Kinetics and mechanism of 1,3-cycloadditions of benzonitrile N-oxides to thiobenzophenones

Abstract

The kinetics of the cycloadditions of 2,4,6-trimethyl- and 4-chloro-2,6-dimethyl-benzonitrile N-oxide to thiobenzophenones to yield 1,4,2-oxathiazoles, have been studied. The reaction rate shows a small substituent effect and is slightly and irregularly influenced by the solvent polarity. ΔS‡ is ca.–26 cal mol^–1 K^–1. The results suggest that the reaction is a concerted process, as predicted by orbital symmetry selection rules for 1,3-dipolar cycloadditions. A four-centre transition state with charge separation is suggested.