Rearrangement of cyclotriveratrylene (CTV) diketone: 9,10-diarylanthracenes with OLED applications

Article abstract of DOI:10.1021/jo302139w

Electroluminescent 9,10-diaryl anthracenes have been shown to be promising host and hole-transporting materials in organic electroluminescence due to their high thermal stability, electrochemical reversibility, and wide band gap useful for organic light-emitting diodes (OLEDs), especially blue OLEDs. Oxidation of cyclotriveratrylene (CTV) to the corresponding diketone and subsequent bromination resulted in an unexpected rearrangement to a highly functionalized 9-aryl-10-bromoanthracene derivative, which was employed in Suzuki couplings to synthesize a series of 9,10-diaryl compounds that are structural analogues of anthracene derivatives used in the preparation of OLEDs but are more highly functionalized, including electron-donating methoxy groups in addition to substitution by a carboxylic acid moiety. The UV/fluorescence solution spectra show strong emissions at 446, 438, and 479 nm, respectively, for the anthracene 10-phenyl, 10-naphthyl, and 10-pyrenyl adducts containing a benzoic acid functional group, whereas the analogues bearing the hydroxymethylene moiety from reduction of the benzoic acid to the corresponding alcohols gave much shorter emission wavelengths of 408, 417, and 476 nm, respectively, and had somewhat higher quantum yields, suggesting they are better candidates for OLED applications.

Full text of DOI:10.1021/jo302139w

Article
pubs.acs.org/joc
Rearrangement of Cyclotriveratrylene (CTV) Diketone: 9,10-
Diarylanthracenes with OLED Applications
Samuel R. S. Sarsah,† Marlon R. Lutz, Jr.,† Matthias Zeller,‡ David S. Crumrine,† and Daniel P. Becker*,†
†Department of Chemistry, Loyola University Chicago, 1032 West Sheridan Road, Chicago, Illinois 60660, United States
‡Department of Chemistry, Youngstown State University, 1 University Plaza, Youngstown, Ohio 44555-3663, United States
S
* Supporting Information
ABSTRACT: Electroluminescent 9,10-diaryl anthracenes have
been shown to be promising host and hole-transporting
materials in organic electroluminescence due to their high
thermal stability, electrochemical reversibility, and wide band
gap useful for organic light-emitting diodes (OLEDs),
especially blue OLEDs. Oxidation of cyclotriveratrylene
(CTV) to the corresponding diketone and subsequent
bromination resulted in an unexpected rearrangement to a
highly functionalized 9-aryl-10-bromoanthracene derivative,
which was employed in Suzuki couplings to synthesize a series
of 9,10-diaryl compounds that are structural analogues of
anthracene derivatives used in the preparation of OLEDs but
are more highly functionalized, including electron-donating
methoxy groups in addition to substitution by a carboxylic acid moiety. The UV/fluorescence solution spectra show strong
emissions at 446, 438, and 479 nm, respectively, for the anthracene 10-phenyl, 10-naphthyl, and 10-pyrenyl adducts containing a
benzoic acid functional group, whereas the analogues bearing the hydroxymethylene moiety from reduction of the benzoic acid
to the corresponding alcohols gave much shorter emission wavelengths of 408, 417, and 476 nm, respectively, and had somewhat
higher quantum yields, suggesting they are better candidates for OLED applications.
lanthacenes (Figure 1) are important blue host emitters in
the preparation of OLEDs, including 9,10-diphenylanthracene
INTRODUCTION
■
The discovery and development of new materials for use in
displaying electronic information has been essential in flat panel
displays in today’s ubiquitous portable devices and common
every-day technologies including cell phones, flat-screen
televisions, and ambient lighting.1 The development of organic
light-emitting diodes (OLEDs)2 holds great promise for the
production of highly efficient light sources, with the advantage
that they can be more economical to use and can exhibit
electroluminescence at relatively low voltages, making them
exceptionally useful for application in electronic devices.3,4 It is
desirable that compounds used in OLEDs have good
morphological properties including a good film-forming ability,
an amorphous or noncrystalline solid state, good thermal
stability characterized by high decomposition temperatures, and
a narrow HOMO−LUMO energy band gap in order to
function in OLEDs. Red and green color electroluminescence is
relatively easy to obtain from OLEDs, but blue color emitters
are rare and tend to degrade rapidly due to the larger energy
band gap required for blue color emission. This has triggered
research into finding more stable organic compounds that can
be used for making efficient OLED devices, especially for blue
OLEDs.
Figure 1. 9,10-Diarylanthracene derivatives used as blue host emitters
for OLEDs.
(DPA)6 and 9,10-di-(2-naphthyl)anthracene (ADN).7 Known
9,10-diarylanthracene host emitters that contain a 2-tert-butyl
group8 include 2-tert-butyl-9,10-bis(β-naphthyl)anthracene
(TBADN),9 2-tert-butyl-9,10-di(9-phenanthryl)anthracene
(TBDHA),10 and 2-tert-butyl-9,10-di(1-pyryl)anthracene
(TBDPA).10 More highly functionalized (9,10-diaryl)-
anthracenes have also been described in recent disclosures.11−13
Three deep-blue-emitting anthracene derivatives, 2-tert-butyl-
9,10-bis(9,9-dimethylfluorenyl)anthracene (TBMFA), 2-tert-
butyl-9,10-bis[4-(2-naphthyl)phenyl]anthracene (TBDNPA),
and 2-tert-butyl-9,10-bis[4-(9,9-dimethylfluorenyl)phenyl]-
Special Issue: Howard Zimmerman Memorial Issue
Received: September 28, 2012
The wide energy band gap of electroluminescent anthracene
compounds makes them potentially useful for organic light-
emitting diodes, especially blue OLEDs,5 and 9,10-diary-
© XXXX American Chemical Society
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Figure 2. CTV and related structures.
