Nomenclature fused systems

All four possible pyridopyrimidine systems, pyrido[2,3-Chemical Abstracts nomenclature is used throughout this Chapter. For the reasons given above (Section 2.15.1), the pyrido[2,3-fused systems, e.g. (5) and (6) (numbering shown), are also known. The linear benzo fused derivatives of pyrido[3,2-[Pg.201]

Note 2. This example would not normally be regarded as a fused system for nomenclature purposes, since it is not ortho- or ortho- and peri-fused [13]. 

Bridging Nomenclature for Use with Fused Systems (IUPAC Rules... 

Chemical Abstracts prefers the sugar terms, especially in the trivial forms however, in some instances, the bicyclo nomenclature is also applied. Surveying the whole original literature, preference is doubtless given to carbohydrate names with frequent use of the trivial isohexide terms, followed by the bridged-systems labeling. The fused systems names are not in vogue. 

The numbering of the skeleton in a ring system is generally a consequence of the way in which the skeleton is named. In order to avoid confusion as to the peripheral numbering sequence and locations of substituents in the fused systems, structural formulae are drawn as in Chemical Abstracts in accordance with the rules of heterocyclic nomenclature. Thereby the reader is not required to possess detailed knowledge of the elaborate series of priorities used in the structural presentation and numbering of ring systems. 

The nomenclature of benzfused or of any fused system or spiral system follows the Hantszch-Widman system of nomenclature. In these fused systems, the first ring or benzene ring is the base component of the second ring system, isoxazole. Thus the complete name becomes benzisoxazole. The bonds in the base component are labeled as a, b, c, d, e, etc. Atoms in the hetero-ring component are numbered as 1-7 as shown in (2) and (3). Two classes of benzfused systems, that is, 1,2-benzisoxazole (or indoxazene) (2) and 2,1-benzisoxazole (or anthranil) (3) exist. 

The formal procedures for analysis of alternative modes of disconnection of fused-ring systems are facilitated by the use of a standard nomenclature for various types of key bonds in such structures. A number of useful terms are illustrated in formulas 111-114, which have been constructed arbitrarily using rings of the most common sizes, 5 and 6. Structures are shown for... 

The nomenclature used to describe the fused benzene-pyrrole-pyridine system of the compounds under discussion has been repeatedly modified, and the compounds have been numbered in an astonishing variety of ways since Perkin and Robinson introduced the name carboline for the ring system, which was encountered for the first time in the harmala alkaloids. In the earliest version of carboline nomenclature, the parent compound of the series, whose trivial name was norharman, was referred to as 4-carboline and numbered as in 1. Harmine (2) then became ll-methoxy-3-methyl-4-carboline. 

The naming of these three heterocyclic fused (5 5 5) ring systems has been carried out according to the IUPAC system of nomenclature. Some examples are given as follows compound la (Table 1) is named (3-hydroxy-4-methoxyphenylthieno[2,3-3]pyrrolizin-8-one. Compound 15a (Table 2) is dithieno[3,2-3 2, 3 - 1thiophene. Compound 23a (Table 2) is dithieno[3,2-3 2, 3 - 1pyrrole. Compound 20a (Table 2) is dithicno[3,2-3 2, 3 -r/]thiophene-4,4-dio ide. Compound 13b (Table 2) is 3,4-dimethyldithieno[3,2-3 2, 3 -i/]thiophene-7,7-dioxide. Compound 38 (Table 4) is fM, r, r-10-azatricyclo[5.2.1.01 10]deca-2,5,8-triene. Compound 39 (Table 4) is cis,cis, m-10-azatricyclo[5.2.1.01 10]deca-2,8-diene. The nomenclature of compound 40 (Table 4) is 1,4,7 triaza tricy-clo[5.2.1.01,10]decane. 

The alcohol portion in hyoscyamine is tropine in hyoscine it is the epoxide scopine. Tropine is an example of an azabicyclo[3,2,l]octane system with a nitrogen bridge, whereas scopine is a tricylic system with a three-membered epoxide ring fused onto tropine. Note that systematic nomenclature considers an all-carbon ring system with one carbon replaced by nitrogen hence, tropane is an azabicyclooctane (see Section 1.4). 

The nomenclature is not quite uniformly used in the literature. According to Chemical Abstracts, perhydro compound 2 is decahydropyr-ido[l,2-a]azepine, but its oxo derivative 3 (Scheme 2), for instance, is named octahydropyrido[l,2-a]azepine-8(2H)-one. Examples of benzo-fused parent systems frequently dealt with in the following sections can also be found in Scheme 2 (98MI2 cf. Section 2.9.1) ... 

Polycyclic parent hydrides. These are classified as bridged polyalkanes (also known as von Baeyer bridged systems, from the nomenclature system developed to name them), spiro compounds, fused polycyclic systems and assemblies of identical rings. The four systems may be either carbocyclic or heterocyclic. In developing their names, the following principles are used. 

Fused polycyclic systems are very numerous and diverse. They are named using the structures and names of their smaller components and the concept of ortho-fusion, which is purely a formal operation encountered in nomenclature. This concept is essential to the naming of larger systems, and is the formation of one bond by the condensation of two bonds belonging to two different cyclic systems, one of them being a mancude ring. 

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. 

This chapter covers literature published since 1982 early materials are included here only where needed as a basis for describing further developments or where not previously mentioned in CHEC-1 <84CHEC-l(5)669>. The structural types surveyed here include 1,2,3-triazoles, benzotriazoles, their dihydro derivatives and carbocyclic fused compounds. Compounds with heterocyclic fused rings are not included. The nomenclature system was discussed in CHEC-T <84CHEC-I(5)670>. 

The nomenclature of ring systems containing the partially or fully hydrogenated monocyclic, bicyclic, and tricyclic fused 1,2-oxazine ring skeleton are shown in Figure 1. 

The second approach for endocyclic N-PACs is to use replacement nomenclature, in which the term aza is a prefix to the corresponding PAH. The position of the N-atom in the fused-ring system of the PAH precedes the term aza. Thus, for example, quinoline is 1-azanaphthalene. We generally use this convention for three or more ring N-PACs with endocyclic nitrogen heteroatoms. 

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