Reactions of Coumarin Diethyl Acetal with Nucleophiles

Abstract

The reactions of coumarin diethyl acetal (2, 2-diethoxy-2 H-benzo[ b ]pyran) [1] with nucleophiles were investigated. [1] Reacts easily with aniline and carbonyl reagents to give corresponding condensation products in high yields. The reactions of [1] with bifunctional nucleophiles proceed on two different types, A and B. In the reaction of type A, 2 moles of ethanol are eliminated from [1] and nucleophiles to give spiropyrans or 2-imino-2 H- benzo[ b ]pyran derivatives, the latter being obtained exclusively when a nucleophile contains unsubstituted amino group. On the other hand, in the reaction of type B, coumarin and ethyl derivatives of nucleophiles are obtained and only 1 mole of ethanol is eliminated. When a nucleophile contains acidic group such as mercapto or carboxyl group, the reaction of type B is predominant. The reaction of type A exclusively occurs when a nucleophile contains less acidic group such as hydroxyl or amino group.