The Mizoroki-Heck reaction in mesoionic 1-butyl-3-methyltetrazolium-5-olate

Abstract

1-Butyl-3-methyltetrazolium-5-olate (1), a mesoionic compound, exists as a liquid at room temperature and can be used as a polar solvent for the Mizoroki-Heck reaction, wherein it has been proven to be a superior solvent to other solvents. The reaction of iodobenzene with ethyl acrylate in the presence of palladium acetate in mesoionic liquid 1 at 40 °C for 24 h gave ethyl cinnamate in 78% yield in the absence of ligands, while the use of other solvents, such as [bmim][BF4], [bmim][PF6], and DMF gave lower yields (43%, 37%, and 17%, respectively) under the same conditions. Heck-type coupling reactions of electron-deficient or electron-rich aryl iodides and bromobenzenes with olefins (15 examples, 7%–97%) were performed in 1. When a phosphine ligand was added to the reaction mixture, aryl bromides could be used, and the mesoionic liquid containing the catalysts could be reused at least five times.