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 Michaeladdition 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
Organocatalytic Enantioselective Conjugate Additions to Enones
作者:Jian Wang、Hao Li、Liansuo Zu、Wei Jiang、Hexin Xie、Wenhu Duan、Wei Wang
DOI:10.1021/ja065187u
日期:2006.10.1
Conjugateaddition reactions of a wide range of nucleophilic enol species with enones, catalyzed by a cinchona alkaloid derived thiourea organocatalyst, have been developed with attending good yields and high enantioselectivities under a mild reaction condition. The general method provides an efficient approach to the preparation of versatile building blocks possessing various functional groups.
Newtypes of mesitylene based tri-site containing asymmetric quaternary ammonium salts 9a and 9b have been prepared and used as efficient chiral phasetransfercatalysts 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