anthracene (TBMFPA), with naphthalene or 9,9-dimethyl-
fluorene side units were recently reported,13 where amorphous
thin film forming derivatives are enabled by effectively
introducing alkyl substituents in the compounds to prevent
the molecules from easily packing to form crystals in thin
films.8,14 Bulky substituents on the anthracene moieties can
improve both thermal and film-forming properties.10
RESULTS AND DISCUSSION
■
Part of our research program is focused on the construction of
apex-modified derivatives15−17 of the trimeric crown-shaped
(bowl-shaped) [1.1.1]orthocyclophane cyclotriveratrylene 1
(CTV, Figure 2)18 with applications in host−guest chemistry.19
Trans-annular rearrangements are known to occur when
attempting to oxidize CTV-5,10-dione 1c to the corresponding
triketone, which leads to rearrangement to the spiro derivative
2,20,21 and we have observed a trans-annular electrophilic
aromatic addition or substitution cascade following a Beckmann
rearrangement reaction on a related system.22 We examined the
bromination of CTV-5,10-dione, indeed trying to avoid the
formation of spiro derivative 2, which resulted instead in a
rearrangement to the highly functionalized 9-aryl-10-bromo
anthracene derivative 3a. Specifically, treating CTV diketone 1c
with N-bromosuccinimide in the presence of benzoyl peroxide
in 1,2-dichloroethane at 70 °C for 5 h afforded a 77% yield of
bromoanthracene benzoic acid 3a. When the reaction was
performed in chloroform, the ethyl ester 3b was also isolated
with a significant NMR upfield shift for the methyl hydrogen
atoms due to anisotropy [δ = 0.31 (3H, t, J = 7.14 Hz)], arising
from acid-catalyzed esterification of the acid with ethanol
present in commercial chloroform as a stabilizer. The exact
identities of both 3a and 3b have been confirmed by single-
crystal X-ray analysis (Figure 3, Figures S1 and S2 and Table S1
in the Supporting Information).
Given the interest in 9,10-diaryl anthracenes as hole-
transporting materials in organic electroluminescence along
with their great importance in the preparation of OLEDs, and
realizing that the 10-bromo substituent of anthracene 3a lends
itself directly to the installation of a second aryl substituent on
the anthracene via palladium-catalyzed coupling reactions, we
were excited to explore the effect of different substituents on
the optical properties of this type of compound. Thus, we set
out to determine the utility of 10-bromoanthracene 3a toward
the preparation of 9,10-diaryl anthracenes with potential
applications in the preparation of OLEDs. To this end, Suzuki
couplings were used to link bromoanthracene 3a with phenyl,
2-naphthyl, and 1-pyrenyl boronic acids to form 9,10-
substituted anthracene derivatives 4a, 4b, and 4c, respectively
(Scheme 1).
Figure 3. Single crystal X-ray structure of bromoanthracene benzoic
acid 3a, 50% thermal probability ellipsoids. A solvate dichloromethane
molecule is omitted for clarity. For details of the structure analyses of
3a and 3b, see Figures S1 and S2, Table S1 in the Supporting
Information.
and sodium carbonate in ethanol/toluene at 115 °C for 24 h
gave only a trace of coupled material. The stronger base sodium
hydroxide in ethanol/n-butanol at 90−100 °C for 24 h,
however, gave 4a (R = Ph) in 29% yield, whereas utilization of
Pd(0)-catalyzed coupling with the milder base potassium
fluoride in the presence of silver(I) oxide23−25 in 2-
methoxyethanol with THF to aid solubility gave 4a in an
excellent yield (96%). Similarly, Suzuki coupling of 2-
naphthylboronic acid utilizing sodium hydroxide as the base
in ethanol gave 4b in 21% yield along with a significant amount
of hydrolytic deboronation26 as well as the typical dehaloge-
nation, but the KF/Ag2O procedure gave 4b in 88% isolated
yield. Coupling with pyrene-1-boronic acid to afford 4c was
more sluggish, suffering from more deboronation and giving
only a trace of coupled material with NaOH/EtOH, but
afforded an isolated yield of 48% with KF/Ag2O. An upfield
shift in the 1H NMR resonances of the methoxy groups
proximal to the added phenyl, naphthyl, and pyrenyl groups is
observed upon replacement of the bromine in the Suzuki
couplings. For adduct 4c with the larger pyrenyl substituent,
hindered rotation of the pyrene versus the dimethoxy benzoic
acid moiety leads to formation of two atropisomers,27 which
were separated by preparative plate chromatography. The two
compounds have nearly identical UV and fluorescence spectra,
1
but the individual H NMR spectra show that the methoxy
groups proximal to the pyrene differ by 0.018 ppm. These two
peaks in the unseparated mixture of atropisomers integrate in a
ratio of 1:1, demonstrating the existence of equal amounts of
each atropisomer at room temperature. Variable temperature
Suzuki coupling of 3a with phenylboronic acid with a
catalytic amount of tetrakistriphenylphosphine palladium(0)
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Scheme 1. Suzuki Couplings To Prepare 9,10-Diaryl Anthracenes 4a−4c and Reduction to Benzyl Alcohols 5a−c
Figure 4. UV and fluorescence solution spectra of compounds 4a−c. The UV trace is shown in dark blue; the fluorescence trace is shown in
magenta. All spectra were recorded at a concentration of 8.6 × 10−6 M in dichloromethane at room temperature. Spectra were recorded in
dichloromethane at the following concentrations and excitation wavelengths: 10-phenyl adduct 4a at 8.6 × 10−6 M, excitation wavelength 374 nm;
10-naphthyl adduct 4b at 4.3 × 10−6 M, excitation wavelength 374 nm; 10-pyrenyl adduct 4c (1:1 mixture of atropisomers) at 4.3 × 10−6 M,
excitation wavelength 372 nm; anthracene at 7.166 × 10−7 M, excitation wavelength 377 nm.
