New C3v-symmetrical tribenzotriquinacenes bearing extended and oxy-functionalised alkyl groups at their benzhydrylic bridgeheads

Article abstract of DOI:10.1039/c0ob00337a

A series of tribenzotriquinacene derivatives bearing three oxy-functionalised alkyl groups at the benzhydrylic bridgeheads (C-4b, C-8b and C-12b) have been synthesised. The 4b,8b,12b-triallyl derivative was used to generate the corresponding TBTQ-tris-acetaldehyde and TBTQ-tris(acetic acid), in which the functional groups stretch out from the convex rigid molecular surface. The corresponding tribromo derivate was found to undergo smooth Lewis acid-catalyzed C-C coupling with appropriate silyl enol ethers to afford a series of threefold 4b,8b,12b-(2-oxoalkyl)-substituted tribenzotriquinacenes. Six-fold nitration at the arene periphery was performed with 4b,8b,12b-tripropyltribenzotriquinacene and with the TBTQ-tris(acetic acid) to check for the effect of the bridgehead groupings as solubilising auxiliaries.

Full text of DOI:10.1039/c0ob00337a

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www.rsc.org/obc | Organic & Biomolecular Chemistry
New C3v-symmetrical tribenzotriquinacenes bearing extended and
oxy-functionalised alkyl groups at their benzhydrylic bridgeheads†
Ehsan U. Mughal and Dietmar Kuck*
Received 28th June 2010, Accepted 18th August 2010
DOI: 10.1039/c0ob00337a
A series of tribenzotriquinacene derivatives bearing three oxy-functionalised alkyl groups at the
benzhydrylic bridgeheads (C-4b, C-8b and C-12b) have been synthesised. The 4b,8b,12b-triallyl
derivative was used to generate the corresponding TBTQ-tris-acetaldehyde and TBTQ-tris(acetic acid),
in which the functional groups stretch out from the convex rigid molecular surface. The corresponding
tribromo derivate was found to undergo smooth Lewis acid-catalyzed C–C coupling with appropriate
silyl enol ethers to afford a series of threefold 4b,8b,12b-(2-oxoalkyl)-substituted tribenzotriquinacenes.
Six-fold nitration at the arene periphery was performed with 4b,8b,12b-tripropyltribenzotriquinacene
and with the TBTQ-tris(acetic acid) to check for the effect of the bridgehead groupings as solubilising
auxiliaries.
Introduction
Tribenzotriquinacene 1 and its derivatives1 represent polycyclic
structures with unique geometrical features and a particularly
high chemical versatility.2 Owing to the rigid, convex–concave
triquinacene core,3,4 the tribenzotriquinacenes contain three in-
dane wings stretching at right angles into space,5 which has
opened a facile access to extended conformationally rigid, convex–
concave scaffolds with pronounced propensity to form non-
covalent adducts with globular partners, such as C60.6,7 In recent
years, the potential of multiple functionalisation and polycyclic
extension of the arene periphery of the tribenzotriquinacene
framework has been demonstrated in detail and the potential
of tribenzotriquinacene-derived building blocks in supramolec-
ular chemistry and other fields of application has become
Scheme 1 Tribenzotriquinacene 1, two particular derivatives (2, 3) and
obvious.2,5–10 Both C3v-symmetrical (and thus achiral, e.g. 2)
and C3-symmetrical (and thus chiral, e.g. 3), derivatives have
been synthesised, as generalised by structure 4 in Scheme 1.
The unique geometrical properties of the tribenzotriquinacene
motif has proven to materialize in self-organised supramolecular
structures, such as in enantiopure cubic aggregates consisting of
the hexafunctionalised derivative 3.11
However, enlargement of highly regular polycyclic structures
is often accompanied by restricted solubility. While introduction
of long-chain solubilising residues at the aromatic periphery
may rather prevent a desired intended supramolecular aggre-
gation, attachment of such groupings at the three benzhydrylic
bridgeheads (C-4b, C-8b and C-12b) of the tribenzotriquinacene
skeleton represents a promising alternative. Thus, three (possibly
functionalised) alkyl groups at these outer bridgehead positions
are expected to increase the solubility of tribenzotriquinacene
derivatives bearing multiple functional groups and/or polycyclic
extensions at the aromatic periphery. In this article, we wish to
report on our first progress in this respect.
generalised derivatisation (4).
Results and discussion
As shown earlier for numerous cases, the 4b,8b,12b-tribromo
derivative 5 of 12d-methyltribenzotriquinacene is the most easily
accessible starting point for bridgehead substitution.12,13 This
compound can be converted by SN1-type reactions into a large
variety of heteroatom-coupled derivatives, including alkyl ethers
and thioethers as well as some respective oligoethers.5,14 However,
coupling of 5 with metal–organic reagents, such as Grignard
compounds or organolithium partners, proved to be difficult.5a
This may be attributed to the inevitable SN1-type reactivity at
the bridgehead positions of the three-fold benzhydrylic bromide
5. In turn, just because of that reactivity, various Lewis acid-
catalyzed condensation reactions of this key compound, includ-
ing the condensation with allyltrimethylsilane (see below), were
found to be useful. In our attempts to introduce various larger
aliphatic residues at the bridgehead positions, condensation of
tribromide 5 with several trimethylsilyl enol ethers was stud-
ied. The silyl enol ethers 6a–6f were synthesised according to
Corey’s method15 and then reacted with tribromide 5 in the
presence of either tin tetrachloride or titanium tetrachloride in
Department of Chemistry, Bielefeld University, Universita¨tsstraße 25, 33615
Bielefeld, Germany
† Electronic supplementary information (ESI) available: 1H NMR spectra.
