Biphenalenylidene: Isolation and Characterization of the Reactive Intermediate on the Decomposition Pathway of Phenalenyl Radical

Article abstract of DOI:10.1021/jacs.5b13033

First isolation and characterization of biphenalenylidenes, which have long been unidentified reactive intermediates on the decomposition pathway of phenalenyl radical, were accomplished. Photoinduced electrocyclic ring-opening reaction of anti-dihydroperopyrene resulted in a successful conversion to E-biphenalenylidene, which enabled a detailed investigation of the electronic structure of E-biphenalenylidene by means of spectroscopic techniques. A stereoisomer, Z-biphenalenylidene, was also observed by suppressing a facile E-Z isomerization to E-biphenalenylidene in a rigid matrix. Furthermore, Z-biphenalenylidene demonstrated a thermal ring-closure in conrotatory process, which is not conforming to the Woodward-Hoffmann rule. These unusual reactivities of biphenalenylidene are ascribed to the ground states destabilized by its singlet biradical character, which was fully supported by theoretical calculations. The presence of E-biphenalenylidene on the decomposition pathway of phenalenyl was confirmed experimentally, leading to the full understanding of the decomposition mechanism of phenalenyl.

Full text of DOI:10.1021/jacs.5b13033

Article
pubs.acs.org/JACS
Biphenalenylidene: Isolation and Characterization of the Reactive
Intermediate on the Decomposition Pathway of Phenalenyl Radical
†
‡
,‡
,§
,†
Kazuyuki Uchida, Soichi Ito, Masayoshi Nakano,* Manabu Abe,* and Takashi Kubo*
†
Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
‡
Department of Materials Engineering and Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka
5
60-8531, Japan
§
Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima
739-8526, Japan
*
S Supporting Information
ABSTRACT: First isolation and characterization of biphena-
lenylidenes, which have long been unidentified reactive
intermediates on the decomposition pathway of phenalenyl
radical, were accomplished. Photoinduced electrocyclic ring-
opening reaction of anti-dihydroperopyrene resulted in a
successful conversion to E-biphenalenylidene, which enabled a
detailed investigation of the electronic structure of E-
biphenalenylidene by means of spectroscopic techniques. A
stereoisomer, Z-biphenalenylidene, was also observed by
suppressing a facile E−Z isomerization to E-biphenalenylidene
in a rigid matrix. Furthermore, Z-biphenalenylidene demon-
strated a thermal ring-closure in conrotatory process, which is
not conforming to the Woodward−Hoffmann rule. These
unusual reactivities of biphenalenylidene are ascribed to the ground states destabilized by its singlet biradical character, which was
fully supported by theoretical calculations. The presence of E-biphenalenylidene on the decomposition pathway of phenalenyl
was confirmed experimentally, leading to the full understanding of the decomposition mechanism of phenalenyl.
INTRODUCTION
unsuccessful. In 2003, an experimental attempt was demon-
17
■
strated by Agranat et al. to synthesize 2 directly.
Phenalenyl is an odd-alternant hydrocarbon radical stabilized
thermodynamically by the delocalization of an unpaired
electron over six α carbon atoms, and has attracted much
interest due to its fascinating solid state properties
unique self-association behaviors.
lenyl radicals in solid state was accomplished by introducing
tert-butyl groups at three β carbon atoms. The steric
Desulfurization followed by dimerization of phenalenethione
afforded a green product that shows a broad absorption band at
647 nm in the electronic absorption spectrum. Unfortunately,
the rapid decomposition into 4 prevented the detailed
characterization and isolation of the colored species. To detect
and characterize the intermediates, a moderate synthetic
approach is required.
We here present the first isolation and characterization of
E,Z-2 in solution state. Successful preparation of E,Z-2 was
accomplished by a photoinduced electrocyclic ring-opening
reaction of a RR/SS form of 3 (anti-3) synthesized efficiently
from a phenalene derivative. Clean conversion of anti-3 to E,Z-
1
2
−4
and
5
−8
First isolation of phena-
9
protection by substituted groups improved the kinetic stability,
leading to a successful isolation and characterization in solution
1
0,11
and solid state.
Various phenalenyl derivatives with steric
and electronic perturbations have been synthesized and
7
,8,12,13
isolated.
Nevertheless, the parent phenalenyl (1) has
not yet been isolated because of the kinetic instability resulting
in a facile decomposition. Early attempts to synthesize 1 were
reported in 1950s. Although preparation from several
precursors gave blue or green products including 1,
isolation was unsuccessful due to the rapid conversion into a
decomposed product. The decomposed product was doubt-
lessly assigned to peropyrene (4),
generated by the dehydrogenation of 1 σ-dimer. The product
analysis suggested that E- and Z-biphenalenylidene (E,Z-2) and
dihydroperopyrene (3) should be the reactive intermediates on
the decomposition pathway of 1 (Scheme 1), whereas
experimental detection of these compounds has long been
2
enabled us to estimate the intriguing electronic structures,
including the contribution of singlet biradical character, on the
basis of spectroscopic techniques. Moreover, the unusual
reactivity, which was ascribed to the singlet biradical characters
of E,Z-2, was fully investigated experimentally and theoretically.
Finally, the decomposition mechanism of 1 in the presence of
an oxidizing reagent was unambiguously clarified by detecting
E-2 directly on the decomposition pathway.
1
4−16
the
1
5,16
which would be
2
Received: December 24, 2015
©
XXXX American Chemical Society
A
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17
Scheme 1. Proposed Mechanism of the Decomposition Pathway of 1
RESULTS
Single crystals of 3 were grown by slow evaporation of a
chloroform/hexane solution under argon atmosphere to
elucidate the molecular geometry by X-ray crystallographic
analysis. Although the geometry obtained includes a structural
ambiguity around the sp carbon atoms due to the disordered
alignment of 3 RR and SS isomers in crystalline state, the planar
■
Synthesis of Dihydroperopyrene (3). Dehydrogenation
of phenalene derivatives is an effective way to synthesize the
corresponding phenalenyl radicals in mild conditions. The key
precursor, biphenalene 11, was obtained according to the
synthetic scheme displayed in Scheme 2. Dibromobinaphtha-
lene 6 prepared from binaphthalene 5 was converted into the
unsaturated ester 7 by the Heck reaction. Hydrogenation of C−
C double bonds and subsequent hydrolysis in basic condition
gave the carboxylic acid 9, and then Friedel−Crafts cyclization
of the acyl chloride derived from 9 afforded biphenalanone 10
in remarkable yield. Reduction followed by dehydration gave
biphenalene 11. Treatment of 11 with an equimolar p-chloranil
under nitrogen atmosphere gave a deep blue solution in the
early stage of the reaction, and subsequent stirring in the dark
resulted in a gradual color change from deep blue to greenish
yellow. The product obtained by the dehydrogenation showed
3
molecular backbone corroborates the anti-configuration of 3
1
(
Figure S2 in Supporting Information). H NMR spectrum
may support this assignment. As shown in Figure 1, 3 gave a
simple spectrum arising from a single diastereomer with
magnetically equivalent two phenalenyl sites. The simplicity
1
of H NMR spectrum evokes two possibilities: (1) 3 obtained
adopts the anti-configuration with C symmetry, (2) 3 adopting
2
the syn-configuration gives an averaged spectrum due to the
dynamic equilibrium between stable C conformations. To
1
exclude the possibility of the dynamic equilibrium, variable
1
temperature (VT) H NMR was conducted within the
1
a well-resolved H NMR spectrum as shown in Figure 1. A
temperature range from 298 to 183 K. 3 showed no signal
splitting even at 183 K, inferring that 3 adopts the anti-
characteristic singlet peak that appeared at 4.4 ppm was
assignable to benzyl protons on the phenalene scaffold, and the
product was unambiguously characterized to 3 on the basis of
D-NMR techniques as well as the computational prediction of
NMR chemical shifts with a GIAO-B3LYP/6-31G** method
configuration having an essential C geometry. The result is
2
consistent with the computational prediction that 3 adopts the
energetically preferred anti-configuration. However, it should
be noted that the possibility of the dynamic equilibrium was not
strictly excluded. The activation barrier for the conformational
change of syn-3, which was estimated with a broken-symmetry
2
(
Figure S1 in Supporting Information).
