Kinetics and mechanism of 1,3-cycloaddition of a substituted benzonitrile oxide to N-sulphinylanilines

Abstract

Reaction of 3,5-dichloro-2,4,6-trimethylbenzonitrile oxide with substituted N-sulphinylanilines, giving rise to 3,4-diaryl-1,2,3,5-oxathiadiazole 2-oxides, was kinetically studied in carbon tetrachloride and in chlorobenzene, mainly at 25°. Variation of substituents from p-OMe to m-Cl increases the rate by a factor of 6 in CCl₄ and of 9 in PhCl; however the Hammett correlation is very poor. Change of solvent has little consequence, whatever the type of substituent. Activation entropies in the range from –28 to –37 e.u. were evaluated. Contrary to a previous suggestion, a concerted mechanism of cycloaddition is put forward, with a charge unbalance in the transition state.