Vinylpyrroles having electron-withdrawing substituents react with dienophiles to give [4+ 21 r adducts while the furan and thiophene analogues do not." he difference in reactivity among the monoheterocycles can be explained in terms of the greater electron-releasing ability of the nitrogen atom in the pyrrole. The s-cis conformation of the (1H-pyrrol-2-y1) maleate derivatives appears to be an important factor in their undergoing the cycloaddition ...
