Chirality-Switchable Polymer-based Ligands for Catalytic Asymmetric Synthesis
소속 :
연사 : Michinori Suginome(Kyoto University)
일시 : 2012-10-11 17:00 ~
장소 : 500동 목암홀
일 시 : 2012년 10월 11일, 5:00 PM
장 소 : 500동 목암홀
-Abstract-
Considerable effort is being made to establish "next-generation" chiral catalysts for asymmetric organic synthesis. Such catalysts are expected to realize new, innovative catalytic reactions, and to afford not only high enantioselectivity, but also high catalytic activity, better recoverability, and reusability. Through these characteristics, the next-generation chiral catalysts shall unequivocally contribute to the development of "green processes" in asymmetric synthesis. It is also expected for such new chiral catalysts to possess "a switch" by which the chirality of the catalyst can be interconverted. This feature allows synthetic organic chemist to escape from preparation of two enantiomeric catalysts for stereoselective production of both enantiomers. In this presentation are discussed new poly(quinoxaline-2,3-diyl)-based chiral ligands PQXphos (R)-L1, which show high enantioselectivities (>95% ee for three different reactions), high reusability (up to 8-time reuse), and higher catalyst activity than do the corresponding low-molecular-weight chiral ligands. In addition, the polymer backbone underwent perfect switch of helical chirality by the effect of solvent. This feature could be successfully applied to new catalytic systems in which either enantiomer can be produced with high enantioselectivities from a single chiral ligand, whose helical chirality is easily switchable. Palladium-catalyzed asymmetric reactions including asymmetric hydrosilylation of styrenes, asymmetric biaryl synthesis via Suzuki–Miyaura coupling, and C–C bond cleaving desymmetrization of meso-methylenecyclopropanes shall be discussed.
장 소 : 500동 목암홀
-Abstract-
Considerable effort is being made to establish "next-generation" chiral catalysts for asymmetric organic synthesis. Such catalysts are expected to realize new, innovative catalytic reactions, and to afford not only high enantioselectivity, but also high catalytic activity, better recoverability, and reusability. Through these characteristics, the next-generation chiral catalysts shall unequivocally contribute to the development of "green processes" in asymmetric synthesis. It is also expected for such new chiral catalysts to possess "a switch" by which the chirality of the catalyst can be interconverted. This feature allows synthetic organic chemist to escape from preparation of two enantiomeric catalysts for stereoselective production of both enantiomers. In this presentation are discussed new poly(quinoxaline-2,3-diyl)-based chiral ligands PQXphos (R)-L1, which show high enantioselectivities (>95% ee for three different reactions), high reusability (up to 8-time reuse), and higher catalyst activity than do the corresponding low-molecular-weight chiral ligands. In addition, the polymer backbone underwent perfect switch of helical chirality by the effect of solvent. This feature could be successfully applied to new catalytic systems in which either enantiomer can be produced with high enantioselectivities from a single chiral ligand, whose helical chirality is easily switchable. Palladium-catalyzed asymmetric reactions including asymmetric hydrosilylation of styrenes, asymmetric biaryl synthesis via Suzuki–Miyaura coupling, and C–C bond cleaving desymmetrization of meso-methylenecyclopropanes shall be discussed.
