Synthesis and properties of trefoil-shaped tris(hexadehydrotribenzo[12] annulene) and tris(tetradehydrotribenzo[12]annulene)

Article abstract of DOI:10.1021/ol060781u

Trefoil-shaped tris(hexadehydrotribenzo[12]annulene) possessing a substructure of the ultimate two-dimensional C(Sp)-C(Sp²) network, graphyne, and the related tris(tetradehydrotribenzo[12]annulene) were synthesized, and their ground- and excite

Full text of DOI:10.1021/ol060781u

ORGANIC
LETTERS
2006
Vol. 8, No. 14
2933-2936
Synthesis and Properties of
Trefoil-Shaped
Tris(hexadehydrotribenzo[12]annulene)
and
Tris(tetradehydrotribenzo[12]annulene)
Takashi Yoshimura,† Akiko Inaba,† Motohiro Sonoda,† Kazukuni Tahara,†
Yoshito Tobe,*,† and Richard Vaughan Williams‡
DiVision of Frontier Materials Science, Graduate School of Engineering Science,
Osaka UniVersity, and CREST, Japan Science and Technology Agency (JST),
Toyonaka, Osaka 560-8531, Japan, and Department of Chemistry, UniVersity of Idaho,
P.O. Box 442343, Moscow, Idaho 83844-2343
tobe@chem.es.osaka-u.ac.jp
Received March 31, 2006
ABSTRACT
Trefoil-shaped tris(hexadehydrotribenzo[12]annulene) possessing a substructure of the ultimate two-dimensional C(sp)
−
C(sp2) network, graphyne,
and the related tris(tetradehydrotribenzo[12]annulene) were synthesized, and their ground- and excited-state properties were investigated.
Carbon-rich organic molecules have been attracting much
interest regarding their novel structures and potential ap-
plications.1 Dehydrobenzoannulenes (DBAs), which were
investigated extensively during the late 1950s through the
mid-1970s with regard to their aromaticity/antiaromaticity,2
constitute one of the central classes of carbon-rich mol-
ecules.3 Thus, multiple fused DBAs have been synthesized
as scaffolds of two-dimensional carbon networks such as
graphyne4a and graphdiyne4 as well as one-dimensional
oligomers.5 These one- and two-dimensional systems are
predicted to exhibit semiconductive and/or nonlinear optical
(2) For selected reviews on annulenes, see: (a) Nakagawa, M. In The
Chemistry of the Carbon-Carbon Triple Bond; Patai, S., Ed.; John Wiley
& Sons: Bristol, 1978; p 635. (b) Balaban, A. T.; Banciu, M.; Ciorba, V.
Annulenes, Benzo-, Hetero-, Homo- DeriVatiVes, and their Valence Isomers;
CRC Press: Boca Raton, 1987; Vol. 1, p 67. (c) Huang, N. Z.; Sondheimer,
F. Acc. Chem. Res. 1982, 15, 96.
(3) For reviews on DBAs, see: (a) Wong, H. N. C. In AdVances in
Theoretically Interesting Molecules; Thummel, R. P., Ed.; JAI Press:
Greenwich, 1995; p 109. (b) Youngs, W. J.; Tessier, C. A.; Bradshaw, J.
D. Chem. ReV. 1999, 99, 3153. (c) Marsden, J. A.; Palmer, G. J.; Haley,
M. M. Eur. J. Org. Chem. 2003, 2355. (d) Tobe, Y.; Sonoda, M. In Modern
Cyclophane Chemistry; Gleiter, R., Hopf, H., Eds.; Wiley-VCH: Weinheim,
2004; p 1. (e) Jones, C. S.; O’Connor, M. J.; Haley, M. M. In Acetylene
Chemistry: Chemistry, Biology and Material Science; Diederich, F., Stang,
P. J., Tykwinski, R. R., Eds.; Wiley-VCH: Weinheim, 2005; p 303.
† Osaka University.
‡ University of Idaho.
(1) For reviews, see: (a) Diederich, F.; Rubin, Y. Angew. Chem., Int.
