J. Patankar, S. S. Athalye, R. Verma
Jul 1, 2000
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ChemInform
Abstract
Benzofurans , pyridazones and pyridones are well known for their broad spectrum biological activities. This has inculcated great interest to synthesise heterocycles bearing benzofuran and pyridazinone or benzofuran and pyridone moieties are present which may show enhanced biological activities. 2-Carboxy-7-methoxy benzofuran-3-acetic acid 1 was chosen as the starting material as it contains the structural features of pentenedioic acid (HOOC-C= C-CH2-COOH). Compound 1 on treatment with acetic anhydride gave 7 -methoxy-1 H -pyrano[3,4-b ]benzofuran-4H-· l ,3-dione 2, which has not only the pyranobenzofuran moiety but also an active methylene group at position 4 . This on further treatment with aryldiazonium chloride at 0°C gave 7-methoxy-4-(4methylphenylhydrazono )-1 H-pyrano[3, 4-b ]benzofuran-1 ,3-dione 3 in a very good yield. It exists in hydrazono form· • In the H NMR spectrum N-H signal appeared at o 13.4 and this down field shift is due to the chelation with the carbonyl group. Dye 3 was treated with different nucleophiles like sodium hydroxide, sodium ethoxide, primary amines, secondary amines and phenylhydrazine. It was observed that all the nucleophiles attacked the carbonyl group adjacent to the hydrazono linkage of the dye to form an intermediate 4 (Scheme 1). Discrimination was observed during cyclization with different nucleophiles, forming different heterocycles. The intermediate 4 contains three reactive func~CO~f/O~COOH