ortho-(Phenylpropioloxy)benzonitrile sulphide, generated in situ by thermal decarboxylation of the oxathiazolone (1), undergoes intramolecular 1,3-dipolar cycloaddition forming the chromenoisothiazole (4a); ortho-cinnamoylbenzonitrile sulphides also yield (4), together with nitrile, chromenoquinoline and amino-chromene by-products.
Brownsort, Peter A.,Paton, Michael R.,Sutherland, Alan G.