Novel [6 + 2] cycloaddition of fulvenes with alkenes: a facile synthesis of the anislactone and hirsutane framework.

[reaction: see text] 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.