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An Extraordinarily Twisted Polycyclic Aromatic Hydrocarbon.

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J =7.5 Hz.2H). 7 21 (t. J = 7 . 5 H z , 2 H ) , 7.38(t, J =7.S Hz, 1 H), MS(E1. 70eV):
21,350 (1.6) [M'], 165 (100). 110 (57); HRMS calcd for
C,,H,,3sCCI0,S ("I)350 0742, found. 350 0727 elemental analysis: calcd C 61.62,
H 5.46: found. C 61.61, H 5.32.
Received: January 3, 1997 [Z9959IE]
German version : Angew. Chem. 1997, 109, I525 - 1527
mi: (Yo):352 (0.6)[M'
Keywords: acetals Pummerer rearrangement
rearrangements - sulfur
[I] Reviews a ) S Ode. T. Numata. T. Yoshimura in The Chemisrrj ofthe Sulphonium Group (Eds : C. J. M. Stirling, S. Patai), Wiley, New York, 1981, p. 571;
b) 0. D. Lucchi, U. Miotti, G. Modena, Organic Reaclions, Voi.40. Wiley,
New York, 1991. chapter 3: c) D S. Grierson, H.-P. Husson in Comprehensive
Organic Sjnfhesis. I411 6 (Eds: B. M Trost, I. Fleming), Pergamon, Oxford,
1991. p. 909; d ) Y. Kita, N. Shibata, Synlert 1996,289-296 Recently published
examples. e) A. Hedhli, A. Baklouti, A. Cambon, Tetrahedron Letr. 1994, 37,
6877- 6878; f ) A. Arnone, P. Bravo. M. Frigerio, G . Salani, F. Viani. Terrahedron 1994. 50. 13485-13492.
R. R. King, .I Org. Chem. 1978, 43, 3784-3785.
M. E. Jung, C. Kim, L. von dem Bussche, J Org. Chem. 1994,59,3248-3249.
M. E. Jung. D Jachiet, S I. Khan, C. Kim, Tetrahedron Letr. 1995, 36, 361364.
S. A k a , Y Takeda. K. lio, Y Yoshida, Y. Kita, J. Chem. SOC.Chem. Commun.
1995. 1013-1014.
S . Akai. Y Takeda, K. 110,K Takahashi, N. Fukuda. Y Kita, J. Org. Chem.
1997. in press.
S . Akai, K. Iio. Y Takeda, H. Ueno, K. Yokogawa. Y Kita, J. Chem. SOC.
Chrm. Commun. 1995, 2319-2320; Y. Kita, Y. Takeda, K. Iio, K. Yokogawa,
K. Takahashi. S. Akai, Tetrahedron Lett. 1996, 37, 7545-7548.
We have elucidated a highly enantioselective Pummerer-type reaction of chiral,
nonracemic aliphatic sulfoxides using 0-silylated ketene acetals [Id], although
the enantiomeric excesses for the reported asymmetric Pummerer reaction induced by acid anhydrides were low [I]. This method was efficiently applied to
the asymmetric Pummerer-type cyclization of chiral, nonracemic sulfoxides
and to the biomimetic conversion of Arnstein tripeptide analogs into optically
active m [j-lactams. This synthesis resembles penicillin biosynthesis [gal. Similar highly enantioselective Pummerer-type reactions of chiral, nonracemic
aliphatic sulfoxides induced by a variety of 1-ethoxyvinyl esters including 2a,b
also gave 1-acyloxy sulfides [9 b,c].
a ) Y Kita, N . Shibata, N. Kawano. T. Tohjo, C. Fujimori, H. Ohishi, J Am.
Cheni. So<.. 1994. 116. 5116-5121; b) Y Kita, N. Shibata, N. Kawano, S.
Fukui. C. Flljimori, Tetrahedron Lett. 1994,38, 3575-3576, c) N. Shibata, M.
Matsugi, N . Kawano, S. Fukui. C. Fujimori, K. Gotanda, K.Murata, Y. Kita,
Tetrrohedron. .4.;l~mmetr?.
1997. 8, 303-310.