See DOI: 10.1039/c0ob00337a
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tripropyl congener 14 in good yield (Scheme 3).16 Since, unfortu-
nately, metathesis reactions of triallyltribenzotriquinacene 13 with
1-alkenes under various conditions proved to be unsuccessful,17,18
we focused our efforts on the use of this hydrocarbon as a starting
material for the synthesis of new bridgehead-oxyfunctionalised
derivatives.
Ozonolysis of hydrocarbon 13 followed by reductive work-
up using triphenylphosphine gave the tribenzotriquinacene-based
tris-acetaldehyde 15 in good yield.19 This work-up procedure
turned out to be productive when run at ambient temperature
for an extended period of time. However, it may be noted
that the cleavage of the three olefinic bonds in compound
13 and/or of the ozonide intermediates is not at all trivial.
In spite of the fact that consumption of three equivalents of
ozone was observed as expected, several reductive work-up
procedures failed, including the use of dimethyl sulfide (in the
presence or absence of methanol),20a zinc and acetic acid,20b and
aqueous acetone.20c None of these reagents gave the desired
tris-aldehyde 15. Similarly, oxidative work-up of the ozonide
mixture by use of hydrogen peroxide and acetic acid20d under
various conditions failed. The extent of conversion was checked
by NMR spectroscopy and the ozonides were found to be
partially persistent under the various conditions and with different
reagents examined. Moreover, the direct attempts to oxidatively
cleave the olefinic double bonds in compound 13 by using
osmium tetroxide/oxone in dimethylformamide,20e aqueous potas-
sium permanganate/Adogen 464 in dichloromethane20f or aque-
ous potassium permanganate/NaIO4/SiO2 in dichloromethane–
acetonitrile20g led to failure.
Scheme 2 Condensation of tribromotribenzotriquinacene 5 with the silyl
enol ethers 6 giving the tris(2-oxoalkyl)tribenzotriquinacenes 7–12.
dichloromethane (Scheme 2). Thus, 4b,8b,12b-tris(acetonyl)-12d-
methyltribenzotriquinacene (7) was synthesised in good yield by
use of SnCl4 as the catalyst. Surprisingly, however, it did not form
when TiCl4 was employed. By contrast, all of the higher 2-oxoalkyl
derivatives 8–12 were obtained in moderate to good yields by
use of the latter catalyst. Most of these triketones (7–10) were
found to crystallize readily and even the long-chain derivatives 11
and 12 formed waxy solids, in spite of the considerably elongated
bridgehead substituents.
Triallyltribenzotriquinacene 13, which is easily accessible from
5 as described previously,5a may also be used as a valuable key
intermediate. Catalytic hydrogenation using Pd/C in ethyl acetate
under normal pressure smoothly afforded the corresponding
Notwithstanding these difficulties, tris-aldehyde 15 obtained
after work-up with triphenylphosphine was found to be sur-
prisingly stable under air and the subsequent oxidation with
Scheme 3 Triallyltribenzotriquinacene 13 as the key intermediate in the synthesis of some new tribenzotriquinacene derivatives, most of which bear
three oxy-functionalised bridgehead groups.
5384 | Org. Biomol. Chem., 2010, 8, 5383–5389
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oxone (2 K2SO5 · K2SO4 · KHSO4) afforded the corresponding
tribenzotriquinacene-tris(acetic acid) 16 in good yield. Esteri-
fication of this compound with methanol in the presence of
thionyl chloride proceeded at ambient temperature to furnish
the corresponding three-fold methyl acetate 17. Reduction of
the tris-aldehyde 15 by use of lithium aluminium hydride in
tetrahydrofuran gave the corresponding tris-ethanol 18, and
subsequent etherification of the latter compound with n-butyl
bromide in dimethyl sulfoxide led to the respective long-chain tris-
ether 19. Yields of these conversions were satisfactory in all cases.
The compounds were obtained in pure form by chromatography
or crystallisation and all of them were found to crystallise quite
readily. In all cases, spectroscopic and other analytical results
documented the absence of products of incomplete (e.g., two-
fold) conversions. The expected C3v molecular symmetry of
compounds 15–19 was confirmed by their 1H and 13C NMR
spectra.
Finally, some of the new bridgehead-substituted triben-
zotriquinacenes were subjected to electrophilic substitution at
the six peripheral arene positions (Scheme 4). Six-fold nitration
of the fully bridgehead-alkylated hydrocarbon 14 was attempted
by use of a mixture of nitric acid (100%) and concentrated
sulfuric acid, in analogy to the very efficient sixfold nitration
of the tetramethyl congener.8 Remarkably, this conversion was
found to be considerably hampered due to a reduced solubility
of 14 in the highly polar acid mixture, resulting in the visible
aggregation of partially nitrated products. However, this problem
was circumvented by use of a mixture of acetic anhydride and
glacial acetic acid as a co-solvent. With this modification, the
2,3,6,7,10,11-hexanitrotribenzotriquinacene 20 was obtained in
virtually quantitative yield. Under the same conditions, the
corresponding hexanitrotribenzotriquinacene-tris(acetic acid) 21
was synthesised from tris-acid 16 in excellent yield albeit with
increased reaction time to ensure the exhaustive nitration of the
six peripheral positions.
gener 13 were used as the starting compounds. On the one hand,
Lewis acid-assisted three-fold C–C coupling of 5 with various
trimethylsilyl enol ethers afforded the introduction of three (2-
oxo)-functionalised alkyl chains; on the other hand, ozonolytic
cleavage of 13 followed by re-functionalisation led us to new
tribenzotriquinacenes bearing three functionalised C2 residues.
