Toolkit for the Installation of Pyrrolo[2,3-c/3,2-c]pyridazine Cores into MedChem-Relevant Compounds

A preparative scalable approach to 3,7-bifunctional 5H-pyrrolo[3,2-c]pyridazines and 3,5-bifunctional 7H-pyrrolo[2,3-c]pyridazines with a diverse set of functionalities (C(sp²)-Br/I, CO₂H, CHO, SO₂Cl, NH₂) in the pyrrole and an active chlorine atom in the pyridazine parts, respectively, was developed. The suitability of these groups for synthesizing various derivatives of the above-mentioned cores is demonstrated, thereby declaring the compounds as MedChem-relevant building blocks. The possibility of introducing a carboxylic function to the pyridazine ring through Pd-catalyzed carbonylation has been provided. A solution for the selective preparative partial hydrogenation of the pyrrole ring to dihydropyrrole was also proposed. As a result, a convenient tool for implementing the "nitrogen walk" approach around indole and azaindole scaffolds was suggested for medicinal chemistry purposes.