NMR in d6-DMSO showed no interconversion up to 100 °C,
and semiempirical AM1 calculations of the equilibrium
geometries show that the two atropisomers differ by only
0.036 kcal/mol.
derivatives 4c show absorptions for both the anthracene moiety
at 276 and 372 nm and for the pyrene moiety at 245, 276, 327,
341, and 368 nm. The onset of absorption for the phenyl
derivative 4a and naphthyl derivative 4b are both red-shifted by
modest conjugation with the anthracene. The pyrenyl
derivatives 4c were the most red-shifted and also had the
smallest energy band gap. The solid-state UV−vis spectra of the
phenyl and naphthyl substituted acids 4a and 4b, respectively,
showed a slight red shift in the long wave absorption maxima
when compared to their solution spectra. The long wavelength
maxima of the pyrenyl-substituted acid 4c and the correspond-
ing alcohols all show blue shifts.
UV−vis and fluorescence spectra were obtained for all three
acids 4a−c (Figure 4) and the three corresponding alcohols
5a−c (Figure 5) in both dichloromethane solution and in the
solid state. In dichloromethane solution, the three benzoic acids
4a−c each show nearly identical UV absorption maxima at 278
(ε ≈ 8 × 104) and 378 nm (ε ≈ 1 × 104) corresponding to two
π−π* excitations. The UV spectra of 4a−b are very similar to
the UV spectrum of anthracene due to minimal conjugation of
the twisted aryl substituents at the 9- and 10-substituents that
have been reported28,29 to be rotated by about 66° with respect
to the anthracene core in the ground state of 9,10-
diphenylanthracene. The UV spectra of the two pyrenyl
With ∼375 nm excitation, all of these compounds show
unstructured blue fluorescence at ∼10−5 M in dichloromethane
solution. The lack of vibronic structure in the fluorescence
suggests some degree of electronic interaction between the π
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Figure 5. UV and fluorescence spectra of reduced adducts 5a−c. Fluorescence spectra were recorded with excitation wavelengths of 274 nm, 377,
and 395 nm, respectively, corresponding to the emission λmax for 5a−c at a concentration of 9.31 × 10−7, 2.38 × 10−7, and 8.6 × 10−7 M, respectively
for 5a−c.
Table 1. Optical Properties and Melting Points of 9,10-Diarylanthracenes 4a−c and 5a−c
UV−vis thin fluor soln fluor thin
rel fluor soln
(quantum
yield, Qf)
rel fluor
ratios thin
films
abs energy
band gap
(nm, eV)
solution
conc
UV−vis soln λmax (ε)
film λmax
λmax
film λmax
mp
(°C)
compd
4a
(nm, 103 M−1 cm−1
)
(nm)
(nm)
(nm)
(10−7 M)
276 (96.8) 374 (12.3)
273 (99.6) 375 (12.4)
276 (83.8) 339 (18.7)
366 (10.2) 372 (10.8)
274 (70.3) 359 (10.6)
276 (122.0) 377 (15.3)
377
378
346
446
438
479
411
428
464
0.063
0.058
0.197
1.0
412, 2.91
418, 2.87
426, 2.82
9.10
3.98
2.23
228−232
234−240
4b
4c
0.37
0.037
120−125
(Tg)
5a
5b
5c
377
361
346
408
417
476
428
437
447
0.325
0.39
0.17
0.040
0.032
0.029
401, 2.99
415, 2.89
420, 2.86
9.31
2.39
1.26
197−203
202−205
277 (150.6) 322 (17.6)
338 (26.6) 370 (18.8)
381 (14.6)
115−120
(Tg)
a
anthracene ND
ND
ND
ND
0.27 (EtOH)36
ND
ND
3.26
ND
a
ND = not determined. Relative fluorescence (rel fluor) ratios are normalized. Solution concentrations shown were used to calculate quantum yields.
systems.30 Phenyl derivative 4a (Figure 4) provided unstruc-
tured fluorescence emission with a 446 nm maximum, while
naphthyl derivative 4b showed unstructured fluorescence with a
438 nm maximum. This lower energy emission in 4a can be
explained if the barrier to excited state rotational relaxation
about the anthracene-naphthyl bond in 4b is greater than the
excited state rotational barrier of the anthracene-phenyl bond in
4a. This is not surprising since we isolated atropisomers of the
pyrenyl-substituted 4c, which means it has a very high ground
state barrier to rotation. The longer wavelength fluorescence
maximum in the phenyl derivative 4a then reflects a lower
energy flatter excited state conformation with respect to 4b.31
In pyrenyl system 4c, the unstructured fluorescence
maximum in dichloromethane is 479 nm. This is quite red-
shifted compared to the fluorescence of 1-phenylpyrene30 and
even more red-shifted than the fluorescence of 1-(9-
anthracenyl)pyrene in acetonitrile, which was attributed to
charge transfer interactions.32 This suggests that the
fluorescence of 4c has a large component of charge transfer
interactions. We know from the 4c atropisomers that we
isolated that the ground state barrier to rotation is large, so 4c
isomers have the least ground state π overlap between the
aromatic systems of these derivatives. The solid-state
fluorescence maxima of the acids were all blue-shifted
compared to their solution-state fluorescence spectra, whereas
the solid-state fluorescence maxima of the phenyl- and
naphthyl-substituted benzyl alcohols were red-shifted, but the
fluorescence maximum of the pyrenyl-substituted benzyl
alcohol was blue-shifted, again in comparison to the
corresponding solution fluorescence maxima.