Among these, the tris-aldehyde 15 promises to be another key
intermediate for the synthesis of long-chain bridgehead TBTQ
derivatives. In line with expectation, the presence of three larger
(and possibly functionalised) bridgehead substituents were found
to affect the solubility of the tribenzotriquinacenes, as observed
in the case of six-fold nitration of the arene periphery. This
first access to tribenzotriquinacenes bearing extended solubilising
bridgehead substituents and multifunctionalised arene peripheries
is encouraging in view of the vast potential of the triben-
zotriquinacenes for the construction of novel three-dimensional,
non-covalent aggregates but also for covalently bound,
nanoscale molecular containers with, for example, nanocubic
topology.2,11,21
Experimental section
General
Melting points (uncorrected): Electrothermal melting point appa-
ratus. Infrared spectra were recorded on an FT-IR spectrometer,
Model Nicolet-380. Most of the NMR spectra were measured on
a Bruker DRX 500 instrument (1H, 500 MHz, 13C: 125.7 MHz);
only in one case a Bruker Avance 600 instrument (1H, 600 MHz,
13C: 150.8 MHz) was employed. Mass spectra were recorded with
a VG Autospec double focusing mass spectrometer. MALDI mea-
surements were made with Voyager-DE MALDI-TOF. Accurate
mass measurements were performed with a VG Autospec X sector-
field instrument and a Bruker APEX III (7.0 T) FT ion cyclotron
mass spectrometer. Combustion analyses were carried out with a
Perkin-Elmer Model 240 instrument. Tetrahydrofuran was dried
over potassium and dichloromethane was used as delivered (p.a).
n-Pentane and ethyl acetate were distilled before use. Reactions
requiring anhydrous conditions were performed in oven-dried
glassware under argon.
General procedure for the preparation of silyl enol ethers 6a–6f
Into an oven-dried 25 mL flask under argon was placed lithium
diisopropyl amide from a commercially available 2.0 M solution
(0.60 mL, 1.2 mmol) in 1 mL of dry tetrahydrofuran at -78 ◦C. A
solution of trimethylsilyl chloride (6.00 mmol) in 2.0 mL of THF
was added and stirred, followed by dropwise addition of the
substrate (1.00 mmol) in 1.0 mL of THF. After 1 min, 0.80 mL of
anhydrous triethylamine was added and stirring was continued for
50 min at the same temperature. Then the mixture was allowed to
warm to ambient temperature and then quenched by addition of
saturated aqueous sodium bicarbonate. The product was extracted
twice into n-pentane and the combined extracts were washed first
with water, then with 0.05 M citric acid solution and again with
water. Drying over Na2SO4 followed by evaporation of the solvent
gave the crude silyl enol ethers, which were purified by Kugelrohr
distillation.
Scheme 4 Six-fold nitration of the tribenzotriquinacenes 14 and 16 at
their arene periphery.
Conclusion
In summary, we have developed a facile access to several new
C3v-symmetrical tribenzotriquinacenes bearing elongated and,
in most cases, functionalised alkyl groups at their benzhydrylic
bridgeheads. The bridgehead tribromide 5 and the triallyl con-
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12d-Methyl-4b,8b,12b-tris(2-oxopropyl)-4b,8b,12b,12d-
12d-Methyl-4b,8b,12b-tris(4-methyl-2-oxopentyl)-4b,8b,12b,12d-
tetrahydrodibenzo[2,3:4,5]pentaleno[1,6-ab]indene (7)
tetrahydrodibenzo[2,3:4,5]pentaleno[1,6-ab]indene (9)
A solution of tribromide 5 (531 mg, 1.00 mmol) in anhydrous
dichloromethane (10 mL) was stirred under argon and cooled
to -42 ◦C. Tin tetrachloride (0.38 mL, 3.3 mmol) was added
under argon through a septum. After dropwise addition of 2-
propenyl trimethylsilyl ether (6a) (0.60 mL, 3.6 mmol), stirring was
continued at the same temperature for a further 2–3 h, while the
reaction was monitored by TLC. After the complete consumption
of compound 5, the reaction mixture was quenched with water and
then extracted several times with dichloromethane. The combined
organic extracts were washed with water and dried over Na2SO4.
