Bicyclo[6.3.0]undecapentaenyl anion: The next higher homolog of the indenyl anion with exceptionally large ion-pairing effects on its tropicity

Article abstract of DOI:10.1002/asia.201301307

The title anion 1 was generated as a fairly thermally stable species in tetrahydrofuran (THF) and dimethylsulfoxide (DMSO) by the action of several bases (sodium hydride, potassium hydride, lithium diisopropylamide, and lithium hexamethyldisilazide) with appropriate bicyclo[6.3.0]undecapentaenes. Variable-temperature ¹H NMR spectra of 1×Li⁺ in [D₈]THF reveal that the anion exhibits exceptionally large ion-pairing effects; proton chemical shifts vary by more than 1 ppm as a function of ion-pairing conditions. Thus, anion 1, in a contact ion pair (Li⁺ at ambient temperature in THF), behaves as an aromatic cyclopentadienyl anion that is perturbed only slightly by the electronic effects of a paramagnetic cyclooctatetraene (COT), whereas 1 in a separated ion pair (Li⁺ at low temperatures in THF or at ambient temperature in DMSO) behaves as an overall paratropic species with a 12 π-electron periphery. ¹³C NMR spectroscopy indicates no major skeletal rearrangement and only small variations of the electron density. The variable tropicity of 1 can be ascribed to small conformational changes of the molecule. In addition to its unusual, tunable tropicity, anion 1 can also serve as a versatile building block for the synthesis of cyclopentanoid conjugated systems fused to a fully unsaturated eight-membered ring. A theoretical calculation predicts that the 10-position of 1 should have the highest electron density. In agreement with this prediction, the reactions of 1 with electrophiles occur predominantly at the 10-position. The corresponding ferrocene, two fulvenes, two diazo derivatives, and a COT-fused azulene were obtained by the reactions of 1 with appropriate electrophiles. Split personality: The bicyclo[6.3.0]undecapentaenyl anion, which is the next higher homolog of the indenyl anion, behaves as an aromatic cyclopentadienide ion slightly perturbed by the effects of a paramagnetic cyclooctatetraene in a contact ion pair, whereas in a solvent-separated ion pair it is an overall paratropic species owing to a 12 π-electron periphery (see picture). Copyright

Full text of DOI:10.1002/asia.201301307

FULL PAPER
DOI: 10.1002/asia.201301307
BicycloACHTUNGTRENNUNG[6.3.0]undecapentaenyl Anion: The Next Higher Homolog of the
Indenyl Anion with Exceptionally Large Ion-Pairing Effects on its Tropicity
Hiroaki Ozoe,[a] Yasutaka Uno,[a] Chitoshi Kitamura,[a] Hiroyuki Kurata,[b] Masaji Oda,[b]
John W. Jones Jr.,[c] Lawrence T. Scott,*[d] and Takeshi Kawase*[a]
Abstract: The title anion 1 was gener-
ated as a fairly thermally stable species
in tetrahydrofuran (THF) and dime-
thylsulfoxide (DMSO) by the action of
several bases (sodium hydride, potassi-
um hydride, lithium diisopropylamide,
and lithium hexamethyldisilazide) with
pentadienyl anion that is perturbed
only slightly by the electronic effects of
cribed to small conformational changes
of the molecule. In addition to its un-
usual, tunable tropicity, anion 1 can
also serve as a versatile building block
for the synthesis of cyclopentanoid
conjugated systems fused to a fully un-
saturated eight-membered ring. A the-
oretical calculation predicts that the
10-position of 1 should have the high-
est electron density. In agreement with
this prediction, the reactions of 1 with
electrophiles occur predominantly at
the 10-position. The corresponding fer-
rocene, two fulvenes, two diazo deriva-
tives, and a COT-fused azulene were
obtained by the reactions of 1 with ap-
propriate electrophiles.
a
paramagnetic
cyclooctatetraene
(COT), whereas 1 in a separated ion
pair (Li+ at low temperatures in THF
or at ambient temperature in DMSO)
behaves as an overall paratropic spe-
cies with a 12 p-electron periphery.
13C NMR spectroscopy indicates no
major skeletal rearrangement and only
small variations of the electron density.
The variable tropicity of 1 can be as-
appropriate
pentaenes.
bicyclo
Variable-temperature
ACHTUNGTREN[NGNU 6.3.0]undeca-
1H NMR spectra of 1·Li+ in [D8]THF
reveal that the anion exhibits excep-
tionally large ion-pairing effects;
proton chemical shifts vary by more
than 1 ppm as a function of ion-pairing
conditions. Thus, anion 1, in a contact
ion pair (Li+ at ambient temperature
in THF), behaves as an aromatic cyclo-
Keywords: aromaticity
·
carban-
ions · fused-ring systems · ion pairs ·
NMR spectroscopy
Introduction
higher homolog of indenyl anion 2. Despite its simple and
fundamental structure, anion 1 has not previously been char-
acterized well. In contrast to 2, a rigid [4n+2]annuleno-
BicycloACHTUNGTRENNUNG[6.3.0]undecapentaenyl anion 1 is a derivative of cy-
clopentadienyl anion 3, fused with COT. It is the next
N
1 represents a flexible
AHCTUNGTRENNUNG
tetraene (benzoCOT) 4,[2] which is an isoelectronic relative
of 1, exhibits little antiaromatic character as a peripheral
conjugated system because its COT ring largely deforms
from planarity.[3] On the other hand, compound 1 is an
anionic system and electron repulsion should promote de-
localization of the negative charge throughout the entire
molecule. This tendency should increase the 4n p-electron
character of the overall molecule and perturb the electronic
properties of the cyclopentadienyl anion moiety as a [4n+2]
p-electron system. The counterbalance between the partial
aromatic character of the five-membered ring and the pe-
ripheral antiaromatic character should determine the overall
electronic and magnetic properties of 1.[4,5] One of the other
[a] H. Ozoe, Y. Uno, Prof. Dr. C. Kitamura,+ Prof. Dr. T. Kawase
Department of Materials Science, Graduate School of Engineering
University of Hyogo, 2167 Shosha, Himeji, 671-2280 (Japan)
E-mail: kawase@eng.u-hyogo.ac.jp
[b] Prof. Dr. H. Kurata,++ Prof. Dr. M. Oda
Department of Chemistry, Graduate School of Science
Osaka University, Toyonaka, Osaka 560-0043 (Japan)
[c] Dr. J. W. Jones, Jr.
