Arenium cation or radical cation? An insight into the cyclodehydrogenation reaction of 2-substituted binaphthyls mediated by Lewis acids

Article abstract of DOI:10.1039/d0ra04213g

Perylene and its derivatives are some of the most interesting chromophores in the field of molecular design. One of the most employed methodologies for their synthesis is the cyclodehydrogenation of binaphthyls mediated by Lewis acids. In this article, we investigated the cyclodehydrogenation reaction of 2-substituted binaphthyls to afford thebay-substituted perylene. By using AlCl₃as a Lewis acid and high temperatures (the Scholl reaction), two new products bearing NH₂and N(CH₃)₂groups at position 2 of the perylene ring were synthesized. Under these conditions, we were also able to obtain terrylene from ternaphthalene in 38percent yield after two cyclodehydrogenation reactions in a single step. The attempts to promote the formation of a radical cation (necessary intermediary for the oxidative aromatic coupling mechanism) by using FeCl₃or a strong oxidant like 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) did not yield the expected products. DFT calculations suggested that the lack of reaction for oxidative aromatic coupling is caused by the difference between the oxidation potentials of the donor/acceptor couple. In the case of the Scholl reaction, the regiochemistry involved in the formation of the σ-complex together with the activation energy of the C-C coupling reaction helped to explain the differences in the reactivity of the different substrates studied.

Full text of DOI:10.1039/d0ra04213g

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Arenium cation or radical cation? An insight into
the cyclodehydrogenation reaction of 2-
Cite this: RSC Adv., 2020, 10, 21974
substituted binaphthyls mediated by Lewis acids†
*
Patricia Camargo Solorzano, Marıa T. Baumgartner,
Marcelo Puiatti
´
´
*
and Liliana B. Jimenez
Perylene and its derivatives are some of the most interesting chromophores in the field of molecular design.
One of the most employed methodologies for their synthesis is the cyclodehydrogenation of binaphthyls
mediated by Lewis acids. In this article, we investigated the cyclodehydrogenation reaction of 2-
substituted binaphthyls to afford the bay-substituted perylene. By using AlCl3 as a Lewis acid and high
temperatures (the Scholl reaction), two new products bearing NH2 and N(CH3)2 groups at position 2 of
the perylene ring were synthesized. Under these conditions, we were also able to obtain terrylene from
ternaphthalene in 38% yield after two cyclodehydrogenation reactions in a single step. The attempts to
promote the formation of a radical cation (necessary intermediary for the oxidative aromatic coupling
mechanism) by using FeCl3 or a strong oxidant like 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)
did not yield the expected products. DFT calculations suggested that the lack of reaction for oxidative
aromatic coupling is caused by the difference between the oxidation potentials of the donor/acceptor
couple. In the case of the Scholl reaction, the regiochemistry involved in the formation of the s-
complex together with the activation energy of the C–C coupling reaction helped to explain the
differences in the reactivity of the different substrates studied.
Received 11th May 2020
Accepted 1st June 2020
DOI: 10.1039/d0ra04213g
rsc.li/rsc-advances
condensation of quinone derivatives (I),9 base-induced dimer-
ization of benzoisoquinoline-diones (II),10 the Ullmann reaction
(III),11 decarboxylation of the perylene-3,4,9,10-tetracarboxylic
Introduction
In the last decades, there has been special interest in the design
of specic chromophoric structures due to their possible
application in molecular devices such as light-collecting
antennas and organic light emitting diodes (OLEDs), among
other applications.1 Among these structures, perylene and its
derivatives are particularly interesting, since they exhibit
excellent electronic and optical properties.2 Perylene shows
characteristic uorescence with high quantum yield, which
varies depending on both the nature of the substituents
attached to the polycycle and their positions (e.g. the axial or
equatorial regions).3 Recent applications of perylene derivatives
(mostly perylene diimides, PDIs),4 include organic eld effect
transistors,5 organic photovoltaic cells,6 optical switches7 and
molecular wires.8
dianhydride mediated by basic conditions (IV),12 and the
cyclodehydrogenation of the binaphthalene (V).13 In general,
the yields of these reactions are good to low. Perhaps, the best
option to obtain large quantities of perylene is route IV, but it
usually requires high temperatures (more than 350 ꢀC). On the
other hand, route V is an attractive option, since it can take
place through up to three different mechanisms depending on
the reactants and the experimental conditions used. For
example, Rickhaus et al.13d were able to obtain quantitative
yields of perylene by using an excess of electrons (route V),
however no bay-substituted perylene was reported following
this last one. Despite these recent advances, the synthetic
procedures to generate perylene are currently limited. Further-
more, only routes I and II can yield substituted perylenes; peri-
substituted (axial region) by route II and ortho- and bay-
substituted by route I.
