Systematic Nomenclature of Heterocyclic Compounds

Many organic compounds, including heterocydic compounds, have a trivial name. This usually originates from the compounds occurrence, its first preparation, or its special properties. 

The derivation of the systematic name of a heterocyclic compound is based on its structure. Nomenclature rules have been drawn up by the lUPAC Commission and these should be applied when writing theses, dissertations, pubhcations, and patents. These rules are Hsted in Section R-2 of the lUPAC Blue Book together with worked examples (H. R. Panico, W. H. Powell, J.-C. Richer, A Guide to lUPAC Nomenclature of Organic Compounds, Recommendations 1993 Blackwell Scientific Oxford, 1993 the previous lUPAC Blue Boole J. Rigandy, S. P. Klesney Nomenclature of Organic Chemistry Pergamon Oxford, 1979). 

The lUPAC rules are not given in detail here, rather instructions are given for formulating systematic names with appropriate reference to the Blue Book. 

Every heterocychc compound can be referred back to a parent ring system. These systems have only H-atoms attached to the ring atoms. The lUPAC rules allow two nomenclatures. 

The Chemistry of Heterocycles Structure, Reactions, Syn iesK, emd Applications, 

The Chemistry of Heterocycles, Second Edition. By Theophil Eicher and Siegfried Hai )tmann Copyright 2003 Wiley-VCH Verlag GmbH Co. KGaA ISBN 3-527-30720-6 

The type of heteroatom is indicated by a prefix according to Table 1. The sequence in this table also indicates the preferred order of prefixes (principle of decreasing priority). 

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Finally, the systematic nomenclature of heterocyclic compounds will be illustrated by a few complex examples. 

There are three types of nomenclature used for heterocyclic compounds. Many heterocycles have trivial names, which are based on their occurrence, special properties, or historical reasons such as discovery of particular material. Systematic names of heterocyclic compounds derived from the structure of the compound are governed by lUPAC rules, which are divided into two groups the Hantzsch-Widman and replacement nomenclatures. In this book, we were trying to follow the guidelines for naming the heterocyclic compounds, which are summarized in Chapter 2 of the excellent book The Chemistry of Heterocycles Structures, Reactions, and Applications ... 

A detailed discussion of the nomenclature for heterocyclic compounds can be found in the first edition of Comprehensive Heterocyclic Chemistry (CHEC-I, Section 1.02). Some of the rules of systematic nomenclature used in Chemical Abstracts and approved by the International Union of Pure and Applied Chemistry are collected here. Important trivial names are listed at the beginning of individual chapters. 

As was done in CHEC-I <84CHEC-1(1)630>, the nomenclature in this chapter follows the borane and the borate nomenclature. Systematic rules are avoided if trivial names are available. If this is not the case, the general nomenclature of heterocycles is used. The following description of the different types of compounds elucidates structures and nomenclature (l)-(22). 

Ollis and Ramsden state that A compound may be appropriately called mesoionic if it is a five-membered heterocycle which cannot be represented satisfactorily by any one covalent or polar structure and possesses a sextet of electrons in association with the five atoms comprising the ring . From the point of view of systematic nomenclature, compounds of this type are difficult to deal with, since most available nomenclature systems are designed so as to name one particular bond- and charge-localized canonical form. 

Another type of anion, confined for practical purposes to boron compounds, has no unshared electrons at the anionic site, and must be thought of as being formed by addition of hydride to a boron atom (or other atom with an incomplete valence shell). Such structures were not anticipated at the time general heterocyclic nomenclature was developed, and they are only recently being fitted into systematic nomenclature (lUPAC Provisional Recommendation 83.2). Proposals for a suffix to indicate such structures are under consideration (1982). 

The naming of organophosphorus compounds is frequently a source of confusion owing to the (co)existence of several, more or less systematic, schemes for compound nomenclature. The designation of the parent neutral heterocycles Ilia as... 

A variety of names has been used for the benzologues of pyran and its derivatives, many of which have been described in two treatises on oxygen heterocyclic compounds <77HC(3l)l, 81HC(36)l). It is of value to indicate the nomenclature which has been adopted in this and the two following chapters, since it is not always considered appropriate to use the more cumbersome and less familiar systematic names. 

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