DFT investigation of the DDQ-catalytic mechanism for constructing C-O bonds.

In this study, we investigated the photo-catalytic mechanisms for the construction of C-O bonds from arenes (benzene, 2',6'-dimethyl-[1,1'-biphenyl]-2-carboxylic acid, or 2,4-dichloro-1-fluorobenzene), catalyzed by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ). All the structures for the Gibbs free surfaces were calculated at the M06-2X-D3/ma-def2-SVP level in the SMD solvent model. Also, TDDFT calculations of DDQ were performed at the PBE1PBE-D3/ma-def2-SVP level in the SMD solvent model. The computational results indicated that DDQ, serving as a photo-catalyst, would be excited under visible light of 450 nm, aligning well with experimental observations as reflected in the UV-vis spectrum. Gibbs free energy surface analyses of the three reactions suggested that the path involving 3DDQ* activating the reactant (-COOH, H2O, or CH3OH) is favorable. Additionally, the role of O2 was investigated, revealing that it could facilitate the recycling of DDQ by lowering the energy barrier for the conversion of the DDQH˙ radical (not DDQH2) into DDQ. The use of ρhole and ρele can reveal the photo-catalytic reaction and charge transfer processes, while localized orbital locator isosurfaces and electron spin density isosurface graphs were employed to analyze structures and elucidate the single electron distribution. These computational results offer valuable insights into the studied interactions and related processes, shedding light on the mechanisms governing C-O bond formation from arenes catalyzed by DDQ.

Mechanistic Study of 1,4-Benzodiazepine-2,5-diones from Diphenylamine and Diethyl 2-Phenylmalonate by Density Functional Theory.

The mechanisms for the reaction between diphenylamine and diethyl 2-phenylmalonate were investigated using M06-2X-D3/6-31+G(d,p) method and level, and the SMD model was applied to simulate the solvent effect. The computational results suggested that diphenylamine and diethyl 2-phenylmalonate can convert into 4-hydroxy-1,3-diphenylquinolin-2(1H)-one via a series of reactions (addition reaction, dealcoholization reaction, enolization reaction, dealcoholization reaction, ring-closure reaction, and H-shift reaction). And H2O, as the catalyst, can play an important role to promote these reactions. In the following reaction, there are two paths to yield the second product 3-chloro-1,3-diphenylquinoline-2,4(1H,3H)-dione and the computational results indicated that the first path (blue line) with the rate-determining step of 24.9 kcal/mol is favorable. With the participation of methanamine, a SN2 reaction happened and the third product 3-(methylamino)-1,3-diphenylquinoline-2,4(1H,3H)-dione had been yielded in the effect of methanamine or Cl anion. The analysis of Gibbs free energy surfaces shows that methanamine is better than Cl anion to extract the proton via an exothermic reaction. Finally, the third product 3-(methylamino)-1,3-diphenylquinoline-2,4(1H,3H)-dione would go through a ring-enlargement reaction, promoted by base (TMG or Triton B), to yield the final product. The computational results demonstrated that this reaction can release much energy with Triton B than that with TMG. And the energy of the highest point is 10.1 kcal/mol (16.8 kcal/mol), which can readily occur at the room temperature. The results could provide valuable insights into these types of interactions and related ones.

CuH-Catalyzed Asymmetric 1,6-Conjugate Reduction of p-Quinone Methides: Enantioselective Synthesis of Triarylmethanes and 1,1,2-Triarylethanes.

The first copper hydride (CuH)-catalyzed asymmetric 1,6-conjugate reduction of p-quinone methides is reported. This protocol provides a new method to access a variety of triarylmethanes and 1,1,2-triarylethanes in good yields with excellent enantioselectivities and broad functional group tolerance.

Linear σ-hole⋯CO⋯σ-hole intermolecular interactions between carbon monoxide and dihalogen molecules XY (X, Y=Cl, Br).

Carbon monoxide can interact with two dihalogen molecules XY (X, Y=Cl, Br) in the form of X(Y)⋯COX(Y)⋯CO⋯X(Y)X(Y) trimeric complex, and their nature and characteristics were investigated at MP2/aug-cc-pVDZ level without and with counterpoise method, together with single point calculations at CCSD(T)/aug-cc-pVDZ level. The optimized geometries, stretching modes and interaction energies of a series of X(Y)⋯COX(Y)⋯CO⋯X(Y)X(Y) trimeric complexes were obtained and discussed. The cooperativity in these complexes was evaluated. EDA analyses reveal that the electrostatic interaction is the dominant net driving force in each trimer, but the contributions of other interactions like exchange, dispersion and polarization interactions are also important. QTAIM and NCI analyses confirm the existence of attractive halogen-bonding interactions. Additionally, EDDMF analysis was employed for the component dimers of these trimers, which indicates that the formation of halogen-bonding interactions is closely related to the charge shift and the rearrangement of electronic density in the formation of these complexes. The results would provide valuable insight into for these linear halogen bonds.

Insights into the Diels-Alder Reaction between 3-Vinylindoles and Methyleneindolinone without and with the Assistance of Hydrogen-Bonding Catalyst Bisthiourea: Mechanism, Origin of Stereoselectivity, and Role of Catalyst.

The Diels-Alder reaction between 3-vinylindoles and methyleneindolinone can proceed both under catalyst-free conditions and with bisthiourea as the catalyst. The reaction with bisthiourea is much faster and results in higher stereoselectivity of the product. The reaction mechanism, origin of stereoselectivity, and role of the catalyst were elaborated based on quantum mechanical calculations and theoretical methods of reactivity indices, NCI, QTAIM, and distortion/interaction models. In the uncatalyzed reaction, the two C-C bonds that are formed undergo conversion from noncovalent to covalent bonding via a concerted asynchronous mechanism. The weak intermolecular interactions formed in the transition state play important roles. The difference between the interaction and distortion energies is responsible for the stereoselectivity. In the catalyzed reaction, bisthiourea induces both the diene and dienophile to approach it via weak intermolecular interactions, which greatly lowers the energy barrier of the reaction and leads to the product with excellent stereoselectivity. The possible pathways of this reaction were explored, which suggested that the formation of the two C-C bonds goes through either a stepwise or concerted asynchronous mechanism. These results detail the reaction mechanism and shed light on both the significant role of the bisthiourea catalyst and the origin of stereoselectivity for this type of Diels-Alder reaction and related ones.

Preparation of α-Acyloxy Ketones via Visible-Light-Driven Aerobic Oxo-Acyloxylation of Olefins with Carboxylic Acids.

We developed a visible-light driven oxo-acyloxylation of aryl alkenes with carboxylic acids and molecular oxygen. A metal-free photoredox system, consisting of an acridinium photocatalyst, an organic base, and molecular sieve (MS) 4 Å, promotes chemoselective aerobic photooxidation of aryl alkenes. This approach may provide a green, practical, and metal-free protocol for a wide range of α-acyloxy ketones.