Pyridine derivatives benzopyridines

The 9ai7-quinolizine structure (82) for the labile adduct from 3,5-dimethylpyridine was clearly established by the nuclear magnetic resonance studies of Richards and Higham, and subsequent work showed the labile adduct from 3-methylpyridine was analogous. As the labile adducts from all the pyridines and benzopyridines so far examined have very similar infrared absorption spectra in the 5-7 yn. (carbonyl and aromatic) region and within quite close limits very similar ultraviolet absorption spectra, it can be concluded that all are derivatives of 9aH-quinolizine,... 

In our discussion, we will divide tautomeric compounds according to the type of substituent involved, and under that heading consider all the various possibilities including structures of both neutral form and those for which only charge-separated forms can be written, and both pyridine and benzopyridine derivatives, and polysubstituted heterocycles. 

The amount of literature on applications of pyridine and benzopyridine derivatives is particularly vast. This necessarily abbreviated presentation is written not as a definitive text, but as an overview in an attempt to convey to the reader the importance and variety of pyridine derivatives in the industrial sphere. 

The commercial availability of basic pyridine derivatives has encouraged a tremendous amount of research into pharmaceutically active compounds. Two reviews in particular list a large number of medicinal compounds (B-80MI20900,77CZ389) based on the pyridine ring. Likewise, the occurrence of benzopyridine natural products with chemotherapeutic activity has stimulated the production of synthetic materials from aromatic amine precursors. Some important examples are presented below. 

Natural products biosynthesis, 1, 83-109 fused oxirane rings, 7, 192 fused thiirane rings, 7, 192-193 as insecticides, 1, 198 nomenclature, 1, 28-31 oxiranes, 7, 120 as pharmaceuticals, 1, 146-156 pyridine derivatives as pharmaceuticals, 2, 516-517 pyridines and benzopyridines, 2, 511-513... 

PYRIDINE DERIVATIVES AND RELATED COMPOUNDS (BENZOPYRIDINES = QUINOLINES)... 

Pyridine Derivatives and Related Compounds (Benzopyridines = Quinolines)... 

Fused benzene rings aid nucleophilic attack on pyridines, pyridinium and pyrylium ions, and pyrones the loss of aromaticity involved in the formation of the initial adduct is less in monobenzo derivatives and still less in linear dibenzo derivatives than in monocyclic compounds. For the same reason, the tendency for this initial adduct to re-aromatize is less for benzopyridines. Fused benzene rings also influence the point of attack by nucleophilic reagents attack rarely occurs on a carbon atom shared with a benzene ring. Thus, in linear dibenzo derivatives, nucleophilic attack is at the y-position (157). 

Benzopyridines are attacked by organometallic compounds at a position a to the nitrogen unless both a-positions are blocked. The dihydro derivatives of quinoline and isoquinoline are more stable and less easily aromatized than those from pyridine, and are hence more frequently isolated. 

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