2.7- Naphthyridine properties

The physical properties of four of the six possible naphthyridines have been examined in some detail, and hydration could not be demonstrated in the neutral species and cations of 1,5-, 1,6-, 1,7-, and... 

Tire purpose of this chapter is to review the chemistry of the nitro-1,5-, -1,6-, -1,7-, and -1,8-naphthyridines (1) [nitro-2,6- and nitro-2,7-naph-thyridines (2) are unknown], with special attention to the results obtained in the laboratories of both authors. Tliis article mainly refers to the synthesis and reactivity of the nitronaphthyridines their physical and spectroscopic properties and biological activity are only covered briefly. For the convenience of the reader a table listing melting points of (di-)nitronaph-thyridines and some derivatives is included (Table III). Tire literature to about 1998 has been covered. 

The benzofuran-naphthyridine linked dye compound (ABAN, see Fig. 1) has been successfully converted to fluorescent organic nanoparticles [34], for which their photophysical properties such as spectral features and emission intensity are remarkably different from those at the molecular level (solution). The results are rationalized by coplanarization of the benzofuran-naphthyridine molecule in the nanoparticle to extend its effective conjugation length and hence increase the oscillator strength, as is similar to the cases described above. 

Comparison of the bond lengths with those of benzene, naphthalene and pyridine suggests that whilst there is certainly aromatic character some bond fixation occurs in the naphthyridines. It is probable that canonical structure (1) (of, for example, 1,5-naphthyridine) and to a lesser extent structures (7) and (8) are the major contributors to the ground state, but the charged structures (9) and (10) must also be included in order to account for the chemical properties of the naphthyridines. 

Numerous other aromatic nitrogen compounds are known, and a significant number have been used to prepare complexes of platinum(II). Phthalazine (101) is one such compound, and the complex ds-PtCl(phthalazine)(PEt3)2 has been prepared in order to compare its fluxional properties with the phenanthroline and naphthyridine analogues. The monodentate complex is fluxional, but in this phthalazine case the orientation of the lone pairs is unsuitable for the five-coordinate intermediate required by an intramolecular process and the mechanism of exchange becomes dissociative.11 6... 

Although not a purine, the ligand properties of 7-azaindole (81) strongly resemble those of deprotonated purines. Metal binding of this anionic ligand may occur to one or two metal ions, just as with 1,8-naphthyridine (Scheme 8).158... 

During the past 20 years several groups of workers19-28 have carried out quantum mechanical calculations on the naphthyridines and have correlated the results with various chemical and physical properties. 

Naphthyridine gave the 5-bromo- and 3,5-dibromo-1,7-naphthyridine. Surprisingly, no 3-bromo-l,7-naphthyridine was detected. Treatment of 1,8-naphthyridine under the same conditions gave by far the lowest yield of bromo products, the 3-bromo- (5%) and the 3,6-dibromo-1,8-naphthyridine (0.5%). The low yield is, perhaps, attributable to the strong complexing properties of 1,8-naphthyridine (see Section IV, C). 

This chapter covers information on the preparation, physical properties, and reactions of 1,5-naphyhyridine and its C-alkyl, C-aryl, /V-alkyl, and /V-aryl derivatives as well as their respective ring-reduced analogs. In addition, it includes methods for introducing alkyl or aryl groups (substituted or otherwise) into 1,5-naphthyridines already bearing substituents and the reactions specific to the alkyl or aryl groups in such compounds. For simplicity, the term alkyl-l,5-naphthyridine in this chapter is intended to include alkyl-, alkenyl-, alkynyl-, aralkyl-, and cycloalkyl-1,5-naphthyridines likewise, aryl-l,5-naphthyridine includes both aryl-and heteroaryl-1,5-naphthyridines. 

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