Synthesis of hexabenzotriphenylene and other strained polycyclic aromatic hydrocarbons by palladium-catalyzed cyclotrimerization of arynes

Article abstract of DOI:10.1021/ol990864t

(matrix presented). To evaluate the potential of the recently developed palladium-catalyzed trimerization of arynes for the synthesis of strained polycyclic hydrocarbons, the trimerizations of 1,2-didehydronaphthalene (1) and 9,10-didehydrophenanthrene (2), generated from the corresponding o-trimethylsilylaryl triflates 5 and 11, respectively, were studied. The synthesis of tribenzo[a,g,o]triphenylene (6), tribenzo[a,g,m]triphenylene (7), and hexabenzo[a,c,g,i,m,o]triphenylene (12) is described.

Full text of DOI:10.1021/ol990864t

ORGANIC
LETTERS
1999
Vol. 1, No. 10
1555-1557
Synthesis of Hexabenzotriphenylene and
Other Strained Polycyclic Aromatic
Hydrocarbons by Palladium-Catalyzed
Cyclotrimerization of Arynes
Diego Pen˜a, Dolores Pe´rez,* Enrique Guitia´n,* and Luis Castedo
Departamento de Qu´ımica Orga´nica, UniVersidad de Santiago de Compostela y
Unidad Asociada al CSIC, 15706 Santiago de Compostela, Spain
qoenrgui@uscmail.usc.es
Received July 26, 1999
ABSTRACT
To evaluate the potential of the recently developed palladium-catalyzed trimerization of arynes for the synthesis of strained polycyclic
hydrocarbons, the trimerizations of 1,2-didehydronaphthalene (1) and 9,10-didehydrophenanthrene (2), generated from the corresponding
o-trimethylsilylaryl triflates 5 and 11, respectively, were studied. The synthesis of tribenzo[a,g,o]triphenylene (6), tribenzo[a,g,m]triphenylene
(7), and hexabenzo[a,c,g,i,m,o]triphenylene (12) is described.
The chemistry of overcrowded polycyclic aromatic hydro-
carbons (PAHs) has become a field of increasing interest
during the past decade. The synthesis of bowl-shaped PAHs
that constitute significant fragments of fullerenes is particu-
larly appealing,1 but also important efforts have been directed
to the construction of highly symmetric PAHs with different
shapes, such as saddles or twists,1,2 and to the synthesis of
other structures that exhibit distortions from planarity, such
as the helicenes.3 In general, the syntheses of these kinds of
compounds have in common the lack of general applicability,
the use of harsh reaction conditions (e.g., FVP), and low
yields. In this Letter we report preliminary results on a novel,
convenient approach to the synthesis of strained PAHs based
on the palladium(0)-catalyzed cyclotrimerization of poly-
cyclic arynes.
Recently we described the palladium-catalyzed cyclotri-
merization of benzyne and substituted derivatives to afford
triphenylenes.4 We planned to apply this reaction to poly-
cyclic arynes,5 which would allow an easy access to complex
polycyclic structures. Particularly, we became interested in
the reaction of two arynes of increasing size and structural
(3) (a) Martin, R. H. Angew. Chem., Int. Ed. Engl. 1974, 13, 649-660.
(b) Laarhoven, W. H.; Prinsen, W. J. C. In Topics in Current Chemistry,
Vol. 125; Boschke, F. L., Ed.; Springer-Verlag: Berlin, 1984; pp 65-127.
(c) Grimme, S.; Harren, J.; Sobanski, A.; Vo¨gtle, F. Eur. J. Org. Chem.
1998, 1491-1509.
(4) Pen˜a, D.; Escudero, S.; Pe´rez, D.; Guitia´n, E.; Castedo, L. Angew.
Chem. Int. Ed. Engl. 1998, 37, 2659-2661.
(1) (a) Siegel, J. S.; Sieders, T. J. Chem. Br. 1995, 31, 313-316. (b)
Rabideau, P. W.; Sygula, A. Acc. Chem. Res. 1996, 29, 235-242. (c) Faust,
R. Angew. Chem., Int. Ed. Engl. 1995, 34, 1429-1432.
(2) (a) Pascal, R. A., Jr. Pure Appl. Chem. 1993, 65, 105-110. (b) Qiao,
X.; Ho, D. M.; Pascal, R. A., Jr. Angew. Chem., Int. Ed. Engl. 1997, 36,
1531-1532.
10.1021/ol990864t CCC: $18.00 © 1999 American Chemical Society
Published on Web 10/10/1999

