Highly enantioselective homogeneous catalysis of chiral rare earth phosphates in the hetero-Diels–Alder reaction

Two types of novel rare earth (RE) complexes were synthesized and used as a chiral Lewis acid catalyst for the hetero-Diels–Alder reaction of carbonyl compounds with the Danishefskyʹs diene under homogeneous conditions. The Y[(R)-H8-BNP]3 (3-Y)-catalyzed reaction of aromatic aldehydes and the Yb[(R)-BNP]3 (1-Yb)-catalyzed reaction of phenylglyoxylates afforded the corresponding cycloadducts with excellent optical purities (up to 99% ee) in high yields at room temperature. The successful recycling uses of the scandium catalyst (3-Sc) are also described.