In quest of reversibility of Friedel-Crafts acyl rearrangements in the pyrene series

Article abstract of DOI:10.1007/s11224-019-01460-4

Friedel-Crafts acyl rearrangements in PPA of diacetylpyrenes (80–120 °C), dibenzoylpyrenes (80–200 °C), and bis(4-flurobenzoyl)pyrenes (80–120 °C) and Scholl reactions in AlCl₃/NaCl of dibenzoylpyrenes (140–200 °C) have been studied. The substrates were 1-AcPY, 2-AcPY, 1,3-Ac₂PY, 1,6-Ac₂PY, 1,8-Ac₂PY, 2,7-Ac₂PY, 1-BzPY, 1,6-Bz₂PY, 1,8-Bz₂PY, 1-4FBzPY, 1,6-4FBz₂PY, 1,8-4FBz₂PY. The mixtures of pyrene, 1-AcPY, 2-AcPY, 1,3-Ac₂PY, 1,6-Ac₂PY, 1,8-Ac₂PY, and 2,7-Ac₂PY were separated by HPLC. The following reversible intermolecular isomerizations were established: 1,6-Ac₂PY ? 1,8-Ac₂PY, 1,6-Bz₂PY ? 1,8-Bz₂PY, and 1,6-4'FBz₂PY ? 1,8-4'FBz₂PY, albeit not in high yields. The results substantiate Gore’s 1955 proposition that “The Friedel–Crafts acylation reaction of reactive aromatic hydrocarbons is a reversible process.” The isomerizations reported here differ from the few previously reported completely reversible intramolecular Friedel-Crafts acyl rearrangements. At ≥ 140 °C, in PPA and in AlCl₃/NaCl, 1,6-Bz₂PY and 1,8-Bz₂PY underwent a highly regioselective double Scholl reaction to give pyranthrone (3) and deacylations to 1-BzPy (and pyrene), followed by mono-Scholl reactions to give 8H-dibenzo[def,qr]chrysen-8-one (1), and 11H-indeno[2,1-a]pyren-11-one (2). The formation of 3 and not the expected tribenzo[a,ghi,o]perylene-7,16-dione (4) from 1,8-Bz₂PY indicates that 1,8-Bz₂PY has first undergone isomerization to 1,6-Bz₂PY. The present study confirms the linkage between Friedel-Crafts acyl rearrangements and the Scholl reaction.

Full text of DOI:10.1007/s11224-019-01460-4

Structural Chemistry
https://doi.org/10.1007/s11224-019-01460-4
ORIGINAL RESEARCH
In quest of reversibility of Friedel-Crafts acyl rearrangements
in the pyrene series
Israel Agranat1 & Tahani Mala’bi1 & Yaacov Netanel Oded1 & Hanna Daniel Kraus1
Received: 10 October 2019 /Accepted: 13 November 2019
#
Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
Friedel-Crafts acyl rearrangements in PPA of diacetylpyrenes (80–120 °C), dibenzoylpyrenes (80–200 °C), and bis(4-
flurobenzoyl)pyrenes (80–120 °C) and Scholl reactions in AlCl3/NaCl of dibenzoylpyrenes (140–200 °C) have been studied.
The substrates were 1-AcPY, 2-AcPY, 1,3-Ac2PY, 1,6-Ac2PY, 1,8-Ac2PY, 2,7-Ac2PY, 1-BzPY, 1,6-Bz2PY, 1,8-Bz2PY, 1-
4FBzPY, 1,6-4FBz2PY, 1,8-4FBz2PY. The mixtures of pyrene, 1-AcPY, 2-AcPY, 1,3-Ac2PY, 1,6-Ac2PY, 1,8-Ac2PY, and 2,7-
Ac2PY were separated by HPLC. The following reversible intermolecular isomerizations were established: 1,6-Ac2PY ⇌ 1,8-
Ac2PY, 1,6-Bz2PY ⇌ 1,8-Bz2PY, and 1,6-4'FBz2PY ⇌ 1,8-4'FBz2PY, albeit not in high yields. The results substantiate Gore’s
1955 proposition that “The Friedel–Crafts acylation reaction of reactive aromatic hydrocarbons is a reversible process.” The
isomerizations reported here differ from the few previously reported completely reversible intramolecular Friedel-Crafts acyl
rearrangements. At ≥ 140 °C, in PPA and in AlCl3/NaCl, 1,6-Bz2PY and 1,8-Bz2PY underwent a highly regioselective double
Scholl reaction to give pyranthrone (3) and deacylations to 1-BzPy (and pyrene), followed by mono-Scholl reactions to give 8H-
dibenzo[def,qr]chrysen-8-one (1), and 11H-indeno[2,1-a]pyren-11-one (2). The formation of 3 and not the expected
tribenzo[a,ghi,o]perylene-7,16-dione (4) from 1,8-Bz2PY indicates that 1,8-Bz2PY has first undergone isomerization to 1,6-
Bz2PY. The present study confirms the linkage between Friedel-Crafts acyl rearrangements and the Scholl reaction.
.
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Keywords Both-direction reaction Reversible process Scholl reaction Regioselectivity Dibenzoylpyrenes Pyranthrone
Introduction
structure [2]. Although pyrene itself is not carcinogenic,
benzo[a]pyrene and dibenzo[a,l]pyrene are considered highly
carcinogenic prototypes of PAHs [3].
Pyrene is the simplest peri-condensed polycyclic aromatic
hydrocarbon (PAH) (which contains internal third-degree ver-
tices, i.e., central carbon atoms that are points of fusion for
three rings). Pyrene is an alternant planar benzenoid C16H10
PAH with D2h symmetry [1]. Pyrene has widely been
exploited for its electronic and photophysical properties and
for its ability to take part in non-covalent interactions. It serves
as a key component in organic electronics [2]. It is a valuable
component for materials, supramolecular, and biological
chemistry (for binding nucleic acids), due to its
photophysical/electronic properties and extended rigid
Pyrene contains ten potential positions for substitutions,
which are divided into three nonequivalent sites:{1,3,6,8},
{2,7}, and {4,5,9,10}. Pyrene is most activated towards elec-
trophilic aromatic substitution at the {1,3,6,8} positions [4].
Direct Friedel-Crafts polyacylations of pyrene give
polyacylpyrenes (AcnPY) for n = 2–4, but not for n = 5–10
[2, 4–13]. Direct Friedel-Crafts benzoylation and acetylation
of pyrene under a variety of classical Friedel-Crafts conditions
have been shown to be highly regioselective. The direct acet-
ylation of pyrene gave 1-acetylpyrene (1-AcPY), 1,3-
diacetylpyrene (1,3-Ac2PY), 1,6-diacetylpyrene (1,6-
Ac2PY), 1,8-diacetylpyrene (1,8-Ac2PY), 1,3,6-
triacetylpyrene (1,3,6-Ac3PY), and 1,3,6,8- tetraacetylpyrene
(1,3,6,8-Ac4PY) (Fig. 1) [10]. The direct benzoylation of
pyrene occurred exclusively at the {1,3,6,8} sites, giving 1-
benzoylpyrene (1-BzPY), 1,3-dibenzoylpyrene (1,3-
Bz2 PY)1,6-dibenzoylpyrene (1,6-Bz2 PY), 1,8-
dibenzoylpyrene (1,8-Bz2PY), 1,3,6-tribenzoylpyrene (1,3,6-
* Israel Agranat
isri.agranat@mail.huji.ac.il
1
Organic Chemistry, Institute of Chemistry, The Hebrew University of
Jerusalem, Philadelphia Bldg. #212, Edmond J. Safra Campus,
9190401 Jerusalem, Israel