Department of Chemistry and Center for Advanced Study
University of Nevada, Reno, Nevada, 89557-0020 (USA)
[d] Prof. Dr. L. T. Scott
Department of Chemistry, Merkert Chemistry Center
Boston College, Chestnut Hill, MA 02467-3860 (USA)
E-mail: lawrence.scott@bc.edu
isoelectronic relatives of 1, the bicycloACTHNUTRGNE[UNG 6.5.0]tridecahexaenyl
[+] Present address:
cation 5, suffers from valence isomerization to a tricyclic
isomer 6 by a symmetry-allowed pericyclic ring-closure reac-
tion to escape antiaromatic destabilization.[6] Spectral data
for 1 provide no evidence for the presence of tricyclic
isomer 7. Although anion 1 remains bicyclic, contrary to 5,
it shows exceptionally large ion-pairing effects in the
1H NMR spectra (Dd>1 ppm). We describe and discuss
herein these ion-pairing effects. Moreover, anion 1 can serve
Department of Materials Science
School of Engineering, University of Shiga Prefecture
2500, Hassaka-cho, Hikone, Shiga 522-8533 (Japan)
[
++] Present address:
Department of Environmental and Biological Chemistry
Faculty of Engineering, Fukui University of Technology
Gakuen 3-6-1, Fukui 910-8505 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201301307.
Chem. Asian J. 2014, 9, 893 – 900
893
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Lawrence T. Scott, Takeshi Kawase et al.
as a versatile synthetic building block for cyclopentanoid
compounds fused with an unsaturated eight-membered ring.
The synthesis and some properties of fulvene, azulene,
diazo, and ferrocene derivatives are described.
Figure 1. Optimized structures of anion 1 from PM3 calculations. a) Top
view and electron density. b) Side view and dihedral angle between
À
À
bonds C2 C3 and C4 C5.
Results and Discussion
that the anion possesses a nonplanar structure (Figure 1),
Generation of 1 and NMR Spectroscopy Studies
À
À
with a dihedral angle between the C2 C3 and the C4 C5
bonds of 123.18. Moreover, the electron density at the 10-
position of 1 is the highest, whereas those of the 3- and 6-
positions are the second highest. Thus, compound 12 is not
the product expected from kinetically favored protonation
of 1, but appears to be formed under conditions of thermo-
dynamic control. Scott and Brunsvold prepared bicyclo-
Six structural isomers of bicycloACTHNUGTRNEUNG[6.3.0]undecapentaene (8–
13) all represent promising precursors to anion 1. Among
them, four isomers 8, 9, 11, and 12 are known. Dꢁrr and
Scheppers
previously
1(8),2,4,6,9-pentaene
prepared
(8) and
bicyclo
bicyclo[6.3.0]undeca-
ACHTUNGTREN[NGNU 6.3.0]undeca-
AHCTUNGTRENNUNG
1(11),2,4,6,9-pentaene (9) by the reaction of benzene and cy-
clopentadienylidene, generated in situ from photodecompo-
sition of diazocyclopentadiene 14 (Scheme 1).[7] Treatment
A
(11)
from
7-
iodobicycloACTHNUTRGNEUG[N 5.3.1]undeca-1,3,5,9-tetraene through a skeletal
rearrangement.[10]
In the first published attempt to prepare anion 1, Schon-
leber reported that treatment of 12 with nBuLi afforded
butyl adduct 15 instead of 1 (Scheme 1).[11] Thus, compound
12 behaves as a pentafulvene derivative. This result indicates
that bicyclo
moiety should be better choices as precursors to anion 1.
Bicyclo[6.3.0]undecapentaenyl anion 1 was generated as
ACHTUNGTREN[NUNG 6.3.0]undecapentaenes without a pentafulvene
Scheme 1. Synthesis
[6.3.0]undecapentaene, which are all promising precursors to anion 1.
Py=pyridine, THF=tetrahydrofuran.
of
structural
isomers
of
bicyclo-
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
deep purple solutions from 8 or 9 under several basic condi-
tions (n-butyllithium, lithium diisopropylamide (LDA), lithi-
um hexamethyldisilazide (LHMDS), NaH, KH in [D8]THF,
and KH in [D6]DMSO; Figure S1 in the Supporting Infor-
of a mixture of pentaenes 8 and 9 with Py afforded
1,4,6,8,10-bicyclo[6.3.0]undecapentaene (12) in high yield.
1
G
mation). H and 13C NMR spectra reveal the clean forma-
Results indicate that anion 1 forms reversibly as an inter-
mediate and undergoes reprotonation at the 3-position to
give 12.
tion of 1 because the signals are reasonably assignable to
the structure of 1. The anion is fairly stable thermally under
inert gas atmospheres; no spectral change was observed
upon heating the anion solution at 508C for 6 h. To our sur-
The optimized structure and electron densities of 1 have
been calculated by the PM3 method.[8,9] The results predict
prise, however, the H NMR spectrum of 1·Li+ in [D8]THF
1
at 218C differed drastically from that of 1·Li+ in [D6]DMSO
at 228C (Figure 2).
In [D8]THF at 218C, the average chemical shifts of the
five-membered ring protons (H9–H11) and the eight-mem-
bered ring protons (H2–H7) of 1·Li+ are d=5.12 and
4.77 ppm, respectively. This value for the five-membered
ring protons is shifted only 0.22 ppm upfield from that of cy-
clopentadienyl anion 3 (d=5.34 ppm).[12] Thus, the effect of
any paratropic ring currents associated with peripheral con-
jugation does not seem to be large under these conditions.
On the other hand, compared with the average chemical
Chem. Asian J. 2014, 9, 893 – 900
894
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Lawrence T. Scott, Takeshi Kawase et al.
Figure 3. Temperature-dependent chemical shift change of protons of
1·Li+ in [D8]THF.
Table 1. 1H NMR (100 MHz) spectroscopy data for 1.
Solvent
Cation
T
H-
[8C] 9,11
[ppm]
H-10 H-2,7 H-3,6 H-4,5 dav
[ppm] [ppm] [ppm] [ppm] [ppm]
Figure 2. 1H NMR spectra (500 MHz) of 1 Li+ a) in [D6]DMSO and b) in
[D8]THF at 218C.
G
G
G
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
Li[a,b]
Li
Na
Na
K
21 5.07
À50 4.37[d]
38 4.99
5.22
5.30
4.06
5.00
4.68
5.14
4.85
4.07
4.14
4.17
4.40
3.20
4.06
3.76
4.19
3.90
3.22
3.27
3.27
4.62
4.89
3.6[e] 3.87
5.10
4.90
5.22
5.05
4.37
4.34
4.09
4.47
4.22
3.66
3.71
3.75
4.65
4.39
4.77
4.54
3.89
3.94
3.97
shifts of the eight-membered ring protons of
4 (d=
[D8]THF
6.09 ppm),[4] the value for 1·Li+ in [D8]THF (d=4.77 ppm)
is shifted by 1.32 ppm to higher magnetic field. This result
indicates that the eight-membered ring protons are highly
sensitive to local ring current effects.
