Abstract
Background: Mannich reaction is one of the most important carbon-carbon bond formation reactions in organic synthesis. Traditional methods require a large amount of ungreen catalysts or much longer reaction time, which limits the scope of their application. So, a recyclable catalyst with high activity and selectivity is highly appreciated, and the highly shortened reaction time is also very appealing.
Methods: An efficient and facile process to prepare a series of β-amino carbonyl compounds was found via Mannich reactions catalyzed by caprolactam-based Brønsted acidic ionic liquids under ultrasonic irradiation.
Results: [Capl][BF4] was the most effective catalyst in the Mannich reaction, and good yields was gained within 2-6 h. The activity and stability of the catalyst was maintained very well even after five times, and ultrasound can effectively shorten the reaction time and enhance the yield at ambient condition.
Conclusion: A convenient procedure for Mannich reaction using acidic ILs catalyst under ultrasonic irradiation has been designed with many superiorities, such as simple manipulation, less reaction time and high yields. The Mannich reaction takes place in no presence of organic solvents such as toluene or ethanol, etc. The new synthetic method reported in this paper would make appreciable contribution to the subject of environmental friendly chemistry and it is available for industrial applications.
Keywords: Ionic liquid, mannich reaction, ultrasound sonochemistry.
Graphical Abstract