Direct Heteroarylation of Tautomerizable Heterocycles into Unsymmetrical and Symmetrical Biheterocycles via Pd/Cu-Catalyzed Phosphonium Coupling

The direct cross-coupling of tautomerizable heterocycles with various unfunctionalized heteroarenes has been achieved through PyBroP-mediated and Pd/Cu-catalyzed sequential C–OH/C–H activation. The methodology allows a facile entry into novel diazine-azole biheterocyclic frameworks. Moreover, an unprecedented Pd-catalyzed phosphonium homocoupling of tautomerizable heterocycles was also developed to afford a direct synthetic route to symmetrical 1,2-, 1,3-, and 1,4-bidiazine units