Superacid-catalyzed dimerization/cyclization of isopropenyl-PAHs - Novel pathways to PAH dimers, phenalenes and their stable carbocations

Article abstract of DOI:10.1002/ejoc.200800252

The isopropenyl derivatives of representative classes of polycyclic aromatic hydrocarbons (PAHs) having four and five fused-ring systems, namely pyrene, chrysene, benzo[c]phenanthrene (BcPh), dibenzo[a,c]anthracene (benzo[f]tetraphene) and perylene, were synthesized by Wittig olefination from the corresponding acetyl-PAHs. Under the influence of triflic acid (TfOH), the isopropenyl derivatives were converted to novel PAH dimers and/or phenalenes in a simple one-pot procedure. A plausible mechanism for this process has been outlined, and the synthetic scope of this chemistry has been explored. Structural features in the PAH dimers were examined by DFT. As representative initial and final carbocation intermediates in the reaction sequence, stable carbocations derived from 3-isopropenylperylene and from 4,6,6-trimethyl-6H- dibenzo[a,kl]anthracene were generated and studied directly by NMR spectroscopy. The NMR characteristics and charge delocalization modes in the resulting benzylic carbocations are discussed. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200800252

FULL PAPER
DOI: 10.1002/ejoc.200800252
Superacid-Catalyzed Dimerization/Cyclization of Isopropenyl-PAHs –
Novel Pathways to PAH Dimers, Phenalenes and Their Stable Carbocations
[a]
[a]
[a]
[a]
Cédric Brulé, Fatima Sultana, Sandro Hollenstein, Takao Okazaki, and
[a]
Kenneth K. Laali*
Keywords: Polycyclic aromatic hydrocarbons / Wittig olefination / Superacids / Carbocations / Phenalenes
The isopropenyl derivatives of representative classes of poly-
cyclic aromatic hydrocarbons (PAHs) having four and five
fused-ring systems, namely pyrene, chrysene, benzo[c]phen-
anthrene (BcPh), dibenzo[a,c]anthracene (benzo[f]tetra-
phene) and perylene, were synthesized by Wittig olefination
from the corresponding acetyl-PAHs. Under the influence of
triflic acid (TfOH), the isopropenyl derivatives were con-
verted to novel PAH dimers and/or phenalenes in a simple
one-pot procedure. A plausible mechanism for this process
has been outlined, and the synthetic scope of this chemistry
has been explored. Structural features in the PAH dimers
were examined by DFT. As representative initial and final
carbocation intermediates in the reaction sequence, stable
carbocations derived from 3-isopropenylperylene and from
4,6,6-trimethyl-6H-dibenzo[a,kl]anthracene were generated
and studied directly by NMR spectroscopy. The NMR charac-
teristics and charge delocalization modes in the resulting
benzylic carbocations are discussed.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
Introduction
In the course of studying regioisomeric α-PAH-substi-
+
tuted carbocations (PAH-C R ) as models for PAH-epox-
2
[1–4]
[5]
ide ring opening,
formation of 2-(phenanthren-9-yl)propan-2-carbenium ion
from the corresponding carbinol (Scheme 1). Upon rais-
ing temperature, 2 is easily cyclized to give the 5,6-dihydro-
H-benzanthracen-4-ium ion 3, leading to the isolation of
we reported a communication on the
2
4
the phenalene 4 on quenching. Attempted conversion of
carbinol 1 to the corresponding chloro derivative led in-
stead to elimination and formation of the isopropenyl deriv-
ative 5, which on treatment with FSO H, either in SO ClF
Scheme 1. Facile formation of the cyclized carbocation 3 from 1
and from 5.
3
2
or in CH Cl at low temperature, led to clean formation
2
2
of the cyclized carbocation 3, which furnished the cyclized
[
5]
compound 4 upon quenching in nearly quantitative yield.
+
cation 8H , formed through protonation–deprotonation
Based on a number of control experiments, the mecha-
nism outlined in Scheme 2 was proposed for this superacid-
catalyzed dimerization/cyclization sequence starting from 1
or 5. Condensation of carbocation 2 (formed either by
ionization of 1 or by protonation of 5) with the isopropenyl
derivative 5 (formed by elimination from 2 upon raising the
temperature) serves as a key step in the formation of a di-
mer cation 6 (not directly detected by NMR in the stable
ion experiment), which is subsequently cyclized, leading to
the dimer carbocation 7. The ipso-protonated dimer carbo-
equilibrium on raising the temperature, is considered a key
intermediate en-route to the phenalene carbocation 3. The
relative stability of dimer 8 in the superacid and its equilib-
rium protonation determines the relative proportion of di-
meric product 8 to phenalene product 4 (this sequence leads
to a 50% maximum yield of 4 based on either 1 or 5). Under
equilibrium conditions, the carbocation 8H+ formed by
ipso-protonation yields the phenalenyl cation 3, and sub-
sequently the hydrocarbon 4 upon quenching. This process
generates one equivalent of phenanthrene, which is proton-
ated in-situ and polymerized (therefore not detected by
NMR in this case). The dimer carbocation 8H+ was not
observed in direct stable ion studies, as it converted rapidly
to the observed carbocation 3. Therefore, no PAH dimer
was isolated from compound 1 or 5 by superacid-catalysis.
