A step toward direct fullerene synthesis: C60 fullerene precursors with fluorine in key positions

Article abstract of DOI:10.1016/j.tet.2010.09.055

Several fluorine containing polycyclic aromatic hydrocarbons with exact carbon atom topology of the C₆₀ fullerene have been synthesized. Different numbers of fluorine atoms were introduced in the key positions, as needed for an efficient intramolecular condensation to the fullerene molecule. The polycyclic aromatic compounds obtained represent attractive precursors for rational, high-yield fullerene synthesis by flash vacuum pyrolysis.

Full text of DOI:10.1016/j.tet.2010.09.055

Tetrahedron 66 (2010) 8587e8593
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
A step toward direct fullerene synthesis: C60 fullerene precursors with fluorine
in key positions
*
Mikhail A. Kabdulov, Konstantin Yu. Amsharov , Martin Jansen
Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 June 2010
Received in revised form 6 September 2010
Accepted 15 September 2010
Available online 21 September 2010
Several fluorine containing polycyclic aromatic hydrocarbons with exact carbon atom topology of the C60
fullerene have been synthesized. Different numbers of fluorine atoms were introduced in the key
positions, as needed for an efficient intramolecular condensation to the fullerene molecule. The poly-
cyclic aromatic compounds obtained represent attractive precursors for rational, high-yield fullerene
synthesis by flash vacuum pyrolysis.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Aldol trimerization
Fullerenes
Fluorinated PAHs
1. Introduction
drasticallyaffects the selectivityof the process. Recently wereported
on an efficient intramolecular fluorine promoted ring closure in
Direct synthesis of fullerenes is of considerable interest as
a method to access new fullerenes, which cannot be obtained in the
uncontrolled process of graphite evaporation or forms in low yields
as a hard-to-isolate mixture. The general strategy of the direct
approach to fullerenes is based on the synthesis of polycyclic aro-
matic hydrocarbons (PAH) that already contain the required carbon
framework. Such ‘unrolled’ molecules can be ‘rolled up’ to form
fullerenes under flash vacuum pyrolysis (FVP) conditions.1e5 The
presence of chlorine or bromine in the initial precursor has been
found to be essential for effective cyclization via free radical mech-
anism.1e5 Although the FVP approach has proven to be prolific for
the synthesis of many small non-planar PAHs, high-yield synthesis
of isomerically pure fullerenes has remained a challenge. The pos-
benzo[c]phenanthrenes under FVP conditions via HF elimination,
and have shown that HF elimination is a synchronous process
leading directly to the target molecule without any intermediates,
thus producing no side products.13,14 The small size and low
molecular weight of fluorine, as well as high thermostability of the
CeF bond, make fluorine a ‘perfect’ activating group for rational
fullerene synthesis. Here we present the synthesis of several C60
fullerene precursors containing fluorine atoms in the key positions.
2. Results and discussion
Two general strategies were found to be effective for the synthesis
of fullerene-related PAHs. The first route starts from heptacyclic hy-
drocarbon truxene, the trianione of which can be alkylated by treat-
ment with bromomethyl-bromoarene. The corresponding trialkylated
truxene can be converted to the fullerene-related PAH by intra-
molecular palladium-catalyzed arylation via HBr elimination.15,16 An
alternative approach is based on the acid catalyzed head-to-tail
cyclotrimerization of cyclic ketones,17,18 which leads directly to the
precursor molecule. In the present work we have examined both ap-
proaches for the synthesis of C60 fullerene precursors containing
a various number of fluorine atoms in the key positions.
sibility of selective fullerene cage formation through FVP has been
6e10
demonstrated by the examples of C60
,
C , .
11 and C84 12 However,
78
the rates of conversion to the target molecules have remained dis-
appointingly low because of lack of efficient promoters of intra-
molecular condensation. The usually employed bromine or chlorine
functionalizations reach their limits in the case of large molecules
due to decomposition of such halogenated precursors during sub-
limation. The molar masses will generally be high, since the large
numbers of new CeC bonds that need to be formed in the fullerene
precursor necessitate the introduction of a considerable number of
promoter groups. Moreover, the radical nature of the condensation
2.1. Synthesis on the base of truxene
The starting fluorinated truxenes can be obtained in one-step
* Corresponding author. E-mail address: k.amsharov@fkf.mpg.de (K.Yu. Amsharov).
synthesisbyacidcatalyzed aldol cyclotrimerizationofcorresponding
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.09.055

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M.A. Kabdulov et al. / Tetrahedron 66 (2010) 8587e8593
fluoroindanones (1a,1b,1c) as it is presented on Scheme 1. Indanone
1c (5,6,7-trifluoro-1-indanone) was prepared in several steps from
3,4,5-trifluorobenzyl bromide. 3,4,5-Trifluoro-hydrocinnamic acid
was synthesized analogously to the known procedure for hydro-
cinnamic acid.19 On the final step, the trifluoro-hydrocinnamic acid
was brought into direct cyclizationbyheating inpolyphosphoric acid
(PPA) (Scheme 1).20
positions (compound 4) has been obtained in just two steps
starting from trifluorinated truxene 1a (Scheme 2) analogously to
the previously reported procedure.15 On the first step 1-bromo-2-
bromomethylnaphthalene was added to trifluorinated truxene
trianion, which was generated in situ by treatment of 2 with 3 equiv
of n-BuLi. Compound 3 was obtained as a mixture of syn and anti
isomers. Interestingly, both syn and anti isomers show good solu-
bility in common organic solvents, whereas the syn isomer of
nonfluorinated analog is a highly insoluble compound.22 As a final
step, palladium-catalyzed intramolecular arylation of the anti/syn
mixture of 3 and the subsequent sublimation gave the compound 4.
