An electrolyte- and catalyst-free electrooxidative sulfonylation of imidazo[1,2-a]pyridines

Direct electrochemical oxidation has been widely applied in organic synthesis due to its simple and mild reaction conditions, high selectivity, few by-products, high product purity and high productivity. Up to now, the efficient synthetic methods for 3-sulfonylated imidazo[1,2-a]pyridines have been the C-H activation of imidazo[1,2-a]pyridines with a photosensitizer or transition-metal-catalyst at a high reaction temperature. In this article, an electrolyte- and catalyst-free electrooxidative approach to produce sulfonylated imidazo[1,2-a]pyridines was investigated. Various imidazo[1,2-a]pyridines and sodium sulfinates could be selectively transformed into the 3-sulfonylated imidazo[1,2-a]pyridines in good to excellent yields. Based on the results of control experiments and theoretical calculations, we proposed that the studied reaction might occur via a radical process. The spectral properties of imidazo[1,2-a]pyridines might be controlled by the modification of their 8-position.