Dihydroperopyrene (3) has two possible stereoisomers, a
diastereomeric pair of 3 RR/SS form (anti-3) and 3 RS form
syn-3), originating from two asymmetric carbon atoms at the
central six-membered ring. Molecular geometries of anti-3 and
syn-3 estimated with a B3LYP/6-31G** method were displayed
in Figure 2. Anti-3 adopted an almost planar structure with C2
symmetry; in contrast, syn-3 demonstrated a highly distorted
(
BS) UB3LYP/6-31G** method, was extremely small (2.3 kcal
(
−1
mol ), and thus, an averaged spectrum might be observed
even at 183 K.
Preparation and Characterization of E-Biphenalenyli-
dene (E-2). With a focus on the electronic structure, anti-3 can
be regarded as a 1,3-cyclohexadiene analogue, which is a well-
known scaffold that demonstrates the electrocyclic ring-
opening reaction to afford a cis-1,3,5-hexatriene structure. As
predicted by the Woodward−Hoffmann rule based on the
orbital symmetry considerations, 1,3-cyclohexadiene scaffold
undergoes a photochemically allowed ring-opening reaction in
conrotatory mode; thus, anti-3 would be converted into Z-2 by
the photoirradiation.
conformation with C symmetry. The structural difference
1
between the diastereomers is crucially reflected on the relative
energy; that is, syn-3 with the structural distortion is 11.8 kcal
−1
−1
−1
mol (1 kcal mol = 4.184 kJ mol ) less stable in energy
than anti-3, which is almost identical to that estimated by
Agranat et al. (12.1 kcal mol at B3LYP/6-31G* level). This
computational result suggests that the experimentally obtained
−1
17
3
should adopt the energetically favored anti-configuration.
B
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a
Scheme 2. Synthetic Procedure for 3
expected that an initial product of the photoinduced ring-
opening reaction is Z-2, and therefore, a rapid isomerization
from a metastable Z-2 to energetically favorable E-2 would take
17
place.
1
A progressive signal broadening was observed in H NMR
spectra of E-2 upon raising temperature, and the signals almost
disappeared at 253 K (shown in Figure 4). In general, the signal
broadening is caused by a slow exchange due to molecular
motions. Although E-2 is expected to undergo E−Z isomer-
ization to Z-2 by the rotation about the central double bond
upon increasing temperature, the disappearance of the signals
cannot be accounted for by the molecular motion. On the other
hand, the presence of paramagnetic species, such as metal
impurities and radical species, also induces the signal
broadening. We here focused on the singlet biradical ground
states of E,Z-2 predicted by Agranat et al. on the basis of
17
theoretical calculations. Twisted geometries of 2 arising from
the overcrowding in cove region of E-2 and fjord region of Z-2
result in the decrease of spatial overlap between two unpaired
electrons on phenalenyl sites, leading to the enhancement of
the singlet biradical nature of E- and Z-2. The singlet biradical
species having small energy gaps (ΔES−T) between the singlet
ground state and the excited triplet state are known to show
broad NMR spectra due to the existence of thermally excited
1
8−22
triplet species.
Actually, ΔE values of E-2 and Z-2 were
S−T
estimated by theoretical calculations to be 4887 K (9.7 kcal
mol ) and 2084 K (4.1 kcal mol ), respectively, which are
small enough to demonstrate the signal broadening in H NMR
−1
−1
1
spectra. Thus, the presence of thermally excited triplet species
1
of E,Z-2 resulted in the signal broadening in the H NMR
spectra, corroborating the singlet biradical ground states of E,Z-
2
.
The electrocyclic ring-opening reaction of anti-3 was also
monitored by the electronic absorption measurement. anti-3
showed no characteristic absorption band in visible region,
whereas E-2 generated by photoirradiation showed an intense
absorption band centered at 619 nm (Figure 5). This result is
fairly consistent with the computational prediction by a time-
dependent (TD) UB3LYP(BS)/6-31G** calculation that the
HOMO−LUMO transition of E-2 is located at 720 nm (f =
a
Reagent and condition: (a) bromine, CHCl , 0 °C, 64% yield; (b)
3
n
methyl acrylate, Pd(OAc) , PPh , K CO , Bu NBr, DMF, 80 °C, 93%
2
3
2
3
4
yield; (c) H (1 atm), 10% Pd−C, DCM/AcOEt (1/9), RT, 88%
2
0
.384). Notably, Z-2 is expected to show its HOMO−LUMO
yield; (d) 10% NaOH(aq), EtOH, 90 °C, 94% yield; (e) (i) (COCl) ,
2
transition at 859 nm (f = 0.106); however, the absorption band
corresponding to Z-2 was not observed in the electronic
absorption spectrum because of the rapid isomerization to E-2.
Direct Observation of Z-Biphenalenylidene (Z-2). Z-2,
which is the key intermediate on the photoinduced ring-
opening process, was observed directly by suppressing the
rotation about the central double bond. The electronic
absorption spectrum was monitored in a glassy 2-methylte-
trahydrofuran (MTHF) matrix at 98 K. Irradiation of UV light
(355 nm) to anti-3 in a rigid matrix of MTHF resulted in the
appearance of a broad absorption band centered at 700 nm
(Figure 6a), which is assignable to the HOMO−LUMO
transition of Z-2 on the basis of a TD-UB3LYP(BS)/6-31G**
calculation (859 nm, f = 0.106). The absorption band remained
unchanged in a MTHF matrix for a long time, indicating that Z-
2 is persistent in a condition that the rotation about the central
double bond is suppressed kinetically. A substantial change was
observed in the electronic absorption spectrum with increasing
the temperature to 120 K (Figure 6b), where a viscosity of a
6
0 °C, (ii) AlCl , DCM, −78 to −30 °C, 88% yield; (f) NaBH ,
3
4
DCM/EtOH (1/1), RT; (g) p-TsOH·H O, toluene, 120 °C, 92%
yield (2 steps); (h) p-chloranil, toluene, RT, 24% yield. p-Chloranil =
2
2
,3,5,6-tetrachloro-1,4-benzoquinone.
