Microwave Assisted Domino Knoevenagel Condensation/6π-electron Electrocyclization Reactions for the Rapid and Efficient Synthesis of Substituted 2H,5H-pyrano[4,3-b]pyran-5-ones and Related Heterocycles

Both natural and unnatural compounds with a 2H,5H‐pyrano[4,3‐b]pyran‐5‐one skeleton are of interest to medicinal chemistry as they exhibit several different biological activities. This heterocyclic ring systems is accessible by a Domino Knoevenagel condensation/6π‐electron electrocyclization. A simple and rapid microwave assisted protocol of this Domino process has been developed for the preparation of libraries of substituted 2H,5H‐pyrano[4,3‐b]pyran‐5‐ones and related heterocyclic systems in a single preparative step by reaction of an α,β‐unsaturated aldehyde with a 6‐substituted 4‐hydroxy‐2H‐pyran‐2‐one.