1- Chloro-4-nitroimidazole, preparation

Nucleophilic displacements of imidazole diazonium salts have some synthetic utility, particularly for the introduction of groups at C-2. Thus 2-nitroimidazoles" and 2-azidoimidazoles" are available via the diazonium fluoroborates. The formation of halogen-substituted imidazoles by the photolytic (but not thermal) decomposition of diazonium fluoroborates has proved useful. " " While 2- and 4-fluoro- and 2-chloro-imidazoles can be prepared in this way, the reaction fails for iodo- and bromo imidazoles." ... 

It is prepared by treating 6-mercaptopurine with 5-chloro-l-methyl-4-nitroimidazole. 

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