Aromatic rings, oxidation

As part of the total synthesis of the triterpene (+)-a-onocerin, one of the first total syntheses in which RuO played a key role, a diphenylethyleneacetoxyketone was oxidised to the corresponding acetoxyketoacid by RuO /aq. Na(10yacetone. Aromatic ring oxidation was also involved (cf. 3.3.1 below) [219]. An oxidative cyclisation of a 1,5-diene to a diol by RuCl3/Na(10 )/wet SiO /THF formed part of the synthesis of the antitumour agent cw-solamin [220]. 

Cumene does not undergo oxidation at a measurable rate. 1-Butylbenzene undergoes oxidation mainly in the side chain, with traces of aromatic ring oxidation, producing 1-phenyl-1-butanol, l-phenyI-3-butanol, and the corresponding ketones (Clerici, 1991). 

A marked difference in hepatic activity of aldehyde oxidase between rats and monkeys was found to be responsible for the reported marked species difference in the metabolism of Zaleplon in vivo. In the postmito-chondrial fractions, S-9s, from liver homogenates of these animals, zaleplon was transformed in the presence of NADPH into the side chain oxidation product, N-desethyl-zaleplon, and the aromatic ring oxidation product, 5-oxo-zaleplon. In the rat S-9, N-desethyl-zaleplon and 5-oxo-zaleplon were a major and a very minor metabolites, respectively. 

To account for the metabolism of benzene as a model for aromatic-ring oxidation and conjugation the speculative transformations on page 217 are suggested. 

Granisetron 60% (increased in hepatic impairment) 2 hours 65% N-demethylation and aromatic ring oxidation followed by conjugation [7] 12% 9 hours (prolonged in hepatic impairment [8]) ... 

Aromatic (-C-C=C-) Chain rigidity, colors, electrical conductivity (if aromatic rings oxidative resistance, high strength, stacking/self-alignment (liquid crystals))... 

Sulfur-centered radical cations derived from aromatic thioethers (Ar-S-Ar) have been investigated much less extensively. An important feature of one-electron oxidation of aromatic thioethers is the lack of dimeric radical sulfur radical cations (ArS.. S-Ar) because of the spin delocalization onto the aromatic ring. Oxidation of thioanisole (Ar-S-CHj) by OH radicals was studied using pulse radiolysis. At neutral pH, OH addition led to the prompt formation of monomeric sulfur radical cations and hydroxycyclohexadienyl radicals (see Scheme 8). 

Partial catalytic oxidation of alkylaromatic hydrocarbons is interesting both from the industrial and the scientific point of view. The industrial interest is due to the availability of these substances from the petrochemical industry and to a number of applications for the possible oxidation products. Conventional gas phase oxidation concerns the side chain and leads mainly to benzoic acid or even to destruction of the aromatic ring. Oxidation under mild conditions could cease the reaction at earlier stages and reduce the number of the products formed. However, the appropriate catalyst for such partial oxidation has not been found yet. 

Other phenolic compounds underwent similar reactions. GAC after application of either free or combined chlorine became capable of promoting reactions such as hydroxylation of the aromatic ring, oxidation to phenols, chlorine substitution, carboxylation, and oxidative coupling (dimer and trimer formation). The formation of chlorohydroxybiphenyls ( hydroxylated PCBs 113) by dimerization of chloro-... 

In this particular instance an altogether new compormd para-toluidine shall be formed which upon oxidation with sodium dichromate and sulphuric acid shall rmdergo aromatic ring oxidation instead, because anilines with strong oxidizing agents, e.g., dichromate usually gives similar products. 

Alternatively, the arene can be left complexed so that the chemistry of the Ti -arene complex can be exploited (see Section 10.3). " The Dotz reaction between the cyclohexenyl carbene 8.52 and the benzylic alkyne 8.53 in the presence of a silylating agent gave the ti -complex 8.54 (Scheme 8.18). Treatment of this complex with LDA resulted in formation of the anion a- to sulfur 8.55 that cyclized by nucleophilic attack onto the chromium-complexed aromatic ring. Oxidative work-up then gave the tetracycle 8.57. 

The oxidation of 1-ethylnaphthalene (11) and 2-ethylnaphthalene (12), which are known polycyclic aromatic hydrocarbons (PAHs), was studied in the presence of TEA salts of Mn or Fe POMs [51], Only the iron-substituted POMs were able to catalyze the oxidation of these two substrates, in moderate conversions. The oxidation of 11 and 12 occurs mainly at the alkyl substituent, along with the formation of phthalic anhydrides resulting from the aromatic ring oxidation. The higher conversions of 11 and 12 were obtained in the presence of BWuFe or PW Fe and when a molar ratio of H202/sub = 9.8 was used [51]. 

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