Mechanistic Insights into the DABCO-Catalyzed Cloke-Wilson Rearrangement: A DFT Perspective

Mechanism and Origin of Regioselectivity in the Phosphine-Catalyzed Heine Reaction

Herein, we present a comprehensive computational study of the reaction mechanism and regioselectivity patterns of the phosphine-catalyzed Heine reaction involving N-benzoylaziridines. Density functional theory (DFT) calculations reveal that the regioselectivity of the process takes place under kinetic control, favoring the formation of the corresponding 4-substituted oxazoline derivatives. Conformational analysis indicates that the predominantly populated ground-state conformation of aziridine does not represent the kinetically active species. Exploration of the conformational space in the transition state (TS) region shows that the preferred pathway for the nucleophilic ring-opening process involves a TS structure where the benzoyl moiety adopts a nearly coplanar arrangement. Furthermore, the main factors controlling the observed regioselectivity as well as the impact of substituents on the reactivity, are quantitatively rationalized using the activation strain model of reactivity in combination with energy decomposition analysis.

Mechanism and Origin of Stereoselectivity for the NHC-Catalyzed Desymmetrization Reaction for the Synthesis of Axially Chiral Biaryl Aldehydes

Organocatalytic desymmetrization reaction is a powerful tool for constructing axial chirality, but the theoretical study on the origin of stereoselectivity still lags behind even now. In this work, the N-heterocyclic carbene (NHC)-catalyzed desymmetrization reaction of biaryl frameworks for the synthesis of axially chiral aldehydes has been selected and theoretically investigated by using density functional theory (DFT). The fundamental pathway involves several steps, i.e., desymmetrization, formation of Breslow oxidation, esterification, and NHC regeneration. The desymmetrization and formation of Breslow processes have been identified as stereoselectivity-determining and rate-determining steps. Further weak interaction analyses proved that the C-H···O hydrogen bond and C-H···π interactions are responsible for the stability of the key stereoselective desymmetrization transition states. This research contributes to understanding the nature of NHC-catalyzed desymmetrization reactions for the synthesis of axially chiral compounds.