complexity: 1,2-didehydronaphthalene (1) and 9,10-dide-
hydrophenanthrene (2) (Figure 1). The cyclotrimerization of
simple arynes4 [CsF (2 equiv), Pd(PPh3)4 (0.1 equiv); CH3-
CN, room temperature], the expected trimers were not
detected. Reasoning that the bulky and strongly coordinated
ligand PPh3 might prevent the reaction of this sterically
demanding aryne, we switched to Pd2(dba)3 as a palladium
source. When 5 was treated with CsF in the presence of 5
mol % of Pd2(dba)3, a mixture of trimers 6 and 7 was
successfully obtained in 60% yield and 2.7:1 ratio,9 with 6
being the major product. Both isomers are structurally
interesting molecules: while tribenzo[a,g,m]triphenylene
(benzo[c]naphtho[2,1-p]-chrysene, 7) has recently attracted
great attention as a potential precursor for the synthesis of
hemifullerene,10 tribenzo[a,g,o]triphenylene (naphtho[1,2-s]-
picene, 6) is a substituted pentahelicene. Furthermore, the
isolation of 6 as a major product showed that sterically
hindered, highly twisted polycyclic hydrocarbons could be
efficiently obtained using this approach, opening the pos-
sibility of synthesizing 12.
Figure 1.
1 would give us a first insight into the possibility of obtaining
strained PAHs using our proposed strategy, and the cyclo-
trimerization of 2 would afford dibenzo[f,j]phenanthro[9,-
10-s]picene (hexabenzo-[a,c,g,i,m,o]triphenylene, 12), a mol-
ecule that has been recently characterized as a highly twisted,
D3-symmetric molecular propeller6 and whose synthesis has
been shown to be difficult so far.6,7
The preparation of 10-trimethylsilylphenanthryl 9-trifluo-
romethanesulfonate (11) from commercially available
9-phenanthrol (8) is shown in Scheme 2. Selective ortho-
On the basis of our previously described methodology,4,8
we selected the corresponding o-trimethylsilylaryl triflates
as adequate aryne precursors for 1 and 2. 1-Trimethylsilyl-
naphthyl 2-trifluoromethanesulfonate (5) was prepared from
commercially available 1-bromo-2-naphthol (3) as shown in
Scheme 1. Treatment of 3 with hexamethyldisilazane (HMDS)
Scheme 2
Scheme 1
bromination was achieved in good yield by reaction of 8
with N-bromosuccinimide (NBS) in the presence of a
catalytic amount of diisopropylamine.11 Sequential treatment
of 9 with n-BuLi and TMSCl (twice) afforded in one pot
trimethylsilyl ether 10, which was highly unstable and
therefore taken to the next step without further purification.
Reaction of crude 10 with n-BuLi and quenching with Tf2O
at 70 °C gave trimethylsilyl ether 4 in quantitative yield,
which was transformed into triflate 5 in one pot by sequential
treatment with n-BuLi (1 equiv, -78 °C to room tempera-
ture) and Tf2O. When 5 was subjected to the reaction
conditions previously reported for the cyclotrimerization of
(6) Barnett, L.; Ho, D. M.; Baldridge, K. K.; Pascal, R. A., Jr. J. Am.
Chem. Soc. 1999, 121, 727-733.
(7) (a) Hacker, N. P.; McOmie, F. W.; Meunier-Piret, J.; Van Meerssche,
M J. Chem. Soc., Perkin Trans. 1 1982, 19-23. Other authors reported the
preparation of 1, but no characterization was given: (b) Halleux, A. L.,
Br. Patent 852,981, 1960. (c) Barton, J. W.; Grinham, A. R. J. J. Chem.
Soc., Perkin Trans. 1 1972, 634-637.
(5) General reviews on aryne chemistry: (a) Hoffmann, R. W.; Dehy-
drobenzene and Cycloalkynes; Academic Press: New York, 1967. (b) Hart,
H. In The Chemistry of Functional Groups, Suppl. C2: The Chemistry of
Triple-Bonded Functional Groups; Patai, S., Ed.; Wiley: Chichester, 1994;
pp 1017-1134.
(8) Pen˜a, D.; Pe´rez, D.; Guitia´n, E.; Castedo, L. J. Am. Chem. Soc. 1999,
121, 5827-5828.
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Org. Lett., Vol. 1, No. 10, 1999

