A DFT Study of N-Heterocyclic Carbene Catalyzed [4+2] Annulation between Saturated Carboxylate withortho-Quinone Methide: Possible Mechanisms and Origin of Enantioselectivity

Chiral phosphoric acid catalyzed asymmetric arylation of indolesvianucleophilic aromatic substitution: mechanisms and origin of enantioselectivity

Asymmetric arylation of indolesvianucleophilic aromatic substitution can be effectively achieved using chiral phosphoric acid as catalyst, where the mechanisms and origin of enantioselectivity were explored theoretically.

A theoretical review for novel Lewis base amine/imine-catalyzed reactions

Recent advances in computational investigations of Lewis base amine/imine-catalyzed reactions have been systematically summarized and reviewed for the first time.

Gold(I)-Mediated Cycloisomerization/Cycloaddition Enables Bioinspired Syntheses of Neonectrolides B-E and Analogues

Development of a synthetic route to the oxaphenalenone (OP) natural products neonectrolides B-E is described. The synthesis relies on gold-catalyzed 6-endo-dig hydroarylation of an unusual enynol substrate as well as a one-pot Rieche formylation/cyclization/deprotection sequence to efficiently construct the tricyclic oxaphenalenone framework in the form of a masked ortho-quinone methide (o-QM). A tandem cycloisomerization/[4 + 2] cycloaddition strategy was employed to quickly construct molecules resembling the neonectrolides. The tricyclic OP natural product SF226 could be converted to corymbiferan lactone E and a related masked o-QM. Our study culminates with the application of the tandem reaction sequence to syntheses of neonectrolides B-E as well as previously unreported exo-diastereomers.

Mechanistic insights and origin of chemoselectivity for S–O bond cleavage in dinitrobenzenesulfonic carbamates

A computational study on the NHC-catalyzed chemoselective S–O bond cleavage in dinitrobenzenesulfonic carbamates.

Why electrostatically enhanced thiourea is better than Schreiner's thiourea in both catalytic activity and regioselectivity?

Electrostatically enhanced thiourea is more active and efficient than Schreiner's thiourea in the ring-opening aminolysis of styrene oxide with aniline, and the underlying reasons were explored by DFT calculations.

Insights into the N-Heterocyclic Carbene (NHC)-Catalyzed Intramolecular Cyclization of Aldimines: General Mechanism and Role of Catalyst

One of the most challenging questions in the Lewis base organocatalyst field is how to predict the most electrophilic carbon for the complexation of N-heterocyclic carbene (NHC) and reactant. This study provides a valuable case for this issue. Multiple mechanisms (A, B, C, D, and E) for the intramolecular cyclization of aldimine catalyzed by NHC were investigated by using density functional theory (DFT). The computed results reveal that the NHC energetically prefers attacking the iminyl carbon (AIC mode, which is associated with mechanisms A and C) rather than attacking the olefin carbon (AOC mode, which is associated with mechanisms B and D) or attacking the carbonyl carbon (ACC mode, which is associated with mechanism E) of aldimine. The calculated results based on the different reaction models indicate that mechanism A (AIC mode), which is associated with the formation of the aza-Breslow intermediate, is the most favorable pathway. For mechanism A, there are five steps: (1) nucleophilic addition of NHC to the iminyl carbon of aldimine; (2) [1,2]-proton transfer to form an aza-Breslow intermediate; (3) intramolecular cyclization; (4) the other [1,2]-proton transfer; and (5) regeneration of NHC. The analyses of reactivity indexes have been applied to explain the chemoselectivity, and the general principles regarding the possible mechanisms would be useful for the rational design of NHC-catalyzed chemoselective reactions.

Origins of halogen effects in bioorthogonal sydnone cycloadditions

Halogen substituents increase sydnone cycloaddition reactivities substantially. Fluoro-sydnones are superior to bromo- and chloro-sydnones, and can achieve extremely high second-order rate constants with strained alkynes. Computational studies have revealed the fluorine substituent increases the reactivity of sydnone mainly by lowering its distortion energy.

Insights into the isothiourea-catalyzed asymmetric [4 + 2] annulation of phenylacetic acid with alkylidene pyrazolone

A computational study on the isothiourea-catalyzed asymmetric [4 + 2] annulation of phenylacetic acid with alkylidene pyrazolone was performed using the DFT method.

Insights into N-heterocyclic carbene-catalyzed [3 + 4] annulation reactions of 2-bromoenals with N-Ts hydrazones

A DFT study toward N-heterocyclic carbene-catalyzed [3 + 4] annulation reactions of 2-bromoenals has been performed for the first time.

Chiral bisoxazoline catalyzed decarboxylative aldol reactions between β-carbonyl acids and trifluoroacetaldehyde hemiacetals as well as trifluoroacetaldehyde: the mechanism, the origin of enantioselectivity and the role of a catalyst

The role of a catalyst in the decarboxylative aldol reactions between β-carbonyl acids and trifluoroacetaldehyde hemiacetals as well as trifluoroacetaldehyde catalyzed by chiral bisoxazoline were unveiled theoretically.