Pyridines diazotisation

The reaction of 2- and 6-amino groups with nitrous acid is similar to that of 2-amino-pyridines, in that diazonium salts are produced but, relative to phenyldiazonium salts, these are unstable. Despite this, they can be utilised for the introduction of groups such as halide or, oxygen by reaction with water, with loss of nitrogen. 8-Diazonium salts are considerably more stable. In 2-aminoadenosine, selective diazotisation occurs at the 2-amino group. ... 

Isothiazolo(3,4-b]and[4,3-cJpyridines.- 3-Aminoisothiazolo[3,4-b ]-pyridines (49 jR jCH CH OjCH S) and 3-amino-6-methyl-7-cyano-isothiazolof4,3-c]pyridine (50)56 are prepared by H202 cyclisation of the corresponding thiocarbamoyl derivatives (48 R as above R =NH2,R2=H and R=CH, R =H,R =NH2, respectively). Azo dyes can be formed from (49) and (50) by diazotisation and coupling with substituted anilines. 

Derivatives of pyridine, quinoline or woqiiinolme may be prepared by causing the diazotised ammo-compounds of such substances to react with antimonites or the corresponding free acids. The parent material may contain substituents, e.g. hydroxy-, ammo-, carboxy- or phenyl- radicals or halogens. The most advantageous proportions appear to be 2 to 3 molecular equivalents of antimomte to each equivalent of heterocyclic compound. Reduction with suitable agents produces stibino-compoimds. ... 

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