First observation of Chapman rearrangement of a pseudosaccharyl ether in the solid state:: the thermal isomerization of 3-(methoxy)1,2-benzisothiazole 1,1-dioxide revisited

3-(Methoxy)-1,2-benzisothiazole 1,1-dioxide, a pseudosaccharyl ether, was long ago known to undergo a thermal Chapman-like [1,3']-isomerization to the corresponding N-methyl pseudosaccharin at temperatures above its melting point (ca. 184 degrees C) [Hettler H., Tetrahedron Lett. 1968, 15, 1793]. In the present study, it is shown that this rearrangement can also take place in the solid state, at temperatures as low as 150 degrees C. This was the first observation of a Chapman-like [1,3']-isomerization in pseudosaccharyl ethers in the solid state. The study has been carried out by a multidisciplinary approach using temperature dependent infrared spectroscopy, differential scanning calorimetry (DSC), and polarized light thermomicroscopy, complemented by theoretical methods. (C) 2008 Elsevier Ltd. All rights reserved.