Generation and characterization of highly strained dibenzotetrakisdehydro[12]- and dibenzopentakisdehydro[14]annulenes

Article abstract of DOI:10.1021/jo047857p

(Chemical Equation Presented) To generate dibenzotetrakisdehydro[12]- and dibenzopentakisdehydro[14]annulenes ([12]- and [14]-DBAs) having a highly deformed triyne moiety, [4.3.2]propellatriene-anneleted dehydro[12]- and dehydro[14]annulenes were prepared

Full text of DOI:10.1021/jo047857p

Generation and Characterization of Highly Strained
Dibenzotetrakisdehydro[12]- and
Dibenzopentakisdehydro[14]annulenes
Ichiro Hisaki,† Takeshi Eda,† Motohiro Sonoda,† Hiroyuki Niino,‡ Tadatake Sato,‡
Tomonari Wakabayashi,§ and Yoshito Tobe*,†
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, Photonics
Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba,
Ibaraki 305-8565, Japan, and Department of Chemistry, School of Science and Engineering, Kinki
University, Higashi-osaka, Osaka 577-8502, Japan
tobe@chem.es.osaka-u.ac.jp
Received December 3, 2004
To generate dibenzotetrakisdehydro[12]- and dibenzopentakisdehydro[14]annulenes ([12]- and [14]-
DBAs) having a highly deformed triyne moiety, [4.3.2]propellatriene-anneleted dehydro[12]- and
dehydro[14]annulenes were prepared as their precursors. UV irradiation of the precursors resulted
in the photochemical [2 + 2] cycloreversion to generate the strained [12]- and [14]DBAs, respectively.
1
The [12]DBA was not detected by H NMR spectroscopy, but it was intercepted as Diels-Alder
adducts in solution, suggesting its intermediacy. Its spectroscopic characterization was successfully
carried out by UV-vis spectroscopy in a 2-methyltetrahydrofuran (MTHF) glass matrix at 77 K
and by FT-IR spectroscopy in an argon matrix at 20 K. On the other hand, the [14]DBA was stable
enough for observation by 1H and 13C NMR spectra in solution, though it was not isolated because
of the low efficiency of the cycloreversion. The [14]DBA was also characterized by interception as
Diels-Alder adducts in solution and by UV-vis spectroscopy in a MTHF glass matrix at 77 K.
The kinetic stabilities of the DBAs are compared with the related dehydrobenzoannulenes with
respect to the topology of the π-systems. In addition, the tropicity of the [14]DBA is discussed based
1
on its experimental and theoretical H NMR chemical shifts.
Introduction
rich molecules,3 in view of the following aspects. First,
DBAs are potential materials for optoelectronic applica-
tions such as conducting and nonlinear optical (NLO)
materials. For example, tribenzohexakisdehydro[18]-
annulenes ([18]DBAs) with electron-donating and -ac-
cepting substituents are shown to possess considerable
hyperpolarizabilities (â) for second-order NLO applica-
Dehydroannulenes and dehydrobenzoannulenes (DBAs)
are the molecules that have been studied both experi-
mentally and theoretically since the 1960s in connection
with aromaticity-antiaromaticity of cyclic π-electron
systems.1 Recently, renewed interests on these molecules
brought about the renaissance of the DBA chemistry,2
in conjunction with the rapidly growing field of carbon-
(2) (a) Marsden, J. A.; Palmer, G. J.; Haley, M. M. Eur. J. Org. Chem.
2003, 2355-2369. (b) Tobe, Y.; Sonoda, M. In Modern Cyclophane
Chemistry; Gleiter, R., Hopf, H., Eds.; Wiley-VCH: Weinheim, Ger-
many, 2004; pp 1-40.
(3) (a) Diederich, F.; Rubin, Y. Angew. Chem., Int. Ed. Engl. 1992,
31, 1101-1123. (b) Bunz, U. H. F.; Rubin, Y.; Tobe, Y. Chem. Soc. Rev.
1999, 28, 107-119. (c) de Meijere, A., Ed. Carbon Rich Compounds I.
Top. Curr. Chem. 1998, 196. (d) de Meijere, A., Ed. Carbon Rich
Compounds II. Top. Curr. Chem. 1999, 201.
† Osaka University and Japan Science and Technology Agency (JST.
‡ National Institute of Advanced Industrial Science and Technology
(AIST).
§ Kinki University.
(1) (a) Sondheimer, F. Acc. Chem. Res. 1972, 5, 81-91. (b) Sondhe-
imer, F. Chimia 1974, 28, 163-172. (c) Nakagawa, M. Pure Appl.
Chem. 1975, 44, 885-924.
10.1021/jo047857p CCC: $30.25 © 2005 American Chemical Society
Published on Web 02/08/2005
J. Org. Chem. 2005, 70, 1853-1864
1853