[5]
[
a] Department of Chemistry, Kent State University,
Kent, OH 44242, USA
Fax: +1-330-672-3816
E-mail: klaali@kent.edu
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
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Contributions to Polycyclic Aromatic Hydrocarbon Chemistry
Scheme 2. Suggested mechanism for the dimerization/cyclization steps via 2 leading to 8 and 4.
However, dimer 8 had been obtained and isolated by using Results and Discussion
[6]
TiCl4 in CH Cl , with no phenalene 4 being formed.
2
2
Therefore, the ease of formation and relative stability of the
ipso-protonated dimer carbocation under equilibrium con-
ditions could determine the dimer to phenalene product ra-
tios.
Synthesis of the Isopropenyl-PAHs
The isopropenyl derivatives of 1-acetylpyrene (9), 4-ace-
tylpyrene (10), 6-acetylchrysene (11), 5-acetylbenzo[c]phen-
The present study sought to address the scope of this anthrene (12), 10-acetyldibenzo[a,c]anthracene (13), and 3-
simple one-pot process as a protocol for the synthesis of acetylperylene (14) (see Figures 1 and 2), were successfully
novel PAH dimers and/or phenalenes from representative synthesized in reasonable yields by Wittig olefination, em-
classes of large PAHs. Since ease of generation of the ipso- ploying the phosphonium ylide Ph P=CH , made from
3
2
protonated dimer under equilibrium protonation conditions methyltriphenylphosphonium bromide and sodium amide
is expected to vary significantly from one PAH to another, in THF. Among the acetylated derivatives, compound 13
due to variations in relative arenium ion energies, it was of was previously unknown. In the dibenzo[a,c]anthracene
interest to explore the relationship between the PAH struc- skeleton, electrophilic attack is typically directed to the
ture and the dimer to phenalene product ratios.
meso-position (C-9). This has been shown in stable ion pro-
Figure 1. Acetyl-PAHs employed in the study.
Eur. J. Org. Chem. 2008, 3700–3708
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C. Brulé, F. Sultana, S. Hollenstein, T. Okazaki, K. K. Laali
FULL PAPER
[
6]
tonation
as well as in nitration and bromination with Reaction of Isopropenyl-PAHs with TfOH
[7]
NBS, whereas bromination with Br in CH Cl led to the
0-bromo derivative. In the present study, under classical
Friedel–Crafts acetylation conditions (MeCOCl/AlCl ), the
0-acetyl derivative 13 was obtained quantitatively. Acety-
lation at C-10 exerts a strong peri-deshielding effect on H-
, which appears as a singlet at δ = 10.26 ppm.
2
2
2
[7]
1
The isopropenyl-PAHs shown in Figure 2 were treated
3
with TfOH in CH Cl initially at –78 °C, and after few min-
2
2
1
utes the reaction mixtures were allowed to warm up to –10
C. The progress of the reactions was monitored by TLC,
°
9
and the reactions were quenched when no further changes
in the dimer/phenalene ratios were observed under these
conditions.
The 1-isopropenylpyrene 9a gave the dimer 9b as the
main product (which was isolated), along with minor
amounts of the phenalene 9c and parent pyrene (which were
detected in the NMR of the crude reaction mixture before
purification) (see Scheme 3 and Figure S1–S2 in the Sup-
porting Information). Unfortunately, it was not possible to
isolate and purify compound 9c from the mixture consisting
of unreacted 9a and parent pyrene.
The 4-isopropenylpyrene 10a was efficiently converted to
dimer 10b as the major product along with the phenalene
10c as the minor product (together with 1 equivalent of
pyrene) (see Scheme 3 and Figure S3–S4).
Product distributions observed with 9a and 10a indicate
that once formed, the dimer-PAHs are relatively stable in
TfOH, and that the subsequent steps leading to phenalenes
have relatively high activation barriers under these reaction
conditions. This is unlike the situation with 9-isopropenyl-
Figure 2. The synthesized isopropenyl derivatives.
