Quinone diacetals oxidation

Phenols with a free ortho position can also give rise to ortfeo-quinone diacetates such as 39a and 41b, in addition to or instead of ortfeo-quinol acetates such as 41a [1, 6]. Phenols bearing a 2-methoxy group are particularly prone to regioselective Wessely oxidation to give 6-... 

Quinone monoacetal, which is obtained by careful hydrolysis of quinone diacetal, can also be prepared directly y anodic oxidation under modified reaction conditions. ... 

Takacs [85] has separated the o- and p-benzoquinol acetates and o-quinone diacetate resulting from oxidation with lead tetraacetate of phenols containing an o-isopropyl, sec-butyl or tert.-butyl group. The o-derivatives were separated and purified on silica gel G. A 1 % solution of p-dimethylaminobenzaldehyde in concentrated sulphuric acid was... 

In an example of the use of this activation method testosterone, with a IT -hydroxy group, was oxidized to A -androstene-3,17-dione very rapidly in high yield, in contrast to the use DMSO-acetic anhydride. During a reaction, when other oxidizing agents were found to be ineffective, sulfur trioxide/dimethyl sulfoxide led to smooth oxidation of the df-diol (16 equation 8) to an o-quinone in 49% yield and the ci.r-diol (17) to (18 equation 9) in 98% yield. - The use of dimethyl sulfoxide-acetic anhydride for this oxidation gave large amounts of the diacetate as the by-product. 

The quinone monoketals 9 and para-quinol ethers 10 mentioned above (Section n.A.l) can be obtained by anodic oxidation of the corresponding O-protected phenols 103 ° (equation 41) or upon oxidation of substituted phenols 104 with one equivalent of phenylrodonium diacetate (PIDA) at an ambient temperature (equation 42). 

Phenols are oxidized by NaBiO3 to polyphenylene oxides, quinones, or cyclohexa-2,4-dienone derivatives, depending on the substituents and the reaction conditions [263]. For example, 2,6-xylenol is oxidized in AcOH to afford a mixture of cyclohexa-dienone and diphenoquinone derivatives (Scheme 14.123) [264] and is oxidatively polymerized in benzene under reflux to give poly(2,6-dimethyl-l,4-phenylene) ether (Scheme 14.124) [265]. Substituted anilines and a poly(phenylene oxide) are oxidatively depolymerized by NaBiO, to afford the corresponding anils [266]. Nal iO, oxidizes olefins to vicinal hydroxy acetates or diacetates in low to moderate yield [267]. Polycyclic aromatic hydrocarbons bearing a benzylic methylene group are converted to aromatic ketones in AcOH under reflux (Scheme 14.125) [268]. 

Brucine is oxidized by 5 V nitric acid (or chromic acid (159)) at 0-5° to a rose-colored solution from which a red bruciquinone (bis-desmethylbrucine, (C21H20O4N2), XCIII) can be isolated as its perchlorate. It is a typical quinone because it is reduced by sulfurous acid to a hydroquinone, bis-apomethylbrucine (diacetate formation brucine yields two moles of methyl chloride when heated with hydrochloric acid but bis-apomethylbrucine could not be isolated from the reaction mixture (191) ). No other alterations occur in the brucine molecule during these transformations since methylation (dimethyl sulfate) converts bis-apomethylbrucine to the quaternary salt of brucine. The hydroquinone has been oxidized, with... 

Among very rare examples of catalytic transformations involving polyene and polyenyl ligands is Pd-catalyzed oxidation of diene derivatives by the use of acetic acid and quinone with unique stereochemical control being achieved by judicious choice of the reaction condition (Scheme 8.65) [121]. Thus, the oxidation carried out with high Cl concentration afforded cis diacetate product, while trans adduct was obtained in the absence of Cl ion. The initial step of the catalytic cycle would be the exo attack of OAc at the Pd-bound diene, giving rise to r -allyl intermediate with OAc and Pd positioned trans to each other. This then underwent either exo or endo attack of the second OAc in the presence or absence of Pd-bound Cl ligand, respectively. The endo attack may have proceeded in a manner similar to Scheme 8.50. The hnal step of the catalysis would be oxidation of Pd(0), formed by the OAc attack at the r -allyl terminus, with benzoquinone as an oxidant. 

Also, oxidation of ( + )-bulbocapnine with mercuric chloride afforded the known quinone (26) this was reduced to the catechol (27). This racemate was resolved as its diacetate derivative, using ( + )-tartaric acid. The resulting ( - )-... 

Indeed, the biosynthesis of the biopolymer melanin involves the oxidative cyclization of dihydroxyphenylala-nine (DOPA) to phenylalanine-3,4-quinone (dopaquinone), which eventnally forms 5,6-dihydroxyindole (DHI). Polymerization of DHI affords melanin [1], Lim and Patil have exploited this biochemical transformation using commercial mushroom tyrosinase in a synthesis of 5,6-dihydroxyindoles protected as the diacetates (2) (Scheme 1) [2], The parent indole (R = R =H) is obtained in less than 10% yield. Carpender has reported a similar oxidative cyclization using manganese dioxide to give 2 (R =Me) in 80% overall yield from epinine (1, R =Me, R =H) [3]. Other oxidants (H, Hp /FeSO, O, NaOCl, NaClOj/ VjOj) gave little or no product. Choi, Nam, and colleagues have effected an electrochemical oxidation of dopamine (1, R = R =H) to 5,6-dihydroxyindole that polymerizes to form films of polydopamine suitable for neural attachment and function [4]. 

In the determination of 2-methyl-1,4-naphthohydroquinone-diacetate a hydrolysis must precede the polarographic electrolysis. Under the conditions used for hydrolysis, the naphthohydro-quinone formed is further decomposed and the conditions of hydrolysis must be strictly controlled. A 10 per cent solution of the preparation in a 0-025 M borate pH 8-5 buffer, is heated for 20 min at 100°C and the oxidation-reduction wave at —0-33 V is measured. 

Oxidation of benzoquinones and naphthoquinones by palladium diacetate in arene-containing acetic acid gave the corresponding aryl-substituted quinones (eq 70). Treatment of 1,4-naphthoquinone with aromatic heterocycles, for example furfural, 2-acetylfuran, 2-acetylthiophene, and 4-pyrone, yielded the corresponding 2-heteroaryl-substituted 1,4-naphthoquinones. 

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