8,9-Didehydrofluoranthenes as building blocks for the synthesis of extended polycyclic aromatic hydrocarbons (PAHs)

Article abstract of DOI:10.1021/ol016391j

(equation presented) The synthesis of phenyl-substituted 8,9-dibromofluoranthene and p-dodecylphenyl-substituted 8,9-fluoranthene anthranilic acid is presented. Their synthetic potential as 8,9-didehydrofluoranthene precursors is demonstrated in combinati

Full text of DOI:10.1021/ol016391j

ORGANIC
LETTERS
2001
Vol. 3, No. 20
3115-3118
8,9-Didehydrofluoranthenes as Building
Blocks for the Synthesis of Extended
Polycyclic Aromatic Hydrocarbons
(PAHs)
Wolf Dietrich Neudorff, Niels Schulte, Dieter Lentz, and A. Dieter Schlu1ter*
Institut fu¨r Chemie, Freie UniVersita¨t Berlin, Takustrasse 3, D-14195 Berlin, Germany
adschlue@chemie.fu-berlin.de
Received July 5, 2001
ABSTRACT
The synthesis of phenyl-substituted 8,9-dibromofluoranthene and p-dodecylphenyl-substituted 8,9-fluoranthene anthranilic acid is presented.
Their synthetic potential as 8,9-didehydrofluoranthene precursors is demonstrated in combination with a new biscyclopentadienone by the
synthesis of novel phenyl-substituted PAHs with up to 14 annulated rings. The crystal structure of 7,16-diphenylfluorantheno[8,9-k]fluoranthene
is given.
Cyclopentene-fused polycyclic aromatic hydrocarbons (CPAH)
of the fluoranthene type are a class of nonalternant polycyclic
aromatic hydrocarbons (PAH) which have been of consider-
able interest because of their structural relationship1 to the
extensively investigated fullerenes2 and because of their
potential use in electroluminescent organic devices.3 This
interest is reflected in recent patent literature.4 Phenyl
substitution of some of these CPAHs is discussed in the
context of organic quantum effect devices and organic
ferromagnets.5
Much is known about acenaphtho[1,2-k]fluoranthenes (n
) 1, Figure 1) and benzo[1,2-k:4,5-k′]difluoranthenes (n )
Figure 1. Homologous series of acenaphthene-capped fluoran-
thenes.
(1) Schlu¨ter, A. D.; Lo¨ffler, F.; Enkelmann, V. Nature 1994, 368, 831.
(2) Fullerenes and Related Structures; Hirsch, A., Ed.; Springer: Berlin,
1999; Vol. 199.
(3) Dicker, G.; Hohenau, A.; Graupner, W.; Tasch, S.; Graupner, M.;
Hermetter, A.; Schlicke, B.; Schulte, N.; Schlu¨ter, A. D.; Scherf, U.; Mu¨llen,
K.; Leising, G. Synth. Met. 1999, 102, 873. List, E. J. W.; Leising, G.;
Schulte, N.; Schlu¨ter, A. D.; Scherf, U.; Graupner, W. Jpn. J. Appl. Phys.
2000, 239, L760.
(4) Ikeda, H.; Hosokawa, C.; Arakane, T. WO 2001023496, 2001.
Nakatsuka, M.; Kitamoto, N. JP 2000 07,594, 2000. Nakatsuka, M.
Kitamoto, N. JP 11040360, 1999.
3), which have even been synthesized as completely aromatic
ladder polymers by conventional Diels-Alder reactions6 and
(6) Schlu¨ter, A. D.; Lo¨ffler, M.; Godt, A.; Blatter, K. Perfect Diels-
Alder Ladder Polymers: Precursor for Extended π-Conjugation. In Desk
Reference of Functional Polymers Synthesis and Application; Arshady, R.,
Ed.; American Chenical Society: Washington, DC, 1997; and references
therein.
(5) Niemz, A.; Cuello, A.; Steffen, L. K.; Plummmer, B. F.; Rotello, V.
M. J. Am. Chem. Soc. 2000, 122, 4798 and references therein.
10.1021/ol016391j CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/11/2001

