Diels-Alder Reaction of Cyclopentadienone Acetal with Pyrrole and Indole

Diels-Alder reactions of a cyclopentadienone acetal with aromatic heterocycles, such as pyrrole or indole, took place with the latter acting as a 2π dienophile. The reaction gave a polycyclic heterocycle in good yield regioselectively. Analysis of the frontier molecular orbitals showed that inverse electron demand interactions control the regioselectivity.