1,3-dipolar cycloadditions of cyclic nitrones with trisubstituted alkenes

A study of the regio- and stereo-chemical behaviour of the 1,3-dipolar cycloaddition of a series of trisubstituted alkenes with the cyclic nitrones 1-pyrroline 1-oxide (1) and 3,4,5,6-tetrahydropyridine 1-oxide (2) has been carried out. Regio- and stereo-selectivity in these cycloadditions have been explained in terms of maximum overlap of frontier orbitals, steric encumbrance, and secondary orbital interactions. The activation parameters and the effect of solvent on the rate constant for the addition reaction of a highly polarized alkene indicate the concerted nature of the reaction. The nitrone (2) is found to be more reactive than the nitrone (1) in all of these additions.