Struct Chem
Fig. 1 Acetylpyrenes and
diacetylpyrenes
Bz3PY), and 1,3,6,8- tetrabenzoylpyrene (1,3,6,8-Bz4PY)
(Fig. 1) [2, 4–13].
The constitutional isomers 1,6-dibenzoylpyrene (1,6-
Bz2PY) and 1,8-dibenzoylpyrene (1,8-Bz2PY) [4, 9] are
attractive substrates for studying the reversibility con-
cept in Friedel-Crafts acyl rearrangement and regioselec-
tivity of Scholl reactions. Their two acyl groups are
positioned at α-positions, farther away from each other,
and are bonded to starred and unstarred positions of the
alternant pyrene nucleus [18]. Thus, they are devoid of
mutual resonance interactions. As such, they are expect-
ed to behave independent of each other. By contrast,
each pair of the two acyl groups of their constitutional
isomers 1,3-dibenzoylpyrene (1,3-Bz2PY) (positioned at
α-positions and close to each other) and 2,7-
dibenzoylpyrene (2,7-Bz2PY) (positioned at β-
positions) is bonded to starred (or unstarred) positions.
As such, each pair is capable of mutual resonance in-
teractions. We have recently shown, using DFT, that the
established experimentally pronounced regioselective
Friedel-Crafts mono-acylation and poly-acylations of
The concept of reversibility of Friedel-Crafts acylation was
introduced in 1955 by Gore, who proposed that “The Friedel-
Crafts acylation reaction of reactive aromatic hydrocarbons is
a reversible process” [5]. In 1973, Olah stated that “acylation
differs from alkylation in being virtually irreversible” [14].
The incursion of reversibility in Friedel–Crafts acylations
and acyl rearrangements was reported in 1974 in the
benzoylation of naphthalene in polyphosphoric acid (PPA) at
elevated temperatures [15]. Reversibility studies of Friedel-
Crafts acylations have focused mainly on unusual aspects of
selectivity, including deacylations, one-way rearrangements,
and kinetic versus thermodynamic control [16, 17].
Experimental evidence in support of complete revesibilty of
Friedel-Crafts acylations is limited [17]. According to Gore,
“unusual orientations may result from a variety of causes,
including multiplicity of mechanisms, reversibility and rear-
rangements, and the variations in the attacking species” [16].

Struct Chem
pyrene (acylations only at the α-positions 1,3,6,8, not at
the β-positions 2,7 and at the γ-positions 4,5,9.10) are
kinetically controlled and not thermodynamically con-
trolled [19]. According to our DFT study, the differ-
ences between the free energies (ΔΔG298) of 1Z,6Z-
Bz2PY and 1Z,8Z-Bz2PY, between their O-protonates
1ZH,6Z-Bz2PY+ and 1ZH,8Z-Bz2PY+, and between
their σ-complexes 1σ,6Z-Bz2PY and 1σ,8Z-Bz2PY are
very small [19]. Therefore, there is hardly any prefer-
ence in Friedel-Crafts acyl rearrangements for the for-
mation of 1,6-Bz2PY versus 1,8-Bz2PY or vice versa, in
contrast to, e.g., 1- and 2-benzoylnaphthalenes [20].
Similar arguments applies to 1,6-diacetylpyrene (1,6-
Ac2PY) and 1,8-diacetylpyrene (1,6-Ac2PY).
We have recently established a linkage between the Scholl
reaction [21] and Friedel-Crafts acyl rearrangements of
benzoylnaphthalenes [20]. The Scholl reaction of 1-BzPY gave
both 8H-dibenzo[def,qr]chrysen-8-one (1) and 11H-
indeno[2,1-a]pyren-11-one (2) in a 1:2 ratio [22]. We report
here the reversible Friedel-Crafts acyl rearrangements 1,6-
Ac2PY ⇌ 1,8-Ac2PY, 1,6-Bz2PY ⇌ 1,8-Bz2PY, and 1,6-
4'FBz2PY ⇌ 1,8-4'FBz2PY, in PPA and the highly regioselec-
tive double Scholl reaction (PPA and AlCl3/NaCl) of both 1,6-
Bz2PY and 1,8-Bz2PY to give pyranthrene-8,16-dione (3).
Diacetylpyrenes
Initial experiments of Friedel-Crafts acyl rearrangements in
the pyrene series were carried out with diacetylpyrenes 1,6-
Ac2PY, 1,8-Ac2PY, 1,3-Ac2PY, and 2,7-Ac2PY in PPA [23,
24]. The composition of the reaction products (relative yields
determined by HPLC; see the “Experimental” section) in-
cludes, in addition to the four diacetylpyrene isomers, the
products of deacylation, pyrene, 1-acetylpyrene (1-AcPY),
and 2-acetylpyrene (2-AcPY). The results are summarized in
Tables 1 and 2. Table 1 gives the ratios of reaction products.
The ratios of the three 1,6-, 1,8-, and 1,3-diacetylpyrene iso-
mers and their total yields are given in Table 2. 2-AcPY was
identified among the reaction products in some experiments
(< 0.5% relative yields).
1,6-Ac2PY isomerizations: At 80 °C (9 h), 1,6-Ac2PY
isomerized to 1,8-Ac2PY and 1,3-Ac2PY in 5.6% and 1.4%
relative yields, respectively. At 100 °C (9 h), the correspond-
ing relative yields were 3.2% and 1.8%, respectively.
1,8-Ac2PY isomerizations: At 80 °C (8 h) and 100 °C (8 h),
1,8-Ac2PYisomerized only to 1,6-Ac2PY, without any forma-
tion of 1,3-Ac2PY. The 1,8-Ac2PY:1,6-Ac2PY relative yields
of were 15.1%, 2.7% and 7.1%, 1.8%, respectively.
1,3-Ac2PY isomerizations: At 80 °C (8 h) and 100 °C (8 h),
1,3-Ac2PYisomerized to 1,6-Ac2PYand 1,8-Ac2PY. The 1,6-
Ac2PY:1,8-Ac2PY:1,3-Ac2PY relative yields were 0.8%,
0.7%, 39.0% and 1.3%, 1.6%, 23.7% relative yields,
respectively.
Results and discussion
The major products of the reactions of 1,6-, 1,8-, and 1,3-
Ac2PY were pyrene and 1-AcPY; their ratios depended on the
temperature. 2,7-Ac2PY was an exception. It has undergone
deacetylation to pyrene only in very low relative yields (< 5%
at 100–140 °C) and proved to be completely resistant to isom-
erization; 2-AcPY was identified among the products only in
≤ 0.4% relative yields. The relative yields of the isomerization
reactions of the diacetylpyrenes were very low, probably due
to the instability of the intermediate acetylium cation, formed
in the initial deacetylation reactions. At 80 °C, the
diacetylpyrene isomers were only a small fraction of the prod-
ucts (11%). In spite of these low yields, the results indicated a
Friedel-Crafts acyl rearrangement reaction, both directions
[25]: 1,6-Ac2PY ⇆ 1,8-Ac2PY. The high yields of the
deacetylation reactions leading first to 1-AcPY and then to
pyrene may be due to their faster reaction rates, as compared
with the rates of the reacetylation reactions leading to the
isomeric diacetylpyrene.
Diacetylpyrenes, dibenzoylbyrenes, and related
compounds
Synthesis
The substrates of the present study were 1,3-diacetylpyrene
(1,3-Ac2PY), 1,6-diacetylpyrene (1,6-Ac2PY), 1,8-
diacetylpyrene (1,8-Ac2PY), 1,6-dibenzoylpyrene (1,6-
Bz2PY) and 1,8-dibenzoylpyrene (1,8-Bz2PY), 1,6-bis(4'-
fluorobenzoyl)pyrene (1,6-4'FBz2PY), and 1,8-bis(4'-
fluorobenzoyl)pyrene (1,8-4'FBz2PY) (Figs. 1 and 2). They
were synthesized by classical Friedel-Crafts acylations of
pyrene with acetyl chloride, benzoyl chloride, and 4-
fluorobenzoyl chloride and AlCl3 according to the literature
with certain modifications using CH2Cl2 as solvent. See the
“Experimental” section.
Friedel-Crafts acyl rearrangements in PPA
For comparison, acetylation of pyrene with acetic acid in
PPA (80 °C, 8 h) gave pyrene, 1AcPY, 1,6-Ac2PY, 1,8-
Ac2PY, and 1,3-Ac2PY in the following relative yields:
50.4:18.0:11.4:19.2:3:0. The reaction of pyrene with acetyl
chloride in an ionic liquid, e.g.,1-methyl-3-ethylimidazolium
chloride-aluminum(III) chloride (20 °C, 2 h), gave 1,6-Ac2PY
and 1,8-Ac2PY (major products) and 1-AcPY (minor product)
The Friedel-Crafts acyl rearrangements of the diacetylpyrenes
and dibenzoylpyrenes have been carried out in PPA under
argon at various temperatures (80–120 °C) and for mostly
8–9 h, according to the representative procedure described in
the “Experimental” section.

