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Enantioselective Synthesis of Biphenyl-Bridged ϵ-Sultams by Organocatalytic Mannich Reactions of Cyclic N-Sulfonylimines with Unactivated Ketones.
Chemistry
January 2024
Key Laboratory of Natural Medicine and, Immuno-Engineering of Henan Province, Henan University, Kaifeng, Henan, 475004, P. R. China.
A highly enantioselective Mannich reaction of biphenyl-bridged seven-membered cyclic N-sulfonylimines with methyl alkyl ketones is disclosed in this study. The reaction was performed under organocatalysis by using a quinine-derived primary amine as the catalyst in combination with a Brønsted acid as the co-catalyst. High yields (up to 89 %) and excellent enantioselectivities (up to 97 % ee) were observed.
View Article and Find Full Text PDFConverging Stereodivergent Reactions: Highly Stereoselective Formal anti-Markovnikov Addition of H O to Mixtures of Olefins.
Chemistry
June 2023
Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Gerhard-Domagk-Straße 1, 53121, Bonn, Germany.
We describe a highly diastereo- and enantioselective two-step formal anti-Markovnikov addition of H O to diastereomeric mixtures of trisubstituted olefins. Our approach overcomes the limits of classical stereospecific addition reactions to olefins for the generation of adjacent stereocenters. In these stereospecific reactions, separation of olefin diastereomers is essential.
View Article and Find Full Text PDFTriplet Energy Transfer from Lead Halide Perovskite for Highly Selective Photocatalytic 2 + 2 Cycloaddition.
ACS Appl Mater Interfaces
June 2022
Department of Chemistry and Biochemistry, San Diego State University, San Diego, California 92182, United States.
Triplet excitons are generally confined within a semiconductor. Hence, solar energy utilization via direct triplet energy transfer (TET) from semiconductors is challenging. TET from lead halide perovskite semiconductors to nearby organic molecules has been illustrated with ultrafast spectroscopy.
View Article and Find Full Text PDFsyn-Selective Epoxidation of Chiral Terminal Allylic Alcohols with a Titanium Salalen Catalyst and Hydrogen Peroxide.
Angew Chem Int Ed Engl
June 2022
Department of Chemistry, Organic Chemistry, University of Cologne, Greinstraße 4, 50939, Cologne, Germany.
In the Sharpless asymmetric epoxidation of chiral secondary allylic alcohols, one substrate enantiomer is predominantly converted to the anti-epoxy alcohol. We herein report the first highly syn-selective epoxidation of terminal allylic alcohols using a titanium salalen complex as catalyst, at room temperature, and aqueous hydrogen peroxide as oxidant. With enantiopure terminal allylic alcohols as substrates, the epoxy alcohols were obtained with up to 98 % yield and up to >99 : 1 dr (syn).
View Article and Find Full Text PDFHighly stereocontrolled total synthesis of racemic codonopsinol B through isoxazolidine-4,5-diol vinylation.
Beilstein J Org Chem
November 2021
Institute of Organic Chemistry, Catalysis and Petrochemistry, Slovak University of Technology in Bratislava, Radlinského 9, 81237 Bratislava, Slovak Republic.
A new highly diastereoselective synthesis of the polyhydroxylated pyrrolidine alkaloid (±)-codonopsinol B and its -nor-methyl analogue, starting from achiral materials, is presented. The strategy relies on the -stereoselective epoxidation of 2,3-dihydroisoxazole with in situ-generated DMDO, the -selective α-chelation-controlled addition of vinyl-MgBr/CeCl to the isoxazolidine-4,5-diol intermediate, and the substrate-directed epoxidation of the terminal double bond of the corresponding γ-amino-α,β-diol with aqueous hydrogen peroxide catalyzed by phosphotungstic heteropoly acid. Each of the key reactions proceeded with an excellent diastereoselectivity (dr > 95:5).
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