Electrochemical asymmetric diacetoxylation of styrenes mediated by chiral iodoarene catalyst Natalia Wojciechowska, Krzysztof Bienkowski, Renata Solarska, and Marcin Kalek Centre of New Technologies, University of Warsaw, Poland Organocatalysis of oxidation reactions with iodoarenes have enabled the conversion of simple reactants into highly complex structures found in biologically active compounds and pharmaceuticals. [1] Moreover, the application of chiral iodoarene catalysts has allowed for performing highly enantioselective transformations. [2] However, the inherent drawback of these processes is that a stoichiometric or even 2-3-fold excess of a terminal oxidant (typically meta -chloroperbenzoic acid) has to be used in order to regenerate the hypervalent iodine(III) species from the iodoarene. The need to use such large quantities of highly oxidizing and potentially dangerous chemical effectively prevents the widespread application of the highly synthetically powerful reactions catalyzed by iodine-containing compounds, especially on a large scale. Related economic and environmental concerns are also considerable. In this context, electrosynthesis is an attractive alternative, as it allows to efficiently provide the driving force for redox transformations, eliminating the need for high energy stoichiometric oxidants and reductants. Herein, we report for the first time the development of an asymmetric electrosynthetic reaction employing a chiral iodoarene catalyst. Namely, the enantioselective diacetoxylation of styrenes mediated by a chiral C 2 -symmetric iodoresorcinol-lactamide catalyst is carried out under the electrochemical conditions. The reaction conditions were optimized to accomplish the indirect electrolysis mediated by the iodoarene with a catalytic turnover. The electrolysis is carried out under simple constant current conditions in an undivided cell, generating hydrogen as the sole side-product. The developed method was tested for a number of substituted styrenes. For some of these, it provides products in high enantiomeric excess, albeit in moderate yields due to side-formation of styrene dimers via a direct anodic oxidation. For easily-oxidized starting materials, the direct uncatalyzed diacetoxylation prevails, affording racemic products.
References 1. a) Y. Kita, T. Dohi, Chem. Rec. 2015 , 15 , 886-906; b) R. Narayan, S. Manna, A. P. Antonchick, Synlett 2015 , 26 , 1785-1803; c) A. Yoshimura, V. V. Zhdankin, Rev . 2016 , 116 , 3328-3435; d) A. D. Lauriers, C. Y. Legault, Asian J. Org. Chem. 2016 , 5 , 1078-1099;
e) Y. Yoshimura, H. Wakamatsu, Y. Natori, Y. Saito, N. Minakawa, Beilstein Org. Chem. 2018 , 14 , 1595-1618; e) F. V. Singh, P. B. Kole, R. Mangaonkar, S. E. Shetgaonkar, Beilstein J. Org. Chem. 2018 , 14 , 1778-1805; f) I. F. D. Hyatt, L. Dave, N. David, K. Kaur, M. Medard, Mowdawalla , Org. Biomol. Chem . 2019 , 17 , 7822-7848; g) A. Bauer, Maulide, Chem. Sci . 2021 , 12 , 853-864. 2. a) M. Ngatimin, D. W. Lupton, Aust. J. Chem . 2010 , 63 , 653-658; b) H. Liang, M. A. Ciufolini, Angew. Chem. Int. Ed. 2011 , 50 , 11849-11851; c) A. Parra, S. Reboredo, Chem. Eur. J. 2013 , 19 , 17244-17260.
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