afforded triflate 11 in 55% overall yield from 9. Treatment
of 11 with CsF in the presence of Pd2(dba)3 as catalyst
afforded a single low-polarity product that was isolated and
characterized12 as hexabenzo[a,c,g,i,m,o]triphenylene (12) in
a remarkable 39% yield. It is worth noting that the previously
reported syntheses of 12 afforded the compound in yields
as low as 5%6 and 13%,7a starting from precursors which
were difficult to prepare, and using severe reaction conditions
(pyrolysis, 700 °C). It is evident that our procedure would
be the method of choice for the preparation of large amounts
of 12.
Acknowledgment. Financial support from the DGES
(PB96-0967) is gratefully acknowledged. We also thank the
Spanish Ministry of Education and Culture for the award of
a research grant to Diego Pen˜a.
(9) Ratio determined by 1H NMR of the mixture. Samples of both isomers
(6 and 7) were separated by flash chromatography and adequately
characterized. Data for 6: 1H NMR (CDCl3) δ 9.03-8.98 (m, 2 H), 8.64
(d, J ) 8.9 Hz, 1 H), 8.59 (d, J ) 8.9 Hz, 1 H), 8.35 (d, J ) 8.5 Hz, 1 H),
8.30 (d, J ) 8.7 Hz, 1 H), 8.12-7.95 (m, 6 H), 7.73-7.48 (m, 4 H), 7.36-
7.28 (m, 2 H); 13C NMR (CDCl3) δ 133.7, 132.1, 132.0, 131.2, 130.6, 129.7,
129.6, 129.5, 129.2, 129.1, 128.7, 128.5, 128.1, 128.0, 127.9, 127.8, 127.6,
126.1, 125.94, 125.92, 125.86, 125.78, 125.5, 124.9, 124.8, 120.5, 120.4;
MS, m/z (%) 378 (M+, 63), 377 (68), 187 (100); HRMS for C30H18 calcd
378.1408, found 378.1408. Spectral data of 7 were in agreement with those
reported in the literature (refs 10b,c).
(10) (a) Laarhoven, W. H.; von Broeckhoven, J. A. M. Tetrahedron Lett.
1970, 73-76. (b) Winter, W.; Langjahr, V.; Meier, H.; Merkuschew, J.;
Juriew, J. Chem. Ber. 1984, 117, 2452-2463. (c) Hagen, S.; Scott, L. T. J.
Org. Chem. 1996, 61, 7198-7199 and references therein. (d) For a related
substituted analogue, see: Mehta, G.; Raghava Sharma, G. V.; Krishna
Kumar, M. A.; Vedavyasa, T. V.; Jemmis, E. D. J. Chem. Soc., Perkin
Trans. 1 1995, 2529-2530.
OL990864T
(11) Fujisaki, S.; Eguchi, H.; Omura, A.; Okamoto, A.; Nishida, A. Bull.
Chem. Soc. Jpn. 1993, 66, 1576-1579.
(12) The spectral data of our product were analogous to those reported
by Pascal (ref 6) and Hacker (ref 7a). In addition, we were able to obtain
a
13C NMR spectra of 12: 1H NMR (CDCl3, 500 MHz) δ 8.54 (dd, J )
8.2, 1.1 Hz, 6H), 8.15 (d, J ) 8.2 Hz, 6H), 7.55 (dt, J ) 7.6, 1.1 Hz, 6H),
7.22 (dt, J ) 7.7, 1.2 Hz, 6H); 13C NMR-DEPT (CD2Cl4, 125 MHz) δ
131.8 (C), 130.9 (CH), 130.3 (C), 128.5 (C), 125.8 (CH), 125.6 (CH), 123.3
(CH); MS, m/z (%) 528 (M+, 29), 264 (16), 261 (66), 254 (100); HRMS
for C42H24 calcd 528.1878, found 528.1869.
Org. Lett., Vol. 1, No. 10, 1999
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