À45 4.78
38 5.07
K
À50 4.92
21 4.39
Li[a,c]
[D6]DMSO Na
K
38 4.43[d]
38 4.45[d]
In [D6]DMSO at 228C, the average chemical shifts of the
five-membered ring protons and the eight-membered ring
protons of 1·Li+ are d=4.38 and 3.65 ppm, respectively. The
anion behaves as an overall paratropic species under these
conditions.
[a] 500 MHz NMR spectroscopy. [b] J
(3,5)=0.0 Hz, (4,5)=13.5 Hz, (9,10)=3.2 Hz. [c] J
(3,4)=8.1 Hz, J(3,5)=0.0 Hz, J(4,5)=13.1 Hz, J(9,10)=3.1 Hz. The cou-
pling constants were determined by using the gNMR (version 4.1) itera-
tive program. [d] A sharp singlet. [e] Overlapped with the solvent signals.
G
ACHTUNGTREN(NGNU 3,4)=6.6 Hz, J-
R
J
A
G
J
E
ACHTUNGTRENNUNG
E
U
ACHTUNGTRENNUNG
It is noteworthy that the proton chemical shifts of 1·Li+ in
[D8]THF exhibit exceptionally large changes with tempera-
tures. The chemical shifts at À508C appear at about 1 ppm
higher magnetic field than those at 388C (Figure 3 and Fig-
ure S2 in the Supporting Information), and the spectra
closely resemble those in [D6]DMSO (Table 1). On the
other hand, the 1H NMR spectra of 1·Na+ and 1·K+ in
[D8]THF show much smaller variations with temperatures.
In light of other studies on ion-pairing effects in solution,[13]
1·Na+, 1·K+, and 1·Li+ in [D8]THF at ambient temperatures
appear to be contact ion pairs, whereas 1·Li+ in [D8]THF at
À508C and 1 in [D6]DMSO appear to be solvent-separated
ion pairs.[14] In the case of 1·Li+ in [D8]THF, the equilibrium
shifts strongly with temperature (Scheme 2).
Scheme 2. The equilibrium, which shifts strongly with temperature, re-
sults in the formation of 1·Li+ in [D8]THF.
Table 2. 13C NMR (22.5 MHz) spectroscopy data and PM3 electron densities of 1.
Solvent
Cation
T
[8C]
C-1,8 C-2,7 C-3,6 C-4,5 C-
[ppm] [ppm] [ppm] [ppm] 9,11
[ppm]
C-10 dav
[ppm] [ppm]
G
G
E
G
G
ACHTUNGTRENNUNG
13C NMR spectroscopy data for 1 under various condi-
tions are summarized in Table 2. The chemical shifts of the
five-membered ring carbon atoms (C1 and C8–C11) appear
at higher field than those of the eight-membered ring
carbon atoms (C2–C7). The chemical shifts of the eight-
membered ring carbon atoms are almost the same as those
of 4,[4] which indicates that the negative charge is mainly lo-
calized on the five-membered ring carbon atoms. The C10
carbon resonates at the highest magnetic field, which is con-
sistent with theoretical calculations. The chemical shift of
C2,7 remains almost constant under all conditions, which
clearly excludes the possibility of structural change based on
AHCTUNGTRENNUNG
Li
Li
Na
K
50 116.6 133.7 120.5 130.2 117.8 107.7 122.3
À50 118.3 134.2 127.3 129.2 114.1 108.5 123.1
28 116.7 133.7 123.0 129.0 117.4 108.8 122.6
28 117.4 133.8 123.6 129.4 118.1 110.9 123.2
40 117.4 133.4 126.3 130.1 112.4 109.2 122.6
1.185 0.946 1.240 1.081 1.210 1.253
[D8]THF
[D6]DMSO Na
electron density
valence isomerization to 7. The chemical shifts of C3,6 and
C9,11 exhibit relatively large changes with the ion-pairing
equilibrium, which indicates that some degree of negative
charge at C3,6 moves to C9,11 as the contact ion pair shifts
Chem. Asian J. 2014, 9, 893 – 900
895
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Lawrence T. Scott, Takeshi Kawase et al.
to the solvent-separated ion pair. The variations are relative-
fulvenes, respectively.[23,24] Similar treatment of 1 affords the
corresponding undecafulvene derivatives 16 and 17 in mod-
erate yields (Scheme 3). The reactions occur predominantly
at the 10-position, in accordance with the calculated electron
density distribution in 1. Fulvene 16 forms modestly ther-
mally stable, bright-red crystals, whereas 17 is a relatively
labile, dark-red solid that decomposes on silica gel at room
temperature. Therefore, chromatographic purification was
carried out at 08C.
ly small (Dd=4–8 ppm), and the charge redistribution is op-
1
posite to the direction suggested by changes in the H NMR
chemical shifts of H3,6.[15]
As expected from the theoretical calculations mentioned
above, the eight-membered ring of 1 possesses a tub form.
Any conformational change should be reflected in the
values of the coupling constants of the eight-membered ring
protons. It is known that the coupling constant JACTHNUGRTNEUNG(3,4) of
deeply bent 4 is 1 Hz.[2c] As the eight-membered ring is flat-
tened, this coupling constant should increase.
The coupling constants of 1 are not first order, so they
were obtained by computer simulation of the experimental
spectra by using the gNMR (version 4.1) iterative program
(Figures S3 and S4 in the Supporting Information). The cou-
pling constant of JACHTUNGTRENNUNG(3,4) increases from 6.6 to 8.1 Hz as the
contact ion pair changes into the solvent-separated ion-pair.
According to the Karplus equation,[16] this variation indi-
cates roughly a 108 change (from 130 to 1408) of dihedral
À
À
À
angles between the C2 C3 (C5 C6) and C4 C5 bonds; the
tub shape of 1 flattens in the solvent-separated ion pair, al-
though the conformational change is not so large. The most
interesting aspect is that such a small conformational change
gives rise to such an exceptionally large tropicity change.
Indenyl anion 2, cyclopentadienyl anion 3, and other aro-
Scheme 3. Preparation of undecafulvenes 16 and 17.
It has been known that protonation on the exo-methylene
carbon atoms of heptafulvene and methanoundecafulvene
derivatives produce the corresponding tropylium and metha-
no[11]annulenyl cations.[25,26] Attempts to generate a stable
cation from fulvene 16 by dissolving it in trifluoroacetic acid
or trifluoromethanesulfonic acid at low temperatures, how-
ever, simply resulted in polymerization of 16. Although
fusion of the COT moiety causes batho- and hyperchromic
effects in the absorption spectra of these new fulvenes, their
properties are essentially consistent with those of the corre-
sponding pentafulvenes.
