1,4-benzoquinone oxidation

Oxidation. Aromatic amines can undergo a variety of oxidation reactions, depending on the oxidizing agent and the reaction conditions. For example, oxidation of aniline can lead to formation of phenyUiydroxylamine, nitrosobenzene, nitrobenzene, azobenzene, azoxybenzene or -benzoquinone. Oxidation was of great importance in the early stages of the development of aniline and the manufacture of synthetic dyes, such as aniline black and Perkin s mauve. 

Cycloadditions of thiophene 1-oxides are well known the 1-oxides seem much more reactive dienes than the 1,1-dioxides. Thus oxidation of 2,5-dimethylthiophene at 0°C in the presence of benzoquinone gives (510), whereas 2,5-dimethylthiophene 1,1-dioxide needs much more drastic conditions to react with benzoquinone. Oxidation of... 

Benzo[7]furan 82 is a very important building block in materials science and drug discovery. Because it is electronically rich at C-2 and C-3, many important synthetic transformations occur at these two positions. For example, o-benzoquinones oxidatively generated from the corresponding substituted 2-methoxyphenols reacted with ben-zo[7]futan 82 to form polycyclic molecules, as depicted in Scheme 56 <1999JA13254>. 

An interesting example of Pd-catalyzed oxidation of a 1,3-conjugated diene is shown in Scheme 20. This reaction type produces stero-defined 1,4-functionalized dienes, which are useful synthetic building blocks and reaction intermediates. Benzoquinone oxidation of an ) -allyl-Pd intermediate is a key step in releasing the organic product. ... 

In a previous study various processes (oxidation of hydroquinone to benzoquinone, oxidation of 1-decane to 2-decanone and allylic oxydation of cyclohexene) were investigated with the use of Fe(Pc)-Y. Beside the simple separation of phases, the high activity of the encaged Fe(Pc)-Y complex was retained during several catalytic cycles [14]. 

Reaction of diarylcyclopropenones with pyridine or 4,4 -bipyridyl, followed by benzoquinone oxidation produced l,r-dioxo-7,7 -bisindolizinylidenes 32. ... 

Scaiano et al. (1989) characterized the parent benzoquinone oxide, various derivatives thereof being obtained from the corresponding cyclic diazo ketones as well as from 9-diazofluorene, and from diazodiphenylmethane by laser flash photolysis at room temperature. The parent benzoquinone oxide has an absorption maximum at 410 nm. The rate constants of 2-diazo-l,2-benzoquinone and of the carbene of this diazo compound with singlet oxygen were found to be 1.0 x 10 m s and... 

Different degradation techniques are commonly used for the analysis of LCC isolated from plant tissues. This approach includes cleavage of lignin-carbohydrate bonds and identification of the resulting products by way of alkaline hydrolysis (saponification) [20], acid hydrolysis [36,66], Smith degradation [67], ozonolysis [68], methylation analysis [69-72], and DDQ (2,3-dichloro-5,6-dicyano-l,4-benzoquinone) oxidation [18,73-76]. The two last techniques are the most common for the analysis of carbohydrate linkage sites in LCC preparations. 

A kinetic study of 3,5-DTBC to 3,5-DTBQ (3,5-di-t-butyl-1,2 benzoquinone) oxidation with molecular oxygen (CHCl, 30 °C) in the presence of copper(II) chelate catalysts has been... 

Non-conjugated dienes ate the source of many palladium enyl complexes. Nucleophilic attack at one of the double bonds of the coordinated diene has been used most, and many examples can be found in COMC (1982) and COMC (1995). The external attack of the nucleophile leads to an overall /rtf r-addition of Pd and the incoming species to the double bond. Oxidation followed by nucleophilic attack on COD affords <7,7 -enyl derivatives from Pd(l,5-COD)(benzoquinone). In the presence of acid, benzoquinone oxidizes Pd(0) to a Pd(n) diene complex with the concomitant formation of hydroquinone. If a suitable nucleophile is present, such as OAc when acetic acid is used, attack on the diene takes place, and a palladium complex is formed (Scheme 80). A weaker nucleophile like CH3S03 is not capable of adding to the double bond, and the reaction stops at the COD Pd(n) complex. The behavior of other quinones and acids was also studied. ... 

The decarboxylative alkenylation of electron-deficient benzoic acids was found to occur by using a cheaper oxidant, benzoquinone, in place of the silver salt (Scheme 4.22) [27]. A CuF2/benzoquinone oxidant system can mediate the reaction of electron-rich benzoic acids [28]. The decarboxylative alkenylation of both electron-rich and electron-deficient benzoic acids using dioxygen as the terminal oxidant can be performed (Scheme 4.23) [29]. 

---