Imidazo pyridine halogenation

Imtdazo[4,5-c]pyridtne, 4,5,6,7-tetrahydro-synthesis, 5, 623, 640, 641 Imidazo[4,5-c]pyridine-6-carboxylic acid, 4,5,6,7-tetrahydro-synthesis, 5, 623, 641 Imidazopyridines as anthelmintic, 1, 202 synthesis, 5, 462 Imidazo[l,2-n]pyridines deuterium exchange, 5, 611 diazo coupling, 5, 614 Dimroth rearrangement, 5, 613 halogenation, 5, 611 hydrogenation, 5, 614 Mannich reaction, 5, 612 nitration, 5, 612 1-oxides... 

Halogenation of the imidazo[4,5-6]pyridine 4-oxides has provided some interesting results. Treatment of compound (123 R = H) with phosphorus oxychloride gave, with loss of the /v-oxide group, a mixture of the 5-chloro (124) and 7-chloro (125) isomers in comparable amounts in an overall 74% yield (Equation 3) <82JHC513>. The reaction of 3-methylimidazo[4,5-6]pyridine 4-oxide (123 R = CH3) with phosphorus oxychloride also gave a mixture of products but the yields were different, i.e. 5-chloro (124) (20%) and 7-chloro (125) (41%). However, with l-methylimidazo[4,5-6]pyridine 4-oxide (126), the chlorine atom was introduced exclusively into the more sterically hindered 7 position to give the 7-isomer (127). None of the 5-isomer was detected in this reaction (Equation (4)). 

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