Struct Chem
Fig. 2 Benzoylpyrenes and
dibenzoylpyrenes
[26]. 2,7-Ac2PY has not undergone any isomerization; in-
stead, it has undergone deacetylation to pyrene in very low
relative yields, even at 140 °C.
fluorobenzoyl)pyrene (1-4'FBzPY) and at elevated temperatures (≥
140 °C), the Scholl reaction products 8H-dibenzo[def,qr]chrysen-8-
one (2) and11H-indeno[2,1-a]pyren-11-one (2), both formed
from 1-BzPY, and pyranthrene-8,16-dione (3) (aka
pyranthrone, Vat Orange 9, 1,2,7,8-dibenzanthanthrene-6.12-
dione) (Fig. 3) (vide infra). The ratios of the products of 1,6-
Ac2PY and 1,8-Ac2PY are given in Tables 3 and 4.
1,6-Bz2PY isomerization: At 80 °C (12 h), 1,6-Bz2PY
isomerized to 1,8-Bz2PY; their ratio was 40:15, respectively.
The ratios of 1-BzPY, pyrene, and benzene were 30:10:5. The
total yield was 90%. At 120 °C (12 h), 1,6-Bz2PY isomerized
to 1,8-Bz2PY; their ratio was 35:5, respectively. The ratios of
1-BzPY, pyrene, and benzene were 45:10:5. The total yield
Dibenzoylpyrenes
The Friedel-Crafts acyl rearrangements of dibenzoylpyrenes
and bis(4-fluorobenzoyl)pyrenes were carried out with 1,6-
Ac2PY, 1,8-Ac2PY, 1,6-4'FBz2PY, and 1,8-4'FBz2PY in
PPA. The composition of the reaction products included in
addition to the two dibenzoylpyrene isomers and the two
bis(4'-fluorobenzoyl)pyrene isomers; the products of
deacelations, pyrene, 1-benozylpyrene (1-BzPY), and 1-(4'-

Struct Chem
Table 1 Friedel-Crafts rearrangements of diacetylpyrenes in PPA, ratios of products
Starting material
T °C
hr
Pyrene
1-AcPY
2-AcPY
1,6-Ac2PY
1,8-Ac2PY
1,3-Ac2PY
2,7-Ac2PY
1,6- Ac2PY
1,6- Ac2PY
1,6- Ac2PY
1,8- Ac2PY
1,8- Ac2PY
1,8- Ac2PY
1,3- Ac2PY
1,3- Ac2PY
1,3- Ac2PY
2,7-Ac2PY
2,7-Ac2PY
2,7-Ac2PY
80
9
9
9
8
8
8
8
8
8
7
9
10
2.3
86.9
82.6
4.6
0.0
0.2
0.3
0.0
0.4
0.3
0.0
0.0
0.4
0.0
0.0
0.0
3.8
3.1
1.2
2.7
1.8
0.5
0.8
1.3
1.9
0.0
0.0
0.0
5.6
3.2
0.0
15.1
7.1
4.9
0.7
1.6
0.4
0.0
0.0
0.0
1.4
1.8
0.0
0.0
0.0
0.0
39.0
23.7
2.6
0.0
0.0
0.0
0.0
100
120
80
9.8
0.0
93.9
2.3
0.0
78.8
37.5
6.9
0.0
100
120
80
53.2
87.4
1.1
0.0
0.0
58.5
71.4
52.0
0.0
0.0
100
120
100
120
140
2.0
0.0
40.7
2.7
0.0
97.3
97.8
95.2
2.2
0.0
4.8
0.0
was 80%. At 60–120 °C, Scholl reaction products were not
formed. At elevated temperatures (140–200 °C), 1,8-Bz2PY
was absent, whereas the Scholl reaction products 1, 2, and
pyranthrone (3) were obtained. Their ratios at 200 °C (12 h)
were 30: 60:10; total yield was 90%.
1,8-Bz2PY isomerization: At 80 °C (12 h), 1,8-Bz2PY
isomerized to 1,6-Bz2P; their ratio was 20:30, respectively.
The ratios of 1-BzPY, pyrene, and benzene were 40:9:1. The
total yield was 96%. At 120 °C (12 h), 1,8-Bz2PY isomerized
to 1,6-Bz2PY; their ratio was 10:40, respectively. The ratios of
1-BzPY, pyrene, and benzene were 40:8:2. The total yield was
93%. At 60–120 °C, Scholl reaction products were not
formed. At 140–200 °C, 1,6-Bz2PY was not isolated, whereas
the Scholl reaction products 1, 2, and pyranthrone (3) were
formed. Their ratios at 200 °C (12 h) were 30:60:10; total
yield was 93%.
difference may be due to the lower stability of acetylium
ion, formed in the initial deacetylation reactions, as compared
with the stability of benzoylium ion, formed in the initial
debenzoylation reactions. The results indicate a Friedel-
Crafts acyl rearrangement reaction, both directions [25]: 1,6-
Bz2PY ⇄ 1,8-Bz2PY. At elevated temperatures, the
dibenzoylpyrene isomers did not survive, and the Scholl reac-
tion pathway in PPA proved to be dominant.
The double Scholl reactions of both 1,6-Bz2PY and 1,8-
Bz2PY in PPA at elevated temperatures (140–200 °C) gave
the vat dyestuff pyranthrene-8,16-dione (3) (aka pyranthrone,
Vat Orange 9, 1.2.7,8-dibenzanthanthrene-6,12-dione, CAS
128-76-1) [4, 27–30]; the expected 6-member ring product
of 1,6-Bz2PY. Tribenzo[a,ghi,o]perylene-7,16-dione (4) (aka
allo-ms-naphthodianthrone, CAS 158626-29-0) [29–32], the
expected 6-member ring product of 1,8-Bz2PY, and the corre-
sponding 5-member ring products were not formed at all in
these double Scholl reactions. In both cases, due to an initial
mono-debenzoylation, 1 and 2, the mono-cyclization products
of 1-BzPY [22], were also formed. At 160 °C, the yields of 3,
The relative yields of the isomerization reactions 1,6-
Bz2PY➔1,8-Bz2PY and 1,8-Bz2PY➔1,6-Bz2PY were con-
siderably higher than the corresponding relative yields of
1,6-Ac2PY➔1,8-Ac2PY and 1,8-Ac2PY➔1,6-Ac2PY. This
Table 2 Friedel-Crafts acyl rearrangements of diacetylpyrene isomers in PPA, ratios of isomers, and total yields of isomers
Starting isomers
T °C
hr
1,6-Ac2PY
1,8-Ac2PY
1,3-Ac2PY
Total yield
of isomers
1,6-Ac2PY
1,6-Ac2PY
1,6-Ac2PY
1,8-Ac2PY
1,8-Ac2PY
1,8-Ac2PY
1,3-Ac2PY
1,3-Ac2PY
1,3-Ac2PY
80
9
9
9
8
8
8
8
8
8
35.2
58.3
100
15.2
20.2
9.3
51.9
39.5
0.0
13.0
22.2
0.0
10.8
8.1
100
120
80
1.2
84.8
29.8
90.7
1.7
0.0
17.8
8.9
100
120
80
0.0
0.0
5.4
2.0
96.3
89
40.5
26.0
4.9
100
120
4.9
6.0
38.8
8.2
53.1