Irradiation of UV light (365 nm) to anti-3 in degassed
1
dichloromethane-d resulted in a dramatic change in H NMR
spectrum, accompanied by a noticeable color change from
yellow to deep blue. H NMR spectrum recorded after the
2
1
irradiation was shown in Figure 3, together with the spectrum
of anti-3 measured before irradiation. Upon irradiation for 30 s,
anti-3 was converted quantitatively into a single product. The
species was unambiguously characterized to the long-
unidentified intermediate 2 by 2D-NMR spectroscopy as well
as the computational calculation of the NMR chemical shifts
conducted at GIAO-UB3LYP(BS)/6-31G** level (Figure S3 in
Supporting Information). The stereochemistry of 2 observed in
1
H NMR spectrum was determined by a ROESY measurement
conducted at 223 K (Figure S3b). 2 showed cross peaks
between H and H in opposite sign with respect to diagonal
peaks, which indicates that H and H are in close proximity to
each other. Thus, 2 observed adopts the E-configuration. It is
7
3
23
MTHF matrix dramatically changes from 10 to 10 P. The
differential spectra were dominated by the bleaching of an
absorption band at 700 nm and by growing with maximum at
a
h
a
h
C
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1
Figure 1. H NMR spectrum of 3 measured in dichloromethane-d .
2
Figure 2. Optimized geometries of (a) anti-3 and (b) syn-3 determined by a UB3LYP(BS)/6-31G** method.
1
Figure 3. H NMR spectra recorded in degassed dichloromethane-d at 183 K (a) before irradiation and (b) after irradiation of UV light (365 nm)
2
for 30 s. (c) Magnified view of aromatic region.
6
30 nm, suggesting the relaxation of a MTHF matrix leads to
through thermal isomerization. From the temperature depend-
ence of the decay rate constant, the activation barrier of the
thermal isomerization from Z-2 to E-2 was determined to be
4.3 ± 0.3 kcal mol− (logA = 12) by using Arrhenius plot
(shown in Figure 6d).
Thermal Ring-Closure Reaction of Biphenalenylidene.
According to the Woodward−Hoffmann rule, interconversion
between anti-3 having a 1,3-cyclohexadiene structure and Z-2
having a cis-1,3,5-hexatriene structure is expected to take place
the thermal isomerization of Z-2 to E-2 by the rotation about
the central double bond. The kinetics of the rapid thermal
isomerization was investigated by the transient absorption
spectrum within the temperature range from 183 to 203 K. The
absorption of Z-2 monitored at 705 nm decayed with a simple
first-order kinetics, and the absorption of E-2 grew with the
same rate constant as the decay rate constant of Z-2 (Figure
1
6c), which indicates that Z-2 is directly converted into E-2
D
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closure reaction in a stepwise pathway via Z-2 as an
intermediate. The activation barrier of E−Z isomerization
determined experimentally was substantially low; thus, the ring-
closure step from Z-2 to anti-3 should be the rate-determining
step. The activation barrier for the rate-determining step was
estimated from the temperature dependence of a decay rate
constant to be 15.7 ± 1.0 kcal mol− (logA = 7.9) by using
Arrhenius plot (Figure 8b).
1
Computational Studies. Detailed calculations of the
molecular geometries and electronic structures of E,Z-2 and
17
anti-3 were reported by Agranat et al., which suggested the
singlet biradical ground states of E,Z-2. Here we focus on the
molecular orbitals and ground state description of E,Z-2 and
anti-3 to account for their unique reactivity. The singlet
biradical indices y of E,Z-2 were estimated with CASSCF-
1
0
Figure 4. VT H NMR spectra of E-2 measured in dichloromethane-d2
(
3
2,2)/6-31G**//UB3LYP(BS)/6-31G** and UB3LYP(BS)/6-
1G** methods. A CASSCF(2,2)/6-31G**//UB3LYP(BS)/6-
1G** calculation gave an admixture of 14% of the doubly
at (a) 253 K, (b) 223 K, and (c) 183 K.
3
excited configuration into the ground state description of E-2;
thus, the y of E-2 was estimated to be 28%. A broken-
0
symmetry UB3LYP/6-31G** calculation gave a similar value;
the natural orbital occupancy number (NOON) of LUMO of
E-2 is 0.36, indicating the y of 36%. The y of Z-2 was also
0
0
determined with the same calculation methods to be 67% and
4%, respectively, which indicates that the biradical character of
9
Z-2 with a larger twisted angle is considerably larger than that
of E-2.
Molecular orbitals of Z-2 and anti-3 reflect the electronic
structures of cis-1,3,5-hexatriene and 1,3-cyclohexadiene,
respectively (shown in Figure S5). Thus, the thermal ring-
closure in conrotatory fashion should be a kinetically
unfavorable pathway according to the Woodward−Hoffmann
rule. To gain an energetic insight into the ring-closure process,
the transition states in conrotatory (TS1) and disrotatory
Figure 5. Electronic absorption spectra of E-2 (blue) and anti-3
(
TS2) modes were estimated with a UB3LYP(BS)/6-31G**
−5
(
black) measured in dichloromethane (1 × 10 M). E-2 was
method (Figure 9). The activation barrier for conrotatory ring-
generated by UV irradiation (365 nm) at 195 K.
−1
closure process was estimated to be 22.6 kcal mol , which is
comparable with that reported in the previous literature by
Agranat et al. (28.6 kcal mol− at UB3LYP/6-31G* level) and
1
17
through photochemically allowed conrotatory mode. Indeed,
anti-3 was converted into Z-2 by UV irradiation. Notably, the
ring-opening reaction did not proceed thermally by heating
even at 393 K in degassed toluene. On the other hand, although
the reconversion of Z-2 to anti-3 is also expected to be a
photochemically allowed process, irradiation (700 nm) of Z-2
in a MTHF matrix resulted in no perceptible change in the
electronic absorption spectrum. In contrast, Z-2 demonstrated
the thermal ring-closure reaction in conrotatory mode, which is
not conforming to the Woodward−Hoffmann rule, being
investigated by spectroscopic analyses.
−1
the experimental value (15.7 ± 1.0 kcal mol ). In contrast to
the facility of the conrotatory process, larger activation energy
−1
(30.8 kcal mol ) is required for the disrotatory process. The
overall energy diagram is displayed in Figure 10. The activation
barrier for E−Z isomerization of Z-2 (TS3) was calculated to
be 0.8 kcal mol , which is considerably lower than that of
general alkenes but is consistent with the estimation from
−1
−1
transient absorption measurements (4.3 ± 0.3 kcal mol ). The
computational results predict that E,Z-2 exhibit the dynamic
equilibrium; thus, the ring-closure step from Z-2 to anti-3
should be a rate-determining step of thermal ring-closure
reaction.
