Further aryl compounds

One other feature of the data in Table 10.10 is worthy of further comment Notice that alkyl substituted acylium ions exhibit a smaller ortho para ratio than the various arpyl systems. If steric factors were dominating the position selectivity, one would expect the opposite result A possible explanation for this feature of the data could be that the aryl compounds are reacting via free acylium ions, whereas the alkyl systems may involve more bulky acyl chloride-catalyst complexes. 

When (253) reacts with phosgene the 1-acyl chloride product (254) can react with amines to give amides (79LA1756X while in a further transfer reaction with ketones the compounds (255) and (256) are produced (Scheme 146) (80H(14)97). Acylation of aromatic hydrocarbons using 1-acylimidazoles in the presence of trifluoracetic acid gives high yields provided that the aryl compounds are electron rich, e.g. p-dimethoxybenzene, thiophene, anisole <80BCJ1638). 

Further support for the proposed mechanism is provided by the results of experiments involving phenylbromide instead of ethylbromide (Jj6). The polarizable TT electrons of this aryl compound allow it to effectively compete with styrene for the sites on the lithium surface and thus the Wurtz coupling reaction becomes dominant. Similar results were obtained with ethyltosylate. Although the reaction of tosylate with living polystyrene is rapid and quantitative, yielding ethyl capped polymers, its reaction with the monomer and metallic lithium produces only 10% of the ethyl capped polymers, the remainder being evolved as butane. Again, the aromatic nature of tosylate allows it to compete with styrene for the lithium sites. 

Further support for the proposed mechanism is provided by the results of experiments involving phenylbromide instead of ethylbromide88. The polarizable re electrons of this aryl compound allow it to effectively compete with styrene for the sites on the lithium surface and thus the Wurtz coupling reaction becomes dominant. Similar results were... 

The use of dibromo-iV-methylmaleimide for the photosubstitution of aryl compounds has been further studied. ... 

One other feature of the data in Table 10.10 is worthy of further comment. Notice that alkyl (acetyl, propionyl) substituted acylium ions exhibit a smaller o p ratio than the various aroyl systems. If steric factors were dominating the position selectivity, one would expect the opposite result. A possible explanation for this feature of the data could be that the aryl compounds are reacting via free acylium ions, whereas the alkyl systems may involve more bulky acid chloride-catalyst complexes. Steric factors clearly enter into determining the o p ratio. The hindered 2,4,6-trimethylbenzoyl group is introduced with a 50 1 preference for the para position. Similarly, in the benzoylation of alkylbenzenes by benzoyl chloride-aluminum chloride, the amount of ortho product decreases (10.3%, 6.0%, 3.1%, 0.6%, respectively) as the branching of the alkyl group is increased along the series methyl, ethyl, 2-propyl, t-butyl. ... 

The a-arylation of ethers was further developed by Vishwakarma [86, 87], who reported that in situ-prepared Grignard reagents react with THE to give the corresponding 2-arylated compounds (Eq. 35). Despite its low solubility, iron oxide was the catalyst of choice, and high yields were reported. 

External coordination to give Cp2TiR L derivatives also stabilizes the Ti-R bond, provided that the ligand itself is not activated towards further reaction, as is frequently the case. Stabilisation by adduct formation is observed for R = alkyl e.g. in THE solution or with phosphines [8], for the aryl compounds stabilizing ligands are, e.g., N2 (formation of (Cp2TiR) N2, [20]), R CEN and R NEC [5,7]. 

Herbicidally active l-aryl-4-carbamoyl-tetrazolinones 304 were recently obtained by reacting 1-aryl-tetrazolinones with phosgene in the presence of a solvent at 0-150 °C, and then reacting the resulting (novel) l-aryl-4-chlorocarbonyl-tetrazolinones 303 with amines in the presence of a solvent, and, where appropriate, in the presence of a further basic compound, at —20 to +100 °C [234]. 

As described above, nickel compounds are liable to afford the 7r-compIex with compounds having a carbon-carbon unsaturated bond such as olefins, acetylenes, allyl and aryl compounds, and further the nickel compounds are also liable to afford (T-compIexes with alkyl or aryl compounds. 

An improved route has been described for the synthesis of 5 -5-aryl (or alkyl)-5 -thionucleosides,7 and it has been shown that the S-aryl compounds can be oxidized directly to 5 -fluoro-5 -thionucleoside derivatives using XeP2, in addition to the two-stage process involving oxidation to the sulfoxide and then treatment with DAST to induce a Pummerer-type process (see Vol. 22, p.212). Further oxidation of the a-fluorosulfides gives sulfones such as (9l).li3 Another reference to the use of such intermediates was discussed earlier, and there has been a further report on the preparation of 5 -(fluoromethylthio)adenosine and 5 -fluoro-5 -methylthioadenosine from the methylsulfinyl derivative and DAST (see Vol. 23, p.216)H - 5 -(Di- and trifluoromethylthio)adenosine have been prepared by alkylation with the appropriate chlorofluoromethane,H as have fluorinated 5-ethyl compounds of type (92),115.ll6 and the 5-(3-fluoropropyl)analogue.H9 The cyclic... 

Further, it has been observed that in a number of reactions between aryl compounds and transition metals, loss of ortho-hydiogtn occurs, viz. 

The reactions of the second class are carried out by the reaction of oxidized forms[l] of alkenes and aromatic compounds (typically their halides) with Pd(0) complexes, and the reactions proceed catalytically. The oxidative addition of alkenyl and aryl halides to Pd(0) generates Pd(II)—C a-hondi (27 and 28), which undergo several further transformations. 

The transmetallation of various organometallic compounds (Hg, Tl, Sn, B, Si, etc.) with Pd(II) generates the reactive cr-aryl, alkenyl, and alkyl Pd compounds. These carbopalladation products can be used without isolation for further reactions. Pd(II) and Hg(II) salts have similar reactivity toward alkenes and aromatic compounds, but Hg(II) salts form stable mercuration products with alkenes and aromatic rings. The mercuration products are isolated and handled easily. On the other hand, the corresponding palladation products are too reactive to be isolated. The stable mercuration products can be used for various reactions based on facile transmetallation with Pd(II) salts to generate the very reactive palladation products 399 and 400 in rim[364,365]. 

Addition of several organomercury compounds (methyl, aryl, and benzyl) to conjugated dienes in the presence of Pd(II) salts generates the ir-allylpalladium complex 422, which is subjected to further transformations. A secondary amine reacts to give the tertiary allylic amine 423 in a modest yield along with diene 424 and reduced product 425[382,383]. Even the unconjugated diene 426 is converted into the 7r-allyllic palladium complex 427 by the reaction of PhHgCI via the elimination and reverse readdition of H—Pd—Cl[383]. 

Phosphoms compounds are effective flame retardants for oxygenated synthetic polymers such as polyurethanes and polyesters. Aryl phosphates and chloroalkyl phosphates are commonly used, although other compounds such as phosphonates are also effective. The phosphoms compounds can promote char formation, thereby inhibiting further ignition and providing an efficient thermal insulation to the underlying polymer. 

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