Because of the importance of perylene and its derivatives,
different strategies have been developed for their synthesis
(Scheme 1, I–V). Among these routes are intramolecular
Although the Lewis acid-mediated cyclodehydrogenation
(another way by which route V can occur) is one of the oldest
methodologies used to obtain polycyclic aromatic hydrocar-
bons,14 i.e. perylene,13b,15 terrylene,16 and dibenzote-
traphenylperianthene,17 the operating mechanism presents
some ambiguities. In front of this discussion, Gryko et al.18
proposed the distinction between two possible mechanisms
´
´
´
INFIQC, Departamento de Quımica Organica, Facultad de Ciencias Quımicas,
´
´
Universidad Nacional de Cordoba, Ciudad Universitaria, X5000HUA, Cordoba,
Argentina. E-mail: mpuiatti@fcq.unc.edu.ar; ljimenez@fcq.unc.edu.ar; Tel:
+54-351-5353867 int. 53330
† Electronic supplementary information (ESI) available: Spectroscopic data and
computational information. See DOI: 10.1039/d0ra04213g
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Scheme 1 Retrosynthesis of perylene. Route: (I) intramolecular condensation of quinone derivatives; (II) dimerization of benzoisoquinoline-
diones in basic media; (III) Ullmann reaction; (IV) decarboxylation of the perylene tetracarboxylic dianhydride mediated by basic conditions and
high temperatures and (V) cyclodehydrogenation of the binaphthalene.
through which polycyclic aromatic products can be generated. mechanism involves the formation of a radical cation, followed
One of the postulated mechanisms is known as the Scholl by an intramolecular cyclization and rearomatization to give the
reaction, that proceeds through the formation of an electro- polycyclic product (Scheme 2, le side).18 The experimental
philic complex or s-complex (shown as H+ for simplicity in conditions to carry out this reaction involve the use of either
Scheme 2, but it could also be a s-complex formed with a Lewis Lewis acids such as FeCl3 (ref. 22) or strong oxidants like 2,3-
acid).18 Usually, methodologies related to this mechanism dichloro-5,6-dicyano-1,4-benzoquinone (DDQ).23
involve the use of strong Lewis acids such as AlCl3 dissolved in
chlorobenzene,19 complexes of fused salts such as AlCl3/NaCl20 sometimes there is no clear evidence of the operating mecha-
or AlCl3/SO2,21 among others.15
nism, and they are said to occur through the Scholl mechanism
The ambiguity of these reactions relies on the fact that
In contrast, the other proposed mechanism for the reactions without any discrimination. One of the reasons contributing to
mediated by Lewis acids is the oxidative aromatic coupling. This this confusion is the fact that most of the Lewis acids used in
Scheme 2 General mechanisms proposed for the cyclodehydrogenation reaction in oxidizing media (mediated by Lewis acids).
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Scheme 3 Formation of perylene-1,12-diol.
the Scholl reaction are also mild oxidants commonly employed the preparation of equatorially functionalized perylenes. The
in oxidative aromatic coupling reactions.22,24 In this regard, in study of the reactivity of these binaphthyl compounds can
some cases DFT calculations have been used to help to solve generate important contributions to the understanding of
this issue.25
mechanisms associated with cyclodehydrogenation reactions
A prominent example in which it is possible to distinguish mediated by Lewis acids. A comparison between the arenium
between oxidative aromatic coupling and Scholl mechanism is cation (s-complex or Scholl) mechanism and the cyclo-
the reaction of 2-naphthol in the presence of an oxidant such as dehydrogenation initiated by radical cations (oxidative aromatic
FeCl3 at 50 ꢀC.26 Under these conditions, 2,20-dihydroxy-1,10- coupling) is presented for all synthesized compounds. The
binaphthalene is formed by an oxidative aromatic coupling discussion is complemented with DFT computational studies.
reaction (Scheme 3). However, it is not possible to obtain the Furthermore, the peculiar formation of two C–C bonds in
perylene-1,12-diol compound, even when additional portions of a single reaction step is presented in the synthesis of terrylene
FeCl3 were added to the system.18 In contrast, the C–C bond (tribenzo[de,kl,rst]pentaphene) from 1,10:40,100-ternaphthalene.
formation (C-8 with C-80) to give the perylene-1,12-diol can be
achieved by heating 2,20-dihydroxy-1,10-binaphthalene with
AlCl3 at 150 C (Scholl conditions).27
ꢀ
Results and discussion
A similar behavior was also observed with naphthyl iso-
quinolines.13e The compound 1-(naphthalen-1-yl)-isoquinoline
reacts with a melted mixture of AlCl3/NaCl at 160 ꢀC to
provide 1-azaperylene in 68% yield, but cyclization does not
occur when 8-(naphthalen-1-yl)-isoquinoline is exposed to the
same conditions. Moreover, neither of the two isomeric naph-
thyl isoquinoline substrates react in the presence of FeCl3 at
Scholl and oxidative aromatic coupling experimental
reactions
In an initial approach, the intramolecular cyclization of the
substrates [1,10-binaphthalen]-2-amine (1), N,N-dimethyl-[1,10-
binaphthalen]-2-amine (2) and 2-methoxy-1,10-binaphthalene
(3) was experimentally evaluated following both reaction
conditions, Scholl (Table 1) and oxidative aromatic coupling.