Struct Chem
Fig. 3 8H-
dibenzo[def,qr]chrysen-8-one (1),
11H-indeno[2,1-a]pyren-11-one
(2), pyranthrone (3),
phenanthro[1,10,9,8-
opqra]perylene-7,14-dione (4), 3-
benzoyl-8H-
dibenzo[def,qr]chrysen-8-one (5),
and 1-benzoyl-8H-
dibenzo[def,qr]chrysen-8-one (6)
Table 3 Friedel-Crafts acyl rearrangements of 1,6-Bz2PY in PPA (product ratios and total yields)
T (°C)
t
1,6-Bz2PY
1-BzPY
(ratio, %)
1,8-Bz2PY
(ratio, %)
Benzene
(ratio, %) (ratio, %)
Pyrene
2
1
Pyranthrone
Total yield,
(%)
(hr) (ratio, %)
(ratio, %) (ratio, %) (ratio, %)3
60
12
12
12
12
12
12
12
12
95
90
40
45
35
10
5
0
0
5
0
0
0
0
75
94
90
78
80
80
85
87
70
0
0
10
5
0
0
0
0
80
30
35
45
30
40
0
15
10
5
10
8
0
0
0
100
120
140
160
200
2
0
0
0
5
10
10
0
0
0
0
0
0
20
30
60
10
15
30
20
10
10
0
0
0
0
0
0

Struct Chem
Table 4 Friedel-Crafts acyl rearrangements of 1,8-Bz2PY in PPA (products ratios and total yields)
T(°C) t
1,8-Bz2PY
1,6-Bz2PY
(ratio, %)
1-BzPY
(ratio, %)
Benzene
(ratio, %)
Pyrene (ratio, 2 (ratio, 1 (ratio, Pyranthrone
Total
yield, (%)
(h) (ratio, %)
%)
%)
%)
(ratio, %)3
60
70
80
12 97
12 95
12 20
0
0
3
5
1
2
2
0
0
0
0
0
0
0
84
85
96
87
93
86
88
92
0
0
0
0
0
0
30
45
40
15
10
0
40
35
40
40
40
0
9
0
0
0
100 24 10
120 24 10
8
0
0
0
8
0
0
0
140 12
160 12
200 12
0
0
0
10
0
20
30
60
10
10
30
5
10
10
0
1, and 2 were 9%, 13%, and 29% (from 1,6-Bz2PY) and 9%,
9%, and 26% (from 1,8-Bz2PY), respectively. The results im-
ply that 1,8-Bz2PY has first undergone Friedel-Crafts acyl
rearrangement to 1,6-Bz2PY, before undergoing the double
Scholl reaction. Thus, these double Scholl reactions were
highly regioselective. It was the 1E,6E-conformer/diastereo-
mer of 1,6-Bz2PY that has undergone the double cyclization.
By the same token, it would have been the 1E,8E-conformer/
diastereomer of 1,8-Bz2PY that would have undergone the
double cyclization leading to tribenzo[a,ghi,o]perylene-7,16-
dione (4). It is interesting to note that pyranthrone (3) was also
formed, along with 1 and 2, in the reaction of 1-BzPY in PPA
at 140–220 °C. At 200 °C, its yield was 9%. This results
indicate a disproportionation of 1-BzPY to pyrene and 1,6-
Bz2PY (with the intermediate benzoylium ion), followed by a
double Scholl reaction of 1,6-Bz2PY to give pyranthrone (3).
Pyranthrone (3) was first reported by Scholl who originally
synthesized it by an alkali condensation of 2,2'-dimethyl-1,1'-
dianthraquinonyl, not by the Scholl reaction [27, 33]. Vollmann
et al. reported in 1937 that the Scholl reactions of 1,6-Bz2PY
and 1,8-Bz2PY in the classical AlCl3/NaCl melt [34, 35] under
oxygen with vigorous stirring at 140–160 °C gave pyranthrone
(3) in 80% and 20–25% yields, respectively [4] (see pages 40–
42 and 117–119). The authors clearly stated that allo-ms-
naphthodianthrone (4) was not formed in these reactions, noting
that the formation of pyranthrone from 1,8-Bz2PY can only be
explained by migration or elimination and readdition of a ben-
zoyl residue upon heating with AlCl3 [4]. According to a 1961
report, the Scholl reaction of 1,8-Bz2PY in AlCl3/NaCl melt
(120 °C, 4 h) gave pyranthrone (3) in 40.7% yield [36]. The
authors noted that benzoyl groups of the dibenzoylpyrene were
cleaved and substituted pyrene at additional positions.
However, in organic solvents, the mutual isomerization of
1,6-Bz2PY and 1,8-Bz2PY did not occur in the presence of
AlCl3 [36]. Pyranthrone (3) was also obtained directly from
pyrene with benzoyl chloride in AlCl3/NaCl melt (e.g., O2,
160 °C, 1 h, 50% yield) [37]. 1,6-Bz2PY and 1,8-Bz2PY were
putative intermediates in this 1932 patent procedure, which
serves as another piece of circumstantial evidence for the 1,8-
Bz2PY ➔ 1,6-Bz2PY acyl rearrangement. The synthesis and
2D structure of the orange allo-ms- naphthodianthrone (4) from
3,4-dimethyl-ms- benzodianthrone by treatment with alkaline
agents have previously been reported in the patent literature
[31], in Venkataraman’s monograph “The Chemistry of
Synthetic Dyes” [29] and in Clar’s monograph “Polycyclic
Hydrocarbons” [30]. It was briefly characterized by its colors
in concentrated sulfuric acid and as a vat dye, but its structure
has not been elucidated [31]. A following patent reported the
reactions of 4 with acidic reagents, e.g., AlCl3, to give the
dehydrogenation product “ms-anthradianthrone,” also a vat
dye [32]. “ms-anthradianthrone” is phenanthro[1,10,9,8-
opqra]perylene-7,14-dione (aka 4,11-bisanthenequinone, CAS
475-64-9). Allo-ms-naphthodianthrone is tribenzo[a,ghi,o]-
perylene-7,16-dione (4). Allo-ms-naphthodianthrone has been
tested on ovarieclomized rats for effective osestrogen activity
[38]. Turker referred to pyranthrone (3) and allo-ms-
naphthodianthrone (4) and noted that these compounds are
characterized by the same primary topological parameters and
exhibit powerful tendering action [39].
The constitutional isomers pyranthrone (3) and
tribenzo[a,ghi,o]perylene-7,16-dione (4) (allo-ms-
naphthodianthrone) differ in their spatial orientation: 3 adopts
a planar conformation (expectedly C2h) with two bay regions on
opposite sides, whereas 4 adopts a non-planar conformation
(expectedly C2). The non-planarity of 4 is due to an intramolec-
ular overcrowding in its single fjord region. It may be considered
a helicene, a bridged helianthrone, and a benzannelated
bianthrone, a prototype of bistricyclic aromatic enes [40].
1,6-4'FBz2PY and 1,8-4'FBz2PY isomerizations in PPA
1,6-4'FBz2PY: At 100 °C (4 h), 1,6-4'FBz2PY isomerized to
1,8-4'FBz2P; their ratio was 7:15, respectively. The corre-
sponding ratio of 1-4'FBzPY and pyrene was 50:0. At 120
°C (6 h), 1,6-4FBz2PY isomerized to 1,8-4'FBz2PY; their
ratio was 33:10, respectively. The ratio of 1-BzPYand pyrene
was 37:21. At 60–120 °C, Scholl reaction products were not
formed.

