Enolonium Species – Umpoled Enolates
2Department of Chemistry, Technical University of Denmark, Kgs. Lyngby
3Department of Chemical Research Support, Weizmann Institute of Science, Rehovot
Nature has determined the roles of chemical reagents in organic synthesis as either electrophiles or nucleophiles. Umpolung or Polarity Reversal is a powerful concept that allows these roles to be switched thereby enabling a much larger array of methods to assemble complex organic molecules.
Umpolung of enolates mediated by hypervalent iodine reagents has shown itself to be the method of choice for functionalizing of carbonyl compounds. This is amply illustrated by numerous papers describing halogenations, oxygenations, aminations, and many other applications.[1] Recently we reported the use of this concept in C-C bond forming reactions.[2,3] These reactions are widely believed to proceed through a iodo(III)-enolate like structure named Enolonium Species.[1] However due to their high reactivity they are difficult to characterize and they have consequently been researched mainly through computational studies.[2,4] We have now characterized the Enolonium Species and shown determined their structure React-IR and NMR. A particular point of discussion in the community and a scientific challenge was to determine whether the hypervalent iodine is attached to the O of the enolate or to the C of its keto-form. The application of the Enolonium Species in various reactions, including chlorination, amination, enol ether coupling and allylation (including examples that lead to the formation of quaternary carbons), will be discussed.[5]
[1] a) V. V. Zhdankin, “Hypervalent Iodine Chemistry: Preparation, Structure, and Synthetic Applications of Polyvalent Iodine Compounds”, Wiley, 2014; b) F. V. Singh, T. Wirth in: Comprehensive Organic Synthesis, 2nd ed., Vol 7, (Eds: G. A. Molander, P. Knochel P.), Oxford: Elsevier, 2014.
[2] O. S. Shneider, E. Pisarevsky, P. Fristrup, A. M. Szpilman, Org. Lett., 2015, 17, 282.
[3] T. A. Targel, J. N. Kumar, O. S. Shneider, S. Bar, N. Fridman, S. Maximenko, A. M. Szpilman Org. Biomol. Chem., 2015, 13, 2546.
[4] a) S. Beaulieu, C. Y. Legault, Chem. Eur. J. 2015, 21, 11206; b) P.-O. Norrby, T. B. Petersen, M. Bielawski, B. Olofsson, Chem. Eur. J. 2010, 16, 8251.
[5] S. Arava, J. N. Kumar, S. Maksymenko, M. A. Iron, K. N. Parida, P. Fristrup, A. M. Szpilman Submitted for Publication.
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