The substrates were allowed to react at 170 ꢀC within the salt
mixture of AlCl3/NaCl during different reaction times (Table 1,
entries 1–4). Compounds 1 and 2 afforded the cyclized products
25 C and 80 C.18
ꢀ
ꢀ
Considering the aforementioned antecedents, 2-substituted
binaphthalenes28 were synthesized and used as substrates for
Table 1 Results of the Scholl reaction for the substrates 1–3
Entry
Scholl reactiona
Productsb (%)
Remaining substratec (%)
1
2
3
AlCl3/NaCl, 170 ꢀC, 15 min
AlCl3/NaCl, 170 ꢀC, 30 min
AlCl3/NaCl, 170 ꢀC, 10 min
AlCl3/NaCl, 170 ꢀC, 20 min
AlCl3/C6H5Cl, 80 ꢀC, 6 h
4 (27)c
4 (12)c
5 (50)
5 (40)
6 (—)
7 (21)
7 (39)
7 (12)
7 (20)
7 (—)
1 (12)
1 (<5)
2 (<5)
2 (<5)
3 (<5)
4
5d
a
AlCl3/NaCl (5 : 1 eq.), substrate (0.2 eq., 0.1 mmol). b Isolated yields. c Quantied by CG-FID using the internal standard method. d Substrate (0.2
mmol), AlCl3 (1.8 mmol), C6H5Cl (10 mL).
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4 and 5, respectively. To the best of our knowledge, this work naphthyl group and chlorobenzene, homocoupling of chloro-
describes a synthetic protocol for obtaining products 4 and 5 for benzene and other chlorinated compounds were detected by
the rst time, since although compound 4 is mentioned in GC-MS.
some patents, no data on the synthetic procedure or the reac-
The intramolecular cyclization by oxidative aromatic
tion performance are known. Compound 4 decomposes under coupling conditions was evaluated by carrying out the reaction
air and during purication in column chromatography (on of substrates 1–3 with triic acid (TfOH) and DDQ in dry
silica gel). On the other hand, compound 5 has never been re- dichloromethane for 1 hour at 0 ꢀC. Under these conditions, the
ported in literature and showed high uorescence (35 (455 nm) formation of cyclized products was not observed and the start-
¼ 6869 Mꢁ1 cmꢁ1; Ff (5) ¼ 0.92 in dichloromethane).30 In all ing materials were fully recovered. Johnson et al. reported that
cases, perylene (7) was found to be the main side product, in 1,10-binaphthalene in presence of TfOH at room temperature
addition to substrate that did not react.
mostly produces the 2,20-binaphthyl as a consequence of rear-
It is known that 1,10-binaphthalene isomerizes to 1,20- rangements;31a nevertheless, this isomerization reaction is not
binaphthalene under acid-catalyzed conditions, as a consequence possible for our 2-substituted compounds. As an alternative
of the formation of an ipso-arenium ion. This process competes methodology, solutions of 1–3 in dry dichloromethane were
with the cyclodehydrogenation to form perylene;31 for example, treated with a solution of FeCl3 in CH3NO2,16a but there was not
formation of benzo[j]uoranthene and related compounds is substrate conversion at all.
observed when isomerization occurs.31a In our case, the C-20
To sum up, substrates 1 and 2 reacted in the Scholl reaction
position is blocked by the amino substituent, precluding isom- conditions, to produce the cyclized products of interest.
erization process. In consequence, no isomerization-derived Substrate 3 reacts by the Scholl pathway, but leading to no
products were observed in the assayed reactions.
cyclodehydrogenation compounds. None of these substrates
On the other hand, we assume that the formation of 7 could would react by the radical cation pathway (oxidative aromatic
come from deamination of the products 4 or 5 due to the coupling).
strongly acidic and high temperature conditions. This hypoth-
esis is supported by the fact that an increase of reaction time
leads to an increase in perylene (7) yield together with
a decrease of the amino-perylene product yield (entries 2 and 4,
Computational modeling
In order to nd the nature of the difference in reactivity of the
substrates, in both the Scholl and oxidative aromatic coupling
conditions, molecular modeling studies based on Density
Functional Theory (DFT)34 were done. All calculations reported
here were carried out at the B3PW91/6-31+G* level of theory.35
The polarizable continuum model (IEFPCM) was employed to
assess solvation using two media with different dielectric
constant: dichloromethane (3 ꢂ 8.93) and N-methylformamide
(3 ꢂ 181.5). Both solvent models afforded similar results, for
simplicity the ones obtained in the latter solvent are included in
the main text.36 The two possible mechanisms were evaluated,
using also reference compounds selected from bibliographic
data, which react, or not, within the same conditions as those
employed within this work.
Table 1). Although there exist several possible mechanisms for
deamination of different amino compounds,32 at this stage we
cannot unequivocally choose the mechanism involved in our
case.
ꢀ
Substrate 3 has a melting point of 109–110 C and decom-
poses at 125–127 C.33 For this reason, milder Scholl reaction
ꢀ
conditions were assayed with this substrate.19 A solution of
ꢀ
AlCl3 in dry chlorobenzene at 80 C was used to promote the
reaction (entry 5, Table 1); however, no intramolecular cycliza-
tion product was observed and 2-methoxynaphthalene was ob-
tained as major product, due to the C1–C10 bond cleavage of the
substrate. Some minor products from coupling between
Table 2 Most probable positions for the protonation to form the s-complex for 1a, 3, 8a and 9a
Substrates
Reference compounds
50 (72%)
80 (18%)
1 (98%)
6 (1%)
50 (31%)
80 (66%)
50 (46%)
80 (39%)
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Scheme 4 Scholl mechanism proposed for the formation of 2-R-perylene.
Since the reactions were carried out in acidic media, the
formation of the arenium cation was the rst evaluated process.
