Modified Asymmetric Transfer Hydrogenation Catalysts

KANTO CHEMICAL CO., INC. launched asymmetric transfer hydrogenation catalysts with Ts-diamine ligand, which were discovered by NOYORI Molecular Catalysis Project of Exploratory Research for Advanced Technology (ERATO) by Japan Science and Technology Corporation (JST). These catalysts are extremely effective for the asymmetric reduction of ketones and imines, and have established their reputation as conventional effective asymmetric reduction catalysts.

A research group of KANTO CHEMICAL CO., INC. examined the reaction conditions to achieve the maximum catalyst performance, and found out that a choice of the hydrogen source is the most important to achieve the higher reactivity and the enantioselectivity.

It was reported that the reaction in a mixture of formic acid and triethylamine is the irreversible reaction, leading to the high efficiency. We revealed that a molar ratio of formic acid and triethylamine is important for the reaction of nitrogen-functionalized acetophenones2 .

Then, it was reported that two phase reaction comprised of ketone and water (if necessary solvent is added) using sodium formate as a hydrogen source gives higher reactivity. We developed this reaction system to the synthesis of some chiral compounds. In this two phase reaction, a drop of enantioselectivity is often observed for the reaction of a certain kind of ketones. Based on the hypothesis that near the end of the reaction, the catalyst abstracts hydrogen from the product alcohol, leading to the drop of the optical purity of the product, the single phase reaction was developed by our group using formic acid salt as a hydrogen source. In the single phase reaction, the high reactivity is maintained with little drop of the optical purity of the product alcohol.

In terms of the modification of the catalysts, easily tunable sulfonyl group affects the enantioselectivity of the reaction, and we, launches modified Ru catalysts with higher catalyst performance.

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Triflate Catalysts

RuCl(Tsdpen)(arene) catalyst is an excellent asymmetric reduction catalyst using a kind of organic hydrogen source, but this catalyst can’t use hydrogen gas. In the project in Chubu Technology Licensing Office of Nagoya Industrial Science Research Institute directed by Prof. Ryoji Noyori of Nagoya University and Prof. Takeshi Ohkuma of Hokkaido University, the asymmetric hydrogenation catalyst using hydrogen gas was developed, which has a similar structure to the above mentioned reduction catalyst5 .

Because this asymmetric hydrogenation reaction proceeds without a base, this reaction system is applicable to the base sensitive ketones. For example, 4-chromanone is reduced in a mixture of formic acid and triethylamine with 97% ee, but in low yield 37% at S/C (substrate/catalyst molar ratio) of 500. In contrast, in this asymmetric hydrogenation reaction, 4-chromanoe is reduced completely even at S/C = 30005a, and the ton (turn over number) over 7000 can be obtained under a higher hydrogen pressure.

KANTO CHEMICAL CO., INC., launches chiral Ru Triflate asymmetric hydrogenation catalysts.

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MODIFIED ASYMMETRIC TRANSFER HYDROGENATION CATALYSTS & TRIFLATE CATALYST