APPLICATION OF BASIC CLAYS IN MICROWAVE ACTIVATED MICHAEL ADDITIONS -PREPARATION OF N-SUBSTITUTED IMIDAZOLES

Imidazole (C3H4N2) was condensed with ethyl acrylate (C5H8O2) using tw o basic clays (Li+ and Cs+ montmorillonites) as catalysts in a microwa ve oven. The catalysts were characterized by chemical analyses, nitrog en adsorption isotherms and X-ray diffraction. Under these experimenta l conditions N-substituted heterocycles can be obtained with a high ac tivity and selectivity. The role of alkali promoters (Li+ and Cs+) in the montmorillonite for the Michael addition was studied. It was evide nced that the greater the basicity and the irradiation time and power of irradiation were, the higher were the conversion. The yield of the N-substituted imidazole presents a maximum for 0.1 g of Cs-montmorillo nite at 850 W in only 5 min of irradiation. (C) 1997 Elsevier Science B.V.