Struct Chem
1,8-4'FBz2PY: At 100 °C (6 h), 1,8-4'FBz2PY isomerized
to 1,6-4'FBz2P; their ratio was 24:30, respectively. The cor-
responding ratio of 1-4'FBzPY and pyrene was 46:0. At 120
°C (6 h), 1,8-4FBz2PY isomerized to 1,6-4'FBz2PY; their
ratio was 13:13, respectively. The ratio of 1-4'BzPY and
pyrene was 38:36. At 60–120 °C, Scholl reaction products
were not formed.
The results indicate a Friedel-Crafts acyl rearrangement
reaction, both directions [25]: 1,6-4'FBz2PY ⇄ 1,8-
4'FBz2PY.
(viii) 1-BzPY ➔ 8H-dibenzo[def,qr]chrysen-8-one (1) and
11H-indeno[2,1-a]pyren-11-one (2).
A note on reversibility
We use the terms “reversibility” and by inference “irreversibility”
according to their meaning revealed in two authoritative state-
ments on Friedel-Crafts Chemistry: Gore’s 1955 proposition
“The Friedel-Crafts acylation reaction of reactive aromatic hy-
drocarbons is a reversible process” [5] and Olah’s 1973 assertion
“acylation differs from alkylation in being virtually irreversible”
[14] (vide supra). Based on these statements, the Friedel-Crafts
acyl rearrangements of 1,6-Bz2PY and 1,8-Bz2PY are reversible
processes. IUPAC Green Book distinguishes between
“equilibrium reaction,” denoted by ⇌ and “reaction, both
direction,” denoted by ⇄ [25]. A reversible reaction means in
the present context, a “reaction, both directions” [25], involving
an acyl rearrangement, not necessarily a “completely reversible
reaction” [41, 42]. According to IUPAC Gold Book, “reversible
processes” (a term included in the definition of “chemical
equilibrium”) are “processes which may be made to proceed in
the forward or reverse direction by the (infinitesimal) change of
one variable” [43]. Such processes “ultimately reach a point
where the rates in both directions are identical, so that the system
gives the appearance of having a static composition at which the
Gibbs free energy, G, is a minimum. At equilibrium the sum of the
chemical potentials of the reactants equals that of the products”
[43]. Application of the distinction between “equilibrium reac-
tion” and “reaction, both direction” to the Friedel-Crafts acyl
rearrangements of 1,6-Bz2PYand 1,8-Bz2PYin PPA, as revealed
in the present study, leads to the conclusion that these rearrange-
ments are formally “reaction, both direction,” 1,6-Bz2PY ⇄ 1,8-
Bz2PY, not “equilibrium” reactions, 1,6-Bz2PY ⇌ 1,8-Bz2PY.
The Scholl reactions of 1,6-Bz2PY and 1,8-Bz2PY in PPA and
in AlCl3/NaCl are necessarily irreversible, due to their
dehydrogenation/aromatization steps.
Scholl reactions in AlCl3/NaCl
The Scholl reactions of 1,6-Bz2PY and 1,8-Bz2PY in the clas-
sical AlCl3/NaCl medium [34, 35] gave consistently at 140–
260 °C, the double-cyclization product pyranthrone (3) and the
mono-cyclization products of 1-BzPY, 1, and 2 in 1:2:4 ratios.
The total yields of the reactions were 56–74% (1,6-Bz2PY) and
61–80% (1,8-Bz2PY). The deacylation and isomerization prod-
ucts 1-BzPY, pyrene, and dibenzoylpyrene isomers were not
among the products of the reactions. Thus, 1,8-Bz2PY has first
undergone Friedel-Crafts acyl rearrangement to 1,6-Bz2PY,
followed by the double Scholl reaction to give pyranthrone
(3). Analogously to the reactions in PPA, these double Scholl
reactions in AlCl3/NaCl were highly regioselective.
Figure 4 depicts the pathways of the Scholl reactions of 1,6-
Bz2PY and 1,8-Bz2PY leading to pyranthrone (3), 8H-
dibenzo[def,qr]chrysen-8-one (1), and 11H-indeno[2,1-a-
]pyren-11-one (2) but not to tribenzo[a,ghi,o]perylene-7,16-
dione (4). I. (i) Isomerization of 1Z,6Z-Bz2PY to 1E,6E-
Bz2PY. (ii) Deacylation of 1E,6E-Bz2PY to 3-benzoyl-8H-
dibenzo[def,qr]chrysen-8-one (5) and benzoylium cation. (iii)
Scholl reaction of 3-benzoyl-8H-dibenzo[def,qr]chrysen-8-one
to pyranthrone (3). II. (iv) Isomerization of 1Z,8Z-Bz2PY to
1E,8E-Bz2PY. (v) Deacylation of 1E,8E-Bz2PY to 1-benzo-
yl-8H-dibenzo[def,qr]chrysen-8-one (6) and benzoylium cat-
ion. (vi) Scholl reaction of 1-benzoyl-8H-dibenzo[def,qr]-
chrysen-8-one to give tribenzo[a,ghi,o]perylene-7,16-dione
(4) (not observed). III. (vii) Isomerization of 1Z,8Z-Bz2PY to
1Z,6Z-Bz2PY then steps (i) –(III).
Conclusions
I.(i) 1Z,6Z-Bz2PY ⇌ 1E,6E-Bz2PY;
(ii)1E,6E-Bz2PY ⇌ 3E-benzoyl-dibenzo[dfe,qr]chrysene-
8-one (5) + benzoylium ion;
(iii) 3E-benzoyl-8H-dibenzo[def,qr]chrysen-8-one (5) ➔
pyranthrone (3).
II.(iv) 1Z,8Z-Bz2PY ⇌ 1E,8E-Bz2PY;
(v) 1E,8E-Bz2PY ⇌ 1E-benzoyl-dibenzo[def,qr]chrysene-
8-one (6) + benzoylium ion;
(vi) 3E-benzoyl-dibenzo[def,qr]chrysene-8-one (6) ➔
tribenzo[a,ghi,o]perylene-7,16-dione (4). (This step was not
observed experimentally).
III.(vii) 1Z,8Z-Bz2PY ⇌ 1-BzPY + benzoylium ion ⇌
1Z,6Z-Bz2PY then steps (i)-(iii).
The Friedel-Craft acyl rearrangements of the pairs [1,6- and
1,8-diacetylpyrenes], [1,6- and 1,8-dibenzoypyrenes], and
(1,6- and 1,8-bis(4'-fluorobenzoyl)pyrene] in PPA, where in
each pair, the two acyl groups are positioned farther away
from each other and are devoid of mutual resonance interac-
tions, resulted in reversible isomerizations, 1,6-Ac2PY ⇌ 1,8-
Ac2PY, 1,6-Bz2PY ⇌ 1,8-Bz2PY, and 1,6-4'FBz2PY ⇌ 1,8-
4'FBz2PY, albeit not in high yields. These results substantiate
Gore’s 1955 proposition that “The Friedel–Crafts acylation
reaction of reactive aromatic hydrocarbons is a reversible
process” (vide supra) [5]. Previously reported completely re-
versible Friedel-Crafts acyl rearrangements were cases of

