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Metal-free graphene oxide-catalyzed aza-semipinacol rearrangement to prepare 2-(indol-2-yl)phenols and benzofuro[3,2-b]indolines containing quaternary carbon centers

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Abstract

We report a metal-free, heterogeneous, inexpensive, and environmentally friendly graphene oxide-catalyzed aza-semipinacol rearrangement of 2-(3-methyleneindolin-2-yl)phenols to prepare 2-(indol-2-yl)phenols and benzofuro[3,2-b]indolines containing quaternary carbon centers in good to excellent yields under mild conditions. The detailed studies demonstrate that graphene oxide can function as a heterogeneous catalyst and provide hydrogen bonding and ion pair interactions on the surface to promote the rearrangement process. The substituent effect on the C2-position of indoline is two-fold, affording 2-(indol-2-yl)phenols by aza-semipinacol rearrangement and benzofuro[3,2-b]indolines by 5-exo-trig cyclization. The stereochemistry of the C3-quaternary carbon center generated from the C2-quaternary carbon center of indoline is retained during the rearrangement. More importantly, the graphene oxide can be easily recovered by washing and recycled seven times without loss of catalytic activity.

Graphical abstract: Metal-free graphene oxide-catalyzed aza-semipinacol rearrangement to prepare 2-(indol-2-yl)phenols and benzofuro[3,2-b]indolines containing quaternary carbon centers

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Article information


Submitted
25 Sep 2019
Accepted
19 Nov 2019
First published
20 Nov 2019

Green Chem., 2020, Advance Article
Article type
Paper

Metal-free graphene oxide-catalyzed aza-semipinacol rearrangement to prepare 2-(indol-2-yl)phenols and benzofuro[3,2-b]indolines containing quaternary carbon centers

H. Zhao, G. Liang, S. Nie, X. Lu, C. Pan, X. Zhong, G. Su and D. Mo, Green Chem., 2020, Advance Article , DOI: 10.1039/C9GC03345A

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