A Heterodinuclear Asymmetric Catalyst For Direct Asymmetric Aldol Reaction Of Aryl Ketones To Aryl Aldehydes

Direct asymmetric Aldol reaction catalyzed by bimetal-containing chiral catalyst in very interesting and challenged of atom efficiency. The direct asymmetric Aldol reaction of aryl ketones with aryl aldehydes was generally performed by the Mukaiyama-type reaction, in which the preconversion of aryl ketones to more reactive intermediates such as silyl enol ethers are indispensable.We found that the C₂-asymmetrical chial ligand 28 derived from (R)-BINOL and (S)-prolinol is effective to the reaction.When the semi-crown aluminum/zincate ligand in situ produced from diethyl zinc trimethylaluminium and ligand 28 was imployed to the aimed asymmetric transformation,in exploring the first example of direct asymmetric aldol reactions of aryl ketones with aryl aldehydes, the best stereocontrol was observed with a aluminum/zincate dinuclel complex where enantiometric excesses ranged up to 51% with up to 79% yield . The result revealed that this novel semi-crown aluminum/zincate chiral catalyst was distinct from the previous reported cases about catalysts in the asymmetric aldol reactions by Shibasaki and Trost, in which bulky alkyl aldehydes generally afforded high enantioselectivities.For its reaction mechanism,it was speculated that aluminium atom acted as Lewis acid to activate aldehyde whereas zincate as Lewis base to tranfer the aryl ketone to active enol aluminium intermediate.