Prof. Dr. Albrecht Berkessel, Silvia Elfert, V. Reddy Yatham, Dr. Jörg-M. Neudörfl, Dr. Nils E. Schlörer and Dr. J. Henrique Teles Umpolung by N-Heterocyclic Carbenes: Generation and Reactivity of the Elusive 2,2-Diamino Enols (Breslow Intermediates) Angewandte Chemie International Edition 51
54 years later: Saturated imidazolidin-2-ylidenes react with aldehydes to smoothly produce the elusive 2,2-diamino enols A (“Breslow intermediates”, first postulated in 1958) of carbene-catalyzed umpolung reactions. The 2,2-diamino enols A react with additional aldehyde in a cross-benzoin reaction. The methylated Breslow intermediates B are accessible by deprotonation of methoxymethyl azolium salts.
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