Hisaki et al.
tions.4 Ladder oligomers of tribenzotrisdehydro[12]-
annulene ([12]DBA) are predicted to exhibit increasing
third-order NLO properties with increasing number of
the [12]DBA units on the basis of the semiempirical
molecular orbital calculations.5 Second, certain members
of DBAs are hypothetical constituent units of the hitherto
unknown two-dimensional carbon networks3,6 (e.g., gra-
phyne or graphdiyne). In this respect, a number of
topologically unique, highly extended π-systems consist-
ing of [18]- and [12]DBAs has been reported.2,7,8 Third,
DBAs would serve as precursors of novel forms of all-
carbon and carbon-rich materials. Thus, onion- and tube-
like closed shell carbon clusters were formed by explosive
decomposition of twisted [20]DBA9 or organometallic
derivatives of [18]- and [20]DBAs.10 Moreover, a regular
polymer was formed by topochemical polymerization of
a [14]DBA containing strained triple bonds.11 In addition
to these materials-oriented interests, owing to the recent
advances in theoretical as well as experimental assess-
ment of tropicity, i.e., induced ring currents, many DBAs
were prepared and their tropicity was examined. These
include the theoretical study of Vollhardt,12 Sundholm,13
and Elguero14 on various DBAs on the basis of nucleus-
independent chemical shifts (NICS),15 the theoretical and
experimental studies on the DBAs fused by a cyclobuta-
diene or cyclopentadienide ring by Bunz16 and on the [14]-
DBAs fused by benzene rings17 or a dimethyldihydropy-
rene ring,18 the unit developed by Mitchell as a probe to
estimate the aromaticity of fused rings,19 by Haley and
Williams.
From these points of view, we became interested in the
title compounds, dibenzotetrakisdehydro[12]- and di-
benzopentakisdehydro[14]annulenes ([12]- and [14]DBAs)
1a and 1b having a highly strained triyne component.
These molecules are expected to give information regard-
ing aromaticity of highly distorted π-systems. In particu-
lar, extremely strained [12]DBA 1a possessing a remark-
ably deformed triyne unit would provide information
about the stability and reactivity of the elusive all-carbon
cyclic polyynes called cyclocarbons.20-22 Additionally, such
highly reactive species are also expected to transform into
carbon clusters by (explosive) decomposition or extended
propeller-shaped π-systems, tris(dehydrobenzo[12]an-
nulene) 2a and tris(dehydrobenzo[14]annulene) 2b, by
[2 + 2 + 2] cyclotrimerization, since such remarkable
reactions have been known.23
(4) (a) Sarkar, A.; Pak, J. J.; Rayfield, G. W.; Haley, M. M. J. Mater.
Chem. 2001, 11, 2943-2945.
(5) Zhou, Y.; Feng, S. Solid State Commun. 2002, 122, 307-310.
(6) Baughman, R. H.; Eckhardt, H.; Kertesz, M. J. Chem. Phys.
1987, 87, 6687-6699.
(7) For [18]DBA systems, see, for example: (a) Haley, M. M.; Brand,
S. C.; Pak, J. J. Angew. Chem., Int. Ed. Engl. 1997, 36, 836-838. (b)
Wan, W. B.; Brand, S. C.; Pak, J. J.; Haley, M. M. Chem. Eur. J. 2000,
6, 2044-2052.
(8) For [12]DBA systems, see: (a) Kehoe, J. M.; Kiley, J. H.; English,
J. J.; Johnson, C. A.; Petersen, R. C.; Haley, M. M. Org. Lett. 2000, 2,
969-972. (b) Miljanic´, O. Sˇ.; Vollhardt, K. P. C.; Whitener, G. D. Synlett
2002, 29-34. (c) Iyoda, M.; Sirinintasak, S.; Nishiyama, Y.; Vorasingha,
A.; Sultana, F.; Nakao, K.; Kuwatani, Y.; Matsuyama, H.; Yoshida,
M.; Miyake, Y. Synthesis 2004, 1527-1531. (d) Sonoda, M.; Sakai, Y.;
Yoshimura, T.; Tobe, Y.; Kamada, K. Chem. Lett. 2004, 33, 972-973.
(9) Boese, R.; Matzger, A. J.; Vollhardt, K. P. C. J. Am. Chem. Soc.
1997, 119, 2052-2053.
We planned to generate 1a and 1b from the respective
precursors 3a and 3b, possessing a [4.3.2]propellatriene
unit as a leaving group, by photochemical [2 + 2]
cycloreversion of their cyclobutene rings extruding indan
as shown in Scheme 1. We have already reported that
various highly reactive polyynes were generated success-
(10) (a) Dosa, P. I.; Erben, C.; Iyer, V. S.; Vollhardt, K. P. C.; Wasser,
I. M. J. Am. Chem. Soc. 1999, 121, 10430-10431. (b) Laskoski, M.;
Steffen, W.; Morton, J. G. M.; Smith, M. D.; Bunz, U. H. F. J. Am.
Chem. Soc. 2002, 124, 13814-13818.
(11) Baldwin, K. P.; Matzger, A. J.; Scheiman, D. A.; Tessier, C. A.;
Vollhardt, K. P. C.; Youngs, W. J. Synlett 1995, 1215-1218.
(12) Matzger, A. J.; Vollhardt, K. P. C. Tetrahedron Lett. 1998, 39,
6791-6794.
(13) Juse´lius, J.; Sundholm, D. Phys. Chem. Chem. Phys. 2001, 3,
2433-2437.
(14) Alkorta, I.; Rozas, I.; Elguero, J. Tetrahedron 2001, 57, 6043-
6049.
(20) (a) Diederich, F. In Modern Acetylene Chemistry; Stang, P. J.,
Diederich, F., Eds.; VCH: Weinheim, 1995; pp 443-471. (b) Diederich,
F.; Gobbi, L. Top. Curr. Chem. 1999, 201, 43-79. (c) Diederich, F.;
Rubin, Y.; Knobler, C. B.; Whetten, R. L.; Schriver, K. E.; Houk, K.;
Li, Y. Science 1989, 245, 1088-1090. (d) Rubin, Y.; Kahr, M.; Knobler,
C. B.; Diederich, F.; Wilkins, C. L. J. Am. Chem. Soc. 1991, 113, 495-
500. (e) McElvany, S. W.; Ross, M. M.; Goroff, N. S.; Diederich, F.
Science 1993, 259, 1594-1596. (f) Diederich, F.; Rubin, Y.; Chapman,
O. L.; Goroff, N. S. Helv. Chim. Acta 1994, 77, 1441-1457.
(21) (a) Tobe, Y. In Advances in Strained and Interesting Organic
Molecules; Halton, B., Ed.; JAI Press: Stamford, 1999; Vol. 7, pp 153-
184. (b) Tobe, Y.; Fujii, T.; Matsumoto, H.; Naemura, K.; Achiba, Y.;
Wakabayashi, T. J. Am. Chem. Soc. 1996, 118, 2758-2759. (c) Tobe,
Y.; Matsumoto, H.; Naemura, K.; Achiba, Y.; Wakabayashi, T. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1800-1802. (d) Wakabayashi, T.;
Kohno, M.; Achiba, Y.; Shiromaru, H.; Momose, T.; Shida, T.; Naemura,
K.; Tobe, Y. J. Chem. Phys. 1997, 107, 4783-4787. (e) Tobe, Y.; Fujii,
T.; Matsumoto, H.; Tsumuraya, K.; Noguchi, D.; Nakagawa, N.;
Sonoda, M.; Naemura, K.; Achiba, Y.; Wakabayashi, T. J. Am. Chem.
Soc. 2000, 122, 1762-1775.
(15) Schleyer, P. v. R.; Maerker, C.; Dransfeld, A.; Jiao, H.; Hommes,
N. J. R. v. E. J. Am. Chem. Soc. 1996, 118, 6317-6318.
(16) (a) Laskoski, M.; Steffen, W.; Smith, M. D.; Bunz, U. H. F.
Chem. Commun. 2001, 691-692. (b) Laskoski, M.; Smith, M. D.;
Morton, J. G. M.; Bunz, U. H. F. J. Org. Chem. 2001, 66, 5174-5181.
(c) Boydston, A. J.; Laskoski, M.; Bunz, U. H. F.; Haley, M. M. Synlett
2002, 981-983.
(17) (a) Boydston, A. J.; Haley, M. M. Org. Lett. 2001, 3, 3599-3601.
(b) Boydston, A. J.; Haley, M. M.; Williams, R. V.; Armantrout, J. R.
J. Org. Chem. 2002, 67, 8812-8819.
(22) Tobe, Y.; Umeda, R.; Iwasa, N.; Sonoda, M. Chem. Eur. J. 2003,
9, 5549-5559.
(18) Kimball, D. B.; Haley, M. M.; Mitchell, R. H.; Ward, T. R.;
Bandyopadhyay, S.; Williams, R. V.; Armantrout, J. R. J. Org. Chem.
2002, 67, 8798-8811.
(23) For cyclotrimerization of highly deformed alkynes, see, for
example: (a) Chapman, O. L.; Gano, J.; West, P. R.; Regitz, M.; Maas,
G. J. Am. Chem. Soc. 1981, 103, 7033-7036. (b) Iglesias, B.; Pen˜a, D.;
Pe´rez, D.; Guitia´n, E.; Castedo, L. Synlett 2002, 486-488.
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1854 J. Org. Chem., Vol. 70, No. 5, 2005

Dibenzotetrakisdehydro[12]- and Dibenzopentakisdehydro[14]annulenes
SCHEME 1
SCHEME 2. Synthesis of Precursor 3aa
fully from the corresponding precursors possessing the
[4.3.2]propellatriene units by laser desorption in the gas
phase as well as by photoirradiation in solution.21,24 In
this paper, we report the syntheses of propellatriene-
annelated DBAs, 3a and 3b, generation of 1a and 1b by
the photochemical [2 + 2] cycloreversion of the respective
precursors 3a and 3b, and characterization of 1a and
1b.25 Characterization in solution was carried out by the
1H and 13C NMR spectra (only for 1b) and by their
interception as Diels-Alder adducts. Spectroscopic iden-
tification of 1a and 1b was done by the measurements
of the UV-vis spectra in a 2-methyltetrahydrofuran
(MTHF) glass matrix at 77 K and FT-IR (only for 1a) in
an argon matrix at 20 K in conjunction with their
theoretical predictions. The kinetic stability of 1a and
1b is compared with that of the related DBAs with
respect to the topology of the π-systems. In addition, the
tropicity of [14]DBA 1b is discussed based on its experi-
a Reaction conditions: (a) Pd(PPh3)4, CuI, Et3N, 60 °C, 3a, 1%;
(b) Pd(PPh3)4, CuI, PPh3, CH3N[(CH2)7CH3]3Cl, NaOH, H2O,
benzene, 80 °C, 3a, 49%.
SCHEME 3. Synthesis of Precursor 3ba
1
mental and theoretical H NMR chemical shifts.
Results and Discussion
Syntheses of Propellane-Annelated [12]- and [14]-
DBAs 3a and 3b. Propellane-anneleted [12]DBA 3a was
prepared by Pd-catalyzed 1:1 cross-coupling of dieth-
ynylpropellatriene 421c,e or its derivative 521c,e with bis-
(2-iodophenyl)acetylene (6)26 (Scheme 2). First, reaction
of 4 with 6 was attempted. To our dismay, the reaction
typically gave a complex mixture of products containing
3a in as low as 1% yield. As byproducts, 2:2 coupling
product 7 (2%) and 1:2 coupling product 8 (6%) were
characterized, but most of the products were uncharac-
terized polymeric materials. Gratifyingly, however, by in
situ deprotection and intermolecular cross-coupling reac-
tion27 of 5 and 6 under the phase-transfer conditions, 49%
yield of 3a was achieved. Synthesis of the precursor 3b
was accomplished by intramolecular oxidative coupling
of 9 as shown in Scheme 3. Thus, dichloropropellatriene
1021c,e was cross-coupled to 2-ethynyl-1-(triisopropylsilyl)-
a Reaction conditions: (a) Pd2(dba)3‚CHCl3, CuI, piperidine/THF
(5:1 v/v), 60 °C, 41%; (b) TBAF, AcOH, THF, rt; (c) Cu(OAc)2,
pyridine, rt, 76% for the two steps.
ethynylbenzene (11)28 to give acyclic tetrayne 12 in 41%
yield. Desilylation of 12 followed by Cu(II)-mediated
oxidative coupling under high dilution conditions gave
3b in 76% yield.
UV-vis spectra of the precursors 3a and 3b are shown
in Figure 1. Both spectra exhibit similar profile in the
wavelength region shorter than 400 nm, with the spec-
trum of 3b being red-shifted by 20 nm compared to that
of 3a. However, the end absorption of 3a extends con-
siderably to the longer wavelength than that of 3b,
reflecting the antiaromatic character of 3a.
Geometries of Precursors and Highly Strained
Dehydroannulenes. To investigate the geometries of
the precursors 3a and 3b and respective strained DBAs
1a and 1b, their optimized geometries were calculated
by the DFT method at the B3LYP/6-31G* level as shown
(24) (a) Tobe, Y.; Nakagawa, N.; Naemura, K.; Wakabayashi, T.;
Shida, T.; Achiba, Y. J. Am. Chem. Soc. 1998, 120, 4544-4545. (b)
Tobe, Y.; Nakanishi, H.; Sonoda, M.; Wakabayashi, T.; Achiba, Y.
Chem. Commun. 1999, 1625-1626. (c) Tobe, Y.; Nakagawa, N.; Kishi,
J.; Sonoda, M.; Naemura, K.; Wakabayashi, T.; Shida, T.; Achiba, Y.
Tetrahedron 2001, 57, 3629-3636. (d) Tobe, Y.; Furukawa, R.; Sonoda,
M.; Wakabayashi, T. Angew. Chem., Int. Ed. 2001, 40, 4072-4074.
(25) For preliminary reports of this work, see: (a) Tobe, Y.; Ohki,
I.; Sonoda, M.; Niino, H.; Sato, T.; Wakabayashi, T. J. Am. Chem. Soc.
2003, 125, 5614-5615. (b) Hisaki, I.; Eda, T.; Sonoda, M.; Tobe, Y.
Chem. Lett. 2004, 33, 620-621.
(26) Kowalik, J.; Tolbert, L. M. J. Org. Chem. 2001, 66, 3229-3231.
(27) (a) Huynh, C.; Linstrumelle, G. Tetrahedron 1988, 44, 6337-
6344. For the use of tricaprylmethylammonium salt in this reaction,
see: (b) Ohkita, M.; Ando, K.; Suzuki, T.; Tsuji, T. J. Org. Chem. 2000,
65, 4385-4390.
(28) Bell, M. L.; Chiechi, R. C.; Johnson, C. A.; Kimball, D. B.;
Matzger, A. J.; Wan, W. B.; Weakley, T. J. R.; Haley, M. M. Tetrahedron
2001, 57, 3507-3520.
J. Org. Chem, Vol. 70, No. 5, 2005 1855

