Scholl Cyclizations of Aryl Naphthalenes: Rearrangement Precedes Cyclization

Abstract

In 1910, Scholl, Seer, and Weitzenbock reported the AlCl3-catalyzed cyclization of 1,1'-binaphthyl to perylene. We provide evidence that this classic organic name reaction proceeds through sequential and reversible formation of 1,2'- and 2,2'-binaphthyl isomers. Acid-catalyzed isomerization of 1,1'-binaphthyl to 2,2'-binaphthyl has been noted previously. The superacid trifluoromethanesulfonic acid (TfOH), 1 M in dichloroethane, catalyzes these rearrangements, with slower cyclization to perylene. Minor cyclization products are benzo[k]fluoranthene and benzo[j]fluoranthene. At ambient temperature, the observed equilibrium ratio of 1,1'-binaphthyl, 1,2'-binaphthyl, and 2,2'-binaphthyl is <1:3:97. DFT calculations with the inclusion of solvation support a mechanistic scheme in which ipso-arenium ions are responsible for rearrangements; however, we cannot distinguish between arenium ion and radical cation mechanisms for the cyclization steps. Under similar reaction conditions, 1-phenylnaphthalene interconverts with 2-phenylnaphthalene, with the latter favored at equilibrium (5:95 ratio), and also converts slowly to fluoranthene. Computations again support an arenium ion mechanism for rearrangements.

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

“…To ascertain the relative likelihood of the two proposed scenarios in the Scholl reaction, namely the arenium cation versus radical cation mechanism, we first focus on the 1,2-shift of the aryl group, which occurs prior to the C−C bond formation. The rearrangement of the aryl groups can follow either the radical cation or the arenium cation protocols 29,47 (Scheme 4). In particular, we compare the protonation of precursor 1a to arenium cation 15 with the formation of radical 29 in the case of phenylnaphtalene, as anticipated from the expected similar acidity of the two aromatic hydrocarbons.…”

“…The rearrangement of the aryl groups can follow either the radical cation or the arenium cation protocols 29,47 (Scheme 4). In particular, we compare the protonation of precursor 1a to arenium cation 15 with the formation of radical 29 in the case of phenylnaphtalene, as anticipated from the expected similar acidity of the two aromatic hydrocarbons. Very interestingly, a much smaller energy penalty (of 0.13 eV) is associated with the formation of structure 12 resulting from a radical cation mechanism.…”

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 .…”

Synthesis ofcis‐ andtrans‐Configured Octahydroperylenes

“…[1] Oxidized derivatives (e.g., perylenequinones 2 [2] ) and partially hydrogenated perylenes [3] have occasionally been used. [1] Oxidized derivatives (e.g., perylenequinones 2 [2] ) and partially hydrogenated perylenes [3] have occasionally been used.…”

“…Perylene (1) and its derivatives have found a plethora of applications in synthesis, in physical chemistry, and in biology, due to their structural, electronic, and physical properties. [1] Oxidized derivatives (e.g., perylenequinones 2 [2] ) and partially hydrogenated perylenes [3] have occasionally been used. Octahydroperylenes 3 have only been prepared casually as intermediates in the synthesis of fully aromatic perylenes.…”