Preface

The books "Modern Amination Methods" and "Amino Group Chemistry - From Synthesis to the Life Sciences" edited by one of us for Wiley-VCH in 2000 and in 2007, respectively, were intended to provide the reader with exhaustive overviews of the most advanced methodologies for the C-N bond formation and with the role played by the amino function in those processes that are closely related to the life sciences.

These books were well received by the chemical community and highlighted the importance of keeping scientists to be continuously aware of the progress in the field of amino group chemistry. In 2018, setting up to discuss the prospect of coediting a new book on amino group chemistry, we asked ourselves if the past decade witnessed sufficient breakthroughs to make such update worth to be read by academicians or industrialists. It did not take too much time to convince ourselves that such endeavor would have been worthwhile and timely. In the past years, most of the breakthrough discoveries in synthetic organic chemistry embed efficient preparations of nitrogen-containing compounds. Arguably, amino group chemistry lies at the core of recent methodological trends. Furthermore, the disclosure of new materials, from medicine to nanoscience, has often been grounded on nitrogen derivatives. Thus, we embarked in this adventure, approaching the selection of the topics with an unbiased and wide-range attitude. In this new book, we aimed at providing not only an overview over specific aspects of amino chemistry but also a unique journey through modern chemistry.

With the very useful insights into the topic selection provided by Wiley anonymous reviewers, we commenced to approach several prospective authors. We have been very lucky to find contact authors among the most authoritative of their fields, who, together with their coworkers, assembled chapters characterized by clear structures, schemes, mechanisms, and figures accompanying the text together with exhaustive and up-to-date reference sections.

Throughout the 10 chapters of the book, amines are discussed with respect to the most advanced methodologies for their preparation, from design to scope surveys to applications to biologically active targets or precursors thereof, including large-scale industrial settings. Because the pharmaceutical and agrochemical industries are nowadays mostly away from the development of racemic compounds, several of the book chapters refer to enantioselective synthesis of chiral amines. It is worth noting that the contributions to this book present interlinks that, as a fil rouge crossing the whole book, allow the reader to face some of the topics under different perspectives.

The book starts with a topic that constitutes a continuum between the 2000s monographies and this one: electrophilic amination. Indeed, substitution-type electrophilic amination has gained a tremendous progress in the decade. This unconventional, yet synthetically appealing approach to C-N bond formation is nowadays performed under transition metal (TM)- and metal-free catalysis aiming to employ bench-stable and easily obtainable reagents for forging new C-N bonds. In this context, Chapter 1 summarizes the most recent achievements complying with the requirements for an ideal simple and versatile synthetic methodology.

The following part of the book brings the reader in the domain of nitrogen radicals as reactive intermediates, a reactivity stream displaying high complementarity to classical ionic and TM mediated processes. The use of photo- and electrochemical induced catalytic strategies is widely discussed (Chapters 2 and 3), overviewing the recent dramatic advances enabling to couple challenging C-H activation processes with C-N bond forming events. Although aminations with high enantioselectivity are yet rarely accessed, these radical methodologies targeting the synthesis of a wide range of heterocyclic systems and an array of complex N-containing structures outline a new and highly promising frontier.

As an enabling methodology, the development and application of asymmetric catalysis is now an integral part of the work of any major research unit in academia and industry. In the past decade, organo- and biocatalysis have flanked TM catalysis as key players for the enantioselective synthesis of chiral amino compounds, as overviewed in the ensuing Chapters 4-7. Worth noting is the possibility that these various catalytic approaches might concur toward attaining the same targets. This is exemplified in Chapter 4 devoted to the synthesis of chiral propargylamines. Many of these compounds possessing pharmaceutical properties have found applications in the treatment of diseases and can be considered among the most efficient building blocks for the synthesis N-containing heterocycles.

The relevance of high atom efficiency and very limited waste production (high atom economy) is of paramount importance for the development of methodologies with industrial prospects. Reactions such as TM-catalyzed asymmetric hydroamination, reductive amination, and hydroaminomethylation, reported in Chapter 5, meet these goals, an additional advantage being the simplicity and the easy availability of the starting materials, which is only partially counterbalanced by the complexity of the used ligands. Because of their relevance, these reactions are occasionally mentioned elsewhere in this book, although in the frame of different contexts, thus providing the reader with an exhaustive set of complementary information.

In the following chapters, metal-free stereoselective catalytic methodologies at the service of amine synthesis, represented by organo- and biocatalysis, are treated with a greater focus on industrial applications reflecting the dynamic nature of these catalytic streams. The central goal of organocatalysis (Chapter 6) is herein addressed to the emerging utilization of this methodology as an exceedingly useful synthetic tool for the large-scale preparation of active pharmaceutical ingredients (APIs) in industrial settings. An emphasis is placed on three case studied in which organocatalysis stands out with respect to other enantioselective strategies, for its versatility and potential for scale-up. The revolutionary approach of enzyme engineering, in the context of oxidoreductase enzymes applied to the synthesis of N-containing biologically relevant intermediates and products, is described in Chapter 7. The intrinsic selectivity of enzymes provides an obvious advantage in the key challenge of developing new synthetic platforms amenable to industrialization.

The following two chapters stand out for their uniqueness, targeting topics that were not even touched in the previous two books on amino chemistry but of exceptional prominence and timeliness. Chapter 8 deals with the use of amines in the synthesis, stabilization, and functionalization of organic-inorganic hybrid nanomaterials, highlighting through a large number of case studies the pivotal role played by the amino group to unlock practical applications in the fields of biology, medicine, and energy production. Conversely, the synthesis of a number of valuable amino compounds is reported in Chapter 9, from the transformation of renewable biomass resources that already incorporate the amino groups such as chitin, chitosan, and amino acids or by modifying bio-based compounds, followed by amination. Rare aminosugars, precursors of medicinal compounds, and a wide range of heterocycles are obtained avoiding the use of fossil-based feedstocks, thus providing a remarkable step forward in the ongoing shift from depleting to renewable resources.

The final Chapter 10 addresses current applications of TM-catalyzed aromatic amination in industrial settings by discussing a large number of case studies related to the manufacturing process of pharmaceutical compounds. In addition, with reference to the seminal work by Ullmann, Buchwald, and Hartwig, this contribution points on new concepts still at academic level, but either further extending the applicability of new methodologies, or on the brink of being industrially used. Also approaches with a focus on process intensification and sustainability (flow chemistry and catalyst immobilization) are presented, together with a view of the accompanying questions when applying the methodology of aromatic amination in the pharmaceutical industry. To make aware the reader about these challenges, themes such as the control of elemental impurities, the TM accounting, and the metal recycling are treated as well. Besides being a highly useful and up-to-date source of information on the TM-catalyzed aromatic amination in industry, this contribution will hopefully provide inspiration for academic research in developing new methodologies amenable to industrialization.

We warmly thank all the distinguished scientists and their coauthors for their rewarding and highly instructive contributions. Without their effort, even more valuable considering it partially coincided with a difficult period at the international level, this volume would have not been possible. Grateful acknowledgments are also addressed to the Wiley-VCH editorial staff, and in particular to Anne Brennführer, Aruna Pragasam, Elke Maase, and Katherine Wong, who encouraged us at project outset and helped us in a very competent manner in all the phases of the preparation of this book.

Alfredo...