title: Characterization of the key intermediates of carbene-catalyzed umpolung by NMR spectroscopy and X-ray diffraction: breslow intermediates, homoenolates, and azolium enolates.
abstract: 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.
authors.affiliation: Cologne University, Department of Chemistry, Greinstrasse 4, 50939 Cologne (Germany) http://www.berkessel.de. berkessel@uni-koeln.de.
authors.forename: Albrecht
authors.initials: A
authors.lastname: Berkessel
authors.forename: Veera Reddy
authors.initials: VR
authors.lastname: Yatham
authors.forename: Silvia
authors.initials: S
authors.lastname: Elfert
authors.forename: Jörg-M
authors.initials: JM
authors.lastname: Neudörfl
mesh_terms: D000438:Alcohols / Q000737:chemistry; D002384:Catalysis; D018360:Crystallography, X-Ray; D007093:Imidazoles / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D013237:Stereoisomerism; D014753:Vinyl Compounds / Q000737:chemistry
chemical_list: D000438:Alcohols; D007093:Imidazoles; D014753:Vinyl Compounds; C030011:carbene; D008697:Methane
keywords: NMR spectroscopy; X-ray diffraction; carbenes; reaction mechanisms; umpolung