Fusion nomenclature

Not considered suitable for use as components in fusion nomenclature (Section 1.02.3.3). 

The two most commonly applied systems for naming polycyclic parents are in some ways complementary. Fusion nomenclature provides names for structures containing the maximum number of non-cumulative double bonds von Baeyer nomenclature (Section 1.02.3.4) names fully saturated structures. Thus names for partially hydrogenated structures can be arrived at either by adding hydro prefixes to fusion names or ene , diene , etc. suffixes to von Baeyer names (see examples 29 and 30). If needed, rules are available for... 

As noted in Section 1.02.3.2, replacement procedures can be applied to heterocyclic analogues of polycarbocycles named by fusion nomenclature. Examples (48) and (49) show... 

When applying this principle to replacement names generated from fusion nomenclature, it is essential to keep in mind that fusion names for hydrocarbons ending in -cycloalkene are for fully unsaturated skeletons the -ene ending implies whatever number of double bonds may be necessary, without a multiplier. Thus (117) has six double bonds in the twelve-membered ring, and one must add ten hydrogens to saturate it to the stage of a simple benzene derivative, compound (118). 

The fusion name l//-triazolo[4,5-d]pyrimidine for (140) is preferred by practitioners in the field and appears in CA indexes. On the other hand, the nonspecialist, who may well be uncertain about his command of fusion nomenclature, might more easily grasp the replacement name l//-l,2,3,4,6-pentaazaindene. (This is an appropriate place to emphasize that, by lUPAC rules, replacement names are to be based only on a completely carbocyclic parent. Notwithstanding the attractive simplicity of 8-azapurine for the example at hand, it has no sanction see, however. Section 1.02.3.2. The purpose of this avoidance is to forestall a multiplicity of names for systems containing several hetero atoms.)... 

However. Chemical Abstracts use fusion nomenclature so that 1, 2 and 3 are named pyrido-[2,1,6-dtjquinolizine, azepino[2,l,7-f<7]indolizine and l,4,9b-triazaphenalene, respectively. 

Note. General natural product fusion nomenclature [26] would require the carbohydrate portion to be cited last (e.g. oxazologlucopyranose), whereas it is cited first here and in the literature. 

When a system does not have a retained name or a name that can be composed systematically as above, and when ortho- and ortho-peri- x% on are possible, it is named using fusion nomenclature, i.e. by combining the names of the two or more systems that are fused. One system is adjudged to be the senior according to criteria described elsewhere and is taken as a parent hydride, and the other is denoted in the name by a non-detachable prefix. The junction of the two systems is indicated in a specific manner. Instead of numerical locants, italic letters a , 6 , c , etc. are used to identify bonds in the parent hydride. The final letter o and normal locants are characteristic of the prefix. The examples below illustrate the fusion operation and the resulting fusion name. 

Lowest letters (lowest means a lower than b, etc.) in the expression of ring junctions in fusion nomenclature. 

Further substitution of the peripheral carbon atoms of the cyclazines by heteroatoms (N, S, etc.) is indicated in this chapter according to the replacement nomenclature system (aza, thia, etc.). Although, strictly, this runs contrary to the rules,lc since it is a heterocyclic, not a hydrocarbon, system which is replaced, the connection between closely related compounds can more clearly be seen. It should be noted that Chemical Abstracts employs the systematic fusion nomenclature I, for instance, is pyrrolo[2,l,5-cd]indolizine. 

The locant indicates the position of the double bond other positions are possible. b Not considered suitable for use as components in fusion nomenclature (Section 1.02.3.3). c 4H-Pyran is also possible. 

Several names have been used in the chemical literature for pyrrolo[l,2-a]pyridine including pyrrocoline, pyrindole, pyrrodine and 8-pyrrolopyridine, but the one which is now used by Chemical Abstracts, and which will be used in this chapter, is indolizine. The numbering of the system is shown in formula (1). The denomination of aza derivatives follows the replacement nomenclature system, e.g. 1-azaindolizine, etc. It should be noted that Chemical Abstracts follows the systematic fusion nomenclature 1-azaindolizine, for instance, is imidazo[l,2-a]pyridine. The cyclazine nomenclature is treated in Section 3.08.9.1. 

Two types of fusion nomenclature are available of these the older Stelzner system" is not recommended for use by IUPAC (except as in Rule B-23.5) or by Chemical Abstracts. Nevertheless, it will be described briefly here since it still appears commonly in the literature. The principles of both systems are best understood in application to polycar bocycles. 

The application of replacement nomenclature has already been discussed (Section II, B, 1, b) and will not be dealt with further here (although replacement names will be given where appropriate). Also it is unnecessary to discuss the use of the trivial names allowed by IUPAC they may be applied whenever it appears appropriate. Those cases in which ring assembly nomenclature should be used are generally obvious and require no comment. Problems do arise, however, in deciding whether to use fusion nomenclature or von Baeyer nomenclature. 

Ending of names of large heteromonocycles (more than 10 ring atoms) with the maximum number of non-cumulative double bonds for use in fusion nomenclature, e.g. 2H- -oxa-4,8,11-triazacyclotetradecine. 

Ending resulting from the change of the ine ending in names of cyclic mancude ring systems to ino to form prefixes in fusion nomenclature. (See Section P-25.3 of the Blue Bookb.)... 

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