Enantioselective Direct Aldol-Type Reaction of Azlactone via Protonation of Vinyl Ethers by a Chiral Bronsted Acid Catalyst

Highly enantio- and diastereosetective direct aldol-type reaction of azlactones with oxocarbenium ions generated by protonation of vinyl ethers using a chiral phosphoric acid catalyst is presented. The method provides efficient access to biologically and pharmaceutically intriguing beta-hydroxy-alpha-amino acid derivatives having a quaternary stereogenic center at the alpha-carbon atom.