Substituent effects in 1,3-dipolar cycloadditions. Variable reaction paths for the cycloaddition of benzonitrile N-oxides to styrenes

Abstract

ρ Constants for the cycloadditions of substituted benzonitrile N-oxides to styrene, p-methoxystyrene, and p-nitrostyrene are small and vary with the nature of the substituent in the phenyl ring of the dipolarophile. The observed variations of the ρ values are interpreted in terms of a one-step concerted mechanism with a different extent of bond formation which produces partial charges in the transition state. An explanation of the relative order of reactivity of the three sets of reactions is given in terms of the polarizability of the carbon–carbon double bond induced by the substituent in the dipolarophile.