To study the regiochemistry of the protonation of each
substrate, the relative energy difference required to form the s-
complex at different positions of the aromatic rings was calcu-
lated. A Boltzmann population analysis for the formation of the
s-complex was estimated at 170 ꢀC (see ESI†), the most favored
positions are shown in Table 2.29 It should be noted that the
amino group must be protonated due to the acidic media used
Scholl reaction
Firstly, we address the following question, is it possible that –
under Scholl reaction conditions – the substrates 1, 2 and 3 may
react via the formation of the s-complex? Two reference
compounds
were
now
included,
1-(naphthalen-1-yl)
isoquinoline (8) and 8-(naphthalen-1-yl)isoquinoline (9).18
From these compounds, 8 reacted by the Scholl experimental
condition whereas 9 could not form the cyclized product; they
should work as positive and negative tests, respectively.
Table 3 Relative free energy of formation of s complex (DDGs), free energies of activation (DG#) and reaction (DGr) for the intramolecular ring
closure by Scholl reaction mechanisma
DG# (kcal
s-Complex
DDGr (kcal molꢁ1
)
DGr (kcal molꢁ1
)
molꢁ1
)
Intermediary
1s
2.0
19.1
24.5
2s
6.7
0.0
18.3
23.2
23.1
26.1
8s
9s
3.0
39.9
40.3
a
All the energies were calculated at B3PW91/6-31+G* using N-methylformamide as solvent, IEFPCM model. The energies correspond to the sum of
electronic energy, solvation, and thermal free energies.
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in the reactions. In this way, the cation of the substrate 1 (1a) carried out, hence the discrimination could take place aer that
was used,37 as well as the isoquinolinium cations (8a and 9a) step.
which come from the protonation of the reference compounds 8
and 9.
When the DG# energies for the intramolecular coupling were
studied, it was found that the DG# for arenium cations 1s and
The protonation at positions 50 and 80 was found to be the 2s were lower than 8s. Particularly, the 9s complex presented
energetically favored for 1a, 8a and 9a. When the s-complex is values of DG# and DGr for ring closure higher than the other
generated on position 50, the redistribution of the charge within compounds. The difference exceeds 15 kcal molꢁ1, which would
the ring leads to an intramolecular electrophilic attack, which indicate that, in this case, the C–C coupling stage does
would generate a new C–C bond between C-8 and C-80 (Scheme discriminate between substrates that cyclize and those that do
2). On the other hand, if the s-complex is generated in position not generate intramolecular cyclization by this mechanism.
80, the cyclization does not take place because a C-sp3 is formed This difference in the DG# and DGr, compared with the values
at this position. For compound 3 the position 1 is the favored for 8s, are ascribed to the differences in the electronic distri-
one for the protonation; however, this position does not favor butions of 1s, 8s and 9s, as presented in Fig. 1. For 1s and 8s
the cyclization reaction.
the charges at position 5 and 80 are negative and positive
To gain a deeper understanding of these reactions, the respectively, whereas in the case of 9s the negative charge is
calculations of two different stages of the proposed Scholl closer to zero due to the protonated nitrogen adjacent to the 80
mechanism (Scheme 4) were carried out. First, the free energy position. The electrostatic potential help to explain how the
values obtained for the formation of the s-complex (DDGs) were charge is distributed aer the formation of the s complex, and
computed, using the reaction of 8a as reference.38 Secondly, the which positions are nucleophilic and/or electrophilic, favoring
activation and reaction free energies (DG# and DGr respectively) (or not) the cyclization by an electrophilic attack.
involved in the intramolecular cyclization were evaluated; the
As it was mentioned before, the cyclized product 6 derived
results are presented in Table 3. The last stage of the total from compound 3 by Scholl reaction was not observed (entry 5,
reaction is an oxidation with re-aromatization of the formed Table 1). According to the analysis of the electrostatic potential
cycle, which should provide an important driving force.
of 3s (with H+ in position 1), C-50 and C-8 do not possess the
The DDGs values for the formation of complexes 1s and 2s expected charges that favor the coupling (see ESI†). In addition,
to promote the Scholl reaction compared to that of 8s, that is the free energy for the intramolecular ring closure of 3s is
used as a reference of a compound that effectively reacts by the higher than the one found for compound 9s which was used as
Scholl mechanism, indicate that it might be a possible step, reference of a nonreactive compound.39
even though it would entail a higher energy cost (2.0 kcal molꢁ1
for 1s and 6.7 kcal molꢁ1 for 2s). According to the energy of
formation of the 9s complex (ꢂ3.0 kcal molꢁ1 higher than that
Oxidative aromatic coupling
of 8s), compound 9 could also lead to the cyclization product.
Finally, the reactivity of substrates 1–3 within oxidative
However, this product was not found when the reactions were
aromatic coupling mechanism was also examined with
Fig. 1 Representation of the electrostatic potential of the s-complex of 1s, 8s and 9s. In the small figure are represented the point charges that
fit the electrostatic potential, according to the Merz–Singh–Kollman40 scheme, for C-5 and C-80.
