The first centrohexaindane bearing twelve functional groups at its outer molecular periphery and related lower veratrole-derived centropolyindanes

Article abstract of DOI:10.1002/ejoc.200501005

The first T_d-symmetrical derivative of centrohexaindane bearing twelve functional groups has been synthesized. Six pairs of methoxy groups, each of which belong to six veratrole units fused to the topologically nonplanar (K₅) core, p

Full text of DOI:10.1002/ejoc.200501005

FULL PAPER
DOI: 10.1002/ejoc.200501005
The First Centrohexaindane Bearing Twelve Functional Groups at Its Outer
Molecular Periphery and Related Lower Veratrole-Derived Centropolyindanes
Marco Harig[a] and Dietmar Kuck*[a]
Keywords: Convex/concave molecules / Three-dimensional frameworks / Cyclization reactions / Indane derivatives
Veratrole derivatives / Propellanes / Triquinacenes / Fenestranes / Topology
The first Td-symmetrical derivative of centrohexaindane
bearing twelve functional groups has been synthesized. Six
pairs of methoxy groups, each of which belong to six vera-
trole units fused to the topologically nonplanar (K5) core,
point outwards from the molecular center into the six direc-
tions of the Cartesian space. The synthesis of this first do-
deca-substituted centrohexaindane was achieved along the
“propellane route” established previously for the parent
centrohexaindane, but the electron-rich character of some of
the intermediates was found to require considerably modi-
fied methodology. Two hexamethoxy-substituted centrotriin-
danes, representing lower congeners of the title compound
and bearing three veratrole units, were also synthesized.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
Introduction
Results and Discussion
Different from the recently described synthesis of several
tetramethoxy-substituted congeners of 1[22] which was
achieved following the “fenestrane route” to the centro-
hexacyclic framework,[5,19] the title compound 2 was ob-
tained by following the complementary “propellane
route”,[5,19,23] making use of appropriate synthons derived
from veratrole (Scheme 2). Starting from 5,6-dimethoxyin-
dane-1,3-dione (6), the preparation of which was improved
recently,[20] the conventional sequence, that is, condensation
of 6 with 3,4-dimethoxybenzaldehyde (7), reduction of the
product, chalcone 8, with sodium borohydride and subse-
quent benzylation of the dihydrochalcone 9 with dimeth-
oxybenzyl chloride (10), furnished the 1,3-indanedione 12
in good overall yield (58% from 6). The alternative, twofold
benzylation of 6 with 3,4-dimethoxybenzyl bromide (11)
gave the diketone 12 in moderate (38%) yield only.[24]
The diketone 12 represents the key intermediate for the
synthesis of two lower congeners of the title centropolyind-
ane 2, namely the isomeric “angular” (“difuso-”[25]) centro-
Centrohexaindane (1, Scheme 1), the largest of the par-
ent centropolyindane hydrocarbons, is a highly unusual hy-
drocarbon because of the topologic non-planarity of its K5-
graph molecular framework[1–4] and the rigidity and strictly
orthogonal orientation of the six centrosymmetrically in-
dane units mutually fused therein.[5,6] Centrohexaindane
may be considered a “Cartesian hexabenzene” owing to the
fact that the aromatic rings are sticking out from the center
of the molecule into the six directions of the three-dimen-
sional space.[6] In view of the lively interest in building
blocks with rigid, well-defined 3D-geometry of the frame-
work and the pendant functionalities,[7–18] access to deriva-
tives of 1 that bear functional groups at the twelve arene
positions of the outer periphery of this C41H24 hydrocarbon
is a promising goal. In this report, we disclose the synthesis
of the first twelve-fold functionalized derivative of 1, na-
mely 2,3,6,7,10,11,14,15,20,21,26,27-dodecamethoxycentro-
hexaindane (2), bearing this particular, still Td-symmetrical
pattern of peripheral substituents. In this context, the syn-
theses of two lower congeners of 2, which also belong to
the centropolyindane family,[19] viz. the hexamethoxycen-
trotriindanes 3 and 4, are reported as well. Together with
the corresponding veratrole-derived tribenzotriquinacenes,
such as isomer 5, published recently[20] and being part of
the skeleton of 2 as well, compounds 3 and 4 complement
the group of three possible regular centrotriindanes[19,21]
bearing three veratrole nuclei in a symmetrical orientation.
triindane 3 and the propellane-type “triptindane”[26]
4
(Scheme 3). Reduction of 12 with lithium aluminum hy-
dride gave the 1,3-indanediol 13 in good yield and exclu-
sively as the trans-isomer, in analogy to previous results
with the parent system.[19,27] Subsequent twofold cyclodehy-
dration (“bicyclization”)[19b] of the diol 13 by use of ortho-
phosphoric acid in chlorobenzene led to the C2-symmetrical
centrotriindane 3, the identity of which was unambiguously
confirmed by mass spectrometry and NMR spectroscopy.
Direct bicyclization of the indanedione 12 by use of or-
thophosphoric acid in refluxing toluene gave the hexameth-
oxy-substituted triptindanone 14, again in good yield. No-
[a] Fakultät für Chemie, Universität Bielefeld,
Universitätsstrasse 25, 33615 Bielefeld, Germany
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Scheme 1. Centrohexaindanes 1 and 2 and the veratrole-type centrotriindanes 3–5. The latter three formulae are presented strictly as
cuttings of the right-hand formula of 2.
Scheme 2. (a) AcOH, ∆, 2 h, 88%; (b) NaBH4, pyridine, 60 °C, 20 min, 84%; (c) KF/celite 545, acetonitrile, 75 °C, 3 h, 79%; (d) KF/
celite 545, acetonitrile, 75 °C, 4 h, 38 %.