1
matic anions also show solvent effects in H NMR spectra
under similar conditions, but the variations of the signals
range within Æ0.2 ppm.[17] To the best of our knowledge,
only a few poly-, di-, and tetranions of macrocyclic annu-
lenes[18] or polycyclic compounds[19,20] show such large sol-
vent effects (Dd>1 ppm). Thus, anion 1 is the first example
of a monoanion to exhibit such behavior. The pronounced
sensitivity is probably due to the delicate counterbalance be-
tween local aromatic and peripheral antiaromatic character
of the anion.
Cycloocta[a]azulene 18
Anion 1 was subjected to the Hafner azulene synthesis by
using bisimmonium salt 19 to afford the corresponding azu-
lene derivative 18.[27] The extended fulvene 20 formed inter-
mediately as a dark reddish purple solution. Because 20 was
sensitive to oxygen, the next reaction was conducted without
chromatographic purification. A brief aqueous workup was
performed, however, to quench the excess potassium hy-
dride; without this quenching procedure the yield of 18 de-
creased drastically. Heating 20 at 2208C in quinoline gave
cycloocta[a]azulene (18) as a deep greenish solid, together
with 2-phenylazulene (21)[28] and a trace amount of azulene
(22). When pure 18 was heated at 2208C in quinoline, com-
pounds 21 and 22 were not obtained. Scheme 4 outlines
pathways that could account for the formation of 18, 21, and
22. One factor that makes it difficult to formulate a mecha-
nism for the formation of azulene is that the oxidation state
of azulene is different from that of 18 and 21; these two hy-
drocarbons can be formed by the loss of HNMe2, whereas
22 and benzene (which is most likely to be the other by-
product) cannot be formed that way. There are not enough
hydrogen atoms left to form azulene and benzene if nitro-
Reactions of the Bicyclo
ACHTUNGTRNE[NUNG 6.3.0]undecapentaenide Ion with
Various Electrophiles
Fulvenes
Undecafulvene derivatives (11-methylideneundeca-1,3,5,7,9-
pentaene) are the next higher homologs of heptafulvene be-
cause the undecapentaenyl cation is a peripherally aromatic
10 p-electron system. For example, the methano[11]annulen-
yl cation is a stable aromatic compound.[21] On the other
hand, the bicycloACHTUNGTRENNUNG[6.3.0]undecapentaenyl cation, which is
a [4n]annuleno[4n]annulene, has not been well characterized
so far.[7] High reactivity would be expected for the four p-
electron cyclopentadienyl cation subunit.[7,22] If the contribu-
tion of the antiaromatic cyclopentadienyl cation emerges
stronger than that of aromatic peripheral undecapentaenyl
cation, these bicyclic undecafulvenes should exhibit charac-
teristics similar to those of pentafulvenes.
Reactions of cyclopentadienyl anion 3 with acetone and
with dimethylformamide (DMF)/dimethyl sulfate (Vilsmei-
er) complex afford 6,6-dimethyl- and 6-N,N-dimethylamino-
Chem. Asian J. 2014, 9, 893 – 900
896
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Lawrence T. Scott, Takeshi Kawase et al.
tropic effect of the azulene
moiety presumably accounts for
the exceptionally low magnetic
field resonances of the 1- and 6-
protons (dꢀ6.70 ppm). The
degree of variation in the chem-
ical shifts of the eight-mem-
bered ring protons is not as
large as those of the azulene
protons of 18. In agreement
with the general character of
other
macrocyclic
[4n]annulenoAHCTUNGTREG[NNUN 4n+2]annulenes,
the chemical shifts of protons
on the 4np ring are not as sensi-
tive to fusion of a (4n+2)p ring
system.[32]
10-DiazobicycloACTHNUTRGNEUGN[6.3.0]undeca-
1(11),2,4,6,8-pentaene 23
Diazocyclopentadiene 14 is
known as an inordinately stable
diazo compound.[33] Treatment
of 1 with p-toluenesulfonyla-
zide[34] in the presence of dieth-
ylamine affords the relatively
stable diazo compound 23 in
30% yield, together with
a small amount of the 9-diazo
compound 24. Compound 23
can be purified by column chro-
matography on silica gel and is
obtained as a dark reddish oil.
On the other hand, compound
24 is labile and gradually de-
composes during column chro-
Scheme 4. Preparation of cycloocta[a]azulene 18 and a proposed mechanism for the formation of 2-phenylazu-
lene 21 and azulene 22.
gen is lost as HNMe2. We propose loss of the nitrogen sub-
matography on silica gel, even at 08C. Consequently, com-
pound 24 has not yet been obtained as a pure sample. IR
spectra of 23 and 24 exhibit characteristic absorptions of
diazo groups at n˜ =2075 and 2085 cmÀ1, respectively. The
chemical shift of the ipso carbon of 23 is observed at d=
À
stituent as Me N=CH2, with addition of a hydrogen atom to
the hydrocarbon, rather than loss of a hydrogen atom. The
final step in this mechanism ([2+2] cycloreversion to form
two aromatic rings) is precedented in the known facile ther-
mal fragmentation of the benzene [2+2] dimer into two
molecules of benzene.[29]
Azulene derivatives exhibit a characteristic weak but
long-wavelength absorption band that arises from an intra-
molecular charge-transfer transition.[30] The long-wavelength
absorption band of 18 appears in the l=600–750 nm range
(Figure S5 in the Supporting Information). Fusion of the
COT moiety causes a bathochromic shift of about 50 nm.
The NMR spectroscopy assignments of 18, together with
those of azulene (22),[31] are shown in Figure 4. The chemical
shifts of the seven- and five-membered ring protons of 18
appear at 0.25 (average) and 0.96 ppm higher magnetic
fields than those of the corresponding protons of 22. These
relatively large upfield shifts are contrary to those of benzo-
COT 4.[4] The eight-membered ring protons of 18 are ob-
served at lower magnetic field than those of 4; the aniso-
Figure 4. 1H NMR chemical shifts of azulenes 18 and 22 and benzoCOT 4
in CDCl3.
Chem. Asian J. 2014, 9, 893 – 900
897
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Lawrence T. Scott, Takeshi Kawase et al.
75.49 ppm. Roberts and co-workers demonstrated that
a plot of the 13C NMR chemical shifts of ipso carbon atoms
against those of the anions of the hydrocarbon atoms, corre-
sponding to replacement of the C=N2 group by CH2, showed
a linear correlation (R2 =0.9362; Figure S6 in the Supporting
Information).[35] The values of 23 and 1·Li+ fit this relation-
ship well.
vealed exceptionally large chemical shift changes (Dd>
1 ppm) with temperature. Moreover, the proton chemical
shifts showed drastic changes as a function of solvent
([D8]THF versus [D6]DMSO), even at ambient temperature.