We were concerned whether the presence of the electron-
withdrawing benzoic acid moiety would reduce the quantum
yields of solution fluorescence, so the benzoic acid group was
converted to the corresponding alcohol by reduction with
lithium aluminum hydride in tetrahydrofuran (Scheme 1).
Fluorescence quantum yields (Qf) were measured using 365
nm excitation with absorbance in dichloromethane of about
0.04 for all compounds. The fluorescence of anthracene (0.27
in ethanol) was the standard.33−38 The alcohols 5a and 5b did
exhibit a marked increase in solution-state fluorescence
quantum yields, although the pyrenyl alcohol 5c was
comparable to the parent carboxylic acid 4c. The alcohols
also exhibit lower emission wavelengths (are blue-shifted)
compared to the corresponding benzoic acid derivatives. The
UV spectra show increased molar absorptivity at 274 nm
(Figure 5), and this is reversed for the benzoic acids 4a−c due
to the presence of the carbonyl group in 4a−c, which can
absorb a significant portion of the incident excitation energy
through an n−π* transition39 and decreases the effective
fluorescence emission and the quantum yields of compounds
4a−c. The hydroxymethyl group is electron-donating, resulting
in increased wavelengths for the π−π* transitions and thereby
increasing solution fluorescence quantum yields for 5a−c.
Absorption and fluorescence spectra of anthracene itself are
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mostly mirror symmetric. In contrast, the prepared derivatives
(4a−c, 5a−c) show a single emission peak. This is due to the
rigid structure of anthracene compared to the derivatives
described herein where large attached substituents result in
increased vibrational degrees of freedom and increased vibronic
coupling of the electronic energy levels in all the derivatives.40
The blue shifts for the solid-state fluorescence maxima of
acids 4a, 4b, and 4c, in comparison to their solution-state
fluorescence maxima, suggest that, in these solid-state excited
states, there is less overlap between the aryl rings and the
anthracene core. This could be understood if, in these solid-
state excited states, the barriers to rotation of the aryl rings
toward coplanarity with the anthracene core are higher than the
corresponding barriers for the solution-state excited states. The
pyrenyl benzyl alcohol 5c also shows a blue shift for the solid-
state fluorescence maxima. In contrast, the other two benzyl
alcohols 5a and 5b show red shifts in their solid-state
fluorescence maxima.
The differences in the relative efficiencies of fluorescence in
solution versus in the solid state are dramatic. In solution, the
phenyl- and naphthyl-substituted benzyl alcohols have quantum
yields much higher than those of the corresponding acids. In
solution, both pyrenyl-substituted anthracene derivatives
showed similar maxima that show considerable charge transfer
character in the excited state. Their solution-state fluorescence
quantum yields were similar to each other, about three times
the quantum yields for the phenyl and naphthyl acids and about
one-half of the value for the phenyl and naphthyl benzyl
alcohols. We recorded the solid-state fluorescence spectra of
each compound and in Table 1 report the solid-state
fluorescence output as the product of the absorbance value at
the wavelength of excitation (370 nm) and the integrated
fluorescence intensity for each compound. It is clear that the
phenyl-substituted acid 4a has the most intense fluorescence.
The solid-state fluorescence spectra were normalized by
division of the product of absorbance times integrated
fluorescence intensity for all of the other compounds by the
product of absorbance times integrated fluorescence intensity
for 4a. Those ratios are shown in Table 1. The solid-state
fluorescence intensities of 4a and 4b are considerably larger
than those for the other compounds.
In summary, we report the rearrangement of a CTV
derivative to a highly functionalized 9-aryl-10-bromoanthracene
derivative. From that bromoanthracene derivative, we have
prepared a series of 9,10-diaryl derivatives utilizing Suzuki
couplings. These Suzuki products were evaluated as the parent
benzoic acids as well as their corresponding reduced alcohol
derivatives by solution and solid-state UV and fluorescence
spectroscopy. We have measured the relative fluorescence
quantum yields (Qf) in addition to the absorption energy band
gaps for each of the 9,10-diaryl anthracene derivatives. Several
of these compounds with higher quantum yields, especially 5a
and 5b (Qf = 32.5% and 39%), show promise as hole-
transporting materials in organic electroluminescence for the
construction of organic light-emitting diodes (OLEDs),
especially blue OLEDs.