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First Centrohexaindane Bearing 12 Groups at Its Outer Molecular Periphery
FULL PAPER
Scheme 3. (a) LiAlH4, THF, ∆, 4 h, 73%; (b) H3PO4 (85%), chlorobenzene, ∆, 1 h, 66%; (c) H3PO4 (85%), toluene, ∆, 7 h, 73%; (d)
NaBH4, CF3COOH/CH2Cl2, 20 °C, 48 h, 68%.
tably, the optimum reaction conditions for this cyclodehy- firmed the identity of this polycyclus and its molecular C3v
dration step were found to be different from those recom- symmetry.[30]
mended for the analogous synthesis of the parent pro-
Subsequently, construction of the centrohexacyclic
pellane ketone, which required use of polyphosphoric framework of the title compound 2 (Scheme 4) required the
acid.[19,28] However, this is not surprising in view of the in- conversion of the monoketone 14 into the corresponding
creased electron density of the aromatic species involved in triketone, viz. 9,10,11-triptindanetrione 15. Instead of the
the course of this two-step cyclodehydration. Also remark- two-step bromination/Kornblum oxidation sequence, which
able is the finding that, besides the Cs-symmetrical pro- had enabled the synthesis of the parent triptindanetrione,[28]
pellane 14, no other regioisomers were observed in the direct oxidation of 14 to 15 by use of chromium() oxide
crude product mixture of the bicyclization. In general, the was successful. The yields were found to be only moderate
twofold, sequential electrophilic attack leading to the trip- (27–52%) but were not optimized.[24b]
tindane skeleton normally involves either of the two ortho
The C3v-symmetrical hexamethoxytriptindanetrione 15 is
positions of the substituted benzyl groups, in spite of steric a particular, non-enolizable 1,3,3Ј-triketone. It bears three
hindrance. This can be used to direct even up to three sub- rigidly fused indanone units, the carbonyl groups of each
stituents into the cavity of the triptindane skeleton.[29] In being in close mutual vicinity at the C3v-symmetrical [3.3.3]-
the present case, it is conceivable that, owing to the in- propellane skeleton. The poor solubility of compound 15
creased electron density of the aromatic units, attack at the in the usual organic solvents and the high-field shift of its
2-positions of the 3,4-dimethoxybenzyl groups is reversible, carbonyl carbon atoms (δ = 183.9 ppm, [D6]DMSO) are
whereas attack at the 6-position is not. Finally, reduction remarkable. Due to the presence of the peripheral methoxy
of the triptindanone 14 to the hexamethoxycentrotriindane groups, the electrophilicity of the triketone should be mark-
4 was achieved (Scheme 3). Once again, however, the stan- edly reduced as compared to the parent triptindanetrione,
dard method applied for the parent triptindane,[29] viz. hy- which was found to undergo threefold addition of nucleo-
drogenolysis of the remaining carbonyl functionality, did philes, such as phenyllithium and methyl- and benzylmag-
not work with the electron-rich ketone 14. Instead, ionic nesium bromide.[5,23,28,31] In the present case, the addition
hydrogenation by use of sodium borohydride in trifluoro- of three veratryl residues to the triketone 15 was carried out
acetic acid was found to occur smoothly in this case, giving by use of 4-veratrylmagnesium bromide, prepared from 4-
the hexamethoxytriptindane 4 in good yield (68%). Mass bromoveratrole (16) in benzene solution at 20 °C. A mixture
spectrometry and NMR spectroscopy, in particular, con- containing the diolone 17 and the triol 18 was obtained, as
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Scheme 4. (a) CrO3, AcOH/H2O, 20 °C, 24 h, 27%; (b) 1. Mg, THF, 16, ∆, 4 h; 2. benzene, 20 °C, 16 h; (c) 1. H3PO4 (85%), chlorobenzene,
∆, 2 h; 2. NaH, CH3I, THF, ∆, 18 h, 6%; (e) see Exp. Sect..
1
determined in particular by the facile water loss from the
The H NMR spectrum of compound 2 is particularly
highly fragile molecular ions 17·+ and 18·+ under EI mass simple and confirms the expected Td molecular symmetry.
spectrometry ([M – H2O]·+ at m/z = 774 and m/z = 912, It exhibits only two sharp singlets for the 12 ortho- and the
respectively). Similarly rapid, and highly stereospecific, loss 36 methoxy protons at δ = 7.14 and δ = 3.89 ppm, respec-
of water is known for other preoriented bridgehead-hydrox- tively, in the ratio of 1:3. Notable is also the extreme de-
ylated centropolyindanes and simpler cyclic alcohols.[32–34] shielding of the central carbon nucleus in the 13C NMR
·+
Attempts to isolate the triol 18 by chromatography failed; spectrum (δ = 100.0 ppm). The C53H48O12 molecular ion
nevertheless, partial separation of the mixture by flash (m/z 876) is hardly visible under standard EI mass spec-
chromatography prior to the next synthesis step proved to trometry conditions due to the low volatility of 2; however,
be favorable.
use of the electrospray (ESI) technique yields sodium ad-
Similar to previous cases, threefold cyclodehydration of duct ions, [C53H48O12 + Na]+ (m/z 899) of high relative
the triol 18 contained in the mixture with 17 was found to abundance.
