An Asymmetric Organocatalytic Povarov Reaction with 2-Hydroxystyrenes

An organocatalytic asymmetric three-component Povarov reaction involving 2-hydroxystyrenes has been established to provide an efficient method to access structurally diverse cis-disubstituted tetrahydroquinolines in high stereoselectivities of up to >99:1 dr and 97% ee. This protocol also provides an easy access to tetrahydroquinolines with chiral quaternary stereocenters upon using α-alkyl 2-hydroxystyrenes as substrates. The theoretical studies revealed that the Povarov reaction proceeded through a sequential vinylogous Mannich reaction and an intramolecular Friedel-Crafts reaction, wherein the phosphoric acid acted as bifunctional catalyst to activate 2-hydroxystyrene and aldimine simultaneously.