Hisaki et al.
transition state between the two unsymmetrical geom-
etries possesses C2v symmetrical geometry. However, the
energy differences between the ground and transition
states are small; ca. 2.2 cal/mol for 1a and ca. 38 cal/mol
for 1b. The most remarkable geometrical characteristic
of 1a is the fact that the CtC-C bonds in the triyne
component of 1a are highly deformed from linearity by
32.9-15.0° for the ground state and by 31.0-15.9° for
the transition state. In the ground state, bond angle of
the most strained central triyne unit is predicted to be
as small as 147.1°! By contrast, the C2 bridge of 1a is
predicted to be slightly deformed to the inside of the
annulene ring by 7.2-7.6°, making both the C2 and C6
bridges curve to the same direction. On the other hand,
the triyne unit of 1b is not as strained as that of 1a, but
it is still considerably deformed; the bending angles are
22.4-15.6° for the ground state and 19.0-12.8° for the
transition state. The diyne unit of 1b is much less
distorted with the bending angles of 3.5-5.2° (ground
state) and 3.9-4.3° (transition state). With regard to the
bond lengths, there is larger bond length alternation in
the 12-membered rings of [12]DBAs 1a and 3a in
comparison with that of the 14-membered rings of the
respective [14]DBAs 1b and 3b, owing to their nonaro-
matic and aromatic characters, respectively. On the
contrary, the bond alternation of the benzene rings of 1a
and 3a are smaller than those of the respective [14]-
FIGURE 1. UV-vis spectra of precursor 3a (red) and 3b
(green) in CHCl3 at 303 K. Expanded spectra are shifted
vertically for clarity.
in Figure 2. The triple bonds of 3a attached the cy-
clobutene ring are slightly distorted to outward, while
the corresponding bonds of 3b are nearly straight. In
contrast to the small bond angle distortion in the annu-
lene rings of the precursors 3a and 3b, DBAs 1a and 1b
exhibit noticeable distortions particularly in their triyne
moieties as shown in Figure 2a,b. While the energy-
minimum structures of 1a and 1b are not symmetrical
with respect to the plane bisecting the triyne unit, the
FIGURE 2. Optimized geometries of (a) 1a, (b) 1b, (c) 3a, and (d) 3b calculated by the DFT method at the B3LYP/6-31G* level.
Selected bond lengths (Å) and angles (deg) are shown in black for the ground-state structures and in red for the transition-state
structures having C2v symmetry. Hydrogen atoms are omitted for clarity.
1856 J. Org. Chem., Vol. 70, No. 5, 2005

Dibenzotetrakisdehydro[12]- and Dibenzopentakisdehydro[14]annulenes
SCHEME 4
annulenes 1b and 3b for the same reason. However, the
bond lengths of the benzene rings within the [12]DBA
derivatives 1a and 3a or within the [14]DBA derivatives
1b and 3b are similar to each other, suggesting that the
tropicity of the annulene rings within each series is not
much different.
To examine the bond length alternation of 3a and 3b
experimentally, their X-ray structural analysis was
undertaken. Recrystallization of 3a and 3b from CH2-
Cl2/hexane afforded single crystals with sufficient quality
for X-ray structural analysis. The structures are shown
in Figures S17 and S18, respectively, in the Supporting
Information. Both the 12- and 14-membered rings of 3a
and 3b are planer. Angles of the CtC-C bond in 3a
determined by X-ray structural analysis were slightly
smaller than those predicted by the DFT calculations (ca.
2.3-0.3°), while in the case of 3b, no constant tendency
was observed in this respect. With regard to the bond
lengths, the calculated structures seem to underestimate
the bond length alternation of the annulene rings of 3a
and 3b compared with the respective X-ray structures;
for example, the bond lengths of C1-C2, C2tC3, and
C3-C4 of 3b are 1.397, 1.219, and 1.424 Å, respectively,
in the theoretical geometries, while those are 1.411,
1.199, and 1.427 Å in the observed structures, respec-
tively. As observed in the theoretical structures 3a and
3b, larger bond length alternation in the 12-membered
ring of 3a was observed in comparison with that of the
14-membered ring of 3b in the X-ray structures, although
the degree of alternation is smaller than that in the
calculated geometries.
Photolysis of 3a and 3b in Solution. As a prelimi-
nary study of the photochemical [2 + 2] cycloreversion,
a solution of 3a in THF-d8 (2.1×10-2 M) was irradiated
at room temperature with a low-pressure mercury lamp
and the reaction was monitored by 1H NMR spectra.
Upon irradiation, the signals of 3a decreased, and
instead, the signals ascribed to indan appeared, indicat-
ing that [2 + 2] cycloreversion of 3a took place. However,
any signal ascribable to 1a was not observed. On the
other hand, the signals at 6.35-6.29 and 3.27-3.24 ppm
appeared, which we assigned to the vinyl and the
methine protons on the bridgeheads, respectively, of 13a
derived by [4 + 2] addition between 1a and 3a as shown
in Scheme 4 (see Figure S1 in Supporting Information
for the NMR spectrum.). We also observed a peak in the
LC-MS analysis of the photolysate at m/z 615.4 corre-
sponding to [13a + 1]+. By preparative scale photolysis
of 3a in THF, [4 + 2] adduct 13a was isolated in 18%
yield as a yellow solid. In addition, irradiation of 3a in
furan gave the furan adduct 14a in 20% yield as an
orange solid. X-ray crystallographic structures of 13a and
14a shown in Figures S19 and S20, respectively, in the
Supporting Information revealed that the propellane unit
of 3a was replaced by another molecule of 3a and furan,
respectively, indicating that the addition took place at
the central, most strained triple bond of the triyne unit
of 1a. These results indicate that the photolysis of 3a
leads to the generation of 1a, but it is too reactive for
characterization by spectroscopic methods in solution.
As shown in Figure S19 in the Supporting Information,
the adduct 13a possesses two [12]DBA units pointing to
the opposite directions. This indicates that the reactive
intermediate 1a added to the cyclohexadiene moiety of
3a from the same side of the cyclopentane ring. This
selectivity can be explained in terms of steric effect of
the propellane moiety of 3a.29 Namely, the dihedral angle
between the cyclohexadiene and cyclopentane rings (131°)
is wider than that between the cyclohexadiene and
cyclobutene rings (116°) as revealed by the X-ray analy-
sis.30
On the other hand, we were able to observe the 1H and
13C NMR signals due to 1b which was generated by
photolysis of the precursor 3b with a low-pressure
mercury lamp in a THF-d8 solution at 213-220 K. The
1H NMR spectrum of 3b in THF-d8 (1.1×10-2 M) and its
change upon irradiation for 24 h at 220 K are shown in
Figure 3. Irradiation of 3b brought about the appearance
of two new multiplets at 7.93-7.91 and 7.63-7.57 ppm,
with a relative integration of 1:3, in addition to those of
indan as shown in Figure 3b. These new signals are in
good agreement with the theoretical chemical shifts of
the aromatic protons in 1b calculated by the GIAO-
B3LYP/6-31G*//B3LYP/6-31G* calculations as described
later. The conversion of 3b to 1b, however, remained low
(ca. 19%) even after prolonged irradiation because of the
absorption of the incident light by the photoproducts 1b
and indan. Irradiation of a more dilute solution of 3b (1.3
× 10-3 M) in THF-d8 for 6 h at 213 K resulted in better
conversion (ca. 31%) (Figure 3, inset). However, further
irradiation of this solution did not push the reaction to
completion. Rather, the intensity of the signals of 1b
decreased presumably because of undesirable decomposi-
tion of 1b. By standing the solution of (b) for 65 h at 303
K, the signals assigned to 1b disappeared and two signals
at 6.47-6.45 and 4.29-4.27 ppm appeared albeit in low
intensities. These signals are ascribed to the vinyl
protons (Hg) and the bridgehead protons (Hh) of the
[4 + 2] adduct 13b, in view of the chemical shifts of the
corresponding protons of 13a mentioned above. This
[4 + 2] adduct 13b was also detected by LC-MS analysis
(29) Tsuji, T.; Ohkita, M.; Nishida, S. J. Org. Chem. 1991, 56, 997-
1003.
(30) The cyclohexadiene, cyclopentane, and cyclobutene rings of the
[4.3.2]propellatriene unit of 3a are defined by the least-squares planes
consist of the bridgehead carbon atoms and their adjacent carbon
atoms.
J. Org. Chem, Vol. 70, No. 5, 2005 1857

