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

Abstract

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.

On the Mechanism of Gold(I)‐Catalyzed Ring Expansion of Cyclopropanols: Theoretical Calculations Uncover a Bottle‐Neck 1,4‐H Shift and Suggest Adequate Reaction Conditions

“…Theoretical calculations have already made it possible to suggest that solvent-assisted hydrogen migration might be crucial for the addition of an alcohol to an Au I activated C-C triple bond [22] and very recently have revealed the important role played by water in the catalysis of a 1,2-H shift in the Nazarov reaction. [23] Figure 2 and Table S2 (Supporting Information) present the results corresponding to the assisted mechanism a. The second reactant molecule coordinates to the gold(I) activated one through an OH(assisting cyclopropanol)··· O(activated cyclopropanol) interaction to form initial complex RC-me-a, which becomes a transient structure (0.8 kcal/mol) when taking into account solvent effects.…”

“…[21][22][23] The aim of the present work is to learn about the two mechanistic proposals for the [AuP(Ph) 3 ] + -catalyzed one carbon ring-expansion reaction of 1-(1-alkynyl)cyclopropanols through nucleophilic attack of a σ bond to the C-C triple bond activated by Au I and to understand the role played by substituents in these processes. To this end, we present a theoretical analysis of mechanisms a and b for the [AuP(Ph) 3 ] + -catalyzed ring-expansion reaction of 1-(1-propynyl)cyclopropanol to yield (E)-2-ethylylidenecyclobutanone, and a theoretical study of the different possible rearrangements of 3 and 4 along mechanism a.…”

Mechanistic insight into water-modulated cycloisomerization of enynyl esters using an Au(i) catalyst

“…2, the conversion from IM10 to B relates to the migration of the hydroxyl H atom to the terminal C1 atom of the C1vC2 moiety, but direct migration is kinetically unachievable (IM10→IM11 in Scheme 3). Previous theoretical studies [62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77] disclosed that reactant or intermediate molecules could sometimes play a key role in lowering the activation barrier. Encouraged by this hint, we proposed a new pathway in which two IM10 molecules concertedly undergo hydrogen migration.…”

Theoretical Elucidation of Au(I)-Catalyzed Cycloisomerizations of Cycloalkyl-substituted 1,5-Enynes: 1,2-alkyl Shift versus C−H Bond Insertion Products

“…However, this intermediate results in a "dead-end" path, which can not carry out the expected transformation, as indicated in previous reports. 34 -37 In other words, cycloisomer- ization reactions of Au-catalyzed enynes can be only elucidated by activating the alkyne group, 38,39 although the Au-alkene complexes might be in equilibrium with the Au-alkyne ones. In addition, it is not geometrically possible that the Au(I) catalyst, which is isolobal to the hydrogen ion, [40][41][42][43][44][45] coordinates with the alkene and the alkyne simultaneously.…”