Reaction of Push–Pull Enaminoketones and <i>in Situ</i> Generated <i>ortho</i>-Quinone Methides: Synthesis of 3-Acyl-4<i>H</i>-chromenes and 2-Acyl-1<i>H</i>-benzo[<i>f</i>]chromenes as Precursors for Hydroxybenzylated Heterocycles

Abstract

A simple and efficient method for the synthesis of 4H-chromenes and 1H-benzo[f]chromenes containing a trifluoroacetyl or aroyl group in the pyran ring from o-quinone methide precursors and push-pull enaminoketones has been developed. The chromenes are presumably formed through an initial oxa-Diels-Alder reaction, followed by an elimination of amine. The possibility of further transformations of given chromenes to o-hydroxybenzylated pyrazoles, isoxazoles, and pyridines has been demonstrated.