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Fig. 2 Structure of the reference compounds for oxidative aromatic coupling mechanism. Blue square: Group 1 (reactive); red square: Group 2
(non reactive). Calculated oxidation potential (eV) in parenthesis.42
computational studies. The feasibility of initiating the reaction These results are in concordance with the previously proposed
through this mechanistic pathway (Scheme 2) was rst evalu- oxidation potential limit by Rathore et al. when DDQ/H+ is used
ated by comparing the computed oxidation potentials.41 They as oxidant agent for cyclization of electron-rich molecules.18,23 It
were calculated for both, substrates and a group of reference should be noted that this estimation of the oxidation potential,
molecules, the results are represented in Fig. 2. The set of could help to predict the reactivity of new compounds toward
reference compounds was split into two groups (Fig. 2): Group 1 these oxidative aromatic coupling reactions.
(blue box) includes those compounds reported as useful for
Cyclization of 1,10:40,100-ternaphthalene
generating intramolecular cyclization mediated by an interme-
diary radical cation (using different oxidant agents, i. e. FeCl3,
DDQ/H+, MoCl5, etc.); Group 2 (red box) includes those
compounds that do not produce cyclization under oxidative
aromatic coupling experimental conditions.42
As expected, the results suggest that compounds from Group
1 have lower oxidation potentials. Meanwhile, the compounds
from Group 2 have higher oxidation potentials (Fig. 3).
The oxidation potential values found for substrates 1–3 are
in the region of the compounds that would hardly generate the
necessary radical cation which initiates the reaction via the
oxidative aromatic coupling mechanism. This could explain the
lack of reactivity of these substrates experimentally observed.
In order to explore the scope of these reactions, we propose the
synthesis of terrylene from 1,10:40,100-ternaphthalene (25),
Scheme 5. In this reaction there is also another challenge, two
new C–C bonds have to be formed to yield the expected product.
Reaction of 1,10:40,100-ternaphthalene with a mixtuꢀre of AlCl3/
NaCl (5 : 1) was carried out during 20 min at 170 C, the cor-
responding double cycled product terrylene (26) was obtained
in 38% isolated yield. It is important to stand out that two new
C–C bonds were generated within the same procedure. Perylene
7 (23%) was also obtained as a side product and substrate 25
(20%) was recovered.
The molecular modeling studies of compound 25 indicated
that the positions 4 (64%) and 5 (11%) are the ones that
protonate mostly, but the DG# and DGr for the coupling are
markedly favored for the s-complex generated in position 5 (see
ESI†). The electrostatic potential of both intermediary s-
complexes are really different and help to explain this energetic
difference observed for the coupling at these positions. Finally,
starting form the s-complex protonated at position 5, the
energies involved in two consecutive C–C couplings of 25s, are
slightly lower than the energy values found for the other
binaphthyl derivatives previously studied (1, 2, and 8).
As it was found for substrates 1–3, when substrate 25 was
also exposed to oxidative aromatic coupling conditions using
DDQ as the oxidant agent, the formation of the product 26 was
not detected. Again, 25 was also treated with a solution of FeCl3
in CH3NO2. The reaction led to the formation of an inseparable
mixture of products that could not be characterized. Moreover,
none of them showed the typical uorescence or UV-absorption
Fig. 3 Calculated oxidation potential of the studied compounds.
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Lewis acids, and again, molecular modeling is a powerful tool
which, on this occasion, helped us to deeply understand the key
points to be considered for achieving a successful reaction.
As Gryko proposed,18 there is a clear mechanistic difference
when any substrate is exposed to Lewis acids to generate
a dehydrogenative aromatic coupling product by Scholl reaction
or by oxidative aromatic coupling. According to the analysis of
both reactions by using molecular modeling methods, it could
be possible to explain differences in reactivity and to predict the
outcome of a reaction with a new substrate.
Experimental section
Scheme 5 Synthesis of terrylene (26) from 1,10:40,100-ternaphthalene General methods
(25) by Scholl or oxidative aromatic coupling experimental conditions.
Sodium chloride (NaCl), nitromethane (CH3NO2), 2,3-dichloro-5,6-
dicyano-p-benzoquinone (DDQ), and triuoromethanesulfonic
acid (TFMSA) were obtained from Sigma-Aldrich and used as
received. Iron trichloride (FeCl3) was obtained from Merck Milli-
pore and used as received. Aluminum trichloride (AlCl3) was ob-
prole of the terrylene.16a The computed oxidation potential
found for 25 was 6.15 eV. Considering Fig. 2, the compound 25
is classied within the group of compounds that do not react by
the methodology of oxidative aromatic coupling.
In brief, the results obtained by computational modeling
help to explain the observed reactivity of the tested ternaphthyl
compound, under both reaction conditions. Moreover, it was
possible to obtain terrylene, going through two consecutive C–C
coupling reactions, in a simple experimental step with Scholl
conditions.
tained
commercially
and
sublimated
before
used.
Dichloromethane was obtained commercially, distilled, and stored
ꢀ
under molecular sieves (4 A). Gas chromatographic analysis was
performed on a Varian GC with a ame ionization detector and
equipped with a VF-5 ms, 30 m ꢃ 0.25 mm ꢃ 0.25 mm column.
Gas chromatographic/mass spectrometer analysis was carried out
on a Shimadzu GC-MS QP 5050 spectrometer equipped with a VF-5
ms, 30 m ꢃ 0.25 mm ꢃ 0.25 mm column. HRMS were recorded on
a Bruker, MicroTOF Q II equipment, operated with an ESI source
in (positive/negative) mode, using nitrogen as nebulizing and
drying gas and sodium formate 10 mM as an internal standard.