According to previous studies, the large chemical shift
changes could be ascribed to ion-pairing effects, that is, dif-
ferences between solvent-separated and contact ion pairs.
Thus, anion 1 in a contact ion pair (Li+ at ambient tempera-
ture in THF) behaved as an aromatic cyclopentadienide ion
slightly perturbed by the effects of a paramagnetic COT,
whereas 1 in a separated ion pair (Li+ at low temperatures
in THF or ambient temperature in DMSO) was an overall
paratropic species in which the magnetic properties were do-
minated by a 12 p-electron periphery. 13C NMR spectra
showed no evidence for skeletal rearrangement and relative-
ly small variations in the electron densities. A relatively
small conformational change appeared to cause the large
change in the paratropic properties. In addition to its unusu-
al, tunable tropicity, anion 1 could also serve as a versatile
building block for the synthesis of cyclopentanoid conjugat-
ed systems fused to a fully unsaturated eight-membered
ring. A theoretical calculation predicted that the 10-position
of 1 should have had the highest electron density and the re-
actions of 1 with electrophiles did occur predominantly at
the 10-position. Corresponding ferrocene, fulvenes, diazo,
and azulene derivatives were prepared by the reaction of
1 with appropriate electrophiles.
The reaction of 23 with triphenylphosphine gives complex
25, which decomposes on silica gel to yield bicyclo-
ACHTUNGTRENNUNG[6.3.0]undeca-1(11),2,4,6,8-pentaen-10-one hydrazone (26) in
69% yield (Scheme 5).[36] The same hydrazone was also ob-
Scheme 5. Synthesis of the corresponding 10-diazo derivative 23 and hy-
drazone 26 and structures of 9-diazo derivative 24, triphenylphosphine
complex 25, and 10-carbene 27.
tained in 33% yield by reduction of 23 with LiAlH4 in
THF.[22] Irradiation of 23 with a high-pressure mercury lamp
promotes the extrusion of N2 to afford bicyclo
G
Experimental Section
1(11),2,4,6,8-pentaenylidene (27). The characterization of
carbene 27 in an argon matrix has been published previous-
ly.[37] Further chemistry of 23 will be reported in due course.
General
1H and 13C NMR spectra were recorded on Varian XL-100, JNM-FX90Q,
or Bruker-Biospin DRX-500 instruments. Spectra are reported (in d) ref-
erenced to Me4Si. Unless otherwise noted, CDCl3 was used as the sol-
vent. Data are reported as follows: chemical shift, multiplicity (s=singlet,
d=doublet, t=triplet, m=multiplet, br=broad), coupling constant (in
Hz), and integration. IR spectra were observed on Hitachi EPI-G3 or
Jasco FT-IR-3 spectrometers. Electronic spectra were obtained on a Hita-
chi U-3400 instrument and are reported in nanometers (loge; sh=
shoulder). Mass spectral analyses were performed on a JEOL JMS-
O1SG-2 instrument. Only the more intense or structurally diagnostic
mass spectral fragment ion peaks are reported. Melting points were de-
termined on a Mettler FP-2 apparatus and are uncorrected. Column
chromatography was carried out on Merck silica gel 60, 70–230 mesh
ASTM, or neutral alumina activity II-III, 70–230 mesh ASTM.
Bis(cyclooctatetraenocyclopentadienyl)iron 28
The corresponding ferrocene derivative was obtained in
59% yield from 1 and FeCl2 by means of the standard pro-
cedure.[38] Ferrocene 28 is com-
posed of thermally labile orange
crystals. It decomposes at
around 808C and on silica gel at
room temperature; chromato-
graphic purification was per-
formed at 08C. The coupling
constant of JACTHNUTRGNE(NUG 3,4) determined by
All solvents were dried by conventional procedures. Reactions involving
air-sensitive reagents were carried out under nitrogen or argon atmos-
pheres.
computer simulation is 5.0 Hz. The value is intermediate be-
tween those of 1 and 4. Thus, the depth of the tub-shaped
structure of 28 appears to be intermediate between that of
1 and 4.
NMR Spectral Measurements of BicycloACTHNUGTRNEUNG[6.3.0]undecapentaenyl Anion
1 in [D8]THF
Solutions of 8 (15 mg) in [D8]THF (0.1 dm3) were added to solutions of
LHMDS (15 mg) or a suspension of NaH (15 mg) or KH (15 mg) in
[D8]THF (0.2 dm3) in NMR spectroscopy tubes (i.d. =5 mm) at À508C
under argon. The tubes were capped with rubber septa and shaken for
a few minutes to give deep-purple solutions. The resulting samples were
examined by NMR spectroscopy measurements.
Conclusion
The title anion 1 was obtained as a thermally fairly stable
species in THF and DMSO by treatments of bicyclo-
NMR Spectral Measurements of 1 in [D6]DMSO
ACHTUNGTRENNUNG[6.3.0]undecapentaenes 8 and 9 with appropriate bases. Vari-
LHMDS (15 mg), NaH (15 mg), and KH (15 mg) were dissolved in
1
able-temperature H NMR spectra of 1·Li+ in [D8]THF re-
[D6]DMSO (0.2 dm3) in NMR spectroscopy tubes (i.d.=5 mm) at room
Chem. Asian J. 2014, 9, 893 – 900
898
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Lawrence T. Scott, Takeshi Kawase et al.
temperature under argon. The solutions were heated at 60–708C for
a few minutes to give solutions of dimsyl anion. A solution of 8 (15 mg)
in [D6]DMSO (0.1 dm3) was added to each solution. After being purged
with argon, the tubes were capped with rubber septa and shaken for
a few minutes to give deep-purple solutions. The resulting samples were
examined by NMR spectroscopy measurements.
from elution with hexane as deep-green needles, 21 (51 mg, 9%) from
elution with hexane/CH2Cl2 (98:2), and 18 (247 mg, 44%) from elution
with hexane/CH2Cl2 (90:10). M.p. 85.0–86.08C; MS (EI) m/z (%): 204
[M]+, 203 (68), 202 (53), 178 (86); IR (KBr): n˜ =3000 (w), 1633 (w), 1575
(m), 1488 (m), 664 cmÀ1 (m); UV/Vis (cyclohexane) (loge): lmax =296
(4.44), 307 (4.45), 332 sh (4.40), 396 (3.55), 620 (2.45), 667 sh (2.41),
730 nm sh (2.00); 1H NMR (500 MHz, CDCl3): d=5.70 (dd, J=4.4,
12.1 Hz, 1H), 5.75 (dd, J=4.3, 12.2 Hz, 1H), 6.08–6.12 (m, 2H), 6.75 (d,
J=12.2 Hz, 1H), 6.80 (d, J=12.1 Hz, 1H), 6.97 (s, 1H), 7.00 (t, J=
9.5 Hz, 1H), 7.02 (t, J=9.5 Hz, 1H), 7.41 (t, J=9.5 Hz, 1H), 7.94 (d, J=
9.5 Hz, 1H), 8.04 ppm (d, J=9.5 Hz, 1H); 13C NMR (125.8 MHz,
CDCl3): d=119.0, 123.5, 124.3, 124.9, 127.3, 129.9, 130.9, 131.6, 132.4,
132.7, 134.0, 136.0, 137.2, 138.6, 142.5, 149.6 ppm; elemental analysis
calcd (%) for C16H12: C 94.08, H 5.92; found: C 93.93, H 5.90.
