Aldehyde umpolung by N-heterocyclic carbenes: NMR characterization of the breslow intermediate in its keto form, and a spiro-dioxolane as the resting state of the catalytic system
Surprises from a classic: The Breslow intermediate of triazolylidene- catalyzed benzoin condensations was characterized for the first time by NMR spectroscopy in its keto form (K, energetic minimum). The hitherto unknown spiro-dioxolane S, generated from
Berkessel, Albrecht,Elfert, Silvia,Etzenbach-Effers, Kerstin,Teles, J. Henrique