[5]
phenanthrene (Scheme 1), whereby cyclization was rapid
and no dimer survived. Based on the relative pyrenium ion
[8]
Formation of the corresponding isopropenyl derivatives stabilities , formation of the requisite ipso-protonated
1
9
a–14a was readily apparent in the H NMR spectra during carbocation from 9b (α position of pyrene) should be more
Wittig olefination, by the appearance of two distinct ole- favorable than 10b (protonation at the α,β position). This
finic proton signals (multiplets), typically in the 5.2 to 5.6 appears to be consistent with the increased formation of 9c
ppm range. The NMR spectroscopic data, including spe- relative to 10c in the product mixture in the low-tempera-
cific assignments based on 2D-NMR (for 10a–14a), are ture experiments (see Scheme 3). In the case of previously
[5]
gathered in the Exp. Section.
studied 9-isopropenylphenanthrene, the observed rapid
Scheme 3. Dimerization/cyclization of 9a and 10a.
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Contributions to Polycyclic Aromatic Hydrocarbon Chemistry
conversion to carbocation 3 via 8H+ can be rationalized favorable energetics of the chrysenium ion of protonation
[9,10]
because it involves ipso-protonation at the meso-position at C-6.
The DFT-optimized structure of 11b is shown
which is energetically favorable over other alternatives. in Figure S5. The computed angles between the average pla-
Specific NMR assignments for the dimeric compounds nes of the benzene rings in the optimized structures of 9b,
b and 10b are gathered in Figure 3, along with relative 10b, and 11b (Table S1, Supporting Information) indicate
9
stereochemistry deduced from NOE experiments. that the pyrene and the chrysene skeletons remain planar
Since attempts to grow suitable crystals from 9b and 10b in these dimers.
for X-ray analysis were unsuccessful, their structures were
A similar reaction of 5-isopropenylbenzo[c]phenanthrene
optimized by DFT (Figure S5). In the optimized structures, 12a with TfOH resulted in the isolation of the correspond-
the trimethylcyclohexenyl rings have envelope conforma- ing phenalene 12c in good yield along with benzo[c]phenan-
tions and their axial methyl groups are close to each other. threne BcPh (Scheme 4 and Figure S6–S7). No 12b was iso-
The distance between the equatorial methyl carbon and the lated from the reaction mixture following the work-up. Fac-
axial hydrogen is 0.3–0.4 Å smaller than that between the ile conversion of 12b to 12c under equilibrium protonation
equatorial methyl carbon and the equatorial hydrogen. conditions may be traced to the highly favorable energetics
[10,11]
These geometrical features are consistent with NOE experi- of C-5 protonation in the BcPh moiety.
The DFT-opti-
ments. mized structure of 12b is shown in Figure S5. In this case,
Reaction of 5-isopropenylchrysene 11a with TfOH re- both BcPh units are severely distorted, the largest angles
sulted in the formation of the corresponding phenalene 11c are found between A/D, A/C and B/D rings (see Table S1).
in 49% yield, with only traces of the dimeric product 11b
Reaction of 10-isopropenyldibenzo[a,c]anthracene 13a
being detected in the crude reaction mixture at completion with TfOH resulted in the isolation of the dimer 13b in
of the reaction. Facile conversion of 11b to 11c reflects the good yields, along with the cyclized phenalene 13c as minor
Figure 3. Specific NMR assignments (by 500 MHz NMR), including relative stereochemistry, for the dimers 9b and 10b.
Eur. J. Org. Chem. 2008, 3700–3708
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C. Brulé, F. Sultana, S. Hollenstein, T. Okazaki, K. K. Laali
FULL PAPER
ring angles indicate some distortion from planarity in one
perylene unit (see Table S1).
Electrophilic attack in the perylene skeleton is directed
[12]
to C-3/C-4/C-9/C-10.
Availability of unsubstituted C-4/
C-9/C-10 positions in the perylene moiety of 14b likely
makes the formation of the requisite ipso-protonated carbo-
cation less likely under equilibrium conditions, leading to
minor formation of the phenalene 14c.
Interestingly, it was possible to force the dimer 14b to
react further, when, in a small-scale control experiment, an
authentic sample of 14b was allowed to react with TfOH in
CH Cl and the temperature was raised up to room temp.
2
2
(the color of the solution changed from deep green to deep
Scheme 4. Dimerization/cyclization of 11a and 12a (dimers 11b and blue). Analysis (TLC and NMR) of the reaction mixture
1
2b were not observed).
showed that the dimer was fully consumed, and a 1:1 mix-
ture of 14c and perylene was formed (75% yield; see Figure
S11).
