Tetradehydrodinaphtho[10]annulene: A hitherto unknown dehydroannulene and a viable precursor to stable zethrene derivatives

Article abstract of DOI:10.1021/ol9015942

The synthesis and structural characterization of hitherto unknown tetradehydrodinaphtho[10]annulene, a hydrocarbon whose synthesis had been attempted four decades ago, was achieved for the first time. Moreover, the dinaphtho[10]annulene was transformed sm

Full text of DOI:10.1021/ol9015942

ORGANIC
LETTERS
2009
Vol. 11, No. 18
4104-4106
Tetradehydrodinaphtho[10]annulene: A
Hitherto Unknown Dehydroannulene and
a Viable Precursor to Stable Zethrene
Derivatives
Rui Umeda,† Daijiro Hibi, Koji Miki,‡ and Yoshito Tobe*
DiVision of Frontier Materials Science, Graduate School of Engineering Science,
Osaka UniVersity, 1-3 Machikaneyama, Toyonaka 560-8531, Japan
tobe@chem.es.osaka-u.ac.jp
Received July 13, 2009
ABSTRACT
The synthesis and structural characterization of hitherto unknown tetradehydrodinaphtho[10]annulene, a hydrocarbon whose synthesis had
been attempted four decades ago, was achieved for the first time. Moreover, the dinaphtho[10]annulene was transformed smoothly into stable
zethrene derivatives substituted at its 7,14-positions, showing that it serves as a good reservoir of zethrene derivatives. Optical and electrochemical
properties of a disubstituted zethrene derivative are also presented.
About four decades ago, Staab and Sondheimer attempted
independently to synthesize tetradehydrodinaphtho[10]annulene
(1) via cross-coupling of iodo and/or ethynylcopper(I)
substituted derivatives of naphthalene by heating in pyridine,
but they isolated zethrene (2a, dibenzo[de,mn]naphthacene)
in 50 or 22% yield instead of the purported 1.1 Although
the first synthesis of 2a was reported by Clar in 1955,2 the
above unexpected finding provides a more convenient access
to 2a,3 which would potentially serve as an organic semi-
conductor. Theoretical calculations predict that the HOMO/
LUMO gap of 2a (2.52 eV) is almost equal to that of the
well-known semiconductor pentacene (2.40 eV).4 Compu-
tational studies also predict that 2a would serve as a potential
candidate for nonlinear optical (NLO) organic materials.5
In addition, there are a few patents for the use of derivatives
of 2a in organic electronic devices, though the preparative
methods are not reported.6 However, 2a was not as well
studied as aromatic compounds of related structures like
(3) Although the formation of 2a was invoked in the purported synthesis
of dinaphtho[10]annulene too, this method is less practical than the one
via reported in ref 1. See ref 1c and the following papers: (a) Kemp, W.;
Storie, I. T.; Tulloch, C. D. J. Chem. Soc., Perkin Trans. 1 1980, 2812–
2817. (b) Gleiter, R.; Schaaff, H. P.; Rodewald, H.; Jahn, R.; Irngartinger,
H. HelV. Chim. Acta 1987, 70, 480–487.
† Present address: Faculty of Chemistry, Materials and Bioengineering,
Kansai University.
‡ Present address: Graduate School of Engineering, Kyoto University.
(1) (a) Mitchell, R. H.; Sondheimer, F. Tetrahedron 1970, 26, 2141–
2150. (b) Staab, H. A.; Nissen, A.; Ipaktschi, J. Angew. Chem., Int. Ed.
Engl. 1968, 7, 226. (c) Staab, H. A.; Ipaktschi, J.; Nissen, A. Chem. Ber.
1971, 104, 1182–1190, The formation of 2a was interpreted in terms of
spontaneous cyclization of 1 to form a diradical intermediate which abstracts
hydrogen atoms from the reaction medium.
