Asymmetric Cyanation of Activated Olefins with Ethyl Cyanoformate Catalyzed by Ti(IV)-Catalyst: A Theoretical Study

• Main Authors: Zhishan Su, Changwei Hu, Nasir Shahzad, Chan Kyung Kim
• Format: Article
• Language: English
• Published: MDPI AG 2020-09-01
• Series: Catalysts
• Subjects: asymmetric conjugate addition; cinchona alkaloid catalysis; cyanation reaction of olefin; self-assembly Ti(IV)-catalysis; density functional theory calculation
• Online Access: https://www.mdpi.com/2073-4344/10/9/1079

The reaction mechanism and origin of asymmetric induction for conjugate addition of cyanide to the C=C bond of olefin were investigated at the B3LYP-D3(BJ)/6-31+G**//B3LYP-D3(BJ)/6-31G**(SMD, toluene) theoretical level. The release of HCN from the reaction of ethyl cyanoformate (CNCOOEt) and isopropanol (HOiPr) was catalyzed by cinchona alkaloid catalyst. The cyanation reaction of olefin proceeded through a two-step mechanism, in which the C-C bond construction was followed by H-transfer to generate a cyanide adduct. For non-catalytic reaction, the activation barrier for the rate-determining C-H bond construction step was 34.2 kcal mol⁻¹, via a four-membered transition state. The self-assembly Ti(IV)-catalyst from tetraisopropyl titanate, (<i>R</i>)-3,3′-disubstituted biphenol, and cinchonidine accelerated the addition of cyanide to the C=C double bond by a dual activation process, in which titanium cation acted as a Lewis acid to activate the olefin and HNC was orientated by hydrogen bonding. The steric repulsion between the 9-phenanthryl at the 3,3′-position in the biphenol ligand and the Ph group in olefin raised the Pauli energy (Δ<i>E</i>^≠_Pauli) of reacting fragments at the <i>re</i>-face attack transition state, leading to the predominant <i>R</i>-product.