product (Scheme 5 and Figure S8–S9). Inefficient conver-
sion of 13b to 13c could again be traced to relative arenium
ion energies in the dibenzo[a,c]anthracene DBA moiety,
which strongly favor protonation at the meso-positions
Model Stable Ion Studies
[6]
(C-9/C-14), therefore disfavoring the formation of the
a) Protonation of 3-Isopropenylperylene 14a: Compound
requisite ipso-protonated carbocation precursor to 13c. The 14a was cleanly protonated in FSO H/SO ClF at –78 °C
3
2
+
DFT-optimized structure of dimer 13b is included in Figure to give the benzylic carbocation 14aH . This carbocation
S5. In this case, one DBA unit is severely buckled, whereas represents the first key intermediate in the dimerization/cy-
the other remains planar (see Table S1).
clization/cleavage sequence, leading to 14b and 14c under
Reaction of 3-isopropenylperylene 14a with TfOH re- equilibrium protonation conditions (see Schemes 5 and 2).
sulted in the formation of dimer 14b, with only traces of Specific NMR assignments for the carbocation are included
the cyclized phenalene 14c being isolated along with per- in Figure 4 along with its charge delocalization mode based
13
ylene (see Scheme 5 and Figure S11). The DFT-optimized on magnitude ∆δ C values. The carbocation center is ob-
structure of 14b is included in Figure S5. The computed served at δ = 191.3 ppm in the 13C NMR spectroscopy.
Scheme 5. Dimerization/cyclization of 13a and 14a.
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Contributions to Polycyclic Aromatic Hydrocarbon Chemistry
13
Figure 4. NMR spectroscopic data and charge delocalization modes in model carbocations 14aH+ and 12cH+ (∆δ C relative to the
corresponding neutral species 14a and 12c).
There is relatively extensive charge delocalization into the ation of the ipso-protonated dimer under equilibrium pro-
perylene moiety, and p–π back-bonding, i.e. the double- tonation conditions, which triggers subsequent cleavage,
+
bond character of perylene-C (Me) bond is reflected in the leading to the phenalene with concomitant loss of one
2
non-equivalence of the methyl groups (see Figure 4 and equivalent of the parent PAH. In four of the six cases
Figures S12–S13 in the Supporting Information).
studied (9a, 10a, 13a, and 14a) the dimer and the phenalene
b) Protonation of the Phenalene 12c Derived from BcPh: were both formed, but the former constituted the major
Low-temperature reaction of compound 12c with FSO H/ product. In the case of 11a and 12a (via chrysene and BcPh)
3
[5]
SO ClF led to clean generation of the benzylic carbocation and the earlier studied isopropenylphenanthrene, forma-
2cH . This carbocation represents the last intermediate in tion of the requisite ipso-protonated dimer is energetically
2
+
1
the reaction sequence and is the immediate precursor to the more favorable and the dimers reacted quickly to produce
cyclic phenalene 12c (see Schemes 4 and 2). Specific NMR the isolated phenalenes.
assignments for the carbocation are included in Figure 4
along with its charge delocalization mode based on the
1
3
magnitude of ∆δ C values. The carbocation center is ob-
1
3
served at δ = 223.6 ppm in the C NMR with the positive
charge delocalized within a naphthalenium moiety (see Fig-
ure 4 and Figures S14–S15).
Experimental Section
General: CH
perature NMR spectra were recorded either on a Bruker Advance
00 or a Varian 500 INOVA instrument, while low-temperature
2 2 2
Cl was dried with CaH under argon. Room tem-
4
NMR spectra were recorded exclusively on the Varian 500 instru-
ment. Electrospray-MS (ES-MS) data were acquired with a Bruker
Comparative Summary
Esquire-LC instrument by mixing a dilute CH
pound with NH NO in CH CN to form the corresponding ammo-
nium clusters [PAH-NH
Bruker Vector 33 spectrometer with Fourier Transform and are ex-
2 2
Cl solution of com-
4
3
3
It has been shown that the isopropenyl derivatives of
various classes of PAHs can be synthesized and isolated in
relatively good yields by Wittig olefination of the acetyl-
PAHs. These compounds react with triflic acid to produce
novel PAH dimers, which can react further to furnish the
corresponding phenalenes under equilibrium protonation
+
4
] . Infrared data were acquired on a
–
1
pressed in cm .
The reported selectivities, given in some cases alongside the yields,
are defined as yield/conversion ϫ100.
conditions. The dimer to phenalene product ratios depend Computational Protocols: Structures were optimized by the density
on the structure of the PAHs and on the feasibility of gener- function theory (DFT) method at B3LYP/6-31G(d) level using the
Eur. J. Org. Chem. 2008, 3700–3708
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C. Brulé, F. Sultana, S. Hollenstein, T. Okazaki, K. K. Laali
(CH), 117.1 (CH ), 25.9 (Me) ppm. IR (KBr): ν˜ = 3042, 2924,
FULL PAPER
Gaussian 03 package. [13,14] All computed geometries were verified
by frequency calculations to have no imaginary frequencies. Ener-
gies of the optimized structures are summarized in Table S2. Struc-
tural features are summarized in Figure S5 and Table S1.