be successful when orthophosphoric acid (85%) was used
As the efficiency of the propellane route to 2 turned out
in chlorobenzene. The product mixture obtained turned out to be low, an alternative approach was also studied accord-
to be very complex, and flash chromatography and ing to some literature reports on the acylation of veratrole
recrystallization did not furnish the desired compound in with aromatic ketones.[35–37] Thus, it appeared conceivable
pure form. Rather, the presence of considerable amounts of that dodecamethoxycentrohexaindane 2 could be accessible
mostly undefined by-products was indicated by spec- by a direct multiple condensation of the propellanetrione
troscopy and, moreover, mass spectrometry pointed to the 15 with veratrole (19), as depicted in Scheme 4. However,
presence of phenolic components in the mixture. In fact, in spite of several efforts using different reaction conditions,
methylation of the crude product mixture by use of a large this strategy proved to be non-productive. For example,
excess of sodium hydride and iodomethane led to a modi- treatment of the triketone 15 with a considerable excess of
fied mixture from which, after another careful gravity col- 19 in hexafluorophosphoric acid for several days at ambient
umn chromatographic separation, the title compound, temperature gave a mixture of products, a major compo-
2,3,6,7,10,11,14,15,20,21,26,27-dodecamethoxycentrohexa- nent of which was found to be 2,3,6,7,10,11-hexameth-
indane (2) was isolated in pure state, albeit in very low yield oxytriphenylene. Use of thiols as catalysts, as suggested by
(6%), as a colorless solid with a m.p. above 360 °C.
Tadao et al.,[38] did not improve the results either.
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First Centrohexaindane Bearing 12 Groups at Its Outer Molecular Periphery
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27.5 mmol) were suspended in glacial acetic acid (30 mL) and
heated for 2 h under reflux. After cooling to ambient temperature,
the precipitate was filtered by suction, washed with glacial acetic
Conclusions
Based on strategies that had enabled the access to several
parent centropolyindanes, such as centrohexaindane and acid and recrystallized from the same solvent, to give compound 8
as a yellow solid (7.82 g, 88%), m.p. 238–239 °C (223–224 °C[40]),
the centrotriindanes, the syntheses of the corresponding
multiply methoxy-functionalized analogues bearing several
veratrole nuclei have been studied. The C2-symmetrical
hexamethoxytriindane 3 and the C3v-symmetrical hexa-
methoxytriptindane 4 were prepared in good overall yields.
In this way, and in particular by following the well-estab-
lished propellane route, the synthesis of the first twelve-fold
functionalized centrohexaindane, viz. the Td-symmetrical
dodecamethoxycentrohexaindane 2, was achieved, albeit in
Rf(hexane/EtOAc, 1:1) 0.59. 1H NMR (500.1 MHz, CDCl3): δ =
3.94 (s, 3 H), 4.00 (s, 3 H), 4.01 (s, 3 H), 4.04 (s, 3 H), 6.90 [d,
3
3JH,H = 8.4 Hz, 1 H], 7.33 (s, 1 H), 7.34 (s, 1 H), 7.59 (dd, JH,H
=
4
4
8.4, JH,H = 1.8 Hz, 1 H), 7.63 (s, 1 H), 8.81 (d, JH,H = 1.8 Hz, 1
H) ppm. 13C NMR (125.8 MHz, CDCl3): δ = 56.0 (p), 56.7 (p),
103.6 (t), 103.7 (t), 110.5 (t), 115.2 (t), 126.88 (q), 126.94 (q), 130.6
(t), 134.9 (q), 137.7 (q), 144.3 (t), 148.7 (q), 153.2 (q), 155.3 (q),
155.4 (q), 189.2 (q), 190.0 (q) ppm. IR (KBr): ν = 2938 cm–1, 2842,
˜
1712, 1664, 1578, 1502, 1303, 1271, 1217, 1161, 1143, 1072, 1024,
low yields. It has become obvious from these studies that 994, 786. MS (EI, 70 eV): m/z (%) = 354 (100) [M·+], 328 (55), 269
(18), 255 (33), 254 (28), 253 (20), 223 (24), 215 (20), 206 (18), 204
(20), 203 (41), 202 (31), 184 (17), 168 (37), 151 (75), 141 (40), 139
(24), 128 (21), 115 (38). Accurate mass by EI-MS (C20H18O6):
calcd. 354.1103; found 354.1117.
the strongly altered electronic properties of the intermedi-
ates involved in the synthesis of highly methoxy-substituted
centropolyindanes, as compared to that of the respective
parent hydrocarbons, requires application of varied meth-
odology and may also set narrower limits to the efficiency
of the synthesis approach. Centrohexaindane 2, containing
six electron-rich veratrole nuclei that are mutually orien-
tated at 90 ° and 180 ° along the three axes of the Cartesian
space, represents another topologically non-planar organic
compound. Once the efficiency of the synthesis access is
improved, the corresponding sixfold catechol analogue
could be studied as a new challenge to construct metal ion
complexes forming novel orthogonally fused three-dimen-
sional networks.
