Acid clay minerals as eco-friendly and cheap catalysts for the synthesis of β-amino ketones by Mannich reaction

Abstract

The characterization and catalytic performance of different smectites, one raw saponite and some commercial montmorillonites, exhibiting mesoporous and acid character are herein reported. The catalysts under study are able to catalyze efficiently via Mannich-type reactions the synthesis of β-amino ketones, which are important building blocks for the drugs synthesis and biologically active natural products. Montmorillonite K10 (Mt-K10) was the most efficient catalyst for the Mannich reaction between the pre-formed imine, N-benzylideneaniline, and cyclohexanone resulting in a recyclable catalyst for at least three catalytic cycles without activity loss. Almost quantitative yield to the β-amino carbonyl compound was obtained after 240min when operating under the most favorable conditions. The catalytic performance of the smectites seemed to be influenced by their porosity, but also by both Brönsted and Lewis acid site concentrations. In fact, the concentration of the Lewis acid catalytic sites would be the key in the Michael addition of cyclohexanone to the imine, although the Brönsted acid sites contribution cannot be neglected. The β-amino carbonyl compound was also synthesized in an excellent yield (86%) in only 15min of reaction time through the one-pot three component reaction, by reaction between benzaldehyde, aniline and cyclohexanone.