2
–
1
+
+
1443, 838 cm . MS (ES): m/z = 260 [M + NH
4
] , 243 [M + H] .
4
-Isopropenylpyrene (10a): 135 mg, yield 93%, m.p. 115–120 °C. IR
–1
(KBr): ν˜ = 3045, 2922, 1467, 824, 720 cm . MS (ES): m/z = 242
+
1
13
[M ]. Specific H and C NMR assignments are shown below.
1
. Acetylation Reactions
General Procedure: To a cooled suspension (0 °C, ice bath) of alu-
minium chloride (1.1 mmol, 1.4 equiv.) in dry CH Cl (3 mL), ace-
2
2
tyl chloride (0.9 mmol, 1.1 equiv.) was added. After stirring until
a clear solution was obtained, a solution of the polycyclic aromatic
hydrocarbon (0.8 mmol, 1.0 equiv.) in dry CH Cl (2 mL) was
2 2
slowly introduced and the reaction mixture was stirred at room
temperature for 1 to 3 hours. Then the mixture was cooled to 0 °C
(
ice bath) and subsequently hydrolyzed with 3 mL of HCl (0.5 ).
After decantation and separation, the aqueous layer was washed
with CH Cl (2ϫ4 mL) and combined organic layers were dried
with MgSO , filtered and concentrated under reduced pressure. The
product was purified by silica column chromatography using
CH Cl /hexane (7:3).
2
2
4
2
2
Compounds 9, 10, 11, 12 and 14 have already been described (see
[4,9,11,15–17]
ref.
).
1
0-Acetyldibenzo[a,c]anthracene (13): Quantitative yield (NMR
6-Isopropenylchrysene (11a): 95 mg, yield 59%; m.p. 150–155°C.
Specific H and C NMR assignments are shown below.
1
13
proof). This compound was used directly in the Wittig reaction
without further purification. Specific 1H and C NMR assign-
ments are shown below.
13
5
-Isopropenylbenzo[c]phenanthrene (12a): 64 mg, yield 40% (conver-
1
13
2. Wittig Olefination Reactions
sion 58%, selectivity 69%). Specific H and C NMR assignments
are shown below.
General Procedure: A mixture of methyltriphenylphosphonium bro-
mide (0.8 mmol, 1.4 equiv.) and sodium amide (0.8 mmol, 1.35
equiv.) was diluted in dry THF (3 mL) and stirred at room tem-
perature under argon until a color change was seen. Then, a solu-
tion of acetylated substrate (0.6 mmol, 1.0 equiv.) in dry THF (2
mL) was added. After stirring for 2 to 4 hours, the reaction mixture
was washed with brine (4 mL) and organic layer was extracted with
diethyl ether (3ϫ5 mL), dried with MgSO
vents evaporated under vacuum. Finally, the product was purified
by column chromatography using CH Cl /hexane (3:7).
4
, filtered and the sol-
2
2
1
-Isopropenylpyrene (9a): 90 mg, yield 62% (conversion 90%, selec-
1
tivity 69%). H NMR (500 MHz, CDCl
3
): δ = 8.32 (d, J = 9.0 Hz,
H), 8.15 (d, J = 7.5 Hz, 2 H, H-6,8), 8.12 (d, J = 8.0 Hz, 1 H),
.05 (d, J = 9.0 Hz, 1 H), 8.03 (s, 2 H), 7.98 (dd, J = 7.5, 7.5 Hz,
H, H-7), 7.85 (d, J = 8.0 Hz, 1 H), 5.56 (m, 1 H, CH ), 5.17 (m,
H, CH ):
), 2.34 (m, 3 H, Me) ppm. 13C NMR (126 MHz, CDCl
1
8
1
1
2
2
3
δ = 145.1 (CMe), 140.1 (CCMe), 131.6 (C), 131.2 (C), 130.4 (C),
27.9 (C), 127.6 (CH), 127.4 (CH), 127.3 (CH), 126.1 (CH), 125.6
CH), 125.4 (CH), 125.2 (C), 125.1 (2 CH), 125.0 (CH), 124.8
10-Isopropenyldibenzo[a,c]anthracene (13a): 122 mg, yield 64%
(conversion 80%, selectivity 80%). Specific H and C NMR as-
signments are shown below.
