Reliable Functionalization of 5,6-Fused Bicyclic N-Heterocycles Pyrazolopyrimidines and Imidazopyridazines via Zinc and Magnesium Organometallics

DFT-calculations allow prediction of the reactivity of uncommon N-heterocyclic scaffolds of pyrazolo[1,5-c]pyrimidines and imidazo[1,2-b]pyridazines and considerably facilitate their functionalization. The derivatization of these N-heterocycles was realized using Grignard reagents for nucleophilic additions to 5-chloropyrazolo[1,5-a]pyrimidines and TMP2Zn center dot 2MgCl(2)center dot 2LiCl allowed regioselective zincations. In the case of 6-chloroimidazo[1,2-b]pyridazine, bases such as TMP2Zn center dot MgCl2 center dot 2 LiCl, in the presence or absence of BF3 center dot OEt2, led to regioselective metalations at positions 3 or 8. Subsequent functionalizations were achieved with TMPMgCl center dot LiCl, producing various polysubstituted derivatives (up to penta-substitution). X-ray analysis confirmed the regioselectivity for key functional heterocycles.