Synthesis of Substituted Imidazo[1,5-a]pyrimidines, 1H-pyrrolo[2,3- b]pyridines and 3-methyl-3H-imidazo[4,5-b]pyridines

Cyclization of in situ generated 5-aminoimidazoles with various malondialdehydes or 1,3-diketones gave substituted imidazo[1,5-a]pyrimidines. However, cyclization of 2-aminopyrroles and 5-amino-1-methylimidazoles resulted in condensations on a carbon atom of the heterocyclic ring instead of nitrogen generating 1H-pyrrolo[2,3- b]pyridines (i.e. 7-azaindoles) and 3-methyl-3H-imidazo[4,5-b]pyridines, respectively. In these cases the addition of pyrrolidine to the reaction mixture after the initial condensation between the amino group and one of the carbonyl groups of the malondialdehydes or 1,3-diketones significantly increased the yields of 1H-pyrrolo[2,3-b]pyridines and 3-methyl- 3H-imidazo[4,5-b]pyridines.