Alkaline–modified montmorillonite K10: an efficient catalyst for green condensation reaction of aromatic aldehydes with active methylene compounds
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An efficient and reusable catalyst, alkaline–modified Montmorillonite K10, has been developed and used in the Knoevenagel condensation. A series of condensation reactions based on ultrasound irradiation of different types of active methylene compounds and a variety of aromatic aldehydes showed the high efficiency of the prepared catalyst. This protocol has notable advantages, such as being eco-friendly, the ease of the work-up and reuse of the catalyst. The isolated compounds were synthesized in high yields (83–100%) in a short reaction time and were obtained, after crystallization, in pure form (IR, NMR and GC) without further purification. When ethyl cyanoacetate was used as active methylene compound, the reaction is highly stereoselective with only E geometry.