1,3-Dipolar Cycloaddition of Nitrones with Nitriles. Scope and Mechanistic Study

Article abstract of DOI:10.1016/S0040-4020(01)89838-0

1,3-Dipolar cycloadditions of nitrones 1-6 with nitriles 14-16, proceeded under thermal as well as under high pressure conditions with complete regioselectivity to give Δ⁴-1,2,4-oxadiazolines 17-19.In general, the cycloaddition seemed to be controlled by a HOMO(nitrone)- LUMO(nitrile) interaction.However, a crossover in the orbital control is probable observed with nitrile 16c.Nitrone-nitrile cycloadditions are normal type II cycloadditions so that the nitriles have a U-shaped reactivity curve.Kinetic study on solvent polarity and Hammett equation demonstrated that mechanistically the nitrone-nitrile cycloaddition is consistent with nitrone-alkene cycloaddition.