Y. Kita. H. Maeda, K. Omori, T. Okuno, Y Tamura, J Chem. SOC.
Trans. 1 1993. 2999-3005, and references therein.
Although the preparation ofp-quinone mono 0.0-acetal compounds has been
widely explored, most of the methods that have been applied thus far are based
on the oxidation of phenol or dihydroquinone derivatives- a) Y. Tamura, T.
Yakura. J. Haruta, Y Kita. J. Org. Chem. 1987. 52, 3927-3930; b) E. C. L.
Gautier. N. I Lewis, A. McKillop. R. J. K. Tayler, Synrh Commun 1994, 24,
2989-3008. and references therein.
An Extraordinarily Twisted Polycyclic Aromatic
Xiaoxin Qiao, Douglas M. Ho, and
Robert A. Pascal. Jr.*
Among the most aesthetically pleasing chemical structures
are polycyclic aromatic hydrocarbons (PAHs) that exhibit helical distortions from planarity."] In recent years a variety of
longitudinally twisted PAHs and PAH derivatives-ssentially
[*I Prof. R. A Pascal, Jr., X. Qiao, Dr D M. H o
Department of Chemistry
Princeton University
Princeton. N J 08544 (USA)
Fax: Int. code +(609)2586746
e-mail : snaketcr
This work was supported by the National Science Foundation (grant CHE9408295)
Angeit. Chem In!. Ed. Engl. 1997, 36, No. 13/14
twisted aromatic ribbons-have been prepared by the substitution of normally planar PAHs with bulky substituents.['- 31
Thus, for example, anthracene is a planar molecule, but decaphenylanthracene exhibits an end-to-end twist of 63".13]In no
case, however, has the overall twist of such a molecule exceeded
70",l4] and we wondered what would be the properties of a PAH
in which the twist exceeded 90". We now report the synthesis and
crystallographic characterization of 9,10,11,12,13,14,15,16-octaphenyldibenzo[u,c]naphthacene(l),a PAH with an extraordinary end-to-end twist of 105".
The synthesis of 1 is similar to that of decaphenylanthracene;L3' the critical step is the addition of a highly substituted aryne to hexaphenylisobenzofuran[3. 'I (2) (Scheme 1). Thus,
Scheme 1.
the anthranilic acid 3[2d1was diazotized in the presence of 2, and
the resulting oxide 4 was deoxygenated with zinc in acetic acid
to yield compound 1 in 1.6% overall yield. Both the cycloaddition of the aryne with isobenzofuran (15 % yield) and the deoxygenation (11 %) suffer from severe steric hindrance, which accounts for the low yield in an otherwise simple procedure.
Compound 1 is an orange solid that is readily soluble in a
wide variety of organic solvents, in contrast with many PAHs.
Orange prisms were obtained from ethanol, and X-ray structure
analysis unambiguously established the structure of 1 (Figure 1).[61The molecule lies on a crystallographic C, axis, thus its
site symmetry is equal to its expected molecular symmetry. The
central naphthacene moiety is a smoothly twisted aromatic ribbon in which the terminal bonds [C(l)- C( 1') and C( 13)-C(13')]
are rotated by 105.4(8)" with respect to each other. However, the
distortion is evenly distributed among the four benzene rings of
the naphthacene, which contribute twists of 26.1(8)", 28.7(8)',
28.6(8)", and 21.9(8)', thus enabling good conjugation to be
maintained within the aromatic x system. Indeed, the UV spectrum of 1, with absorption maxima at 496, 470. and 364 nm,
retains most of the features found in the spectrum of the parent
but shifted by about
hydrocarbon, dibenzo[u,~]naphthacene,[~~
50 nm to the red.
Compound 1 is very stable in the solid state. Crystals heated
to 400°C in an open capillary appear unchanged (apart from
some cracking) by visual inspection and mass spectrometric and
thin-layer chromatograpic analyses. Concentrated solutions of
1 appear to undergo slow decomposition at room temperature,
but the factors governing this process are unclear. However, a
dilute solution of 1 (1.8 x IO-'M in dimethyl sulfoxide), monitored spectrophotometrically, was indefinitely stable at 50 "C
even in the presence of air and added HCl, and an NMR sample
( 1 . 6 ~1 0 - 3 in
~ CDC1,) showed no decomposition after one
week at room temperature.