Hisaki et al.
FIGURE 3. 1H NMR spectral change of 3b upon photolysis in THF-d8 (1.1×10-2 M) (a) before irradiation, (b) after irradiation
for 24 h at 220 K, (c) after standing the solution of (b) for 65 h at 303 K. (Inset) spectrum of a more dilute solution of 3b (1.3×10-3
M) after irradiation for 6 h at 210 K.
(m/z 663.5) of the solution, though we were unable to
isolate it because of the low efficiency of its formation.
The [4 + 2] adduct 14b of 3b with furan was isolated by
irradiation of 3b in furan. However, unlike the case of
3a, a large amount of polymeric materials were formed
and isolated yield of 14b was very low (ca. 2%). In the
1H NMR spectrum of 14b, the vinyl protons and the
bridgehead protons resonate at 7.30 and 5.88 ppm,
respectively, which are downfield shifted relative to those
of 14a by 0.26 and 0.60 ppm, respectively. These down-
field shifts are attributed to the diamagnetic ring current
of the [14]annulene ring of 14b. The lower yields of [4 +
2] adduct 13b and 14b than those of 13a and 14a indicate
FIGURE 4. Partial 13C NMR spectrum of 3b after irradiation
that the central triple bond of the triyne moiety of 1b is
in THF-d8 for 24 h at 213 K. Marked resonances are due to
much less reactive toward thermal cycloaddition than
3b (O) and 1b (b), respectively.
that of 1a.
with the signals of 3b, one signal appears at distinctly
low field, while the other four signals seem to move
upfield. To assign the remarkably downfield shifted
carbon signal of 1b, theoretical chemical shifts were
estimated by the GIAO-B3LYP/6-31G* calculations. As
a result, C1, C2, C3, C10, and C11 are predicted to
resonate at 78.8, 79.9, 101.2, 80.0, and 79.1 ppm,
respectively, indicating that the signal in question should
be assigned to C3. It was reported that the sp carbon
atoms of diphenylhexatriyne (15a) resonate at 66.4, 74.4,
and 78.6 ppm31 and those of [20]DBA 16 having a slightly
strained triyne unit resonate at 68.9-81.6 ppm,32 sug-
gesting that the distinctly deshielded resonance observed
for 1b is due to the considerable distortion of its triyne
unit. To estimate the effect of distortion on the 13C NMR
chemical shifts of diphenylhexatriyne (15a), the chemical
shifts of 15a and hypothetical triyne 15b having the same
bending angles as those of the triyne unit of 1b were
estimated by the same theoretical method. The calculated
The 13C NMR spectrum obtained after irradiation of a
solution of 3b in THF-d8 (3.4 × 10-2 M) for 24 h at 213
K is shown in Figure 4. Besides the signals of the sp
carbons of unphotolyzed 3b at 94.0, 87.1, 83.6, and 79.4
ppm, five weak signals at 101.4, 82.6, 81.6, 80.4, and 79.2
ppm are observed, which we ascribe to 1b. Compared
chemical shifts (15a: C1 64.3, C2 73.7, C3 72.2 ppm,
15b: C1 77.0, C2 74.2, C3 101.3 ppm) clearly indicate
(31) Orita, A.; Yoshioka, N.; Struwe, P.; Braier, A.; Beckmann, A.;
Otera, J. Chem. Eur. J. 1999, 5, 1355-1363.
(32) Wan, W. B.; Kimball, D. B.; Haley, M. M. Tetrahedron Lett.
1998, 39, 6795-6798.
1858 J. Org. Chem., Vol. 70, No. 5, 2005

Dibenzotetrakisdehydro[12]- and Dibenzopentakisdehydro[14]annulenes
FIGURE 5. UV-vis spectral change of 3a upon irradiation
for 14 h in MTHF matrix at 77 K. (Inset) comparison between
spectrum after irradiation (blue line) and that after thaw and
refreeze (red line).
that C3 experiences the most remarkable downfield shift
owing to the bending of the triple bonds. This is probably
attributed to the large decrease of charge at C3 by
bending the triple bonds.33 Thus, although [14]DBA 1b
1
was stable enough for characterization by H and 13C
NMR spectroscopy in solution, we were unable to isolate
it because of its high reactivity and the low efficiency of
its generation.
FIGURE 6. (a) UV-vis spectral change of 3b upon photolysis
for 12 h in MTHF matrix at 77 K. (b) Spectral change of
photolysate upon standing the thawed solution for 50 h at 303
K. For sake of comparison, the spectrum of precursor 3b
measured in a MTHF solution was shown by a dotted line,
which is sifted vertically for clarity.
357 nm decreased dramatically, and a new band at 380
nm, which we ascribed to 1b, grew simultaneously as
shown in Figure 6a. In addition, the band of 3b at 344
nm bathochromically shifted by 1 nm and its intensity
increased slightly. After irradiation, the MTHF glass
matrix was thawed by warming to 303 K, and the
solution of the photolysate was kept at 303 K for 50 h.
As shown in Figure 6b, upon standing the solution, the
absorption bands due to 1b at 343 and 378 nm became
ambiguous owing to the gradual rise of the baseline. The
weak bands increased at 368, 354, and 382 nm are
ascribed to unphotolyzed 3b, which presumably became
apparent because of the rise of the baseline.
Characterization of 1a by FT-IR Spectroscopy. To
characterize highly reactive 1a, irradiation of the precur-
sor 3a was carried out in an argon matrix film at 20 K
and the FT-IR spectra were measured. [12]DBA 1a was
identified by comparing the IR spectra observed experi-
mentally with those theoretically calculated by the DFT
method at the B3LYP/6-31G* level. It has been estab-
lished that theoretical IR spectra predicted by the DFT
calculation at this level can well reproduce the experi-
mental spectra and, thus, can be used to identify the
unusual molecules isolated in low-temperature matri-
ces.35
Photolysis of 3a and 3b in 2-Methyltetrahydro-
furan (MTHF) Matrices. In order for UV-vis spectro-
scopic characterization of 1a and 1b, precursors 3a and
3b were dispersed in MTHF glass matrices at 77 K and
irradiated with a low-pressure mercury lamp. In the case
of 3a, as shown in Figure 5, a new prominent absorption
band due to a photoproduct at 361 nm grew simulta-
neously with the decay of that of 3a at 366 nm.34
Additionally, the bands of 3a at 350 and 339 nm slightly
shifted to shorter wavelength region. When the matrix
was thawed by warming to room temperature and then
refrozen at 77 K, the new absorption band at 361 nm was
completely lost while the bands at 366, 350, and 339 nm
due to unphotolized 3a were still alive (Figure 5, inset),
indicating the formation of a reactive intermediate, which
we ascribed to 1a. Similarly, by irradiation of 3b, the
intensity of the absorption bands of 3b at 386, 367, and
(33) The calculations predict that the charges on C1, C2, and C3
atoms changed by -0.30, -0.40, and +0.72, respectively, upon bending
of 15a into 15b.
(34) UV-vis spectroscopic measurement of 3a was also carried out
in an Ar matrix at 20 K to give an identical spectral change as that
observed upon irradiation in MTHF matrix at 77 K.; decay of the band
at 359 nm ascribed to 3a and growth of the band at 355 nm due to the
formation of the new chemical species, presumably 1a (see Figure S5
in the Supporting Information).
The FT-IR spectrum in an argon matrix observed after
irradiation are shown in Figure 7a. The observed spec-
trum of the precursor 3a and indan are also shown as
(35) (a) Scott, A. P.; Radom, L. J. Phys. Chem. 1996, 100, 16502-
16513. (b) Sato, T.; Arulmozhiraja, S.; Niino, H.; Sasaki, S.; Matsuura,
T.; Yabe, A. J. Am. Chem. Soc. 2002, 124, 4512-4521.
J. Org. Chem, Vol. 70, No. 5, 2005 1859

