Synthesis and Reactivity

Fused benzene rings are treated as substituents. Thus quinoline, for example, is considered as a substituted pyridine, albeit a very special and important one, and treated alongside other substituted pyridines in the discussion of its structure, reactivity and synthesis. Reactions of quinoline at positions 1-4 are considered as reactions at ring atoms, whilst reactions at positions 5-8 are regarded as reactions of the substituent . 

A wide range of ring sizes have been synthesized, from the very small [1.1.0] fused ring systems to the macro-bicyclic systems. The reactivity and synthesis of the fused ring systems is reviewed first followed by the nonfused compounds. As the synthetic methods used to produce the various examples in this class of compounds were well reviewed in CHEC-II(1996), the synthetic methods section, Section 12.12.8, will outline selected types of compound within this group that have received more attention over the review period. 

Chapter 5.18 presents over 50 heterocyclic systems whose chemistry usually depends more on the nature of the heteroatoms than on the systems being seven-membered heterocycles. At the present state of knowledge, organizing the chapter in separate sections on structure, reactivity and synthesis would not produce a happy result, especially for the reactivity section. Little is presently known about the reactivities of the majority of the systems, many of which have been prepared to explore their pharmacological activities. The chapter, therefore, has been organized according to the number and nature of the heteroatoms. 

Three general chapters on structure, reactivity, and synthesis precede the monograph chapters in each of Parts 2 to 5 of CHEC. The purpose is to introduce each family of ring systems and to emphasize the logical correlations within them, and so to help in the understanding of known reactions and in the prediction of new ones. These 12 general chapters thus provide an overview of the whole subject of heterocyclic chemistry and they should be of particular interest to students and teachers. These general chapters also appeared in the 1985 version of the Handbook of Heterocyclic Chemistry and it is planned that they will appear in a new revised version of the Handbook. 

In CHEC(1984), the ring system for the 1,2-diazepines was covered as a part of bigger chapter on seven-membered rings with two or more heteroatoms <1984CHEC(7)593>. The main focus was on the synthesis and reactivity. However, in CHEC-II(1996), in addition to the sections on reactivity and synthesis as seen in CHEC(1984), there are few sections on the structure of 1,2-diazepines, such as theoretical methods, experimental methods and thermodynamics aspects <1996CHEC-II(9)113>. Since CHEC-II(1996), 1,2-diazepines have been extensively studied... 

Chemical and physicochemical properties for saturated, partially saturated and fully conjugated ring systems are discussed under the appropriate section on structure, reactivity and synthesis. 

The structure, reactivity and synthesis of the l,4,5,8-tetrahydro-l,4,5,8-tetrachal-cogenafulvalenes containing selenium and tellurium are also considered in this chapter. These structures are summarized in Scheme 2 and correspond to C6S2Se2 systems (dithiadiselenafulvalenes), C6SSe3 systems (thiatriselenafulvalenes), C6Se4 systems (tetraselenafulvalenes) and CeTe4 systems (tetratellurafulvalenes). 

The text Heterocyclic Chemistry by A. R. Katritzky and J. M. Lagowski was the subject s first modern treatment it appeared SO years ago, treating structure, reactivity, and synthesis systematically in terms of molecular structure. This text and its sequels, which were translated into Chinese, French, German, Greek, Italian, Japanese, Polish, Russian, and Spanish, revolutionized the practice and teaching of the subject worldwide. The 1st Edition of Handbook of Heterocyclic Chemistry (Handbook-I) followed in 1985 as part of Comprehensive Heterocyclic Chemistry 1st Edition (CHEC-I). Handbook-II appeared in 2000 alongside CHEC-II. We now present Handbook-Ill following the publication of CHEC-III in 2008. 

Handbook-Ill retains the essentials of the treatments of Handbooks-I and -II in dividing the subject into the three main areas of structure, reactivity, and synthesis. We have striven both to be reasonably comprehensive and to keep the physical size of Handbook-Ill to a minimum, so it can be conveniently handled and consulted. 

Azaazulenes, reactivity and synthesis of 81H(15)547, 81YGK690. Azadienes, heterocyclic, Diels-Alder reactions of 86CRV781. 

Cyclic phosphenium cations, reactivity and synthesis of 85CRV367. 

The original review on selenazoles in the first edition of Comprehensive Heterocyclic Chemistry <84CHEC-I(6)333> was divided into three sections structure, reactivity, and synthesis. In the structural section a discussion of H and C NMR concerned only benzoselenazole. No mention of Se NMR was made unfortunately, little has been done in this area since. More information concerning fragmentation patterns of selenazoles in the mass spectrum has been reported. The chapter did not mention IR, UV, and other less-used analytical methods. The reactivity discussion was limited to electrophilic additions at the 5-position and reactions of 2-methylbenzoselenazoles. The synthesis section was more extensive. 

We have maintained the principal aim of the earlier editions - to teach the fundamentals of heterocyclic reactivity and synthesis in a way that is understandable by undergraduate students. However, in recognition of the level at which much heterocyclic chemistry is now normally taught, we include more advanced and current material, which makes the book appropriate both for post-graduate level courses, and as a reference text for those involved in heterocyclic chemistry in the work place. 

The main body of factual material is to be found in chapters entitled Reactions and synthesis of... a particular heterocyclic system. Didactic material is to be found partly in advanced general discussions of heterocyclic reactivity and synthesis (Chapters 3, 4 and 6), and partly in six short summary chapters (such as Typical Reactivity of Pyridines, Quinolines and Isoquinolines Chapter 7), which aim to capture the essence of that typical reactivity in very concise resumes. These last are therefore suitable as an introduction to the chemistry of that heterocyclic system, but they are insufficient in themselves and should lead the reader to the fuller discussions in the Reactions and Synthesis of. .. chapters. They will also serve the undergraduate student as a revision summary of the typical chemistry of that system. 

The above examples amply illustrate the strong influence physics exerts on chemistry. Bunsen was perceptive in remarking A chemist who is not at the same time a physicist is nothing at all. (Schlag 1998). Of the major areas of chemistry (molecular structure, properties of substances, reactivity and synthesis), only synthesis is least affected by physics. When chemists synthesize new molecules, particularly in the... 

In the first edition of Comprehensive Heterocyclic Chemistry (CHEC-I), published early in 1984, Cook exhaustively reviewed the six-membered rings with more than one oxygen or sulfur atom <84CHEC-1(3)943>. In 1990, Joule in Advances in Heterocyclic Chemistry provided a very comprehensive discussion of the structure, physical properties, reactivity, and synthesis of thianthrenes <90AHC(48)301>. 

This volume normally treats reactivity and synthesis in separate sections. However, such an arrangement of the present chapter would result in separation of material which it is more appropriate, for considerations of space, to discuss together. Reactivity and synthetic methods are therefore dealt with in the same section. 

---