Regioselectivity of 1,3-Dipolar Cycloadditions of Benzonitrile Oxide to Alkenyl Boronic Esters: An Experimental and Computational Study.

of benzonitrile oxide to monosubstituted or 1,1-disubstituted alkenyl boronic ester gave only 2-isoxazolines, bearing the boronic ester group at the 5-position of the ring. On the other hand, the of benzonitrile oxide with trans-1,2-disubstituted alkenyl boronic esters produced 2-isoxazolines, bearing the boronic ester group at the 4-position of the ring. We used quantum mechanical calculations to investigate two regioisomeric channels that were associated with the formation of 2-isoxazolines, bearing the boronic ester group at the 4-position or 5-position. The study revealed that the experimental results agreed well with the parameters based on the transition state energies in gas or solvent phase. The study also informed that all the proceed in a spontaneous and exergonic fashion. [ABSTRACT FROM AUTHOR]