Struct Chem
Fig. 4 Pathways of the Scholl
reactions of 1,6-Bz2PY and 1,8-
Bz2PY

Struct Chem
intramolecular isomerizations [41, 42]. By contrast, the isom-
erizations reported here are reversible intermolecular isomer-
izations. Moreover, at elevated temperatures (≥ 140 °C), in
PPA and in AlCl3/NaCl, 1,6-Bz2PY and 1,8-Bz2PY both
underwent a highly regioselective double Scholl reactions,
resulting in the formation of pyranthrone (3). Finally, the pres-
ent study confirms the linkage between Friedel-Crafts acyl
rearrangements and the Scholl reaction [20].
carried out by Dr. Carina Hazan and her team (ibid) with a
Perkin-Elmer 2400 series II Analyzer, (950–1000 °C) and by
Dr. Shoshana Blum and her team (ibid).
1,3-Diacetylpyrene (1,3-Ac2PY), 1,6- diacetylpyrene
(1,6-Ac2PY), and 1,8- diacetylpyrene (1,8-Ac2PY)
1,3-Ac2PY, 1,6-Ac2PY, and 1,8-Ac2PY were synthesized by
direct diacetylation of pyrene with acetyl chloride and AlCl3
according to the literature [45] (RT, 2 h) with certain modifi-
cations, using CH2Cl2 instead of CS2 as a solvent. The prod-
ucts consisted of a mixture of the three constitutional isomers
in 1:3:3 ratios, respectively. The isomers were separated by
column chromatography on silica, using a gradient of PE-
CH2Cl2 as eluent (3:7–8:3 ratio). Pure 1,6-Ac2PY and 1,8-
Ac2PY and mixtures of 1,3-Ac2PY/1,6-Ac2PY and 1,3-
Ac2PY/1,8-Ac2PY were obtained. These mixtures were sep-
arated by recrystallization from CH2Cl2 to give pure 1,3-
Ac2PY.
2,7-Ac2PY was synthesized in two steps from 4,5,9,10-
tetrahydropyrene according to the literature [46] with certain
modifications: (1) Friedel-Crafts diacetylation of 4,5,9,10-
tetrahydropyrene with acetyl chloride and AlCl3 in CH2Cl2 at
room temperature to give 2-acetyl-4,5,9,10-tetrahydropyrene
and 2,7-diacetyl-4,5,9,10-tetrahydropyrene; the two products
were separated by column chromatography on silica, using
CH2Cl2-PE as eluent; (2) aromatization of the diacetyl deriva-
tive, using 2,3-dichloro-5,6-dicyano-benzoquinone (DDQ) in
boiling benzene.
Experimental
General
Melting points are uncorrected. NMR spectra were recorded
with BrukerAvance II 500, AMX 400, and WH-200 spectrom-
eters; 1H-NMR spectra were recorded at 500.2 MHz, 400.13
MHz, and 200 MHz in CDCl3, as a solvent and as an internal
standard (δ(CHCl3) = 7.258 ppm, reference Me4Si). 13C-
NMR spectra were recorded using CDCl3 as solvent and as
internal standard, (δ(CDCl3) = 77.01 ppm). 13C-NMR (related
to Me4Si of 1H) = SF(500.2000104)MHz × χ(0.125504), 19F-
NMR spectra were recorded at using CDCl3 as solvent (refer-
ence CCl3F), 19F-NMR (related to Me4Si of 1H) =
SF(500.2000104)MHz × χ(0.94094011 [44]. Complete as-
signments were made through two dimensional correlation
spectroscopy (DQF-COSY, HSQC, HMBC, and NOESY).
The starting compounds and pyranthrone (3) were purchased
from Merck Sigma-Aldrich (formerly Merck KGaA and
Sigma-Aldrich Israel). PPA (94% weight of P2O5, ρ = 1.9
g/mL) was purchased from Arcos Organics™, Israel. The sol-
vents diethyl ether, petroleum ether (40–60 °C, PE) benzene,
toluene, and THF were purchased from Bio-LAB, Israel.
Column chromatography was carried out on Silica Gel 60
(0.063–0.200 mm) (Merck KGaA). TLC was performed on
silica plates Merck Art 5554, DC-Alufolien Kieselgel 60
F254. PLC was performed on silica gel 1-mm plates (0.063–
0.200 mm) (Merck KGaA). HPLC was carried out on Merck
Hitachi 655 instrument with a UV monitor (254 nm) connect-
ed to integrator p = 2000.The separations were performed by
injection of each sample (10 μ) to a Merck silica-gel
Lichrosorb 0 Si60 column (25 × 4 mm). The flow rate was 1
mm/sec. The eluent was CH2Cl2. The temperature range was
60–250 °C with ingredients of 10 °C/min. FTIR spectra were
recorded on an FT-IR BRUKERTENSOR II Platinum ATR
(solid state) spectrometer and on Perkin Elmar 157-G instru-
ment. UV-Vis spectra were recorded on a linear silicon CCD
detector spectrometer and on KONTRON UVIKON-8320
spectrometer. Mass spectrometry measurements were per-
formed by Dr. Carina Hazan (Analytical Chemistry
Laboratory, Institute of Chemistry, The Hebrew University
of Jerusalem) with 6520 QTOF LC/MS analyzer, using an
electrospray ionizing method. Elemental analyses were
The structures of 1,3-Ac2PY, 1,6-Ac2PY, 1,8-Ac2PY, and
1
2,7-Ac2PY were confirmed by melting points and H-NMR
spectra [45, 46].
Separation of a mixture of pyrene, acetylpyrene,
and diacetylpyrene isomers by HPLC (Fig. 5)
A mixture of pyrene, 1-AcPY, 2-AcPY, 1,6-Ac2PY, 2,7-
Ac2PY, 1,3-Ac2PY, and 1,8-Ac2PY was successfully separat-
ed into its components by HPLC (silica-gel column, CH2Cl2
eluent, flow rate 1 ml/sec). The retention times were 2.57,
6.24, 5.78, 12.89, 15.54, 16.44, and 26.25 min, respectively.
The compositions (relative %) of the crude mixture of reac-
tants and products of the Friedel-Crafts acyl rearrangement
reactions of the diacetylpyrenes in PPA (after workup) were
determined by HPLC. The compositions (yields) of reactants
and products of the Friedel-Crafts acyl rearrangement reac-
tions and of the Scholl reactions in AlCl3/NaCl of 1,6-
Bz2PYand 1,8-Bz2PYin PPA (after column chromatography)
were determined on the basis of the weights of isolated
products.

