Preparation and DFT studies of chiral Cu (I)-complexes of biphenyl bisoxazolines and their application in enantioselective Kharasch–Sosnovsky reaction

Abstract

Effect of a range of t-butyl perbenzoates bearing electron-withdrawing and electron-donating substitutions on the phenyl ring and HZSM-5 as a porous additive at 0 °C in enantioselective allylic C–H bond oxidation of cyclic and acyclic olefins in the presence of Cu (I)-(S,aS,S) complexes of biphenyl bisoxazoline ligands, produced easily through the chelation-induced process, were investigated. The enantioenriched allylic esters were obtained in reasonable times with excellent enantioselectivities and yields using electron-withdrawing substituted peresters in the presence of Cu (I)-(S,aS,S)-1a complex, containing phenyl groups at the stereogenic centers of the oxazoline moieties. To reach a better insight on geometry, chemical activity, enantioselectivity, and thermodynamic stability of the Cu (I)-BOX complexes, DFT calculations with B3LYP-D3/6-31G (d, p) level of theory were applied to them. Moreover, NBO analysis was used to illustrate interactions between orbitals.

Chiral Pseudohomogeneous Catalyst Based on Amphiphilic Carbon Quantum Dots for the Enantioselective Kharasch–Sosnovsky Reaction

“…Also, the results indicated that reducing the reaction temperature resulted in a decrease in the reaction rate and a slight increase of the enantiomeric excess; however, yield and enantioselectivity were aligned at room temperature (Table , entries 9 vs. 25–29). The absolute configuration of the product was assigned based on the evaluation of the optical rotations with the literature report. − …”

“…The obtained results confirmed that cyclohexene had a number of merits such as good yield, enantiomeric excess, and short reaction time (Table ). Acyclic alkenes like 1-octene and 1-hexene caused the reaction to proceed with low enantioselectivities up to 10% and low yields up to 26%. ,, According to the importance of the ability to recycle and reuse heterogeneous catalysts, the reactivity of the PHC catalyst after recyclization was investigated. For this purpose, after performing the reaction and extraction of the product, the catalyst was filtered and washed with ethyl acetate and dichloromethane, and the resulting precipitate was dried at 50 °C and used in the optimal reaction again.…”

“…Thereafter, through a pericyclic rearrangement of the resulting allyl-copper­(III) intermediate, including a stereospecific reductive-elimination and migration of the π-bond, the carboxyl group attacks the Si -face of cyclohexnyl (as shown in Scheme ), and a product–catalyst complex can be formed. Finally, by releasing the enantioenriched allylic ester as the final product through exchanging it with cyclohexene, the initial cyclohexene–catalyst complex is regenerated. , …”

“…After that, for extraction of the product, 5 mL of NH 4 OH (10%) was added to the mixture, and the solution was extracted with EtOAc (5 mL × 3). After evaporation of the solvent, a yellow residue was obtained and purified by column chromatography on silica gel, affording the product ( S )-2-cyclohexenyl- p -nitrobenzoate as a white solid. − …”

“…After evaporation of the solvent, a yellow residue was obtained and purified by column chromatography on silica gel, affording the product (S)-2-cyclohexenyl-p-nitrobenzoate as a white solid. 26…”