Hisaki et al.
the corresponding bands are apparently observed in the
differential spectrum at 1480, 756, and 2180, 2149, and
2117 cm-1, respectively, though the intensities of the last
three bands are very weak. Thus, the observed bands in
spectrum (d) are, in total, in good agreement with the
theoretical IR spectrum of 1a. These results indicate that
highly strained [12]DBA 1a was produced in an argon
matrix at 20 K and it was characterized successfully by
UV-vis and FT-IR spectra.
To investigate the CtC stretching vibrations of triyne
unit of 1a in more detail, irradiation of the precursor 3a
and then Raman spectroscopic measurement was carried
out in a neon matrix at 5 K. After irradiation of 3a,
photoproduct 1a was observed by UV-vis and IR spec-
troscopy as was in an argon matrix. However, the Raman
spectra of 1a, even of 3a, could not be recorded because
of the disturbance by strong fluorescence from 3a.
Kinetic Stability of Highly Strained DBAs 1a, 1b,
and Their Homologues. To elucidate the feature of the
deformed triyne units in 1a and 1b, we compared the
geometries and kinetic stability of 1a and 1b with those
of related DBAs with different number of carbon atoms
and topologies of the annulene ring. The theoretical or
experimental bond angles of the strained acetylene units
and the characterization status of [8]DBAs 1736 and 18,37
[10]DBA 19,12 [12]DBAs 1a and 20,38 and [14]DBA 1b
are listed in Table 1.
Structural optimization of 17 by the DFT calculation
indicates that 17 does not possess a planar conformation
but it has a C2 symmetrical structure with an ap-
proximately 50° twist between the benzene rings, owing
to the steric repulsion between the closely located aro-
matic hydrogen atoms. The diyne unit of 17 is extremely
deformed from linearity; the bending angles are predicted
to be 45° and 41°. Because of this extraordinary distor-
tion, attempts to prepare 17 by elimination reactions
from the corresponding bromide turned out unsuccess-
ful.36 On the other hand, its geometrical isomer 18,39
whose benzene rings are located on the opposite side of
the eight-membered ring, is kinetically stable and is fully
characterized, even though its X-ray crystal structure
shows that the triple bond is highly deformed from
linearity by 24°.37b Though [10]DBA 19 is only reported
in connection with its theoretical NICS value,12 it must
be difficult to isolate it because of its significantly
strained diyne moiety. Further ring enlargement to [12]-
DBA 1a makes the situation worse; the bent angle of the
central triple bond of 1a is more than 30°. Thus, as
described above, 1a was only characterized in matrices
FIGURE 7. Selected FT-IR spectra of C-C stretching of
acetylenes (column 1), in-plane C-H bending (column 2), and
out-of-plane C-H bending (column 3) vibrations. (Top) ob-
served spectra in an argon matrix at 20 K: (a) after irradiation,
(b) precursor 3a, (c) indan, and (d) differential spectra obtained
by subtraction of (b) and (c) from (a); (Bottom) theoretical IR
spectra calculated at the B3LYP/6-31G* level: precursor 3a
(green), 1a (blue), and indan (red). Oscillation intensities are
shown in parentheses.
spectra (b) and (c) in Figure 7. The spectrum (d) is the
differential spectrum obtained by subtracting spectra (b)
and (c) from (a) with appropriate scaling factors to remove
the contribution from the latter two. Columns 1, 2, and
3 in Figure 7 show vibrational regions for CtC stretch-
ing, C-H out-of-plane bending, and C-H in-plane bend-
ing modes, respectively, which are characteristic to 1a,
3a, and indan. In the observed spectrum after irradiation,
two recognizable absorption bands at 1481 and 737 cm-1
appeared as shown in Figures 7(2)(a) and (3)(a), respec-
tively, which can be attributed to indan by comparing
with Figures 7(2)(c) and (3)(c). In the high-frequency
region (spectrum (1)(a)), three weak IR bands at 2117,
2149, and 2170 cm-1 appeared, which may be ascribed
to the CtC stretching bands of 1a, in addition to those
of the precursor 3a (2199 and 2222 cm-1) which are
shown in spectrum (1)(b).
In the bottom of Figure 7, the theoretical IR spectra of
1a, 3a, and indan are shown as blue, green, and red bars,
respectively. The theoretical spectra of both 3a and indan
nicely reproduce those observed in the matrices, though
the former spectra exhibit constant shift from the latter.
For example, the predicted absorptions at 741 and 678
cm-1 for 3a correspond to those observed at 755 and 690
cm-1, respectively, and the theoretical bands at 740 and
(36) Wong, H. N. C.; Sondheimer, F. J. Org. Chem. 1980, 45, 2438-
2440.
(37) (a) Wong, H. N. C.; Garratt, P. J.; Sondheimer, F. J. Am. Chem.
Soc. 1974, 96, 5604-5605. (b) Destro, R.; Pilati, T.; Simonetta, M. J.
Am. Chem. Soc. 1975, 97, 658-659.
(38) (a) Behr, O. M.; Eglinton, G.; Galbraith, A. R.; Raphael, R. A.
J. Chem. Soc. 1960, 3614-3625. (b) Zhou, Q.; Carroll, P. J.; Swager,
T. M. J. Org. Chem. 1994, 59, 1294-1301. (c) Tovar, J. D.; Jux, N.;
Jarrosson, T.; Khan, S. I.; Rubin, Y. J. Org. Chem. 1997, 62, 3432-
3433. (d) Tovar, J. D.; Jux, N.; Jarrosson, T.; Khan, S. I.; Rubin, Y. J.
Org. Chem. 1998, 63, 4856. (e) Bunz, U. H. F.; Enkelmann, V. Chem.
Eur. J. 1999, 5, 263-266. (f) Gallagher, M. E.; Anthony, J. E.
Tetrahedron Lett. 2001, 42, 7533-7536. (g) Nishinaga, T.; Nodera, N.;
Miyata, Y.; Komatsu, K. J. Org. Chem. 2002, 76, 6091-6096.
(39) (a) Vogler, H. Tetrahedron 1979, 35, 657-661. (b) Vogler, H.
J. Am. Chem. Soc. 1978, 100, 7464-7471. (c) Stollenwerk, A. H.;
Kannellakopulos, B.; Vogler, H. Tetrahedron 1983, 39, 3127-3129. (d)
Wilcox, C. F., Jr.; Weber, K. A. J. Org. Chem. 1986, 51, 1088-1094.
726 cm-1 for indan are observed at 753 and 738 cm-1
,
respectively. A similar tendency is observed in columns
(1) and (2). Theoretical absorptions of 1a are predicted
to appear at 1458 cm-1 for C-H in-plane bending, 743
cm-1 for C-H out-of-plane bending, and 2188, 2150, and
2089 cm-1 for CtC stretching. As shown in spectrum (d),
1860 J. Org. Chem., Vol. 70, No. 5, 2005

Dibenzotetrakisdehydro[12]- and Dibenzopentakisdehydro[14]annulenes
TABLE 1. Theoretical or Experimental Bond Angles and Characterization Status of DBAs 1a, 1b, and 17-20
a The angles are theoretical values calculated by the DFT method at the B3LYP/6-31G* level. b The molecule has a C2-symmetrical
structure with an approximately 50° twist between the benzene rings. c The angles are determined by X-ray crystallographic analysis.
d The molecule has C2v symmetrical structure. e Listed angles are for 20 (R1 ) n-Bu, R2 ) H) from ref 38b.
at low temperatures. In contrast with 1a, the sym-
metrical isomer 2038 and a number of its derivatives are
successfully synthesized and are found to be stable at
ambient temperature. The remarkable difference be-
tween the stabilities of 1a and 20 is attributed to the
presence of highly deformed triyne unit in 1a. Finally,
although [14]DBA 1b having both diyne and triyne
bridges was detected in solution, its isolation was not
achieved because of its lability. These results indicate
that the kinetic stabilities of DBAs are related to the
symmetry of the annulene rings; the more symmetric the
rings are, the more stable DBAs are, since the triple bond
are increasingly deformed with decreasing symmetry.
Aromaticity of [14]DBA 1b and its Precursor 3b.
As mentioned above, [12]DBA 1a was too reactive for
observation by 1H NMR spectroscopy in solution. There-
fore, it is not possible to discuss its tropicity on the basis
of the experimental 1H NMR chemical shifts. On the
other hand, the 1H NMR spectra of the less strained
homologue 1b was observed. As shown in Figure 3b, the
aromatic protons of 1b show distinctly different chemical
shifts from those of its precursor 3b though both have a
[14]annulene ring. These differences can be attributed
to the following factors, (1) increase or decrease of
diatropicity of 1b because of the rehybridization of the
C(sp2)-C(sp2) bond into the C(sp)-C(sp), (2) change of
local anisotropy due to the triple bond39 because of the
geometrical change, and (3) change of anisotropy due to
the 14-membered macrocycle because of the geometrical
change. To clarify which factors dominate the difference
of the chemical shift between 1b and 3b, we carried out
a theoretical study for 1b and 3b.
Theoretical chemical shifts of the aromatic protons and
the NICS values at the center of the 14-membered rings
were calculated by the GIAO-DFT method on the B3LYP/
6-31G*-optimized geometries. The results are listed in
Table 2. The theoretical chemical shifts of the aromatic
protons of 1b and 3b show reasonable agreement with
those observed experimentally. As indicated by the values
∆δ(1b-3b), Ha and Hd, which are located close to the 14-
membered cycle, are predicted to show distinct upfield
shift (Ha: -0.45 ppm) or downfield shift (Hd: +0.12 ppm),
respectively, upon structural change from 3b to 1b. On
the other hand, Hb and Hc are not predicted to show much
change. The NICS values may indicate that 1b (-5.70)
is slightly more diatropic than 3b (-4.32). However, since
the distance between the center of the ring and the ring
carbon of 1b is different from that of 3b,40 anisotropy
experienced at the center of 14-membered ring of 1b
(40) The distance between the center of the ring and the adjacent
sp carbons (C1 and C11) in 1b are 2.19 and 1.82 Å, respectively, while
the corresponding distance in 3b are 2.80 and 2.07 Å, respectively.
J. Org. Chem, Vol. 70, No. 5, 2005 1861