by electropolymerization.7 Little was known, however, about
the synthesis of the homologous fluorantheno[8,9-k]fluoran-
thenes (n ) 2),8 which can be seen as planar parts of the
C60-fullerene’s belt region.
Scheme 2a
Here we report on the synthesis of “monomeric” and
“dimeric” phenyl-substituted fluoranthenofluoranthenes via
new 8,9-didehydrofluoranthenes and a new biscyclopenta-
dienone serving as an efficient diene in Diels-Alder reaction
with one of these didehydrofluoranthenes.
It is difficult to regiospecifically functionalize PAHs by
introducing substituents to the parent molecule. Often the
only way to do this is to introduce the substituents while
building up the aromatic system. To obtain a vicinal
difunctionalization in the 8,9-position of fluoranthene, from
which the corresponding aryne can be generated, we started
from the cyclopentadienone 1a (Scheme 1).9 After several
Scheme 1a
a (a) BuLi, toluene, -40 °C, 71%, (b) tetracyclone, EtOH, 78
°C, 88%, (c) toluene 112 °C, 82%, (d) p-TsOH, toluene, 112 °C,
76%. For chemical shifts (*), see Table 1.
a Method A: o-xylene, reflux, 20-40%. Method B: melt, 130
°C, 62%.
unsuccessful attempts to add acetylene derivatives, which
should give the aryne precursor either directly or after
subsequent transformation, we finally found the new dibro-
moepoxynaphthaline 2 to be a suitable dibromoacetylene
equivalent. It was made from 3,4-dibromofuran10 and an-
thranilic acid by a standard procedure in 93% yield.
generated in situ by heating 5 in toluene and trapping with
acenaphthene to give the epoxy-bridged fluoranthenofluo-
ranthene 7 in 82% isolated yield with an endo-exo ratio of
1:3. The isomers were separated and individually character-
ized. Finally, diphenylfluoranthenofluoranthene 8 was ob-
tained by dehydration with p-toluenesulfonic acid (p-TsOH)
in 76% isolated yield. The yellow green product showed a
strong fluorescence even in the solid state.
The synthesis of 8,9-dibromofluoranthene 3 from 1a and
2 follows the same well-known reaction sequence of Diels-
Alder, decarbonylation, and retro-Diels-Alder reactions
which is normally used to generate isobenzofurans from
tetraphenylcyclopentadienone (tetracyclone) and epoxynaph-
thalines.11 Isobenzofuran is the side product here, and reaction
conditions have to be more drastic due to the bulkiness of
the bromo substituents in 2. For dibromofluoranthene 3, there
was a 20-40% yield, when the reaction was carried out in
solution, and up to a 62% yield from a melt of 1a in 2. An
intermediate structure comparable to 5 (Scheme 2) could not
be detected because of the high-temperature conditions
required. The comparably low yields are caused by side
reactions of 1a which were not further investigated. The
aryne was generated from 3 with butyllithium (BuLi) and
in situ trapped by furan to give 4 in 71% yield.12 Subsequent
Diels-Alder reaction of 4 with tetracyclone yielded the
isobenzofuran precursor 5 in 88%. Isobenzofuran 6 was
A crystal structure analysis was performed for 8.13 Figure
2 shows a pair of molecules in the crystal. The phenyl groups
Figure 2. Structure of 8 in the crystal (ORTEP plot).
(7) Debad, J. D.; Bard, A. J. J. Am. Chem. Soc. 1998, 120, 2476.
(8) Clar, E.; Stephen, J. F. Tetrahedron 1964, 20, 1559.
(9) Stille, K.; Noren, G.; Green, L. J. Polym. Sci. Part A 1970, 8, 2245.
(10) Gorzzynski, M.; Rewicki, D. Liebigs Ann. Chem. 1986, 625.
(11) Fieser, L. F.; Haddadin, M. J. Can. J. Chem. 1965, 43, 1599.
(12) Hart, H.; Lai, C.-Y.; Godson, C. N.; Shamouil, S. Tetrahedron 1987,
43, 5203.
are almost perpendicular to the main plane of the molecule
as expected14 and slightly bent toward the neighboring
acenaphthene unit. The latter is assigned to a packaging effect
originating from an intermolecular repulsion of the phenyl
3116
Org. Lett., Vol. 3, No. 20, 2001

