benzyl alcohols 20 (equation 13) . ... 

Aromatic Compounds.—A number of 2,3-dihydroxyoestra-l,3,5(10)-trienes have been prepared from the corresponding 2-amino-3-hydroxy-compounds using a novel inverse oxidation procedure followed by reduction with KI. Addition of the substrate to sodium metaperiodate in high dilution ensures no coupling with the intermediate quinonimines. 2-Bromo-oestradiol was readily converted into 2-methoxyoestradiol by treatment with NaOMe-MeOH-DMF-CuI. Novel preparations of the biologically interesting 11/3-methyl- and 11/3-ethyl-oestradiol have been reported in full. The key intermediates were the 11-oxo-oestradiol 3-benzyl ether (82) and its 9/3-epimer (83). The latter was derived from the 9,H-epoxides (81) by treatment with KOH followed by benzylation. The thermodynamically unstable 9a-epimer (82) was prepared from the 9j8-epimer (83) by... 

The second important use of superbases is side-chain alkylation of aromatic compounds [22, 34]. In these reactions a benzyl anion generated by the superbase catalyst subsequently attacks olefins such as ethene or propene as a nucleophile. The result of such a nucleophilic addition of a carbanion is side-chain alkylation of the arene by ethene. The reaction was commercialized by Sumitomo for the side-chain alkylation of cumene (Scheme 5, a) [34]. 

The O radical abstracts hydrogen from aliphatic compounds relatively rapidly (but about a factor of two more slowly than OH) while it adds to olefinic and aromatic compounds very slowly, if at all. E.s.r. experiments have demonstrated that the reaction of O" with toluene or crotonate leads predominantly to the radicals formed by abstraction and not by addition (Neta et al., 1972) as shown by reactions (26) and (27) above. These findings have since been used for the production of radicals by abstraction from compounds which tend normally to add. For example, a series of substituted benzyl radicals have been produced by reaction of O with substituted toluenes (Neta and Schuler, 1973). 

Treatment of saturated azlactones with aromatic compounds under Friedel-Crafts conditions gives acylamino ketones in high yield (equation 46). 4-Benzyl-2-methyl-5(4H)-oxazolone undergoes an intramolecular reaction to yield an acetamidoindanone (equation 47). Friedel-Crafts reactions of 4-(arylmethylene)-5(4H)-oxazolones are complicated by the presence of an additional electrophilic centre (cf. 201) and may follow three courses. The unsaturated azlactone (189) adds benzene under the influence of aluminum chloride to form the saturated azlactone (207) in inert solvents (189) undergoes an intramolecular acylation to yield a mixture of the indenone (208) and the isoquinoline (209 Scheme 20). 

The first kinetic study of the Friedel-Crafts alkylation reaction was repotted by Brown and Grayson in 1953. This involved the reactions of some substituted benzyl halides with aromatic compounds in the presence of AlClj-PhNOa catalyst. The transition state for the rate-determining step (attack of the aromatic component on a polar alkyl halide-AlCb addition compound) was depicted as a o -complex. 

Figure 19 shows the LAMMA 1000 positive spectra of Irganox 1010 (Clba Geigy a high molecular weight (1176), multifunctional anti-oxidant and thermal stabilizer. The LAMMA matches the EI spectra well, with the LAMMA giving additional information the t-butyl, phenyl and benzyl ions suggest an aromatic compound. 

This methodology has been elegantly utilized as a key step in a total synthesis of the antitumor antibiotic fredericamycin (Scheme 40) [80]. Thus, 1-azadiene 225 was found to react with olefin 226 to yield adduct 227 as a 1 1 mixture of stereoisomers. This compound could then be aromatized to pyridine 228. In an interesting transformation, 4-methylpyridine 228 reacts with cyclopentenone via an initial Michael addition, followed by a Claisen condensation, to afford tricycle 229. This compound could be aromatized and O-benzylated to produce ketone 230, which was homologated to nitrile ester 231. The ester functionality of 231 could be transformed to ,E-diene 232. It was then possible to utilize this DEF fragment in a sequence leading to fredericamycin. 

When RX is easily reduced, as in the case of allyl iodides and benzyl bromides, the competing further reduction of the intermediate radical is suppressed and radical reactions such as dimerization, addition to double bonds and aromatic compounds or reaction with anions can be favored. The radical pathway can be also promoted by catalysis with reduced forms of vitamin Bn, cobaloximes or nickel complexes. These react with the alkyl halide by oxidative addition and release the alkyl radical by homolytic cleavage. 

A novel ring-opening reaction of oxirans, catalysed by copper and pyridine, generates c/s-diols under mild conditions. The bicyclic epoxides (186 = 1 or 2) yield (187 n = 1) (95%) and (187 = 2) (85%) in neutral, phosphate-buffered, solution. This type of reaction may have some relevance to the metabolic pathways for fused aromatic compounds, which are thought to proceed via arene oxides and diol epoxides. The catalyst system may be used to add OH", Cr, or MeO regiospecifically to the benzylic centre of indene oxide, with proton addition to the oxygen atom of oxiran. 

Metal-arene n-complexes show a rich and varied chemistry. The metal adds a third dimension to the planar aromatic compounds and the two faces of an arene with different ortho or raefa-substituents are enantiotopic. Therefore, coordination of a metal to an arene not only alters the reactivity of ring-carbons and substituents as well as groups in benzylic positions but, in addition, also allows reactions with high stereoselectivities to be carried out. The aim of this book is to provide a coherent picture of the state-of-the-art in this field. It covers the entire spectrum of arene activation from the electrophilic activation of a q -bound... 

Electrophilic quench of aryllithium species with carbonyl electrophiles is particularly efficient. However, alkyl halides (other than iodomethane) are poor electrophiles, probably owing to competing elimination reactions (see Section 2.1). The formation of alkyl-substituted aromatic compounds can be achieved, however, by using epoxide electrophiles or by lithiation and reaction of 2-methylbenzamides, themselves generated by orr/ o-lithiation. For example, the benzamide 128 can be deprotonated at the benzylic position and treated with a variety of electrophiles. Addition of aromatic aldehydes gives, after lactonization, 3-aryl-3,4-dihydroisocoumarins (1.119). 

Benzylic Bromination of Aromatic Compounds. An efficient and fast microwave-assisted method for the preparation of benzylic bromides has appeared The 2-trimethylsilylethyl substituent on the benzenoid ring of 3 undergoes benzylic bromination followed by elimination of MesSiBr and addition of bromine to produce the dibromo compound (4) (eq 31). The ketone (5) is also observed from the hydrolysis of (4). ... 

It was found that aromatic imide and amide forming components with a functionality of more than two yield products that are soluble in cresol." Additives for wire enamels are phenolic resins, melamine resins, fluori-nated compounds, or, benzyl alcohol. Crosslinking catalysts are zinc oc-toate, cadmium octoate, or titanates, such as tetrabutyl titanate. Extenders are xylene, toluene, ethylbenzene, or cumene, and commercial available similar compounds. 

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