An efficient and environmentally friendly procedure for synthesis of pyridazine derivatives in ionic liquids

Imidazolium ionic liquids have been investigated as reaction media in inverse-type Diels-Alder reactions between 1, 2, 4, 5-tetrazine and a series of dienophiles to synthesize pyridazine derivatives for the first time. Comparing to conventional synthetic methods, using easily accessible imidazolium ionic liquids as solvent and catalyst, the reaction time reduced from 13 d to 6 h and product yields increased from 64.0% to 85.5%. The interaction between ionic liquid and reactants in theoretical way was further researched and the most possible catalytic mechanism was proposed. The reaction condition is mild and easy to operate, avoiding using the volatile organic solvents and additional catalysts. Moreover, ionic liquids can be used for more than six times without obvious loss of product yields. Therefore, the current synthetic approach is more in accordance with green chemistry and atom economy requirements.