(4) Ruiz-Morales, Y. J. Phys. Chem. A 2002, 106, 11283–11308.
(5) (a) Knezˇevic´, A.; Maksic´, Z. B. New J. Chem. 2006, 30, 215–222.
(b) Nakano, M.; Kishi, R.; Takebe, A.; Nate, M.; Takahashi, H.; Kubo, T.;
Kamada, K.; Ohta, K.; Champagne, B.; Botek, E. Comp. Lett. 2007, 3,
333–338.
(6) For examples, see: (a) Sotoyama, W.; Sato, H.; Matuura, A. PCT
Int. Appl. WO 03/002687, A1, 2003. (b) Moon, J. M. KR 2007101430, A,
2007.
(2) Clar, E.; Lang, K. F.; Schulz-Kiesow, H. Chem. Ber. 1955, 88, 1520–
1527.
10.1021/ol9015942 CCC: $40.75
Published on Web 08/12/2009
 2009 American Chemical Society

pentacene7 because of the still low accessibility and high
sensitivity in the presence of oxygen particularly in dilute
solution. In this respect, attachment of substituents at the
most sensitive 7,14-position of 2a possessing the largest
HOMO coefficients would substantially enhance its kinetic
stability as in the case of large acenes.7a In this connection,
and in view of the interest inherent in the hitherto unknown
dehydroannulene 1 itself, we report here the first synthesis
and structural characterization of 1 and its transformation
into stable 7,14-disubstituted zethrene derivatives 2b and 2c
based on an electrophile-induced transannular cyclization of
1.
8-iodonaphthalene (5a),1b,c under standard Sonogashira-
Hagihara conditions at room temperature. Although a trace
1
amount of 1 was detected in the H NMR spectra of the
products, the major products were unidentified oligomeric
products derived from random coupling and the results lacked
reproducibility too. Next, we adopted cross-coupling ac-
companying in situ desilylation.9 The optimization results
are summarized in Table 1. After several trials, the best result
was obtained when the coupling reaction of 3 and 4b was
undertaken in the presence of 1 equiv of aqueous NaOH,
furnishing 1 in 22% yield together with monoiodozethrene
2d1a (4%) (entry 5). In the absence of NaOH, the reaction
terminated at the stage of single coupling product 61a (entry
4). To the contrary, desilylation-coupling reaction of iodo-
ethynyl derivative 5b under similar conditions did not give
the desired product 1, resulting in recovery of the starting
material (entries 1 and 2).10 However, the use of powerful
desilylation reagent (TBAF) was not useful (entries 3 and
6). It is worth noting that 1 is easily handled without any
visible decomposition at room temperature, in contrast to
the structurally resembled compounds such as
tetradehydro[10]annulene11
and
dinaphtho-8
and
diacenaphthooctadehydro[14]annulenes.12 The aromatic pro-
tons of 1 resonate at 7.80 (dd), 7.71 (dd), and 7.45 (dd) ppm,
indicating that 1 does not exhibit 10π aromaticity.13 In accord
with this observation, the NICS value (+1.45) at the center
of the 10π system of 1 suggests its nonaromatic character.14
Compound 1 exhibits strong fluorescence at 422 and 448
nm with a quantum yield of 0.91 as shown in Figure 1 and
Table S1 (Supporting Information).
