Unexpected formation of novel pyrrole derivatives by the reaction of thioamide with dimethyl acetylenedicarboxylate

The reaction of thioamides with DMAD gave the pyrrole derivatives in good yield and the thiophene derivatives as a byproduct. These were formed by 1,3-dipolar cycloaddition of themodynamicaly stable azomethine ylide or less stable thiocarbonyl ylide with DMAD, followed by elimination of thioaldehyde or imine derivatives.