Conclusions
To summarize, three compounds derived from perylene, two of HPLC analysis was carried out on a Waters 1525 Binary HPLC
them functionalized in the equatorial region, were synthesized Pump connected to a Waters 2998 Photodiode Array Detector, and
by a cyclodehydrogenation reaction mediated by Lewis acids, employing an Agilent Rx-Sil Analytical column (4.6 ꢃ 150 mm, 5
from their respective 2-substituted binaphthalene compounds mm). Elemental analysis was determined on a Perkin Elmer 2400
1
through a mechanistic pathway that involves the formation of Series II CHNS/O with a thermal conductivity detector (TCD). H
the s-complex. Regarding the studies performed by computa- NMR and 13C NMR were recorded on a 400 MHz Bruker nuclear
tional methods, the regiochemistry for the formation of the s- magnetic resonance spectrometer.
complex should be studied. An analysis of the electrostatic
The substrates 1,28a,28c 3,43 and 25 (ref. 44) were synthesized
potential isosurface of the s-complexes was very useful to and puried by previously published methods, their NMR
predict the outcome of the cyclization reaction. According to spectra are shown in ESI.† The new compound N,N-dimethyl-
these analyses, within this experimental condition (AlCl3/NaCl, [1,10-binaphthyl]-2-amine (2) was obtained by the methylation
ꢀ
170 C), substrates 1, 2 and 25 can generate the s-complex to of amine 1 (see ESI†).
initiate the reaction and consequently, produce an intra-
General procedure for the cyclodehydrogenation by Scholl
molecular cyclization. For substrate 3, the results suggest that reaction. A mixture of dry sodium chloride (30 mg, 1 eq.) and
the formation of the initial s-complex is possible on position 1, aluminum chloride (333 mg, 5 eq.) was heated and stirred at
but the ring closure from the s-complex is not energetically 170 ꢀC under nitrogen atmosphere. Once this mixture is melted,
favored, consequently the product 6 was not observed.
the substrate (0.2 eq., 0.1 mmol) was added. In the reactions
On the other hand, the formation of the 2-substituted per- carried out with substrates 1 and 2, aer the reaction nished
ylene products by cyclodehydrogenation reactions via oxidative (reaction times are indicated in Table 1), the mixture was cooled
aromatic coupling (FeCl3 or DDQ as oxidants), e.g. radical to room temperature and extracted with CH2Cl2 and H2O (3 ꢃ
cations as intermediates, was not detected. The studies carried 25 mL). The organic layer was dried under Na2SO4, ltered, and
out with DTF methods support that substrates 1, 2, 3, and 25 evaporated under reduced pressure. The crudes were analyzed
could not be experimentally oxidized and therefore, could not by GC and GC-MS. In the case of the reaction of substrate 25,
generate the intermediary radical cation, which is necessary to aer the end of the reaction time (20 min), the mixture was
initiate the reaction and produce the cycled perylene derivative. cooled at room temperature and quenched with diluted (10%)
In summary, we introduce an experimental system where it can HCl (5 mL). The resulting precipitate was ltered under suction
be raised the difference between both mechanisms mediated by and rinsed with H2O.
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When milder conditions were employed in the Scholl reac- (CAr–H); 122.9 (CAr–H); 122.2 (CAr–H); 121.7 (CAr–H); 121.5 (CAr–
tion, 2-methoxy-1,10-binaphthalene (3) (0.2 mmol, 1 eq.) was H); 118.9 (CAr–H); 109.7 (Cq). 1H–1H COSY NMR ((CD3)2CO): dH/
dissolved in dry dichloromethane (10 mL). Aer stirring for dH 7.97/7.01; 7.71/6.81; 7.69/7.04; 7.23/7.04; 7.16/6.81; 7.11/6.72;
20 min under N2 atmosphere, anhydrous aluminum chloride 7.13/7.01. 1H–13C HSQC NMR ((CD3)2CO): dH/dC 7.97/121.5;
ꢀ
(1.8 mmol, 9 eq.) was added. The solution was stirred at 80 C 7.71/121.7; 7.69/118.9; 7.23/126.7; 7.16/128.2; 7.13/124.8; 7.11/
for 6 h. For the extraction process, CH2Cl2 and H2O (3 ꢃ 20 mL) 128.9; 7.04/126.7; 7.01/126.9; 6.81/122.9; 6.72/122.2. 1H–13C
were used.
HMBC NMR ((CD3)2CO): dH/dC 7.97/109.7; 7.97/124.8; 7.97/
General procedure for the oxidative cyclodehydrogenation 129.7; 7.71/128.2; 7.71/130.5; 7.71/131.6; 7.69/126.7; 7.69/
with DDQ and methanesulfonic acid. A solution of the substrate 129.1; 7.69/129.7; 7.23/118.9; 7.23/124.8; 7.23/129.7; 7.16/
(0.4 mmol, 1 eq.) in dry dichloromethane (4 mL) containing 121.7; 7.16/128.9; 7.16/130.5; 7.13/121.5; 7.13/126.7; 7.13/
methanesulfonic acid (10% v/v, 0.8 mL) at ꢂ0 ꢀC was exposed to 129.7; 7.11/128.2; 7.11/130.5; 7.11/145.6; 7.04/131.6; 7.04/
DDQ (0.4 mmol, 1 eq. per C–C bond formation). The reaction 134.6; 7.01/132.3; 7.01/134.6; 6.81/127.9; 6.81/129.1; 6.72/
was stirred under a nitrogen atmosphere from 30 min to 5 h, at 109.7; 6.72/127.9; 5.58/109.7; 5.58/122.2. MS (EI): m/z 267
room temperature. The progress of the reaction was monitored (100.0%), 133 (36.0%), 118 (19%).
by TLC. The reaction was quenched with a saturated aqueous
solution of NaHCO3 (20 mL). The dichloromethane layer was
separated, washed with water and brine solution, dried over
anhydrous NaSO4, and ltered.