It is easy to see that additional fluorine atoms can be introduced in
all other key positions by using appropriately fluorinated bromo-
methyl arenes. For instance, the C60 fullerene precursor in which all
six fjord regions are activated can be obtained starting from 2a and
1-bromo-8-fluoro-2-bromomethylnaphthalene. The possibility of
adding fluorinated bromomethyl arenes to the truxene trianione
was previously demonstrated.23
Scheme 1. Synthetic route to 5,6,7-trifluoro-1-indanone (a) NaOEt/EtOH; (b) KOH;
(c) H2SO4 (overall yield 32%); (d) PPA 80 ꢀC (40%). Synthesis of fluorinated truxenes by
aldol cyclotrimerization (2a: 27%, 2b: 31%, 2c: 45%).
6,11,16-Trifluorotruxene (compound 2a) was prepared in 27% yield
by the classical route consisting in refluxing of 7-fluoro-1-indanone
(1a) in a 1:2 mixture of concentrated HCl and acetic acid (HOAc).21 All
attempts to trimerize 1b and 1c under the same conditions failed.
Condensation of 5,7-difluoro-indanone (1b) in a HCl/HOAc mixture
e.g., results in the formation of the pure dimer (2-(2,3-dihydro-4,
6-difluoro-1H-inden-1-ylidene)-2,3-dihydro-4,6-difluoro-1H-Inden-
1-one) with 44% yield. The reaction probably stops after dimerization
because of the low solubility of the dimer, which precipitates out of
the reaction mixture as soon as it is formed. Sterical reasons can be
excluded since the trifluorotruxene 2a containing three fluorine
atoms insterically hampered regionsreadilyforms bytrimerization of
fluoroindanone 1a. Applying the improved protocol for aldol trime-
rization (p-toluenesulfonic acid (TsOH)) in o-dichlorobenzene
(ODCB),17 gave the desired truxene 2b, but the product is contami-
nated by the dimer and tetramer, according to MS data. Pure
2b can be obtained after recrystallization from boiling o-xylene or 1,
2-dichlorobenzene with an overall yield of about 30%. However,
condensation of 1b in aprotonic medium, using TiCl4 in ODCB,18 gave
the pure product with more than 50% yield. Introducing a third fluo-
rine atom in the indanone molecule additionally reduces the ability to
undergo aldol trimerization. Thus, whereas difluoro-indanone 1b
trimerizes to hexafluorotruxene 2b in fair yield using TsOH/ODCB
system underrelative mild conditions (110 ꢀC), thetrifluoro-indanone
1c gives no more than traces of the trimer, in a wide range of tem-
peratures. In contrast, the condensation of 1c in ODCB in presence of
TiCl4 gave truxene 2c with moderate yield (45%).
Scheme 2. The synthetic route to the trifluorinated C60 precursordC60H27F3. (a) n-BuLi/
THF, ꢁ78 ꢀC; (b) 1-bromo-2-bromomethylnaphthalene (61%); (c) Pd(OAc)2, DMA,
Cs2CO3, Me3BzNBr, 140 ꢀC (67%).
Hexa- and nona-fluorinated truxenes represent alternative
building blocks for synthesis of multi-fluorinated precursors.
However, all attempts to synthesize hexa- and nona-fluorinated
precursor starting from truxenes 2b and 2c failed on the alkylation
step. This is probably because of low stability of the corresponding
truxene trianione and/or enhanced acidity of protons neighboring
to fluorine. The reaction of 1-bromo,2-bromomethylnaphthalene
with the corresponding fluorinated truxene trianion results in
a complex mixture, which is difficult to analyze.
2.2. Aldol trimerization route
An alternative way to fullerene-related PAHs is based on the
aldol trimerization of cyclic ketones. Although this reaction was
discovered more than 100 years ago, it only recently became
a powerful method for the synthesis of large molecules. It was
demonstrated that large PAHs can be obtained effectively via aldol
trimerization of cyclic ketones using TsOH in ODCB,24,25 or TiCl4 in
ODCB.6,8,18 In this work, both methods have been examined for
synthesis of fluorinated precursors.
The synthetic route to hexa- and nona-fluorinated precursors is
summarized on Scheme 3. Fluorinated methylbenzo[c]phenan-
threnes (5a and 5b) were synthesized by standard Wittig olefination
of correspondingly fluorinated acetophenones with subsequent
Mallory photocyclization using Katz improvement.26 Benzylic
The fluorinated truxenes represent useful building blocks for
synthesis of different fluorine-containing fullerene precursors.
Thus a C60 precursor containing three fluorine atoms in the fjord

M.A. Kabdulov et al. / Tetrahedron 66 (2010) 8587e8593
8589
bromination with N-bromosuccinimide (NBS) and subsequent
treatment with aqueous ethanolic sodium cyanide gave cyanome-
thylbenzophenanthrenes (7a, 7b), which were hydrolyzed into acid
(8a, 8b). Ketones 9a and 9b were obtained after transforming the
acids (8a, 8b) to the corresponding acid chlorides with subsequent
intramolecular FriedeleCrafts acylation in the presence of AlCl3.
Fig. 1. The MS spectra of condensation products of 9a in TsOH/ODCB system (the full
MS spectra can be found in Supplementary data).
conditions (HCl/AcOH, 100 ꢀC or TsOH/ODCB, 100 ꢀC). In this case all
intermediates can be easily detected in the MS spectra. According to
MS data the reaction mixture contains the dimer and several prod-
ucts of its subsequent condensation. The molecular masses of trimer,
tetramer, and pentamer are slightly less than expected which
additionally confirms the presence of ‘wrongly’ connected benza-
cephenanthrylenone fragments (for details see Supplementary
data). Although the mechanism of condensation is not fully clear,
it obviously involves unusual tail-to-tail ketone condensation and is
probably accompanied by numerous redox processes.
