Bu₄NI-Catalyzed Synthesis of Imidazo[1,2-a]pyridines via Oxidative Coupling of Aminopyridines with Nitroolefins

Abstract

A metal-free method for the synthesis of imidazo[1,2-a]pyridines via double C–N oxidative coupling of aminopyridines with nitroolefins using TBAI as the catalyst and TBHP as oxidation agent has been developed.

Key words

TBAI - imidazo[1,2-a]pyridines - oxidative coupling - aminopyridines - ­nitroolefins

• References and Notes

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• 11 General Experimental Procedure and Spectroscopic Data: To a solution of 1 (0.5 mmol), 2 (0.6 mmol) and TBAI (0.1 mmol) in DMF (2 mL) was added TBHP (1.0 mmol, 70% aq solution). The reaction mixture was stirred at 80 °C for 4 h. After the mixture was cooled to r.t., the solvent was diluted with CH₂Cl₂ (10 mL), washed with brine (5 mL), and dried over anhyd Mg₂SO₄. After the solvent was evaporated in vacuo, the residues were purified by column chromatog-raphy, eluted with petroleum ether–EtOAc to afford imidazo[1,2-a]pyridines. 3aa: yellow solid; mp 168−170 °C. ¹H NMR (500 MHz, CDCl₃): δ = 9.52–9.54 (d, J = 7.0 Hz, 1 H), 7.90–7.92 (m, 2 H), 7.84–7.87 (d, J = 8.9, 1.1 Hz, 1 H), 7.65–7.69 (m, 1 H), 7.50–7.53 (m, 3 H), 7.28–7.31 (q, 1 H).
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