1
13
1
(
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Contributions to Polycyclic Aromatic Hydrocarbon Chemistry
H, H-10 or H-11), 7.95 (d, J = 7.6 Hz, 1 H, H-11 or H-10), 7.94
d, J = 8.0 Hz, 1 H, H-2), 5.91 (q, J = 1.4 Hz, 1 H, H-4), 2.35 (d,
(
3
5
13
J = 1.4 Hz, 3 H, C Me), 1.57 (s, 6 H, C Me) ppm. C NMR (101
MHz, CDCl ): δ = 143.4 (C-3), 137.1 (C-4), 131.6 (C), 131.5 (C),
30.4 (C), 130.2 (C-2a), 127.5 (CH), 126.8 (CH), 126.0 (CH), 125.0
CH), 124.3 (C), 124.2 (C), 124.1 (C), 123.9 (CH), 123.8 (CH),
3
1
(
1
5
3
23.5 (CH), 123.4 (C), 120.7 (CH), 37.5 (C-5), 33.6 (C CH ), 20.0
3
(C CH
3
) ppm.
4
1
2
,6,6-Trimethyl-6H-benzo[hi]chrysene (11c): 15 mg, yield 49%, m.p.
+
+
70-175 °C. ES-MS: m/z = 309 [M + H] , 294 [M + H–CH
3
] , 267,
1
13
53 (loss of C H ). Specific H and C NMR assignments are
4 8
shown below.
3-Isopropenylperylene (14a): 110 mg, yield 63% (conversion 86%,
selectivity 74%), m.p. 170-180 °C. IR (KBr): ν˜ = 3048, 2923, 810,
–1
1
13
7
66 cm . Specific H and C NMR assignments are shown below.
4
,6,6-Trimethyl-6H-dibenzo[a,kl]anthracene (12c): 12 mg, yield
1
13
39%. Specific H and C NMR assignments are given below.
3. Dimerization–Cyclization–Cleavage Reactions
General Procedure: To a cooled (–78 °C, dry ice/acetone) solution
of the isopropenylated substrate (0.1 mmol) in dry CH Cl (2 mL)
2
2
under argon was added triflic acid (2-3 drops). After 5 min of stir-
ring at –78 °C, the reaction mixture was warmed to –10 °C (NaCl,
ice). The reaction was monitored by TLC until no further reaction
was observed. Then the mixture was quenched with 2 mL of KOH
1
,3,3-Trimethyl-1-(dibenzo[a,c]anthracen-10-yl)-2,3-dihydro-3H-di-
1
benzo[hi,p]chrysene (13b): 38 mg, yield 60%. H NMR (500 MHz,
(
10%) and extracted with CH
ganic extracts were dried with MgSO
under vacuum. The resulting products were separated and purified
by silica column chromatography using hexane/CH Cl (8:2). The
2
Cl
2
(3ϫ3 mL). The combined or-
CDCl
.5 Hz, 1 H), 8.79 (m, 2 H), 8.73 (d, J = 8.0 Hz, 1 H), 8.67 (m, 2
H), 8.46 (d, J = 7.5 Hz, 1 H), 8.37 (br. d, J = 7.5 Hz, 1 H), 8.02
d, J = 8.5 Hz, 1 H), 7.98 (d, J = 8.0 Hz, 1 H), 7.78–7.46 (m, 10
3
): δ = 9.72 (s, 1 H), 9.16 (s, 2 H), 9.05 (s, 1 H), 8.85 (d, J =
4
, filtered and concentrated
7
2
2
(
reported isolated yields for the phenalenes are based on the isopro-
penyl derivatives (50% is maximum).
2
2
H), 3.18 (d, J = 12.5 Hz, 1 H, CH
CH ), 2.19 (s, 3 H, CH ), 1.56 (s, 6 H, CH
MHz, CDCl ): δ = 158.0, 134.1, 133.1, 130.5, 130.4, 130.3, 130.2,
30.1, 130.0, 129.8, 129.7, 129.5, 129.3, 128.2, 128.0, 127.7, 127.6,
2
), 2.64 (d, J = 12.5 Hz, 1 H,
1
3
2
3
3
) ppm. C NMR (125
3,3,5-Trimethyl-5-(pyren-1-yl)-4,5-dihydro-3H-benzo[cd]pyrene (9b):
3
21 mg, yield 44%. See Figure 3 for NMR spectroscopic data.
1
3
,5,5-Trimethyl-3-(pyren-4-yl)-4,5-dihydro-3H-benzo[cd]pyrene
127.5 (2C), 127.4, 127.3 (2C), 127.2 (2C), 127.1, 125.4, 125.2, 123.6
(2C), 123.5 (2C), 123.4, 123.3, 123.1, 123.0, 121.8, 118.2, 59.8, 51.5,
45.8, 31.7, 31.4, 29.7 ppm (the signals of seven quaternay carbon
atoms were not detectable).
+
(10b): 35 mg, yield 72%. MS (ES): m/z = 502 [M + NH
4
] , 485 [M
+
–1
+
H] . IR (KBr): ν˜ = 3040, 2924, 1602, 1450, 873, 822, 724 cm .
See Figure 3 for NMR spectroscopic data.
