Synlett 2020; 31(07): 695-698
DOI: 10.1055/s-0039-1691587
letter
© Georg Thieme Verlag Stuttgart · New York

Diiodine-Mediated Oxidative Reaction for the Construction of Imidazo[1,5-a]pyridines under Metal-Free Conditions

Kexin Su
a  State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Gansu Lanzhou, 730000, P. R. of China   Email: chenbh@lzu.edu.cn
,
Mingda Qin
a  State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Gansu Lanzhou, 730000, P. R. of China   Email: chenbh@lzu.edu.cn
,
Yongxin Chen
b  Key Laboratory of Petroleum Resources, Gansu Lanzhou, 730000, P. R. of China   Email: chenyongxin@lzb.ac.cn
,
Yafeng Liu
a  State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Gansu Lanzhou, 730000, P. R. of China   Email: chenbh@lzu.edu.cn
,
Yuan Tian
a  State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Gansu Lanzhou, 730000, P. R. of China   Email: chenbh@lzu.edu.cn
,
a  State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Gansu Lanzhou, 730000, P. R. of China   Email: chenbh@lzu.edu.cn
› Author Affiliations
Financial support for this study from the Key Laboratory Project of Gansu Province (Grant No. 1309RTSA041).
Further Information

Publication History

Received: 21.11.20219

Accepted after revision: 05 January 2020

Publication Date:
04 February 2020 (online)


Abstract

An efficient and general protocol has been developed for preparing imidazo[1,5-a]pyridines in moderate to excellent yields by an I2-mediated sequential dual oxidative C(sp3)–H amination of ethyl pyridin-2-ylacetates with benzylamines. The metal- and peroxide-free reaction involves oxidative dehydrogenation and two C–N couplings.

Supporting Information

 
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  • 15 Ethyl 3-Phenylimidazo[1,5-a]pyridine-1-carboxylate (3aa); Typical Procedure A 10-mL Schlenk tube was charged with 1a (0.2 mmol), 2a (1.1 equiv, 0.22 mmol), and I2 (1 equiv, 0.2 mmol). CH2Cl2 (2 mL) was then added and the mixture was stirred at 100 ℃ for 8 h under air. The solvent was removed, and the mixture was filtered and evaporated under vacuum. The residue was purified by column chromatography [silica gel, EtOAc–PE (10:1)] to give a white solid; yield: 88%; mp 127–130 °C. 1H NMR (300 MHz, CDCl3): δ = 8.28 (dd, J = 16.6, 8.2 Hz, 2 H), 7.79 (d, J = 6.6 Hz, 2 H), 7.57–7.46 (m, 3 H), 7.13 (dd, J = 8.9, 6.7 Hz, 1 H), 6.78 (t, J = 6.8 Hz, 1 H), 4.50 (q, J = 7.1 Hz, 2 H), 1.47 (t, J = 7.1 Hz, 3 H). 13C NMR (75 MHz, CDCl3): δ = 163.8, 139.4, 135.6, 129.8, 129.3, 129.2, 129.0, 124.5, 122.7, 121.9, 120.2, 114.7, 60.6, 14.9.