“…Inspired by the theoretical studies of the Povarov 's reaction mechanism, these reactions may proceed via a stepwise ion pair mechanism ] where the first step is the electrophilic interaction of the substituted cyclopentadienone with the in situ formed iminium G probably activated by protonation with TFA, which would then undergo ring closure via intramolecular electrophilic attack on the phenyl ring ( Friedel–Crafts ) via a reactive intermediate H, furnishing the desired products 1a , 1b and 2a , 2b ( Scheme ). This hypothesis is supported by Mellor , which has showed that with o ‐phenylenediamine and cyclopentadiene, in similar conditions, a tricyclic amine with a 7‐ring skeleton was formed as by‐product, which proves that mechanism is not concerted …”