groups. This effect should not be present in solution which
becomes apparent from molecular mechanics simulations.15
UV/vis data are given in Table 1.
yield. The moderate yield predominately results from loss
during workup. The lack of intensive color in the TLC
indicates that 1b was completely converted.
The decision to introduce long flexible solubilizing side
chains to 11 in addition to the phenyl groups was made to
aid the future synthesis of even longer PAHs and polymeric
structures and to increase their solubility. Scheme 4 shows
Table 1. Selected UV/Vis and Proton NMR Data
absorption
emission
Stokes shif
[nm]
chemical shiftc
λ
max [nm]
λ
max [nm]
δ [ppm]
8
11
15
454a
469b
542b
455a
475b
550b
1
6
8
*6.6d
*5.6
**5.15/*5.7
Scheme 4a
a CHCl3. b CH2Cl2. c 8, 270 MHz/CDCl3; 11, 15 250 MHz/CDCl3. d As-
terisks assign the marked protons in Schemes 2-4.
A limitation in generating arynes from vicinal dibromides
with BuLi is this method’s intolerance to strong electrophilic
groups. Therefore, we used the method of Pascal Jr.16 to
obtain the fluoranthene anthranilic acid 10 (Scheme 3).
Scheme 3a
a (a) EtOH, KOH, 50 °C, 45%; (b) THF/CH2Cl2, isoamyl nitrite
50 °C. For chemical shifts (*/**), see Table 1.
the synthesis of the “dimeric” fluoranthenofluoranthene 15.
In the first step the new biscyclopentadienone 14 was
synthesized by a 4-fold Knoevenagel reaction between the
tetraketopyracene 1217 and the alkyl-substituted diphenyl-
acetone 1318 in 45% yield. 13 was synthesized by an
improved four-step sequence with 60% over all yield.19
The reaction of 10 with 14 was carried out under
conditions similar to those for the synthesis of 11 and yielded
15 in 56% isolated yield. 15 is a red amorphous solid with
a bright red fluorescence in solution. Table 1 gives UV/vis
data of compounds 8, 11, and 15. The relatively small Stokes
shifts indicate considerable rigidity of the structures. The
electrooptical properties of 8, 11, and 15 are presently under
investigation.
a (a) Maleimide, C6H5Br, reflux; (b) C6H5Br, Br2, rt, 78%; (c)
MeOH, NaOH, NaOCl, reflux; (d) propanol, KOH, reflux, 62%;
(e) THF/CH2Cl2, isoamyl nitrite, 50 °C. For chemical shifts (*),
see Table 1.
Chemical shifts for the inner protons of the terminal and
that of the centered naphthalenic units for compounds 8, 11,
and 15, respectively, which are marked with asterisks in
Schemes 2-4, are given in Table 1. An increase in phenyl
substitution causes an increase in upfield shift. This is the
result of the almost perpendicular orientation of the phenyl
groups to the molecules’ main planes, which brings the
naphthalenic protons right into the phenyl groups upfield
cones. The additional upfield shift of approximately 1 ppm
going from diphenyl substitution to tetraphenyl substitution
can be assigned to a bending of the phenyl groups toward
the terminal naphthalenic units, which becomes evident from
molecular mechanics simulations.15 This is due to their
Diels-Alder reaction of the acecyclone 1b with maleimide
and subsequent dehydrogenation with bromine gave the
imidofluoranthene 9 in 78% yield. A Hofmann rearrangement
on 9 yielded 10 in 62%. From diazotation of 10 with isoamyl
nitrite at 50-60 °C, the corresponding aryne was generated
in situ which added to 1b. The primary adduct underwent
decarbonylation during reaction to give the tetraphenyl-
substituted fluoranthenofluoranthene 11 in 62% isolated
(13) Crystal data for 8: C42H24, M ) 528.61, monoclinic, P2(1)/n, a )
15.010(3), b ) 9.2219(16), and c ) 20.202(4) Å, R ) 101.725°, V ) 2738.2-
(8) Å3, Z ) 4, Dc ) 1.282 g cm-1. A total of 6279 observed reflections [I
> 2o´(I)] and 379 variable parameters converged to R ) 0.0464 and wR )
0.1302.
(14) Watson, W. H.; Kashyap, R. P. Acta Crystallogr. 1991, C47, 1848.
(15) Hyperchem release 6.03, geometry optimization using implemented
mm+ force field, AM1, and PM3 with Polak-Ribiere algorithm.
(16) Qiao, X.; Padula, M. A.; Ho, D. M.; Vogelaar, N. J.; Schutt, C. A.;
Pascal, R. A., Jr. J. Am. Chem. Soc. 1996, 102, 873.
(17) Clayton, M. D.; Marcinow, Z.; Rabideau, P. W. J. Org. Chem. 1996,
61, 6052.
(18) Schlicke, B.; Frahn, J.; Schlu¨ter, A. D. Synth. Met. 1996, 83, 173.
(19) See Supporting Information.
Org. Lett., Vol. 3, No. 20, 2001
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intramolecular peri-interactions in contrast to the above-
mentioned intermolecular interaction in the solid state of 8.
A further shift of 0.45 ppm is observed for the protons of
the central naphthalenic unit of 15. This shift is assigned to
the influence of two phenyl groups flanking these protons.
In summary, we have presented the first two routes for
the synthesis of 8,9-didehydrofluoranthene precursors and
demonstrated their potential in the synthesis of novel
extended CPAHs. The didehydrofluoranthenes either served
as building blocks for the synthesis of a highly reactive
isobenzofuran diene or were used directly as dienophile in
Diels-Alder reactions with a acecyclone and a new bis-
cyclopentadienone which allowed a convenient synthesis of
a fully annulated 14 ring system. The synthesized CPAHs
may be of interest both for their electrooptical properties,
which are presently under investigation, and as a building
block in the synthesis of larger fragments of C60-fullerene
to which they are structurally related. Future efforts in our
laboratory will be directed at the synthesis of more extended
CPAHs and polymeric structures.
Acknowledgment. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der Che-
mischen Industrie.
Supporting Information Available: Experimental pro-
cedures and characterization for all compounds, CIF file for
compound 8. This material is available free of charge via
the Internet at http://pubs.acs.org.
OL016391J
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