Iron-catalysed chemo-selective oxidation of unprotected sugars David Branquet, Mohamed Vall Sidi Boune, Nicolas Hucher, Catherine Taillier, Vincent Dalla, Sébastien Comesse, Laure Benhamou URCOM, Université le Havre Normandie, France We present a novel catalytic method for the oxidation of unprotected sugars using an iron catalyst, in contrast to more traditional strategies employing a stoichiometric amount of halogenated reagents or precious metals. 1 Even though organometallic catalytic strategies have already been described for this transformation, they were only relying on precious metals such as palladium, rhodium or ruthenium. 2–5 Our approach relies on a transfer hydrogenation methodology where dihydrogen is formally transferred from a monosaccharide to an acceptor. The Kn lker catalyst, already known for the oxidation of alcohols into ketones, 6,7 and more recently for the oxidation of diols into lactones was selected for our transformation. 8 The reaction proceeds, without a strong oxidant only in the presence of a formal hydrogen acceptor (e.g. acetone). Our procedure allows the selective oxidation of the anomeric position of several unprotected carbohydrates into lactones (δ & g lactones). Sugars were converted in high yields and the sugars lactones were isolated without employing chromatographic techniques. Moreover, we managed to drastically decrease the stoichiometry of the acceptor required without compromising the equilibrium shift of the reaction by using a carefully selected acceptor. Finally, by taking advantage of the difference in reactivity of hexoses and pentoses, we devised a method using a resin work-up, to selectively oxidise pentoses from a mixture of sugars. Thus, a pentose was selectively upgraded into a lactone while the hexoses remained mostly untouched References 1. M. Xavier, A. P. Rauter and Y. Queneau, Top. Curr. Chem. , 2010, 295 , 19–62. V. R. Jumde, N. N. H. M. Eisink, M. D. Witte and A. J. Minnaard, J. Org. Chem. , 2016, 81 , 11439–11443. 2. S. Manna and A. P. Antonchick, ChemSusChem , 2019, 12 , 3094–3098. M. Bierenstiel and M. Schlaf, European J. Org. Chem. , 2004, 1474–1481. 3. G. de Wit, J. J. de Vlieger, A. C. Kock-van Dalen, R. Heus, R. Laroy, A. J. van Hengstum, A. P. G. Kieboom and H. van Bekkum, Carbohydr. Res. , 1981, 91 , 125–138. 4. H. J. Kn lker, E. Baum, H. Goesmann and R. Klauss, Angew. Chemie - Int. Ed. , 1999, 38 , 2064–2066. 5. M. Akter and P. Anbarasan, Chem. - An Asian J. , 2021, 16 , 1703–1724. Y. Tang, R. I. L. Meador, C. T. Malinchak, E. E. Harrison, K. A. McCaskey, M. C. Hempel and T. W. Funk, J. Org. Chem. , 2020,85, 1823–1834I
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