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Synlett 2020; 31(07): 695-698
DOI: 10.1055/s-0039-1691587
DOI: 10.1055/s-0039-1691587
letter
Diiodine-Mediated Oxidative Reaction for the Construction of Imidazo[1,5-a]pyridines under Metal-Free Conditions
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.
Key words
imidazopyridines - metal-free synthesis - amination - benzylic amines - ethyl pyridinylacetatesSupporting Information
- Supporting information for this article is available online at https://doi.org/10.1055/s-0039-1691587.
- 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.