Search results
Search for "NHC activation" in Full Text gives 1 result(s) in Beilstein Journal of Organic Chemistry.
A quantitative approach to nucleophilic organocatalysis
- Herbert Mayr,
- Sami Lakhdar,
- Biplab Maji and
- Armin R. Ofial
Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166
- ; kinetics; NHC activation; organocatalysis; structure reactivity relationships; Review Introduction The most comprehensive nucleophilicity and electrophilicity scales presently available, are based on Equation 1, in which electrophiles are characterized by one solvent-independent parameter E, and
Graphical Abstract
Figure 1: Second-order rate constants for reactions of electrophiles with nucleophiles.
Figure 2: Mechanism of amine-catalyzed conjugate additions of nucleophiles [23-28].
Figure 3: Kinetics of the reactions of the iminium ion 3a with the silylated ketene acetal 7a [35].
Figure 4: Laser flash photolytic generation of iminium ions 3a.
Figure 5: Correlations of the reactivities of the iminium ions 3a and 3b toward nucleophiles with the corresp...
Figure 6: Comparison of the electrophilicities of cinnamaldehyde-derived iminium ions 3a–3i.
Figure 7: Nucleophiles used in iminium activated reactions [35,42,44-52].
Figure 8: Counterion effects in electrophilic reactions of iminium ions 3a-X (at 20 °C, silyl ketene acetal 7b...
Figure 9: Comparison of calculated and experimental rate constants of electrophilic aromatic substitutions wi...
Figure 10: Aza-Michael additions of the imidazoles 15 with the iminium ion 3a [58].
Figure 11: Plots of log k2 for the reactions of enamides 17a–17e with the benzhydrylium ions 18a–d in CH3CN at...
Figure 12: Comparison of the nucleophilicities of enamides 17 with those of several other C nucleophiles (solv...
Figure 13: Experimental and calculated rate constants k2 for the reactions of 17b and 17g with 3a and 3b in th...
Figure 14: Comparison between experimental and calculated (Equation 1) cyclopropanation rate constants [64].
Figure 15: Electrostatic activation of iminium activated cyclopropanations with sulfur ylides.
Figure 16: Sulfur ylides inhibit the formation of iminium ions.
Figure 17: Enamine activation [65].
Figure 18: Electrophilicity parameters E for classes of compounds that have been used as electrophilic substra...
Figure 19: Quantification of the nucleophilic reactivities of the enamines 32a–e in acetonitrile (20 °C) [83]; a d...
Figure 20: Proposed transition states for the stereogenic step in proline-catalyzed reactions.
Figure 21: Kinetic evidence for the anchimeric assistance of the electrophilic attack by the carboxylate group....
Figure 22: Differentiation of nucleophilicity and Lewis basicity (in acetonitrile at 20 °C): Rate (left) and e...
Figure 23: NHCs 41, 42, and 43 are moderately active nucleophiles and exceptionally strong Lewis bases (methyl...
Figure 24: Nucleophilic reactivities of the deoxy Breslow intermediates 45 in THF at 20 °C [107].
Figure 25: Comparison of the proton affinities (PA, from [107]) of the diaminoethylenes 47a–c with the methyl catio...
Figure 26: Berkessel’s synthesis of a Breslow intermediate (51, keto tautomer) from carbene 43 [112].
Figure 27: Synthesis of O-methylated Breslow intermediates [114].
Figure 28: Relative reactivities of deoxy- and O-methylated Breslow intermediates [114].
Figure 29: Reactivity scales for electrophiles and nucleophiles relevant for organocatalytic reactions (refere...
