Halogeno-2,7-Naphthyridines

Halogeno-1,5-naphthyridines have proved very useful as intermediates for the synthesis of many other 1,5-naphthyridine derivatives in this respect, the more easily available chloro and bromo derivatives have been used almost exclusively. 

Halogeno-l,5-naphthyridines have also shown useful bioactivity in their own right, for example, as the herbicide 2-chloro-7-[p-(2-carboxyethoxy)phenoxy]-l, 5-naphthyridine. 470 The mass spectra of a variety of halogeno-1,5-naphthyridines have been reported.546 Antimalarial activity has been detected.1161 1165 

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Some halogeno-1,5-naphthyridines have been made by primary syntheses (see Chapter 1), but several other preparative routes have been more widely used, as indicated in the following subsections. 

This route has occasionally been followed to make both nuclear and extranuclear halogeno-1,5-naphthyridines. Some examples follow. 

Most such naphthyridinones have been made by primary synthesis (see Chapter 1) and some by hydrolysis of halogeno-1,5-naphthyridines (see Section 3.2.3). Other preparative routes are illustrated by the following examples. 

Note The conversion of 1,5-naphthyridine N-oxides to C-halogeno-1,5-naphthyridines (Meissenheimer reaction) has been discussed in Section 3.1.3. Other reported reactions are illustrated here. 

Note 1,5-Naphthyridinethiones have been made by thiolysis of halogeno-1,5-naphthyridines (see Section 3.2.3). 

In contrast to the situation in halogeno-1,5-naphthyridines (see Chapter 3), a halogeno substituent on 1,6-naphthyridine will be activated at the 2-, 4-, 5-, and 7-positions and much less so at the 3- and 8-positions. 

Ch. 2 1,5-Naphthyridine, Alkyl-1,5-naphthyridines, and Aryl-1,5-naphthyridines Ch. 3 Halogeno-1,5-naphthyridines Ch. 4 Oxy-1,5-naphthyridines Ch. 5 Thio-1,5-naphthyridines... 

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