Evaporation of the solvent furnished the crude product, which
was recrystallised from ethanol to give the triketone 7 (yield
356 mg, 77%) as colorless crystals, mp 290–292 ◦C; IR (neat):
Yield 394 mg, 67%; colorless crystalline solid, mp 202–203 ◦C; IR
-1
1
˜
(neat): n = 3023, 2948, 2867, 1707, 1479, 747, 607, 580 cm . H
NMR (500 MHz, CDCl3): d 7.24 and 7.12 (AA¢BB¢, 2 ¥ 6H, Ar–
H), 3.61 (s, 6H, 3 ¥ CH2), 2.30 (d, J = 6.9 Hz, 6H, 3 ¥ CH2), 2.10
(m, 3H, 3 ¥ CH), 1.32 (s, 3H, 12d-CH3), 0.88 (d, 3J = 6.6 Hz, 18H,
3 ¥ C(CH3)2); 13C NMR (125.7 MHz, CDCl3): d 208.8 (CO), 146.7
(C), 126.7 (CH), 121.4 (CH), 69.9 (C), 64.8 (C), 51.8 (3 ¥ CH2),
50.2 (3 ¥ CH2), 23.9 (3 ¥ CH), 21.8 (3 ¥ C(CH3)2), 14.8 (12d-CH3);
∑
MS (EI, 70 eV): m/z (%), 588 (11, [M]+ ), 489 (100), 389 (12), 319
∑
(10), 289 (17); accurate mass (EI-MS) of [M]+ : calcd. for C41H48O3
588.3604; found 588.3600.
12d-Methyl-4b,8b,12b-tris(3,3-dimethyl-2-oxobutyl)-4b,8b,
12b,12d-tetrahydrodibenzo[2,3:4,5]pentaleno[1,6-ab]indene (10)
-1
1
˜
n = 3023, 2917, 2359, 1705, 1588, 1480, 1154, 746, 553 cm . H
NMR (600 MHz, CDCl3): d 7.22 and 7.11 (AA¢BB¢, 2 ¥ 6H,
Ar–H), 3.59 (s, 6H, 3 ¥ CH2), 2.10 (s, 9H, 3 ¥ COCH3), 1.29 (s,
3H, 12d-Me); 13C NMR (150 MHz, CDCl3): d 207.9 (CO), 147.6
(C), 127.9 (CH), 122.5 (CH), 71.1 (C), 65.9 (C), 51.3 (3 ¥ CH2),
31.3 (3 ¥ CH3), 15.7 (CH3, 12d-Me); MS (EI, 70 eV): m/z (%),
Yield 494 mg, 84%; colorless crystalline solid, mp 259–261 ◦C;
-1
˜
IR (neat): n = 3024, 2965, 2359, 1708, 1478, 1054, 997, 972 cm .
1H NMR (500 MHz, CDCl3): d 7.24 and 7.12 (AA¢BB¢, 2 ¥ 6H,
Ar–H), 3.73 (s, 6H, 3 ¥ CH2), 1.21 (s, 3H, 12d-CH3), 1.17 (s,
27H, 3 ¥ C(CH3)3); 13C NMR (125.7 MHz, CDCl3): d 214.7 (CO),
147.6 (C), 127.3 (CH), 122.0 (CH), 70.5 (C), 65.2 (C), 44.6 (3 ¥
CH2), 44.3 (3 ¥ C(CH3)3), 26.9 (3 ¥ C(CH3)3), 15.2 (12d-CH3);
∑
462 (19, [M]+ ), 405 (100), 347 (54), 305 (14), 289 (40); accurate
∑
mass (EI-MS) of [M]+ : calcd. for C32H30O3 462.2195; found
462.2192.
∑
MS (EI, 70 eV): m/z (%), 588 (4, [M]+ ), 489 (100), 389 (9), 319
∑
(12), 289 (16); accurate mass (EI-MS) of [M]+ : calcd. for C41H48O3
General procedure for the preparation of the tribenzotriquinacene-
based triketones 8–12
588.3604; found 588.3597.
12d-Methyl-4b,8b,12b-tris(2-oxoheptyl)-4b,8b,12b,12d-
tetrahydrodibenzo[2,3:4,5]pentaleno[1,6-ab]indene (11)
A
solution of tribromide 5 (1.00 mmol) in anhydrous
dichloromethane (10 mL) was stirred under argon and cooled
to -23 ◦C. Titanium tetrachloride (0.36 mL, 3.3 mmol) was
added under argon through a septum followed by the dropwise
addition of the appropriate silyl enol ether (6b–6f) (3.6 mmol).
Stirring was continued at the same temperature for a further 2–
3 h, while the reaction was monitored by TLC. After the complete
consumption of compound 5, the reaction mixture was allowed
to warm to ambient temperature, then quenched with water
and extracted several times with dichloromethane. The combined
organic extracts were washed with water and dried over Na2SO4.
Evaporation of the solvent furnished the crude product, which was
recrystallised from ethanol to give the respective pure triketones
8–12.
Yield 378 mg, 60%; colorless solid; mp 166–168 ◦C; FT-IR (neat):
-1
1
˜
n = 3023, 2955, 2871, 1710, 1479, 1368, 1065, 739, 508 cm . H
NMR (500 MHz, CDCl3): d 7.25 and 7.13 (AA¢BB¢, 2 ¥ 6H, Ar–
3
H), 3.61 (s, 6H, 3 ¥ CH2), 2.43 (t, J = 7.5 Hz, 6H, 3 ¥ CH2),
1.54–1.51 (m, 6H, 3 ¥ CH2), 1.30–1.22 (m, 15H, 6 ¥ CH2 and 12d-
CH3), 0.90 (t, 3J = 7.0 Hz, 9H, 3 ¥ CH3); 13C NMR (125.7 MHz,
CDCl3): d 209.2 (CO), 146.7 (C), 126.7 (CH), 121.8 (CH), 69.9
(C), 64.8 (C), 49.6 (3 ¥ CH2), 42.9 (3 ¥ CH2), 30.7 (3 ¥ CH2), 22.9
(3 ¥ CH2), 21.8 (3 ¥ CH2), 14.9 (12d-CH3), 13.2 (3 ¥ CH3); MS (EI,
∑
70 eV): m/z (%), 630 (6, [M]+ ), 517 (100), 405 (11), 403 (11), 305
∑
(11), 289 (19); accurate mass (EI-MS) of [M]+ : calcd. for C44H54O3
630.4073; found 630.4058.
