Reactions of formylchromone derivatives. Part 5. Transformations of 3-formylchromones into pyrroles and pyridines

Abstract

4-Oxo-4H-1-benzopyran-3-carbaldehyde (3-formylchromone)(1) was treated with various bi-functional nucleophiles. With ethyl aminoethanoate it gave a mixture of ethyl 4-(2-hydroxybenzoyl)-6-(4-oxo-4H-1-benzopyran-3-yl)pyridine-2-carboxylate (2) and ethyl 4-(2-hydroxybenzoyl)pyrrole-2-carboxylate (3) whereas with 2-aminoethanonitrile, only the pyridine, 2-cyano-4-(2-hydroxybenzoyl)-6-(4-oxo-4H-1-benzopyran-3-yl)pyridine (7) was obtained. Ethyl 2-aminopropanoate or ethyl 2-amino-2-phenylethanoate both gave the same pyrrole, 4-(2-hydroxybenzoyl)-2-(4-oxo-4H-l-benzopyran-3-yl)pyrrole (8). and N-methylethanoic acid yielded 3-(2-hydroxybenzoyl)-N-methyl-pyrrole (9). Corresponding products were usually obtained when various substituted 3-formylchromones were used in the reactions. Mechanistic pathways are proposed to account for all the products and the pyridine structure was confirmed by degradation.