Enamino-thiones 1 prepared from the corresponding enaminones by thiation with Lawesson's Reagent, were allowed to react with 2-chloroacrylonitrile and dimethyl acetylenedicarboxylate giving dihydro-2H-thiopyrans, 2, and 4H-thipyrans, 3, respectively. The reaction of 1a with ethyl propiolate at room temperature afforded 4H-thipyrans, 4a, which on standing rearranged to 2H-thiopyran, 5a (1, 3 amide shift). The reaction of 1b ...