Hisaki et al.
to the decrease of diatropicity of the 14-membered ring
and/or the decrease of anisotropic effect due to increasing
distance. For Hd, most of the observed downfield shift
(+0.12 ppm) can be attributed to the local anisotropy
effect (+0.13 ppm). The more extended structures 1d and
3d are expected to reproduce better the chemical shifts
due to the local anisotropic effect for 1b and 3b. As in
the case of 1c and 3c, the geometrical change of 3d into
1d would make Ha shift upfield (-0.28 ppm), while it
would shift Hd downfield (+0.21 ppm). Accordingly, even
after subtracting the contribution of the local anisotropic
effect, Ha and Hb of 1b would show another upfield by
0.17 and 0.09 ppm, respectively. Since both Ha and Hd
are thus expected to show upfield shift, it is deduced that
the diatropicity of the 14-membered annulene ring of 1b
is slightly smaller than that of 3b. This may be due to
the smaller conjugation energy between the adjacent
triple bonds, i.e., 1,3-butadiyne than that of double
bonds,41 though there exists controversy regarding this
issue.42
FIGURE 8. Schematic representation for geometrical param-
eters θ and d.
TABLE 2. Theoretical 1H NMR Chemical Shift and
NICS Values for 1b-d and 3b-d
chemical shifta
Ha
Hb
Hc
Hd
NICS
1b
3b
7.55
(7.59)
8.00
7.55
(7.59)
7.57
7.58
(7.59)
7.51
8.02
(7.92)
7.91
-5.7
-4.4
(7.83)
-0.45
7.15
(7.54)
-0.02
7.07
(7.50)
+0.06
7.08
(7.76)
+0.12
7.35
∆δ(1b-3b)
1c
3c
7.32
7.08
7.08
7.22
∆δ(1c-3c)
1d
-0.17
6.89
-0.01
7.07
+0.00
7.06
+0.13
7.28
3d
7.17
7.06
6.98
7.07
∆δ(1d-3d)
-0.28
+0.01
+0.08
+0.21
a Observed chemical shifts are given in parentheses.
TABLE 3. Geometrical Parameters for 1b and 3b
Ha
Hd
d/Å
θ/deg
d/Å
θ/deg
1b
3b
∆
3.23
3.08
+0.15
152.1
137.7
+14.5
3.11
3.16
-0.05
139.5
144.4
-5.0
(1b-3b)
should be different from that of 3b and, therefore, it is
difficult to compare the tropicities of 1b and 3b on the
basis of their NICS values.
Conclusion
To estimate the change of local anisotropy due to the
triple bond induced by the geometrical change, we defined
geometrical parameters d and θ as shown in Figure 8.
The parameter d denotes the distance between the
aromatic proton (Ha or Hd) and the center (Q) of the
adjacent triple bond (C2tC3 or C10tC11), and θ refers
to the angle H-Q-C. The value, ∆d, is the difference
between d(3b) and d(1b), and ∆θ is the difference
between θ(3b) and θ(1b). The values of d, ∆d, θ, and ∆θ
for the optimized structures of 1b and 3b are shown in
Table 3. The notable changes are the remarkably wid-
ened θ(Ha) by 14.5° and shortened θ(Hd) by 5.0°. Ad-
ditionally, the distance d(Ha) is considerably lengthened
by 0.15 Å, while d(Hd) is only slightly shortened by 0.05
Å. To estimate the effect on the local anisotropy of the
triple bond, we calculated the theoretical chemical shifts
for the hypothetical acyclic molecules 1c and 3c and the
larger structures 1d and 3d, whose bond lengths and
angles are kept same as those of 1b and 3b, respectively.
Theoretical chemical shifts of 1c, 3c, 1d, and 3d, and
∆δ(1c-3c) (the difference the between chemical shifts of 3c
and those of 1c) and ∆δ(1d-3d) (the difference between the
chemical shifts of 3d and those 3d) are shown in Table
2. It turned out that the geometrical change of 3c into
1c would make Ha shift upfield (-0.17 ppm), while it
would shift Hd downfield (+0.13 ppm). Accordingly, for
Ha, more than one-thirds (-0.17 ppm) of the observed
upfield shift (-0.45 ppm) is ascribed to the change of local
anisotropy. The residual upfield shift may be ascribed
We prepared [4.3.2]propellatriene-annelated DBAs 3a
and 3b as precursors of dibenzotetrakisdehydro[12]- and
dibenzopentakisdehydro[14]annulenes 1a and 1b having
a highly distorted triyne unit, and generated 1a and 1b
by their photochemical [2 + 2] cycloreversion. Irradiation
of [12]DBA 3a in a furan or THF solution gave [4 + 2]
adducts 13a and 14a, respectively. Though 1a was too
reactive for observation by 1H NMR spectroscopy, it was
successfully characterized by UV-vis spectra in a MTHF
matrix at 77 K and by FT-IR spectra in an argon matrix
at 20 K. On the other hand, [14]DBA 1b was character-
1
ized by H and 13C NMR spectra in THF-d8 solutions at
ambient temperatures as well as by UV-vis spectrum
in a MTHF matrix at 77 K. Upon structural change of
3b into 1b, chemical shifts of aromatic protons moved
substantially, which is attributed to the decrease of
tropicity of the 14-membered in addition to the change
of the local acetylenic anisotropy.
Experimental Section
Synthesis of Precursor 3a (Method A). A suspension of
521c,e (407 mg, 1.32 mmol) and powdered KOH (670 mg, 11.9
mmol) in benzene (20 mL) was deoxygenated several times
by freeze and thaw cycles (10-1 Torr). The mixture was stirred
(41) Rogers, D. W.; Matsunaga, N.; Zavitsas, A. A.; McLafferty, F.
J.; Liebman, J. F. Org. Lett. 2003, 5, 2373-2375.
(42) Kollmar, H. J. Am. Chem. Soc. 1979, 101, 4832-4840.
1862 J. Org. Chem., Vol. 70, No. 5, 2005