12d-Methyl-4b,8b,12b-tris(2-oxohexyl)-4b,8b,12b,12d-
12d-Methyl-4b,8b,12b-tris(2-oxononyl)-4b,8b,12b,12d-
tetrahydrodibenzo[2,3:4,5]pentaleno[1,6-ab]indene (8)
tetrahydrodibenzo[2,3:4,5]pentaleno[1,6-ab]indene (12)
◦
Yield 370 mg, 63%; colorless crystalline solid, mp 175–176 ◦C; IR
Yield 357 mg, 50%; colorless solid, mp 157–159 C; IR (neat): n =
˜
-1
˜
(neat): n = 3022, 2956, 2871, 1709, 1588, 1489, 1031, 690 cm .
3023, 2955, 2921, 1708, 1480, 1368, 1127, 730, 615 cm-1. 1H NMR
(500 MHz, CDCl3): d 7.24 and 7.13 (AA¢BB¢, 2 ¥ 6H, Ar–H), 3.61
(s, 6H, 3 ¥ CH2), 2.43 (t, 3J = 7.3 Hz, 6H, 3 ¥ CH2), 1.53–1.50 (m,
6H, 3 ¥ CH2), 1.30–1.26 (m, 27H, 12 ¥ CH2 and 12d-CH3), 0.90
(t, 3J = 7.0 Hz, 9H, 3 ¥ CH3); 13C NMR (125.7 MHz, CDCl3): d
209.3 (CO), 146.7 (C), 126.7 (CH), 121.4 (CH), 69.9 (C), 64.8 (C),
49.6 (3 ¥ CH2), 42.9 (3 ¥ CH2), 31.0 (3 ¥ CH2), 28.5 (3 ¥ CH2),
28.4 (3 ¥ CH2), 23.2 (3 ¥ CH2), 21.9 (3 ¥ CH2), 14.8 (12d-CH3),
1H NMR (500 MHz, CDCl3): d 7.25 and 7.13 (AA¢BB¢, 2 ¥
6H, Ar–H), 3.61 (s, 6H, 3 ¥ CH2), 2.44 (t, J = 7.5 Hz, 6H,
3 ¥ CH2), 1.52-1.49 (m, 6H, 3 ¥ CH2), 1.30-1.25 (m, 9H, 3 ¥
3
CH2 and 12d-CH3) 0.91 (t, J = 7.5 Hz, 9H, 3 ¥ Me); 13C NMR
(125.7 MHz, CDCl3): d 209.9 (CO), 147.3 (C), 127.4 (CH), 122.1
(CH), 70.1 (C), 65.5 (C), 50.2 (3 ¥ CH2), 43.3 (3 ¥ CH2), 26.0 (6 ¥
CH2), 22.3 (3 ¥ CH3) 13.9 (12d-CH3); MS (EI, 70 eV): m/z (%),
∑
∑
588 (13, [M]+ ), 489 (100), 389 (12), 305 (9), 289 (18); accurate
13.4 (3 ¥ CH3); MS (EI, 70 eV): m/z (%), 714 (7, [M]+ ), 573 (100),
433(7), 431 (9), 305 (11), 319(9), 289 (15); accurate mass (EI-MS)
of [M]+ : calcd. for C50H66O3 714.5012; found 714.5013.
∑
mass (EI-MS) of [M]+ : calcd. for C41H48O3 588.3604; found
∑
588.3604.
5386 | Org. Biomol. Chem., 2010, 8, 5383–5389
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12d-Methyl-4b,8b,12b-tri-n-propyl-4b,8b,12b,12d-
tetrahydrodibenzo[2,3:4,5]pentaleno[1,6-ab]indene
[12d-methyl-4b,8b,12b-tri(n-propyl)tribenzotriquinacene, 14]
crude product, which was then purified by diffusion crystallisation
using chloroform and diethyl ether giving the tris-acid 16 (yield
374 mg, 80%) as colorless cr◦ystals (containing some incorporated
˜
diethyl ether), mp 281–283 C; IR (neat): n = 3234, 2905, 2525,
A solution of triallyltribenzotriquinacene 13 (414 mg, 1.00 mmol)
in anhydrous EtOAc (30 mL) was mixed with palladium on
charcoal (10%, Sigma-Aldrich) (40 mg) in a hydrogenation flask
and the mixture was vigorously agitated in a hydrogenation shaker
at ambient temperature and pressure for 24 h. Filtration through
a pad of silica gel and evaporation of the solvent under reduced
pressure gave a colorless solid which was recrystallised from
ethanol furnishing hydrocarbon 1◦4 (yield 378 mg, 90%) as fine,
1
1736, 1692, 1479, 749, 514 cm-1. H NMR (500 MHz, DMSO-
d6): d 11.88 (s, 3H, 3 ¥ COOH), 7.49 and 7.08 (AA¢BB¢, 2 ¥ 6H,
Ar–H), 3.26 (s, 6H, 3 ¥ CH2), 1.56 (s, 3H, 12d-CH3); 13C NMR
(125.7 MHz, acetone-d6): d 172.4 (COOH), 147.5 (C), 127.2 (CH),
122.7 (CH), 70.6 (C), 65.4 (C), 40.7 (CH2), 14.7 (12d-CH3); MS
∑
(EI, 70 eV): m/z (%), 468 (29, [M]+ ), 409 (100), 349 (84), 303 (23),
∑
289 (35); accurate mass (EI-MS) of [M]+ : calcd. for C29H24O6
468.1573; found 468.1590.
