Intramolecular [4+2]-cycloaddition reactions of cyclic 2-thiomethyl-5-amidofurans

Cyclic 2-thiomethyl-5-amidofurans possessing tethered π-bonds were prepared by a dimethyl(methyl-thio) sulfonium tetrafluoroborate (DMTSF) induced cyclization of various amido dithioacetals. Upon heating, these systems undergo an intramolecular 4+2-cycloaddition reaction. The initially formed Diels–Alder cycloadduct further rearranges by ring opening of the oxygen bridge followed by a subsequent 1,2-thiomethyl shift.