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Solid-phase Synthesis of [4.4] Spirocyclic Oximes
Published on: February 6, 2019
Unveiling Hydrogen Bonding and Solvent Effects on Directed Nitrile Oxide [3 + 2] Cycloaddition Reactions: Selectivity
Sofiane Benmetir1,2, Lakhdar Benhamed3, Noureddine Tchouar1
1Process and Environmental Engineering Laboratory (LIPE), Faculty of Chemistry, University of Science and Technology of Oran Mohamed BOUDIAF, P.O. Box 1503, El Mnaouer, 31000 Oran, Algeria.
Abstract:
The role of hydrogen bond and solvent effects on the regio- and diastereoselectivity of the [3 + 2] cycloaddition reaction (32CA) between 2,2-dimethylpropanenitrile oxide (NO) and N-(cyclopent-2-en-1-yl)benzamide has been theoretically studied at the B3LYP/6-311++G(d,p) level using the molecular electron density theory (MEDT). Solvent effects of dichloromethane (DCM) and benzene were taken into account. The electron localization function (ELF) classifies NO as a three-atom component with a zwitterionic electronic structure, which participates in zwitterionic-type 32CA reactions. The reactions occur through a one-step mechanism and present high activation Gibbs free energies in DCM and in benzene, with a slight difference favoring the reaction in benzene. Along the intrinsic reaction coordinate reaction pathway, the topological analysis of the ELF shows the asynchronous formation of the C-C bond prior to the C-O bond by coupling the two-carbon pseudoradical centers. The low global electron density transfer indicates that these reactions have a nonpolar character, which accounts for their high Gibbs free activation energies. Analysis of the noncovalent interactions associated with the TSs reveals a hydrogen bond in the favored TS, which confirms its participation in the experimental selectivities.
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