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ONE-POT PREPARATION OF COUMARINS BY KNOEVENAGEL CONDENSATION IN SOLVENT-FREE CONDITION UNDER MICROWAVE IRRADIATION

3-Substituted coumarins were prepared by the Knoevenagel reaction of 2-hydroxybenzaldehyde derivatives and 2-hydroxy-l-naphthaldehyde in the presence of ammonium aceteate on basic alumina or silica gel under microwave irradiation. High yields, low reaction times, being environmentally friendly, elimination of organic base and solvent are advantages of this method. Introduction Coumarins substituted at C-3 are an important class of organic compounds which are used in pharmaceutical chemistry as intermediates in the synthesis of pesticides and bioactive compounds (1). Coumarins have wide range of activities, i.e anthelmintic, hypnotic and insecticidal properties (2a), anticoagulant (2b), coronary and fluorescent brighthners (2c), photographical sensitizers and fluorescent dyes (3). Naphtho-[2,l-b]-pyran-3-oxo have shown antimicrobial (4a) antiinflammatory (4b) and anticancer activities (4c). In view of the biological importance of coumarin derivatives, we have developed a new method for rapid synthesis of these compounds. There are many methods for the synthesis of coumarins (5) such as Perkin reaction (6), Pechmann reaction (7), Knoevenagel reaction (8), Reformatsky (9) and Wittig reaction (2a, 2c, 10) . Solvents are often expensive, toxic, difficult to remove from reaction mixture and are environmentally polluting agents. Solvent-free condition under microwave irradiation as an efficient method in organic synthesis (11) has several advantages i.e. cleaner reaction, shorter reaction time and ease of manipulation.