Struct Chem
1
2.57
1. Pyrene
2. 1-Acetylpyrene (1-AcPY)
3. 2-Acetylpyrene (2-AcPY)
4. 1,6-diacetypyrene (1,6-Ac2PY)
5. 2,7-diacetypyrene (2,7-Ac2PY)
6. 1,3-diacetypyrene (1,3-Ac2PY)
7. 1,8-diacetypyrene (1,8-Ac2PY)
3
5.7
2
4
5.24
12.09
6
7
5
16.44
26.25
15.54
Fig. 5 HPLC chromatogram of a mixture of pyrene, acetylpyrene, and diacetylpyrene isomers
1,6-dibenzoylpyrene (1,6-Bz2PY) and 1,8-dibenzoylpyrene
(1,8-Bz2PY)
1,6-4'FBz2PY and 1,8-4'FBz2PY were synthesized by di-
rect Friedel-Crafts dibenzoylation of pyrene with 4-
fluorobenzoyl chloride and AlCl3 (1.0:2.3:2.3) in
CH2Cl2.under anhydrous conditions, starting at 5 °C then at
RT (2 h). The crude product after workup consisted of 1,6-
4'FBz2PYand 1,8-4'FBz2PY in 58:42 ratio. Recrystallization
first from benzene then from ethanol gave 1,6-4'FBz2PY, yel-
low crystals, m.p. 257–258 °C, and 1,8-4'FBz2PY, yellow
crystals, m.p. 187.5–189 °C, in 43.0% and 30% yields, respec-
tively. Their structures were substantiated by elemental anal-
ysis, 1H-, 13C-,19F-NMR, IR, and mass spectra (vide infra).
8H-Dibenzo[def,qr]chrysen-8-one (1) and 11H-
indeno[2,1-a]pyren-11-one (2) were synthesized by the
Scholl reaction of 1-benzoulpyrene (1-BzPY) in AlCl3/NaCl
according to the literature [22].
1,6-Bz2PYand 1,8-Bz2PY were synthesized by two methods:
(1) Direct dibenzoylation of pyrene with benzoyl chloride and
AlCl3 according to the literature [45] (− 5 °C, 3 h) with certain
modifications, using CH2Cl2 instead of CS2 as a solvent. The
product consisted of a mixture of the two constitutional iso-
mers in 3:2 ratio, respectively. Pure 1,6-Bz2PY was obtained
by recrystallization from benzene; yield, 30%. When the re-
action was carried out at room temperature, pure 1,8-Bz2PY
was obtained in 20% yield, using column chromatography on
silica. (2) Benzoylation of 1-BzPY in CH2Cl2 (benzoyl chlo-
ride, AlCl3, RT 4 h). The two dibenzoylpyrene isomers (1:1
,
ratio) were separated by column chromatography on silica
(TLC Rf = 0.29 and 0.24). The yields were 37% (1,6-
Bz2PY) and 31% (1,8-Bz2PY).The structures of 1,6-Bz2PY
and 1,8-Bz2PY were confirmed by melting points, 1H-NMR
spectra [45], and elemental analyses.
Representative procedures
1-(4'-Fluorobenzoyl)pyrene (1-4'FBzPY)
1-(4'-Fluorobenzoyl)pyrene (1-4'FBzPY),
1,6-bis(4'-fluorobenzoyl)pyrene (1,6-4'FBz2PY)
and 1,8-bis(4'-fluorobenzoyl)pyrene (1,8-4'FBz2PY)
AlCl3 (3.29 gr, 24.71 mmol) was suspended in dry CH2Cl2
and treated dropwise with 4-fluorobenzoyl chloride (3.0 ml,
24.71 mmol) at RT. Pyrene (5 gr, 24.71 mmol) was then added
in one portion, and the reaction mixture was left with stirring
for 2 h at RT. After workup, the crude product was purified by
recrystallization from PE to give 1-4'FBzPY (5.0 gr) as yel-
low powder, m.p. 136.5–137.5 °C yield 62.4%; m.p. 136.5–
137.5 °C. TLC Rf = 0.49. A single crystal of 1-4F'BzPY was
obtained by recrystallization from CHCl3.
1-4'FBzPY was synthesized by direct Friedel-Crafts mono-
benzoylation of pyrene with 4-fluorobenzoyl chloride and
AlCl3 (1:1:1) in CH2Cl2 under anhydrous conditions (RT, 2
h). Recrystallization from PE gave 1-4'FBzPYas yellow pow-
der, m.p. 136.5–137.5 °C, in 62% yield. Its structure was
substantiated by elemental analysis, 1H-, 13C-,19F-NMR, IR,
and mass spectra (vide infra).
Anal. calculated for C23H13FO: C = 85.17%, H = 4.04%, F
= 5.86%. Found: C = 84.83%, H = 4.41%, F = 5.40% MS, m/z

