Synlett 2015; 26(03): 335-339
DOI: 10.1055/s-0034-1379015
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© Georg Thieme Verlag Stuttgart · New York

Copper-Catalyzed Synthesis of N-Aryl and N-Sulfonyl Indoles from 2-Vinyl­anilines with O2 as Terminal Oxidant and TEMPO as Cocatalyst

Timothy W. Liwosz
Department of Chemistry, The State University of New York at Buffalo, Buffalo, NY, 14620, USA   Fax: +1(716)6456963   eMail: schemler@buffalo.edu
,
Sherry R. Chemler*
Department of Chemistry, The State University of New York at Buffalo, Buffalo, NY, 14620, USA   Fax: +1(716)6456963   eMail: schemler@buffalo.edu
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Publikationsverlauf

Received: 30. Juni 2014

Accepted after revision: 01. August 2014

Publikationsdatum:
25. August 2014 (online)


Abstract

A copper-catalyzed intramolecular alkene oxidative ­amination that utilizes TEMPO as cocatalyst and O2 as the terminal oxidant has been developed. The method furnishes N-aryl and N-sulfonyl indoles from N-aryl and N-sulfonyl 2-vinylanilines, ­respectively. Additionally, sequential copper-catalyzed reactions where initial Chan–Lam coupling of 2-vinylanilines with aryl­boronic acids is followed by oxidative amination of the alkene can generate N-aryl indoles in one pot.

Supporting Information

 
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  • 9 Representative Procedure for the Copper-Catalyzed Intramolecular Alkene C–H Amination An oven-dried 100 mL round-bottom flask was charged with 1a (50 mg, 0.174 mmol, 1 equiv), Cu(2-ethylhexanoate)2 (9 mg, 0.026 mmol, 15 mol%), TEMPO (5 mg, 0.035 mmol, 20 mol%), and dry toluene (1.74 mL, 0.1 M). The flask was purged with O2, put under an O2 atmosphere using an O2 balloon, and stirred for 24 h at 120 °C. Filtration of the cooled reaction mixture through a pad of silica gel with EtOAc (100 mL) and subsequent evaporation of the solvent in vacuo afforded the crude mixture. Flash chromatography of the resulting crude mixture on silica gel (0–20% EtOAc in hexanes gradient) afforded indole 2a (36 mg, 71% yield) as an off-white solid.6 1H NMR (400 MHz, CDCl3): δ = 7.99 (d, J = 8.4 Hz, 1 H), 7.74 (d, J = 8.0 Hz, 2 H), 7.45 (d, J = 7.2 Hz, 1 H), 7.34–7.29 (m, 2 H), 7.26–7.22 (m, 1 H), 7.19 (d, J = 8.4 Hz, 2 H), 2.32 (s, 3 H), 2.24 (d, J = 0.8 Hz, 3 H).