Methanol-Assisted Phthalimide Ring Opening: Concerted or Stepwise Mechanism?

Mechanism and Origin of Stereoselectivity of N-Heterocyclic Carbene (NHC)-Catalyzed Transformation Reaction of Benzaldehyde with o-QDM as Key Intermediate: A DFT Study

N-heterocyclic carbene (NHC)-bound ortho-quinodimethane, served as a nucleophile, has occupied an important position for constructing various all-carbon or heterocyclic compounds and attracted increasing attention for the functionalization of benzylic carbon of aromatic aldehydes, whereas the mechanistic studies on the generation and transformations of dienolate intermediate are rare. In the present study, the mechanism of activation/transformation of aldehyde catalyzed by NHC was theoretically studied using the density functional theory (DFT) method. Based on the calculations, the nucleophilic addition process is the stereoselectivity-determining step with RS-configured product being generated preferentially. Furthermore, non-covalent index (NCI) and atoms-in-molecules (AIM) analyses have been performed to disclose the origin of stereoselectivity, by which the larger number and stronger weak interactions are the key for stabilizing the low-energy transition state and thus leading to the stereoselectivity inducing.

Mapping Catalyst–Solvent Interplay in Competing Carboamination/Cyclopropanation Reactions

Group 9 metals, in particular Rh^III complexes with cyclopentadienyl ligands, are competent C−H activation catalysts. Recently, a Cp*Rh^III‐catalyzed reaction of alkenes with N‐enoxyphthalimides showed divergent outcome based on the solvent, with carboamination favored in methanol and cyclopropanation in 2,2,2‐trifluoroethanol (TFE). Here, we create selectivity and activity maps capable of unravelling the catalyst‐solvent interplay on the outcome of these competing reactions by analyzing 42 cyclopentadienyl metal catalysts, Cp^XM^III (M=Co, Rh, Ir). These maps not only can be used to rationalize previously reported experimental results, but also capably predict the behavior of untested catalyst/solvent combinations as well as aid in identifying experimental protocols that simultaneously optimize both catalytic activity and selectivity (solutions in the Pareto front). In this regard, we demonstrate how and why the experimentally employed Cp*Rh^III catalyst represents an ideal choice to invoke a solvent‐induced change in reactivity. Additionally, the maps reveal the degree to which even perceived minor changes in the solvent (e. g., replacing methanol with ethanol) influence the ratio of carboamination and cyclopropanation products. Overall, the selectivity and activity maps presented here provide a generalizable tool to create global pictures of anticipated reaction outcome that can be used to develop new experimental protocols spanning metal, ligand, and solvent space.