Ed. Engl. 1992, 31, 1101. (b) Carbon Rich Compounds I; de Meijere, A.,
Ed.; Springer: Berlin, 1998. (c) Carbon Rich Compounds II; de Meijere,
A., Ed.; Springer: Berlin, 1999. (d) Bunz, U. H. F.; Rubin, Y.; Tobe, Y.
Chem. Soc. ReV. 1999, 28, 107.
10.1021/ol060781u CCC: $33.50
© 2006 American Chemical Society
Published on Web 06/06/2006

properties. A number of such molecules consisting of
aromatic [18]DBA6 or [14]DBA7 subunits have been re-
ported. On the other hand, there are few examples of such
systems constructed from hexadehydrotribenzo[12]annulene,
[12]DBA (1a).8 This is presumably because of the difficulty
associated with the construction of the [12]DBA framework.
The weakly antiaromatic [12]DBA exhibits interesting
properties such as complexation with transition metals9 and
forbidden electronic transitions between S0 and S1 states.10
Only diamond-shaped11 and bow-tie-shaped11a,12 bis[12]DBA
derivatives have been prepared. We therefore undertook the
synthesis of the trefoil-shaped tris[12]DBA 2b to investigate
the effect of the mode of fusion of the [12]DBA rings on
the ground- and excited-state properties of multiply fused
[12]DBAs and to establish a synthetic route to the “full
wheel-shaped” hexakis[12]DBA, a substructure motif of
graphyne. In addition, the structure and magnetic properties
of the parent compound 2a were investigated by DFT
calculations. We also planned to prepare tris[12]DBA 3,
having peripheral double bonds with internal hydrogens that
should allow better assessment of the effect of the multiple
fusion on the tropicity on the [12]DBA ring.
Figure 1. Structures and numbering of the internal benzene ring
of 2a,b and the aromatic protons of tris[12]DBAs and their
corresponding reference compounds.
DFT calculations (B3LYP/6-31G* level) of 2a predict that
it possesses a D3 symmetric structure in which the three 12-
membered rings are twisted slightly (with a dihedral angle
of 7.5° between the peripheral triple bond and the bond
shared by the 12-membered ring and the central benzene
ring) because of the steric repulsion between the hydrogen
atoms of the peripheral benzene rings. The central benzene
ring adopts a very shallow chair conformation with a dihedral
angle of 0.8° (C(1)-C(2)-C(3)-C(4) ) 0.838°, C(2)-
C(3)-C(4)-C(5) ) -0.840°); see Figure 1 for numbering.
In general, fusion of the antiaromatic [12]annulene ring to a
benzene ring causes bond length alternation in the latter, in
such a way that the endocyclic bond shared by the [12]-
annulene ring becomes longer than that of the exocyclic
bond.13 It is expected that the fusion of three [12]annulene
rings to the central benzene ring of 2a in an alternate fashion
would emphasize the bond length alternation. However, this
is not the case because the calculated bond lengths of the
internal benzene ring of 2a (C(2)-C(3), C(4)-C(5), C(1)-
C(6)) are slightly longer than those of 1a and the peripheral
ring of 2a presumably for the above-mentioned steric
repulsion.14 The other calculated bond lengths of 2a,
however, are similar to those of 1a. The chemical shift of
the aromatic protons and nucleus-independent chemical shifts
(NICS)15 of 1a and 2a were calculated using the GIAO-HF/
6-31G*//B3LYP/6-31G* methods.16 The NICS values of the
12-membered ring (4.41) and benzene rings (-6.79) of 1a
using the GIAO-B3LYP/6-31G*//B3LYP/6-31G* methods
were reported by Vollhardt et al.17 Our results are sum-
marized in Table 1 together with the experimental data for
the tert-butyl derivatives 1b and 2b described later. Despite
the smaller bond length alternation of the central benzene
ring of 2a, the less negative NICS value (-7.83) indicates
that this ring is substantially less aromatic than those of 1a
(-10.35) and the peripheral benzene rings of 2a (-10.25).
Because of the slight twisting of the [12]annulene rings of
2a, they are slightly less paratropic than that of 1a, and the
chemical shifts of peripheral benzene protons are predicted
to resonate at a lower field than those of 1a.