The preparation of 1 establishes a new record for the twisting
of an aromatic x-electron system, and its end-to-end twist of
8 VCH Veriagsgeselischaft mbH. 0-69451 Weinheim, 1997
0570-0833/Y7/3613-IS31 $17.50+.50/0
Keywords: arenes
Figure 1. Molecular structure of compound 1 (thermal ellipsoids are drawn at the
50% probability level, hydrogen atoms have been omitted for clarity, and only the
rpso-carbon atoms of the phenyl rings are shown in the lower illustration).
105" is more than 1.5 times as great as that observed in any
previous PAH.['O1 Looking to the future, two such molecules,
fused to appropriate acenes to form a ring, would be sufficient
to form a polycyclic aromatic Mobius strip. In addition, AM1
which yield a geometry for 1 that is in excellent
agreement with the X-ray
structure, indicate that the hexacene 5 should have a twist of
178". Such compounds are no
longer unreasonable synthetic
Experimental Section
1: A solution of 3 (0.530 g, 1.21 mmol) in 1,2-dichloroethane (80 mL) was added
dropwise to a solution of 2 (1.10 g, 1.92 mmol) and isoamyl nitrite (0.5 mL) in
1,2-dichloroethane (55mL) at refux under argon. After 1 h, the solution was
cooled, and ethanol (12 mL) and 1% NaOH (40 mL) were added. The resulting
mixture was extracted with CHCI, (200 mL), and the organic extract was washed
with saturated NaHCO,, dried over MgSO,, and concentrated to dryness. The
residue was fractionated by column chromatography (silica gel; 1 : 1 hexanes:CH,CI,, then 1 :2 hexanes:CH,CI,) to yield compound 4 as an off-white solid
(0.174g); ' H N M R (500MHz, CDCI,): 6 = 6.60-6.76 (m, 18H), 6.80 (d,
- aromaticity - chirality -
[l] K. P. Meurer, F. Vogtle, Top. Curr. Chem. 1985, 127, 1-76.
[2] a) R. A. Pascal. Jr., W D. McMillan, D. Van Engen. J. Am. Chen?.Sor. 1986,
108, 5652-5653; b) R. A. Pascal, Jr., W. D. McMlllan, D. Van Engen, R. G.
Eason, ihid. 1987, 109, 4660-4665; c) P. J. Fagan, M . D. Ward, J. V. Caspar,
J. C. Calabrese, P. J. Krusic, ihid. 1988, 110, 2981 -2983; d) N Smyth, D Van
Engen, R. A. Pascal, J r , J Org. Chem. 1990.55, 1937-1940.
[3] X. Qiao, M. A. Padula, D. M. Ho, N. J. Vogelaar, C. E. Schutt, R. A. Pascal,
Jr., J. Am. Chem. SOC.1996, 118, 741-145.
[4] Only three polycyclic aromatic compounds have crystallographically characterized end-to-end twists (defined in note 17 of ref. [2b]) of more than 65":
9.1 8-diphenyItetrabenz[u,c,kJanthracene(65.7') [2 a]. its bis(trifluoromethy1)
derivative (69.7') [Zb], and a tetrakis[q5-pentarnethylcyclopentadienyl)ruthenium] complex of rubrene (67.3') [2c]
[5] W. Ried, K. H. Bonnighausen, Liebigs Ann. Chem. 1961,639,61-67.