10-(Isopropylidene)bicycloACTHNUGRTNEUNG[6.3.0]undeca-1(11),2,4,6,8-pentaen-10-ylidene
(16)
nBuLi (1.5 dm3, 1.6 molLÀ1, 2.4 mmol) was added at À788C under Ar to
a solution of diisopropylamine (0.35 dm3) in THF (10 dm3). The mixture
was allowed to warm to 08C in an ice bath and stirred for 30 min at that
temperature. A solution of pentaene 8 (320 mg, 2.25 mmol) in THF
(4 dm3) was added to the resulting LDA solution. The dark-purple reac-
tion mixture was stirred at 08C for 30 min and acetone (5 dm3) was then
added. The purple color of the solution immediately turned to orange.
After being stirred for 30 min, the mixture was diluted with hexane
(10 dm3) and quenched with water. The organic layer was separated,
washed with brine, and dried over anhydrous MgSO4. The solvent was
evaporated under reduced pressure. The residue was charged on silica gel
and purified by column chromatography (hexane/CH2Cl2 (98:2) as the
eluent) to give 16 (230 mg, 57%) as red needles (from hexane). M.p.
75.0–75.88C; IR (KBr): n˜ =2980 (w), 1635 (m), 1615 (m), 853 (s), 698 (s),
485 cmÀ1 (s); UV/Vis (cyclohexane) (loge): lmax =232 sh (3.83), 289
(4.52), 300 (4.73), 312 (4.73), 376 (3.52), 397 (3.54), 421 (3.56), 449 (3.53),
485 nm (3.30); 1H NMR (100 MHz, CDCl3): d=2.07 (s, 3H), 5.65–5.80
(m, 4H), 6.35 (brd, 2H), 6.56 ppm (s, 2H); 13C NMR (22.5 MHz, CDCl3):
d=22.3, 123.4, 125.0, 126.3, 131.4, 138.7, 141.4, 144.0 ppm; elemental
analysis calcd (%) for C14H14: C 92.26, H 7.74; found: C 92.10, H 7.74.
10-DiazobicycloACTHNUTRGNEU[GN 6.3.0]undeca-1(11),2,4,6,8-pentaene (23)
Diethylamine (1.5 dm3) was added to a mixture of pentaene 8 (740 mg,
5.2 mmol) and TsN3 (2.0 g) in THF (15 dm3) in an ice bath under Ar. The
mixture was stirred for 3 h, diluted with hexane (20 dm3), and quenched
with water. The organic layer was separated, washed with a 10% aqueous
solution of NaOH, water, and brine; and dried over anhydrous MgSO4.
The solvent was evaporated under reduced pressure. The residue was
charged on silica gel and purified by column chromatography (hexane as
the eluent) to give recovered pentaene (277 mg), 24 (95 mg, 11%), and
23 (230 mg, 26%) as an orange oil. 23: MS (EI) m/z (%): 164 [M]+ (42),
140 (56), 139 (100); IR (KBr): n˜ =3000 (m), 2075 (s), 1480 (m), 1352 (m),
816 cmÀ1 (m); UV/Vis (CH3CN) (loge): lmax =225 (4.01), 290 (4.33),
353 nm (3.94); 1H NMR (100 MHz, CDCl3): d=5.50–5.60 (m, 2H), 5.68
(m, 2H), 6.15 (d, J=12.0 Hz, 2H), 6.41 ppm (s, 2H); 13C NMR
(22.5 MHz, CDCl3): d=75.5, 120.2, 127.7, 127. 8, 127.9, 130.3 ppm. 24:
Orange oil; IR (KBr): n˜ =3000 (m), 2942 (w), 2085 (s), 1300 (m),
650 cmÀ1 (w); 1H NMR (100 MHz, CDCl3): d=5.55~6.20 (m, 7H), (5.67,
(d, J=4.5 Hz, 1H)), 6.75 ppm (d, J=4.5 Hz, 1H).
10-(N,N-Dimethylaminomethylidene)bicycloACTHNUTRGNEU[GN 6.3.0]undeca-1(11),2,4,6,8-
pentaen-10-ylidene (17)
A mixture of DMF (0.8 g) and dimethylsulfate (1.3 g) was heated at
608C for 3 h to prepare the Vilsmeier complex (10 mmol). A solution of
pentaene 8 (670 mg, 4.7 mmol) in THF (5 dm3) was added to a solution
of LDA prepared from diisopropylamine (0.75 dm3) and nBuLi (3.2 dm3,
1.6 molLÀ1, 2.4 mmol) in THF (20 dm3) at À788C under Ar. The mixture
was stirred for 30 min. The Vilsmeier complex (10 mmol) was added to
the solution of the anion and the mixture was stirred for 2 h. The solution
was then diluted with toluene (20 dm3). The organic layer was separated,
washed with brine, and dried over anhydrous MgSO4. The solvent was
evaporated under reduced pressure. The residue was charged on silica gel
and purified by column chromatography (hexane/AcOEt (1:1) as the
eluent) at 08C to give 17 (345 mg, 48%) as red needles. M.p. 158.0–
159.08C; MS (EI) m/z (%): 197 (100) [M]+, 182 (17) [MÀ15]+, 171 (50);
IR (KBr): n˜ =2980 (w), 1610 (vs), 1368 (s), 1250 (m), 965 cmÀ1 (m); UV/
Vis (CH3CN) (loge): lmax =262 (3.89), 337 (4.64), 390 sh (4.08), 470 nm
sh (3.51); 1H NMR (100 MHz, CDCl3): d=3.17 (s, 6H), 5.35–5.55 (m,
4H), 6.05–6.20 (m, 3H), 6.30 (m, 1H), 6.75 ppm (s, 1H); elemental analy-
sis calcd (%) for C14H15N: C 85.24, H 7.66, N 7.10; found: C 85.10, H
7.69, N 6.98.
