Differences in reactions of vinyl derivatives of pyrrole and thiophene with acetylenic esters

1‐Methyl‐2‐vinylpyrrole and 2‐vinylthiophene showed remarkable differences in reactivity and regioselectivity upon reaction with methyl propiolate, respectively forming dimethyl 1‐methylindole‐4,7‐dicarboxylate and dimethyl benzo[ b ]thiophene‐4,6‐dicarboxylate. 1‐Methyl‐2‐(1‐propenyl)pyrrole reacted with dimethyl ace‐tylenedicarboxylate to give Diels‐Alder and Michael‐type adducts. On the other hand, 2‐(1‐propenyl)thiophene gave a 1:2 adduct which results via an initial cycloaddition and subsequent ene reaction.