P-quinone and

The addition of p-quinone to enamines normally produces furan derivatives, especially when the enamine possesses a 3 hydrogen (see Section III. A). 1,2 Cycloaddition is claimed to take place to give a cyclobutane derivative when p-quinone and an enamine with no jS hydrogens are allowed to react at low temperatures (51). However, little evidence is reported to verify this structural assignment, and the actual structure probably is a benzofuranol (52). Reaction of a dienamine (formed in situ) with p-quinone in the presence... 

Me3SiCN reacts with both saturated and unsaturated aldehydes and ketones to given silylated cyanohydrines. This reaction has been particularly useful for the regioselective protection of a carbonyl in p. quinones and p. quinol antibiotic metabolite has been prepared. 

Chemical/Physical. Ozonolysis products reported are p-quinone and dibasic acids (Verschueren, 1983). Moussavi (1979) studied the autoxidation of hydroquinone in slightly alkaline (pH 7 to 9) aqueous solutions at room temperature. The oxidation of hydroquinone by oxygen followed first-order kinetics that yielded hydrogen peroxide and / -quinone as products. At pH values of 7.0, 8.0, and 9.0, the calculated half-lives of this reaction were 111, 41, and 0.84 h, respectively (Moussavi, 1979). 

Several charge-transfer complexes of HMTTeF with TeNQs, p-quinone and other accepting re-acceptors have been prepared and electrical resistivities measured with compaction samples. 

In the presence of a protic acid, triazolium thiolates underwent 1,4-Michael addition to p-quinones, and formed the corresponding thioether-substituted hydroquinone salts, which could be oxidized to quinones (85JA6987 85JOC433). This addition is also possible with o-quinones. Since they are... 

Porphyrin quinones serve as biomimetic models for fundamental studies on photo-induced ET. Most studies have been performed with the well-known porphyrin p-quinones and the isomeric porphyrin o-quinones have been mostly neglected due to their higher chemical reactivity but in fact they should be better electron acceptors. Speck et al. synthesized several porphyrin o-quinones and have shown that a facile and simple variation of AGEt can be achieved by using in situ formed semiquinones for metal chelation230. 

Aromatic hydrocarbons which do not have side chains in general form p-quinones and acid anhydrides. Benzene, naphthalene and anthracene have been dealt with above. In the case of phenanthrene, no p-quinone is formed as the adjacent C—H groups of the central nucleus are the most reactive. Phthalic anhydride is the main partial oxidation product, in addition to minor products such as 9,10-phenanthraquinone. Andreikov and... 

Very useful building blocks have been generated by silylation of succinic anhydrides to afford 2,5-bis(trimethylsiloxy)furans (80TL3423). These compounds react with various dienophiles to give p-quinones and hydroquinones. The bis(silyloxy)furan thus functions as an equivalent of the inaccessible diketene (38). With an unsymmetrical dienophile, the regioisomer derived from para orientation predominates (Scheme 8). 

In what sequence should transformation into a p-quinone and hy- Tips... 

S. Akai and Y. Kita, Recent progress in the synthesis of p-quinones and p-dihydroquinones through oxidation of phenol derivatives, Org. Prep. Proced. Int. 1998, 30, 603-629. 

Cu2(L )(NCS)2] (66), which has been shown (c.f. Fig. 8) [43] to contain two tetrahedrally coordinated Cu(I) ions held 2.796(8) A apart and linked inter-molecularly via the sulfur atoms of the thiocyanate ions. For the complexes 63 and 64, the reduction product is the diamagnetic complex [Cu2(L )(MeCN)2](Y)2 (67) (Y = CIO4 or BPh4) in which each three coordinate Cu(I) ion is bonded to two of the four macrocyclic nitrogen atoms and to the nitrogen of one of the two MeCN molecules (Fig, 9) [43]. In the presence of certain substrates the reduction of 63 or 64 is accompanied by substrate oxidation. For example, PhSH, PhC=CH, hydrazobenzene, catechols, hydroquinone, and ascorbic acid afford PhSSPh, PhC=CCsPh, azobenzene, o-quinones, p-quinone, and dehydroascorbic acid, respectively, together with the reduced species 67 and/or other copper complexes... 

Excited states undergo reaction at the C=0 bond to give oxetanes, whilst (7r,7r ) states react at the C=C bond to give cyclobutanes. In a similar way.p-quinones and alkynes on irradiation give quinone methides (equation 91) if the quinone has a... 

Reactions. These silyloxyfuranes undergo Diels-Alder reactions much more readily than furane itself (6, 161). The reaction provides a route to p-quinones and hydroquinoncs (equation I). 

NH3)5N3] has been investigated and the first step has been shown to be the formation of the phenoxyi radical. 2,6-Dimethylphenol gives the corresponding p-quinone and the dimer Ic. In degassed solutions only the dimer is formed . Dimerization of o-phenylphenol can also be brought about by irradiation in the presence of [Co(NH3)5N3] + with concomitant reduction of Co + to its Co + state . Similar dimerization has been... 

The activated carbon-carbon double bonds of p-quinones and p-quinoneimines are suitable for the [3+2] cycloaddition [467]. Interestingly, the reaction of naphthoquinone at -78 °C provides a mixture of [2+2] and [3+2] adducts, although the former product is not observed at 0°C (vide infra). 

UP Agarwal. Assignment of the Photoyellowing-Related 1675 Cm" Raman/IR Band to P-Quinones and Its Implications to the Mechanism of Color Reversion in Mechanical Pulps. J. Wood Chem. Technol. 18 381 02, 1998. 

Side chain displacement with the formation of p-quinones and hydroquinones were the primary reactions observed. The product of oxidation by singlet oxygen was a function of the structure of the lignin model compound and the pH, as seen in Scheme 16.13. For example, vanillin, 43 produced methoxy-p-hydroquinone, 50... 

Additives to effect curing can be used. These include o-dihydroxy-benzene, p-quinone and quinhydrone. ... 

Depending on the structure of the p-quinones and the nature of the trivalent phosphorus compounds being used, two types of products may result from their reactions. The initial attack is directed at either the O or the C of the quinones (64, 65), and both sites are soft. 

A model reaction of hydrogen transfer has been proposed that describes well the results of kinetic studies of the photoreduction of o- and p-quinones and fluorenone in the presence of p-substituted A,A-dimethylanilines and polyalkylbenzenes/° Photosubstitution of the sulfo group for hydrogen is observed upon irradiation of sulfonated derivatives of hydroquinone. The reaction can be promoted by visible light, with eosin as sensitizer/°°... 

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