BicycloACTHUNRTGNEUNG[6.3.0]undeca-1(11),2,4,6,8-pentaen-10-one Hydrazone (26)
Triphenylphosphine (250 mg, 1 mmol) was added to a solution of 23
(178 mg, 1 mmol) in CH2Cl2 (5 dm3) at room temperature. The solvent
was evaporated under reduced pressure. The residue was charged on
silica gel and purified by column chromatography (toluene/ether (99:1)
as the eluent) to give hydrazone 26 (120 mg, 69%) as dark-red needles.
M.p. 116.8–117.28C; MS (EI) m/z (%): 170 (100) [M]+, 154 (91), 139
(42); IR (KBr): n˜ =3450 (m), 3310 (m), 1560 (s), 1385 (s), 1095 cmÀ1 (s);
UV/Vis (CH3CN) (loge): lmax =295 sh (4.56), 326 (4.78), 404 sh (3.71),
1
425 (3.72), 450 sh (3.70), 480 nm (3.56); H NMR (100 MHz, CDCl3): d=
5.85–6.40 (m, 6H), 6.44 (s, 2H), 6.45–6.60 ppm (m, 2H) ; elemental anal-
ysis calcd (%) for C11H10N2: C 77.49, H 5.84, N 16.33; found: C 77.62, H
5.92, N 16.46.
Alternative Route to Hydrazone 26
Compound 23 (190 mg, 1.1 mmol) was added to a suspension of LiAlH4
(100 mg) in diethyl ether (6 dm3) in an ice bath under Ar. The mixture
was stirred for 1.5 h at 08C, quenched with water (0.5 dm3), and stirred
for another 1.5 h. Anhydrous MgSO4 was then added to the mixture. The
solid was filtered and the filtrate was condensed under reduced pressure.
The residue was charged onto silica gel and purified by column chroma-
tography (toluene/ether (99:1) as the eluent) to give hydrazone 26
(63 mg, 33%).
Cycloocta[a]azulene 18
Pentaene
8 (510 mg, 3.5 mmol) was added to a suspension of KH
(300 mg, 7.5 mmol) in THF (2 dm3) in an ice bath under Ar. After vigo-
rous foaming, the resulting purple reaction mixture was diluted with
THF (6 dm3). The mixture was stirred for 30 min in an ice bath and
cooled to À508C. Immonium salt 19 (700 mg, 2.8 mmol) was added to
the reaction mixture. The mixture was allowed to warm to room temper-
ature and was stirred for 30 min. The color of the solution turned to dark
reddish purple. The mixture was cooled to 08C and quenched with water
(0.5 dm3). After vigorous foaming, quinoline (25 dm3) was added. The
mixture was heated at 2208C for 2 h and then cooled to room tempera-
ture. The mixture was diluted with hexane. The organic layer was washed
with hydrochloric acid (20 mL, 2 molLÀ1) three times, water, and brine.
The separated organic layer was dried over anhydrous MgSO4 and the
solvent was evaporated under reduced pressure. The residue was charged
on silica gel and purified by column chromatography to give 22 (10 mg)
Bis(1,8,9,10,11-h5-bicyclo
ACTHNUTRGNEU[GN 6.3.0]undecapentaenyl)iron (28)
A suspension of anhydrous FeCl3 (1 g) and iron powder (100 mg) in THF
(30 dm3) was heated at reflux for 4 h to prepare a solution of FeCl2 in
THF. Pentaene 8 (1.0 g, 11.7 mmol) was added to a suspension of KH
(1.0 g, 25 mmol) in THF (0.5 dm3) in an ice bath under Ar. After vigo-
rous foaming, the purple reaction mixture was diluted with THF (5 dm3).
The mixture was stirred at 08C for 30 min to prepare the solution of
anion 1. The resulting solution was added dropwise to the solution of
FeCl2 in THF by using a syringe. The mixture was heated at reflux for
2 h under Ar, cooled to room temperature, and diluted with hexane. The
Chem. Asian J. 2014, 9, 893 – 900
899
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Lawrence T. Scott, Takeshi Kawase et al.
organic layer was then separated, washed with water and brine, and dried
over anhydrous MgSO4. The solvent was evaporated under reduced pres-
sure. The residue was charged onto charged onto silica gel and purified
by column chromatography (hexane) to give recovered 8 (240 mg) and
ferrocene 28 (851 mg, 59%) as orange plates. M.p. 808C (decomp);
1H NMR (100 MHz, CDCl3): d=4.09 (d, J=2.6 Hz, 2H), 4.44 (t, J=
2.6 Hz, 1H), 5.55 (m, J=3.1, 1.6 Hz, 2H), 5.84 (m, J=11.5, 3.1, 1.6 Hz,
2H), 6.20 ppm (d, J=11.5 Hz, 2H); 13C NMR (22.5 MHz, CDCl3): d=
74.1 (two signals overlapped), 82.2, 127.9 (two signals overlapped),
129.0 ppm; IR (KBr): n˜ =1628 (brs), 1212 (m), 830 (s), 799 (s), 664 cmÀ1
(s); UV/Vis (cyclohexane) (loge): lmax =260 (4.35), 289 (4.20), 385 sh
(3.40), 455 nm sh (3.14); elemental analysis calcd (%) for C22H18Fe: C
78.28, H 5.38, found: C 78.12, H 5.36.
[10] L. T. Scott, W. R. Brunsvold, J. Am. Chem. Soc. 1978, 100, 6535–
6536.
[11] D. Schçnleber, Chem. Ber. 1969, 102, 1789–1801.
[12] D. H. OꢂBrien, C. R. Russell, A. J. Hart, J. Am. Chem. Soc. 1976, 98,
7427–7429.
[13] a) M. Szwarc, Ions and Ion Pairs in Organic Reactions, Wiley, New
York, 1974; E. Buncel, B. Menon in Comprehensive Carbanion
Chemistry, Part 1 (Eds.: E. Buncel, T.Durst), Elsevier, Amsterdam,
1980, p. 97; b) C. Reichardt, Solvents and Solvent Effects in Organic
Chemistry, VCH, Weinheim, 1988.
[14] R. E. Hoffman, E. Shabtai, M. Rabinovitz, V. S. Iyer, K. Mꢁllen„
A. K. Rai, E. Bayrd, L. T. Scott, J. Chem. Soc. Perkin Trans. 2 1998,
1659–1664.
[15] R. J. Hunadi, J. Am. Chem. Soc. 1983, 105, 6889–6895.
[16] M. J. Minch, Concepts Magn. Reson. 1994, 6, 41–56.
[17] C. Gooijer, N. H. Velthorst, Org. Magn. Reson. 1979, 12, 684–686.
