Steric interactions controlling the syn diastereofacial selectivity in the [3 + 2] cycloaddition reaction between acetonitrile oxide and 7‐oxanorborn‐5‐en‐2‐ones: A molecular electron density theory study

• Published in: Journal of physical organic chemistry 2017-12, Vol.30 (12), p.e3710-n/a
• Main Authors: Adjieufack, A. I., Ndassa, I.M., Ketcha Mbadcam, J., Ríos‐Gutiérrez, M., Domingo, L.R.
• Format: Article
• Language: English
• Subjects: Acetonitrile; Activation energy; Carbonyl groups; Carbonyls; Cycloaddition; Electron density; Regioselectivity; Selectivity; Steric hindrance
• ISSN: 0894-3230; 1099-1395
• DOI: 10.1002/poc.3710

A Molecular Electron Density Theory study of the zw‐type 32CA reactions of acetonitrile oxide (NO) with two 7‐oxanorborn‐5‐en‐2‐ones (ONBs) has been performed at the DFT B3LYP/6‐31G(d) computational level. These cycloadditions proceed through one‐step mechanisms with high activation energies and present low para regio and complete syn diastereofacial selectivities. While the non‐polar character of these zw‐type 32CA reactions, which is the consequence of the insufficient electrophilic activation of ONBs, according to the analysis of the conceptual DFT reactivity indices, accounts for the high activation energies, and low para regioselectivity, NCI topological analyses at the anti/syn pairs of para TSs reveal that the steric hindrance encountered between the NO framework and the ONB side containing the carbonyl group along the anti approach mode is responsible for the complete syn diastereofacial selectivity. The zw‐type [3 + 2] cycloaddition reactions between acetonitrile oxide and 7‐oxanorborn‐5‐en‐2‐ones present low para regio and complete syn diastereofacial selectivities. The nonpolar character of these zw‐type [3 + 2] cycloaddition reactions accounts for the high activation energies and low para regioselectivity, while the steric hindrance found along the anti approach mode is responsible for the complete syn diastereofacial selectivity.