Metal-free Cross-Dehydrogenative Coupling for α-Arylation of 3-Aryloxindoles
Fangzhi Hu1,2,3, Peng Wang2, Jiawei Li2
1Department of Chemistry, National Demonstration Centre for Experimental Chemistry Education, Yanbian University, Yan Bian Chao Xian Zu Zi Zhi Zhou, Yanji, 133002, China.
Abstract:
The creation of quaternary carbon centers has been a formidable challenge in organic synthesis due to steric impediments, especially for the polyaryl substituted quaternary carbon centers. Up to now, a few of methods were reported for achieving the α-arylation of 3-aryloxindoles to construct 3,3-diaryloxindoles. We now asserted the TfOH-catalyzed cross-dehydrogenative coupling reaction between the tertiary C(sp3)-H and readily available arenes under air atmosphere in green reaction medium for rapid construction of 3,3-diaryloxindoles. In addition, the mechanism of the metal-free cross-dehydrogenative coupling with air as oxidant was meticulously explored.
Related Concept Videos
Vicinal Diols via Reductive Coupling of Aldehydes or Ketones: Pinacol Coupling Overview
Aryldiazonium Salts to Azo Dyes: Diazo Coupling
Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide
Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction
Acid-Catalyzed α-Halogenation of Aldehydes and Ketones
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an ÃÂñ-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the âÃÂÃÂOH group.


