Kinetics of the reaction of 1-p-tosylazocyclohexene with maleic anhydride

In the presence of maleic anhydride in aprotic solvents, 1-p-tolylsulphonylazocyclohexene undergoes in part a spontaneous transformation by a process in which free radicals are not formed as intermediates and in part enters into a cycloaddition reaction with formation of 3a,4,6,6a-tetrahydro-4,6-dioxo-3H-furo[3,4-c]pyrazole-3-spiro-cyclohex-2′-yl p-tolyl sulphone (II). The cycloaddition process takes place by two independent mechanisms, one first order and the other second order. In the first mechanism the formation of the ion pair (III) is rate determining; this species reacts immediately with maleic anhydride to form the adduct (II) by a [3 + 2 → 5] cycloaddition. The second mechanism is characterized by a low solvent effect, relatively high entropy of activation and activation energy, and moderate sensitivity to steric effects.