N,N-Dimethylperylene-1-amine (5)
The compound was puried as an orange oily solid by semi-
preparative TLC using as eluent a solvent gradient of pentane/
ethyl acetate (100 : 0 / 90 : 10). Isolated yield: 50% (15 mg).
1H, 13C, COSY, HMBC and HSQC-DEPT NMR spectra are
showed in ESI.† 1H NMR (400 MHz, (CD3)2CO) d: 9.21 (dd, 1J ¼
General procedure for the oxidative cyclodehydrogenation
using FeCl3. A solution of anhydrous iron(III) chloride (3.2
mmol) in dry nitromethane (3.2 mL) was injected to a solution
of the substrate (0.4 mmol) in dry dichloromethane (30 mL)
through a syringe. The solution was stirred at room temperature
for 24 h under nitrogen atmosphere. Dry methanol (30 mL) was
added to the solution. The resulting precipitate was ltered,
rinsed with methanol, and dried.
2
1
2
7.8, J ¼ 1.0 Hz, 1H); 8.21 (dd, J ¼ 7.5, J ¼ 1.1 Hz, 2H); 7.73–
7.64 (m, 4H); 7.54–7.46 (m, 3H); 7.38 (t, 1J ¼ 7.8 Hz, 1H); 2.85 (s,
6H). 13C NMR (100 MHz, (CD3)2CO) d: 151.0 (Cq, C–N); 135.6
(Cq); 132.5 (Cq); 132.4 (Cq); 131.9 (Cq); 131.6 (Cq); 131.6 (Cq);
130.8 (Cq); 129.5 (CAr–H); 128.5 (CAr–H); 128.2 (CAr–H); 127.5
(CAr–H); 127.1 (CAr–H); 127.0 (CAr–H); 125.2 (CAr–H); 124.5 (CAr–
H); 122.1 (CAr–H); 121.5 (CAr–H); 120.1 (CAr–H); 119.6 (Cq); 43.4
N,N-Dimethyl-[1,10-binaphthalen]-2-amine (2)
The compound was puried as a pale yellow solid by column (2C, CH3). HRMS (ESI-TOF) m/z [M + Na]+ calcd for C22H17NNa:
chromatography using as eluent a solvent gradient of pentane/ 318.1253; found: 318.1261.
ethyl acetate (100 : 0 / 90 : 10). Mp: 193–195 ꢀC. Yield: 47%
1
1
(0.17 mmol, 52 mg). H NMR (400 MHz, CDCl3) d: 7.92 (t, J ¼
Perylene (7)
8.0 Hz, 3H); 7.82 (d, 1J ¼ 8.0 Hz, 1H); 7.61 (m, 1H); 7.50 (d, 1J ¼
The product was puried as a pale yellow solid by semipreparative
1
8.0 Hz, 1H); 7.48–7.44 (m, 2H); 7.37 (d, J ¼ 8.0 Hz, 1H); 7.31–
TLC using as eluent pentane/ethyl acetate (90 : 10). H and 13C
1
7.25 (m, 2H); 7.18–7.14 (m, 1H); 7.09 (d, 1J ¼ 8.5 Hz, 1H); 2.51 (s,
6H). 13C NMR (100 MHz, CDCl3) d ¼ 149.9 (Cq, CAr–N); 137.2
(Cq); 134.4 (Cq); 133.9 (Cq); 133.2 (Cq); 129.7 (Cq); 129.1 (CAr–H);
128.9 (CAr–H); 128.3 (CAr–H); 127.8 (Cq), 127.8 (CAr–H); 127.6
(CAr–H); 126.7 (CAr–H); 126.1 (CAr–H); 125.9 (CAr–H); 125.8 (CAr–
H); 125.8 (2 ꢃ CAr–H); 123.7 (CAr–H); 119.8 (CAr–H); 44.0 (2 ꢃ
CH3). HRMS (ESI-TOF) m/z [M + Na]+ calcd for C22H19NNa:
320.1410; found: 320.1424.
1
NMR spectra are showed in ESI.† H NMR (400 MHz, CDCl3) d:
1
1
1
8.19 (d, J ¼ 7.8 Hz, 4H); 7.68 (d, J ¼ 8.0 Hz, 4H); 7.48 (t, J ¼
7.7 Hz, 4H). 13C NMR (100 MHz, CDCl3) d: 134.9 (2 ꢃ Cq); 131.4 (2
ꢃ Cq); 129.0 (4 ꢃ Cq); 128.0 (4 ꢃ CAr–H); 126.7 (4 ꢃ CAr–H); 120.4
(4 ꢃ CAr–H). MS (EI): m/z 252 (100%), 125 (18%), 113 (7%).
Terrylene (26)16a
Aer reaction the crude was extracted in a Soxhlet apparatus, using
solvents in increasing polarity starting from ethyl acetate (100 mL,
reuxing for 24 h) and then toluene (100 mL, reuxing for 24 h).
