P-Quinone structures

Sometimes the sole presence of one of these groups is not sufficient to confer a color to the molecule that brings it. In order to develop a color, it must possess a supplementary group called an auxochrome (increasing the color). In most cases, but not necessarily, the coloration change due to the medium s acidity is related to the appearance of a p-quinonic structure a or, more rarely, to that of an o-quinonic structure b ... 

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... 

For instance, poly-p-phenylenes in their doped states manifest high electric conductivity (Shacklette et al. 1980). Banerjee et al. (2007) isolated the hexachloroantimonate of 4" -di(tert-butyl)-p-quaterphenyl cation-radical and studied its x-ray crystal structure. In this cation-radical, 0.8 part of spin density falls to the share of the two central phenyl rings, whereas the two terminal phenyl rings bear only 0.2 part of spin density. Consequently, there is some quinoidal stabilization of the cationic charge or polaron, which is responsible for the high conductivity. As it follows from the theoretical consideration by Bredas et al. (1982), the electronic structure of a lithium-doped quaterphenyl anion-radical also differs in a similar quinoidal distortion. With respect to conformational transition, this means less freedom for rotation of the rings in the ion-radicals of quaterphenyl. This effect was also observed for poly-p-phenylene cation-radical (Sun et al. 2007) and anion-radical of quaterphenyl p-quinone whose C—O bonds were screened by o,o-tert-hutyl groups (Nelsen et al. 2007). 

Bernardo, P. H., Chai, C. L. L., Le Guen, M.,Geoffrey D., Smith, G. D., Waring, P. (2006) Structure-activity delineation of quinones related to the biologically active Calothrixin B. Bioorg Med Chem Lett 17, 82-85. 

This chapter will focus on o- and p-quinone methides and will be divided into two parts. The first will present methods for generating quinone methides in photochemical and solvolysis reactions and will emphasize how the structure and stability of quinone methides dictates the pathways for their formation. The second section will discuss the results of experiments to characterize the reactivity of quinone methides with nucleophilic reagents, and the broader implications of these results. The scope of this presentation will reflect our interests, and will focus on studies carried out at Buffalo. We considered briefly writing a comprehensive chapter on quinone methides, but abandoned this idea when we learned of Steven Rokita s plans to edit a 12-chapter text, which presents an extremely comprehensive coverage of the chemistry and biochemistry of quinone methides.9... 

The reaction of rhodium(II) pivalate dimer, Rh2(02CCMe3)4, with 1,4-benzo-quinone (BQ) in hexane gave a chain complex, [Rh2(02CCMe3)4 BQ] , where the rhodium(II) pivalate dimers are connected by the bifunctional ligation of the p-quinone through its carbonyl oxygen or C = C double bond, i.e., the chain structure consists of two kinds of dimer units 963 and 964 [235-237] ... 

Pan, S., Andrews, P.A., Glover, C.J., and Bachur, N.R., 1984, Reductive activation of mitomycin C and mitomycin C metabolites catalysed by NADPH-cytochorome P-450 reductase and xantine oxidase. J. Biol. Chem. 259 959-962 Pollakis, G., Goormaghtigh, E., and Ruysschaert, J.-M., 1983, Role of quinone structure in the mitochondrial damage induced by antitumor anthracyclines. FEBS Lett. 155 267-272 Rappaport, S.M., McDonald, T.A., and Yeowell-O Connell, K., 1996, The use ofprotein adducts to investigate the disposition of reactive metabolites of benzene. Environ. Health Perspect. 104Suppl6 1235-1237... 

From the viewpoint of organic synthesis, nature provides us with a number of target molecules, which have novel structures and a variety of biological activities. As already shown in Section II.A, electrochemical oxidation of phenols has been applied successfully to natural products synthesis. Hypervalent (diacyloxyiodo)benzenes have also been proved to be effective for natural products synthesis. Generally, oxidation of o- and p-methoxyphenols in MeOH provides the corresponding o- and p-quinone monoketals, respectively. They are utilized as promising synthons for natural products and related bioactive compounds, as demonstrated by Swenton . Recently, these quinone monoketals have been utilized for syntheses of terpenoids, neolignans, anthraquinones, alkaloids and related compounds. 

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