[6] An orange needle of 1. cut to, was used for the X-ray
diffraction studies. Crystal data: C,,H,,, M = 937.12, orthorhombic, Pbcn,
u = 16.562(2), h = 17.796(2), c = 17.641(2)A, V = 5199.6(10)A,, 2 = 4,
P.~,.,, = 1.197 Mgm-,. Intensity measurements were made by using graphitemonochromated Mo,, radiation ( i = 0.71073 A) at 298 K on a Siemens P4
diffractometer. A total of 4260 reflections were measured (3' s 20 5 45'. o scan
mode), of which 3406 were unique (R,,, = 0 057), and 831 have I>2o(l)
Corrections were made for Lorentzian polarization hut not for absorption or
extinction. The structure was solved by direct methods (SHELXTL [7]) and
refined by full-matrix least-squares on F z (SHELXL-93 [S]). All non-hydrogen
atoms were refined with anisotropic displacement coefficients, and hydrogen
atoms were included with a riding model and isotropic displacement coefficients [U(H) = 1.2U(C)]. The refinements converged to R(F) = 0 047,
wR(FZ)= 0.032, and S e1.07 for 831 reflections with I > 2 ~ ( 1 ) , and
R ( F ) = 0.237, w R ( F z ) = 0.049, and S = 0.67 for 3406 unique reflections and
334 variables. The residual electron density ranged from -0.15 to 0.17 eA-3.
Crystallographic data (excluding structure factors) for the structure reported in
this paper have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC-100115. Copies of the data
can be obtained free of charge on apphcation to The Director, CCDC, 12
Union Road, Cambridge CB2 lEZ, UK (fax int. code +(1223) 336-033;
G M. Sheldrick. SHELXTL, Version 4.2. Siemens Analytical X-ray Instruments, Madison, Wisconsin, USA, 1991.
G. M. Sheldrick, SHELXL-93. Program for the Refinement of Crystal Structures. University of Gottingen, Germany, 1993.
a) E. Clar, Chem. Ber. 1948,81,253-269. b) E. Clar, Polycyclic Hydrocarbons,
Vol. 1. Academic Press, London, 1964, p 407.
An enantiomerically pure sample of compound 1 might be expected to show
exceptional optical activity. No attempt has been made to resolve 1; however,
the 500 MHz 'H NMR spectrum of 1 in the chiral solvent mixture d-trifluoromethylbenzyl alcohol/deuterochloroform (112) is broadened, hut not cleanly
split into enantiomeric subspectra, suggesting that it may have a significant
barrier to racemization. Previously prepared longitudinally twisted aromatic
polycycles show evidence of great conformational flexibility, possess only modest harriers to racemization, and none has been successfullyresolved [2 b, 3,111
K. Shibata, A. A. Kulkarni, D. M. Ho, R. A. Pascal, Jr., J. Org. Chem. 1995,
60, 428-434.
M. J. S. Dewar, E. G. Zoebisch, E. F. Healy, J. J. P. Stewart, J. Am. Chem. SOC.
1985, 107, 3902-3909.
7.42 (d, J = 8 Hz, 2H), 8.37 (d, J = 8 Hz, 2H); FAB MS: m / z ( O h ) 953 ( M i + H,
46), 849 (49), 662 (99), 575 (100). Without further purification, this material was
treated with a large excess ofactivated Zn dust (0.3 g) in glacial acetic acid (50 mL)
at reflux for 5 h. The mixture was filtered hot, and after cooling, water was added
to the filtrate. The resulting orange precipitate was collected by filtration and rinsed
with water. After drying, the solid was subjected to preparative TLC (silica gel, 2: 1
hexanes:CH,CI,) to give pure 1 as an orange solid (18.6mg, 0.020 mmol, 1.6%
yield): M.p. >400"C; ' H N M R (500 MHz, CDCI,): b = 6.19 (d, J = 8 Hz, 2H).
6.26 (t, J = 7 Hz, 2 H), 6.37 (m, 4H), 6.49 (m, 12 H), 6.61 -6.84 (m, 18 H). 6.92 (m.
(KBr): i = 3078,3055,3022,1600,1493,1442cm-'; UV (CHCI,): i,,, (Ig 6) = 496
(3.69), 470 (3.78), 446 (sh, 3.68). 364 (4.78). 352 (sh, 4.69); FAB MS: mi: ( X ) 937
( M ' t H, 100). 460 (31).
Received: January 2, 1997 [Z99541E]
German version. Angew. Chem. 1997, 109, 1588- 1589
VCH Verlagsgesellschufr mbH. 0.69451 Weinheim. 1997
Angew. Chem. Int. Ed. Engl. 1997,36, N o . 13/14
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extraordinary, hydrocarbonic, twisted, polycyclic, aromatic
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