Synthesis of 2,7-naphthyridine derivatives

2,7-Naphthyridines have been the least known from all of the six structural isomers of pyridopyridines. The broad spectrum of biological activity of 2,7-naphthyridine derivatives [1] is the main of reason for obtaining of the new compounds containing this scaffold (Fig. 1). Gabriel and Colman were the first to obtain isomer 2,7-naphthyridine in 1902 and they called it ‘copiryne’ (Fig. 2) [2]. The goal of this study is the presentation of various methods for the preparation of 2,7-naphthyridine derivatives. Compounds containing copyrine scaffold can be obtained from a different substrates, but that synthesis may be classified into three main categories: from pyridine derivatives, from quinoline derivatives and from other compounds. Most of 2,7-naphthyridines have been synthesized by cyclocondensation (Scheme 5, 7–10, 13–14, 16–18, 20, 28–29, 32, 35–36) or intramolecular cyclization (Scheme 1–4, 6, 11–12, 15, 19, 21–25, 30–31, 33–34, 38) of pyridine derivatives by annulation of the other pyridine ring [3–24, 27–31]. Intramolecular rearrangement of pyrrolo [3,4-c] pyridines (Scheme 26–27) and pyrano [3,4-c] pyridine or thiopyrano [3,4-c] pyridine (Scheme 35–37) also gave the 2,7-naphthyridine scaffold [32-34]. There are also many syntheses of benzo[c][2,7]naphthyridine, benzo [f] [2,7] naphthyridine or benzo [ c,f] [2,7] naphthyridine scaffolds, in which the substrates are quinoline derivatives (Scheme 39–48) [35–43]. 2,7-naphthyridines have been least often obtained by cyclocondensation of non-cyclic substrates (Scheme 49–53) [44–49]