˜
transparent needles, mp 240–241 C; IR (neat): n = 3063, 3021,
2953, 1477, 1452, 1026, 741, 655 cm-1. 1H NMR (500 MHz,
3
CDCl3): d 7.31 and 7.14 (AA¢BB¢, 2 ¥ 6H, Ar–H), 2.19 (t, J =
4b,8b,12b-Tris(methoxycarbonylmethyl)-12d-methyl-4b,8b,12b,
12d-tetrahydrodibenzo[2,3:4,5]pentaleno[1,6-ab]indene (trimethyl
12d-methyltribenzotriquinacene 4b,8b,12b-tris-acetate, 17)
8.1 Hz, 6H, 3 ¥ CH2), 1.63 (s, 3H, 12d-CH3), 1.24-1.16 (m, 6H, 3 ¥
CH2), 0.95 (t, 3J = 7.5 Hz, 9H, 3 ¥ CH3); 13C NMR (125.7 MHz,
CDCl3): d 148.1 (C), 127.1 (CH), 123.3 (CH), 71.7 (C), 67.2 (C),
40.8 (CH2), 20.5 (CH2), 15.1 (12d-CH3 and 4b, 8b,12b-CH3); MS
A solution of the triacid 16 (468 mg, 1.00 mmol) in anhydrous
methanol (12.0 mL) was stirred and cooled to 0 ◦C. Thionyl
chloride (0.89 mL, 12.0 mmol) was added dropwise under argon
through a septum and then stirring was continued for 48 h at
25 ◦C. The solvent was removed under reduced pressure and the
residual product was extracted with diethyl ether. The ethereal
layer was washed first with saturated sodium bicarbonate solution
and then with water, and then dried over Na2SO4. Evaporation of
solvent under reduced pressure gave the crude product, which was
recrystallised from ethanol to give◦triester 17 (yield 372 mg, 73%)
∑
(EI, 70 eV): m/z (%), 420 (3, [M]+ ), 377 (100), 334 (3), 305 (8),
289 (10); Elemental analysis: Found C, 91.25; H, 8.62; Calc. for
C32H36: C, 91.37; H, 8.63.
4b,8b,12b-Tris(formacylmethyl)-12d-methyl-4b,8b,12b,12d-
tetrahydrodibenzo[2,3:4,5]pentaleno[1,6-ab]indene
(12d-methyltribenzotriquinacene 4b,8b,12b-tris-acetaldehyde, 15)
A solution of triallyltribenzotriquinacene 13 (414 mg, 1.00 mmol)
in anhydrous dichloromethane (6.0 mL) was placed in a
two-necked round bottom flask and cooled to -78 ◦C. An
ozone/oxygen mixture was bubbled through the solution until
the blue color appeared. After a further 3 min, the excess of
ozone was removed by flushing the solution with argon. Then
triphenylphosphine (2.36 g, 9.00 mmol) was added to the solution.
˜
as colorless crystals, mp 197–198 C; IR (neat): n = 3627, 2949,
2600, 1732, 1558, 1478, 1154, 750, 680 cm-1; 1H NMR (500 MHz,
CDCl3): d 7.34 and 7.19 (AA¢BB¢, 2 ¥ 6H, Ar–H), 3.55 (s, 9H, 3 ¥
OCH3), 3.41 (s, 6H, 3 ¥ CH2), 1.69 (s, 3H, 12d-CH3); 13C NMR
(125.7 MHz, CDCl3): d 171.2 (COOCH3), 145.7 (C), 126.7 (CH),
121.5 (CH), 69.8 (C), 64.3 (C), 50.3 (CH3), 40.4 (CH2), 14.4 (12d-
◦
∑
CH3); MS (EI, 70 eV): m/z (%), 510 (13, [M]+ ), 437 (100), 363
The mixture was allowed to warm to 20 C and then stirred for
∑
(15), 303 (14), 289 (29); accurate mass (EI) of [M]+ : calcd. for
15 h. The solvent was removed under reduced pressure and the
crude mixture was then purified by chromatography through silica
gel (EtOAc/c-C6H12 1 : 3) to furnish the tris-aldehyde 15 (yield
353 mg, 84%) as colorless crystals, mp 260–262 ◦C; IR (neat):
C32H30O6 510.2042; found 510.2048.
