Sonochemical cycloadditions in ionic liquids. Lessons from model cases involving common dienes and carbonyl dienophiles

This contribution describes a series of sonochemical cycloadditions involving either cyclopentadiene or 1,3-cyclohexadiene with carbonyl dienophiles in an imidazolium-based ionic liquid as reaction medium. In general, ultrasound does effectively improve these processes in terms of higher yields and/or shorter reaction times when compared with the corresponding silent reactions. Stereoselectivities, however, remain practically unaffected by sonication. The role of ionic liquids under ultrasonic activation is also discussed.