2-(3,4-Dimethoxybenzyl)-2,3-dihydro-5,6-dimethoxy-1H-indene-1,3-
dione (9): A suspension of 5,6-dimethoxy-2-(3,4-dimethoxy-
benzylidene)indane-1,3-dione (8) (7.09 g, 20.0 mmol) in anhydrous
pyridine (20 mL) was stirred while powdered sodium borohydride
(0.83 g, 22.0 mmol) was added in small portions. The yellow sus-
pension is converted into a deep-red solution while the temperature
of the mixture increases to ca. 60 °C. Stirring was contined for
20 min at 60 °C; then the mixture was cooled to 0 °C. Addition of
hydrochloric acid (2 , 80 mL) precipitated a yellow solid, which
was filtered off by suction and then suspended in ethanol (50 mL)
under reflux. Finally, the product was filtered by suction and dried
to give compound 9 as a light-yellow solid (5.97 g, 84%), m.p. 177–
178 °C, Rf(hexane/EtOAc, 1:1) = 0.43. 1H NMR (500.1 MHz,
CDCl3): δ = 3.25–3.22 (m, 3 H), 3.73 (s, 3 H), 3.76 (s, 3 H), 3.95 (s,
6 H), 6.65–6.59 (m, 3 H), 7.19 (s, 2 H) ppm. 13C NMR (125.8 MHz,
CDCl3): δ = 32.0 (s), 54.7 (t), 55.62 (p), 55.67 (p), 56.6 (p, 2C),
103.0 (t, 2C), 110.7 (t), 112.7 (t), 121.7 (t), 129.5 (q), 137.8 (q, 2C),
Experimental Section
General: Melting points (uncorrected): Electrothermal Melting
Point Apparatus. Infrared (IR) spectra: Perkin–Elmer 841; KBr
pellets or NaCl plates. Nuclear magnetic resonance (NMR) spec-
troscopy: Bruker DRX 500; spectra referenced to the solvent used.
1H NMR spectra: 500.1 MHz. 13C NMR spectra: 125.8 MHz,
broad band decoupled, DEPT and APT method used generally;
the notation p, s, t and q refer to the degree of substitution of the
C atoms. In some cases, special NMR techniques were used (1H,1H
COSY, HMBC, HSQC). EI and/or CI mass spectra and accurate
mass measurements: Autospec X sector-field instrument with EBE
geometry (Vacuum Generators, Manchester, UK) equipped with a
combined EI and CI source. Samples were introduced in aluminum
crucibles by a direct inlet rod. Acceleration voltages 8 kV (EI) and
6 kV (CI). Data given as relative intensities as compared to the
base peak. Other ionization methods are detailled individually. Per-
fluorokerosine (PFK) was used as a reference to determine the ac-
curate masses. Combustion analysis: Perkin–Elmer model 240.
Thin-layer chromatography: silica gel (Kieselgel 60 F254) on Al foil
(Merck). Gravity column chromatography: silica gel (Kieselgel 60,
Ø = 0.063–0.200 mm, from J. T. Baker, Macherey–Nagel, or
Merck). Flash chromatography: silica gel (Kieselgel 60, Ø Ͻ
0.063 mm) for column chromatography (Merck). Alkylation by use
of “KF/celite”: celite (Kieselgur) 545 (Fluka). All solvents were
purified by distillation before use and dried according standard
procedures were necessary.[39]
147.5 (q), 148.3 (q), 155.7 (q, 2C), 199.3 (q) ppm. IR (KBr): ν =
˜
2998 cm–1, 2961, 2911, 2841, 1729, 1697, 1584, 1497, 1338, 1301,
1271, 1243, 1027, 867, 844, 808. MS (EI, 70 eV): m/z (%) = 356
(100) [M·+], 328 (14), 325 (11), 287 (8), 176 (5), 164 (6), 151 (93),
136 (5), 107 (5). Accurate mass by EI-MS (C20H20O6): calcd.
356.1260; found 356.1267. C20H20O6 (356.38): calcd. C 67.41, H
5.66; found C 68.29, H 5.40.
5,6-Dimethoxy-2,2-bis(3,4-dimethoxybenzyl)-2,3-dihydro-1H-
indene-1,3-dione 12. A. By Single Benzylation of 9: A solution of
5,6-dimethoxy-2-(3,4-dimethoxybenzyl)indane-1,3-dione (9)
(10.7 g, 30.0 mmol) in acetonitrile (p.a. quality, 100 mL) was stirred
while 3,4-dimethoxybenzyl chloride (10)[41] (14.0 g, 75.0 mmol) and
potassium fluoride/celite 545 (20.0 g)[42] were added. The suspen-
sion was stirred and heated to 75 °C (bath temperature) for 3 h.
The mixture was cooled to ambient temperature and then filtered
through a sintered glass filter, and the residue was washed with
small portions of acetonitrile until decolorization. The solvent was
removed under reduced pressure and the residue was recrystallized
from methanol/glacial acetic acid (9:1). Satisfying purification re-
quires recrystallization at ambient temperature for several days.
Yield of compound 12: 12.0 g (79%); m.p. 136–137 °C, Rf(hexane/
EtOAc, 1:1) 0.25. 1H NMR (500.1 MHz, CDCl3): δ = 3.17 (s, 4 H),
3.71 (s, 6 H), 3.74 (s, 6 H), 3.88 (s, 6 H), 6.54–6.53 (m, 6 H), 6.97
(s, 2 H) ppm. 13C NMR (125.8 MHz, CDCl3): δ = 41.0 (s), 55.6
2-(3,4-Dimethoxybenzylidene)-2,3-dihydro-5,6-dimethoxy-1H- (p), 55.7 (p), 56.5 (p), 62.1 (q), 102.3 (t), 110.5 (t), 112.9 (t), 122.0
indene-1,3-dione (8): 5,6-Dimethoxyindane-1,3-dione (6) (5.16 g,
25.0 mmol) and 3,4-dimethoxybenzaldehyde (7) (4.57 g,
(t), 128.2 (q), 138.2 (q), 147.5 (q), 148.0 (q), 155.5 (q), 202.7 (q)
ppm. IR (KBr): ν = 2998 cm–1, 2948, 2840, 1735, 1696, 1581, 1517,
˜
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1466, 1443, 1421, 1363, 1305, 1261, 1240, 1222, 1163, 1138, 1119,
1039, 1026, 1003, 877, 863, 850, 807, 623. MS (EI, 70 eV): m/z (%)
= 506 (20) [M·+], 355 (16), 287 (7), 151 (100), 107 (10), 106 (7).
