Free Radicals in Synthesis and Biology

Free-radical reactions have been for long time the domain of the physical chemists and the basic chemical industry (polymerization of vinyl monomers, oxidation by molecular oxygen, chlorination of methane etc.), where the use of simple molecules and the possibility of partial conversions without heavy problems of product separations makes less dramatic the aspects of regio and chemoselectivity. As synonym of unselectivity, free radical reactions were considered of poor use in the synthesis of fine chemicals or sophisticated molecules, where a high selectivity is an essential condition for the success, or in the involvement of biological processes. Within the last 15 years, however, an authentic explosion of synthetic applications of free radical reactions occurred; they have gained a remarkable position among the selective methods of synthesis. At the same time the great importance of free radical reactions in fundamental biological processes and in the metabolism of drugs has been recognized. Thus a specialized meeting on these topics was generally felt appropriate. I had the honour and the onus to organize this workshop because for more than 30 years I have been involved in the research of free radical reactions. Thanks to a generous grant from NATO Scientific Affairs Division and the financial support of CNR and chemical industry (Montedison, Enichem, Zambon) such a meeting among almost 50 specialists and 15 observers of sufficient standard to take advantage of the discussion, became possible at Bardolino (Italy). Front Matter....Pages i-xx Captodative Substituent Effects in Synthesis....Pages 1-26 The Influence of gem.-Substitution on the CC-Bond....Pages 27-36 Iodine Atom Transfer Reactions in Organic Synthesis....Pages 37-51 ALKYL Iodides as Source of ALKYL Radicals, useful for Selective Syntheses....Pages 53-69 Introduction of a Single Electron-Withdrawing Carbon-Substituent into π-Deficient N-Heteroarenes by Means of Free-Radical Reactions: Strategies and Synthetic Applications....Pages 71-79 Free Radical Synthesis of Pyridylderivatives: Influence of the Solvent....Pages 81-88 Photoinitiated Radical Reactions of l-(4′-Pyridyl)-4-Pyridone and its N-Protio and N-Methyl Derivatives. Dimerization and Polymerization Reactions....Pages 89-95 Radical Reactions with Organocobalt Complexes....Pages 97-106 New Ways of Generating Stannyl Radicals for Organic Syntheses....Pages 107-114 Silanes as New Reducing Agents in Organic Synthesis....Pages 115-123 ACYL, IMIDOYL, and Other Hetero-Substituted Free Radicals as Intermediates in the Synthesis of Cyclic Organic Compounds....Pages 125-134 Some Studies on Carbonyl Radical Cyclizations and on the Synthesis of 2-Deoxy-β-D-Glycosides by Stereoselective Radical Reactions....Pages 135-143 Stereoselective Formation of Linear AZA-Triquinanes by Three Consecutive Radical Ring Closures....Pages 145-153 Synthetic Applications of Substitution and Addition Reactions Promoted by Cerium(IV) Ammonium Nitrate....Pages 155-185 Use of Homolytic Redox Processes in Organic Syntheses....Pages 187-212 One-Electron Redox Reactions Between Radicals and Molecules. Dominance of Inner-Sphere Mechanisms....Pages 213-231 Electron-Transfer Photosensitization in the Oxidation of Alkyl Aromatics and Heteroaromatics....Pages 233-251 Selenium Radical Ions in Organic Synthesis....Pages 253-262 A Synthetically Useful Source of Alkyl and Acyl Radicals....Pages 263-268 Chlorination by Hypochlorous Acid. Free-Radical Versus Electrophilic Reactions....Pages 269-282 Induced Decomposition of Peroxycompounds in Synthesis: Free Radical Functionalization of Crown Ethers....Pages 283-292 Unwanted Synthesis in Combustion and Pyrolysis; Soot and Dioxins....Pages 293-302 Polar Effects on Radical Addition Reactions: An Ambiphilic Radical....Pages 303-316 The Effect of Temperature in the Reactions of Arenesulphonyl Radicals....Pages 317-324 Synthesis of New 5-Nitroimidazoles Highly Active Against Anaerobes by Substitution Reactions which Proceed via Radical and Radical-Anion Intermediates....Pages 325-333 Detection of Free Radicals in Biochemistry by Electron Spin Resonance Spectroscopy....Pages 335-359 Error in Enzymic Stereospecificity as a Probe for the Occurrence of Radical Intermediates....Pages 361-372 Kinetics of Peroxyl Radical Reactions in Model Biomembranes....Pages 373-390 Rearrangements of Optically Pure Hydroperoxides....Pages 391-406 In Vivo Detection of Free Radical Metabolites....Pages 407-421 The Involvement of Free Radicals in the Metabolism of Drugs....Pages 423-436 The Formation of Fluorescent Pigments due to Radicals in Biological Tissues....Pages 437-460 The Chemistry/Biochemistry Interface in Free-Radical Reactions....Pages 461-468 Back Matter....Pages 469-474 ....Pages 475-482 Proceedings of the NATO Advanced Research Workshop, Bardolino (VR), Italy, May 8-13, 1988