(4) (a) Baughman, R. H.; Eckhardt, H.; Kerteszz, M. J. Chem. Phys.
1987, 87, 6687. (b) Narita, N.; Nagai, S.; Suzuki, S.; Nakano, K. Phys.
ReV. B 1998, 58, 11009. (c) Narita, N.; Nagai, S.; Suzuki, S.; Nakano, K.
Phys. ReV. B 2000, 62, 11146.
(5) Zhou, Y.; Feng, S. Solid State Commun. 2002, 122, 307.
(6) (a) Wan, W. B.; Brand, S. C.; Pak, J. J.; Haley, M. M. Chem.-Eur.
J. 2000, 6, 2044. (b) Wan, W. B.; Haley, M. M. J. Org. Chem. 2001, 66,
3893. (c) Marsden, J. A.; Haley, M. M. J. Org. Chem. 2005, 70, 10213.
(7) (a) Marsden, J. A.; O’Cnnor, M. J.; Haley, M. M. Org. Lett. 2004,
6, 2385. (b) Marsden, J. A.; Miller, J. J.; Haley, M. M. Angew. Chem., Int.
Ed. 2004, 43, 1694.
(8) Staab, H. A.; Graf, F. Tetrahedron Lett. 1966, 7, 751.
(9) For example, see: (a) Ferrara, J. D.; Tessier-Youngs, C. A.; Youngs,
W. J. J. Am. Chem. Soc. 1985, 107, 6719. (b) Ferrara, J. D.; Djebli, A.;
Tessier-Youngs, C. A.; Youngs, W. J. J. Am. Chem. Soc. 1988, 110, 647.
(10) Wirz, J. In Excited States in Organic Chemistry and Biology;
Pullman, B., Goldblum, N., Eds.; D. Reidal Publishing Company: Dor-
drecht, 1977; p 283.
(11) (a) Koehoe, J. M.; Kiley, J. H.; English, J. J.; Johnson, C. A.;
Petersen, R. C.; Haley, M. M. Org. Lett. 2000, 2, 969. (b) Sonoda, M.;
Sakai, Y.; Yoshimura, T.; Tobe, Y.; Kamada, K. Chem. Lett. 2004, 33,
972.
As we wished to extend our synthetic strategy to the
synthesis of the full wheel-shaped hexakis[12]DBA, we
avoided using cross-coupling reactions, which are extensively
employed to construct [12]DBA structures, to form the
peripheral triple bonds. To introduce the peripheral triple
(14) Calculated bond lengths of 1a and 2a are listed in Table S1 in the
Supporting Information.
(12) (a) Iyoda, M.; Sirinintasak, S.; Nishiyama, Y.; Vorasingha, A.;
Sultana, F.; Nakao, K.; Kuwatani, Y.; Matsuyama, H.; Yoshida, M.; Miyake,
Y. Synthesis 2004, 1527. (b) Miljanic´, O. Sˇ.; Vollhardt, K. P. C.; Whitener,
G. D. Synlett 2003, 29.
(13) Mitchell, R. H.; Zhang, R.; Fan, W.; Berg, D. J. J. Am. Chem. Soc.
2005, 127, 16251.
(15) Schleyer, P. v. R.; Maerker, C.; Deansfeld, A.; Jial, H.; Hommes,
N. J. R. v. E. J. Am. Chem. Soc. 1996, 118, 6317.
(16) The NICS value of the 12-membered ring of 2a using GIAO-
B3LYP/6-31G*// B3LYP/6-31G* methods (3.57) was also smaller than that
of 1a (4.41).
(17) Matzger, A. J.; Vollhardt, K. P. C. Tetrahedron Lett. 1998, 39, 6791.
