Photochemistry: Volume 35 (Specialist Periodical Reports - Photochemistry)

Product description Excerpt. © Reprinted by permission. All rights reserved. Photochemistry Volume 35A Review of the Literature Published between July 2002 and June 2003By I. DunkinThe Royal Society of ChemistryCopyright © 2005 The Royal Society of ChemistryAll rights reserved.ISBN: 978-0-85404-445-0ContentsIntroduction and Review of the Year By Ian R. Dunkin, ix, Chapter 1 Photolysis of Carbonyl Compounds By William M. Horspool, 1, Chapter 2 Enone Cycloadditions and Rearrangements: Photoreactions of Dienones and Quinones By William M. Horspool, 17, Chapter 3 Photochemistry of Alkenes, Alkynes and Related Compounds By William M. Horspool, 47, Chapter 4 Photochemistry of Aromatic Compounds By Andrew Gilbert, 79, Chapter 5 Photo-oxidation and Photo-reduction By Niall W.A. Geraghty, 116, Chapter 6 Photoelimination By Ian R. Dunkin, 179, Chapter 7 Polymer Photochemistry By Norman S. Allen, 206, CHAPTER 1Photolysis of Carbonyl CompoundsBY WILLIAM M. HORSPOOLThe focus of organic photochemistry continues to change. Over the years considerable research devoted to simple carbonyl compounds was published, however, this emphasis has been diminishing on an annual basis and continues to diminish in the period of this review.Reviews of general interest in this area highlights microreactors that can be used for a variety of photochemical reactions such as the synthesis of large ring ketones. Interest in the control that can be exercised on the outcome of photochemical reactions in constrained environments continues to increase and reviews dealing with the enantioselective photoreactions of achiral compounds in chiral crystals and inclusion crystals have been published.Other studies have been aimed at systems to protect a variety of functional groups with photolabile attachments. A mild CN bond-cleavage process has been described for the release of primary and secondary amines from a coumarin substrate. Fedoryak and Dore have reported the value of the quinoline derivatives (1) as photolabile protecting groups.A patent has been lodged dealing with the formation of photo releasable phenacyl carbonate protecting groups. Others have examined the photochemical deprotection of carboxylic acids from phenacyl and 2,5-dimethylphenacyl esters that can be carried out in a two-phase system. The results indicate, in benzene-water with added cetyltrimethylammonium bromide, that the yield of liberated acid is enhanced. Ashraf et al. have described the use of the hydroxyketone (2) as a further example of molecules that can be used as photoactivatable protecting groups for acids. The hydroxy group is readily esterified with a variety of acids to afford the esters (3). These, on excitation in methanol or ethanol with no need to exclude air, release the free acid in excellent yields and afford the furan (4) as the by-product. This furan is photochemically active under the reaction conditions and undergoes cis-stilbene type cyclization. Klan and Zabadal have reviewed the area of photoremovable protecting groups.1 Norrish Type I ReactionsThe photochemical decomposition of methanal in a solid Xe matrix has been studied. Work has also been reported dealing with the photodissociation dynamics of methanal, and ab initio calculations have been carried out on the photochemical decomposition of acetaldehyde into methane and CO. The photocatalytic decomposition of acetaldehyde to yield carbon dioxide has also been reported. The threshold for CC bond fission in propanal and the release of the CHO fragment has been shown to be at a wavelength of 326.26 nm. Chowdhury has reported the dissociation of propynal using multiphoton irradiation. Gas-phase photolysis of butyraldehyde in the 280-330 nm range has shown that the CHO radical is produced.Laser-flash irradiated benzaldehyde in ethylene glycol has been examined using TRESR and CIDEP techniques. Benzoyl radicals and a-hydroxybenzyl radicals were detected. The photochemical dehalogenation and decarbonylation of 2-, 3- and 4-chlorobenzaldehydes has been studied.Induced pre-dissociation is reported to be a photochemical path to ethane during the irradiation of acetone in the gas phase. Irradiation at 193 nm of ethyl vinyl ketone results in the formation of a variety of products such as n-butane, but-1-ene and buta-1,3-diene. The study was used to determine the rate of combination of ethyl radicals to yield butane and of vinyl radicals to afford buta-1,3-diene.Supramolecular complexes of benzyl radicals are formed upon irradiation of the ketones (5) in supramolecules. Turro has reviewed some aspects of the decarbonylation of dibenzyl ketone derivatives in supercages.A study of the benzoyl radicals obtained by irradiation of the ketones (6-11) has shown that the α-cleavage results from the excited triplet state. endo and exo-(2-Hydroxy-[2.2.2]bicyclo-5-en-1-yl)-phenylmethanones have been synthesized and studied as potential photoinitiators for radical polymerization. The photoinitiators (12) have been invest