C29H30O8 (506.56): calcd. C 68.76, H 5.97; found C 68.76, H 5.76.
4
3
6 H), 5.11 (s, 2 H), 6.76 (d, JH,H = 1.9 Hz, 2 H), 6.790 (d, JH,H
= 8.1 Hz, 2 H), 6.791 (s, 2 H), 6.82 (dd, 3JH,H = 8.2, 4JH,H = 1.9 Hz,
2 H) ppm. 13C NMR (125.8 MHz, CDCl3): δ = 36.9 (s), 55.79 (p),
55.88 (q), 55.92 (p), 56.1 (p), 79.3 (t), 107.1 (t), 111.1 (t), 113.9 (t),
122.3 (t), 131.5 (q), 135.1 (q), 147.5 (q), 148.6 (q), 149.8 (q) ppm.
B. By Twofold Benzylation of 6: To a solution of 5,6-dimethoxyin-
dane-1,3-dione (6) (1.03 g, 5.00 mmol) in acetonitrile (p.a. quality,
20 mL) were added 3,4-dimethoxybenzyl bromide (11) (2.80 g,
15.0 mmol) and 8.0 g of potassium fluoride on celite 545.[42] This
suspension was stirred and heated to 75 °C (bath temperature) for
4 h. The mixture was cooled to ambient temperature and then fil-
tered through a sintered glass filter, the residue was washed with
small portions of acetonitrile until it was decolorized. After re-
moval of the solvent under reduced pressure, the residue was recrys-
tallized from methanol/chloroform (9:1). Slow recrystallization of
the product over several days gave compound 12 as yellow crystals
(968 mg, 38%). The properties and analytical data of the product
were found to be identical with those of the product described
above.
IR (KBr): ν = 3403 cm–1, 2994, 2929, 2835, 1606, 1588, 1513, 1449,
˜
1418, 1345, 1264, 1186, 1156, 1141, 1114, 1071, 1027, 980, 872,
856, 821, 813, 769. MS (EI, 70 eV): m/z (%) = 510 (1) [M·+], 474
(37), 341 (9), 323 (8), 151 (22), 92 (70), 91 (93), 86 (60), 84 (100),
65 (16), 63 (11), 51 (57). C29H34O8 (510.59): calcd. C 68.22, H 6.71;
found C 68.19, H 6.70.
2,3,6,7,10,11-Hexamethoxy-4b,8b,13,14-tetrahydrodiindeno[1,2-
a:2Ј,1Ј-b]indene (3): In a reaction apparatus equipped with a Thi-
ele–Pape extractor containing molecular sieves (4 Å), a mixture of
orthophosphoric acid (85%, 0.50 mL) and chlorobenzene (50 mL)
was heated under reflux while a solution of trans-5,6-dimethoxy-
2,2-bis(3,4-dimethoxybenzyl)indane-1,3-diol (13) (2.04 g,
4.00 mmol) in chlorobenzene (50 mL) was added slowly. After ad-
dition was completed, heating was continued for 1 h. Later the mix-
ture was cooled, aqueous sodium hydroxide (2 , 100 mL) was
added. The organic layer was separated and the aqueous layer was
extracted thrice with dichloromethane (100 mL each). The com-
bined organic layers were washed with water and dried with sodium
sulfate and the solvent was evaporated. The residue was recrys-
tallized from methanol to give compound 3 as a colorless solid
C. 5,6-Dimethoxy-2-(3,4-dimethoxybenzyl)-2-[3,4-dimethoxy-6-(3,4-
dimethoxybenzyl)benzyl]-2,3-dihydro-1H-indene-1,3-dione (A, see
ref.[24]): During the two syntheses described above, varying
amounts of a by-product were formed as a compound that was
difficult to separate but which could be isolated by column
chromatography using hexane/ethyl acetate (1:1) as the eluent. Use
of 3,4-dimethoxybenzyl bromide (11) as the alkylation reagent pro-
duced markedly more amounts of A than use of 3,4-dimethoxy-
benzyl chloride (10). Compound A was obtained as a yellow, non-
crystallizing oil, Rf(hexane/EtOAc, 1:1) = 0.16. 1H NMR
(500.1 MHz, CDCl3): δ = 3.16 (s, 2 H), 3.19 (s, 2 H), 3.66 (s, 3 H),
3.67 (s, 3 H), 3.71 (s, 3 H), 3.73 (s, 3 H), 3.83 (s, 3 H), 3.86 (s, 3
H), 3.89 (s, 6 H), 3.98 (s, 2 H), 6.41 (s, 1 H), 6.54–6.52 (m, 5 H),
1
(1.26 g, 66%), m.p. 202–203 °C, Rf(hexane/EtOAc, 1:1) = 0.25. H
NMR (500.1 MHz, CDCl3): AB (δA = 3.28, δB = 3.09, JAB
=
–16.0 Hz, 4 H), δ = 3.83 (s, 6 H), 3.84 (s, 6 H), 3.87 (s, 6 H), 4.32
(s, 2 H), 6.72 (s, 2 H), 6.83 (s, 2 H), 6.85 (s, 2 H) ppm. 13C NMR
(125.8 MHz, CDCl3): δ = 44.5 (s), 56.0 (p), 56.17 (p), 56.21 (p),
62.1 (t), 64.7 (q), 107.6 (t, 4 C), 108.0 (t), 134.3 (q), 135.7 (q), 136.0
(q), 148.4 (q), 148.7 (q), 148.9 (q) ppm. IR (KBr): ν = 2929 cm–1,
˜
3
6.65 (s, 1 H), 6.76 (d, JH,H = 8.2 Hz, 1 H), 7.00 (s, 2 H) ppm. 13C
2835, 1607, 1502, 1464, 1334, 1275, 1253, 1223, 1191, 1099, 1091,
1072, 1030, 986, 845. MS (EI, 70 eV): m/z (%) = 474 (100) [M·+],
459 (8), 443 (7), 336 (7), 323 (14), 151 (8). C29H30O6 (474.56): calcd.
