Unsymmetric Twofold Scholl Cyclization of a 5,11‐Dinaphthyltetracene: Selective Formation of Pentagonal and Hexagonal Rings via Dicationic Intermediates

Abstract

Even though the Scholl reaction is one of the most powerful processes for the synthesis of polycyclic aromatic hydrocarbons (PAHs), its mechanism still remains a subject of discussion. Herein, we report a unique twofold Scholl cyclization of a 5,11-dinaphthyltetracene. Single-crystal X-ray diffraction analysis of the cyclization product revealed that unsymmetric cyclizations of the two naphthyl groups resulted in the formation of fully unsaturated pentagonal and hexagonal rings. The thus obtained product exhibits a twisted π-surface and an absorption band that reaches up to 950 nm. A combined experimental and theoretical study showed that such unsymmetric Scholl cyclizations can be rationalized in terms of a mechanism that involves dicationic intermediates, which stands in contrast to previously reported pathways based on radical cations and arenium ions.

Functionalized Contorted Polycyclic Aromatic Hydrocarbons by a One‐Step Cyclopentannulation and Regioselective Triflyloxylation

“…In most cases six‐membered rings are formed during the Scholl reaction, but also examples are known where five‐, or more rare, seven‐or eight‐membered rings are generated. From a fundamental point of view, those systems are interesting where for example, a competing situation exists and both five‐ or six‐membered rings are possible, to understand why in some cases the system tends to six‐membered rings and in the other to the five‐membered ones . In most cases, the precursor for this Scholl‐type oxidation contains all necessary aromatic rings including side‐chains, substituents such as functional groups or further aryl rings (that will not participate to the PAH backbone).…”

Synthetic Applications of Oxidative Aromatic Coupling—From Biphenols to Nanographenes

“…Under oxidative coupling conditions (FeCl 3 or DDQ), acenes bearing aryl groups attached to the central benzene rings generally cyclize to form new five‐membered rings . Scheme depicts an especially interesting example, where oxidation of symmetric tetracene 161 led to the unsymmetric product 162 containing two new rings of different sizes: five‐ and six‐membered …”

Syntheseanwendungen der oxidativen aromatischen Kupplung – von Biphenolen zu Nanographenen

“…Unter oxidativen Kupplungsbedingungen (FeCl 3 oder DDQ) cyclisieren Acene mit Arylgruppen, die an die zentralen Benzolringe gebunden sind, im Allgemeinen zu neuen fünfgliedrigen Ringen . Schema zeigt ein besonders interessantes Beispiel, bei dem die Oxidation von symmetrischem Tetracen 161 zum unsymmetrischen Produkt 162 führte, das zwei neue Ringe unterschiedlicher Größe enthält: fünf‐ und sechsgliedrig …”