Naphthyridines diazanaphthalenes

Unlike the other diazanaphthalenes (i.e., naphthyridines/ cinno-line, phthalazinc/ and quinoxaline), quinazoline shows abnormal behavior when converted into its cation. This anomaly was first discovered by Albert et who noticed that 4-methylquinazoline was a w eaker base (tenfold) than quinazoline (see Table I). This was... 

The naphthyridines consist of those diazanaphthalenes which have one nitrogen atom in each ring neither of which occupies a bridgehead position. Alternatively they can be named as pyridopyridines. The six possible isomers (1)—(6) are shown below. ... 

The parent 2,7-naphthyridine and some of its simple alkyl derivatives have found a natural place in many comparative studies on physical aspects of aza- and diazanaphthalenes (see Section 30.2.2). Moreover, the natural occurrence of the system as several alkaloids (see, e.g., the synthesis of jasminine, Section 30.1.3) and its use in analytical procedures e.g.,1290 have stimulated interest in the system. 

The six possible pyridopyridine systems have been known almost universally since circa 1930 as 1,5- (1), 1,6- (2), 1,7- (3), 1,8- (4), 2,6- (5), and 2,7-naphthyridine (6), However, the occasional use of an appropriate pyridopyridine or diazanaphthalene may still be found in some publications, Historically, the word naphthyridin(e) was coined by Arnold Reissert in 1893 specifically for the 1,8-naphthyridine system (4) and was so used for some years, especially in the German literature. Other terms, such as isonaphthyridine [for 1,5-naphthyridine (1)], benzodiazines (very misleading), pyridinopyridines , 2,5-naphthyridine [for 1,6-naphthyridine (2)], and copyrin(e) 13,40 or copurine39 [for 2,7-naphthyridine (6)] have appeared in the literature. 

The pyridopyridines, also called benzodiazines, and more commonly naphthyridines, consist of a group of diazanaphthalenes with one nitrogen in each ring and none at the bridgehead position. From the six possible isomers, one example of each of the series 1-X and 2-X, and the numbering scheme, are represented in (1) and (2). 

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