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A new catalytic cycle involving only soluble proline complexes or adducts is proposed for the reactions in eq 1 based on kinetic observations and molecular modeling studies. This reaction pathway circumventing free proline and incorporating hydrogen-bonded reaction product helps to rationalize the observations of accelerating reaction rate in both the alpha-aminooxylation and alpha-amination reactions.

Under aprotic conditions, the stoichiometric reaction of N‐heterocyclic carbenes (NHCs) such as imidazolidin‐2‐ylidenes with aldehydes affords Breslow Intermediates (BIs), involving a formal 1,2‐C‐to‐O proton shift. We herein report kinetic studies (NMR), complemented by DFT calculations, on the mechanism of this kinetically disfavored H‐translocation. Variable time normalization analysis (VTNA) revealed that the kinetic orders of the reactants vary for different NHC‐to‐aldehyde ratios, indicating different and ratio‐dependent mechanistic regimes. We propose that for high NHC‐to‐aldehyde ratios, the H‐shift takes place in the primary, zwitterionic NHC‐aldehyde adduct. With excess aldehyde, the zwitterion is in equilibrium with a hemiacetal, in which the H‐shift occurs. In both regimes, the critical H‐shift is auto‐catalyzed by the BI. Kinetic isotope effects observed for R‐CDO are in line with our proposal. Furthermore, we detected an H‐bonded complex of the BI with excess NHC (NMR). [ABSTRACT FROM AUTHOR]

Kinetic study of organic reactions, especially multistep catalytic reactions, is crucial to in-depth understanding of reaction mechanisms. Here we report our kinetic study on the chiral disulfonimide-catalyzed cyanosilylation of an aldehyde, which revealed that two molecules of TMSCN are involved in the rate-determining C–C bond-forming step. In addition, the apparent activation energy, enthalpy of activation, and entropy of activation were deduced through a study of the temperature dependence of the reaction rates. More importantly, a novel and efficient method that makes use of the progress rates was developed to treat kinetic data obtained by continuous monitoring of the progress of a reaction by in situ FTIR. [ABSTRACT FROM AUTHOR]

Common and non‐toxic aldehydes are proposed as reagents for alkylation of ketones instead of carcinogenic alkyl halides. The developed reductive alkylation reaction proceeds in the presence of the commercially available ruthenium catalyst [(cymene)RuCl2]2 (as low as 250 ppm) and carbon monoxide as the reducing agent. The reaction works well for a broad substrate scope, including aromatic and aliphatic aldehydes and ketones. It can be carried out without a solvent and often gives nearly quantitative yields of the products. This straightforward and cost‐effective method is promising not only for laboratory application but also for industry, which produces carbon monoxide as a large‐scale waste product. [ABSTRACT FROM AUTHOR]

Keywords: Autocatalysis; Breslow Intermediate; Carbenes; NMR; Reaction Mechanisms EN Autocatalysis Breslow Intermediate Carbenes NMR Reaction Mechanisms 1 1 1 06/01/22 20220607 NES 220607 B Breslow intermediates b (BIs) are pivotal species in Umpolung catalysis effected by N-heterocyclic carbenes (NHCs). Inside Back Cover: Formation of Breslow Intermediates from N-Heterocyclic Carbenes and Aldehydes Involves Autocatalysis by the Breslow Intermediate, and a Hemiacetal (Angew. Autocatalysis, Breslow Intermediate, Carbenes, NMR, Reaction Mechanisms. [Extracted from the article]