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 ELUMO confirmed that [1,2,5]thiadiazolo[3,4‐d]pyridazine is one of the strongest electron–acceptor systems. The 4,7‐dibromo derivative of highly electron‐deficient [1,2,5]thiadiazolo[3,4‐d]pyridazine was synthesized. Conditions for the selective formation of both mono‐ and di‐aryl(hetaryl)ated [1,2,5]thiadiazolo[3,4‐d]pyridazines by palladium‐catalysed cross‐coupling reactions were found. [ABSTRACT FROM AUTHOR]