1
Thermal ring-closure reaction of E-2 was monitored by H
NMR spectroscopy. The signals of E-2 generated in degassed
dichloromethane-d almost disappeared after storing in the dark
In addition, S energies were estimated by using a spin flip
1
2
for 1 h, and the peaks of anti-3 were recovered (Figure 7). This
result suggests that E-2 underwent the kinetically unfavorable
conrotatory ring-closure even at 298 K. It should be noted that
syn-3, which would be a product of a kinetically favorable
TDDFT calculations at BHHLYP/6-311G* level to elucidate
the mechanism of the photoinduced ring-opening reaction of
anti-3 to Z-2 (shown in Figure 11). Spin flip TDDFT
calculation is a sophisticated method to estimate the electronic
structure of the excited states of singlet biradical species. Singlet
biradicals are known to have a low-lying doubly excited states
1
disrotatory process, was not found in H NMR spectrum.
Detailed kinetics of the thermal ring-closure was studied by
time dependence of the electronic absorption spectrum. As
shown in Figure 8a, the absorption band of E-2 at 619 nm
decayed with a simple first-order kinetics, and an intense
absorption band attributed to anti-3 at shorter wavelength
region was recovered. E-2 is expected to undergo the ring-
24
(HOMO,HOMO → LUMO,LUMO); thus, detailed assign-
ments of the S states of E,Z-2 are required for the mechanistic
1
studies on the photoinduced ring-opening reaction. The
computational results suggest that the HOMO,HOMO →
LUMO,LUMO doubly excited states are always higher in
E
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−4
Figure 6. (a) Differential electronic absorption spectrum of Z-2 generated by UV irradiation (355 nm) in a MTHF matrix (1 × 10 M) at 98 K. (b)
−4
Differential absorption spectra measured periodically at 120 K. (c) Transient absorption dynamics measured in MTHF (1 × 10 M) at 175 K. The
decay rate of Z-2 and the glow rate of E-2 were monitored at 705 and 630 nm, respectively. (d) Arrhenius plot to determine the activation barrier for
thermal isomerization from Z-2 to E-2.
anti-3 in the S state results in the changes of the twisted angle
1
between two phenalenyl moieties and the bond lengths of the
central six-membered ring, leading to the formation of Z-2 in
exothermic process. In contrast, the conrotatory ring-closure of
Z-2 to anti-3, which is expected to be a photochemically
allowed path according to the Woodward−Hoffmann rule, is
energetically uphill on the S energy surface. Therefore, the
1
photoinduced ring-closure reaction of Z-2 was not observed at
least in the experimental condition conducted at 98 K. The
structural optimization in the S state by the BHHLYP spin flip
1
TDDFT calculation gives two local minima, Z-2′ between Z-2
and TS3 found in the UB3LYP TDDFT calculation, and E-2′
between E-2 and TS3, depending on the initial structures E-2
or Z-2. This indicates the presence of an activation barrier
between Z-2′ and E-2′ in the S potential energy surface.
1
Frequency analyses with spin flip TDDFT were not performed
due to its computational cost. Thus, the photoinduced ring-
1
Figure 7. H NMR spectra measured in dichloromethane-d at 183 K
(
(
opening reaction is considered to proceed by anti-3(S ) → anti-
2
0
a) before irradiation, (b) just after irradiation UV light (365 nm), and
c) after storing in the dark for 1 h.
3(S ) → Z-2′(S ) → Z-2′(S ) → Z-2(S ) process. This
1
1
0
0
computational prediction strongly supports the experimental
results of spectroscopic analyses that Z-2 was generated
selectively by the photoinduced ring-opening reaction of anti-3.
Decomposition of Dihydroperopyrene to Peropyr-
ene. anti-3 showed a gradual decomposition in air-saturated
solution. Storing the solution of anti-3 in air resulted in the
energy than the HOMO → LUMO singly excited state.
Therefore, the S state dominating the photochemical reaction
is ascribed to the singly excited state, and the doubly excited
state is assignable to the S state. The structural relaxation of
1
2
F
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Figure 8. (a) Time dependence of the electronic absorption spectra of E-2 measured in dichloromethane (1 × 10−5 M) at room temperature. (b)
Arrhenius plot to determine the activation barrier for the ring-closure process.
Figure 11. Energy diagram calculated with a spin flip TDDFT
calculation at BHHLYP/6-311G* level. The structures of E,Z-2 and
Figure 9. Energy diagram of the electrocyclic reaction in conrotatory
anti-3 were optimized by a spin flip TDDFT calculations at BHHLYP/
and disrotatory processes. Transition states were identified by one
imaginary frequency at the saddle point. The relative energies were
estimated after ZPE correction.
̀
6
-311G* level. The energies of TS3 in the excited states were
calculated with the geometry obtained by a UB3LYP(BS)/6-31G**
method.
1
substantial change in H NMR spectrum (Figure 12), and
approximately 50% of anti-3 decomposed after 2 weeks to give
orange crystals of peropyrene 4. The decomposed product was
unambiguously assigned to 4 by X-ray crystallographic analysis.
The crystal structure of 4 was almost identical to that reported
25
previously by Bardeen et al. A half-life of anti-3 in air-
saturated solution was estimated to be 11 days from intensity
1
change of H NMR signals.
Direct Observation of the Decomposed Products of
the Parent Phenalenyl. Previous reports described that the
generation of 1 by the dehydrogenation of phenalene is
accompanied by the formation of blue or green products that
16
show an absorption band centered at 613 nm. We suspected
that the colored species is E-2. To an excess amount of
phenalene was added p-chloranil in degassed dichloromethane,
and the electronic absorption spectra were recorded periodi-
cally. Actually, a characteristic absorption band centered at 620
nm was observed in the early stage of the reaction, and then,
the absorption gradually decreased in intensity and disappeared
within 1 h, along with increasing the band intensity of
peropyrene (390, 414, and 441 nm), as shown in Figure 13.
Figure 10. Energy diagram calculated with a UB3LYP(BS)/6-31G**
method. Transition states were identified by one imaginary frequency
at the saddle point. The relative energies were estimated after ZPE
correction.
G
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Figure 12. 1H NMR spectra of anti-3 recorded (a) just after preparation, and (b) after storing in air-saturated CDCl3 for 2 weeks.
Hexamethylbenzene was used as an internal standard to normalize the intensity of anti-3 signals. (c) Determination of a half-life of anti-3 at room
temperature from the time dependence of a signal intensity corresponding to benzyl protons of anti-3.
1
,3-Cyclohexadiene and cis-1,3,5-hexatriene analogues that
show the unusual electrocyclization were shown in Scheme 3.
Scheme 3. (a and b) Thermal Electrocyclization in
Conrotatory Process between 1,3-Cyclohexadiene and cis-
1
,3,5-Hexatriene Analogues; (c) Thermal Reactions
Demonstrated by Pleiadene Derivatives
Figure 13. Electronic absorption spectra of phenalenyl 1 in
−
5
dichloromethane (2 × 10 M). The spectra were measured
periodically after preparation of 1 (every 10 min for 1 h, then 1.5,
2, 3, 4, 5, and 6.5 h).
