On the reaction of 2‐aminopyridines with alpha‐halocarbonyl compounds

The reactions of 6‐substituted‐2‐aminopyridines with bromoacetone and 3‐bromo‐2‐butanone have been investigated. In contrast to bromoacetone which gives a high yield of the imidazo[1,2‐a]pyridine, bromobutanone also produces significant amounts of material derived from substitution on the exocyclic nitrogen atom. These adducts, which are not a source of imidazopyridine in the reaction mixture, may be isolated and cyclised under more forcing conditions. The reactions of 2‐aminopyridine with 2‐chlorocyclohexanone and phenacyl bromide have been re‐examined and all the major products identified.