Amino Acid-Derived Phosphonium Salts-Catalyzed Michael Addition of 3-Substituted Oxindoles

A new type of phosphonium phase-transfer catalyst prepared from easily available chiral amino acids was evaluated in a model reaction between oxindole and methyl vinyl ketone, and the catalyst derived from isoleucine was found to be the best. Michael additions of 3-monosubstituted oxindoles to methyl vinyl ketone, acrolein or propargyl aldehyde proceeded smoothly to afford 3,3-disubstituted oxindoles in good to excellent yields with moderate to excellent ees.