The feature of the absorption band at 620 nm is identical to
that of E-2, suggesting strongly that E-2 exists as an
intermediate on the decomposition pathway of 1. Notably, a
weak band observed at 565 nm, which would arise from 1,
remained unchanged for a couple of days after disappearance of
E-2, suggesting the persistency of 1 in the condition without
any oxidants.
DISCUSSION
■
E,Z-2 exhibited the unusual reactions: conrotatory ring-closure
to anti-3, and rapid E−Z isomerization. The thermal ring-
closure in conrotatory process is kinetically unfavorable process
for cis-1,3,5-hexatriene analogues with respect to the disrotatory
process according to the Woodward−Hoffmann predictions,
whereas Z-2 demonstrated a facile ring-closure in conrotatory
fashion to give anti-3. Moreover, E,Z-2 underwent a rapid E−Z
isomerization. The activation energy determined experimentally
4a,4b-Dihydrophenanthrene (12a), which is analogous to 1,3-
cyclohexadiene, is well-known to demonstrate a facile ring-
26
opening in conrotatory process to afford cis-stilbene (12b).
Loss of aromatic stabilization energy destabilizes 12a with
respect to 12b, resulting in the decrease of a relative activation
barrier to induce the thermal ring-opening in conrotatory
fashion. On the other hand, 13a undergoes a thermal ring-
closure in conrotatory mode to give corresponding 1,3-
−1
is extremely small (4.3 ± 0.3 kcal mol ) compared to that for
isomerization of general alkenes. These unique reactivities of
E,Z-2 are ascribed to their singlet biradical nature.
27,28
cycrohexadiene analogue (13b).
In this case, the structural
H
DOI: 10.1021/jacs.5b13033
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Journal of the American Chemical Society
Article
strain of 13a leads to the conrotatory ring-closure not
conforming to the Woodward−Hoffmann prediction.
Scheme 4. E−Z Isomerization of (a) Alkenes and (b) E,Z-2
through Biradical Transition Structures
The orbital symmetry forbidden reaction of the singlet
29,30
biradical species was reported by Michl et al.
Pleiadene is a
singlet biradical compound having the o-quionodimethane
scaffold. The parent pleiadene (14a) showed a facile
dimerization to form 14b owing to its singlet biradical ground
2
9,31
state,
whereas a dimethyl derivative (15a) underwent the
intramolecular ring-closure in disrotatory process to give a
30
corresponding cyclobutene derivative (15b). The thermal
interconversion between 1,3-butadiene and cyclobutene in
disrotatory mode is expected to be a kinetically unfavorable
process by the Woodward−Hoffmann rule, whereas the
activation energy for the ring-closure reaction is considerably
−1
small (21.3 kcal mol ). The facile ring-closure was accounted
for by the destabilized ground state of pleiadene due to its
singlet biradical character. A small HOMO−LUMO gap of the
singlet biradical species leads to an admixture of the doubly
excited configuration into the ground state description,
resulting in the decrease of covalent bonding interactions and
destabilization of the ground state.
The unusual ring-closure reaction of Z-2 can be rationalized
by the destabilized ground state of Z-2. Indeed, the
contribution of the doubly excited configuration to the ground
state description was corroborated by the CASSCF(2,2)/6-
reaction in conrotatory process to afford anti-3, which is against
the Woodward−Hoffmann prediction. The activation barrier
was also determined by spectroscopic techniques to be 15.7 ±
−1
1
.0 kcal mol . These unique reactions can be rationalized by
the singlet biradical nature of E,Z-2. Admixture of the doubly
excited configuration into the ground state description resulted
in the decrease of the intramolecular covalent bonding
interaction and destabilized the ground states of E,Z-2. In
addition, the biradical transition state of E−Z isomerization
3
1G**//UB3LYP(BS)/6-31G** calculation (see above). The
admixture of the doubly excited configuration results in the
destabilization of the ground state of Z-2, decreasing the
relative activation barrier for the conrotatory ring-closure
reaction. In contrast, the activation energy of the disrotatory
process is considerably larger. With a focus on the computa-
tional result, the transition structure of disrotatory ring-closure
process (TS2 in Figure 9) is highly contorted, leading to the
large activation energy. Therefore, the ring-closure in
conrotatory process is the kinetically and thermodynamically
favored process, which is fully consistent with the experimental
finding that thermal ring-closure of Z-2 solely gave anti-3.
The facile E−Z isomerization is also ascribed to the biradical
ground states of E,Z-2. The destabilized ground states of E,Z-2
lead to the decrease of an activation barrier for the
isomerization. In addition, the transition state for the
isomerization (TS3 in Figure 10) is stabilized in comparison
with that for general alkenes. The isomerization of alkene is
considered to proceed through a biradical transition structure
as illustrated in Scheme 4. In the case of 2, the biradical
transition state can be stabilized thermodynamically by the
delocalization of unpaired electrons over phenalenyl moieties.
Thus, the combination of destabilization of the ground state of
E,Z-2 and stabilization of TS3 leads to the facility of E−Z
isomerization.
(
TS3 in Figure 10) was stabilized by the delocalization of
unpaired electrons over phenalenyl moieties, facilitating the
unusual E−Z isomerization.
Deeper understanding of the electronic structure and
reactivities of E,Z-2 and anti-3 enabled us to confirm the
decomposition mechanism of the parent phenalenyl (1). The
presence of E-2 in the decomposition pathway was
unambiguously corroborated; thus, the colored product
14−16
reported in previous literatures
was not the desired
product 1 but the decomposed product E-2. The decom-
position of 1 in the presence of oxidants proceeds as the
following mechanisms: (1) 1 exists as an equilibrium mixture
with 1 σ-dimer, (2) dehydrogenation of 1 σ-dimer gives E,Z-
2
2
2
, (3) thermal E−Z isomerization and conrotatory ring-closure
lead to anti-3, and then (4) dehydrogenation of anti-3 forms
peropyrene 4 as a final product.
EXPERIMENTAL SECTION
■
General. All experiments with moisture- or air-sensitive com-
pounds were performed in anhydrous solvents under nitrogen
atmosphere in well-dried glassware. Dried solvents were prepared by
distillation under nitrogen. Toluene and DMF were dried and distilled
over calcium hydride. 2-Methyltetrahydrofuran (MTHF) was dried
and distilled over sodium. Anhydrous dichloromethane was purchased
from Kanto Chemical Co., Inc. and used without further purification.
Column chromatography was performed with silica gel [Silica gel 60N
CONCLUSIONS
■
In summary, first isolation of E,Z-biphenalenylidene (E,Z-2) in
solution state was accomplished by means of the photoinduced
electrocyclic ring-opening reaction of anti-dihydroperopyrene
(
Kanto Chemical Co., Inc.)]. Melting points were taken on a Yanako
(anti-3). The structural characterizations of E,Z-2 and anti-3
1
13
1
MP 500D apparatus. H NMR and C NMR spectra were obtained
on JEOL ECS400 and ECA500 spectrometers. The chemical shifts
were recorded by using tetramethylsilane (0.00 ppm) as an internal
were performed by spectroscopic analyses ( H NMR and
electronic absorption measurements) as well as computational
studies. Z-2, which was trapped in a rigid matrix of a solvent,
demonstrated the rapid E−Z isomerization to E-2, and the
1
13
standard for H NMR and CHCl (77.00 ppm) for C NMR spectra.
