Electrochemical di-oxygenation of quinolines

Electrochemical methods for the synthesis and transformation of organic compounds have recently received increased interest by both academic and industrial research1. Electrochemistry represents a mild and green way to obtain useful molecules, avoiding the stoichiometric use of harsh and often hazardous or waste-generating oxidating and reducing agents, that can limit large-scale applications. Moreover, the highly selective nature of this method allows to avoid the sometimes tedious protection/deprotection steps. The renaissance of organic electrochemistry has been accompanied by an increased attention to flow electrochemistry, that, thanks to the small interelectrode gap, reduces the resistance and improves the mass transport of the substrates from the bulk to the electrode surface, with the advantage of reducing the reaction time2. Di-oxygenation of olefins is generally achieved with several methods including the use of transition metals, for example Sharpless reaction3. In very recent years, electrochemical approach has emerged as an alternative method to perform di-oxygenation not only of olefins, but also of heterocycles, like indoles and thiophenes4. In this context, we envisioned the possibility to perform the di-oxygenation of activated quinolines. Dihydroquinolines, that can be pre-formed by classic chemical activation, are subjected to electrochemical transformation, opening new frontiers in the synthesis of highly functionalized tetrahydroquinolines. Alternatively, the one-pot procedure will be attempted. 1. C. Schotten, T. P. Nicholls, R. A. Bourne, N. Kapur, B. N. Nguyen, C. E. Willans, Green Chem. 2020, 22, 3358–3375 2. T. Noel, Y. Cao, G. Laudadio, Acc. Chem. Res. 2019, 52, 10, 2858–2869 3. S. G. Hentges, K. B. Sharpless, J. Am. Chem. Soc. 1980, 102, 4263- 4265. 4. a) S. Zhang, L. Li, P. Wu, P. Gong, R. Liu, K. Xu, Adv. Synth. Catal. 2019, 361, 485–489. b) C. Y. Cai, H. C. Xu, Nat Commun 2018, 9. c) J. Wu, Y. Dou, R. Guillot, C. Kouklovsky, G. Vincent, J. Am. Chem. Soc. 2019, 141, 2832−2837.