Dibenzotetrakisdehydro[12]- and Dibenzopentakisdehydro[14]annulenes
at 80 °C with continuous removal of the solvent containing
acetone. After 30 min, water and 10% HCl were added to the
reaction mixture and it was extracted with ether. The extract
was washed with brine. The organic layer was dried over
anhydrous MgSO4, filtered, and concentrated to a small
volume. The residue was subject to column chromatography
(silica gel, hexane) to afford a colorless solution of 4 in hexane.
The solvent was replaced by a small amount of Et3N by
evaporation followed by immediate dilution, and the solution
was used in next reaction immediately.
dark viscous oil. The products were purified by column
chromatography (silica gel, 1% AcOEt in hexane) followed by
preparative HPLC to afford 362 mg (41%) of 12 as an orange
viscous oil, together with 233 mg (46%) of monosubstitution
product as a pale yellow oil. 12: 1H NMR (270 MHz, 30 °C,
CDCl3) δ 7.49-7.43 (m, 4H), 7.24-7.19 (m, 4H), 5.93-5.84 (m,
4H), 2.10-2.04 (m, 2H), 1.63-1.55 (m, 2H), 1.32-1.17 (m, 2H),
1.11 (s, 42H); 13C NMR (67.8 MHz, 30 °C, CDCl3) δ 132.9 (t),
132.8 (t), 132.4 (q), 128.8 (t), 127.9 (t), 127.7 (t), 125.6 (q), 125.3
(q), 121.6 (t), 105.2 (q), 95.4 (q), 93.5 (q), 85.6 (q), 56.3 (q), 33.2
(s), 18.9 (t), 11.5 (t); IR (KBr) 3060, 3027, 2942, 2864, 2361,
2343, 2156, 1473, 755 cm-1; MS (EI) m/z 704.3 (M+); HRMS
calcd for C49H60Si2 704.423, found 704.421. Monosubstitution
The deoxygenated solution of 421c,e and 626 (347 mg, 806
µmol) in Et3N (100 mL) was added dropwise to a deoxygenated
suspension of Pd(PPh3)4 (194 mg, 168 µmol) and CuI (63 mg,
330 µmol) in Et3N (10 mL) over 12 h with stirring at 60 °C.
After stirring for another 9 h at 60 °C, the solvent was removed
in vacuo and the reaction mixture was diluted with ether and
10% HCl. The mixture was extracted with ether, and the
extract was washed with saturated NaHCO3 solution and
brine. The organic layer was dried over anhydrous MgSO4,
filtered, and concentrated to give 187 mg of a dark viscous
oil. The product was purified by column chromatography (silica
gel, 1% AcOEt in hexane) followed by preparative HPLC to
afford 4.2 mg (1%) of 3a as a yellow solid along with 6.5 mg
(2%) of 7 and 18.2 mg (6%) of 8. 3a: mp > 184 °C dec; 1H
NMR (270 MHz, CDCl3, 30 °C) δ 7.13-6.94 (m, 8H), 5.92-
5.87 (m, 2H), 5.81-5.77 (m, 2H), 1.94 (dd, J ) 12.7, 5.8 Hz,
2H), 1.78-1.59 (m, 2H), 1.24-1.13 (m, 2H); 13C NMR (67.8
MHz, CDCl3, 30 °C) δ 137.4 (q), 132.9 (t), 130.7 (t), 128.7 (t),
128.5 (t), 128.2 (q), 127.7 (t), 126.2 (q), 121.8 (t), 97.5 (q), 92.7
(q), 88.0 (q), 55.6 (q), 33.1 (s), 19.1 (s); IR (KBr) 3057, 3029,
2952, 2847, 2181, 1638, 1484, 749 cm-1; UV (CHCl3, 30 °C)
λmax (log ꢀ) 273 (4.8), 283 (4.7), 291 (4.7), 302 (5.0), 338 (3.5),
349 (3.5), 364 (3.6), 391 (3.1), 411 (3.2), 423 (3.2), 441 (3.1),
449 (3.1), 463 (3.0), 496 (2.6) nm; MS (LD-TOF) m/z 366.2 (M-),
248.1 (M- - 118.1). Anal. Calcd for C29H18: C, 95.05; H, 4.95.
Found: C, 94.68; H, 4.85. 7: 1H NMR (270 MHz, CDCl3, 30
°C) δ 7.78 (dd, J ) 7.7, 1.2 Hz, 2H), 7.60-7.57 (m, 4H), 7.43-
7.40 (m, 2H), 7.28 (ddd, J ) 7.4, 7.4, 1.7 Hz, 2H), 7.24 (ddd, J
) 7.4, 7.4, 1.7 Hz, 2H), 7.10 (ddd, J ) 7.7, 7.7, 1.2 Hz, 2H),
6.88 (ddd, J ) 7.7, 7.7, 1.7, 2H), 5.88-5.81 (m, 4H), 2.09-
2.04 (m, 2H), 1.30-1.18 (m, 4H); MS (APCI) m/z 796.5 (M-)
677.7 (M- - 118.8). 8: 1H NMR (270 MHz, CDCl3, 30 °C) δ
7.82-7.79 (m, 2H), 7.65-7.61 (m, 2H), 7.58 (dd, J ) 7.7, 1.7
Hz, 2H), 7.51-7.47 (m, 2H), 7.38-7.29 (m, 6H), 6.97 (ddd, J
) 7.7, 7.7, 1.5 Hz, 2H), 5.90-5.80 (m, 8H), 2.09-1.95 (m, 4H),
1.31-1.20 (m, 8H); MS (APCI) 986.2 (M-), 868.2 (M- - 118.0),
750.2 (M- - 236.0).
Method B. To a deoxygenated suspension of 5 (648 mg, 2.10
mmol), 6 (902 mg, 2.10 mmol), CuI (21 mg, 0.11 mmol), Pd-
(PPh3)4 (257 mg, 0.23 mmol), PPh3 (55 mg, 0.21 mmol), and
tricaprylmethylammonium chloride (270 mg, 0.63 mmol) in
benzene (200 mL) was added 2.5 N solution of NaOH (20 mL),
and the reaction mixture was stirred at 80 °C under argon.
After 8 h, another 2.5 N NaOH solution (20 mL) was added
and the reaction was continued for another 7 h. After the
mixture was cooled to room temperature, it was diluted with
10% HCl and extracted with AcOEt. The extract was washed
with saturated NaHCO3 solution, water, and brine. The
organic layer was dried over anhydrous MgSO4, filtered, and
concentrated to give a dark viscous oil. The product was
purified by column chromatography (silica gel, 10% AcOEt in
hexane) followed by preparative HPLC to afford 376 mg (49%)
of 3a as a yellow solid.
1
product: H NMR (270 MHz, 30 °C, CDCl3) δ 7.49-7.43 (m,
2H), 7.22-7.14 (m, 2H), 5.96-5.79 (m, 4H), 2.08-1.98 (m, 2H),
1.65-1.42 (m, 2H), 1.30-1.18 (m, 2H), 1.14 (s, 21H); 13C NMR
(67.8 MHz, 30 °C, CDCl3) δ 132.9, 132.7, 130.6, 128.9, 128.1,
127.8, 127.4, 125.9, 125.7, 124.9, 122.4, 121.5, 105.0, 95.5, 92.7,
82.4, 59.5, 56.2, 32.4, 31.8, 18.9, 18.8, 11.5; IR (KBr) 3057,
3029, 2943, 2865, 2359, 2157, 755 cm-1; MS (EI) m/z 458.2
(M+); HRMS calcd for C30H35Cl 458.220, found 458.218.
Synthesis of Precursor 3b. A 1.0 M solution of Bu4NF in
THF (3.27 mL) and AcOH (294 mg, 4.90 mmol) were added
dropwise to a solution of 12 (329 mg, 0.467 mmol) in THF (20
mL) with stirring at room temperature. After 4 h, the mixture
was diluted with ether (20 mL) and washed with water and
brine. The organic layer was dried over anhydrous MgSO4 and
filtered. After concentration, the product 9 was dissolved in a
small volume of pyridine and was used immediately in the next
reaction.
A solution of the terminal acetylene 9 dissolved in pyridine
(300 mL) was added dropwise over 23 h to a solution of Cu-
(OAc)2 (8.36 g, 46.0 mmol) in pyridine (200 mL) with stirring
at room temperature. After another 18 h, the reaction mixture
was concentrated and filtered through a short column of silica
gel (chloroform). Purification by preparative HPLC gave 138
mg (75%, for two steps) of 3b as a pale yellow solid. 3b: mp >
160 °C dec; 1H NMR (270 MHz, 30 °C, CDCl3) δ 7.90-7.82
(m, 2H), 7.80-7.72 (m, 2H), 7.52 (ddd, J ) 7.4, 7.4, 1.7 Hz,
2H), 7.47 (ddd, J ) 7.4, 7.4, 1.5 Hz, 2H), 6.12-5.91 (m, 4H),
2.27-2.16 (m, 2H), 1.70-1.39 (m, 4H); 13C NMR (67.8 MHz,
30 °C, CDCl3) δ 132.3 (q), 131.6 (t), 129,9 (t), 129.1 (t), 128.3
(t), 127.9 (t), 127.7 (q), 124.0 (q), 121.8 (t), 94.2 (q), 87.4 (q),
84.0 (q), 79.9 (q), 56.7 (q), 33.7 (s), 19.0 (s); IR (KBr) 3057,
3030, 2952, 2928, 2844, 2204, 2147, 1597, 1470, 747 cm-1; UV
(30 °C, CDCl3) λmax (log ꢀ) 415 (3.0), 384 (4.3), 355 (4.3), 343
(4.3), 321 (5.1), 310 (4.7), 301 (4.8), 263 (4.4) nm; MS (FAB)
m/z 390.1 (M+). Anal. Calcd for C31H18: C, 95.35; H, 4.65.
Found: C, 95.14; H, 4.60.
Photolysis of 3a in THF-d8. A solution of 3a (6.0 mg, 16
µmol) dissolved in THF-d8 (750 µL) was placed in a quartz
NMR tube. The solution was deoxygenated by bubbling argon
for 5 min before irradiation with a low-pressure mercury lamp
(60 W) at room temperature for 31 h. The progress of the
photolysis was monitored by 1H NMR spectroscopy. The color
of the solution of 3a turned dark and a film was formed on
the wall of the tube after irradiation.
Isolation of [4 + 2] Adduct 13a. A solution of 3a (45 mg,
0.12 mmol) dissolved in THF (30 mL) was placed in a quartz
tube and deoxygenated by bubbling argon. The solution was
irradiated with a low-pressure mercury lamp (60 W) for 30 h
in a water bath. The color of the solution of 3a turned brown.
After removal of the solvent in vacuo, the product was purified
by column chromatography (silica gel, 5% AcOEt in hexane
to chloroform) followed by preparative HPLC to afford 6.8 mg
(18%) of 13a as a yellow solid together with recovered 3a in
Synthesis of Acyclic Tetrayne Derivative 12. A solution
of 1128 (938 mg, 3.32 mmol) dissolved in piperidine/THF (10
mL, 5:1 v/v) was added dropwise over 45 min to a deoxygenated
suspension of dichloropropellatriene 1021c,e (266 mg, 1.25
mmol), Pd2(dba)3‚CHCl3 (52 mg, 0.050 mmol), CuI (65 mg, 0.34
mmol), and PPh3 (112 mg, 0.425 mmol) in piperidine/THF (2
mL, 5:1 v/v) with stirring at 60 °C. After stirring for 8 h at 60
°C, the reaction mixture was filtered through a short column
of silica gel and the solvent was removed in vacuo to give a
1
44% yield. 13a: mp > 150 °C dec; H NMR (400 MHz, CD2-
Cl2, 30 °C) δ 7.08-6.88 (m, 16H), 6.37-6.33 (m, 2H), 3.31-
3.29 (m, 2H), 2.09-2.03 (m, 2H), 1.56-1.49 (m, 4H); 13C NMR
(100 MHz, CD2Cl2, 30 °C) δ 138.9, 137.7, 133.4, 132.7, 132.5,
131.8, 131.2, 129. 5, 129.2, 128.5, 127.6, 127.4, 126.5, 100.5,
99.4, 94.1, 93.22, 93.18, 88.2, 64.2, 47.7, 30.1, 27.6; IR (KBr)
J. Org. Chem, Vol. 70, No. 5, 2005 1863

