Regioselectivity in the Controversial Scholl Reaction of 1-Benzoylpyrene: Formation of a Five-Member Ring Is Not Unexpected

Abstract

Intramolecular Scholl reaction of 1-benzoylpyrene (1) gave 8H-dibenzo[def,qr]chrysen-8-one (2) and 11H-indeno[2,1-a]pyren-11-one (3) in a 1:2 ratio. The structures of 2 and 3 were determined, using H NMR,C NMR, and IR spectroscopies. A DFT B3LYP/6-311G(d,p) study of the reaction's arenium-cation mechanism of (E)-1 and (Z)-1 giving 2 and 3, respectively, indicated the reaction's regioselectivity and kinetic control. The analogous reaction of 1-(1'-naphthoyl)pyrene gave exclusively 13H-benz[4,5]indeno[2,1-a]pyren-13-one. Contrary to previous claims, the preferred formation of five-member rings in Scholl reactions is not unexpected.

Novel Fluorophores based on Regioselective Intramolecular Friedel–Crafts Acylation of the Pyrene Ring Using Triflic Acid

“…It is worthwhile to note that the cyclisation of 1 f with MSA at 75 °C gives a 35:65 ratio and then the 5‐membered ring is now the major product (Scheme ). Similar regioselectivity has been observed for the intramolecular Scholl reaction of 1‐benzoylpyrene 1 h (Scheme ) . Surprisingly, the cyclisation of 1 g bearing a sulfoxide function with TfOH in CH 2 Cl 2 at room temperature produces only the 6‐membered ring thienoacene after demethylation (Scheme ) …”

“…Similar regioselectivity has been observed for the intramolecular Scholl reaction of 1-benzoylpyrene 1h (Scheme 4). [10] Surprisingly,t he cyclisation of 1g bearing as ulfoxide functionw ith TfOH in CH 2 Cl 2 at room temperaturep roduces only the 6-membered ring thienoacene after demethylation (Scheme 4). [11] As the second cyclisation is more difficult due to the presence of one ketone group that deactivates the pyrene ring, it is necessary to heat the reaction mixture at 90 8Ca fter the formation of the monocylisedp roduct obtained at room temperature (Scheme 5, Ta ble 1).…”

Scholl reaction as a powerful tool for the synthesis of nanographenes: a systematic review

“…This reaction proved to he highly regioselective as only one product was formed out of the four expected products. 50 In 2018, Huang and co-workers introduced a method for the synthesis of microporous organic polymers (MOPs) using the Scholl reaction to promote the key C-C coupling reaction. During this process, two aryl hydrogens were removed from adjacent phenyl rings by treating reactant 52 with anhydrous AlCl 3 in chloroform to construct a new aryl-aryl bond in product 53 (Scheme 22).…”

Helical Nanographenes Containing an Azulene Unit: Synthesis, Crystal Structures, and Properties

“…The successful formation of 1 can be attributed to the rotation of the 8‐iodobenzo[ c ]chrysene of 8 (highlighted in blue in Scheme a) following HI elimination after the 1,2‐aryl migration during the Scholl‐type cyclization. The proposed mechanism is described in Scheme S3 …”