3
Positive EI mass spectra were taken by using Shimadzu QP-5050. High
resolution mass spectra were analyzed by using Applied Biosystems
Japan Ltd. Analyst QS 2.0. Data collection for X-ray crystal analysis
was performed on Rigaku/Varimax diffractometer (Mo-Kα, λ =
kinetic investigation indicated that the activation barrier of 4.3
0.3 kcal mol− is extraordinarily smaller than that of general
1
±
alkenes. Furthermore, Z-2 showed the unusual ring-closure
I
DOI: 10.1021/jacs.5b13033
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Journal of the American Chemical Society
Article
0
.71069 Å). The structure was solved with direct methods and refined
After removal of Pd−C by filtration, filtrate was evaporated. The
residue was purified by column chromatography on silica gel
with full-matrix least-squares (teXsan). Infrared spectra were recorded
on a JASCO FT/IR-660 M spectrometer. Steady-state UV−vis
absorption spectra were measured in anhydrous dichloromethane
and MTHF with a JASCO V-570 spectrometer. The nanosecond time-
resolved difference absorption spectra were obtained using the third
harmonic (THG) of a Nd :YAG laser (Continuum Mini-lite II, λ
3
system comprised a 150-W Xe lamp as the light source, a UNISOKU-
MD200 monochromator, and a photomultiplier.
Computational Details. All geometry optimizations and tran-
sition state calculations were performed with the Gaussian 09 program.
The optimized structures of E,Z-2 and syn,anti-3 have no imaginary
frequency, and the transition structures have one imaginary frequency
at the saddle points. The single point calculations with UB3LYP/6-
(dichloromethane/hexane 70%) to give 8 as a colorless oil (0.40 g,
1
88%). R = 0.14 (dichloromethane/hexane 50%); H NMR (400 MHz,
f
CDCl ) δ 8.12 (d, J = 8.8 Hz, 2H), 7.52 (td, J = 6.8 Hz, 1.5 Hz, 2H),
3
7.45 (d, J = 6.8 Hz, 2H), 7.41 (dd, J = 8.4 Hz, 0.8 Hz, 2H), 7.39 (d, J =
6.8 Hz, 2H), 7.28 (td, J = 6.4 Hz, 0.8 Hz, 2H), 3.75 (s, 6H), 3.55−3.51
3+
=
ex
13
55 nm, 4−6 ns pulse width, 7 mJ) for the excitation. The monitoring
(m, 4H), 2.90−2.86 (m, 4H); C NMR (126 MHz, CDCl ) δ 173.50,
3
137.55, 136.23, 133.29, 131.57, 127.56 (broad, 2C), 125.95, 125.62,
125.42, 123.51, 51.74, 34.98, 28.23; IR (KBr) ν = 3068 (w), 3010 (w),
2950 (m), 2844 (w), 1737 (s), 1590 (w), 1512 (w), 1436 (s), 1364
(m), 1295 (m), 1256 (s), 1198 (s), 1170 (s), 1029 (w), 984 (w), 842
−
1
(m), 765 (s) cm ; HRMS (ESI, positive): m/z Calcd for
+
C H O Na: 449.1723 [M + Na] . Found: 449.1729.
28
26
4
3,3′-([1,1′-Binaphthalene]-4,4′-diyl)dipropionic Acid (9). To
3
1G**, RHF/6-31G**, and CASSCF(2,2)/6-31G** methods were
conducted with the optimized geometries calculated at UB3LYP(BS)/
-31G** level of theory by using the Gaussian 03 program. TD-
a solution of dimethyl 3,3′-([1,1′-binaphthalene]-4,4′-diyl)-
dipropionate 8 (0.40 g, 0.94 mmol) in ethanol (30 mL) was added
10% aqueous sodium hydroxide (15 mL), and the solution was heated
at 90 °C for 14 h. After the solution cooled to room temperature, the
reaction mixture was poured into 6 M hydrochloric acid and extracted
with ether. The organic layer was separated and washed with brine,
dried over anhydrous sodium sulfate. After filtration, the filtrate was
evaporated, and then the residue was collected and washed with ether
6
UB3LYP(BS)/6-31G** and GIAO-(U)B3LYP/6-31G** calculations
were also performed with the optimized geometries obtained by a
UB3LYP(BS)/6-31G** method. Spin-flip TDDFT calculation was
performed with the GAMESS 2014 program package, employing the
BHHLYP exchange-correlation functional and the 6-311G* basis set
because the SF-DFT benchmark calculations show a better perform-
ance with hybrid functionals including a larger fraction of HF
exchange, e.g., 50% HF plus 50% Becke exchange, than that with the
to give 9 as a white powder (0.35 g, 94%). Mp 256−257 °C; R
= 0.07
) δ 8.25
6
f
1
(ethyl acetate/hexane 50%); H NMR (400 MHz, Acetone-d
(d, J = 8.4 Hz, 2H), 7.59−7.55 (m, 4H), 7.42 (d, J = 7.2 Hz, 2H),
32,33
conventional B3LYP functional.
,4′-Dibromo-1,1′-binaphthalene (6). 1,1′-Binaphthalene 5
0.79 g, 3.1 mmol) was dissolved in chloroform (30 mL) and the
7.33−7.32 (m, 4H), 3.53 (t, J = 8.0 Hz, 4H), 2.87 (t, J = 8.0 Hz,
1
3
4
overlapped with a broad proton signal of carboxyl group); C NMR
(
(126 MHz, DMSO-d ) δ 173.87, 136.71, 136.57, 132.57, 131.27,
6
solution was cooled to 0 °C with an ice-bath. To the solution was
added bromine (2.6 g, 16 mmol) over 20 min. After the mixture stirred
for 2.5 h, aqueous sodium sulfite was added for quenching. The
organic layer was separated and washed with brine, dried over
anhydrous sodium sulfate. After filtration, the filtrate was evaporated
127.31, 126.64, 126.06, 125.81, 125.31, 123.87, 34.53, 27.49; IR (KBr)
ν = 3040 (m), 2936 (m), 2688 (m), 2611 (m), 1705 (s), 1592 (w),
1513 (w), 1424 (m), 1384 (m), 1303 (m), 1211 (m), 936 (w), 836
−
1
(m), 765 (m) cm ; HRMS (ESI, positive): m/z Calcd for
+
C
H
O
Na: 421.1410 [M + Na] . Found: 421.1415.
