Editorial pubs.acs.org/CR
Introduction: Photochemistry in Organic Synthesis
O
Christian Bochet provides an in-depth review surveying the multiple reaction pathways and product distributions that are generated by this unique reaction. Photoexcitation is a means to potentially generate some of the most reactive intermediates known. Maurizio Fagnoni has led efforts in utilizing and understanding the reactivity of these highly reactive species in forming carbon−carbon bonds and provides a review of modern developments in this area. Nearly 25 years ago, V. Ramamurthy and Nicholas Turro organized the seminal collection of photochemistry reviews in a Chemical Reviews thematic issue.5 V. Ramamurthy has now teamed up with Jayaraman Sivaguru to provide an in depth overview of photochemical reactions enabled and/or controlled by supramolecular interactions. They also worked together to provide the excellent artwork for the cover of this issue. One of the most utilized applications of photoexcitation is generation of singlet oxygen; these reactions can be a powerful tool and are utilized in subfields ranging from polymer synthesis to pharmaceutical manufacturing, and Alexander Greer provides an overview of the most compelling recent examples. Chemists have often associated photochemistry with high energy photons at UV wavelengths inducing organic molecules into reactive excited states. One of the most exciting advancements in chemistry (as a whole) has been the development of reactions utilizing visible light photocatalysts. This manifold of reactivity has greatly expanded the repertoire and utility of photochemistry and has enabled the use of longer wavelengths, often into the visible region. Two leaders in the area of photoredox catalysis, Tehshik Yoon and David Nicewicz, each contribute reviews that provide an excellent overview of modern photocatalysis. Yoon’s offering focuses on the development and implementation of dual-catalytic systems, while Nicewicz provides details on the development and application of organic photocatalysts. For decades, photochemical reactions have been key for the synthesis of many macromolecules. Jeremiah Johnson presents a broad overview of polymerization reactions which utilize photochemistry, and Yusuf Yagci provides an in-depth review of photoinduced electron transfer reactions in the synthesis of numerous macromolecules. For many decades, some of the prevailing challenges facing photochemistry have been reproducibility, scale, and efficiency. Many of these issues may be overcome by utilizing flow chemistry platforms which have become a broadly adopted and powerful tool for chemists. Timothy Noël reviews the recent technological and chemical advances in flow photochemistry, providing a glimpse of what photochemical reaction development could potentially look like in the coming decades. It has been a wonderful experience bringing together a remarkable group of authors for this thematic issue. I would like to thank all of them for the exceptional work and for providing
ne of the most venerable stories of discovery in synthetic chemistry is that of lumisantonin.1 The reaction, starting from the natural product santonin, was initiated by exposure to sunlight and is a stunning example of the dualistic simplicity and complexity often associated with photochemical reactions. This discovery inspired early organic photochemistry in the late 19th century and subsequently a truly remarkable structure elucidation.2 But perhaps the true impact was the inspiration of chemists in the mid-20th century to pioneer modern organic photochemistry through a multidisciplinary approach.3 In the decades following, there was a so-called “golden age” of photochemistry, where chemists learned to leverage photochemical reactivity in a breathtaking variety of reactions, applying those reactions to enable groundbreaking syntheses.4 Through the turn of the century, it could be said that there was less excitement and fewer new reactions developed, somewhat dampening the advancement of photochemistry. However, due in part to many of the Authors contributing to this thematic issue of Chemical Reviews, the past decade has seen a true renaissance for photochemistry. This issue brings together innovators in photochemistry from a breadth of disciplines and highlights its importance in nearly all fields in which the chemical synthesis of molecules plays a crucial role. Astrochemistry is one of the most intriguing yet perhaps underexplored areas of chemistry. The complexity of organic molecules and chemical reactions in space is astounding and gives great insight into the power of photochemistry. A review by Karin Ö berg outlines the challenges and complexity of interstellar photochemical reactions. On Earth the sun provides a source of light (in both the ultraviolet and visible spectrum) that can be readily harvested for photochemical reactions. Michael Oelgemö ller provides a review of the humble beginnings of photochemistry by solar reactions and highlights the current technologies to harvest solar radiation for the preparation of small molecules. Although photochemistry could be considered one of the simplest manifolds of chemical reactivity, it has been utilized to enable transformations that are, at times, inconceivable (or even impossible) by alternative means. Thus, few types of reactions can invoke the imagination of chemists as does photochemistry. This is exemplified by the many examples of chemists generating astonishing structural complexity, often rapidly through a single photochemical step. Corey Stephenson and John Porco, Jr. provide an overview of photochemical reactions that were critical in the syntheses of complex natural products. Cyclobutanes can be deceptive in their apparent simplicity and can pose great challenges in succumbing to synthesis. They are found in numerous molecules isolated from a wide range of natural sources and have been a central motif in some widely utilized therapeutics. Thorsten Bach has led the development of modern photochemical methods of the [2 + 2]-cycloaddition and outlines recent advancements in this area. Arene−alkene cycloadditions are a related photochemical reaction that can generate remarkably complex and distinct chemotypes. © 2016 American Chemical Society
Special Issue: Photochemistry in Organic Synthesis Published: September 14, 2016 9629
DOI: 10.1021/acs.chemrev.6b00378 Chem. Rev. 2016, 116, 9629−9630
Chemical Reviews
Editorial
us all with insight into the power of photochemistry and perhaps a glimpse of the potential in its new “golden age”.
Aaron B. Beeler
Department of Chemistry, Boston University
AUTHOR INFORMATION Notes
Views expressed in this editorial are those of the author and not necessarily the views of the ACS. Biography
Aaron Beeler received his B.Sc. in biology from Belmont University in 1998. In 2002 he earned a Ph.D. in medicinal chemistry at the University of Mississippi under the mentorship of John Rimoldi. He then joined the group of John Porco, Jr. as a postdoctoral fellow, eventually moving into the Center for Chemical Methodology and Library Development at Boston University, now the Center for Molecular Discovery (BU-CMD). He served as the Associate Director until 2012, at which point he joined the Department of Chemistry at Boston University as an assistant professor. Aaron’s multidisciplinary educational and research background has translated to his independent research. His group is active in developing reactions for the synthesis and medicinal chemistry of molecules that may be powerful tools to better understand biological processes important to human health and has a particular focus on leveraging flow chemistry to enable challenging photochemical transformations.
REFERENCES (1) Roth, H. D. The Beginnings of Organic Photochemistry. Angew. Chem., Int. Ed. Engl. 1989, 28, 1193−1207. (2) Barton, D. H. R; De Mayo, P.; Shafiq, M. Photochemical Transformations. Part II. The Constitution of Lumisantonin. J. Chem. Soc. 1958, 140−145. (3) Zimmerman, H. E. Five Decades of Mechanistic and Exploratory Organic Photochemistry. Pure Appl. Chem. 2006, 78, 2193−2203. (4) Hoffmann, N. Photochemical Reactions as Key Steps in Organic Synthesis. Chem. Rev. 2008, 108, 1052−1103. (5) Ramamurthy, V.; Turro, N. J. Photochemistry: Introduction. Chem. Rev. 1993, 93, 1.
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DOI: 10.1021/acs.chemrev.6b00378 Chem. Rev. 2016, 116, 9629−9630
