Regio‐, stereo‐, and site‐selectivities of 1,3‐dipolar Cycloaddition reaction of benzonitrile oxide with unsymmetrically substituted norbornenes and norbornadienes: A computational study

Abstract

AbstractIn this computational study, density functional theory (DFT) calculations at the M06/6‐311G(d,p) level of theory were employed to study the regio‐, stereo‐, and site‐selectivities of 1,3‐dipolar cycloadditions of benzonitrile oxide (BNO) with unsymmetrically substituted norbornenes and norbornadienes. The reactions between BNO and unsymmetrically‐substituted 2‐norbornes and unsymmetrically‐substituted 2‐norbornadienes proceed with the oxygen of the BNO attacking the more hindered side of the double bond in all cases except when strong EWGs are introduced. For the reaction between BNO and unsymmetrically‐substituted 2‐norbornadienes, varying degrees of selectivities are observed depending on the substituent, indicating that site‐selectivity is largely influenced by nature of substituents. Generally, the regio‐isomers in which the oxygen of the BNO is bonded to the more hindered side of the double bond are favored except when strong EWGs are introduced, and exo stereo‐isomers are generally favored over the endo stereo‐isomers. Electrophilic (Pk+) and nucleophilic (Pk‐) Parr functions computations are in complete agreement with the selectivity predicted by the activation barrier trends.