October 22, 2020
Manipulation of the regioselectivity with radical/acid-base cooperative catalysis
A research group of RIKEN Cluster for Pioneering Research and RIKEN CSRS has successfully completed the development of regiodivergent dehydrogenative cross-coupling.
Oxidation reactions are important reactions that account for more than 30% of chemical industry processes. However, the dehydrogenative (oxidative) cross-coupling reactions with use of the molecular oxygen is difficult. Specifically, controlling the coupling selectivity (homo- vs cross-coupling) and the chemo- (C−C vs C−O) and regioselectivity in the reaction of two distinct enolizable substrates under aerobic conditions is notoriously challenging.
The research group developed regiodivergent oxidative cross-coupling reaction with catechols by using persistent radicals generated by homolysis of oxindole or benzofuranone dimers as key active species. The oxidative cross-coupling proceeds at the C(6) position of 4-substituted catechols under catalyst-free conditions, while the Pd(II) catalyst promotes the reaction at the C(5) position. Furthermore, a series of experimental and computational investigations revealed how the Pd complex catalyst selectively gives C(5) products. In the newly developed acid-base/redox cooperative system, catalyst-enabled endothermic carbon−carbon formation and the exothermic oxidative aromatization with O2 leads to the facile production of the kinetically controlled C(5) adducts. This will be a useful design guideline for developing new reactions and catalysts.
The results of this study are expected to make contribution to selective supply of the catechols by means of the oxidative cross-coupling reaction.
ACS Catalysis doi:10.1021/acscatal.0c03986
M. Sugawara, R. Ohnishi, T. Ezawa, M. Akakabe, M. Sawamura, D. Hojo, D. Hashizume, Y. Sohtome, M. Sodeoka,
"Regiodivergent Oxidative Cross-Coupling of Catechols with Persistent tert-Carbon Radicals".
Yoshihiro Sohtome; Senior Research Scientist
Mikiko Sodeoka; Group Director
Catalysis and Integrated Research Group