Arene derivatives arylation

Condensation of aryl halides with various active methylene compounds is readily promoted by catalytic action of palladium to give the corresponding arene derivatives containing a functionalized ethyl group [7]. Yamanaka et al. extended this chemistry to haloazoles including oxazoles, thiazoles and imidazoles [8]. Thus, in the presence of Pd(Ph3P)4,2-chlorooxazole was refluxed with phenylsulfonylacetonitrile and NaH to form 4,5-diphenyl-a-phenylsulfonyl-2-oxazoloacetonitrile, which existed predominantly as its enamine tautomer. In a similar fashion, 4-bromooxazole and 5-bromooxazole also were condensed with phenylsulfonylacetonitrile under the same conditions. 

Decarboxylative rearrangement. Trimethylsilyl benzoates undergo this radical reaction with XeFj in CHjClj. Interestingly, the reaction in MeCN does not proceed with rearrangement, and the main products are arenes derived from aryl radicals. 

Scheme 8.6 Pd-catalyzed oxidative esterification of arenes to aryl esters and phenol derivatives.

Yasuda and Pac and their co-workers " have significantly extended the scope of ET-sensitized addition in their studies of the photoamination reactions of arenes and aryl olefins (Scheme 2). DCNB is a powerful electron acceptor (Table 1) capable of oxidizing the singlet slates of most arenes and aryl olefins (Table 2). Benzene does not undergo photoamination however a di-methoxy derivative and biphenyl are reactive. Photoamination products are generally obtained in high preparative yield using ammonia or primary amines however, secondary amines can only be used successfully with arenes such as anthracene which have oxidation potentials lower than those of secondary amines. When the amine oxidation potential is comparable to... 

In contrast to the diaryl-1,10-phenanthrolines 2. the calix[6]arene derivatives 3 contain an oxygen atom and a methylene group between the aryl bridgehead and the... 

Photochemistry offers a convenient access to the formation of aryl—alkyl bonds under mild reaction conditions. This can be accomplished either via fragmentation of an aromatic derivative to produce a trappable aryl radical or aryl cation as intermediate, or via the activation of an aliphatic component that then reacts with the arene derivative. 

We use the term arene to describe aromatic hydrocarbons, by analogy with alkane and alkene. Benzene is the parent arene. Just as we call a group derived by the removal of an H from an alkane an alkyl group and give it the symbol R—, we call a group derived by the removal of an H from an arene an aryl group and give it the symbol Ar—. 

As already mentioned, the C-H/C-X coupling between simple arenes and aryl halides to form biphenyl derivatives is difficult in terms of reactivity and regiose-lectivity without directing group. In 2004, Fujita and Yamaguchi [28] reported the iridium-catalyzed direct arylation of benzene with aryl iodides. For example, when the reaction was carried out in the presence of the [Cp IrHCl]2 catalyst (5mol%) and KOt-Bu (3.3 equiv.) at 80°C, 4-methoxybiphenyl 34 was obtained in 66% yield. However, when substituted arenes were used instead of benzene, several... 

Reaction with Arenes. Benzenesulfonyl bromide reacts readily with trifluoromethanesulfonyl derivatives, yielding the corresponding mixed anhydrides (eq 6) which have been used to convert arenes to aryl phenyl sulfones under Friedel-Crafts-type conditions. 

Oxazoline was shown to be an efficient directing group for arylation of arene derivatives with Ru(II) catalyst [(Eq. 5)] [61], A -Acylimidazole was also shown to be a directing group promoting ortho monoarylation of arene. Ort/io-alkenylation of 2-phenyl oxazoline with alkenylbromide was performed using the same mthe-nium(II) catalyst [61]. 

Recently, Shinkai et al [20] studied PVC membrane electrodes based on the calix[4]arene derivative and reported that the p-t rt-octyl-calix[4]aryl tetraethyl ester-FPNPE system electrode allowed high Na" selectivity. The Na selectivity coefficient being 3.1 [20], though its value was not evaluated by a fixed interference method (FIM). Its excellent Na selectivity compared with those of our similar derivative, p-rerr-octylcalix[4]aryl tetradecyl ester [6,21], is probably derived from the introduction of shorter alkyl groups such as the ethyl ester and tert-oct group into the upper rim moiety to produce lipophilicity, as already mentioned. 

Direct arylation of arene derivatives with aryl iodides and bromides proceeds in the presence of catalytic amounts of iron(II) acetate and bathophenanthroline (Scheme 4-228, Table 4-1). ... 

If aryl azides are irradiated in acidic medium in the presence of arenes, derivatives of diphenylamine are formed." For the diphenylnitrenium ion, G-complexes with benzene have been detected by laser flash photolysis. In reactions with alkenes, nitrenium ions react more rapidly with electron-deficient olefins. Rate constants for the reaction of diphenylnitrenium with electron-rich olefins such as cyclohexanone trimethylsilyl enol ether are of the order of 1.9 x 10 M" s". In the reaction of 2-fluorenylni-trenium with 2 -deoxyguanosine, reaction at C8 of the guanine base takes place. ... 

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