A multicomponent reaction giving easy and cheap access to a variety of bicyclic 5,5-fused hetero-rings has been developed. Then, an usual rearrangement of imidazo[1,5-a]imidazoles or imidazo[1,2-b]pyrazoles leading to bi-heterocyclic imidazo- and pyrazolo[1,5-a]pyrimidines in the presence of a specific amount of I₂ in THF at room temperature has been achieved. This new method enables the hitherto unreported synthesis of functionalized imidazo- and pyrazolo[1,5-a]pyrimidines.