On the other hand the condensation of 9a and 9b in an aprotonic
medium, using TiCl4 in ODCB, gave the desired products with good
yields (60e80%), and in high purity. The optimal conditions for this
reaction are given in the Experimental section. In both cases, the
MS analyses shows the single ion peaks at 858.2 m/z for the hexa-
fluorinated precursor (10a) and 912.2 m/z for nona-fluorinated
precursor (10b), which corresponds to the expected structures. Both
compounds show poor solubility and cannot be analyzed by NMR
spectroscopy. However, MS and MS/MS analyses have provided
sufficient structural information. Thus, applying a higher ionization
energy causes partial condensation of the precursor exclusively by
HF elimination. No loss of two hydrogen atoms under high energy
ionization confirms the expected structure (absence of ‘wrongly’
oriented benzophenanthrene fragments), because only in this case
there is no possibility for intramolecular condensation via H2 elim-
ination. In the MS/MS experiment the monoisotopic precursor ions
were selected and subjected to collision-induced dissociation with
Scheme 3. The synthetic route to the hexa- and nona-fluorinated C60 precursors.
(a) Ph3PCH2Phþ Brꢁ, NaOEt/EtOH; (b) hv, I2, propylene oxide (5a: 67%; 5b: 65%);
(c) NBS, DBPO,CCl4 (6a: 68%; 6b: 72%); (d) NaCN, EtOH/H2O (7a: 75%; 7b: 85%);
(e) H2SO4, H2O, HOAc (8a: 90%; 8b: 84%); (f) SOCl2; (g) AlCl3/DCM (9a: 30%; 9b: 23%);
(k) TiCl4/ODCB (10a: 57%; 10b: 85%).
Despite the quite smooth trimerization conditions needed for
indanones 1b and 1c, the condensation scenario changes drastically
in the case of structurally related benzacephenanthrylenones 9a
and 9b. Thus, the condensation of 9a in ODCB in presence of TsOH
at 100e140 ꢀC gave a complex mixture containing mainly dimer,
tetramer, and hexamer according to MS data. Interestingly only
a trace amount of trimer and pentamer were detected in MS.
Condensation at 160 ꢀC gave a highly insoluble product, which
shows three groups of signals at 858.3, 856.3, and 854.3 m/z (Fig. 1).
The sample was purified by sublimation and analyzed. MS anal-
yses have shown almost exclusively the ion peak at 854.2 m/z, which
is 4 Da less than the mass of the expected trimer (Fig.1). However, for
the targeted structure a respective hydrogen elimination cannot
take place since all possible condensation ways are blocked by the
fluorine atoms (formation of new CeC bond requires HF elimina-
tion). The elimination of hydrogen atoms would have only become
possible if one of the benzophenanthrene fragments is ‘wrongly’
oriented, as it shown in Fig. 1. Indeed, the analysis of intermediate
products confirms this supposition. A more detailed MS analysis of
the reaction mixture shows the presence of a dimer containing two
carbonyl groups confirming the possibility of 9a for atypical tail-to-
tail dimerization. More information about the mechanism can
be obtained by analysis of reaction products obtained at mild
argon. The respective analyses show that H2 elimination is a main
27
fragmentation process for the non-substituted precursor C60H30
,
which is a result of intramolecular condensation in the fjord
regions. In the case of the trifluorinated precursor (4), the intra-
molecular condensation is accompanied byelimination of HFand H2
molecules, which is in good agreement with the structure of
the precursor. The hexa-fluorinated precursor (10a) is not able to
undergo intramolecular condensation via H2 elimination, since all
fjord regions contain fluorine atoms. Therefore no [MꢁH2]þ ions are
observed in the respective MS/MS spectra. Interestingly, the cycli-
zation via HF elimination results in the formation of a new fjord
region and H2 elimination as a subsequent step become possible.
Indeed, the corresponding ion peak ([MꢁHFꢁH2]þ) was detected in
the MS/MS spectra of 10a (Fig. 2). In contrast, the nona-fluorinated

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M.A. Kabdulov et al. / Tetrahedron 66 (2010) 8587e8593
3. Conclusion
Several C60 fullerene-related structures containing a various
number of fluorine atoms in the key positions have been synthe-
sized. It has been shown that trifluorinated truxene is a promising
starting block for the synthesis of fluorine-containing fullerene
precursors. Alternatively, the aldol cyclotrimerization of cyclic ke-
tones can be used as well for the synthesis of C3 symmetrical
fluorine containing precursors. In contrast to chlorine, the fluorine
can be introduced quite easily into the sterically hampered fjord
regions of the precursor molecules as a result of the small size of
fluorine atom. The aldol condensation of fluorinated cyclic ketones
in aprotonic medium using TiCl4/ODCB was found to be an effective
route for the synthesis of fluorine containing PAHs, whereas the
condensation using TsOH/ODCB, which is the best route for the
synthesis of related chlorinated PAHs completely failed.
The fluorinated PAHs obtained represent attractive precursor
molecules for rational fullerene synthesis by flash vacuum pyrol-
ysis. Taking into consideration that fluorine can promote the ring
closure only if hydrogen is placed in a neighboring position in the
precursor structure it appears to be possible to fully control the
direction of the process. Moreover, the highly efficient intra-
molecular condensation to geodesic PAHs via homo-HF elimina-
tion is expected to occur.14 Using fluorine as an activating group
could solve the problem of selectivity in FVP and should provide
an effective conversion of the planar PAH precursors to the desired
fullerene cage. In contrast to the catalytic dehydrogenation of
hydrocarbon analogues on the Pt surface,28 the FVP technique
should provide access to bulk amounts of new fullerenes.