C 73.40, H 6.37; found C 73.33, H 6.40.
NMR (125.8 MHz, CDCl3): δ = 37.0 (s), 37.6 (s), 41.2 (s), 55.53
(p), 55.57 (p), 55.63 (p), 55.8 (p), 55.9 (p), 56.5 (p, 2 C), 62.0 (q),
102.3 (t, 2 C), 110.5 (t), 111.0 (t), 111.9 (t), 112.9 (t), 113.4 (t, 2 C),
120.3 (t), 122.1 (t), 126.4 (q), 128.1 (q), 131.3 (q), 133.9 (q), 138.3
(q, 2 C), 146.5 (q), 147.1 (q), 147.3 (q), 147.5 (q), 148.0 (q), 148.8
(q), 155.6 (q, 2 C), 202.9 (q, 2 C) ppm. The resonances of two
2,3,6,7,13,14-Hexamethoxy-9H,10H-4b,9a-([1,2]benzenomethano)-
indeno[1,2-a]inden-9-one (2,3,6,7,13,14-Hexamethoxytriptindan-9-
one, 14): A solution of 5,6-dimethoxy-2,2-bis(3,4-dimethoxybenzyl)
indane-1,3-dione (12) (5.07 g, 10.0 mmol) in toluene (p.a. quality,
100 mL) was stirred in a reaction apparatus equipped with a
Thiele–Pape extractor containing molecular sieves (4 Å). Ortho-
phosphoric acid (85%, 2.00 mL) was added and the mixture was
heated under reflux for 7 h. The mixture was cooled, the organic
layer was separated and the residue was diluted with water
(100 mL). The aqueous solution was extracted thrice with dichloro-
methane; the combined organic solutions were washed with water,
dried with sodium sulfate, and the solvent was evaporated. The
residue was recrystallized from cyclohexane to give compound 14
as a light-yellow solid (3.54 g, 73%), m.p. 127–128 °C, Rf(hexane/
EtOAc, 1:1) = 0.18. 1H NMR (500.1 MHz, CDCl3): AB (δA = 3.45,
δB = 3.17, JAB = –16.8 Hz, 4 H), δ = 3.78 (s, 6 H), 3.84 (s, 3 H),
3.91 (s, 6 H), 4.02 (s, 3 H), 6.65 (s, 2 H), 7.12 (m, 3 H), 7.17 (s, 1
H) ppm. 13C NMR (125.8 MHz, CDCl3): δ = 40.7 (s), 56.0 (p, 2
C), 56.1 (p), 56.3 (p), 56.8 (p, 2 C), 69.5 (q), 72.9 (q), 105.0 (t),
105.3 (t), 107.1 (t, 2 C), 108.4 (t, 2 C), 127.5 (q), 133.8 (q, 2 C),
136.2 (q, 2 C), 148.9 (q, 2 C), 149.86 (q, 2 C), 149.95 (q), 152.9 (q),
methoxy-carbon nuclei were found to be isochronous. IR (KBr): ν
˜
= 3005 cm–1, 2941, 2839, 1728, 1693, 1578, 1513, 1464, 1358, 1304,
1263, 1141, 1115, 1098, 1028, 1000, 869, 733. MS (CI, isobutane):
m/z (%) = 657 (37) [M + H]+, 519 (42), 367 (7), 355 (7), 341 (6),
301 (19), 300 (10), 287 (37), 269 (10), 151 (100), 137 (18). Accurate
mass by EI-MS (C38H40O10): calcd. 656.2621; found 656.2617.
trans-5,6-Dimethoxy-2,2-bis(3,4-dimethoxybenzyl)-2,3-dihydro-1H-
indene-1,3-diol (13): A suspension of lithium aluminum hydride
(607 mg, 16.0 mmol) in anhydrous tetrahydrofuran (40 mL) was
stirred while a solution of 5,6-dimethoxy-2,2-bis(3,4-dimethoxy-
benzyl)indane-1,3-dione (12) (2.03 g, 4.00 mmol) in 40 mL of the
same solvent was added slowly. The mixture was heated under re-
flux for 4 h. Subsequently, the major part of the solvent was re-
moved under reduced pressure and replaced by diethyl ether
(100 mL). This mixture was stirred and cooled in an ice/water bath
while a saturated aqueous solution of sodium chloride (50 mL) was
added cautiously. The organic layer was separated and the aqueous
layer was extracted thrice with diethyl ether (50 mL each). The
combined organic solutions were washed with brine, dried with so-
dium sulfate and concentrated to dryness. The residue was recrys-
tallized from toluene to give compound 13 as a colorless solid
(1.49 g, 73 %), m.p. 120 °C, Rf(hexane/EtOAc, 1:1) = 0.10. 1H
NMR (500.1 MHz, CDCl3): δ = 1.37 (br., 2 H), AB (δA = 2.95, δB
= 2.87, JAB = –14.1 Hz, 4 H), 3.83 (s, 6 H), 3.85 (s, 6 H), 3.86 (s,
156.0 (q), 207.3 (q) ppm. IR (KBr): ν = 2932 cm–1, 2853, 1697,
˜
1604, 1500, 1465, 1420, 1407, 1300, 1269, 1221, 1121, 1097, 1073,
1029, 1008, 877, 776. MS (EI, 70 eV): m/z (%) = 488 (100) [M·+],
487 (55), 473 (5), 337 (12), 336 (6), 288 (27), 287 (50), 257 (11), 244
(6), 238 (14), 223 (8), 185 (7), 165 (18), 161 (6), 151 (32), 149 (12).