Hisaki et al.
3057, 2954, 2922, 2857, 2210, 2177, 1486, 1470, 759, 747 cm-1
;
nitrogen vessel and the glass matrix was irradiated with a
low-pressure mercury lamp (60 W) through a window of the
vessel for 14 h. Photolysis was monitored by UV-vis spec-
troscopy (Figure 5). After irradiation, the matrix was thawed
by warming to room temperature and then refrozen at 77 K
to measure a UV-vis spectrum again (Figure 5, inset).
Photolysis of 3b in a MTHF Matrix. Photolysis of 3b was
carried out for 12 h with a matrix of 3b in MTHF (6.2 ×1 0-6
M) according to the same procedure as that of 3a. After
irradiation, the matrix was thawed by warming to 303 K and
left for 50 h at this temperature. The changes were monitored
by UV-vis spectroscopy (Figure 6).
Photolysis of 3a in an Argon Matrix. Compound 3a
was vaporized at 150-155 °C and co-deposited with argon
(99.9999%) on a CsI plate cooled at 20 K in a sample chamber
whose pressure was kept at <10-3 Torr. Matrix-isolated
precursor 3a was photolyzed by using a forth harmonic
generation (FHG) pulses of Nd:YAG laser (λ ) 266 nm, 10 Hz,
ca. 0.8 mJ cm-2 pulse-1). Deposition-irradiation cycle was
repeated seven times to increase the concentration of the
photoproducts. In the cycle, the precursor 3a was deposited
for 15-20 min and then photolyzed by irradiation for 1-2 h.
Both sides of the CsI substrate were used for the matrix
preparation to avoid the peeling off the matrix: first to forth
deposition was carried out on the one side, and fifth to seventh
was on the other side. Total irradiation time was 12 h. The
photolysis was followed by UV-vis (see Figure S5 in the
Supporting Information) and FT-IR spectra.
Computational Methods. The DFT calculations were
performed with the Gaussian 03 program package.43 The
geometries of the compounds were optimized by using the
B3LYP method in combination with the 6-31G* basis set. The
nature of the stationary points was assessed by means of
vibration frequency analysis. The theoretical IR spectra of 1a,
3a, and indan were calculated for their optimized geometries.
The chemical shifts and the NICS values of 1b and 3b were
calculated by the GIAO-DFT method, where C2v symmetry was
adopted for the optimized structure of 1b. Hypothetical
molecules 1c, 3c, 1d, and 3d were constructed on the Gauss-
View 03 by removal of the redundant part from the parent
molecules 1b and 3b followed by attaching hydrogen atoms
on the terminal carbon atoms with keeping the original bond
angles (for 1d and 3d) or keeping the CtC-H angles 180°
(for 1c and 3c). The C-H bond lengths were kept 1.06622 Å
for a C(sp)-H bond and 1.0833 Å for a C(sp2)-H bond.
X-ray Crystallographic Structure Analyses. See the
Supporting Information.
MS (FAB) m/z 614.3 (M+).
Isolation of [4 + 2] Furan Adduct 14a. A solution of 3a
(31 mg, 84 µmol) dissolved in fruan (50 mL) was placed in a
quartz tube. The solution was deoxygenated by argon bubbling
before irradiation with a low-pressure mercury lamp for 32 h
in an ice-water bath. The furan was removed in vacuo and
the product was isolated by column chromatography (silica gel,
1% AcOEt in hexane) followed by preparative HPLC to afford
5.7 mg (20%) of 14a as an orange solid together with recovered
1
3a in 50% yield. 14a: mp > 160 °C dec; H NMR (270 MHz,
CDCl3, 30 °C) δ 7.09-6.93 (m, 10H), 5.27 (dd, J ) 1.0, 1.0 Hz,
2H); 13C NMR (67.8 MHz, CDCl3, 30 °C) δ 146.5 (q), 142.1 (t),
132.7 (t), 130.8 (t), 129.1 (t), 128.8 (t), 127.8 (q), 126.6 (q), 108.0
(q), 93.0 (q), 88.9 (q), 84.5 (q); IR (KBr) 3053, 3028, 2195, 2174,
1485, 874, 854, 751 cm-1; UV (CHCl3, 30 °C) λ
(log ꢀ) 262
max
(4.7), 276 (4.8), 307 (sh, 4.5), 318 (4.7), 345 (3.3), 359 (3.3),
376 (3.4), 436 (sh, 3.1), 470 (3.1), 490 (sh, 3.0), 525 (2.7) nm;
MS (LD-TOF) m/z 316.1 (M-).
Photolysis of 3b in THF-d8. A solution of 3b (3.2 mg, 8.2
µmol) dissolved in THF-d8 (750 µL) was placed in a quartz
NMR tube. The solution was deoxygenated several times by
freeze and thaw (10-3-10-4 Torr) cycles and then sealed. The
solution was irradiated for 24 h with a low-pressure mercury
lamp in an EtOH bath cooled at 220 K equipped with a
refrigerating device. The color of the solution turned dark and
dark precipitates were formed in the tube after irradiation.
Standing the solution for 56 h at 30 °C led to the decomposition
1
of 1b and the formation of 13b (see Figure 5b). 1b: H NMR
(400 MHz, 30 °C, THF-d8) δ 7.93-7.91 (m, 2H), 7.63-7.57 (m,
6H); 13C NMR (400 MHz, -30 °C, THF-d8) δ 132.3, 129.6,
129.23, 129.17, 127.5, 125.1, 101.5, 82.0, 81.6, 80.4, 79.2.
Photolysis of 3b in Furan. A solution of 3b (41.5 mg,
0.106 mmol) dissolved in furan (45 mL) was placed in a quartz
tube. The solution was deoxygenated by argon bubbling and
sealed. The solution was irradiated with a low-pressure
mercury lamp (60 W) in a water bath for 26 h. The color of
the solution turned dark and dark precipitates were formed
in the tube after irradiation. The furan was removed in vacuo
and the product was isolated by column chromatography (silica
gel, 10% AcOEt in hexane) followed by preparative HPLC to
afford a small amount of 14b as a brown solid. The recovered
starting material 3b (32.8 mg) was irradiated again by same
1
way for 20 h to afford 1 mg (2%) of 14b. 14b: H NMR (400
MHz, CDCl3, 30 °C) δ 7.96-7.94 (m, 2H), 7.83-7.81 (m, 2H),
7.59 (ddd, J ) 7.6, 7.6, 1.5 Hz, 2H), 7.54 (ddd, J ) 7.6, 7.6, 1.5
Hz, 2H), 7.30 (dd, J ) 1.0, 1.0 Hz, 2H), 5.88 (dd, J ) 1.0, 1.0
Hz, 2H); MS (APCI) m/z 341.2 (M+ + 1).
Acknowledgment. We are grateful to Prof. Rainer
Herges (Universita¨t Kiel) for the discussion on aroma-
ticity of dehydroannulenes. I.H. thanks JSPS for a
Research Fellowships for Young Scientists and the 21st
Century COE Program “Integrated Ecochemistry”, Os-
aka University, for a research fellowship.
Photolysis of 3a in a 2-Methyltetrahydrofuran (MTHF)
Matrix. A solution of 3a in MTHF (5.8×10-5 M) placed in a
UV cell was degassed by freeze and thaw cycles (10-3-10-4
Torr) and then sealed. The cell was immersed into a liquid
(43) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A.; Vreven, T., Jr.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo,
C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin,
A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma,
K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.;
Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui,
Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.;
Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challa-
combe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. Gaussian 03, revision B.03; Gaussian, Inc.:
Pittsburgh, PA, 2003.
Supporting Information Available: Full-scale 1H NMR
spectra of 3a and 3b and their change upon photolysis, a full-
scale 13C NMR spectrum of 3b after irradiation, UV-vis and
full-scale FT-IR spectra of 3a upon photolysis, optimized
geometries of 1a, 3a, indan, 1b, 3b, 15a, 17, and 19 by the
DFT calculations, theoretical IR spectra of 1a, 3a, and indan,
theoretical chemical shifts of 1b, 3b, and 15a, coordinates and
theoretical chemical shifts of hypothetical molecules 1c, 3c,
1d, 3d, and 15b, calculated Mulliken atomic charges of 15a
and 15b, 1H and 13C NMR spectra of 3a, 12, 3b, 13a, and 14a,
X-ray crystal structures of 3a, 3b, 13a, and 14a, and X-ray
crystallographic files of 3a, 3b, 13, and 14 (CIF). This material
is available free of charge via the Internet at http://pubs.acs.org.
JO047857P
1864 J. Org. Chem., Vol. 70, No. 5, 2005