The product 26 was isolated as a dark solid. Isolated yield: 38% (29
mg). UV-visible spectrum is showed in ESI.† UV-vis: lmax in
dichloromethane/nm: 550.4, 508.9, 476.1. Elemental analysis: calc.
for C30H16: C 95.7%, H 4.28%; found: C 95.82%, H 4.18%.
Perylene-1-amine (4)
The product was puried as a yellow oily solid by semi-
preparative TLC using as eluent pentane/ethyl acetate (90 : 10).
In this specic case, a second consecutive semipreparative TLC
was made. The product decomposes when it is exposed to air.
1
Isolated yield: 14% (4 mg). H, COSY, HMBC and HSQC-DEPT
NMR spectra are showed in ESI.† 1H NMR (400 MHz,
(CD3)2CO) d ¼ 7.97 (d, 1J ¼ 7.6 Hz, 1H); 7.73–7.69 (m, 2H); 7.23
Computational procedure
(d, 1J ¼ 7.7, 1H); 7.17–7.10 (m, 3H); 7.06–6.99 (m, 2H); 6.81 (t, 1J All the calculations were performed with the Gaussian09
¼ 7.6 Hz, 1H); 6.72 (d, J ¼ 8.8 Hz, 1H); 5.58 (s, 2H, NH2). 13C program.34 Based on previous results,45 the B3PW91 DFT func-
1
NMR (100 MHz, (CD3)2CO) d ¼ 145.6 (Cq, C–N); 134.6 (Cq); 132.3 tional46 and the 6-31+G(p) basis set were selected. Calculations
(Cq); 131.6 (Cq); 130.5 (Cq); 129.7 (Cq); 129.1 (Cq); 128.9 (CAr–H); were performed with full geometry optimization including in all
128.2 (CAr–H); 127.9 (Cq); 126.9 (CAr–H); 126.7 (2C, CAr–H); 124.8 cases the effect of the solvent through the Tomasi's polarized
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continuum model (IEFPCM)36a as implemented in the Gaussian
package. Aer renement, the characterization of stationary
points was done by Hessian matrix calculations, with all posi-
tive eigenvalues for a minimum and only one negative eigen-
value for the TSs. The xyz coordinates of all the obtained
geometries are included in the ESI,† together with the SCF
energy, in the case of TSs, the value of the negative frequency is
also included.
Diimides: Synthesis, Physical Properties, and Use in
Organic Electronics, J. Org. Chem., 2011, 76, 2386–2407.
¨
4 (a) M. Sun, K. Mullen and M. Yin, Water-soluble
perylenediimides: design concepts and biological
applications, Chem. Soc. Rev., 2016, 45, 1513–1528; (b)
A. Venkateswararao, S.-W. Liu and K.-T. Wong, Organic
polymeric and small molecular electron acceptors for
organic solar cells, Mater. Sci. Eng., R, 2018, 124, 1–57; (c)
F. Feng, W. Jiang and Z. Wang, Synthesis and Application
of Rylene Imide Dyes as Organic Semiconducting
Materials, Chem.–Asian J., 2018, 13, 20–30; (d) G. Zhang,
J. Zhao, P. C. Y. Chow, K. Jiang, J. Zhang, Z. Zhu, J. Zhang,
F. Huang and H. Yan, Nonfullerene Acceptor Molecules for
Bulk Heterojunction Organic Solar Cells, Chem. Rev., 2018,
118, 3447–3508.
Conflicts of interest
There are no conicts to declare.
Acknowledgements
This work was partly supported by the Consejo Nacional de
5 (a) B. A. Jones, M. J. Ahrens, M. Yoon, A. Facchetti, T. J. Marks
and M. R. Wasielewski, High-Mobility Air-Stable n-Type
´
´
´
Investigaciones Cientıcas y Tecnicas (CONICET), Secretarıa de
´
´
Ciencia
y
Tecnologıa, Universidad Nacional de Cordoba
Semiconductors
with
Processing
Versatility:
´
´
(SECyT), and the Agencia Nacional de Promocion Cientıca y
Dicyanoperylene-3,4:9,10-bis(dicarboximides),
Angew.
´
Tecnica (ANPCyT). P. C. S. gratefully acknowledges a fellowship
Chem., Int. Ed., 2004, 43, 6363–6366; (b) M. Gsanger,
J. H. Oh, M. Konemann, H. W. Hoen, A.-M. Krause,
Z. Bao and F. Wurthner, A Crystal-Engineered Hydrogen-
Bonded Octachloroperylene Diimide with a Twisted Core:
An n-Channel Organic Semiconductor, Angew. Chem., Int.
Ed., 2010, 49, 740–743; (c) L. Wang, X. Zhang, G. Dai,
W. Deng, J. Jie and X. Zhang, High-mobility air-stable n-
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processed organic single-crystal arrays, Nano Res., 2018, 11,
882–891; (d) L. Zonga, Y. Gonga, Y. Yua, Y. Xiea,
X. Guohua, Q. Peng, Q. Li and Z. Li, New perylene diimide
derivatives: stable red emission, adjustable property from
ACQ to AIE, and good device performance with an EQE
value of 4.93%, Sci. Bull., 2018, 63, 108–116.
from CONICET.
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