Transition metal catalysis has emerged as an important means for C–C activation that allows mild and selective transformations. However, the current scope of C–C bonds that can be activated is primarily restricted to either highly strained systems or more polarized C–C bonds. In contrast, the catalytic activation of non-polar and unstrained C–C moieties remains an unmet challenge. Here we report a general approach for the catalytic activation of the unstrained C(aryl)–C(aryl) bonds in 2,2′-biphenols. The key is to utilize the phenol moiety as a handle to install phosphinites as a recyclable directing group. Using hydrogen gas as the reductant, monophenols are obtained with a low catalyst loading and high functional group tolerance. This approach is also applied to the synthesis of 2,3,4-trisubstituted phenols. A further mechanistic study suggests that the C–C activation step is mediated by a rhodium(i) monohydride species. Finally, a preliminary study on breaking the inert biphenolic moieties in lignin models is illustrated.
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Crystallographic data for the structures reported in this article have been deposited at the Cambridge Crystallographic Data Centre, under deposition nos CCDC 1848268 (2z), 1848266 ([Rh(2al)Cl)]2) and 1848267 (8g). Copies of the data can be obtained free of charge from www.ccdc.cam.ac.uk/structures/. All other data that supporting the findings of this study are available within the article and its Supplementary Information, or from the corresponding author upon reasonable request.
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We thank the University of Chicago, NIGMS (R01GM109054) and the Sloan Foundation for research support. We acknowledge G. Lu and P. Liu (University of Pittsburgh) for helpful discussion on the computational study. Calculations were performed at the Extreme Science and Engineering Discovery Environment (XSEDE) supported by the NSF. J.Z. acknowledges the financial support from Shanghai Institute of Organic Chemistry (SIOC), Pharmaron and Zhejiang Medicine for a joint postdoctoral fellowship. We are grateful to H. N. Lim for providing some rhodium catalysts and K.-Y. Yoon for X-ray analysis. V. Rawal, Z. Dong and J. Xie are thanked for helpful suggestions. We thank Z. Rong for assistance with using the autoclave and Y. Xu for checking the experimental procedures.