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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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Publication details

The article was received on 25 Sep 2019, accepted on 19 Nov 2019 and first published on 20 Nov 2019


Article type: Paper
DOI: 10.1039/C9GC03345A
Green Chem., 2020, Advance Article

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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

    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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