,5,5-Trimethyl-5H-benzo[cd]pyrene (10c): 2 mg, yield 7%. 1H
NMR (400 MHz, CDCl ): δ = 8.13 (d, J = 8.0 Hz, 1 H, H-1), 8.11
dm, J = 7.0 Hz, 1 H, H-7), 8.08 (s,1 H, H-6), 8.07 (dd, J = 8.0,
1
3
1,3,3-Trimethyl-3H-dibenzo[hi,p]chrysene (13c): 3 mg, yield 8%. H
3
3
NMR (500 MHz, CDCl ): δ = 9.28 (s, 1 H), 9.18 (s, 1 H), 8.79 (m,
(
2 H), 8.59 (m, 2 H), 8.09 (m, 1 H), 7.72–7.55 (m, 5 H), 6.30 (m, 1
1
.0 Hz, 1 H, H-9), 8.01 (dd, J = 8.0, 7.0 Hz, 1 H, H-8), 7.98 (m, 1
H, Me
2
CCH=), 2.27 (s, 3 H, CH
3
), 1.57 (s, 6 H, CH
www.eurjoc.org
3
) ppm.
Eur. J. Org. Chem. 2008, 3700–3708
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3707

C. Brulé, F. Sultana, S. Hollenstein, T. Okazaki, K. K. Laali
,3,3-Trimethyl-1-(perylen-3-yl)-2,3-dihydro-3H-benzo[cd]perylene carbocations and computational data (Figures S1–S15 and Tables
FULL PAPER
1
1
(
14b): 38 mg, yield 64%. H NMR (400 MHz, CDCl
3
): δ = 8.31 (d,
S1–S2).
J = 7.6 Hz, 1 H), 8.28 (m, 2 H), 8.21 (d, J = 7.2 Hz, 1 H), 8.12 (d,
J = 7.6 Hz, 1 H), 8.03 (d, J = 7.2 Hz, 1 H), 7.99 (d, J = 7.6 Hz, 1
H), 7.92 (m, 2 H), 7.70 (m, 2 H), 7.67 (d, J = 8.4 Hz, 1 H), 7.64
Acknowledgments
(
(
(
8
1
1
d, J = 8.0 Hz, 1 H), 7.61 (d, J = 8.0 Hz, 1 H), 7.52 (m, 1 H), 7.49
dd, J = 8.0, 7.6 Hz, 1 H), 7.45 (dd, J = 8.0, 7.6 Hz, 1 H), 7.39
dd, J = 8.0, 7.6 Hz, 1 H), 7.22 (d, J = 8.8 Hz, 1 H), 6.99 (dd, J =
Support of our work in the PAH area under “reactive intermediates
of carcinogenesis of PAHs” by the National Cancer Institute of the
National Institutes of Health (2R15CA078235-02A1 and
.4, 8.0 Hz, 1 H), 6.91 (d, J = 8.0 Hz, 1 H), 2.99 (d, J = 14.4 Hz,
H, CH ), 2.06 (s, 3 H, CH ), 1.98 (d, J = 14.4 Hz, 1 H, CH ),
.67 (s, 3 H, CH ), 1.56 (s, 3 H, CH
) ppm. 13C NMR (101 MHz,
): δ = 146.0, 144.4, 143.5, 134.6, 134.5, 131.8, 131.7 (2C),
31.6, 131.2, 130.4, 130.3, 129.4, 129.3, 129.0, 128.5, 128.2, 127.5,
1R15CA078235-01A1) is gratefully acknowledge.
2
3
2
3
3
CDCl
3
[
1] T. Okazaki, K. K. Laali, B. Zajc, M. K. Lakshman, S. Kumar,
W. M. Baird, W.-M. Dashwood, Org. Biomol. Chem. 2003, 1,
509–1516.
2] K. K. Laali, S. Hollenstein, J. Chem. Soc. Perkin Trans. 2 1998,
1
1
1
27.4, 127.2, 127.0, 126.6 (2C), 125.7, 125.2, 123.9, 120.8, 120.7,
20.1, 119.9, 119.7, 119.6, 119.5, 49.9, 44.1, 34.9, 34.6, 33.7, 31.9
1
[
ppm (the signals of seven quaternay carbon atoms were not detect-
able).
897–904.
[3] K. K. Laali, M. Tanaka, S. Hollenstein, M. Cheng, J. Org.
Chem. 1997, 62, 7752–7757.
[4] K. K. Laali, P. E. Hansen, J. Org. Chem. 1997, 62, 580–5810.
[5] S. Hollenstein, K. K. Laali, Chem. Commun. 1997, 2145–2146.
