Z-tribenzo[c,g,k]-1,2,5,6-tetradehydro[12]annulene, a concave π-electron system

Article abstract of DOI:10.1246/cl.2000.860

Synthesis of Z-tribenzo[c,g,k]-1,2,5,6-tetradedydro[12]-annulene 1 has been carried out in a good total yield. The Bergman reaction of the closely situated acetylene bonds in the endiyne structure of 1 and the reaction of 1 with AuCl produced the corresponding cyclization products.

Full text of DOI:10.1246/cl.2000.860

860
Chemistry Letters 2000
Z-Tribenzo[c,g,k]-1,2,5,6-tetradehydro[12]annulene, a Concave π-Electron System
Masahiko Iyoda,* Kazuyuki Fuchigami, Ayako Kusaka, Tadahiro Yoshida, Masato Yoshida, Haruo Matsuyama,
and Yoshiyuki Kuwatani
Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397
(Received May 8, 2000; CL-000438)
Synthesis of Z-tribenzo[c,g,k]-1,2,5,6-tetradedydro[12]-
from VCl3(THF)3 and Zn in CH2Cl2–DMF at room temperature
produced selectively the erythro-5 (59%) together with a small
amount of the threo-isomer (3.4%). The reaction of 5 with
TCDI (1,1'-thiocarbonyldiimidazole) in refluxing toluene for 27
h afforded the thionocarbonate 6 (80%), which, on treatment
with DMPD (1,3-dimethyl-2-phenyl-1,3,2-diazaphospholidine)7
in refluxing benzene for 14 h, produced the desired [12]annu-
lene 1 in 77% yield.
annulene 1 has been carried out in a good total yield. The
Bergman reaction of the closely situated acetylene bonds in the
endiyne structure of 1 and the reaction of 1 with AuCl produced
the corresponding cyclization products.
Concave and bowl-shaped π-conjugated hydrocarbons
attract current interest, because of host/guest interactions,1 self-
assembly,2 formation of metal complexes,3 and biological
activities in some cases.4 In order to reduce the molecular
strain, Z-tribenzo[c,g,k]-1,2,5,6-tetradedydro[12]annulene 1
possesses a concave π-framework, and hence the two acetylene
linkages are located so close together that their electron clouds
begin to overlap. Therefore, 1 can be expected to show inter-
esting chemical behavior. We now report the synthesis of 1
and the reactivities of its acetylenic bonds.
The synthesis of 1 was carried out according to the reac-
tion sequence outlined in Scheme 1. The Sonogashira coupling
of o-diiodobenzene 3 with 2 (2 equiv) in refluxing Et3N for 1 h
gave the dialdehyde 4 (81%).5 The intramolecular pinacol cou-
pling of 4 with a low valent vanadium complex6,7 generated
Although the [12]annulene 1 was expected to hold a fairly
large strain energy, 1 proved to be a thermally stable com-
pound. Recrystallization of 1 from CH2Cl2–isopropyl ether
gave single crystals, and the crystal structure has been deter-
mined by the X-ray diffraction method.8 The crystal lattice
contains two crystallographically independent molecules,
which are found to have essentially the same structure. As
shown in Fig. 2, 1 has an approximate Cs symmetry, and the Z-
double bond in 1 rises up from the molecular plane to form a
cage structure. Interestingly, the intramolecular Csp···Csp dis-
tances of C2···C5 (2.77 Å) and C1···C6 (3.57 Å) are definitely
shorter than those (2.85 and 4.05 Å) of tribenzohexadehy-
dro[12]annulene 79 and those (2.87 and 4.11 Å) of 1,2-
diethynylbenzene 8,9 respectively (Figure 3). It is worth noting
that the averaged distance between the Z-olefinic and acetylenic
carbons is 2.88 Å which is 15% shorter than the sum of van der
Waals radii, and the C–C bond formation can be expected for
the olefinic (C10 and C9) and acetylenic (C1 and C6) carbons.
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
861
(C1 and C6) carbons.13 Interestingly, a solution of 14 in CHCl3
shows an intense deep blue color corresponding to the electron-
ic absorption of λmax 570 nm.
Financial support for this study was provided by a Grant-in-
Aid (06224223) for Scientific Research on Priority Areas from
the Ministry of Education, Science, Sports and Culture, Japan.
References and Notes
Recently, thermal and photochemical Bergman reactions
have been investigated extensively.4,10 Since 1 has closely situ-
ated acetylenic bonds in the endiyne structure, a ready Bergman
cyclization can be expected. Therefore, we attempted thermal
and photochemical Bergman reactions (Scheme 2). The irradi-
ation of 1 under a high-pressure mercury lamp in benzene at