C29H28O7 (488.54): C 71.30, H 5.78; found C 71.41, H 6.06.
1652
www.eurjoc.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 1647–1655

First Centrohexaindane Bearing 12 Groups at Its Outer Molecular Periphery
2,3,6,7,13,14-Hexamethoxy-9H,10H-4b,9a-([1,2]benzenomethano)- was extracted thrice with dichloromethane (200 mL). The com-
FULL PAPER
indeno[1,2-a]indene (2,3,6,7,13,14-Hexamethoxytriptindane, 4): A
solution of 2,3,6,7,13,14-hexamethoxytriptindan-9-one (14) (2.44 g,
5.00 mmol) in trifluoroacetic acid (15.0 mL) and dichloromethane
(15.0 mL) was stirred under argon while sodium borohydride
(1.13 g, 30.0 mmol) was added in small pieces, such that the hydro-
gen evolution was kept well under control. The mixture was stirred
for 24 h at ambient temperature. Further sodium borohydride
(1.13 g, 30.0 mmol) was added in small pieces. After stirring was
continued for additional 24 h, ice/water was added and the solution
was brought to pH Ͼ 7 by adding solid sodium hydroxide. The
solution was extracted five times with dichloromethane (50 mL
each). The combined organic solutions were washed twice with sat-
urated aqueous sodium chloride (50 mL each), dried with sodium
sulfate, and the solvent was evaporated. The residue was recrys-
tallized from cyclohexane or methanol to give compound 4 as a
light-brown, crystalline solid (1.62 g, 68 %), m.p. 224–225 °C,
Rf(hexane/EtOAc, 1:1) = 0.36. 1H NMR (500.1 MHz, CDCl3): δ =
3.03 (s, 6 H), 3.81 (s, 9 H), 3.90 (s, 9 H), 6.71 (s, 3 H), 7.00 (s, 3
H) ppm. 13C NMR (125.8 MHz, CDCl3): δ = 43.2 (s), 56.0 (p),
56.5 (p), 65.4 (q), 76.6 (q), 107.2 (t), 108.4 (t), 134.7 (q), 137.4 (q),
bined organic solutions were washed with water, dried with sodium
sulfate, and the solvent was removed under reduced pressure. The
residue was subjected to flash chromatography with chloroform as
the eluent to remove veratrol (19), bromoveratrole (16) and
3,3Ј,4,4Ј-tetramethoxybiphenyl. The fraction containing the ad-
dition products (17 and 18) was eluted by use of ethyl acetate and
used without isolation of the triol 18 in the next conversion.
A mixture of orthophosphoric acid (85%, 4.00 mL) and chloroben-
zene (200 mL) was heated to reflux for 30 min in an apparatus that
was equipped with a Thiele–Pape extractor filled with molecular
sieves (4 Å). The mixture was stirred and continuously heated to
reflux while a solution of the product mixture containing the trip-
tindane derivatives 17 and 18 (see above) in chlorobenzene (50 mL)
was added dropwise. After the addition was completed, heating was
continued for another 1.5 h. The mixture was cooled, the solvent
was removed under reduced pressure and the residue was diluted
with dichloromethane (300 mL). The organic layer was washed
twice with aqueous sodium hydroxide (2 n, 100 mL) and then with
water (100 mL), dried with sodium sulfate, and concentrated to
dryness. The residue was subjected to flash chromatography with
hexane/ethyl acetate (1:2) as the eluent. The fraction containing the
centrohexaindane products, including 2, was eluted by use of ethyl
acetate and the crude product was recrystallized from ethanol.
148.7 (q), 148.9 (q) ppm. IR (KBr): ν = 2997 cm–1, 2936, 2839,
˜
1607, 1503, 1463, 1317, 1279, 1220, 1192, 1113, 1078, 1025, 778.
MS (EI, 70 eV): m/z (%) = 474 (100) [M·+], 460 (17), 355 (4), 323
(72), 309 (9), 293 (5), 265 (4), 237 (5), 151 (33). C29H30O6 (474.56):
calcd. C 73.40, H 6.37; found C 73.30, H 6.35.
