Electrochemical Oxidative C–H Thiocyanation or Selenocyanation of Imidazopyridines and Arenes

Abstract

Regioselective electrochemical oxidative C–H thiocyanation or selenocyanation of imidazopyridines was achieved by using an undivided electrolytic cell. Transition-metal- and oxidant-free conditions are striking features of this protocol. A library of thiocyanated imidazopyridines with a broad range of functional groups were synthesized in high yields. This method was also applicable to the thiocyanation or selenocyanation of some electron-rich arenes.

Key words

electrochemical oxidation - C–H functionalization - thiocyanation - selenocyanation - imidazopyridines - arenes

Publication History

Received: 12 September 2020

Accepted after revision: 28 October 2020

Accepted Manuscript online:
28 October 2020

Article published online:
27 November 2020

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• 27 2-Phenylimidazo[1,2-a]pyridin-3-yl Thiocyanate (3a):^21a Typical Procedure An undivided 25 mL three-necked flask was charged with 2-phenylimidazo[1,2-a]pyridine (1a, 38.8 mg, 0.2 mmol), NH₄SCN (2a, 30.5 mg, 0.4 mmol, 2 equiv), Bu₄NPF₆ (194 mg, 0.5 mmol, 2.5 equiv), and MeCN (10 mL). The flask was equipped with two platinum plate electrodes (10 × 10 mm) as the anode and cathode, respectively. The reaction mixture was electrolyzed and stirred at a constant current (5 mA) under air at r.t. for 6 h. When the reaction was complete, the mixture was diluted with H₂O (30 mL) and extracted with CH₂Cl₂ (3 × 10 mL). The combined organic phases were dried (Na₂SO₄), filtered, and concentrated in vacuo. The resulting crude product was purified by chromatography [silica gel, PE–EtOAc (5:1)] to give a white solid; yield: 42.7 mg (85%); mp 115–117 °C. ¹H NMR (400 MHz, CDCl₃): δ = 8.48 (d, J = 6.6 Hz, 1 H), 8.08 (d, J = 7.3 Hz, 2 H), 7.80 (d, J = 8.9 Hz, 1 H), 7.58–7.48 (m, 4 H), 7.16 (t, J = 6.7 Hz, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 153.0, 147.9, 131.9, 129.5, 128.8, 128.8, 128.1, 124.4, 118.3, 114.5, 108.2, 94.7.