EXPERIMENTAL SECTION
■
All solvents and reagents were used without further purification unless
otherwise noted. Solvents used in the synthesis of the final compound
were distilled from calcium hydride. Reactions were performed under
an atmosphere of nitrogen. Silica gel 60 (230−400 mesh) was used for
flash chromatography. Aluminum-backed silica gel plates (0.25 mm)
were used for TLC. 1H NMR spectra were obtained with either a 300
MHz, a 400 MHz, or a 500 MHz spectrometer with tetramethylsilane
(TMS) as an internal standard. Noise-decoupled 13C NMR spectra
were recorded at 75 or 125 MHz. IR spectra were recorded on an FT-
IR using NaCl crystal polished optical discs, (25 mm × 4 mm). HRMS
spectra were measured on a TOF instrument. UV−vis spectra were
obtained using an UV−vis Spectrometer. Single crystal X-ray
structures were collected on a CCD area detector X-ray diffractometer
at 100 K. Solution UV absorbance spectra were measured with a UV−
vis spectrophotometer while the fluorescence was measured with a
spectrofluorometer. Semiempirical AM1 calculations were performed
using Spartan 2003. For the solid-state UV/fluorescence spectra, a
solution of sample (1.0 mM) in dichloromethane was spin coated on
thin glass slides in an evacuated chamber preflushed with nitrogen. UV
spectra were recorded on a single beam array detector spectropho-
tomer. Solid-state fluorescence was recorded in a right angle mode
with excitation at λ = 370 nm.
Relative Fluorescence Quantum Yields. Quantum yields (Qf)
were measured at an excitation wavelength of 365 nm with an
absorbance of about 0.04 for all compounds in dichloromethane and
were compared to anthracene in ethanol (Qf = 0.27). Qf = (As/Ax)(Ix/
Is)(nx/ns)2(0.27) . The symbols A, I, and n refer to the absorbance,
integrated fluorescence intensity (area under the curve), and refractive
indices of solvents dichloromethane (nx = 1.42) for compounds x and
ethanol (ns = 1.38) for the anthracene standard solution, respectively.
The areas under the curve were measured using the ORIGINpro
computer software.
Solid-state fluorescence spectra are strongly influenced by
intermolecular steric forces41 and crystal structure, which
determine distance and orientation between neighboring
molecules.42−44 Changing substituents on molecules can
change crystalline forms45 and fluorescence efficiencies.46
Thus, the differences in solid-state fluorescence could be
attributed to a greater angle between the core anthracene and
the phenyl and naphthyl rings in the acids 4a and 4b, which
would then increase the distance between successive planes of
solid molecules and increase the fluorescence efficiencies with
respect to the solution efficiencies. On the other hand, the
solid-state UV spectra show slight red shifts for 4a and 4b, so
we continue to look for the best explanation.
(2,3,7,8,12,13)-Hexamethoxy-5H-tribenzo[a,d,g]cyclo-
nonene-5,10(15H)-dione (CTV-Diketone, 1c). To a 500-mL
reactor charged with cyclotriveratrylene (CTV, 1a; 4.28 g, 9.50
mmol) were added a finely ground uniform mixture of potassium
permanganate (60 g, 380 mmol) and activated manganese dioxide
(66.0 g, 760 mmol) and 120 mL of pyridine. The reaction mixture was
stirred vigorously under reflux for 18 h. The reaction mixture was then
vacuum filtered hot (90 °C) through a bed of Celite. The reactor and
Celite bed were rinsed with ethyl acetate followed by dichloromethane
(100 mL each). The organic solvent was removed under reduced
pressure (50 °C, 10 mmHg). The crude material was further dried in
vacuo at 100 °C for 1 h to give a pale yellow solid (3.62 g).
Chromatography on silica gel (40:1 loading ratio) eluting with
methylene chloride followed by a step gradient of ethyl acetate/
methylene chloride (5/95 to 50/50) afforded CTV-monoketone
1b20,47 (1.40 g, 32%) followed by CTV-diketone 1c48 (1.88 g, 41%):
The band gap values were calculated from the wavelength at
the onset of absorbance.
(3)
v = c/λ
hv = EHOMO − ELUMO
(4)
1
where c is light velocity in vacuum, λ is the wavelength of the
absorption onset, and h is Plank’s constant.
mp 138−144 °C. H NMR of 1c: δ 7.20 (2H, s), 6.98 (2H, s), 6.52
(2H, s), 3.92 (12H, s), 3.88 (2H, bs), 3.86 (6H, s). 13C NMR δ 196.2,
E
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151.7, 150.2, 147.5, 135.2, 133.6, 131.1, 111.7, 111.3, 109.5, 109.4,
55.8, 55.7, 55.7, 55.6, 55.6.
NMR δ 168.5, 152.8, 149.2, 148.8, 148.1, 139.6, 139.1, 135.3, 133.4,
131.3, 131.1, 130.9, 128.68, 128.66, 127.5, 125.80, 125.76, 125.70,
122.4, 114.9, 113.8, 104.1, 103.2, 56.3, 56.1, 55.6, 55.5. ESI HRMS m/
z calcd for M − 1 C33H29O8 553.1862, found 553.1833. FTIR (neat):
ν 3527 (br), 2999, 2936, 2831, 1491, 1238 cm−1; Td = 381.2 °C
4,5-Dimethoxy-2-(2,3,6,7-tetramethoxy-10-(naphthalen-2-
yl)anthracen-9-yl)benzoic Acid (4b). Bromo-anthracene 3a (156
mg, 0.280 mmol), Pd(PPh3)4 (97.1 mg, 0.084 mmol), naphthyl-2-
boronic-acid (145 mg, 1.40 mmol), potassium fluoride (60 mg, 1.03
mmol), and silver(I) oxide (71.4 mg, 0.308 mmol) were added to a
mixture of 2-methoxyethanol (4.5 mL) and THF (6.5 mL). The
mixture was degassed by flushing with nitrogen and heated in a sealed
tube at 90−100 °C for 48 h. The reaction mixture was allowed to cool
to room temperature and diluted with cold deionized water (20 mL).
