Isolation of 6,13-dipropylpentacene and its tautomerization

6,13-Dipropyl-5,14-dihydropentacene was aromatized by the combination of the formation of pentacene-DDQ adduct and abstraction of DDQ from the pentacene-DDQ adduct with 50 equiv of gamma-terpinene to give 6,13-dipropylpentacene cleanly. It was stable and isolable. In the presence of a catalytic amount of acid, 6,13-dipropylpentacene was isomerized to its tautomer.