Highly enantioselective Michael addition reactions with new trimeric chiral phase transfer catalysts
New types of mesitylene based tri-site containing asymmetric quaternary ammonium salts 9a and 9b have been prepared and used as efficient chiral phase transfer catalysts for enantioselective Michael addition reactions between the chalcones and diethylmalonate under mild reaction conditions such as lower concentration of base, catalyst and ultrasonic conditions with very good chemical yields (up to 98%) and ee's (up to 99%).
Unexpected solvent/substitution-dependent inversion of the enantioselectivity in Michael addition reaction using chiral phase transfer catalysts
New cinchonium salts bearing 5,5′-bis(methyl)-2,2′-bipyridine 1 group show solvent/substitution-dependent reversal of enantioselectivity. When used as chiral phase transfer catalyst in the asymmetric Michael addition of chalcones with diethylmalonate within two hours these catalysts result in high chemical yield (up to 98%) and enantiomeric excess (up to 99%) under lower concentrations of base and cold conditions.
Highly enantioselective asymmetric Michael addition reactions with new chiral multisite phase-transfer catalysts
Highly enantioselective Michael addition reactions of diethyl malonate to various chalcones have been achieved under mild chiral multisite phase-transfer reaction conditions by the successful utilization of 2,4,6- (triscinchoniummethyl)phenyl-1,3,5-triazines as new chiral quaternary ammonium catalysts. This simple asymmetric Michael addition process was found to be quite effective and to obtain Michael adducts with very good yields and enantiomeric excesses. Georg Thieme Verlag Stuttgart New York.