Novel [6 + 2] Cycloaddition of Fulvenes with Alkenes: A Facile Synthesis of the Anislactone and Hirsutane Framework

In contrast to the Diels−Alder reaction of fulvenes and various alkenes, 6-aminofulvenes react with maleic anhydride (or maleimide) to give
[6 + 2] cycloaddition adducts, constituting an efficient and novel route to pentaleno[1,2-c]furan, pentaleno[1,2-c]pyrrole, and cyclopenta[a]pentalene skeleton.