-1
1
˜
n = 3420, 3069, 2967, 2740, 1715, 1480, 763, 510 cm . H NMR
(500 MHz, DMSO-d6): d 9.48 (s, 3H, 3 ¥ CHO), 7.62 and 7.21
(AA¢BB¢, 2 ¥ 6H, Ar–H), 3.47 (s, 6H, 3 ¥ CH2), 1.21 (s, 3H, 12d-
CH3); 13C NMR (125.7 MHz, DMSO-d6): d 202.8 (CHO), 146.4
(C), 127.9 (CH), 123.3 (CH), 70.2 (C), 64.8 (C), 50.7 (CH2), 18.6
4b,8b,12b-Tris(2-hydroxyethyl)-12d-methyl-4b,8b,12b,12d-
tetrahydrodibenzo[2,3:4,5]pentaleno[1,6-ab]indene
(12d-methyltribenzotriquinacene 4b,8b,12b-tris-ethanol, 18)
To a suspension of ground lithium aluminium hydride (74 mg,
2.0 mmol) in anhydrous tetrahydrofuran (30 mL) was added
dropwise a solution of tris-acetaldehyde 15 (420 mg, 1.00 mmol)
and then the mixture was refluxed for 8 h. After cooling with
ice/water, the product mixture was carefully hydrolyzed with
crushed ice and extracted several times with diethyl ether. The
combined organic extracts were washed with water and dried over
Na2SO4. The solvent was evaporated to give the trialcohol 18 (yield
294 mg, 69%) as a colorless, fluffy solid, mp 289–291 ◦C; IR (neat):
∑
(12d-CH3); MS (EI, 70 eV): m/z (%), 420 (15, [M]+ ), 377 (100),
348 (42), 335 (28), 289 (46). Elemental analysis: Found C, 82.68;
H 5.84; Calc. for C29H24O3: C, 82.83; H, 5.75.
4b,8b,12b-Tris(carboxylmethyl)-12d-methyl-4b,8b,12b,12d-
tetrahydrodibenzo[2,3:4,5]pentaleno[1,6-ab]indene
[12d-methyltribenzotriquinacene 4b,8b,12b-tris(acetic acid), 16]
-1
1
˜
A solution of tris-aldehyde 15 (420 mg, 1.00 mmol) in dimethyl-
formamide (25 mL) was stirred while oxone (9.8 g, 16.00 mmol)
was added in one portion. Stirring was continued for 24 h and
the reaction was monitored by TLC. Aqueous hydrochloric acid
(1 N) was added to dissolve the salts and the organic products were
extracted with ethyl acetate. The combined organic extracts were
washed with HCl (1 N), brine and water and dried over Na2SO4.
The solvent was removed under reduced pressure to obtain the
n = 3299, 2922, 2363, 1478, 1439, 1000, 752, 508 cm . H NMR
(500 MHz, DMSO-d6): d 7.47 and 7.14 (AA¢BB¢, 2 ¥ 6H, Ar–H),
4.46 (s, 3H, 3 ¥ OH), 3.20 (m, 6H, 3 ¥ CH2), 2.40 (t, J = 7.5, 6H, 3 ¥
CH2), 1.56 (s, 3H, 12d-CH3); 13C NMR (125.7 MHz, DMSO-d6):
d 146.9 (C), 127.0 (CH), 123.2 (CH), 70.0 (C), 65.5.3 (C), 58.8
(CH2), 48.4 (CH2), 15.9 (12d-CH3); MS (EI, 70 eV): m/z (%), 426
∑
(3, [M]+ ), 381 (100), 335 (38), 319 (14), 289 (22); accurate mass
(EI-MS) of [M]+ : calcd. for C29H30O3 426.2196; found 426.2176.
∑
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— Compound 18 was also obtained by the reduction of tris-acid
16 under similar conditions and in the same (69%) yield.
[M - NO]-: calcd. for C32H30N6O12 690.1927; found 690.1936;
calcd. for C32H30N5O11 660.1947; found 660.1944. —Mass and 1H
NMR spectral analyses of compound 20 indicate that the crystals
tend to incorporate minor amounts of chloroform (<25 mol%).
Moreover, the combustion analyses repeatedly resulted in the same
deficiencies for each C, H and N (35–38% in one series and 50–
52% in another). The major reason for this finding is tentatively
attributed to a too vigorous decomposition of this hexanitro
compound upon heating.