The solid obtained in this way was redissolved in anhydrous tetra-
hydrofuran (100 mL) and this solution was added to sodium hy-
dride (60% in paraffin, 300 mg, 12.5 mmol). The mixture was
heated under reflux for 2.5 h and then cooled to ambient tempera-
ture. Then iodomethane (3.55 g, 25.0 mmol) was added and the
mixture was heated under reflux for an additional 16 h. After cool-
ing in an ice/water bath, the excess of sodium hydride was destroyed
first by cautious addition of water and then of aqueous hydrochlo-
ric acid (2 ). The solvent was removed under reduced pressure
and the residue was diluted with dichloromethane (100 mL). This
solution was washed with aqueous sodium thiosulfate (10%) and
then with water, dried with sodium sulfate, and concentrated to
dryness in vacuo. The residue was subjected to column chromatog-
raphy with chloroform/ethyl acetate (3:1) to give compound 2 as a
colorless solid (98.0 mg, 6%), m.p. Ͼ 360 °C, Rf(hexane/EtOAc,
2,3,6,7,13,14-Hexamethoxy-9H,10H-4b,9a-([1,2]benzenomethano)-
indeno[1,2-a]indene-9,10,11-trione (2,3,6,7,13,14-Hexamethoxytript-
indane-9,10,11-trione, 15): A solution of 2,3,6,7,13,14-hexameth-
oxytriptindan-9-one (14) (2.44 g, 5.00 mmol) in glacial acetic acid
(90 mL) was stirred while a solution of chromium() oxide (3.00 g,
30.0 mmol) in water (10 mL) was added slowly. Stirring at ambient
temperature was continued for 24 h. Then the mixture was concen-
trated to dryness in vacuo, water (50 mL) was added to give a pre-
cipitate which was filtered off by suction. The filtrate was extracted
thrice with dichloromethane (50 mL), the combined organic solu-
tions were washed with water (20 mL), dried with sodium sulfate,
added to the product that had precipitated, and the solvent was
removed under reduced pressure. The solid residue was recrys-
tallized from ethyl acetate to give compound 15 as a colorless solid
(707 mg, 27 %), m.p. Ͼ 360 °C, Rf(EtOAc) = 0.21. 1H NMR
(500.1 MHz, [D6]DMSO): δ = 3.75 (s, 9 H) 4.10 (s, 9 H), 7.02 (s, 3
H), 8.03 (s, 3 H) ppm. 13C NMR (125.8 MHz, [D6]DMSO): δ =
55.9 (p), 57.4 (p), 60.6 (q), 86.9 (q), 105.2 (t), 107.7 (t), 125.4 (q),
1
1:2) = 0.19, Rf(CHCl3/EtOAc, 3:1) = 0.25. H NMR (500.1 MHz,
CDCl3): δ = 3.89 (s, 36 H), 7.14 (s, 12 H) ppm. 13C NMR
(125.8 MHz, CDCl3): δ = 56.7 (p), 100.0 (centro-C), 71.7 (q), 107.6
(t), 140.2 (q), 150.2 (q) ppm. IR (KBr): ν = 2937 cm–1, 2855, 1610,
˜
1494, 1461, 1312, 1287, 1235, 1141, 1079, 1029, 994. MS (EI,
70 eV): m/z (%) = 876 [M·+] (very low ion current). MS (ESI):
m/z = 899 [M + Na]+. C53H48O12 (876.97): calcd. C 72.59, H 5.52;
148.4 (q), 150.8 (q), 156.8 (q), 183.9 (q) ppm. IR (KBr): ν =
˜
2945 cm–1, 2839, 1742, 1591, 1500, 1464, 1413, 1299, 1235, 1092,
1013, 871, 783. MS (EI, 70 eV): m/z (%) = 516 (100) [M·+], 488
(12), 485 (9), 473 (7), 457 (5), 258 (5), 149 (6), 44 (6), 40 (7).
C29H24O9 (516.51): calcd. C 67.44, H 4.68; found C 67.14, H 4.95.
found C 70.88, H 6.28. Accurate mass by ESI-MS (C53H48O12
+
Na+) calcd. 899.3043; found 899.3020.
2,3,6,7,10,11,14,15,20,21,26,27-Dodecamethoxy-4b,12b-
Attempts to Synthesize Centrohexaindane 2 from Triptindanetrione
[1Ј,2Ј]:8b,16b[1ЈЈ,2ЈЈ]dibenzenodibenzo[a,f]dibenzo[2,3:4,5]pentaleno- 15 and Veratrole: The following experiments were carried out: (A)
[1,6-cd]pentalene (2,3,6,7,10,11,14,15,20,21,26,27-Dodecameth- Triptindanetrione 15 was treated with an excess of veratrole (19) in
oxycentrohexaindane, 2): 4-Bromoveratrole (16) (43.4 g, 200 mmol) a dichloromethane solution in the presence of anhydrous aluminum
was heated under argon with magnesium turnings (4.86 g,
200 mmol) and a few crystals of iodine in anhydrous tetra-
hydrofuran (600 mL) to reflux for 4 h. The solvent was removed
under reduced pressure and the residue was partially redissolved in
anhydrous benzene (500 mL). This mixture was stirred while
2,3,6,7,13,14-hexamethoxytriptindane-9,10,11-trione (15) (1.03 g,
2.00 mmol) was added. Stirring under argon was continued for 16 h
at ambient temperature by use of a gas-tight mechanical stirrer.
Then saturated aqueous ammonium chloride (300 mL) was added
cautiously. The organic layer was separated and the aqueous layer
trichloride at 20 °C for 24 h. (B) Use of orthophosphoric acid
(85%), Amberlyst 15, or concentrated sulfuric acid, all in chloro-
benzene as the solvent. (C) Use of pure 19 as the solvent and con-
centrated sulfuric acid, or aluminum tribromide, or trifluoroacetic
acid, or hexafluorophosphoric acid as the catalyst, all experiments
being run at 20 °C for 16 h. (D) Use of pure 19 as the solvent and
concentrated sulfuric acid, thiophenol at 65 °C for 5 h. Unfortu-
nately, centrohexaindane 2 could not be detected (by mass spec-
1
trometry and H NMR spectrometry) in, or isolated from, any of
the product mixtures obtained from these experiments.
Eur. J. Org. Chem. 2006, 1647–1655
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1653

M. Harig, D. Kuck
FULL PAPER
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Acknowledgment
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First Centrohexaindane Bearing 12 Groups at Its Outer Molecular Periphery
FULL PAPER
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Received: December 23, 2005
Published Online: February 24, 2006
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