Different from the traditional role of Brønsted base, the amine/imine has been widely employed as Lewis base to activate the electrophilic allene, olefin, and carbonyl compounds during the past decades....
A computational study was contributed to explore the origin of stereoselectivity of NHC‐mediated cyclization reaction between benzoic acid and o‐phthalaldehyde for asymmetric construction of phthalidyl ester. The most energetically favorable pathway mainly includes the following steps: (1) nucleophilic attack on carbonyl carbon of o‐phthalaldehyde by catalyst NHC, (2) formation of Breslow intermediate, (3) oxidation by DQ, (4) asymmetric formation of dual C−O bonds, and (5) dissociation of catalyst with the product. The C−O bond formation was testified as the stereoselectivity‐determining step, the R‐configurational pathway is more energetically favorable than the S‐configurational one. The non‐covalent interaction (NCI) and atom‐in‐molecule (AIM) analyses were performed to reveal that the O−H ⋅⋅⋅ O and C−H ⋅⋅⋅ O hydrogen‐bond interactions are the key factors for controlling the stereoselectivity. The detailed mechanism and origin of stereoselectivity give useful insights for understanding organocatalytic reactions for asymmetric construction of C−O bond.
Generally, the bigger π bond order of conjugated olefins is corresponding to the shorter bond length. However, some π bond orders of naphthalene calculated by the Hückel molecular orbitals (HMO) method do not match the experimentally measured bond lengths, thus many students questioned the accuracy of the computed results using the HMO method. In this work, we employed ab initio Hartree-Fock (HF) method and suggested a revised HMO method with correction factor to recalculate and provide more reasonable π bond orders of naphthalene. By comparing the results calculated by the semi-empirical HMO and HF methods, this article can make the students understand origin of the computational error by using HMO method.
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