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.
Caught in the act: Diamino enols, diamino dienols, azolium enolates, and azolium enols are postulated intermediates of the N-heterocyclic carbene catalyzed umpolung of aldehydes and enals. Several of these elusive reaction intermediates were generated with the saturated imidazolidin-2-ylidene SIPr (R=2,6-bis(2-propyl)phenyl) and characterized by NMR spectroscopy and X-ray crystallography.
54 Jahre später: Durch Reaktion von gesättigten Imidazolidin‐2‐ylidenen mit Aldehyden werden 2,2‐Diaminoenole A („Breslow‐Intermediate“, 1958 postuliert), generiert, die Schlüsselintermediate in carbenkatalysierten Umpolungsreaktionen sind. Die 2,2‐Diaminoenole A reagieren mit weiterem Aldehyd in einer gekreuzten Benzoinkondensation. Die methylierten Breslow‐Intermediate B sind durch Deprotonierung von Methoxymethylazolium‐Salzen zugänglich.
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