Synthesis of and Catalysis with Novel Chiral Lanthanoid Complexes

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Exploring new lanthanoid catalysts in asymmetric synthesis, we have prepared some optically active rare earth metal complex which work as Lewis acid or base catalysts. A chiral samarium(II) complex-induced asymmetric reaction which involves a radical process has also been developed.1. A remarkably high asymmetric amplification was realized in the Yb[(R)-BNP]ィイD23ィエD2-catalyzed hetero Diels-Alder reaction as the first example in the metal/chiral ligand = 1 : 3 system. The mechanism may be explained by the autogenetic formation of the enantiopure complex and this phenomenon turned out to be quite general within the lanthanide metal ions with similar ionic radii to that of the ytterbium ion. The reaction of α-keto esters were effectively catalyzed by the Yb-complex affording the cycloadducts with high enantioselectivities (up to 99.6% ee) at room temperature.2. The chiral La-BINOL-triphenylphosphine oxide-cumene hydroperoxide complex was found to be an excellent catalyst for the asymmetric epoxidation of enones yielding the epoxy ketones with high enantioselectivities (up to 99.8% ee). A remarkable asymmetric amplification was also observed suggesting the autogenetic formation of an optically pure dinuclear complex as the active catalyst. The use of tri-(p-fluorophenyl) phosphine oxide in place of triphenylphosphine oxide largely improved the turnover frequencies of the catalyst thus affording an epoxide with 98% ee in 98% yield in the epoxidation of chalcone using only 0.5mol% of the catalyst. The new chiral lanthanum complex has a wide applicability for the catalytic asymmetric epoxidation of various types of enones.3. The chiral samarium(II) complex prepared from SmIィイD22ィエD2, (R)-BINOL, and an achiral tertiary amine promoted the reductive homo-coupling reaction of β-monosubstituted acrylic acid amides to give the corresponding 3, 4-trans-disubstituted adipamides with high enantioselectivities (up to 85% ee).