Selective and Stepwise Functionalization of the Pyridazine Scaffold by Using Thio-Substituted Pyridazine Building Blocks.

We described a regioselective tri- and tetra-functionalization of the pyridazine scaffold using two readily available building blocks: 3-alkylthio-6-chloropyridazine and 3,4-bis(methylthio)-6-chloropyridazine by performing selective metalations with TMPMgCl ⋅ LiCl and catalyst-tuned cross-coupling reactions with arylzinc halides. Several of the resulting pyridazines were converted into more elaborated N-heterocycles such as thieno[2,3-c]pyridazines and 1H-pyrazolo[3,4-c]pyridazines.