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Direct synthesis of annulated indoles through palladium-catalyzed double alkylations

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Abstract

A facile, one-step synthesis of annulated indoles from (N–H) indoles and dibromoalkanes was developed through a palladium-catalyzed double alkylation process. The reaction proceeds through a palladium-catalyzed norbornene-mediated C2-alkylation of indoles and subsequent regioselective cyclization. The reaction is compatible with various indole substituents, as well as a range of simple and functionalized dibromoalkyl reagents. The detailed reaction mechanism was investigated by key intermediate experiments, NMR spectroscopic analyses, and DFT calculations. The results of a preliminary mechanistic study show a catalytic cycle consisting of initial C2-alkylation of indoles that is followed by N-alkylation or palladium promoted intramolecular C3-nucleophilic substitution to yield, respectively, [a]- or [b]-annulated indoles.

Graphical abstract: Direct synthesis of annulated indoles through palladium-catalyzed double alkylations

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Article information


Submitted
30 Jan 2020
Accepted
14 Mar 2020
First published
24 Mar 2020

Org. Chem. Front., 2020, Advance Article
Article type
Research Article

Direct synthesis of annulated indoles through palladium-catalyzed double alkylations

Y. Gao, J. Li, S. Bai, D. Tu, C. Yang, Z. Ye, B. Hu, X. Qi and C. Jiang, Org. Chem. Front., 2020, Advance Article , DOI: 10.1039/D0QO00135J

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