[6] K. K. Laali, T. Okazaki, R. G. Harvey, J. Org. Chem. 2001, 66,
1
,3,3-Trimethyl-3H-benzo[cd]perylene (14c): Less than 2 mg, yield
1
Ͻ 5%. H NMR (400 MHz, CDCl
.15 (m, 3 H), 7.63 (m, 2 H), 7.53 (d, J = 8.1 Hz, 1 H), 7.46 (m, 2
H), 7.36 (d, J = 8.0 Hz, 1 H), 5.81 (q, J = 1.3 Hz, 1 H), 2.20 (d, J
1.3 Hz, 3 H), 1.54 (s, 6 H) ppm.
3
): δ = 8.23 (d, J = 8.0 Hz, 1 H),
8
3
977–3983.
7] R. G. Harvey, Polycyclic Aromatic Hydrocarbons, Wiley-VCH,
New York, 1997, pp. 140–143.
8] K. K. Laali, P. E. Hansen, J. Org. Chem. 1991, 56, 6795–6803.
[
=
[
[
4. Stable Carbocation Generation from 14a and 12c
9] K. K. Laali, S. Hollenstein, R. G. Harvey, P. E. Hansen, J. Org.
Protonation of 14a: In a 5-mm NMR tube 6 mg of 3-isopropenylper-
ylene 14a was introduced and tube was flushed with argon and
Chem. 1997, 62, 4023–4028.
[10] K. K. Laali, T. Okazaki, S. Kumar, S. E. Galembeck, J. Org.
Chem. 2001, 66, 780–788.
11] C. Brulé, K. K. Laali, T. Okazaki, M. K. Lakshman, J. Org.
Chem. 2007, 72, 3232–3241.
12] R. G. Harvey, Polycyclic Aromatic Hydrocarbons, Wiley-VCH,
cooled to –78 °C. About 0.3 mL of SO
the NMR tube directly. After completion of SO
drops of FSO H were slowly added in order to prevent any local
overheating. The mixture immediately turned deep-green. After
vigorous stirring at –78 °C (vortex), 4–5 drops of CD Cl were
slowly introduced into the NMR tube (vortex mixing) and the sam-
2
ClF was condensed into
[
2
ClF addition, 3
3
[
New York, 1997, pp. 153.
13] W. Koch, M. C. Holthausen, A Chemist’s Guide to Density
2
2
[
Functional Theory, 2nd ed., Wiley-VCH, Weinheim, 2000.
ple was analyzed by NMR at –65 °C. Afterwards, the sample was [14] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
warmed to –10 °C (NaCl/ice/water bath) and kept at this tempera-
ture for 30 minutes (regular vortex mixing). The sample was
checked by NMR at –65 °C but no changes were detected. Then
the sample was kept in a 0 °C (ice/water) for 3 hours and checked
again by NMR at –65 °C. However, still no changes occurred (sam-
ple was deep green). In an attempt to observe the dimerization step
directly by NMR, a tiny amount of 14a was added to the superacid
M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr, T. Vreven,
K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tom-
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G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratch-
ian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gom-
perts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C.
Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A.
Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dap-
prich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick,
A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q.
Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov,
G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin,
D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayak-
kara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian 03, Revision
E.01, Gaussian, Inc., Wallingford CT, 2004.
+
solution of 14aH while at 0 °C, but no noticeable changes could
1
be seen via H NMR at –65 °C.
Protonation of 12c: In a 5-mm NMR tube, 10 mg of a 1:1 mixture
of cyclized 12c and BcPh was introduced. The NMR tube was then
flushed with argon, cooled to –78 °C and about 0.3 mL of SO
was condensed into it. After completion of SO ClF addition, 3–4
drops of FSO H were slowly added in order to avoid local over-
heating. The mixture immediately turned deep-blue. After vigorous
stirring at –78 °C (vortex), 6–8 drops of CD Cl were slowly intro-
2
ClF
2
3
2
2
[
15] K. K. Laali, T. Okazaki, P. E. Hansen, J. Org. Chem. 2000, 65,
816–3828.
16] M. Sarobe, L. W. Jenneskens, J. Wesseling, U. E. Wiersum, J.
duced into the NMR tube (vortex mixing) and the sample was
3
+
studied by NMR at –65 °C. Only resonances due to 12cH were
[
[10]
observed. As shown previously,
protonated BcPh can not be
Chem. Soc., Perkin Trans. 2, 1997, 703–708.
[17] M. Sarobe, H. C. Kwint, T. Fleer, R. W. A. Hevenith, L. W.
Jenneskens, E. J. Vlietstra, J. H. Van Lenthe, J. Wesseling, Eur.
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generated under persistent ion conditions (likely due to radical
cation formation).
Supporting Information (see also the footnote on the first page
Received: March 6, 2008
of this article): Selected NMR spectra for the products and the
Published Online: June 11, 2008
3708
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 3700–3708