Editorial pubs.acs.org/joc
Radicals in Action: A Festival of Radical Transformations
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O
f all the reactive species manipulated by chemists, free radicals have had perhaps the most unusual development. They started life stealthily in the guise of Fremy’s salt, the first man-made persistent radical discovered in 1845 by Edmond Frémy,1 a Professor at Ecole Polytechnique and the first to have prepared anhydrous hydrogen fluoride (and survived!), then became a curiosity at the turn of the 20th century with Gomberg’s triphenylmethyl radical.2 Their possible implication as reaction intermediates had to wait until the 1930s.3 While this development had an enormous impact on the rise of polymers with their incalculable and dramatic effect on the improvement of the quality of life, the influence of radical reactions on the synthesis of small molecules remained strangely subdued until the early 1970s. The rather sudden availability of reliable kinetic data from laser flash photolysis experiments and the emergence of powerful methods based mostly on organotin chemistry ushered an explosive growth in the application of radicals in synthesis. This heady period lasted for about 20 years, after which the enthusiasm waned and radical chemistry faded again somewhat into the background. But the situation has again changed in the past decade or so, with the availability of cheap and convenient LED devices and the rediscovery of photoredox catalysis,4 as well as the urgent need expressed by the pharmaceutical and agrochemical industries for reactions allowing the late-stage modification of bioactive substances and the fast optimization of the biological activity profiles. Another exciting era thus appears to be emerging, triggered by a very fruitful marriage of radicals with transition-metal chemistry and catalysis. As often found in science, this relationship was simmering for a while and has now come out brazenly into the open. In this respect, the tremendous importance of the so-called persistent radical effect, also known as the Fischer−Ingold effect, will become more and more apparent.5 Most paramagnetic metal complexes are persistent or semipersistent radicals, and their behavior is under the invisible but powerful control of the Fischer−Ingold effect. The implications in biology are also far-reaching, for nature relies heavily on radical processes, which can operate in water, and on a number of persistent radicals (vitamin B12, a CoII complex; nitric oxide, a key cellular messenger, etc.).6 This ACS Select Virtual Issue on radicals highlights 24 excellent representative papers selected from the 2015 and 2016 issues of Organic Letters, The Journal of Organic Chemistry, and the Journal of the American Chemical Society. It covers recent developments and will hopefully convey the liveliness and dynamism of the field and the astonishing variety of chemical transformations enabled by radicals. Last, but not least, it is hoped that it will encourage younger chemists to enter the fray energetically and keep the flame burning. So, do go through the articles of this virtual issue, enjoy a festival of radical reactions, and read the full editorial published in Organic Letters.
AUTHOR INFORMATION
Notes
Views expressed in this editorial are those of the author and not necessarily the views of the ACS.
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REFERENCES
(1) Frémy, E. Compt. Rend. 1845, 21, 218. (2) (a) Gomberg, M. J. Am. Chem. Soc. 1900, 22, 757. For a fascinating account of the hexaphenyethane riddle, see: (b) McBride, J. M. Tetrahedron 1974, 30, 2009. (3) Tidwell, T. T. The History of Free Radical Chemistry. In Encyclopedia of Radicals in Chemistry, Biology, and Materials; Chatgilialoglu, C., Studer, A., Eds.; Wiley: Hoboken, 2012. (4) (a) Romero, N. A.; Nicewicz, D. A. Chem. Rev. 2016, 116, 10075. (b) Yan, M.; Lo, J. C.; Edwards, J. T.; Baran, P. S. J. Am. Chem. Soc. 2016, 138, 12692. (5) (a) Fischer, H. J. Am. Chem. Soc. 1986, 108, 3925. (b) Fischer, H. Chem. Rev. 2001, 101, 3581. (c) Studer, A. Chem. - Eur. J. 2001, 7, 1159. (d) Studer, A.; Curran, D. P. Angew. Chem., Int. Ed. 2016, 55, 58. (6) Frey, P. A.; Hegeman, A. D.; Reed, G. H. Chem. Rev. 2006, 106, 3302.
Samir Z. Zard Laboratoire de Synthèse Organique, UMR 7652 CNRS/Ecole Polytechnique © 2017 American Chemical Society
Published: March 17, 2017 2805
DOI: 10.1021/acs.joc.7b00431 J. Org. Chem. 2017, 82, 2805−2805
