[4-(2-Hydroxyphenyl)imidazolium Salts as Organocatalysts for Cycloaddition of Isocyanates and Epoxides to Yield Oxazolidin-2-ones

Novel salts based on 1,3-dibutyl-4-(2-hydroxyphenyl)-1H-imidazolium bromide or iodide have been developed as bifunctional organocatalysts for the cycloaddition reaction of epoxides and isocyanates to form 3,4- and 3,5-disubstituted oxazolidin-2-ones. The molecular structure of these compounds was determined spectroscopically and confirmed by X-ray diffraction analysis. Imidazolium compounds were screened as catalysts to produce a range of oxazolidinones. The influence of the substituents on the aromatic ring and the counterion of the catalysts on the catalytic activity have been studied, showing that 1,3-dibutyl-4-(5-fluro-2-hydroxyphenyl)-1H-imidazolium iodide (4 d) was the most active catalyst for this process in the absence of a cocatalyst.