Various trivalent rare earth-chiral phosphate complexes [(R)-1-RE, (R)-3-RE, and (R)-4-Ce] were prepared and evaluated as a Lewis acid catalyst for the asymmetric hetero-Diels-Alder reaction of aldehydes with the Danishefsky's diene. Some of them effectively promoted the reaction at room temperature in the presence or absence of achiral additives under homogeneous conditions to afford the corresponding cycloadducts with high ee's (up to 99% ee). During these reactions, remarkably high asymmetric amplifications (positive nonlinear effects) were observed as the first example in the metal ion-chiral ligand 1:3 catalytic system. A scandium catalyst bearing the H 8-BNP ligand, (R)-3-Sc, could be recovered after the reaction and successfully reused for the next round of reactions. In addition, the hetero-Diels-Alder reaction of α-keto esters was effectively catalyzed by the ytterbium complex, (R)-1-Yb, without any additives thus producing the asymmetric quaternary carbon in excellent enantioselectivities (up to >99% ee).
All Science Journal Classification (ASJC) codes
- Drug Discovery
- Organic Chemistry