Table 1. In-situ Desilylation and Pd(0)/Cu(I)-catalyzed Coupling
Reactions of 5b or 3 and 4ba
An X-ray crystallographic structure analysis of 1 (Figure
2) showed that the bond lengths and bond angles of its
[10]annulene framework are in good agreement with the
starting
entry material(s)
calculated values.14 As expected from the H NMR study,
1
additive
H2Ob
products (yieldf)
no reactiong
the [10]annulene framework of 1 clearly exhibits bond length
alternation (Table S2, Supporting Information). The acetylene
units are almost linear with bending angles of less than 5°
and the π-conjugated backbone is distinctly planar. The
crystal packing structure revealed that π-π stacking interac-
tions of the two naphthalene units lead to the formation of
a dimeric unit, which contacts with two neighboring dimeric
units by π-π stacking and CH/π interactions, respectively,
furnishing an alignment classified as sandwich-herringbone.15
1
2
3
4
5
6
5b
5b
5b
3 and 4b
3 and 4b
3 and 4b
NaOH/H2Oc no reactiong
TBAFd
H2Ob
2d (6%)
1 (6%), 2d (trace), 6 (33%)
NaOH/H2Oc 1 (22%), 2d (4%)
TBAFe
2a (<3%)
a General reaction conditions: A solution of starting material(s) (0.23
mmol (each), 1 equiv), Pd(PPh3)4 (0.2 equiv), CuI (0.2 equiv), DBU (2
equiv), and additive in benzene (ca. 8 mL) was stirred at rt for 4-8 h. b
A
few drops. c NaOH (1 equiv)/H2O (0.1 mL). d One equivalent of a solution
of TBAF in THF. e Two equivalents of a solution of TBAF in THF. f Isolated
yield. g Most of starting material 5b was recovered.
(9) In-situ desilylation and Pd(0)/Cu(I)-catalyzed coupling methods were
reported previously: (a) Mio, M. J.; Kopel, L. C.; Braun, J. B.; Gadzikwa,
T. L.; Hull, K. L.; Brisbois, R. G.; Markworth, C. J.; Grieco, P. A. Org.
Lett. 2002, 4, 3199–3202. (b) Wan, W. B.; Kimball, D. B.; Haley, M. M.
Tetrahedron Lett. 1998, 39, 6795–6798.
For the synthesis of 1, we planned to use the Sonogashira-
Hagihara reaction that can be performed at ambient temper-
ature to form the C(sp)-C(sp2) bonds of 1. First, we examined
the reactions of terminal acetylene derivatives with iodides,
that is, coupling of 1,8-diiodonaphthalene (3) with 1,8-
diethynylnaphthalene (4a)1c,8 and self-coupling of 1-ethynyl-
(10) We do not understand the reason for the innertness of 5b under
the basic conditions.
(11) Myers, A. G.; Finney, N. S. J. Am. Chem. Soc. 1992, 114, 10986–
10987.
(12) Palmer, G. J.; Parkin, S. R.; Anthony, J. E. Angew. Chem., Int. Ed.
2001, 40, 2509–2512.
(13) For example, the aromatic protons of 1,8-diethynylnaphthalene (4a)
resonate at 7.85-7.80 (m, 4H) and 7.42 (dd, 2H) ppm (300 MHz, CDCl3).
(14) The structure optimization was carried out by DFT method with
the B3LYP/6-31G(d) basis-set and the NICS value was calculated by GIAO-
HF/6-31G(d) using Gaussian 03.
(7) For recent reviews, see: (a) Anthony, J. E. Angew. Chem., Int. Ed.
2008, 47, 452–483. (b) Ruiz, R.; Choudhary, D.; Nickel, B.; Toccoli, T.;
Chang, K.-C.; Mayer, A. C.; Clancy, P.; Blakely, J. M.; Headrick, R. L.;
Iannotta, S.; Malliaras, G. G. Chem. Mater. 2004, 16, 4497–4508. (c) Katz,
H. E. Chem. Mater. 2004, 16, 4748–4756.
(15) (a) Desiraju, G. R.; Gavezzotti, A. J. Chem. Soc., Chem. Commun.
1989, 621–623. (b) Gavezzotti, A.; Desiraju, G. R. Acta Crystallogr., Sect.
B 1988, 44, 427–434.
(8) Mitchell, R. H.; Sondheimer, F. Tetrahedron 1968, 24, 1397–1405
.
