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Chromium–Salen Complex / Nitroxyl Radical Cooperative Catalysis:A New Combination for Aerobic Intramolecular Dearomative Coupling of Phenols
preprintsubmitted on 07.09.2020, 01:37 and posted on 07.09.2020, 12:44 by Shota Nagasawa, Shogo Fujiki, Yusuke Sasano, Yoshiharu Iwabuchi
Herein we describe an aerobic intramolecular dearomative coupling reaction of phenols using a catalytic system with the combination of a chromium–salen (Cr–salen) complex and a nitroxyl radical. This novel catalytic system enables the construction of a spirocyclic dienone product, which is a potentially useful intermediate for the synthesis of various natural products such as alkaloids and phenylpropanoids from bisphenol in good yield under mild reaction conditions (under O2 and ambient temperature). A preliminary mechanistic study suggests that this reaction system is promoted by a cooperative electron transfer between the Cr(III)–salen complex, nitroxyl radical and bisphenol substrate.