Second-Ring Diels-Alder Adducts of Substituted Pentacenes

Substituted pentacene derivatives, 1,4,6,13-tetrabutyl-2,3-bis(methoxycarbonyl)pentacene 1 and 1,2,3,4,6,8,9,10,11,13-decapropylpentacene 2, occurred Diels-Alder reaction with most dienophiles at the central-ring. The second ring adduct was obtained only in the case of TCNE or chloranil probably due to the steric hindrance of such dienophiles. On the other hand, reaction of substituted dihydropentacene derivatives with dienophiles was followed by aromatization gave second-ring adducts in perfect selectivity.