Org. Lett., Vol. 11, No. 18, 2009
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ferrocene/ferrocenium (Fc/Fc+), respectively. In addition,
irreversible second oxidation and reduction waves were
observed at oxE2 ) 0.79 V and redE2 ) -2.03 V vs Fc/Fc+,
respectively. The first oxidation and reduction potentials of
2c are comparable to those of pentacene17 and its bis(triiso-
propylsilyl)ethynyl derivative,18 suggesting that 2c may serve
as a good organic semiconductor.
Figure 1. UV-vis (blue line) and FL (orange line) spectra of 1
and UV-vis (purple line) and FL (red line) spectra of 2c in CH2Cl2
at 25 °C. The FL intensities are normallized to the corresponding
lowest energy absorption bands.
Figure 3. Cyclic voltammogram of 2c (1.0 mM, V versus (Ag/
Ag+) in 0.1 M with nBu4NClO4 in CH2Cl2, scan rate: 100 mV/s,
working electrode Pt, Fc/Fc+ ) 0 V).
In conclusion, the first synthesis of tetradehydrodinaph-
tho[10]annulene (1) was achieved by in situ desilylation and
a cross-coupling reaction. Annulene 1 was transformed
smoothly into stable zethrene derivatives 2b and 2c having
substitutes at the 7,14-positions based on transannular
cyclization of the proximate triple bonds. Thus, 1 turned out
to serve as a good reservoir for 7,14-disubstituted zethrene
derivatives. Preparation of other zethrene derivatives and
investigation of their physical properties are currently un-
derway.
Figure 2. ORTEP drawing (left) and crystal packing (right) of 1.
Treatment of a solution of 1 in CHCl3 with I2 at room
temperature afforded 2b in 65% isolated yield as a sole
product. With the key intermediate 2b for functionalization
at the 7,14-positions of the zethrene framework in hand, we
undertook cross-coupling reaction with an acetylene deriva-
tive. Thus, reaction of 2b with phenylacetylene gave 7,14-
bis(phenylethynyl)zethrene (2c) in 65% yield. The zethrene
derivatives 2b and 2c display significantly enhanced stability
than extremely sensitive 2a.16 UV-vis absorption maxima
(CH2Cl2) of 2c are observed at 576 (31600) and 537 (22900)
nm and its fluorescence emission at 610 nm with a quantum
yield of 0.07 (Figure 1 and Table S1, Supporting Informa-
tion). To evaluate the electrochemical properties of 2c, cyclic
voltammetry measurement was undertaken (Figure 3). As
shown in Figure 3, 2c showed reversible first oxidation and
reduction waves at oxE1 ) 0.29 and redE1 ) -1.64 V vs
Acknowledgment. We thank Dr. I. Hisaki (Graduate
School of Engineering, Osaka University) for helpful discus-
sion about X-ray crystallography. This work was supported
by a Grant-in-Aid for Scientific Research from the Ministry
of Education, Culture, Sports, Science and Technology,
Japan.
Supporting Information Available: Experimental details,
spectroscopic data; X-ray crystallographic data in CIF format.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OL9015942
(17) oxE ) 0.3 V, redE ) -1.87 V, vs Fc/Fc+ in C6H4Cl2: Sakamoto,
Y.; Suzuki, T.; Kobayashi, M.; Gao, Y.; Fukai, Y.; Inoue, Y.; Sato, F.;
Tokito, S J. Am. Chem. Soc. 2004, 126, 8138–8140.
(16) Neither dilute solutions of 2b and 2c were sensitive to light and
oxygen. When heated, solid samples of 2b and 2c started to decompose
from 120 and 220 °C, respectively, and did not show melting points.
(18) oxE1 ) 0.38 V, redE1 ) -1.72 V, redE2 ) -2.23 V, vs Fc/Fc+ in
THF: Swartz, C. R.; Parkin, S. R.; Bullock, J. E.; Anthony, J. E.; Mayer,
A. C.; Malliaras, G. G. Org. Lett. 2005, 7, 3163–3166.
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