Reactions of Enaminones with p-Quinone Methides: Access to 4H-Chromene and 4H-Chromen-4-one Derivatives

Abstract

A one-pot approach for the synthesis of oxygen-containing heterocycles such as 4H-chromenes and 4H-chromen-4-ones has been established through the reaction of enaminones with p-quinone methides (p-QMs). This transformation basically involves an acid-catalyzed 1,6-conjugate addition of enaminones to p-QMs followed by annulation. In the case of reaction between 2-hydroxyphenyl-substituted p-quinone methides and N,N-dimethyl enaminones, 4H-chromene derivatives were obtained in moderate to excellent yields. Similarly, the reaction between simple p-quinone methides and 2-hydroxyphenyl-substituted N,N-dimethyl enaminones led to 4H-chromen-4-one derivatives in good yields.