4,4′,5,5′-Tetrahydro-6H,6′H-[1,1′-biphenalene]-6,6′-dione
10). 3,3′-([1,1′-Binaphthalene]-4,4′-diyl)dipropionic acid 9 (0.34 g,
.85 mmol) was dissolved in oxalyl chloride (20 mL) and heated at 60
C for 14 h. After removal of excess oxalyl chloride under reduced
26
22
4
and the residue was recrystallized from chloroform to give 6 as a white
1
(
0
°
crystal (0.82 g, 64%). Mp 217−219 °C; R = 0.48 (hexane); H NMR
f
(
400 MHz, CDCl ) δ 8.36 (d, J = 8.8 Hz, 2H), 7.90 (d, J = 7.6 Hz,
H), 7.62−7.58 (m, 2H), 7.35−7.31 (m, 6H); C NMR (126 MHz,
CDCl ) δ 137.63, 133.83, 131.93, 129.44, 128.11, 127.45, 127.39,
3
13
2
pressure, the residue was dissolved in dichloromethane (30 mL) and
cooled to −78 °C under nitrogen atmosphere. To the solution was
added aluminum chloride (0.46 mg, 3.4 mmol). The reaction mixture
was stirred at −78 °C for 2 h, then warmed gradually to −30 °C. The
reaction was quenched with 1 M hydrochloric acid and extracted with
dichloromethane. The organic layer was separated and washed with
aqueous sodium carbonate, dried over anhydrous sodium sulfate. After
filtration, the filtrate was evaporated and the residue was purified by
column chromatography on silica gel (dichloromethane/hexane 70%)
3
1
26.98, 126.92, 123.00.
Dimethyl 3,3′-([1,1′-Binaphthalene]-4,4′-diyl)(2E,2′E)-diacry-
late (7). A flask was charged with 4,4′-dibromo-1,1′-binaphthalene 6
(
0.50 g, 1.2 mmol), palladium(II) acetate (54 mg, 0.24 mmol),
triphenylphosphine (0.13 g, 0.49 mmol), potassium carbonate (0.67 g,
.9 mmol), and tetrabutylammonium bromide (2.0 g, 6.2 mmol)
4
under nitrogen atmosphere. Methyl acrylate (0.33 mL, 3.6 mmol) in
DMF (25 mL) was added, and the solution was heated at 80 °C for 11
h. After the solution cooled to room temperature, the precipitates were
filtered out, and the filtrate was poured into water. The reaction
mixture was extracted with dichloromethane, and the organic layer was
washed with water and brine, dried over anhydrous sodium sulfate.
After filtration, the filtrate was evaporated and the residue was purified
by column chromatography on silica gel (dichloromethane/hexane
to give 10 as a pale yellow powder (0.27 g, 88%). Mp 216 °C
1
(decomposition); R
(400 MHz, CDCl
2H), 7.59 (d, J = 6.8 Hz, 2H), 7.50 (d, J = 7.2 Hz, 2H), 7.43 (t, J = 7.6
= 0.15 (dichloromethane/hexane 70%); H NMR
f
) δ 8.22 (d, J = 7.2 Hz, 2H), 7.64 (d, J = 8.4 Hz,
3
1
3
Hz, 2H), 3.55 (t, J = 7.2 Hz, 4H), 3.08 (t, J = 7.2 Hz, 4H); C NMR
(126 MHz, CDCl ) δ 198.47, 136.39, 133.31, 132.78, 132.57, 131.70,
3
7
0
8
2
5%) to give 7 as a white solid (0.48 g, 93%). Mp 203−204 °C; R =
129.98, 128.28, 125.87, 125.25, 125.17, 38.44, 28.62; IR (KBr) ν =
3056 (w), 3018 (w), 2979 (w), 2945 (w), 2924 (w), 1691 (s), 1599
(m), 1504 (m), 1457 (m), 1434 (m), 1407 (m), 1355 (w), 1317 (m),
1276 (s), 1234 (m), 1214 (m), 1018 (m), 849 (m), 822 (s), 777 (s),
f
1
.14 (dichloromethane/hexane 50%); H NMR (400 MHz, CDCl ) δ
3
.64 (d, J = 15.6 Hz, 2H), 8.30 (d, J = 8.4 Hz, 2H), 7.87 (d, J = 7.6 Hz,
H), 7.58 (td, J = 6.8 Hz, 1.6 Hz, 2H), 7.50 (d, J = 7.6 Hz, 2H), 7.43
−1
(
dd, J = 8.8 Hz, 1.6 Hz, 2H), 7.35 (td, J = 6.8 Hz, 1.6 Hz, 2H), 6.63 (d,
725 (s) cm ; HRMS (ESI, positive): m/z Calcd for C26
H
O
18
2
Na,
13
+
J = 15.6 Hz, 2H), 3.89 (s, 6H); C NMR (126 MHz, CDCl ) δ
385.1199 [M + Na] . Found: 385.1205.
3
1
67.29, 141.80, 140.56, 132.86, 131.91, 131.46, 127.44, 127.21, 126.89,
4H,4′H-1,1′-Biphenalene (11). To a suspension of 4,4′,5,5′-
tetrahydro-6H,6′H-[1,1′-biphenalene]-6,6′-dione 10 (0.34 g, 0.94
mmol) in DCM (30 mL) and ethanol (20 mL) was added sodium
borohydride (0.14 g, 3.8 mmol) under nitrogen atmosphere. After it
stirred for 1 h at room temperature, the reaction was quenched with
aqueous ammonium chloride. The organic layer was separated and
washed with brine, dried over anhydrous sodium sulfate. After
filtration, the filtrate was evaporated and the residue was purified by
column chromatography on hydrous (6%) silica gel (ethyl acetate/
dichloromethane 10%) to give 5,5′,6,6′-tetrahydro-4H,4′H-[1,1′-
biphenalene]-6,6′-diol as a diastereomer mixture (0.28 g, 81%).
126.46, 124.48, 123.65, 120.75, 51.85; IR (KBr) ν = 3044 (w), 2991
(
1
w), 2947 (m), 2844 (w), 2367 (w), 1714 (s), 1630 (s), 1576 (m),
437 (s), 1381 (m), 1307 (s), 1249 (m), 1230 (m), 1194 (s), 1174
−1
+
(
s), 1114 (m), 977 (s), 844 (s), 768 (s) cm ; EI-MS m/z 422 (M );
Anal. Calcd for C H O : C, 79.60; H, 5.25. Found: C, 79.33; H, 5.21.
28
22
4
Dimethyl 3,3′-([1,1′-Binaphthalene]-4,4′-diyl)dipropionate
(
7
8). Dimethyl 3,3′-([1,1′-binaphthalene]-4,4′-diyl)(2E,2′E)-diacrylate
(0.45 g, 1.1 mmol) was dissolved in dichloromethane (10 mL) and
ethyl acetate (90 mL); then 10% Pd−C (50 mg, 10 wt %) was added.
The reaction mixture was stirred for 3 h under hydrogen atmosphere.
