Synthesis of the 4,7-Dibromo Derivative of Highly Electron-Deficient [1,2,5]Thiadiazolo[3,4-d]pyridazine and Its Cross-Coupling Reactions

An efficient synthesis of 4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine is reported. For the first time, palladium-catalysed cross-coupling reactions of a dihalo derivative was found to be a powerful tool for the selective formation of various mono- and diarylated derivatives of strongly electron-accepting heterocycles. Suzuki-Miyaura coupling can be successfully employed for the preparation of mono-arylated derivatives, whereas Stille coupling is useful for both mono- and diaryl(hetaryl)ated heterocycles. The cyclic voltammogram showed that 4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine can be easily oxidized to form a stable anion radical. The calculated values of E-LUMO confirmed that [1,2,5]thiadiazolo[3,4-d]pyridazine is one of the strongest electron-acceptor systems.