4b,8b,12b-Tris(2-butoxyethyl)-12d-methyl-4b,8b,12b,12d-
tetrahydrodibenzo[2,3:4,5]pentaleno[1,6-ab]indene
[12d-methyl-4b,8b,12b-tris(3-oxaheptyl)tribenzotriquinacene, 19]
A suspension of powdered potassium hydroxide (196 mg,
3.5 mmol) in dimethyl sulfoxide (5 mL) was vigorously
stirred for 15 min. Stirring was continued while trialcohol 18
(106 mg, 0.25 mmol) and, immediately thereafter, n-butyl bromide
(0.25 mL, 2.25 mmol) were added. After stirring for a further 3 h,
the mixture was poured onto water and extracted repeatedly with
diethyl ether. The combined organic extracts were washed with
water and dried over Na2SO4. Evaporation of the solvent gave
the crude product which was purified by chromatography through
silica gel (EtOAc/c-C6H12 1 : 3) to give the triether 19 (yield 238 mg,
4b,8b,12b-Tris(carboxymethyl)-12d-methyl-2,3,6,7,10,11-
hexanitro-4b,8b,12b,12d-tetrahydrodibenzo[2,3:4,5]pentaleno[1,6-
ab]indene [12d-methyl-2,3,6,7,10,11-hexanitrotribenzotriquinacene
4b,8b,12b-tris(acetic acid), 21]
Nitric acid (100%, 6.0 mL) was placed into a 25-mL flask and
then cooled to 0 ◦C with stirring. Sulfuric acid (98%, 8.0 mL) was
admixed, followed by the dropwise addition of a 1 : 1 (v/v) mixture
of acetic anhydride and glacial acetic acid (6.0 mL). After allowing
˜
40%) as a light-yellow, viscous oil; IR (neat): n = 2926, 2850, 2358,
2252, 1464, 1377, 1099, 903, 726, 649 cm-1. 1H NMR (500 MHz,
CDCl3): d 7.34 and 7.17 (AA¢BB¢, 2 ¥ 6H, Ar–H), 3.33–3.26 (m,
12H, 6 ¥ OCH2), 2.56 (t, J = 7.2 Hz, 6H, 3 ¥ CH2), 1.54 (t, J =
7.2 Hz, 6H, 3 ¥ CH2), 1.36–1.28 (m, 9H, 3 ¥ CH2 and 12d-CH3),
0.94 (t, 3J = 7.5 Hz, 9H, 3 ¥ CH3); 13C NMR (125.7 MHz, CDCl3):
d 146.9 (C), 127.6 (CH), 123.3 (CH), 71.0 (3 ¥ OCH2), 70.8 (3 ¥
OCH2) 68.8 (C), 66.1 (C), 38.2 (3 ¥ CH2), 31.7 (3 ¥ CH2), 29.7
(3 ¥ CH2), 19.3 (3 ¥ CH3), 14.1 (12d-CH3); MS [(+)-ESI, CHCl3–
MeOH]: m/z 617 (95, [M + Na]+), 612 (82, [M + NH4]+), 595 (100,
[M + H]+); accurate mass [(+)-ESI, CHCl3–MeOH] of [M + H]+:
calcd. for C41H55O3 595.4145; found 595.4141.
◦
the mixture to warm to 20 C, tris-acid 16 (234 mg, 0.50 mmol)
was added in small portions with vigorous stirring. Stirring was
continued under TLC monitoring of the reaction progress. After
completion of the process (50–55 h), the mixture was poured onto
crushed ice and carefully neutralised with sodium hydroxide to
pH 5. The product was extracted thrice with ethyl acetate and
the combined organic extracts were washed twice with water
and dried over Na2SO4. Evaporation of the solvent under reduce
pressure gave a yellowish crude product, which was recrystallised
by applying the vapor diffusion method (CHCl3–EtOAc) giving
the hexanitro-triacid 21 (yield 295 mg, 80%) as yellowish crystals,
◦
˜
mp 339–341 C; IR (neat): n = 3629, 3466, 3041, 2359, 1738, 1540,
1482, 1344, 864, 786, 615 cm-1. 1H NMR (500 MHz, acetone-d6):
d 8.69 (s, 6H, Ar–H), 3.80 (s, 6H, 3 ¥ CH2), 1.84 (s, 3H, 12d-CH3);
13C NMR (125.7 MHz, acetone-d6): d 171.9 (COOH), 151.3 (C),
143.7 (C), 120.9 (CH), 70.3 (C), 66.2 (C), 39.8 (CH2), 14.0 (12d-
CH3); MS [(-)-ESI, acetone/MeOH]: m/z 737 (100, [M - H]-), 693
(4, [M - CO2]-), 605 (28, [M -3 CO2]-); accurate mass [(-)-ESI,
acetone–MeOH) of [M - H]-: calcd. for C29H17N6O18 737.0605;
found 737.0613.
12d-Methyl-2,3,6,7,10,11-hexanitro-4b,8b,12b-tri(n-propyl)-
4b,8b,12b,12d-tetrahydrodibenzo[2,3:4,5]pentaleno[1,6-ab]indene
[12d-methyl-2,3,6,7,10,11-hexanitro-4b,8b,12b-tri(n-propyl)-
tribenzotriquinacene, 20]
Nitric acid (100%, 5.0 mL) was placed into a 25-mL flask and
then cooled to 0 ◦C with stirring. Sulfuric acid (98%, 7.0 mL)
was admixed, followed by the dropwise addition of a 1 : 1 (v/v)
mixture of acetic anhydride and glacial acetic acid (6.0 mL).
The mixture was allowed to warm to 20 ◦C and then, under
vigorous stirring, hydrocarbon 14 (220 mg, 0.50 mmol) was added
in small portions. Stirring was continued for 7–8 h under TLC
monitoring. After completion of the reaction, the mixture was
poured onto crushed ice and neutralised with sodium hydroxide.
The mixture was extracted thrice with ethyl acetate and the
combined extracts were washed with saturated aqueous sodium
bicarbonate and then with water and dried over Na2SO4. Removal
of the solvent under reduced pressure furnished a yellowish
crude product, which was recrystallised from chloroform to
give hexanitrotribenzotr◦iquinacene 20 (yield 338 mg, 98%) as a
Acknowledgements
A generous stipend by the Heinrich–Hertz–Stiftung (Du¨sseldorf,
Germany) is gratefully acknowledged. We are also thankful to
Dieter Barth for his technical assistance in some of the experi-
ments and to Dr Matthias Letzel for expert mass spectrometric
measurements.
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1
2961, 1476, 1343, 846, 748, 507, 457 cm-1. H NMR (500 MHz,
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The Royal Society of Chemistry 2010
Org. Biomol. Chem., 2010, 8, 5383–5389 | 5389
©