It was then acidified with conc HCl to pH 2−3 and then extracted
with dichloromethane (4 × 20 mL). The combined organic layers
were washed with water (2 × 40 mL) and dried with Na2SO4. The
solution was then concentrated under reduced pressure and purified
by silica gel chromatography using methylene chloride/ethyl ether
followed by ethyl ether/ethyl acetate (100% to 10% with 10%
increments for each interval) to afford naphthyl derivative 4b as a light
2-(10-Bromo-2,3,6,7-tetramethoxyanthracen-9-yl)-4,5-dime-
thoxybenzoic Acid (3a). CTV-diketone 1c (256 mg, 0.535 mmol)
was added to N-bromosuccinimide (95.2 mg, 0.535 mmol) and
benzoyl peroxide (1.3 mg, 0.0046 mmol) dissolved in 1,2-dichloro-
ethane (3 mL), and the mixture was heated to 70 °C for 2 h and then
cooled to room temperature, diluted with 20 mL deionized water, and
acidified to pH 2−3 using conc hydrochloric acid. The resulting
mixture was extracted with dichloromethane (3 × 40 mL), and the
combined organic layers were washed with brine (3 × 40 mL) and
dried over MgSO4. Concentration under reduce pressure afforded a
residue that was purified by silica gel column chromatography eluting
with ethyl acetate/dichloromethane to afford bromoanthracene 3a
(231 mg, 77%): mp 224−226 °C. 1H NMR δ 7.73 (1H, s), 7.71 (2H,
s), 6.73 (1H, s), 6.53 (2H, s), 4.10 (6H, s), 4.03 (3H, s), 3.83 (3H, s),
3.69 (6H, s). 13C NMR δ 169.9, 153.0, 150.7, 149.6, 148.4, 135.2,
132.9, 126.52, 126.48, 122.5, 118.2, 114.9, 114.0, 105.6, 103.9, 56.6,
56.4, 56.2, 56.0. The benzoic acid proton was not observed due to
exchange with water. The structure was ultimately confirmed by X-ray
crystallography (CH2Cl2/heptane) as seen in Figure 3 (and Figure S1,
Table S1 in the Supporting Information).
1
tan solid (111 mg, 88%): H NMR δ 8.1−7.9 (4H, m), 7.80 (1H, s),
2-(10-Bromo-2,3,6,7-tetramethoxyanthracen-9-yl)-4,5-dime-
thoxybenzoic Acid (3a) and 2-Ethyl (10-Bromo-2,3,6,7-tetra-
methoxyanthracen-9-yl)-4,5-dimethoxybenzoate (3b). A vial
was charged with CTV-diketone 1c (95.6 mg, 0.20 mmol), N-
bromosuccinimide (35.6 mg, 0.20 mmol), benzoyl peroxide (0.5 mg,
0.002 mmol), and chloroform (1.1 mL). The reaction was stirred at 70
°C for 5.5 h, during which time the reaction solution had turned from
an orange to a dark brown. The mixture was then cooled to room
temperature and diluted with deionized water (5 mL) and methylene
chloride (5 mL), and the pH was adjusted to pH 10−11 with 2 M
aqueous sodium hydroxide solution. The aqueous layer was extracted
with methylene chloride (2 × 5 mL). The combined organic layers
were successively washed with brine and dried over sodium sulfate.
Concentration under reduced pressure (10 mmHg) gave 93 mg of
crude material. Purification via column chromatography on silica gel
(50:1 loading ratio) eluting with methylene chloride followed by an
ethyl acetate/methylene chloride gradient (0/100 to 20/80, then 30/
70 containing 3% AcOH) afforded the ethyl ester 3b (21.3 mg,
18.4%): mp 261−263 °C. 1H NMR δ 7.77 (1H, s), 7.72 (2H, s), 6.81
(1H, s), 6.62 (2H, s), 4.11 (6H, s), 4.09 (3H, s), 3.87 (3H, s), 3.74
(6H, s), 3.66 (2H, q, J = 7.14 Hz), 0.31 (3H, t, J = 7.14 Hz). 13C NMR
δ 166.8, 152.2, 150.6, 149.4, 148.4, 133.9, 133.6, 126.5, 126.4, 124.4,
117.6, 114.7, 114.6, 113.5, 113.4, 105.5, 105.4, 104.1, 104.0, 60.6, 56.5,
56.4, 56.3, 56.1, 56.0, 55.9. The identity of 3b was ultimately
confirmed by X-ray crystallography (Figure S2, Table S1 in the
Supporting Information). Continued elution yielded the free acid 3a
(46.6 mg, 58.3%) that was identical to the material prepared in 1,2-
dichloroethane above. Continued elution afforded a very small amount
of the spirolactone derivative 2 (2.3 mg, 2.4%) that was identical to
material reported in the literature.20,21
4,5-Dimethoxy-2-(2,3,6,7-tetramethoxy-10-phenylanthra-
cen-9-yl) Benzoic Acid (4a). Bromo-anthracene 3a (154 mg, 0.28
mmol), Pd(PPh3)4, (971 mg, 30 mol %), phenyl boronic-acid (102.4
mg, 0.84 mmol), potassium fluoride (97 mg, 1.68 mmol), and silver(I)
oxide (71.4 mg, 0.308 mmol) were added to 2-methoxyethanol (0.5
mL) and THF (0.5 mL). The mixture was degassed by flushing with
nitrogen and heated in a sealed tube at 90−100 °C for 24 h. The
reaction mixture was allowed to cool to room temperature and diluted
with 20 mL cold deionized water. It was then acidified with conc HCl
to pH 2−3 and extracted four times with 20 mL of dichloromethane.