[18] K. Mꢁllen, W. Huber, T. Meul, N. Nakagawa, M. Iyoda, Tetrahedron
1983, 39, 1575–1581.
Acknowledgements
[19] T. Sternfeld, M. Rabinovitz in Carbon-Rich Compounds (Eds.:
M. M. Haley, R. R. Tykwinsky), Wiley-VCH, Weinheim, 2006,
p. 566.
[20] A. Ayalon, A. Sygula, P.-C. Cheng, M. Rabinovitz, P. W. Rabideau,
L. T. Scott, Science 1994, 265, 1065–1067; N. Treitel, T. Sheradsky,
L. Peng, L. T. Scott, M. Rabinovitz, Angew. Chem. 2006, 118, 3351–
3355; Angew. Chem. Int. Ed. 2006, 45, 3273–3277.
[21] W. Grimme, H. Hoffmann, E. Vogel, Angew. Chem. 1965, 77, 348–
349.
[22] R. Breslow in Topic in Nonbenzenoid Aromatic Chemistry, Vol. I
(Eds.: T. Nozoe, R. Bresolow, K. Hafner, S. Ito, I. Murata), Hiroka-
wa Publishing, Tokyo, 1973, p. 81.
[23] J. Thiele, Ber. Dtsch. Chem. Ges. 1900, 33, 666.
[24] J. Becker, C. Wentrup, K.-P. Zeller, E. Katz, J. Am. Chem. Soc.
1980, 102, 5110–5112.
T.K. and C.K. were supported by a Grant-in-Aid for Scientific Research
on Innovative Areas (no. 21108520, 21108521, and 23108720, “p-Space”)
from the Ministry of Education, Culture, Sports, Science and Technology,
Japan. L. T. S thanks the US National Science Foundation and Depart-
ment of Energy for financial support of this work.
[1] M. Nakagawa, The Chemistry of Annulenes: From the Standpoint of
Organic Chemistry, Osaka University Press, Suita, Japan, 1996; E. L.
Spitler, C. A. Johnson II, M. M. Haley, Chem. Rev. 2006, 106, 5344–
5386.
[2] a) R. Breslow, J. Napierski, T. C. Clarke, J. Am. Chem. Soc. 1975, 97,
6275–6276; b) F. A. Kaplan, B. W. Roberts, J. Am. Chem. Soc. 1977,
99, 513, 518–522.
[3] a) G. Wittig, H. Eggers, P. Duffner, Liebigs Ann. Chem. 1958, 619,
10–27; b) H. P. Figeys, A. Dralants, Tetrahedron Lett. 1971, 12,
3901–3904; c) G. W. Buchanan, A. R. McCarvilie, Can. J. Chem.
1973, 51, 177–182.
[25] M. Oda, Y. Kitahara, J. Chem. Soc. D 1969, 352a.
[26] L. Knothe, D. Forster, H. Achenbach, H. Friebolin, H. Printzbach,
Tetrahedron Lett. 1970, 11, 3075–3078.
[27] a) K. Ziegler, K. Hafner, Angew. Chem. 1955, 67, 301; b) K. Hafner,
Angew. Chem. 1955, 67, 301–302; c) K. Hafner, Liebigs Ann. Chem.
1957, 606, 79–87.
[4] L. A. Paquette, G. D. Ewing, S. Traynor, J. M. Gardlik, J. Am.
Chem. Soc. 1977, 99, 6115–6117.
[5] For theoretical treatments of [4n]annulenoACTHNUGRTENUNG[4n+2]annulenes,
[28] A. D. Jones, T. D. Alger, D. M. Grant, W. M. Litchman, J. Am.
Chem. Soc. 1970, 92, 2386–2394.
see:a) R. C. Haddon, J. Am. Chem. Soc. 1979, 101, 1722–1728; b) J.
Aihara, J. Am. Chem. Soc. 1981, 103, 5704–5706.
[29] H. Rçttele, W. Martin, J. F. M. Oth, G. Schroder, Chem. Ber. 1969,
102, 3985–3995; N. C. Yang, T. Noh, H. Can, S. Halfon, B. J. Hrnjez,
J. Am. Chem. Soc. 1988, 110, 5919–5920; H. Gan, M. G. Horner,
B. J. Hrnjez, T. A. McCormack, J. L. King, Z. Gasyna, G. Chen, R.
Gleiter, N. C. Yang, J. Am. Chem. Soc. 2000, 122, 12098–12111.
[30] H. Mçllerstedt, M. C. Piqueras, R. Crespo, H. Ottosson, J. Am.
Chem. Soc. 2004, 126, 13938–13939; W. C. Patalinghug, M. Chang, J.
Solis, J. Chem. Educ. 2007, 84, 1945.
[31] Y. N. Porshnev, E. M. Tereshchenko, V. A. Churkina, Z. Org. Chim.
1974, 10, 881.
[32] Y. Yoshikawa, M. Iyoda, M. Nakagawa, S. Nakatsuji, S. Akiyama,
Tetrahedron Lett. 1981, 22, 5209–5212.
[33] W. von E. Doering, C. H. Depuy, J. Am. Chem. Soc. 1953, 75, 5955–
5957.
[34] M. Regitz, J. Hocker, A. Leidhegener, Organic Syntheses Collective,
Vol. V (Ed.: H. E. Baumgarten), Wiley, New York, 1964, p. 179.
[35] R. O. Duthaler, H. G. Forster, J. D. Roberts, J. Am. Chem. Soc.
1978, 100, 4974–4979.
[36] F. Ramirez, S. Levy, J. Org. Chem. 1958, 23, 2036–2037.
[37] S. Murata, H. Tomioka, T. Kawase, M. Oda, J. Org. Chem. 1990, 55,
4502–4504.
[6] R. Breslow, W. Horspool, H. Sugiyama, W. Vital, J. Am. Chem. Soc.
1966, 88, 3677–3678.
[7] H. Dꢁrr, G. Scheppers, Tetrahedron Lett. 1968, 9, 6059–6062.
[8] Gaussian 03, Revison D.01, M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgom-
ery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S.
Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani,
N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J.
Dannenberg, G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C.
Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cio-
slowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaro-
mi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng,
A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.
Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian, Inc., Pitts-
burgh, PA, 2003.
[38] R. B. King, Organometallic Syntheses, Vol. 1, Academic Press, New
York, 1965, p. 73.
[9] We also performed a theoretical calculation for the optimized struc-
ture of the anion by using DFT methods (MP2/6-31+G(d)revel)
with the Spartan software or Gaussian 03. The calculations predicted
that the anion possessed a more flattened structure than the predict-
ed one by the PM3 calculation.
Received: September 26, 2013
Published online: December 2, 2013
Chem. Asian J. 2014, 9, 893 – 900
900
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim