In the course of nearly every program of research in organic chemistry, the investigator finds it necessary to use several of the better‐known synthetic reactions. To discover the optimum conditions for the application of even the most familiar one to a compound not previously subjected to the reaction often requires an extensive search of the literature; even then a series of experiments may be necessary. When the results of the investigation are published, the synthesis, which may have required months of work, is usually described without comment. The background of knowledge and experience gained in the literature search and experimentation is thus lost to those who subsequently have occasion to apply the general method. The student of preparative organic chemistry faces similar difficulties. The textbooks and laboratory manuals furnish numerous examples of the application of various syntheses, but only rarely do they convey an accurate conception of the scope and usefulness of the processes.

For many years American organic chemists have discussed these problems. The plan of compiling critical discussions of the more important reactions thus was evolved. The volumes of Organic Reactions are collections of chapters each devoted to a single reaction, or a definite phase of a reaction, of wide applicability. The authors have had experience with the processes surveyed. The subjects are presented from the preparative viewpoint, and particular attention is given to limitations, interfering influences, effects of structure, and the selection of experimental techniques. Each chapter includes several detailed procedures illustrating the significant modifications of the method. Most of these procedures have been found satisfactory by the author or one of the editors, but unlike those in Organic Syntheses, they have not been subjected to careful testing in two or more laboratories. Each chapter contains tables that include all the examples of the reaction under consideration that the author has been able to find. It is inevitable, however, that in the search of the literature some examples will be missed, especially when the reaction is used as one step in an extended synthesis. Nevertheless, the investigator will be able to use the tables and their accompanying bibliographies in place of most or all of the literature search so often required. Because of the systematic arrangement of the material in the chapters and the entries in the tables, users of the books will be able to find information desired by reference to the table of contents of the appropriate chapter. In the interest of economy, the entries in the indices have been kept to a minimum, and, in particular, the compounds listed in the tables are not repeated in the indices.

The success of this publication, which will appear periodically, depends upon the cooperation of organic chemists and their willingness to devote time and effort to the preparation of the chapters. They have manifested their interest already by the almost unanimous acceptance of invitations to contribute to the work. The editors will welcome their continued interest and their suggestions for improvements in Organic Reactions.

In the intervening years since “The Chief” wrote this introduction to the second of his publishing creations, much in the world of chemistry has changed. In particular, the last decade has witnessed a revolution in the generation, dissemination, and availability of the chemical literature with the advent of electronic publication and abstracting services. Although the exponential growth in the chemical literature was one of the motivations for the creation of Organic Reactions, Adams could never have anticipated the impact of electronic access to the literature. Yet, as often happens with visionary advances, the value of this critical resource is now even greater than at its inception.

From 1942 to the 1980's the challenge that Organic Reactions successfully addressed was the difficulty in compiling an authoritative summary of a preparatively useful organic reaction from the primary literature. Practitioners interested in executing such a reaction (or simply learning about the features, advantages, and limitations of this process) would have a valuable resource to guide their experimentation. As abstracting services, in particular Chemical Abstracts and later Beilstein, entered the electronic age, the challenge for the practitioner was no longer to locate all of the literature on the subject. However, Organic Reactions chapters are much more than a surfeit of primary references; they constitute a distillation of this avalanche of information into the knowledge needed to correctly implement a reaction. It is in this capacity, namely to provide focused, scholarly, and comprehensive overviews of a given transformation, that Organic Reactions takes on even greater significance for the practice of chemical experimentation in the 21^st century.

Adams' description of the content of the intended chapters is still remarkably relevant today. The development of new chemical reactions over the past decades has greatly accelerated and has embraced more sophisticated reagents derived from elements representing all reaches of the Periodic Table. Accordingly, the successful implementation of these transformations requires more stringent adherence to important experimental details and conditions. The suitability of a given reaction for an unknown application is best judged from the informed vantage point provided by precedent and guidelines offered by a knowledgeable author.

As Adams clearly understood, the ultimate success of the enterprise depends on the willingness of organic chemists to devote their time and efforts to the preparation of chapters. The fact that, at the dawn of the 21^st century, the series continues to thrive is fitting testimony to those chemists whose contributions serve as the foundation of this edifice. Chemists who are considering the preparation of a manuscript for submission to Organic Reactions are urged to contact the Editor‐in‐Chief.

It has long been recognized that, in a molecule containing a system of conjugated double linkages, the influence of a functional group may sometimes be propagated along the chain and make itself apparent at a remote point in the molecule.

Reynold C. Fuson

Chem. Rev. 1935, 16, 1

In 1935, Reynold Clayton Fuson (University of Illinois) articulated the “ Principle of Vinylogy” to formalize the empirical observation that the electronic properties of functional groups are transmitted through “vinylene residues” (i.e. double bonds). The manifestation of those electronic properties can be enhancement of both electrophilic character and nucleophilic character, terms introduced just the year prior by Ingold (Chem. Rev. 1934, 16, 225). Although this phenomenon is easily understood from contemporary theory of organic chemistry, it is instructive to remember that the foundation of this principle originates in Robinson's electronic theory of organic reactions published in two lectures in 1932 (Institute of Chemistry, London, pp. 1–52). Robinson's illustration of “conjugated electromeric systems” are of tremendous historical significance as it introduces the use of “curly arrow notation” to signify the movement of electrons under the mandates of the “anionoid or cationoid” characteristics of the functional groups. The two chapters that comprise Volume 98 represent both manifestations of the principle of vinylogy, though not in the same way.

Although the reaction covered in the first chapter does not illustrate the principle of vinylogy, it does create the substrates that are essential for the manifestation of the vinylogous cationoid character of unsaturated carbonyl compounds. Chapter 1 in this volume, entitled “The Saegusa Oxidation and Related Procedures” by Jean Le Bras and Jacques Muzart, provides a comprehensive treatment of the catalytic dehydrogenation of enoxysilane derivatives to form α,β‐unsaturated carbonyl compounds. This transformation pioneered by Ito, Hirato and Saegusa has achieved the enviable status of a name reaction owing to its mildness, generality and ease of operation. Although many methods exist for the desaturation of native carbonyl compounds, these suffer from the need for stoichiometric amounts of strong oxidants and also the lack of site selectivity in case of ketones. By harnessing the ability to control the position of enolization and subsequent silylation, the Saegusa method solves a key limitation of earlier methods. Moreover, after initially requiring stoichiometric amounts of a palladium(II) oxidant, recent modifications have reduced the palladium loading considerably and have simultaneously introduced inexpensive and atom‐economical terminal oxidants to render the process highly efficient. In the spirit of the Organic Reactions style, the authors have done an outstanding job in compiling tables in the text portion that summarize the best methods for a given type of carbonyl compound and a given type of oxidant. Furthermore, in the Comparison with Other Methods section, the authors list representative cases wherein other methods are superior to the catalytic dehydrogenation and those for which the Saegusa protocol is superior. The Tabular Survey is organized by the carbonyl function that undergoes dehydrogenation, making the discovery of the best set of conditions for the interested reader extremely easy.

On the other hand, the second chapter is squarely in the domain of manifesting the principle of vinylogy for anionoid reactivity of enol ethers. Chapter 2 in this volume entitled “The Asymmetric Vinylogous Mukaiyama Aldol Reaction” by Martin H. C. Cordes and Markus Kalesse constitutes a tour de force treatment of another eponymous reaction. The 1973 report by Mukaiyama, Narasaka and Banno was a watershed event in the evolution of the aldol addition reaction. These authors demonstrated the ability to preordain one carbonyl component as the nucleophile by preforming the derived silyl enol ether, thus addressing one of the greatest disadvantages of this reaction, namely the inability to control the identity of donors and acceptors. The historical development of this reaction has been extensively chronicled but perhaps nowhere better than in Chapter 3 of Volume 28 entitled “Directed Aldol Reactions” by Teruaki Mukaiyama. It will therefore come as no surprise that Prof. Mukaiyama was also the pioneer of the vinylogous extension of his own invention. Cordes and Kalesse have composed an outstanding overview of the various modes of activation of vinylogous enol ethers derived from a myriad of different carbonyl precursors and have expertly described the stereochemical model for relative and absolute stereoselection. A reaction of this scope and generality has been extensively applied in complex molecule syntheses, particularly in recent years with the advent of catalytic, enantioselective variants. Perhaps the most impressive component of this chapter is the extraordinary resolution of the Tabular Survey. The primary rubric for tabular organization is the structure of the nucleophile and comprises ten tables for all of the different functional groups involved. However, each of these tables is further subdivided according to a secondary rubric that represents all of the different electrophiles employed with that nucleophile. In the case of β‐keto ester derived dienolates, this collection comprises 26 different electrophile types! Accordingly, readers will easily locate the pairwise combination of reactants of greatest interest to their particular goal. Truly, a field guide of the first rank for executing this reaction.

The organic chemistry community mourns the passing of Professor Teruaki Mukaiyama who died on 17 November 2018 at the age of 91. In honor of his towering contributions to our discipline and his authorship of two chapters in the Organic Reactions series, we felt it fitting to dedicate Volume 98 to his memory.

It is appropriate here to acknowledge the expert assistance of the entire editorial board, in particular Jin K. Cha (Chapter 1) and Gary A. Molander (Chapter 2) who shepherded these chapters to completion. The contributions of the authors, editors, and publisher were expertly coordinated by the board secretary, Dena Lindsay. In addition, the Organic Reactions enterprise could not maintain the quality of production without the dedicated efforts of its editorial staff, Dr. Danielle Soenen, Dr. Linda S. Press, Dr. Engelbert Ciganek, and Dr. Robert M. Coates, Dr. Landy Blasdel, and Dr. Devra Dolliver. Insofar as the essence of Organic Reactions chapters resides in the massive tables of examples, the authors' and editorial coordinators' painstaking efforts are highly prized.