Convenient synthesis of imidazo[1,5-a]pyrimidine derivatives and their unusual recyclization into 3H-imidazo[4,5-b]pyridine derivatives

New derivatives of imidazo[1,5- a ]pyrimidine have been synthesized by cyclization of in situ generated 1 H -imidazol-4(5)-amine with 1,3-diketones or malondialdehyde derivatives. Utilization of asymmetrical 1,3-diketones leads to the formation of a mixture of regioisomers. The discovered conversion of imidazo[1,5- a ]pyrimidine core into 3 H -imidazo[4,5- b ]pyridine that takes place only under acidic conditions can be considered as a new version of Dimroth rearrangement involving cleavage of C–N bond and formation of C–C bond.