Brønsted Acid Catalyzed Domino 1,6-Addition/Intramolecular Cyclization Reactions: Diastereoselective Synthesis of Dihydrocoumarin Frameworks

Abstract

An efficient domino 1,6-addition/intramolecular cyclization reaction between para-quinone methides (p-QMs) and azlactones under Brønsted acid catalysis was established. A series of highly functionalized dihydrocoumarins were constructed in good to excellent yields (up to 96%) with excellent diastereoselectivities (all >20:1 d.r.). In this process, the Brønsted acid plays a crucial role not only in activating the two substrates, but also in controlling the diastereoselectivity of the reaction via hydrogen-bonding interactions. In addition, this protocol demonstrates the great practicability of utilizing p-QMs in domino reactions.