Heterocyclic trivial names

Systems in which at least two neighbouring atoms are common to two or more rings are known as fused systems. For several bicyclic benzo-fused heterocycles, trivial names are permitted, e.g. ... 

Table 1.5 Trivial Names of Heterocyclic Systems Suitable for Use in Fusion...

Table 1.6 Trivial Names for Heterocyclic Systems That Are Not Recommended...

These trivial names are permitted -y-butyrolactone, -y-valerolactone, and 5-valerolactone. Names based on heterocycles may be used for all lactones. Thus, -y-butyrolactone is also tetrahydro-2-furanone or dihydro-2(3/f)-furanone. 

Replacing one carbon atom of naphthalene with an a2omethene linkage creates the isomeric heterocycles 1- and 2-a2anaphthalene. Better known by their trivial names quinoline [91-22-5] (1) and isoquinoline [119-65-3] (2), these compounds have been the subject of extensive investigation since their extraction from coal tar in the nineteenth century. The variety of studies cover fields as diverse as molecular orbital theory and corrosion prevention. There is also a vast patent Hterature. The best assurance of continuing interest is the frequency with which quinoline and isoquinoline stmctures occur in alkaloids (qv) and pharmaceuticals (qv), for example, quinine [130-95-0] and morphine [57-27-2] (see Alkaloids). 

Some of the partially and fully reduced heterocyclic six-membered rings are sufficiently important to have trivial names with which the reader should be familiar. Thus hexahy-dropyridine (38) is known as piperidine, and tetrahydro-l,4-oxazine (39) is morpholine. Tetrahydropyridines are also sometimes referred to as piperideines, with the position of the double bond denoted by a A, but this system is obsolescent (at the least). 

As described in Section 1.02.2.3, any heterocycle can be named by indicating (with appropriate prefixes) the positions of heteroatoms in the corresponding carbocycle. The carbocycle can be named systematically, as described in later Sections however, the replacement procedure can also be applied to naming heterocyclic analogues of trivially named carbocycles. A list of polycarbocycles with their trivial names is given in Table 5 (taken from Rule A-21.2 in the lUPAC Blue Book (B-79MI10200)) replacement names may be derived as shown in examples (27) and (28). As demonstrated by example (28), it is unnecessary to add hydro prefixes if the heterocycle cannot accommodate as many double bonds as the original carbocycle. 

The antimicrobial activity of thiosemicarbazones against Mycobacterium tuberculosis in vitro was first reported by Domagk et al. [28] and later confirmed in vivo [29]. Screening revealed that only certain substituted be-nzaldehyde and heterocyclic thiosemicarbazones possess antitubercular activity [30-32]. The most widely used is p-acetamidobenzaldehyde thiosemicarbazone (trivial name = thiacetazone), 1. 

Lactams are named in several ways. They are named as alkanolactams by the IUPAC substitutive system, such as 3-propanolactam, 4-butanolactam, 5-pentanolactam, and 6-hexano-lactam, respectively, for the 4-, 5-, 6-, and 7-membered rings, respectively. An alternate IUPAC method, the specialist heterocyclic nomenclature system, names these lactams as 2-azetidinone, 2-pyrrolidinone, 2-piperidinone, and hexahydro-2f/-azepi n-2-one, respectively. These lactams are also known by the trivial names fl-propiolactam, a-pyrrolidone (y-butyrolactam), a-piperidone (8-valerolactam), and e-caprolactam, respectively. 

Heterocyclic parent hydrides. These compounds form a large and diverse group. The names of these parent hydrides are usually formed systematically. However, some 50 trivial names are retained and used in preference to their systematic counterparts. 

Quinacridone is the trivial name given to the five-ring heterocyclic system exemplified by the linear irani-quinacridone (2.69). The yellow-red to reddish-violet shade pigments based on this ring system show outstanding durability and are used in plastics, in industrial and automotive finishes and in exterior finishes. Like copper phthalocyanines the unsubstituted linear quinacridone exhibits polymorphism and two crystal forms, the reddish violet P-form and the red y-form, are commercially... 

A problem arises with trivial names when a sp hybridized atom is present in an otherwise unsaturated ring. A good example is pyran, a heterocycle that is formally the product of the addition of a single hydride ion to the pyrylium cation. However, as this addition could occur either at C-2 or C-4, two isomers of pyran are possible so the question is, how can you distinguish between them The solution is to call one compound 2/f-pyran and the other 4/f-pyran, using the number of the ring atom and the letter H, in italics, to show the position of the hydrogen (see Box 1.2). This system of nomenclature works tolerably well in many related cases and is widely used other examples will be found in this book. 

Using this terminology, furan becomes oxole and tetrahydrofuran is named oxolane pyridine is azine and piperidine is azinane. As with trivial names, the potential difficulty over partly reduced heterocycles is resolved... 

Many heterocycles are fused to other ring systems, notably benzene, giving in this case benza derivatives some of these compounds are also extremely well known and have trivial names of their own, such as indole and. Here, however, it is possible to relate these compounds... 

The IUPAC nomenclature of S-atom PACs is also similar to that for N-PACs. Thus the trivial name thiophene (XIV) is a basis for the common names of S-heterocycles containing one endocyclic S-atom in a 5-membered fused ring. Addition of two benzo groups gives dibenzothiophene (XV) ... 

Most of the heterocycles are known hy their trivial names, e.g. pyridine, indole, quinoline, thiophene and so on. However, there are some general rules to he followed in a heterocycle, especially in the use of suffixes to indicate the ring size, saturation or unsaturation as shown in the following table. For example, from the name, pyridine, where the suffix is -ine, one can understand that this heterocyclic compound contains nitrogen, has a six-memhered ring system and is unsaturated. 

Replacement of CH in benzene by an oxonia group (0+) gives the pyrylium cation, but no neutral oxygen analogue of pyridine is possible. Both 2H- and 4//-pyran contain -hybridized carbon atoms. Many trivial names exist for oxygen heterocycles and the more important of these are shown in Scheme 3. 

The benzo[a] (19), benzo[/t (15) and benzo[c] (16) fused heterocycles are heterocyclic analogues of naphthalene, with the dibenzo heterocycles (17) bearing a similar electronic relationship to phenanthrene. Some of these compounds are still known by their trivial names indole (15 Z = NH), isoindole (16 Z = NH), carbazole (18) and indolizine (19). The names thianaphthene and pyrrocoline for (15 Z = S) and (19) respectively are now little used. Particular confusion can arise in consulting... 

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