Thermal rearrangement of 3-allyloxy-1,2-benzisothiazole 1,1-dioxides: an unusual inversion of products of sigmatropic [3,3]-shift to give the [1,3]-isomers

3-Allyloxy-1,2-benzisothiazole 1,1-dioxides 4 isomerize thermally to give [ 3,3]- and [1,3]-products 5, 6 of sigmatropic shift, of which the former rea cts further to give solely the [1,3]-isomer.