Domino inverse electron demand Diels-Alder reactions of chromones with ethyl vinyl ether

Abstract

E)-Ethyl 3-(4-oxo-4H-chromen-3-yi)acrylate (3), (E)-3-(4-oxo-4H-chromen-3-yl)-2-propenenitrile (12) and their 5-hydroxy-derivatives 11 and 13 undergo alternative, solvent dependent, domino reactions with ethyl vinyl ether. Inverse electron demand Diels-Alder (IEDDA)-elimination-IEDDA generates isomeric tetracycles 15a-d and 16a-d. Instead, IEDDA-elimination-intramolecular elimination reactions provides xanthone 17 or 2-hydroxybenzophenones 18a-d, respectively. In non-polar solvents propenenitriles 12 and 13 experience a third alternative domino sequence: IEDDA-elimination-ene reaction, yielding the highly functionalized tricyclic compounds 21 and 22.