Struct Chem
= 325.10 (M + 1); IR, 1637.06 cm−1 (C=O); UV/VIS (nm):
395.0, 368.0, and 333.0. 1H-NMR (CDCl3, δ ppm: 8.31 (d, 3J
= 9.0 Hz, 1H, H10), 8.27 (d, 3J = 7.5 Hz, 1H, H6), 8.24 (d, 3J
= 7.0 Hz, 1H, H8), 8.21 (d, 3J = 7.5 Hz, 1H, H3), 8.19 (d, 3J =
9.0 Hz, 1H, H5), 8.12 (dd,3J = 9.0 Hz, 4J = 1.5 Hz, 2H, H4,
H9), 8.07 (t, 3J = 7.5 Hz, 3 J = 8.0 Hz, 1H, H7), 8.06 (d, 3J =
8.0 Hz, 1H, H2), 7.93 (2d, 3J = 9.0 Hz, 3J = 9.0 Hz, 2H, H2`,
residue was recrystallized from EtOH to give 1,8-4'FBz2PY
(4.0 gr) as a yellow solid, m.p. 187.5–189 °C, yield 30.0%,
TLC Rf = 0.25. A single crystal was obtained by recrystalli-
zation from EtOAc.
Anal. calculated for C30H16F2O2: C = 80.71%, H = 3.61%,
F = 8.51%. Found: C = 79.95%, H = 3.43 and F = 8.23%. MS,
m/z = 447.11(M + 1), 448.122 (M + 2); IR, 1647.90 cm−1
(C=O); UV/VIS (nm): 396.00, 368.00 and 328.00.
1H-NMR (δ CDCl3), ppm): 8.30 (d,3J = 7.5 Hz, 2H, H3,
H6), 8.27 (s, 2H, H9, H10), 8.23 (s, 2H, H4, H5), 8.11 (d, 3 J =
8.0 Hz, 2H, H2, H7), 7.90 (2d, 3 J = 8.5 Hz, 3J = 9.0 Hz, 4H,
H2`, H2``, H6`, H6``), 7.15 (t, 3J = 8.5 Hz, 3J = 9.0 Hz, 4H,
H3`, H3``, H5`, H5``).
H6`), 7.15 (t, J = 9.0 Hz, J = 8.5 Hz, 2H, H5`, H3`). 13C-
NMR (CDCl3, δ ppm): 196.81 (C11), 167.37 (C4`), 135.15
(C1`), 133.19 (C2`, C6`), 133.04 (C3a), 132.88 (C1), 131.21
(C5a), 130.69 (C8a), 129.66 (C10a), 129.2 (C5), 128.96 (C9),
127.18 (C4), 126.66 (C2), 126.47 (C7), 126.14 (C6), 125.99
(C8), 124.84 (C10b), 124.59 (C10), 124.44 (C10c), 123.82
(C3), 115.65 (C3`, C5`). 19F-NMR (CDCl3, δ ppm): − 104.88.
3
3
13C-NMR (δ CDCl3, ppm): 196.53 (C11, C11`), 165.97
(C4`, C4``), 134.81(C1`, C1``), 133.95 (C1, C8), 133.22
(C2` ,C2``, 152 C6`, C6``), 133.06 (C3a, C5a), 129.04
(C10a, C8a), 128.92 (C4, C5), 126.98 (C7, C2), 126.03 (C9,
C10), 125.05 (C3, C6), 124.64 (C10b, C10c), 115.78 (C3`,
C3``, C5`, C5``).
1,6-Bis(4'-fluorobenzoyl)pyrene (1,6-4'FBz2PY)
and 1,8-bis(4'-fluorobenzoyl)pyrene (1,8-4'FBz2PY)
To a cooled suspension of AlCl3 (7.5 gr, 56.8 mmol) in dry
CH2Cl2 (100 ml) at − 5 °C, 4-fluorobenzoyl chloride (6.7 ml,
56.8 mmol) was added followed by pyrene (5 gr, 24.72 mmol)
in one portion. The reaction was stirred at − 5 °C, then grad-
ually warmed to RT, and left with stirring for 2 h at RT. After
workup, the crude product was consisted of 1,6-4'FBz2PY
and 1,8-4'FBz2PY in the ratio 58:42.
19F-NMR (δ CDCl3, ppm): − 104.331.
Friedel-Crafts acyl rearrangement of a selected
diacetylpyrene isomer in PPA The reaction was carried out in
a 100-ml double-neck round-bottomed flask equipped with a
magnetic stirrer and a reflux condenser with a CaCl2 drying
tube. PPA (40 g) was placed in the reaction flask and stirred at
RT for a few minutes, and the temperature was raised to 100
°C. A diacetylpyrene isomer was added, and the reaction mix-
ture was stirred for, e.g., 8 h. The reaction mixture was then
poured into ice-cooled dilute aqueous HCl solution (1 M) and
stirred overnight. CH2Cl2 (150 ml) was added and the organic
crude product was extracted. The organic and aqueous phases
were separated; the organic phase was washed several times
with water, dried over MgSO4; and the solvent was evaporat-
ed in vacuum (i.e., workup). The content of the crude product
1,6-4'FBz2PY
Recrystallization of the crude product from benzene gave 1,6-
4'FBz2PY (4.7 gr) as a yellow solid, m.p. 257–258 °C, yield
43.0%; TLC Rf = 0.33. A single crystal of 1,6-4'FBz2PY was
obtained by recrystallization from EtOAc.
Anal. calculated for C30H16F2O2: C = 80.71%, H = 3.61%,
F = 8.51%. Found: C = 78.17%, H = 3.49%, F = 7.91%. MS,
m/z = 447.11(M + 1), 448.122 (M + 2); IR, 1645.3 cm−1
(C=O); UV/VIS (nm): 395.00, 368.00, and 340.00.
1H-NMR (δ CDCl3, ppm): 8.39 (d, 3J = 9.5 Hz, 2H, H5,
H10), 8.27 (d, 3J = 8.0 Hz, 2H, H3,H8), 8.16 (d, 3J = 9.5 Hz,
2H, H4, H9), 8.11 (d, 3J = 8.0 Hz, 2H, H2 , H7), 7.94 (2d, 3J =
9.0 Hz, 3 J = 9.0 Hz, 4H, H2`, H2``,H6`, H6``), 7.17 (t, 3J =
8.5 Hz, 3J = 8.5 Hz, 4H, H3`,H3``, H5`, H5``).
1
was qualitatively examined by H-NMR and TLC. The
quantative composition (relative yield %) of the crude mixture
of reactants and products of the Friedel-Crafts acyl rearrange-
ment reactions of the diacetylpyrene isomer in PPA (after
workup) was determined by HPLC.
13C-NMR (δ CDCl3), ppm: 196.61 (C11, C11`), 165.98
(C4`,C4``),134.86 (C1`, C1``), 134.01 (C1, C6),133.27 (C2`,
C2``, C6`, C6``), 132.51 (C3a , C8a), 129.65 (C10a, C5a),
128.72 (C4, C9), 128.33 (C10c), 127.02 (C7, C2), 126.25
(C5, C10), 124.83 (C3, C8), 124.83 (C10b), 115.79 (C3`,
C3``, C5`, C5``).
Friedel-Crafts acyl rearrangement of 1,6-dibenzoylpyrene
(1,6-Bz2PY) in PPA The reaction was carried out under argon
atmosphere in a 150-ml round-bottomed flask equipped with a
magnetic stirrer, a Y adaptor, a reflux condenser, and a ther-
mometer. PPA (40 g) was placed in the reaction flask and
stirred at RT for a few minutes. 1,6-Bz2NA (0.3 g mmol)
was added and the mixture stirred for 6 h at 160 °C. The
reaction mixture was then poured into ice-cooled dilute aque-
ous HCl solution (1 M) and stirred overnight. CH2Cl2 (150
ml) was added and the organic crude product was extracted.
The organic and aqueous phases were separated; the organic
phase was washed with aqueous sodium bicarbonate and
19F-NMR (δ CDCl3, ppm: − 104.305.
1,8-4'FBz2PY
The filtrate from the recrystallization of the mixture of isomers
was evaporated to dryness under reduced pressure, and the

Struct Chem
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C,88.61; H.3.50. HRMS (O-TOF)ESI m/z: calculated for
C30H12O ([M+]-H2O): 388.08827; Found: 388.088479.
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UV-VIS (DMSO): λ, nm (ε, M−1 cm−1) 331(39,780), 425
(20,410), 449 (21,590), 479 (27,430).
1
All data of the latter compound, including H-NMR and
13C-NMR spectra, were essentially identical with the corre-
sponding data of authentic sample of pyranthrone (3) synthe-
sized by the Scholl reaction of 1,6-Bz2PY in AlCl3/NaCl,
The compositions (yields) of reactants and products of the
Friedel-Crafts acyl rearrangement reactions and of the Scholl
reactions in of 1,6-Bz2PY and 1,8-Bz2PY in PPA (after col-
umn chromatography) were determined on the basis of the
weights of isolated products.
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Compliance with ethical standards
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interest.
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