The combined organic layers were washed twice with water (40 mL),
dried over anhydrous Na2SO4, and concentrated under reduced
pressure, and the crude material was purified by silica gel
chromatography using methylene chloride/ethyl ether and ethyl
ether/ethyl acetate: 100/0 to 10/100 with 10% increments for each
ratio to afford 10-phenyl anthracene 4a as a light orange solid (72 mg,
96%): 1H NMR δ 7.81 (1H, s), 7.75−7.40 (6H, m), 6.83 (1H, s), 6.81
(2H, s), 6.61 (2H, s), 4.07 (3H, s), 3.86 (3H, s), 3.71 (6H, s). 13C
7.70−7.55 (3H, m), 6.80 (3H, s), 6.60 (2H, s), 4.06 (3H, s), 3.9 (3H,
s), 3.7 (6H, s), 3.6 (6H,s). 13C NMR δ 170.2, 153.0, 149.3, 149.2,
148.3, 137.6, 137.4, 135.8, 135.8, 133.9, 133.1, 133.1, 133.0, 133.0,
132.2, 130.4, 130.2, 129.8, 129.6, 128.5, 128.4, 128.3, 128.2, 128.1,
126.6, 126.5, 126.4, 125.9, 122.8, 115.2, 114.0, 104.3, 103.6, 56.6, 56.4,
55.9, 55.8. MS-TOF calcd for C37H32O8 604.21, found m/z 603.3 (M
− 1); HRMS ESI calcd for MH+ C37H33O8 605.2175, found 605.2163.
FTIR (neat): ν 3526 (br), 2935, 2831, 1491, 1237 cm−1. Tg = 143.5
°C.
4,5-Dimethoxy-2-(2,3,6,7-tetramethoxy-10-(pyren-1-yl)-
anthracen-9-yl)benzoic Acid (4c). Bromo-anthracene 3a (100 mg,
0.179 mmol), Pd (PPh3)4, (75.2 mg, 0.065 mmol), pyrene-1-boronic-
acid (199 mg, 0.809 mmol), potassium fluoride (93.9 mg, 1.62 mmol),
and silver(I) oxide (50.3 mg, 0.217 mmol) were added to 2-
methoxyethanol (25 mL). The mixture was degassed by flushing with
nitrogen and heated in a sealed tube at 130 °C for 48 h. The reaction
was allowed to cool to room temperature, diluted with 20 mL cold
deionized water, acidified with concentrated HCl to pH 2−3, and then
extracted four times with 20 mL of dichloromethane. The combined
organic layers were washed twice with water (40 mL) and dried over
anhydrous Na2SO4. Concentration under reduced pressure and
purification of the resulting residue by silica gel chromatography
eluting with methylene chloride/ethyl ether followed by ethyl ether/
ethyl acetate (100% to 10% with 10% increments for each interval)
afforded pyrenyl derivative 4c (95.5 mg, 79%) as a light cream-colored
1
solid: H NMR (mixture of atropisomers; doubled peaks noted) δ
8.42−8.40 and 8.41−8.38 (1H, 2d, J = 7.8 Hz), 8.28−8.01 (8H, m),
7.90 (1H, s), 7.86−7.83 and 7.85−7.82 (1H, 2d, J = 9.0 Hz), 7.52−
7.49 and 7.51−7.48 (1H, 2d, J = 9 Hz,), 7.00 and 6.99 (1H, 2s), 6.72
(2H, s), 6.51 (2H, s), 4.12 (3H, s), 3.96 and 3.93 (3H, 2s), 3.74 (6H,
s), 3.35 (6H, s); 13C NMR δ 168.8, 168.6, 152.8, 149.28, 149.25,
149.18, 149.14, 148.15, 135.53, 135.41, 134.7, 132.1, 132.0, 131.4,
131.3, 131.2, 131.16, 131.0, 130.43, 130.36, 129.6, 129.2, 129.0, 128.2,
127.6, 126.9, 126.8, 126.1, 125.8, 125.7, 125.3, 125.2, 125.1, 124.9,
122.6, 122.5, 115.0, 114.9, 113.9, 109.7, 104.3, 104.23, 104.16, 103.4,
56.4, 56.1, 55.7, 55.6, 55.43, 55.37. MS −TOF calcd for C43H34O8
678.23, found m/z 677.3 (M − 1). HRMS ESI MH+ calcd for
C43H35O8 679.2332, found 679.2289. FTIR (neat): ν 3527 (br), 2920,
2851, 1738 and 1717 (atropisomer CO’s), 1461, 1260 cm−1; Tg =
130.13 °C, Tm = 228.78 °C, Td = 348.37 °C. Tg = 120−125 °C. The
individual atropisomers were separated by preparative plate
1
chromatography to afford the two separate atropisomers of 4c: H
NMR for second eluted isomer δ 8.41 (1H, d, J = 7.9 Hz), 8.28 (1H,
dd, J = 7.9, 4.0 Hz, 3.9 Hz), 8.23 (2H, d, J = 4.4 Hz), 8.04 (1H, t, J =
8.0 Hz), 8.12 (2H, m), 7.90 (1H, s), 7.83 (1H, d, J = 9.2 Hz) d), 7.49
(1H, d, J = 9.2 Hz), 6.99 (1H, s), 6.75 (2H, s), 6.50 (2H, s), 4.12 (3H,
s), 3.96 (3H, s), 3.75 (6H, s), 3.35 (6H, s).
