J . Org. Chem. 1997, 62, 2285-2287
2285
F a cile Ar om a tiza tion Rea ction s of
Over cr ow d ed P olycyclic Ar om a tic En es
Lea d in g to F u ller en e F r a gm en ts
Sergey Pogodin, P. Ulrich Biedermann, and
Israel Agranat*
Department of Organic Chemistry, The Hebrew University of
J erusalem, J erusalem 91904, Israel
Received J anuary 21, 1997
Overcrowded polycyclic aromatic enes (PAEs),1,2 e.g.,
bi-9H-fluoren-9-ylidene (1),3,4 are potential starting ma-
terials for the preparation of bowl-shaped fragments of
fullerenes (buckybowls).5-7 Recently, the thermal and
catalyzed dehydrocyclization of 1 to diindeno[1,2,3,4-
defg;1′,2′,3′,4′-mnop]chrysene (2) via the intermediates
benz[e]indeno[1,2,3-hi]acephenanthrylene (3) and benz-
[g]indeno[1,2,3,4-mnop]chrysene (4) by flash vacuum
pyrolysis (FVP) at temperatures above 700 °C in the gas
phase have been reported by Zimmermann et al.8,9
Buckybowl 2 could also be synthesized by a two-fold
thermal (>1000 °C) elimination of CO from 7,14-dioxo-
7,14-dihydrophenanthro[1,10,9,8-opqra]perylene9 and by
FVP of (E)-1,1′-dibromobi-9H-fluoren-9-ylidene at 1050
°C.6 Previous claims of the formation of 3 by the
debromocyclization of 9,9′-dibromo-1,1′-bifluorenyl10 and
from a fluorene pyrolyzate11 have been questioned.7 The
oxidative photocyclization of 1 to give 3 has also been
claimed.12 However, the 1H NMR data of the product was
not consistent with those of 3 (vide infra).13 The syn-
thesis of bridged derivatives of 3 by oxidative photo-
cyclization reactions of (Z)-2,2′-tethered bifluorenylidenes
have been reported by Luh et al.13 The success of the
last method was attributed to the bridged (Z)-stereo-
chemistry and to the tether functionality in the starting
materials.7,13 We report here a facile synthesis of 3, and
its 1-chloro-derivative 5, by a reductive cyclodechlorina-
tion and a cyclodehydrochlorination of (E)- and (Z)-1,1′-
dichlorobi-9H-fluoren-9-ylidene (6), using palladium ace-
tate as a homogenous catalyst.14,15 We note that 3 and
5 are fullerene fragments which are not buckybowls.5
The introduction of two chlorine atoms in the fjord
regions (positions 1 and 1′) of 1 was aimed to serve
several purposes. Firstly, an intramolecular reductive
dechlorination (Ullman reaction)16,17 of (Z)-6 to 3 in
solution under homogeneous catalysis conditions14,15 at
reasonable temperatures may be feasible. Secondly, the
overcrowding in the fjord regions of (E)-6 and (Z)-6 was
predicted to be more pronounced, as compared with 1,18
resulting in a further destabilization of the reactants.
This spatial alignment could allow the cyclization of 6 to
3 to be carried out at lower temperatures (as compared
e.g., with the FVP method6). Thirdly, the enhanced
overcrowding of 6 versus 1 results in relatively fast E,Z-
isomerizations.18 Thus, both (E)-6 and (Z)-6 could be
used as starting materials for affecting the aromatization
of 6 to 3.
The starting material for the reductive dechlorination
reaction was pure (Z)-6, obtained by recrystallization of
a mixture of (E)-6 and (Z)-619 from CH2Cl2. A solution
of (Z)-6 (under argon) in dry DMF was treated with
K2CO3, n-Bu4NHSO4 and Pd(OAc)2 and heated with
magnetic stirring at 119-122 °C for 51 h. The crude
products were purified by column chromatography and
by fractional recrystallization. The following compounds
were isolated: 6, 3, 1-chlorobenz[e]indeno[1,2,3-hi]-
acephenanthrylene (5), 1-chloro-9H-fluoren-9-one, and
9H-fluoren-9-one. The structures of the products were
(1) Shoham, G.; Cohen, S.; Suissa, R. M.; Agranat, I. In Molecular
Structure: Chemical Reactivity and Biological Activity; Stezowski, J .