4. Experimental section
4.1. General
Fig. 2. MS/MS spectra of precursors 4, 10a, 10b, and C60H30.
precursor (10b) does not show any H2 elimination since the new
fjord regionwhich forms afterHFelimination still contains a fluorine
atom. The MS/MS patterns obtained indicate that all fjord regions in
10a and 10b contain fluorine atoms, which confirm the absence of
‘wrongly’ orientated benzophenanthrene fragments in the struc-
ture. Additionally, the comparison of UV spectra of nona-fluorinated
(10b), hexa-fluorinated (10a), trifluorinated (4) precursors with well
LDI-mass spectra were recorded on a Shimadzu/Kratos (Colum-
bia, MD) AXIMA CFR mass spectrometer. Rf were determined onTLC-
PET sheets coated with silica gel with fluorescent indicator 254 nm
(layer thickness 0.25 mm, medium pore diameter 60 Å), Fluka.
Chromatographic purifications were carried out with flash grade
silica gel Kieselgel 60 (0.06e0.2 mm), Roth.
characterized C60H30 precursor,27 reveals the similarity of
for all four compounds (Fig. 3.)
p-system
4.1.1. 3-(3,4,5-Trifluoro) propionic acid. Yield 1.0 g (44 mmol) of
metallic sodium were dissolved in 50 mL of absolute ethanol. 7.13 g
(45 mmol) of diethylmalonate were added to the stirred solution of
sodium ethoxide obtained. After gradual addition of 10.0
g
(44.4 mmol) of the ntrifluorobenzylbromide the mixture was reflux
for2 h and cooled down. Thesodiumbromidewasfiltered outand the
major partof ethanol was removed in vacuo. The residuewas distilled
under reduced pressure. The colorless oil obtained was mixed with
aqueous KOH (5 g KOH in 10 mL H2O) and reflux for 3 h. Afterward the
ethanolformedwasremovedunderdiminishedpressure, 5mLofH2O
and 25 mL of 5 M H2SO4 were added additionally and the resulting
mixture was reflux for 5 h. After cooling the mixture was diluted with
50 mL of water, three times extracted with Et2O, dried over MgSO4,
and evaporated. Theyellowish oil had crystallized during cooling. The
product was filtered, washed with hexane, and dried. White crystal-
line powder (3.1 g, 32% yield). 1H NMR (CDCl3, 300 MHz)
(m, 2H), 2.8e2.9 (m, 2H), 6.7e6.8 (m, 2H). Rf¼0.29 (DCM).
d¼2.5e2.6
4.1.2. 5,6,7-Trifluoro-1-indanone. Yield 2.8 g (12.8 mmol) of 3-(3,4,
5-trifluoro) propionic acid and 25 mL of polyphosphoric acid were
stirred for 24 h at 80 ꢀC. After cooling down the mixture was diluted
with 50 mL of water and extracted with DCM. Extract was dried over
MgSO4 and evaporated. The crude product was purified chromato-
graphically using DCM as an eluent. White solid (1.0 g, 40% yield).
Fig. 3. UV/vis spectra of C60 fullerene precursors: C60H30, 4 (C60H27F3), 10a (C60H24F6),
and 10b (C60H21F9) (1,2,4-trichlorobenzene).
Rf¼0.40 (DCM). 1H NMR (CDCl3, 300 MHz)
¼2.68 (t, J¼6.1, 2H), 3.05
d

M.A. Kabdulov et al. / Tetrahedron 66 (2010) 8587e8593
8591
(t, J¼5.7, 2H), 7.00 (t, J¼6.8, 1H). 13C NMR (CDCl3, 75 MHz)
d
¼25.76,
warmed to 0 ꢀC. After 1 h the solution of 1-bromo-2-bromome-
thylnaphthalene 250 mg (0.83 mmol) in THF (15 mL) was drop-
wise added to the red solution of truxene trianione. The resulting
mixture was stirred for 2 h and diluted with EtOAc, washed with
saturated aqueous NaCl solution, dried over Na2SO4, and concen-
trated. The product was precipitated through addition of hexane,
filtered, and dried, resulting in compound 3, which was used
without additional purification (mixture of syn/anti isomers).
White powder (162 mg, 61%). 1H NMR aliphatic/aromatic proton
ratio 1/3. Rf1¼0.21, Rf2¼0.30 (CCl4/hexane 1:1). The mixture of
150 mg of 3, Pd(OAc)2 (45 mg), trimethylbenzylammoniumbromide
(70 mg), Cs2CO3 (500 mg) and 10 mL of dimethylacetamide was
stirred at 140 ꢀC for 72 h. The mixture was cooled and solid was
filtered off, washed with DCM, acetone, and water. The solid
obtained was suspended in aqueous NaCN and stirred for 3 h, fil-
tered off, and washed with water, acetone, and DCM to give 4 as
yellow solid (83 mg, 67%). LDI-TOF MS: m/z¼804.2 [M]þ (Exact
mass: 804.20648). UV: lmax (1,2,4-trichlorobenyene)/[nm] 322, 371,
390, 408, 521. Mp>300 ꢀC.
37.11, 110.08 (dd, J1¼4.5, J2¼18.1). LDI-TOF MS: m/z¼186.03 [M]þ
(Exact mass: 186.0292).
