Cover Picture: Umpolung by N-Heterocyclic Carbenes: Generation and Reactivity of the Elusive 2,2-Diamino Enols (Breslow Intermediates) (Angew. Chem. Int. Ed. 49/2012)



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Breslow intermediates of N-heterocyclic carbene (NHC) catalyzed Umpolung reactions have been generated by combining saturated NHCs with aldehydes. In their Communication on page 12370 ff., A. Berkessel et al. report the observation of these pivotal but hitherto elusive intermediates. Indeed, much water has flown down the Rhine since the first postulation of amino enols as the “umpoled” form of aldehydes in 1958 until their characterization reported herein! (Graphics & photo: Adrian von der Höh.)