J .; Huang J .-L.; Shao, M.-C., Eds.; IUC Crystallographic Symposia 2,
Oxford University Press: Oxford, 1988; pp 290-312.
(2) Biedermann, P. U.; Levy, A.; Stezowski, J . J .; Agranat, I.
Chirality 1995, 7, 199.
(3) de la Harpe, C.; van Dorp, W. A. Ber. Dtsch. Chem. Ges. 1875,
8, 1048.
(4) Biedermann, P. U.; Levy, A.; Suissa, M. R.; Stezowski, J . J .;
Agranat, I. Enantiomer 1996, 1, 75.
(5) Rabideau P. W.; Sygula, A. Acc. Chem. Res. 1996, 29, 235.
(6) Scott, L. T. Pure Appl. Chem. 1996, 68, 291.
(7) Biedermann, P. U.; Luh, T.-Y.; Weng, D. T.-C.; Kuo, C.-H.;
Stezowski, J . J .; Agranat, I. Polycycl. Aromat. Compd. 1996, 8, 167.
(8) Hagen, S.; Nuechter, U.; Nuechter, M.; Zimmermann, G. Tetra-
hedron Lett. 1994, 35, 7013.
1
established by mass and by 1D and 2D H NMR and 13C
NMR spectroscopies. PAH 3 was isolated in 5.6% yield
(49.7% based on consumed 6) as yellow crystals. In C2v
3, as expected, no NOE cross peak between the protons
at the overcrowded region (H1, H14 and H7, H8) was
observed. By contrast, in the isomeric C2h rubicene
(7),20,21 an NOE cross peak between the overcrowded
(9) Hagen, S.; Nuechter, U.; Nuechter, M.; Zimmermann, G. Poly-
cyclic Aromat. Compd. 1995, 4, 209.
(10) Yukhno, G. F.; Bikkulov, A. Z. Dokl. Neftekhim. Sekts. Bashk.
Resp. Vses. Khim. O-va. 1971, 7, 5; Chem. Abstr. 1975, 83, 9606y.
(11) Lang, K. F.; Buffleb, H.; Kalowy, J . Chem. Ber. 1961, 94, 523.
(12) De Gunst, G. P. Recl. Trav. Chim. Pay-Bas 1969, 88, 801.
(13) Kuo, C.-H.; Tsau, M.-H.; Weng, D. T.-C; Lee, G. H.; Peng, S.-
M.; Luh, T.-Y.; Biedermann, P. U.; Agranat, I. J . Org. Chem. 1995,
60, 7380.
(14) Dyker, G. J . Org. Chem. 1993, 58, 234.
(15) Grigg, R.; Teasdale A.; Sridharan, V. Tetrahedron Lett. 1991,
32, 3859.
(16) Bacon, R. G. R.; Hill, H. A. O. Quart. Rev. 1965, 19, 95.
(17) Sainsbury, M. Tetrahedron 1980, 36, 3327.
(18) Agranat, I.; Rabinovitz, M.; Weitzen-Dagan, A.; Gosnay, I. J .
Chem. Soc., Chem. Commun. 1972, 732.
(19) Gosnay, I.; Bergmann, E. D.; Rabinovitz, M.; Agranat, I. Isr. J .
Chem. 1972, 10, 423.
(20) Sachweh, V.; Langhals, H. Chem. Ber. 1990, 123, 1981.
(21) Clar, E. Polycyclic Hydrocarbons; Academic Press: London,
1964; Vol. 2, p 345.
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