4.1.3. 6,11,16-Trifluorotruxene (2a). Yield4.5g(30mmol)of7-fluoro-
1-indanone were added to a mixture of 20 mL of acetic acid and 10 mL
of concentrated (34%) HCl and stirred for 36 h at 100 ꢀC. After cooling
down the mixture was poured into ice. The solid was filtered, washed
with water, acetone, and DCM to give a white powder. White solid
(1.1 g, 27% yield). 1H NMR (C2Cl4D2, 300 MHz)
d
¼4.37 (s, 6H), 7.03
(t, J¼10.6, 3H), 7.17e7.3 (m, 3H), 7.3e7.45 (m, 3H). 19F NMR (C2 Cl4D2,
235 MHz)
d
¼ꢁ112.5 (sex, J¼6.01). LDI-TOF MS: m/z¼395.04 [MꢁH]ꢁ
(Exact mass: 395.1048).
4.1.4. 6,8,11,13,16,18-Hexafluorotruxene (2b). Route 1. A mixture of
5,7-difluoro-1-indanone (1 g, 5.95 mmol), p-toluenesulfonic acid
monohydrate (3.45 g, 20.8 mmol), propionic acid (1.54 mL,
20.55 mmol), and o-dichlorobenzene (5 mL) was transferred in
round-bottom flask. The mixture was heated at 110 ꢀC for 16 h. After
cooling down the mixture was poured into 50 mL of methanol
containing aqueous KOH. The precipitate was filtrated, washed with
methanol, H2O, acetone, DCM, and petroleum ether resulting in
a greenish powder (0.52 g). Recrystallization from boiling o-xylene
gave a product as a white powder (0.28 g, 31% yield).
4.1.8. 1,3 Difluoro 5-methylbenzo[c]phenanthrene (5a). Yield 8.0 g
(28.6 mmol) of naphthalene, 2-[2-(3,5-difluorophenyl)-1-ethyl-
ethenyl] as a mixtureof cis/trans isomers weredissolved in 350 mL of
cyclohexane. The resulting solution was placed in a 500 W water
cooled quartz photochemical reactor and 8.0 g (31.4 mmol) of iodine
werethen added. Argonwas bubbled through thestirredsolution for
15 min before excess of propylene oxide (40 mL) was added. After
irradiation for 20e30 h the color of iodine had disappeared. The
mixture was washed with aqueous Na2S2O3 to remove residual io-
dine traces, concentrated in vacuo, and then purified by flash chro-
matography on silica gel. The mixture of light petroleum and DCM
1:1 was used as an eluent. The targeted compound was obtained
with 67% yield as a white solid (5.2 g). Rf¼0.17 (hexane). 1H NMR
Route 2. 5,7-Trifluoro-1-indanone (200 mg), 6 mL of o-di-
chlorobenzene and 0.72 mL of TiCl4 (6 M equiv) were transferred in
a glass ampoule. The ampoule was evacuated and sealed by melting
while the reaction mixture was frozen by liquid nitrogen to prevent
the solvent from evaporation. The ampoule was heated at 180 ꢀC for
20 h. After cooling down the ampoule was opened and the mixture
was poured into 50 mL of acetone. The precipitate was filtrated,
washed with acetone, DCM, and petroleum ether. Pink crystals
(92 mg, 52% yield). 1H NMR (C2Cl4D2, 250 MHz, 120 ꢀC)
d
¼4.38 (d,
J¼5.75, 6H), 6.81 (t, J¼10.25, 3H), 7.10 (d, J¼7.25, 3H). 19F NMR
(CDCl3, 300 MHz)
d
¼2.68 (s, 2H), 7.08e7.2 (m,1H), 7.48e7.7 (m, 5H),
(C2Cl4D2, 235 MHz, 120 ꢀC)
d
¼ꢁ112.04 (q, J¼7.29), ¼ꢁ109.2 (sex,
d
7.82e7.95 (m, 2H), 8.08e8.22 (m, 1H). 13C NMR (CDCl3, 75 MHz)
J¼5.88). LDI-TOF MS: m/z¼449.07 [MꢁH]ꢁ (Exact mass: 449.0765).
d
¼19.83, 102.37 (t, J¼28.2), 104.89 (dd, J1¼3.5, J2¼21), 124.97 (d,
J¼2.86), 125.44, 125.8, 127.48, 128.37, 128.96, 129.11, 129.34.
4.1.5. 6,8,9,11,12,13,16,17,18-Nonafluorotruxene (2c). Compound 2c
was synthesized analogously to 2b (route 2) starting from 5,6,7-
trifluoro-1-indanone. The mixture was heated at 170 ꢀC for 16 h.
Pink crystals (50 mg, 45%). 1H NMR (C2Cl4D2, 250 MHz, 120 ꢀC)
4.1.9. 1,2,3 Trifluoro 5-methylbenzo[c]phenanthrene (5b). Compound
2c was synthesized analogously to 2b starting from 5.25
g
(17.86 mmol) of naphthalene, 2-[2-(3,4,5-trifluorophenyl)-1-ethyl-
ethenyl]. Compound 2c was obtained with 65% yield as a white solid
(3.25 g). Rf¼0.45 (hexane/DCM, 2:1). 1H NMR (CDCl3, 300 MHz)
d
¼4.35 (d, J¼5.75, 6H), 7.19 (t, J¼7.25, 3H). 19F NMR (C2Cl4D2,
235 MHz,120 ꢀC)
d
¼ꢁ166.57 (td, J1¼6.03, J2¼19.6), ¼ꢁ152e(ꢁ141)
d
(m). LDI-TOF MS: m/z¼503.03 [MꢁH]ꢁ (Exact mass: 503.0482).
d
¼2.66 (s, 3H), 7.48e7.72 (m, 5H), 7.86e7.94 (m, 2H), 8.07e8.2 (m,
1H). 13C NMR (CDCl3, 75 MHz)
d
¼19.65, 106.02 (dd, J1¼3.7, J2¼17.3),
4.1.6. 2-(2,3-Dihydro-4,6-difluoro-1H-inden-1-ylidene)-2,3-dihydro-
4,6-difluoro-1H-inden-1-one. Yield 5.0 g (29.7 mmol) of 5,7-difluoro-
1-indanone were added to a mixture of 20 mL of acetic acid and
10 mL of concentrated HCl. The mixture was stirred for 72 h at
100 ꢀC, cooled down, and poured into ice. The solid precipitate was
filtered, washed with water, acetone, and DCM to give a white
125.29 (d, J¼2.9),125.97,127.56,128.3 (broad),128.66,128.89,128.93.