2934
Org. Lett., Vol. 8, No. 14, 2006

1
Scheme 1
Table 1. Calculated and Experimental H NMR Chemical
Shifts and NICS Values for 1a,b and 2a,ba
1a
2a
1H NMR Chemical Shift b
7.56 (7.26)
H1
H2
H3
H4
7.62 (7.38)
7.45 (7.29)
7.45
7.36 (7.20)
(7.39)
7.90 (7.41)
NICSc
peripheral benzene ring
central benzene ring
[12]annulene ring
-10.35
-10.25
-7.83
2.92
2.72
a Calculated values were obtained using the GIAO-HF/6-31G*//B3LYP/
6-31G* method. b Experimental values observed for the tert-butyl derivatives
1b and 2b are listed in parentheses. c At the center of each ring.
bonds while avoiding severe steric crowding, we employed
double elimination from an intermediate with peripheral
single bonds and appropriate leaving groups. We viewed the
coupling of a sulfone with an aldehyde18 and the pinacol
coupling as reasonable routes to such an intermediate.
The syntheses of compounds 2b and 3 are shown in
Scheme 1. Triol 6 was prepared in 48% yield by the
regioselective Sonogashira coupling of 4a with hydroxy-
alkyne 5.19 After conversion of 6 to sulfone 8, the Sono-
gashira coupling with formylalkyne 9 gave 10 in 44% yield.20
Treatment of 10 with lithium hexamethyldisilazide and
diethyl chlorophosphonate followed by an excess amount of
lithium diisopropylamide furnished trefoil-shaped tris[12]-
DBA 2b in 3% yield as a yellow solid. The low yield of 2b
is ascribed to intermolecular reactions because the nucleo-
philic C-C bond formation could take place randomly,
leaving unreacted functional groups which are susceptible
to further reactions.
To assess the effect of the mode of fusion on the tropicity
of the [12]DBA rings of 2b and 3, we compared their H
Next, for the pinacol coupling approach, hexaaldehyde 11
was prepared in 72% yield by the Sonogashira coupling of
hexabromobenzene (4b) with an excess of 9. Pinacol
coupling of 11 using a low-valent vanadium reagent gave
1
NMR chemical shifts with those of reference compounds
1b and 14.21 The chemical shifts of H1, H2, and H4 of 2b
(7.38, 7.29, and 7.41 ppm, respectively) appeared at a slightly
lower field than those of 1b (7.26, 7.20, and 7.39 ppm,
respectively), indicating a small decrease of paratropicity in
2b compared to 1b. It seems likely that H1 of 2b suffers
from the anisotropic effect of the neighboring benzene rings
to show more pronounced downfield shifts than H2 and H4.
The observed chemical shifts agree qualitatively with the
theoretical values obtained for the DFT optimized geometry
of 2a (Table 1). It is, therefore, concluded that the observed
downfield shifts are attributed to the slight twisting of the
[12]annulene ring. Similarly, in the case of 3, the chemical
shifts of its aromatic protons (7.42, 7.19, and 7.31 ppm)
shifted slightly downfield compared to the corresponding
reference compound 14 (7.40, 7.13, and 7.29 ppm). More-
over, the vinyl protons of 3 and 14 serve as good probes for
the assessment of their tropicity, which appear as sharp
singlets owing to the fast rotation of the vinyl group. The
1
hexaol 12 as a mixture of isomers in 74% yield. The H
NMR spectrum of 12 indicates that the hydroxy groups are
anti in each 12-membered ring. Chlorination of 12 using
thionyl chloride gave hexachloride 13, in which the stereo-
centers possessed both syn and anti stereochemistry. Finally,
double elimination using potassium tert-butoxide gave 2b
in 10% yield. Compound 3 was prepared by the McMurry
coupling of 11. Treatment of 11 with TiCl4, Zn, and CuI in
a mixture of DME and THF (1:2) gave 3 in 9% yield as a
sparingly soluble orange solid. The low yield of 3 is again
ascribed to the site-random coupling reaction as in the case
of the cyclization of 10.
(18) Orita, A.; Yoshioka, N.; Struwe, P.; Braier, A.; Beckmann, A.; Otera,
J. Chem.-Eur. J. 1999, 5, 1355.
(19) Sonoda, M.; Inaba, A.; Itahashi, K.; Tobe, Y. Org. Lett. 2001, 3,
2419.
(20) Compound 10 was synthesized only by this sequence of coupling
reactions. Namely, the first coupling of 4a with 9 followed by the second
coupling with 5 or the phenyl sulfone derived from 5 did not give the desired
hexaethynylbenzene derivatives.
