Enamine chemistry-XXVI: The [4 + 2] cycloaddition reactions of 3-amino-1-(4-nitrophenyl)-prop-2-ene-1-thione with electrophilic olefins and acetylenes

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-2$\text{H}$-thiopyrans, 2, and 4$\text{H}$-thipyrans, 3, respectively. The reaction of 1a with ethyl propiolate at room temperature afforded 4$\text{H}$-thipyrans, 4a, which on standing rearranged to 2$\text{H}$-thiopyran, 5a(1, 3 amide shift). The reaction of 1b with ethyl propiolate produced 4b and 5b. Some of the ¹³C NMR data are reported.