4.1.10. 1,3Difluoro 5-(bromomethyl)benzo[c]phenanthrene (6a). Yield
4.65 g (16.7 mmol) of 5a and 2.98 g (16.7 mmol) of NBS with catalytic
amount of dibenzoyl peroxide (5 mg) were dissolved in 70 mL of CCl4
and refluxed until the reaction had gone to completions as moni-
tored by TLC (2e6 h). The reaction mixture was then allowed to cool,
washed twice with water, dried over MgSO4 and concentrated in
vacuo. The crude product was purified chromatographically on silica
gel using petrol ether as an eluent. Grayish solid (4.1 g, 68% yield). Rf
powder (2.1 g, 44% yield). 1H NMR (CDCl3, 300 MHz)
d
¼3.01 (t,
J¼6.28, 2H), 3.5 (t, J¼6.1, 2H), 3.95 (d, J¼5.35, 2H), 6.6e6.8 (m, 2H),
6.88 (d, J¼7.6, 1H), 6.94 (d, J¼6.25, 1H). 19F NMR (C2Cl4D2, 235 MHz,
120 ꢀC)
d
¼ꢁ112.8 (dd, J1¼9.6, J2¼2.6),
d
¼ꢁ105.3 (q, J¼8.9), ¼ꢁ100.5
d
(7, J¼5.2),
d
¼ꢁ100.1 (dt, J1¼8.9, J2¼12), LDI-TOF MS: m/z¼319.06
(hexane/DCM, 1:1)¼0.76. 1H NMR (CDCl3, 300 MHz)
¼4.9 (s, 2H),
d
[MþH]þ (Exact mass: 319.2783).
7.1e7.22 (m, 1H), 7.48e7.6 (m, 2H), 7.63e7.74 (m, 2H), 7.82e7.95 (m,
3H), 8.08e8.22 (m, 1H). 13C NMR (CDCl3, 75 MHz)
d
¼31.36, 103.14 (t,
4.1.7. Compound C60H27F3 (4). THF was refluxed over KOH and
distilled over metallic sodium. THF was degassed using ‘freeze-
thaw-pump’ technique and additionally distilled under reduced
pressure before use. All follow-up manipulations were carried out
under argon atmosphere using Schlenk technique. 100 mg
(0.25 mmol) of 2a were suspended in 10 mL of THF. 0.5 mL of 1.6 M
n-BuLi in hexane (0.8 mmol) were slowly added to the mixture at
ꢁ78 ꢀC. After stirring for about 40 min, the mixture was slowly
J¼27.8), 105 (dd, J1¼3.8, J2¼21.4), 125.31 (d, J¼3.02), 125.44, 126.63,
127.56, 128.84, 129.34, 129.59, 130.56, 133.28.
4.1.11. 1,2,3 Trifluoro 5-(bromomethyl) benzo[c]phenanthrene (6b).
Compound 6b was synthesized analogously to 6a starting from
3.2 g (11.0 mmol) of 5b.
Yellowish solid (2.9 g, 72% yield). Rf (hexane/DCM, 2:1)¼0.40. 1H
NMR (CDCl3, 300 MHz)
d
¼4.87 (s, 2H), 7.49e7.6 (m, 2H), 7.68 (d,

8592
M.A. Kabdulov et al. / Tetrahedron 66 (2010) 8587e8593
J¼8.5, 2H), 7.76e7.86 (m, 2H), 7.87e7.94 (m, 2H), 8.03e8.19 (m, 2H).
13C NMR (CDCl3, 75 MHz)
75 MHz)
128.89, 129.14, 129.2.
d
¼42.08, 124.75, 125.64 (d, J¼2.88), 126.62, 127.74,
d¼30.99, 106.23 (dd, J1¼3.6, J2¼18)
125.43, 125.63 (d, J¼2.9), 126.8, 127.65 (d, J¼1.1), 128.91, 129.14,
129.40, 129.83, 130.9 (broad), 133.19.
4.1.17. 10,11,12 Trifluoro benz[l]acephenanthrylen-9(8H)-one (9b).
Compound 9b was synthesized analogously to 9a starting from
1.38 g (3.85 mmol) of 8b. Cream solid (0.3 g, 23% yield). Rf (DCM)¼
4.1.12. 1,3 Difluoro benzo[c]phenanthrene-5-acetonitrile (7a). Yield
3.85 g (11 mmol) of 6a were dissolved in mixture of 200 mL of EtOH
and 20 mL of H2O. NaCN (600 mg, 12 mmol) was added and the
solution was refluxed for 24 h, diluted with H2O, and extracted with
DCM. The extract was washed with H2O, dried over Na2SO4, and
evaporated in vacuo resulting in an orange oil. The oil was purified
by chromatography using a mixture of DCM and petroleum 1:1 as
eluent. Yellow solid (2.5 g, 75% yield). Rf (hexane/DCM, 1:1)¼0.20.