(21) Staab, H. A.; Bader, R. Chem. Ber. 1970, 103, 1157.
Org. Lett., Vol. 8, No. 14, 2006
2935

remarkably low field resonance of 14 (8.54 ppm) was
ascribed to both the local anisotropic effect of the triple bonds
to the inner hydrogen and the paratropicity of the 12-
membered ring, either upfield or downfield shifting depend-
ing on the position (inner or outer) of the hydrogen.21 The
observed upfield shift of the vinyl proton of 3 (8.42 ppm)
relative to that of 14 indicates that the paratropicity of the
former is smaller than that of the latter.
is a strongly allowed absorption band at around 290 nm, a
weakly allowed band at ca. 350 nm, and a strongly forbidden
band at 400 nm. Even though 14 is not of D3h symmetry, it
also exhibits a similar absorption spectrum. On the other
hand, the spectra of 2b and 3 are different from those of 1a
and 14, as shown in Figure 2a. Not only do 2b and 3 exhibit
bathochromic shifts compared to 1a and 14 but also the
intensities of the bands relative to those of 1a and 14 are
completely different. The difference between the absorption
spectra can be ascribed to the loss of D3h symmetry in 2b
and 3. However, the profiles of the spectra of 2b and 3 are
different from that of a hexaethynylbenzene derivative 15;
the former exhibit absorptions at a longer wavelength owing
to their extended conjugation.
To investigate the excited-state properties of 2b and 3,
UV-vis and fluorescence spectra were measured, as shown
in Figures 2a and 2b, respectively, together with those of
The characteristic fluorescence spectrum of 1a exhibits
apparent vibrational splitting.10 The profile of the fluores-
cence spectrum of 2b is different from that of 1a, with the
0-0 transition band as the strongest band, a typical profile
for phenylacetylene derivatives such as 15 (Figure 2b). The
profiles of 3 and 14 are similar, though the fluorescence band
of 3 exhibits a considerable red shift relative to that of 14.23
In conclusion, trefoil-shaped tris[12]DBA 2b and 3 have
been synthesized by constructing the 12-membered rings
through peripheral single-bond formation using intramolecu-
lar coupling followed by double elimination. Their [12]-
annulene rings show slightly smaller paratropicities than that
of the corresponding mono[12]DBAs 1a and 14 presumably
because of the decrease of planarity due to steric repulsion.
Similarly, their excited-state properties are considerably
different from those of 1a and 14.
Acknowledgment. Support to T.Y. from the 21st Century
COE Program “Integrated Eco-Chemistry” is gratefully
acknowledged. K.T. is grateful for a JSPS Research Fel-
lowship for Young Scientists.
Supporting Information Available: Experimental pro-
cedures and spectral data of new compounds. This material
is available free of charge via the Internet at http://pubs.acs.org.
Figure 2. (a) Electronic absorption spectra of 1a (black), 2b (red),
3 (blue), 14 (violet), and 15 (green) in CHCl3 at 25 °C. (b)
Normalized fluorescence spectra of 1a (black), 2b (red), 3 (blue),
14 (violet), and 15 (green) in CHCl3 at 25 °C.
OL060781U
(22) For the UV spectrum, see: Nierle, J.; Barth, D.; Kuck, D. Eur. J.
Org. Chem. 2004, 867.
(23) Quantum yields of the fluorescence of 1a, 2b, 3, 14, and 15 were
determined to be 0.10 (lit., 0.15 in methylcyclohexane at room tempera-
ture24), 0.03, <0.01, 0.01, and 0.21 in CHCl3 at 25 °C, respectively.
(24) Janecka-Styrcz, K.; Lipin˜ski, J.; Ruziewicz, Z. J. Lumin. 1978, 17,
83.
1a, 14, and hexakis(phenylethynyl)benzene (15).22 It has been
reported by Wirz that compound 1a exhibits characteristic
absorption/emission spectra owing to its unique electronic
structure due to the D3h symmetry of the molecule.10 There
2936
Org. Lett., Vol. 8, No. 14, 2006