Quinones, photochemical

The next level of sophistication involved studies of systems where separate donors and acceptors interact across an interface. Chlorophyll-quinone photochemical studies have been conducted using liposomes (23-25) and acetate films (26). Calvin and his coworkers (27) have conducted a variety of experiments... 

Redox catalysis is the catalysis of redox reactions and constitutes a broad area of chemistry embracing biochemistry (cytochromes, iron-sulfur proteins, copper proteins, flavodoxins and quinones), photochemical processes (energy conversion), electrochemistry (modified electrodes, organic synthesis) and chemical processes (Wacker-type reactions). It has been reviewed altogether relatively recently [2]. We will essentially review here the redox catalysis by electron reservoir complexes and give a few examples of the use of ferrocenium derivatives. 

Gritsan, N. R, and Klimenko, L. S. Photochromism of qumonoid compounck - Properties of photoinduced ana-quinones./. Photochem. Photobiol. A 1993,70, 103-117. 

Photochemical Reactions. Increased knowledge of the centraUty of quinone chemistry in photosynthesis has stimulated renewed interest in their photochemical behavior. Synthetically interesting work has centered on the 1,4-quinones and the two reaction types most frequentiy observed, ie [2 A 2] cycloaddition and hydrogen abstraction. Excellent reviews of these reactions, along with mechanistic discussion, are available (34,35). 

Photochemical 2 + 2 cycloadditions can also take place intramolecularly if a molecule has two double bonds that are properly oriented. " The cyclization of the quinone dimer shown above is one example. Other examples are... 

Ordinary aldehydes and ketones can add to alkenes, under the influence of UV light, to give oxetanes. Quinones also react to give spirocyclic oxetanes. This reaction, called the Patemo-BUchi reaction,is similar to the photochemical dimerization of alkenes discussed at 15-61.In general, the mechanism consists of the addition of an excited state of the carbonyl compound to the ground state of the alkene. Both singlet (5i) and n,n triplet states have been shown to add to... 

Photochemical transformation of pyrene in aqueous media produced the 1,6- and 1,8-quinones as stable end products after initial formation of 1-hydroxypyrene (Sigman et al. 1998). 

The transformation of isoquinoline has been studied both under photochemical conditions with hydrogen peroxide, and in the dark with hydroxyl radicals (Beitz et al. 1998). The former resulted in fission of the pyridine ring with the formation of phthalic dialdehyde and phthalimide, whereas the major product from the latter reaction involved oxidation of the benzene ring with formation of the isoquinoline-5,8-quinone and a hydroxylated quinone. 

The photochemical transformation of phenanthrene sorbed on silica gel (Barbas et al. 1996) resulted in a variety of products including c -9,10-dihydrodihydroxyphenanthrene, phenanthrene-9,10-quinone, and a number of ring fission products including biphenyl-2,2 -dicarboxaldehyde, naphthalene-l,2-dicarboxylic acid, and benzo[c]coumarin. 

Much attention has been devoted to the development of methods to generate quinone methides photochemically,1,19-20 since this provides temporal and spatial control over their formation (and subsequent reaction). In addition, the ability to photogenerate quinone methides enables their study using time-resolved absorption techniques (such as nanosecond laser flash photolysis (LFP)).21 This chapter covers the most important methods for the photogeneration of ortho-, meta-, and para-quinone methides. In addition, spectral and reactivity data are discussed for quinone methides that are characterized by LFP. 

Pyrans and napthopyrans (chromenes) are photochromic compounds that undergo photochemically induced electrocyclic ring opening to give colored ortho-quinone methides.95-98 For example, chromene 153 opens on irradiation to give 154 (Eq. 1.41). 

Xu, M. Lukeman, M. Wan, P. Photogeneration and chemistry of biphenyl quinone methides from hydroxybiphenyl methanols. Photochem. Photobiol. 2006, 82, 50-56. 

Brousmiche, D. W. Wan, P. Photogeneration of quinone methide-type intermediates from pyridoxine and derivatives. J. Photochem. Photobiol. A Chem. 2002, 149, 71-81. 

Nakatani, K. Higashida, N. Saito, I. Highly efhcient photochemical generation of o-quinone methide from Mannich bases of phenol derivatives. Tetrahedron Lett. 1997, 38, 5005-5008. 

Pirkle, W. H. Smith, S. G. Koser, G. F. Stereospecificity and wavelength dependence in the photochemical rearrangement of spiro[2.5]octa-4,7-dien-6-ones to quinone methides. j. Am. Chem. Soc. 1969, 91, 1580-1582. 

Schuster, D. I. Krull, I. S. Photochemistry of unsaturated ketones in solution. XIX. Photochemistry of spiro[2.5]octa-4,7-dien-6-one. 2. Mechanistic aspects and the relationship to the photochemistry of quinone methides. Mol. Photochem. 1969, 1, 107-133. 

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