DFT Study On The Mechanisms Of Several Asymmetric Cyclized Reactions Catalyzed By Transition Metal

In present paper, the density functional method (B3LYP) is employed to study the asymmetric annular-addition of methylenecyclopropanes (MCPs) with 1,3-dicarbonyl compounds radical, and the cyclization mechanisms of allylic alkynoates and carbamates catalyzed by PdCl₂, respectively. The main transition states of these reactions are found out. The mechanisms of these asymmetric cyclized reactions are discussed in detail.1. DFT Study of Annular-addition of MCPs with 1,3-Dicarbonyl radicalThe density functional theory is employed to study the mechanism of the annular-addition of methylenecyclopropanes (MCPs) with 1,3-dicarbonyl radical. All the predicted structures appeared on the potential energy profile were optimized completely at the B3LYP/6-311G(d,p) level. The calculations suggested that the annularaddition is endothermic, and it goes mainly through the following steps: the attacking of the dicarbonyl radical on the MCPs, the forming of the chiral radical complexes, the oxidation of radical complexes into the chiral carbon cations, and the forming of annulation oxygen cations and so on. The chirality-determining step is the formation of the chiral radical complex which is also the rate-determining step. The dominant products predicted theoretically are furan-ring derivates, which are in agreement with the experimental observations.2. Theoretical Study on the Cyclization of Allylic Alkynoates Catalyzed by PdCl₂The mechanism of cyclization of allylic alkynoates catalyzed by PdCl₂ was studiedby means of density functional theory. The geometries were optimized using the B3LYP functional with the 6-311G^** basis sets. According to the calculated results, it was found that the P-heteroatom and P-hydrogen elimination reactions are competitive each other. As shown, the cyclization reaction is exothermic, and it mainly undergoes the halopalladation of alkyne, the formation of the palladium-vinyl intermediate by the intermolecular olefin insertion, and the breaking of the carbon-palladium bond due to the P-heteroatom elimination. The predicted chirality-determining step is the intermolecular olefin insertion, but the rate-controlling step is the P-heteroatom elimination. Our rerults suggested that the (Z, R)-α-methylene-γ-butyrolactone derivative was the dominant products, which confirmed the experimental conclusions.3. DFT Study on the asymmetric cyclization of carbamate Catalyzed by PdCl₂In this section, the mechanism of asymmetric cyclization of carbamate catalyzed by PdCl₂ was investigated using the theoretical calculations. All the studied geometries were optimized basing on the B3LYP functional method. To evaluate the solvent effect, the single-point computations were performed for these optimized structures at the same level by using Polarizable Continuum Model in CH₃OH. The results suggested that the cyclization reaction is exothermic and the insertion of olefin is the chirality-determining step as well as the rate-controlling step. It is predicted that the mechanism of asymmetric cyclization for carbamate is similar to that of cyclization for allylic alkynoates. The predicted product is trans-oxazolidinone derivative, and the conclusion is reasonable.