Editorial pubs.acs.org/accounts
Enabling Chemical Synthesis with Visible Light Guest Editorial for the Accounts of Chemical Research special issue on “Photoredox Catalysis in Organic Chemistry”.
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on his group’s development of methods for the synthesis of polyfluorinated arenes. A remarkable feature of photoredox catalysis is the recognition that it can be readily combined with other, more established strategies for catalytic synthesis. Several papers in this issue are premised on this theme. Molander demonstrates that photooxidative radical generation can be coupled to versatile nickel-catalyzed cross-coupling reactions. Glorius similarly combines the chemistry of photogenerated radicals with the unique reactivity of gold catalysts. The Account by Rueping describes a strategy for combining C−H functionalization reactions with photoredox catalysis, focusing particularly on the important role of molecular oxygen and reactive oxygen intermediates for the success of these processes. Yoon describes a strategy for stereocontrol in photoinduced reactions that involves the combination of photoredox and chiral Lewis acid catalysis. Knowles shows how the addition of Brønsted acidic and basic cocatalysts can be profoundly beneficial in photoredox reactions by enabling substrate activations via protoncoupled electron transfer. The vast majority of the recent activity in photoredox catalysis has exploited the robust photocatalytic properties of visible light absorbing ruthenium and iridium coordination complexes. One important direction in this field has thus been search for photoredox catalysts that avoid the use of these precious transition metals. Two contributions by Collins and Reiser describe the development of new photoactive copper complexes and emerging applications in photoredox catalysis. Two complementary contributions by Scaiano and Jacobi von Wangelin describe the use of photoactive organic compounds as photoredox catalysts and show that a variety of techniques are applicable to studying the mechanisms of these reactions. Finally, this issue on photoredox catalysis concludes with two Accounts that describe its application. Overman has developed fragment coupling strategies involving photogenerated tertiary radicals that are applicable to the synthesis of complex terpene natural products. In the field of materials chemistry, Dumur and Lalevee provide a perspective on the advantages of the use of visible light in the synthesis of functional materials. The field of photoredox catalysis has generated substantial interest from a variety of researchers within a relatively short period of time, a fact that is clearly evident from the contributions included herein. The surge of activity in this area is remarkable, and one might reasonably wonder what is responsible for the sudden reemergence of photoinduced electron transfer as a theme of research in synthetic organic chemistry. One possibility is the increasing awareness of the importance of sustainable practices in chemical synthesis. Visible light photons are near-ideal reagents in this regard: they generate no waste, require no workup, and can be obtained
he study of the interaction between light and matter is a central theme that connects multiple areas of scientific research, from fundamental physics and spectroscopy on one extreme to applied materials chemistry and biology on the other. Some of the most important light-mediated phenomena in chemistry are associated with electronic transitions in small molecules. The electronically excited states produced upon photoactivation of closed-shell species enjoy increased redox activity; they are simultaneously stronger oxidants and stronger reductants than their ground-state counterparts. This property has been of particular importance in the development of technologies for the conversion of solar energy into usable electricity and chemical fuels. Over the past decade, these concepts have become increasingly applied to problems in synthetic organic chemistry. The recognition that light, and in particular relatively low-energy visible light, can be used to promote versatile photoredox reactions involving activation of a wide range of organic substrates by a photoactive catalytic species has emerged as an active and diverse area of research. This special issue on “Photoredox Catalysis in Organic Chemistry” collects Accounts from some of the most active researchers in this rapidly expanding area and features an impressive scope of chemical transformations with broad applications in pharmaceuticals, natural products, and materials science. Interest in synthetic photoredox catalysis over the past decade has largely been driven by the ease with which oddelectron species can be generated by these mild photoactivation conditions and by the new transformations they enable. Thus, the largest group of Accounts in this issue center on reaction development. Stephenson provides an Account of the evolution of the use of photoredox reactions to access organoradical chemistry in his laboratory. Fensterbank summarizes recent work on the development of new precursors for radical formation via photoredox activation. Nishibayashi focuses his discussion on the chemistry of α-aminoradical intermediates, which can be useful in the synthesis of highly functionalized adducts, and König describes reactions involving highly electrophilic arene radicals that are readily produced by photoredox catalysis. In contrast, Nicewicz provides an Account of his group’s research on alkene radical cation intermediates, a productive effort that has provided an intriguing solution to the general problem of anti-Markovnikov alkene functionalization. Zheng describes research using amine radical cations, focusing particularly on complexity-building cascade reactions. Xiao similarly describes photoredox methods that result in the formation of complex heterocyclic structures. Finally, several research groups have become interested in photoredox catalysis as a means of producing fluorinated compounds. Akita and Cho describe their groups’ respective contributions to perfluoroalkylation reactions. Weaver reports © 2016 American Chemical Society
Published: October 18, 2016 2059
DOI: 10.1021/acs.accounts.6b00502 Acc. Chem. Res. 2016, 49, 2059−2060
Accounts of Chemical Research
Editorial
from renewable sources. Another factor may be the contemporaneous resurgence of interest in radical chemistry. The pioneering efforts of the organoradical chemistry community have now firmly dispelled the notion that radical reactions are capricious and uncontrollable, and the unique transformations they make accessible are increasingly becoming part of the standard repertoire of synthetic chemistry. Finally, much of the current work in photoredox catalysis is influenced by research in the area of solar energy conversion, including the design of the catalysts used and the methods used to interrogate their activity. Thus, photoredox catalysis exemplifies how one area of chemistry learns from another, adapting a welldeveloped set of tools from an adjacent field to advance its own goals. Our hope is that this special issue serves as a concise summary of some of the most exciting new developments in the field of photoredox catalysis and provides a tutorial for synthetic chemists interested in adapting these techniques for their own studies.
Corey Stephenson, Guest editor University of Michigan
Tehshik Yoon, Guest editor
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University of WisconsinMadison
AUTHOR INFORMATION
Notes
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS.
2060
DOI: 10.1021/acs.accounts.6b00502 Acc. Chem. Res. 2016, 49, 2059−2060
