Impact of Backbone Substitution on Organocatalytic Activity of Sterically Encumbered NHC in Benzoin Condensation
Rinat R Aysin1, Konstantin I Galkin2,3
1A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilova Street 28, bld. 1, 119991 Moscow, Russia.
Abstract:
In this study, we provide a theoretical explanation for the experimentally observed decrease in the organocatalytic activity of N-aryl imidazolylidenes methylated at the C4/5-H positions in the benzoin condensation of aromatic aldehydes. A comparative quantum chemical study of energy profiles for the NHC-mediated benzoin condensation of furfural has revealed a high energy barrier to the formation of the IPrMe-based furanic Breslow intermediate that can be attributed to the negative steric interactions between the imidazole backbone methyl groups and N-aryl substituents.
More Related Videos
19:58Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
Published on: July 30, 2017
07:50Efficient Synthesis of All-Carbon Quaternary Centers via the Conjugate Addition of Functionalized Monoorganozinc Bromides
Published on: May 26, 2019
Related Concept Videos
Directing and Steric Effects in Disubstituted Benzene Derivatives
Reduction of Benzene to Cyclohexane: Catalytic Hydrogenation
Nucleophilic Aromatic Substitution: Elimination–Addition
meta-Directing Deactivators: –NO2, –CN, –CHO, –⁠CO2R, –COR, –CO2H
ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3
Regioselectivity and Stereochemistry of Hydroboration
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn...
