The reactivities of some cyclic nitrones in 1,3-dipolar cycloaddition reactions

Abstract

Rate constants for the cycloaddition of 1-pyrroline 1-oxide, (1), 3,4,5,6-tetrahydropyridine 1-oxide (2), and 3-oxo-3,4,5,6-tetrahydropyridine 1-oxide (3) to methyl acrylate, ethyl vinyl ether, and hex-1-ene have been determined at different temperatures by ¹H n.m.r. spectroscopy. The activation parameters and solvent effect on rate constant indicate the concerted nature of the reaction. Strain energy in the transition state plays an important role in the addition reactions of these cyclic nitrones. It is found that (2) is the most reactive among these cyclic nitrones. Methyl acrylate and ethyl vinyl ether are found to react faster than hex-1-ene. The presence of a protic solvent minimizes the dimerization of nitrone (2).