Unexpected Scholl Reaction of 6,7,13,14-Tetraarylbenzo[k]tetraphene: Selective Formation of Five-Membered Rings in Polycyclic Aromatic Hydrocarbons

Abstract

Cyclodehydrogenation is a versatile reaction that has enabled the syntheses of numerous polycyclic aromatic hydrocarbons (PAHs). We now describe a unique Scholl reaction of 6,7,13,14-tetraarylbenzo[k]tetraphene, which "unexpectedly" forms five-membered rings accompanying highly selective 1,2-shift of aryl groups. The geometric and optoelectronic nature of the resulting bistetracene analogue with five-membered rings is comprehensively investigated by single-crystal X-ray, NMR, UV-vis absorption, and cyclic voltammetry analyses. Furthermore, a possible mechanism is proposed to account for the selective five-membered-ring formation with the rearrangement of the aryl groups, which can be rationalized by density functional theory (DFT) calculations. The theoretical results suggest that the formation of the bistetracene analogue with five-membered rings is kinetically controlled while an "expected" product with six-membered rings is thermodynamically more favored. These experimental and theoretical results provide further insights into the still controversial mechanism of the Scholl reaction as well as open up an unprecedented entry to extend the variety of PAHs by programing otherwise unpredictable rearrangements during the Scholl reaction.

Synthesis of extended polycyclic aromatic hydrocarbons by oxidative tandem spirocyclization and 1,2-aryl migration

“…Subsequently, the spirocyclization proceeds through the intramolecular Friedel-Craft reaction to afford a spirocyclic radical species B , which may undergo a second single-electron oxidation by the excess oxidants to form a spirocyclic cation C . Next, the direct 1,2-aryl migration363738 of the cation C or more likely through an arenium cation intermediate D affords the cation E , which undergoes the rapid deprotonation to give the stable aromatic product 2a .…”

Fused Dibenzo[a,m]rubicene: A New Bowl-Shaped Subunit of C70 Containing Two Pentagons

“…Thus far, most studies on fullerene chemistry have been focused on the synthesis of bowl-shaped molecules as subunits of fullerene C 60 , the synthesis of fragments of C 70 remains elusive mostly due to the lack of proper synthetic protocols as well as their accessibility in reasonable amounts. [ [26,27] derivative as the key reaction (Scheme 1). Compound 1, with 34 carbon atoms, is a fragment for investigating C 70 , because it contains all the types of carbon atoms present in C 70 (Scheme 1).…”

“…Then a Scholl reaction of 5 was carried out with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and trifluoromethanesulfonic acid (TfOH) in dry dichloromethane (DCM) at 0 °C, affording 5,14-bis(4-(tert-butyl)phenyl)-9,18-dichlorodibenzo[a,m]rubicene (6) in 45% yield including a highly selective 1,2-shift of aryl groups. [26] Finally, intramolecular cyclization of 6 was performed in the presence of [Pd-(PCy 3 ) 2 Cl 2 ] and a stoichiometric amount of 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU) in N,Ndimethylformamide (DMF) providing compound 1 in 34% yield. [4] The chemical identity of 1 was firstly confirmed by MALDI-TOF MS analysis, as depicted in Figure S1.…”

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

“…[1,2] Today,the Scholl reaction is widely used for the synthesis of two-or three-dimensionally expanded PA Hs,a sw ell as for the synthesis of heteroatomcontaining PA Hs. [8] Based on density functional theory (DFT) calculations,p athways based on both radical cations and arenium ions were suggested to be involved in this unique cyclization. Although the Scholl reaction is considered to proceed through pathways that include either radical cations [6] or arenium ions, [7] these do not always explain or allow to predict the regioselectivity.R ecently,M üllen and co-workers reported an oxidative C À Hc oupling of at etraaryl benzotetraphene,w hich included at wofold cyclization accompanied by aryl migrations to furnish ap roduct with two pentagonal rings.…”

“…[3] In most cases,the Scholl reaction involves the formation of hexagonal rings while in some cases,t he unexpected or expected formation of products that contain pentagonal [4] or heptagonal rings [3a, 5] has been reported. [8] PA Hs with fully unsaturated pentagonal ring(s), so-called cyclopenta-fused polycyclica romatic hydrocarbons (CP-PA Hs), have received considerable attention owing to their unusual properties,which include high electron affinity [9] and chemical reactivity, [10] as well as for their potential use in organic electronic devices. [8] Based on density functional theory (DFT) calculations,p athways based on both radical cations and arenium ions were suggested to be involved in this unique cyclization.…”