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Synlett 2019; 30(10): 1219-1221
DOI: 10.1055/s-0037-1611541
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© Georg Thieme Verlag Stuttgart · New York

Electrochemical Deoxygenation of N-Heteroaromatic N-Oxides

P. Xu
,
H.-C. Xu  *
College of Chemistry and Chemical Engineering, Xiamen University, 422 South Siming Road, Xiamen 361005, P. R. of China   Email: haichao.xu@xmu.edu.cn
› Author AffiliationsFinancial support of this research from the Ministry of Science and Technology of the People’s Republic of China (MOST, Grant No. 2016YFA0204100) and the National Natural Science Foundation of China (NSFC, Grant No. 21672178) is acknowledged. We also acknowledge the support of Fundamental Research Funds for the Central Universities.
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Publication History

Received: 19 April 2019

Accepted after revision: 25 April 2019

Publication Date:
10 May 2019 (online)

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Published as part of the Cluster Electrochemical Synthesis and Catalysis

Abstract

An electrochemical method for the deoxygenation of N-heteroaromatic N-oxide to give the corresponding N-heteroaromatics has been developed. Several classes of N-heterocycles such as pyridine, quinoline, isoquinoline, and phenanthridine are tolerated. The electrochemical reactions proceed efficiently in aqueous solution without the need for transition-metal catalysts and waste-generating reducing reagents.

Key words

reduction - organic electrosynthesis - deoxygenation - electrolysis - heterocycles

Supporting Information

    Supporting information for this article is available online at https://doi.org/10.1055/s-0037-1611541.
  • Supporting Information
 

  • References and Notes

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  • 5 General Procedure for the Electrochemical Deoxygenation Reactions A 10 mL three-necked round-bottomed flask was charged with the N-heteroaromatic N-oxide (0.30 mmol, 1.0 equiv) and Et4NPF6 (0.06 mmol, 0.2 equiv). The flask was then equipped with a condenser, a reticulated vitreous carbon (100 PPI, ca. 65 cm2 cm−3, 1.2 cm × 1.0 cm × 0.8 cm) anode, and a Pb plate (1.0 cm × 1.0 cm) cathode and flushed with argon. MeCN and H2O (4:1, 10.0 mL) were added. The electrolysis was carried out at 80 °C using a constant current of 10 mA until complete consumption of the substrate (monitored by TLC or 1H NMR). The reaction mixture was concentrated under reduced pressure. The residue was chromatographed through silica gel eluting with ethyl acetate/hexane to give the desired product.
  • 6 Spectral Data for 2b Colorless oil; yield 70%; 2.4 F mol–1. 1H NMR (400 MHz, CDCl3): δ = 8.04–7.95 (m, 2 H), 7.73 (dt, J = 8.3, 1.6 Hz, 1 H), 7.65 (ddt, J = 8.5, 6.9, 1.6 Hz, 1 H), 7.45 (ddt, J = 8.0, 6.9, 1.2 Hz, 1 H), 7.26–7.21 (m, 1 H), 2.72 (s, 3 H). 13C NMR (101 MHz, CDCl3): δ = 159.1, 148.0, 136.2, 129.5, 128.7, 127.6, 126.6, 125.7, 122.1, 25.5.
  • 7 Spectral Data for 2c Colorless oil; yield 65%; 2.2 F mol–1. 1H NMR (400 MHz, CDCl3): δ = 8.94–8.83 (m, 1 H), 8.10 (d, J = 8.2 Hz, 2 H), 7.82–7.63 (m, 2 H), 7.56–7.45 (m, 1 H), 7.35 (dq, J = 7.5, 3.8 Hz, 1 H). 13C NMR (101 MHz, CDCl3): δ = 150.5, 148.4, 136.1, 129.6, 129.5, 128.4, 127.9, 126.6, 121.2.
  • 8 Spectral Data for 2e Colorless oil; yield 77%; 4.0 F mol–1. 1H NMR (400 MHz, CDCl3): δ = 8.45–8.37 (m, 2 H), 6.85–6.68 (m, 2 H), 3.82 (s, 3 H). 13C NMR (101 MHz, CDCl3): δ = 165.7, 151.2, 110.0, 55.2.