Description
Oxidation of phenols using catalytic amounts of solid-supported IBS-based catalysts in Continuous Flow
J.P. Nau, Dr. A. Gómez-Suárez, Prof. Dr. S.F. Kirsch
As reactive intermediates, 1,2-quinones (o-quinones) have gained importance in organic synthesis. They can undergo many kinds of follow-up reactions like [4+2]-cycloadditions[2], formal [3+2]-photoadditions with vinyl ethers[3] or 1,4-additions with nitrogen-centered nucleophiles, respectively 1,6-additions with thiols as nucleophiles[4]. A reliable method for the synthesis of o-quinones is the application of λ^5-Iodanes which show a remarkable regioselectivity favouring the formation of 1,2-quinones compared to 1,4-quinones[7]. Catalytic applications of λ^5-Iodanes for the dearomatization of phenols were first described by Ishihara and co-workers in 2012. They discovered the suitability of 2-Iodosulfonic acid (IBS)-derived catalysts which are superior to their IBX-analogues[5]. Based on this work and the solid-supported IBX (SP-IBS)-catalyzed oxidation of alcohols in flow, first published by Kirsch et al.[6], we are now developping a method for the oxidation of phenols to 1,2-quinones in flow using solid-supported IBS-based catalysts and tetrabutyl ammonium Oxone (nBu4NHSO5) as co-oxidant.
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[4] L. Valgimigli, O. Creszenzi et al., J. Org. Chem., 2022, 87, 4580-4589.
[5| K. Ishihara et al., Molecules, 2012, 17(7), 8604-8613.
[6] S.F. Kirsch et al., Chem. Eur. J., 2024, 30, e202304011.
[7] R.G. Harvey et al., Tetrahedron, 2010, 66, 2111-2118.
