Behaviour of Thiophenes Substituted with Electron-Withdrawing Groups in Cycloaddition Reactions

Substituted thiophenes can act as dienophiles in normal electron demand Diels-Alder reactions, nitro being one of the substituents. Cycloaddition with Danishefsky's diene provides the benzothiophene derivatives with nitro side selectivity, α-substituted substrates being the more dienophilic. The reaction with isoprene leads mainly to the corresponding (pyrrol-1-yl)thiophenes.