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Iridium‐Catalyzed Enantioselective Hydrogenation of Oxocarbenium Ions: A Case of Ionic Hydrogenation
Author(s) -
Yang Tilong,
Sun Yongjie,
Wang Heng,
Lin Zhenyang,
Wen Jialin,
Zhang Xumu
Publication year - 2020
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201916677
Subject(s) - catalysis , chemistry , iridium , oxocarbenium , enantioselective synthesis , ionic bonding , ionic liquid , asymmetric hydrogenation , photochemistry , combinatorial chemistry , organic chemistry , ion , nucleophile
Ionic hydrogenation has not been extensively explored, but is advantageous for challenging substrates such as unsaturated intermediates. Reported here is an iridium‐catalyzed hydrogenation of oxocarbenium ions to afford chiral isochromans with high enantioselectivities. A variety of functionalities are compatible with this catalytic system. In the presence of a catalytic amount of the Brønsted acid HCl, an α‐chloroether is generated in situ and subsequentially reduced. Kinetic studies suggest first‐order kinetics in the substrate and half‐order kinetics in the catalyst. A positive nonlinear effect, together with the half kinetic order, revealed a dimerization of the catalyst. Possible reaction pathways based on the monomeric iridium catalyst were proposed and DFT computational studies revealed an ionic hydrogenation pathway. Chloride abstraction and the cleavage of dihydrogen occur in the same step.