0.47. 1H NMR (CDCl3, 300 MHz)
d¼3.87 (s, 1H), 7.58e7.67 (m, 2H),
7.72e7.82 (m, 2H), 7.91e8.2 (m, 2H), 8.22e8.39 (m, 2H). 13C NMR
(CDCl3, 75 MHz)
128.48, 129.78.
d¼41.58, 124.08, 125.96, 126.63, 126.80, 127.86,
4.1.18. Compound C60H27F6 (10a). Yield 20 mg of indanone 9a,
1.5 mL of o-dichlorobenzene, and 0.045 mL of TiCl4 (6 M equiv)
were transferred in a glass ampoule and sealed. The ampoule was
heated at 180 ꢀC for 20 h. After cooling down the glass ampoule was
opened and the mixture was poured into 50 mL of acetone. The
precipitate was filtered, washed with acetone, DCM, and petroleum
ether resulting in orange-brown solid (12 mg, 57% yield.). LDI-TOF
MS: m/z¼858.2 [M]þ (Exact mass: 858.1782). UV: lmax (1,2,4-tri-
chlorobenzene)/[nm] 324, 373, 415. Mp>300 ꢀC.
1H NMR (DMSO, 300 MHz)
d
¼4.51 (s, 2H), 7.6e7.7 (m, 2H), 7.7e7.81
(m, 1H), 7.88e7.97 (m, 1H), 7.99e8.05 (m, 1H), 8.06e8.22 (m, 4H).
13C NMR (DMSO, 75 MHz)
d
¼21.17, 103.71 (t, J¼28.1), 105.30 (dd,
J1¼3.7, J2¼22.1), 118.76, 125.64 (d, J¼2.88), 126.43 (dd, J1¼3.1,
J2¼7.8), 126.77, 127.78, 128.81 (d, J¼3.2), 128.93, 129.11, 129.15,
129.26, 130.38, 132.82.
4.1.13. 1,2,3 Trifluoro benzo[c]phenanthrene-5-acetonitrile (7b).
Compound 7b was synthesized analogously to 7a starting from
2.7 g (7.2 mmol) of 6b. White solid (1.95 g, 85% yield). Rf¼0.16
4.1.19. Compound C60H21F9 (10b). Compound 10b was synthesized
analogously to 10a starting from 20 mg of 9b. Orange solid (16 mg,
85% yield.). LDI-TOF MS: m/z¼912.2 [M]þ (Exact mass: 912.14995).
UV: lmax (1,2,4-trichlorobenzene)/[nm] 322, 374, 410. Mp>300 ꢀC.
(hexane/DCM, 1:1). 1H NMR (CDCl3, 300 MHz)
d
¼4.10 (s, 2H),
7.49e7.61 (m, 3H), 7.71e7.79 (m, 1H), 7.90e8.0 (m, 3H), 8.08e8.20
(m, 1H). 13C NMR (CDCl3, 75 MHz)
d
¼22.07, 104.74 (d, J¼3.47),
104.88 (d, J¼3.84), 106.65, 116.70, 125.4, 125.71, 125.83, 126.85,
Acknowledgements
127.71, 128.8, 128.93, 129.02, 129.7, 130.87, 133.16.
We thank Prof. D. Gudat for the measurement of 19F NMR and
€
4.1.14. 1,3 Difluoro benzo[c]phenanthrene-5-acetic acid (8a). Yield
2.5 g (8 mmol) of 7a were dissolved in mixture of acetic acid
(60 mL), H2SO4 (40 mL), and water (40 mL). The mixture was
heated under stirring at 120 ꢀC for 24 h. After cooling down,
100 mL of H2O were added and the product was filtrated,
washed with H2O, and dried. Purification of the crude product
was performed by dissolution in DCM, addition of active carbon
followed by filtration. The product was precipitated by addition
of hexane, filtered, and dried. Gray solid (2.3 g, 90% yield).
Dr. T. Brauniger for helpful discussions.
Supplementary data
The supplementary data contains MS, 1H NMR, 13C NMR, and 19
NMR spectra for all new compounds. Supplementary data associ-
ated with this article can be found in online version, at doi:10.1016/
j.tet.2010.09.055.
F
Rf¼0.36 (EtOAc/DCM, 1:2). 1H NMR (CDCl3, 300 MHz)
¼4.06 (s,
d
References and notes
2H), 7.08e7.18 (m, 1H), 7.48e7.58 (m, 3H), 7.68e7.75 (m, 2H),
7.88e7.95 (m, 2H), 8.09e8.2 (m, 1H). 13C NMR (CDCl3, 75 MHz)
1. Mehta, G.; Rao, H. S. P. Tetrahedron 1998, 54, 13325e13370.
2. Plater, M. J.; Praveen, M.; Schmidt, D. M. Fullerene Sci. Technol. 1997, 5, 781e800.
3. Scott, L. T. Pure Appl. Chem. 1996, 68, 291e300.
4. Scott, L. T. Angew. Chem., Int. Ed. 2004, 43, 4994e5007.
d
¼38.71, 125.14, 125.18, 125.42, 126.32, 127.53, 128.70, 129.3,
129.52, 131.12.
5. Tsefrikas, V. M.; Scott, L. T. Chem. Rev. 2006, 106, 4868e4884.
6. Boorum, M. M.; Vasil’ev, Y. V.; Drewello, T.; Scott, T. Science 2001, 294, 828e831.
7. Gomez-Lor, B.; Koper, C.; Fokkens, R. H.; Vlietstra, E. J.; Cleij, T. J.; Jenneskens, L. W.;
Nibbering, N. M. M.; Echavarren, A. M. Chem. Commun. 2002, 4, 370e371.
