Density functional theory study on the mechanism of Rh-catalyzed decarboxylative conjugate addition: diffusion- and ligand-controlled selectivity toward hydrolysis or ß-hydride elimination.

The mechanism of Rh-catalyzed decarboxylative conjugate addition has been investigated with Density Functional Theory (DFT). Calculations indicate that the selectivity toward hydrolysis or ß-hydride elimination of the investigated reaction is a compromise between diffusion control and kinetic control. Ligand control can be adjusted by modifying the intermolecular interaction between the Rh(I) enolate intermediate and water.

N-heterocyclic carbene-catalyzed cross-coupling of aldehydes with arylsulfonyl indoles.

3-(1-Arylsulfonylalkyl)indoles as electrophiles in the N-heterocyclic carbene-catalyzed umpolung reaction of aldehydes were realized for the first time. This intermolecular Stetter-type reaction features the commercially available catalyst and mild reaction conditions, providing alpha-(3-indolyl) ketone derivatives in high yields for a wide range of substrates.

Origins of enantioselectivity in the chiral Brønsted acid catalyzed hydrophosphonylation of imines.

The results of an experimental and ONIOM-based computational investigation of the mechanism and the origins of enantioselectivity in the asymmetric synthesis of alpha-amino phosphonates by an enantioselective hydrophosphonylation of imines catalyzed by chiral Brønsted acids are reported. It was found that the enantioselectivity observed in the enantioselective hydrophosphonylation of the imine with a benzothiazole moiety was poor. A detailed computational study with a two-layer ONIOM (B3LYP/6-31G(d)/AM1) method on the mechanism of the investigated reaction was carried out to explore the origins of the enantioselectivity. Calculations indicate that the investigated reaction is a two-step process involving proton-transfer and nucleophilic addition, which is the stereo-controlling step. The investigated reaction prefers a di-coordination pathway to a mono-coordination pathway. The different enantioselectivities exhibited by three kinds of catalyst and two kinds of nucleophile were rationalized. Calculations indicate that si-facial attack is higher in energy than re-facial attack by only 0.1 kcal/mol, which accounts well for the low ee value observed in the enantioselective hydrophosphonylation of the imine with a benzothiazole moiety. The energy barrier for phosphonate-phosphite tautomerism catalyzed by chiral Brønsted acid in toluene is only 1.8 kcal/mol, which could explain why the investigated reaction can take place at room temperature.

DFT study of the mechanisms of in water Au(I)-catalyzed tandem [3,3]-rearrangement/Nazarov reaction/[1,2]-hydrogen shift of enynyl acetates: a proton-transport catalysis strategy in the water-catalyzed [1,2]-hydrogen shift.

A computational study with the Becke3LYP density functional was carried out to elucidate the mechanisms of Au(I)-catalyzed reactions of enynyl acetates involving tandem [3,3]-rearrangement, Nazarov reaction, and [1,2]-hydrogen shift. Calculations indicate that the [3,3]-rearrangement is a two-step process with activation free energies below 10 kcal/mol for both steps. The following Nazarov-type 4pi electrocyclic ring-closure reaction of a Au-containing dienyl cation is also easy with an activation free energy of 3.2 kcal/mol in CH2Cl2. The final step in the catalytic cycle is a [1,2]-hydride shift, and this step is the rate-limiting step (with a computed activation free energy of 20.2 kcal/mol) when dry CH2Cl2 is used as the solvent. When this tandem reaction was conducted in wet CH2Cl2, the [1,2]-hydride shift step in dry solution turned to a very efficient water-catalyzed [1,2]-hydrogen shift mechanism with an activation free energy of 16.4 kcal/mol. Because of this, the tandem reaction of enynyl acetates was found to be faster in wet CH2Cl2 as compared to the reaction in dry CH2Cl2. Calculations show that a water-catalyzed [1,2]-hydrogen shift adopts a proton-transport catalysis strategy, in which the acetoxy group in the substrate is critical because it acts as either a proton acceptor when one water molecule is involved in catalysis or a proton-relay stabilizer when a water cluster is involved in catalysis. Water is found to act as a proton shuttle in the proton-transport catalysis strategy. Theoretical discovery of the role of the acetoxy group in the water-catalyzed [1,2]-hydrogen shift process suggests that a transition metal-catalyzed reaction involving a similar hydrogen shift step can be accelerated in water or on water with only a marginal effect, unless a proton-accepting group such as an acetoxy group, which can form a hydrogen bond network with water, is present around this reaction's active site.