room temperature produced 9 as the sole product in 93% yield,
and 9 was stable under photolysis conditions.11 In contrast, the
reaction of 1 in o-dichlorobenzene in the presence of 1,4-cyclo-
hexadiene (50 equiv) at 250 °C for 96 h afforded the desired
product 11 in 52% yield, together with 4% of 9, and 43% of 1
was recovered. The low reactivity of 1 for the Bergman
cyclization may be due to the difficulty to form the strained
diradical intermediate 10.
1
J. Gross, G. Harder, A. Siepen, J. Harren, F. Vögtle, H. Stephan,
K. Gloe, B. Ahlers, K. Cammann, and K. Rissanen, Chem. Eur.
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Commun., 1999, 1859, and references cited therein.
T. Nishinaga, T. Kawamura, and K. Komatsu, Chem. Commun.,
1998, 2263, and references cited therein.
Reviews: K. C. Nicolaou and W.-M. Dai, Angew. Chem., Int.
Ed. Engl., 30, 1387 (1991); M. E. Maier, Synlett, 1995, 13; H.
Lhermitte and D. Grierson, Contemp. Org. Synth., 3, 93 (1996);
J. W. Grissom, G. U. Gunawardena, D. Klingberg, and D.
Huang, Tetrahedron, 52, 6453 (1996).
All new compounds gave satisfactory analytical and spectral
data. 1: colorless prisms, mp 159.5–163 °C (decomp.); EI-MS
m/z 302 (M+); 1H NMR (CDCl3) δ 6.90 (s, 2H), 7.13 (t, J = 7.3
Hz, 2H), 7.18–7.26 (m, 4H), 7.31–7.32 (m, 2H), 7.39 (m, 2H),
7.48–7.50 (m, 2H); 13C NMR (CDCl3) δ 93.3, 94.1, 122.2,
126.7, 128.0, 128.1, 129.1, 129.7, 130.5, 132.4, 140.9. 11: col-
2
3
4
5
orless cryst., mp 147–149 °C, EI-MS m/z 304 (M+); H NMR
1
(CDCl3) δ 6.77 (s, 2H), 7.11 (m, 2H), 7.24–7.29 (m, 6H), 7.49
(m, 2H), 7.63 (s, 2H), 7.86 (m, 2H); 13C NMR (CDCl3) δ 126.2,
127.0, 127.1, 127.4, 127.7, 128.6, 130.1, 132.5, 132.6, 137.3,
141.0, 141.5. 12: orange needles, mp 233.5–236 °C; EI-MS m/z
1
318 (M+); H NMR (CDCl3) δ 4.25 (s, 2H), 7.31 (m, 1H), 7.40
(m, 1H), 7.45–7.68 (m, 6H), 7.91 (d, J = 8.5, 1H), 8.14 (d, J =
7.5, 1H), 8.33 (d, J = 7.5, 1H), 9.13 (d, J = 8.5, 1H). 14: dark
1
blue prisms, mp 333–334.5 °C; FAB-MS m/z 605 (M+1)+; H
NMR (CDCl3) δ 1.96 (d, J = 22.0, 2H), 3.52 (d, J = 22.0, 2H),
6.88–6.91 (m, 4H), 7.23–7.27 (m, 12H), 7.37–7.43 (m, 4H),
8.75–8.77 (m, 2H), 8.45–8.46 (m, 2H); 13C NMR (CDCl3) δ
35.1, 121.6, 122.7, 124.1, 124.3, 124.4, 124.5, 124.7, 125.7,
126.1, 126.5, 128.3, 129.1, 132.4, 132.8, 140.7 (two), 141.0,
142.2, 143.6, 144.0, 144.2, 145.4, 145.7; UV–vis (CH2Cl2) λmax
(log ε) 370 (2.84), 570 nm (3.01).
6
7
8
J. H. Freudenberger, A. W. Konradi, and S. F. Pedersen, J. Am.
Chem. Soc., 111, 8014 (1989).
In order to examine the formation of metal complexes, we
attempted the synthesis of gold(I), silver(I), and copper(I) com-
plexes. Although no complex formation of 1 with AgOTf and
CuOTf was observed in solutions, the reaction of 1 with AuCl12
in CHCl3 proceeded smoothly to form the corresponding
cyclization products 12, 13, and 14 in 35, 25, and 14% yields,
respectively (Scheme 3). The formation of 12, 13, and 14 indi-
cates the reaction of the olefinic (C10 and C9) and acetylenic
Y. Kuwatani, T. Yoshida, A. Kusaka, and M. Iyoda,
Tetrahedron Lett., 41, 359 (2000).
Crystal data. 1: C24H14, M = 302.37, monoclinic, space group
P21/n (#14), a = 12.402(6) Å, b = 11.071(9) Å, c = 24.171(5) Å,
β = 97.98(2)°, V = 3286(2) Å3, T = 296 K, Z = 8, dcalcd = 1.222
g cm–3, R = 0.0377 and Rw = 0.0349 for 546 observed reflec-
tions out of 3852 unique reflections.
9
The intramolecular C···C distances in 7 and 8 are estimated
based on the MOPAC AM1 calculations of 7 and 8.
10 C.-S. Kim and K. C. Russell, Tetrahedron Lett., 40, 3835
(1999); T. Kaneko, M. Takahashi, and M. Hirama, Angew.
Chem., Int. Ed. Engl., 38, 1267 (1999); Tetrahedron Lett., 40,
2015 (1999).
11 Although 1 and 9 show similar electronic spectra, the ring strain
in 1 causes preferentially its photochemical isomerization to the
less-strained 9.
12 G. Brauer, "Handbook of Preparative Inorganic Chemistry," 2nd
ed., Academic Press, New York (1965), Vol. 2, p. 1055.
13 Reductive cyclization of tribenzo[c,g,k]-1,2,5,6,9,10-hexadehy-
dro[12]annulene was reported to produce indenofluorene deriv-
atives: W. J. Youngs, A. Djebli, and C. A. Tessier,
Organometallics, 10, 2089 (1991); D. Malaba, A. Djebli, L.
Chen, E. A. Zarate, C. A. Tessier, and W. J. Youngs,
Organometallics, 12, 1266 (1993).