Design and synthesis of chiral ligands and their applications in asymmetric catalysis.

摘要

Two families of chiral ligands were designed and synthesized. One was made from para-substituted benzene and the other one was synthesized from chiral Binol through a key intermediate 1,1′-dichloromethyl binaphthyl. These novel chiral ligands allowed us to explore a lot of useful applications in asymmetric catalysis.; Monophosphine PBH with a bicyclic [2,2,1] structure was found excellent performance in Pd-catalyzed allylic alkylation reaction (>99% ee) and phosphine catalyzed [3+2] cycloaddition reaction (93% ee). A mechanistic rationale was provided in [3+2] cycloaddition reaction.; Asymmetric hydrogenations of different substrates have been extensively studied with the transition metal-phosphine complex as the catalysts. Cationic Rh-PennPhos was proved highly effective in enantioselective hydrogenation of cyclic enol acetates and enamides (up to 99% ee) while other chiral ligands such as BINAP and DuPhos gave very low enantioselectivities. The highest enantioselectivity (up to 99% ee) was achieved in asymmetric hydrogenation of electron rich trisubstituted enamides (for mixture of isomer ( E) and (Z)) with Rh-Binaphane as catalyst. The Ir-f-Binaphane complex showed high enantioselectivity (96% ee) on hydrogenation of (E)-β-dehydroaminoacid and lower enantioselectivity on (Z)-β-dehydroaminoacid.; The simple ketone, one of the toughest substrates in asymmetric hydrogenation, was reduced by Rh-PennPhos complex with high enantioselectivity (up to 95% ee). Unprecedented results (75–94% ee) were obtained in Rh- PennPhos catalyzed hydrogenation of alkyl-alkyl ketones. A pull-push mechanism for asymmetric hydrogenation of simple ketones was proposed based on the interesting additive effect in the reaction.; Highly Enantioselective hydrogenation of N-arylimines was accomplished by employing the Ir-f-Binaphane complex as the catalyst. The highest enantiselectivity (up to 99% ee) was achieved on the hydrogenation of N-(1-phenylethylidene)2,6-xylxlamine. The aryl groups in the substrate play a very important role in highly asymmetric induction. Additive I₂ was proved very effective in increasing the enantioselectivity and reactivity for hydrogenation of some substrates while ineffective for other substrates. Different mechanism was proposed to explain the observations. A new synthetic route to make primary chiral amines was developed based on new methodology. Potential application of Ir- f-Binaphane in asymmetric hydrogenation of MEA-imine to synthesize chiral agrochemical (S)-Metolachlor was envisioned.