1,2,3-BENZOXATHIAZOLE 2,2-DIOXIDES - SYNTHESIS, MECHANISM OF HYDROLYSIS, AND REACTIONS WITH NUCLEOPHILES

The rates of base-induced hydrolysis of some five-membered cyclic sulfamates, X-3-(p-tolylsulfonyl)-1,2,3-benzoxathiazole 2,2-dioxides (1a, X = H; 1b, X = 5-Me; 1c, X = 5-t-Bu; 1d, X = 5-Br; 1e, X = 5-Cl; 1f, X = 5-Ac; 1g, X = 5-NO2; 8a, X = 6-NO2) were measured in aqueous acetonitrile. The hydrolyses occurred with cleavage of the endocyclic N-SO2 bond. A Hammett plot using sigma-m values for 1a-g and sigma-p for 8a had rho = +2.20. Activation enthalpies and entropies were measured for 1a and for 3-methyl-1,2,3-benzoxathiazole 2,2-dioxide (10). Volumes of activation were determined for 1g and for 8a. The mechanistic profile for hydrolysis resembled that for the saponification of the analogous sultones and cyclic sulfates. These first examples of 1,2,3-benzoxathiazole 2,2-dioxides (1a-g, 8a) were prepared by treating N-(2-hydroxyphenyl)-p-toluenesulfonamides with sulfuryl chloride and triethylamine or by oxidizing the monoxide precursors using m-chloroperbenzoic acid. Treatment of 1a with potassium fluoride gave 1,2,3-benzoxathiazole 2,2-dioxide (9), which was methylated to give 10. Sulfamate 1a was treated with various nucleophilic reagents: phenyllithium, methyllithium, potassium fluoride, methylamine, tert-butylamine, and sodium methoxide. The first three attacked the tosyl sulfur atom and cleaved the exocyclic N-SO2 bond. The amines attacked the endocyclic sulfonyl sulfur atom and cleaved the endocyclic N-SO2 bond. Sodium methoxide attacked both sulfonyl groups.