8. Scott, L. T.; Boorum, M. M.; McMahon, B. J.; Hagen, S.; Mack, J.; Blank, J.;
Wegner, H.; de Meijere, A. Science 2002, 295, 1500e1503.
9. Amsharov, K. Y.; Jansen, M. Z. Naturforsch., B: Chem. Sci. 2007, 62, 1497e1508.
10. Amsharov, K. Y.; Simeonov, K.; Jansen, M. Carbon 2007, 45, 337e343.
11. Amsharov, K. Y.; Jansen, M. J. Org. Chem. 2008, 73, 2931e2934.
12. Amsharov, K. Y.; Jansen, M. Chem. Commun. 2009, 19, 2691e2693.
13. Amsharov, K. Y.; Kabdulov, M.; Jansen, M. Eur. J. Org. Chem. 2009, 36, 6328e6335.
14. Amsharov, K. Y.; Kabdulov, M.; Jansen, M. Chem.dEur. J. 2010, 16, 5868e5871.
15. (a) de Frutos, O.; Gomez-Lor, B.; Granier, T.; Monge, M. A.; Gutierrez-Puebla, E.;
Echavarren, A. M. Angew. Chem., Int. Ed. 1999, 38, 204e207; (b) Gomez-Lor, B.;
de Frutos, O.; Echavarren, A. M. Chem. Commun. 1999, 23, 2431e2432.
16. Echavarren, A. M.; Gomez-Lor, B.; Gonzalez, J. J.; de Frutos, O. Synlett 2003, 5,
585e597 and references cited herein.
4.1.15. 1,2,3 Trifluoro benzo[c]phenanthrene-5-acetic acid (8b).
Compound 8b was synthesized analogously to 8a starting from
1.95 g (6.07 mmol) of 7b. Gray solid (1.73 g, 84% yield). Rf¼0.33
(EtOAc/DCM, 1:2). 1H NMR (DMSO-d6, 300 MHz)
d¼3.38 (s,
2H), 6.78e6.89 (m, 2H), 7.1e7.19 (m, 2H), 7.2e7.48 (m, 4H). 13C
NMR (DMSO-d6, 75 MHz)
d
¼39.02, 107.91 (d, J¼18.3), 126.32,
127.16, 128.36, 129.13, 129.35, 129.94, 130.59, 131.15, 131.9, 133.11,
172.9.
4.1.16. 10,12 Difluoro benz[l]acephenanthrylen-9(8H)-one (9a). Yield
2.3 g (7.2 mmol) of 8a were stirred with more than 10 times
excess of SOCl2 (10 mL) for 2 h at 65 ꢀC. After cooling down SOCl2
was evaporated and a yellow-brown oil was obtained. The oil was
dissolved in DCM (20 mL) and 1.43 g of AlCl3 (11 mmol) were
added in small portions while stirring. A black solution obtained
was stirred for 3 h and then poured into ice resulting in an
orange mass. After extraction with DCM the solution was dried
over Na2SO4 and evaporated. The crude product was purified by
chromatography using DCM as eluent. White solid (0.66 g, yield
17. Amick, A. W.; Scott, L. T. J. Org. Chem. 2007, 72, 3412e3418.
18. Boorum, M. M.; Scott, L. T. In Modern Arene Chemistry; Astruc, D., Ed.; Wiley-
VCH: Weinheim, Germany, 2002; pp 20e31; and references cited herein.
19. Vogel, A. I. A. Textbook of Practical Organic Chemistry, 3rd ed;; Wiley: New York,
N.Y., 1956; p 768.
20. Panetta, C. A.; Sha, D.; Torres, E.; He, Z.; Hussey, C. L.; Fang, Z.; Heimer, N. E.
Synthesis 1997, 1085e1090.
21. Dehmkow, E. V.; Kelle, T. Synth. Commun. 1997, 27, 2021e2031.
22. Soxhlet extraction of pure syn-5,10,15 tris(1-bromo-2-naphtylmethyl)truxene
with toluene for 20 h shows no remarkable solubility of the material.
23. de Frutos, O.; Granier, T.; Gómez-Lor, B.; Jiménez-Barbero, J.; Monge, A.;
Gutiérrez-Puebla, E.; Echavarren, A. M. Chem.dEur. J. 2002, 8, 2879e2890.
24. Hill, T. J.; Hughes, R. K.; Scott, L. T. Tetrahedron 2008, 64, 11360e11369.
30%). Rf (DCM)¼0.53. 1H NMR (CDCl3, 300 MHz)
¼3.88 (s, 2H),
d
7.21e7.29 (m, 1H), 7.57e7.68 (m, 2H), 7.78e7.84 (m, 2H),
7.91e8.02 (m, 2H), 8.25e8.4 (m, 1H). 13C NMR (CDCl3,

M.A. Kabdulov et al. / Tetrahedron 66 (2010) 8587e8593
8593
25. Mueller, A.; Amsharov, K. Yu.; Jansen, M. Tetrahedron Lett. 2010, 51, 3221e3225.
26. Liu, L.; Yang, B.; Katz, T. J.; Poindexter, M. K. J. Org. Chem. 1991, 56, 3769e3775.
27. The C60H30 precursor used in this work was synthesized previously according
Ref. 15.
28. Otero, G.; Biddau, G.; Sanchez-Sanchez, C.; Caillard, R.; Lopez, M. F.; Rogero,
C.; Palomares, F. J.; Cabello, N.; Basanta, M. A.; Ortega, J.; Mendez, J.;
Echavarren, A. M.; Perez, R.; Gomez-Lor, B.; Martin-Gago, J. A. Nature 2008,
454, 865e868.