Catalytic Activation of Unstrained C(Aryl)–C(Alkyl) Bonds in 2,2′-Methylenediphenols
2022
Zhu, Jun | Xue, Yibin | Zhang, Rui | Ratchford, Benjamin L. | Dong, Guangbin
Catalytic activation of unstrained and nonpolar C–C bonds remains a largely unmet challenge. Here, we describe our detailed efforts in developing a rhodium-catalyzed hydrogenolysis of unstrained C(aryl)–C(alkyl) bonds in 2,2′-methylenediphenols aided by removable directing groups. Good yields of the monophenol products are obtained with tolerating a wide range of functional groups. In addition, the reaction is scalable, and the catalyst loading can be reduced to as low as 0.5 mol %. Moreover, this method proves to be effective to cleave C(aryl)–C(alkyl) linkages in both models of phenolic resins and commercial novolacs resins. Finally, detailed experimental and computational mechanistic studies show that with C–H activation being a competitive but reversible off-cycle reaction, this transformation goes through a directed C(aryl)–C(alkyl) oxidative addition pathway.
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