Chlorination of 5-[2-(N-Silylamino)vinyl]isothiazole and Related Derivatives with N-Chlorosuccinimide. Inhibition of Ring-Transformation (Bond Switch) by Steric Hindrance

The selective monochlorination of 5-[2-(N-silyl-amino)vinyl] isothia- zoles (1a,b) and their related compounds (1c,d, 2a-g, 3a-c, and 4a,b) with N-chlorosuccinimide is described. Chlorination of (1a,b) occurred at vinyl carbon to give (5a,b) and the geometry was determined to be Z-isomer according to spectral data. It is noteworthy that (1d) smoothly occurred bond switch at room temperature but (5)d did not ring-trans- form under the same conditions