Organocatalytic Approach for Assembling Flavanones via a Cascade 1,4-Conjugate Addition/oxa-Michael Addition between Propargylamines with Water

A DBU-catalyzed one-pot cascade reaction of propargylamines and water for the synthesis of flavanones has been developed. This process proceeds via a sequence of 1,4-conjugate addition of water to alkynyl o-quinone methide (o-AQM), followed by the alkyne–allene isomerization and subsequent intramolecular oxa-Michael addition. This strategy provides a convenient method for accessing a broad range of flavanones in good to excellent yields with good functional-group tolerance, in particular, the reactive halo functional groups.