Highly Regio- and Chemoselective Oxidative C–H/C–H Cross-Couplings of Anilines and Phenols Enabled by a Co-Oxidant-Free Rh(I)/Zn(NTf2)2/Air Catalytic System
journal contributionposted on 01.05.2019, 00:00 by Luoqiang Zhang, Yanbing Wang, Yang Shi, Yimin Wu, Jingbo Lan, Weixin Ma, Jingsong You
An urgent yet challenging task is to overcome the limitations in substrate scope and regio- and chemoselectivity in the oxidative couplings between two arenes for the construction of unsymmetrical 2,2′-difunctional biaryls with diverse application requirements. In this work, a co-oxidant-free Rh(I)/Zn(NTf2)2/air catalytic system has been developed for dual chelation-assisted oxidative C–H/C–H cross-couplings between two anilines, between two phenols, and between phenols and anilines, which enables rapid assembly of rich libraries of 2,2′-bianilines, 2,2′-biphenols, and 2′-aminobiphenyl-2-ols. This protocol features air as the sole oxidant, complete regioselectivity, high chemoselectivity, low molar ratio of substrates (even 1:1), convenient operation, and scale-up synthesis. The established catalytic system is tolerant of the substrates having both electron-donating and electron-withdrawing substituents at different positions of the aryl ring. This work further discloses that the chemoselectivity of cross-coupling over homocoupling mainly relies on a suitable combination of two directing groups (i.e., a pair of strongly and weakly coordinating directing groups) rather than the electronically distinct properties between two substrates, which provides an inspiration for designing the matching directing group pair for the dual chelation-assisted oxidative Ar–H/Ar–H cross-couplings. Thus, this strategy allows the highly chemoselective cross-coupling between electronically similar coupling partners, which represents a challenging task in the oxidative Ar–H/Ar–H cross-coupling reactions.