F
dx.doi.org/10.1021/jo302139w | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
(4,5-Dimethoxy-2-(2,3,6,7-tetramethoxy-10-phenylanthra-
cen-9-yl)phenyl)methanol (5a). Phenyl anthracene derivative 4a
(122 mg, 0.22 mmol) was dissolved in THF (0.4 mL). A solution of
lithium aluminum hydride (0.45 mL, 0.45 mmol, 1.0 M in THF) was
added gradually via syringe, and the reaction was then heated to reflux
under nitrogen for 19 h. The reaction was then allowed to cool to
room temperature, diluted with 15% aqueous sodium hydroxide (1.0
mL), stirred for 10 min, and then diluted with THF (1.0 mL) followed
by water (1.0 mL). The reaction was dried over MgSO4, filtered, and
washed successively with THF, dichloromethane, and ethyl acetate.
Concentration under reduced pressure afforded a residue which was
purified by silica gel column chromatography eluting with toluene/
dichloromethane and dichloromethane/ether (100% to 10% with 10%
increments for each interval) to obtain 5a as a light orange solid (92.6
HRMS-ESI m/z calcd for C43H36O7 664.2456, found 664.2456; M −
OH calcd for C43H35O6 (M − OH) 647.2428, found 647.2446; calcd
for C43H36O7Na (M + Na+) 687.2353, found 687.2356. Tg = 115−120
°C.
CCDC 899435 and 899436 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
ASSOCIATED CONTENT
* Supporting Information
■
S
Copies of spectral data (1H NMR, 13C NMR, IR, and HRMS),
X-ray structure orteps of ethyl ester 3b, and complete X-ray
crystallography tables for both bromoanthracenes 3a and 3b.
This material is available free of charge via the Internet at
http://pubs.acs.org.
1
mg, 88%): H NMR (500 MHz, CDCl3) δ 7.63−7.45 (5H, m), 7.29
(1H, s), 6.87 (1H, s), 6.83 (2H, s), 6.70 (2H, s), 4.24 (2H, s), 4.07
(3H, s), 3.86 (3H, s), 3.74 (6H, s), 3.73(6H, s); 13C NMR δ 149.0,
148.7, 148.3, 148.2, 139.23, 139.14, 133.1, 132.3, 130.6, 130.1, 129.6,
129.4, 128.3, 127.2, 125.8, 125.5, 113.43, 113.39, 110.9, 103.9, 103.8,
102.94, 102.88, 62.8, 55.8, 55.7, 55.5, 55.4, 55.3, 55.2, 55.1. HRMS-
TOF m/z calcd for [C33H32O7] + Na+ 563.2046, found 563.2048 (M
+ Na+). FTIR (neat): ν 3498 (br), 2916, 2848, 1489, 1235 cm−1; Tg
=165.6 °C. Tm = 197−203 °C.
AUTHOR INFORMATION
Corresponding Author
*E-mail: dbecke3@luc.edu.
■
Notes
The authors declare no competing financial interest.
(4,5-Dimethoxy-2-(2,3,6,7-tetramethoxy-10-(naphthalen-2-
yl)anthracen-9-yl)phenyl)methanol (5b). Naphthyl anthracene
derivative 4b (88 mg, 0.145 mmol) was dissolved in THF (0.29
mL). A solution of lithium aluminum hydride (0.29 mL, 0.29 mmol,
1.0 M in THF) was added gradually via syringe, and the reaction was
heated to reflux under nitrogen for 24 h. The reaction was then
allowed to cool to room temperature, diluted with aqueous 15%
sodium hydroxide (1.0 mL), stirred for 10 min, then diluted with THF
(1.0 mL) followed by 1.0 mL water, dried with MgSO4, filtered and
washed with THF, dichloromethane, and ethyl acetate, concentrated
under reduced pressure, and purified by silica gel column
chromatography eluting with toluene/dichloromethane and dichloro-
methane/ether (100% to 10% with 10% increments for each interval)
ACKNOWLEDGMENTS
■
NSF Grant DBI-0216630 is gratefully acknowledged for the
Varian UNITY-300 NMR obtained through the NSF Biological
Major Instrumentation Program. The X-ray diffractometer was
funded by NSF Grant 0087210, Ohio Board of Regents Grant
CAP-491, and by Youngstown State University.
DEDICATION
■
Dedicated to the memory of the late Professor Howard E.
Zimmerman.
1
to obtain 5b as a light orange solid (85.9 mg, 100%): H NMR (500
MHz, CDCl3) δ 8.07 (1H, dd, J = 8.4, 3.9 Hz), 8.04−7.92 (3H, m),
7.68−7.56 (3H, m), 7.31 (1H, s), 6.891 and 6.886 (1H, two s,
atropisomers), 6.86 (2H, s), 6.73 (2H, s), 4.26 (2H, s), 4.08 (3H, s),
3.874 and 3.872 (3H, two s, atropisomers), 3.74 (6H, s), 3.64 (6H, s),
2.30 (1H,s); 13C NMR δ 149.6, 149.4, 148.9, 148.8, 137.4, 137.37,
134.0, 133.4, 133.0, 132.93, 130.8, 130.3, 130.2, 129.6, 129.3, 128.6,
128.5, 128.4, 128.2, 126.6, 126.5, 126.3, 125.6, 114.0, 114,0, 111.6,
104.5, 104.4, 103.6, 103.57, 63.5, 56.4, 56.2, 56.0, 55.96, 55.88, 55.83;
HRMS-ESI calcd for C37H34O7 590.2299, m/z found 590.2293 (M+);
M − OH calcd for C37H33O6 573.2272, m/z found 573.2279 (M −
OH)+; M + Na+ calcd for C37H34O7Na 613.2197, m/z found 613.2188
(M + Na+). Tm = 202−205 °C.
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