J
DOI: 10.1021/jacs.5b13033
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Journal of the American Chemical Society
Article
The diastereomer mixture of the diol derivative (41 mg, 0.11 mmol)
was dissolved in toluene (10 mL) under nitrogen atmosphere. To the
solution was added a catalytic amount of p-toluenesulfonic acid
monohydrate, and the solution was heated at 120 °C for 5 min. The
reaction mixture was cooled at 0 °C and then the solution diluted with
responsive Chemical Species” (No. 24109008) from MEXT,
Japan. T.K. thanks JSPS for KAKENHI Grant No. 26288016
and MEXT for a Grant-in-Aid for Scientific Research on
Innovative Areas “Photosynergetics” (15H01086).
hexane (21 mL) was filtered rapidly on hydrous (6%) silica gel to give
1
1
1 as a pale green solid (34 mg, 92%). R = 0.18 (hexane); H NMR
REFERENCES
f
■
(
400 MHz, CDCl ) δ 7.36−7.32 (m, 4H), 7.10−7.09 (m, 4H), 6.97
3
(
1) In phenalenyl derivatives the positions 1, 3, 4, 6, 7, and 9 are
referred to as α and 2, 5, and 8 as β.
(
d, J = 4 Hz, 2H), 6.64 (d, J = 10 Hz, 2H), 6.10 (m, 2H), 4.16 (s, 4H);
1
3
C NMR (126 MHz, CDCl ) δ 135.85, 133.85, 132.76, 132.07,
3
(
(
2) Haddon, R. C. Nature 1975, 256, 394.
3) Chi, X.; Itkis, M. E.; Patrick, B. O.; Barclay, T. M.; Reed, R. W.;
1
29.41, 127.92, 127.84, 127.61, 126.24, 125.48, 124.61, 122.22, 32.28;
IR (KBr) ν = 3028 (m), 2919 (s), 2853 (w), 2794 (w), 1587 (m),
506 (w), 1415 (m), 1394 (w), 1352 (w), 1219 (w), 1054 (w), 949
Oakley, R. T.; Cordes, A. W.; Haddon, R. C. J. Am. Chem. Soc. 1999,
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9) Goto, K.; Kubo, T.; Yamamoto, K.; Nakasuji, K.; Sato, K.;
1
1
(
−1
(w), 837 (m), 824 (s), 764 (s), 734 (m) cm ; HRMS (ESI, positive):
+
m/z Calcd for C H , 329.1325 [M−H] . Found: 329.1331.
26
17
anti-Dihydroperopyrene (anti-3). To a solution of 4H,4′H-1,1′-
biphenalene 11 (34 mg, 0.10 mmol) in toluene (10 mL) was added p-
chloranil (27 mg, 0.11 mmol) under nitrogen atmosphere. After it
stirred for 3 h, the reaction mixture was filtered rapidly on hydrous
(
(
(
6%) silica gel to give anti-3 as a crude product. The product was
(
reprecipitated from dichloromethane/hexane, and then the precipitate
containing impurity was filtered out. The filtrate was evaporated, and
the residual pale green powder was washed with hexane and collected.
(
1
anti-3 was obtained as a greenish yellow powder (8.0 mg, 24%). H
(
NMR (400 MHz, dichloromethane-d ) δ 7.97 (d, J = 6.8 Hz, 2H), 7.76
2
Shiomi, D.; Takui, T.; Kubota, M.; Kobayashi, T.; Yakusi, K.; Ouyang,
J. J. Am. Chem. Soc. 1999, 121, 1619.
(
d, J = 6.8 Hz, 2H), 7.59 (d, J = 6.8 Hz, 2H), 7.32 (dd, J = 6.4 Hz, 5.6
Hz, 2H), 7.09 (d, J = 5.6 Hz, 2H), 6.81 (d, J = 8.0 Hz, 2H), 6.37 (d, J
8.0 Hz, 2H), 4.42 (s, 2H); HRMS (ESI, positive): m/z Calcd for
(
10) Suzuki, S.; Morita, Y.; Fukui, K.; Sato, K.; Shiomi, D.; Takui, T.;
Nakasuji, K. J. Am. Chem. Soc. 2006, 128, 2530.
11) Fukui, K.; Sato, K.; Shiomi, D.; Takui, T.; Itoh, K.; Gotoh, K.;
Kubo, T.; Yamamoto, K.; Nakasuji, K.; Naito, A. Synth. Met. 1999, 103,
257.
12) Koutentis, P. A.; Chen, Y.; Cao, Y.; Best, T. P.; Itkis, M. E.; Beer,
=
+
C H , 328.1247 [M] . Found: 328.1257.
26
16
(
ASSOCIATED CONTENT
Supporting Information
■
2
(
*
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/jacs.5b13033.
L.; Oakley, R. T.; Cordes, A. W.; Brock, C. P.; Haddon, R. C. J. Am.
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Characterization data ( H− H COSY, NOESY and of
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dependent electronic absorption spectra of E-2 at each
temperature, calculated molecular orbitals and spin
density maps of E-2 and anti-3, and Gaussian input
data (PDF)
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X-ray crystallographic data of anti-3 (CIF)
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AUTHOR INFORMATION
Corresponding Authors
mnaka@cheng.es.osaka-u.ac.jp
mabe@hiroshima-u.ac.jp
■
Nakano, M.; Shiomi, D.; Sato, K.; Takui, T.; Morita, Y.; Nakasuji, K.
Angew. Chem., Int. Ed. 2005, 44, 6564.
(
Champagne, B.; Shiomi, D.; Sato, K.; Takui, T.; Matsumoto, K.;
Kurata, H.; Kubo, T. J. Am. Chem. Soc. 2010, 132, 11021.
*
*
*
20) Konishi, A.; Hirao, Y.; Nakano, M.; Shimizu, A.; Botek, E.;
kubo@chem.sci.osaka-u.ac.jp
(
21) Li, Y.; Heng, W.-K.; Lee, B. S.; Aratani, N.; Zafra, J. L.; Bao, N.;
Notes
Lee, R.; Sung, Y. M.; Sun, Z.; Huang, K.-W.; Webster, R. D.; Lopez
Navarrete, J. T.; Kim, D.; Osuka, A.; Casado, J.; Ding, J.; Wu, J. J. Am.
Chem. Soc. 2012, 134, 14913.
́
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(
22) Shimizu, A.; Kishi, R.; Nakano, M.; Shiomi, D.; Sato, K.; Takui,
This article is dedicated to Professor Ichiro Murata on the
occasion of his 88th birthday (Beijyu). K.U. and S.I.
acknowledge support from the JSPS Fellowship for Young
Scientists (No. 2615260 and No. 2604505, respectively). M.N.
thanks a Grant-in-Aid for Scientific Research (A) (No.
T.; Hisaki, I.; Miyata, M.; Tobe, Y. Angew. Chem., Int. Ed. 2013, 52,
6
076.
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013, 117, 16802.
2
5248007) from JSPS, a Grant-in-Aid for Scientific Research
on Innovative Areas “Stimuli-Responsive Chemical Species”
A24109002a), “pi-System Figuration” (15H00999), “Photo-
(
(
synergetics” (A26107004a), MEXT, the Strategic Programs for
Innovative Research (SPIRE), MEXT, and the Computational
Materials Science Initiative (CMSI), Japan. Theoretical
calculations are partly performed using Research Center for
Computational Science, Okazaki, Japan. M.A. thanks a Grant-
in-Aid for Science Research on Innovative Areas “Stimuli-
2
(
(
(
26) Muszkat, K. A.; Fischer, E. J. Chem. Soc. B 1967, 662.
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