Synthesis of push-pull chromophores by the sequential [2 + 2] cycloaddition of 1-azulenylbutadiynes with tetracyanoethylene and tetrathiafulvalene

Article abstract of DOI:10.1039/c2ob26028j

Azulene-substituted butadiynes have been prepared by Cu-mediated cross- and homo-coupling reactions. The azulene-substituted butadiynes reacted with tetracyanoethylene in a formal [2 + 2] cycloaddition reaction to afford the corresponding 1,1,4,4-tetracya

Full text of DOI:10.1039/c2ob26028j

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PAPER
Synthesis of push–pull chromophores by the sequential [2 + 2] cycloaddition
of 1-azulenylbutadiynes with tetracyanoethylene and tetrathiafulvalene†
Taku Shoji,*a Shunji Ito,b Tetsuo Okujimac and Noboru Moritad
Received 27th May 2012, Accepted 10th August 2012
DOI: 10.1039/c2ob26028j
Azulene-substituted butadiynes have been prepared by Cu-mediated cross- and homo-coupling reactions.
The azulene-substituted butadiynes reacted with tetracyanoethylene in a formal [2 + 2] cycloaddition
reaction to afford the corresponding 1,1,4,4-tetracyanobutadiene chromophores, in excellent yields.
Further [2 + 2] cycloaddition with TTF and TCNE gave novel donor–acceptor chromophores and novel
azulene-substituted 6,6-dicyanofulvene derivatives.
chromophores, which exhibit a multistep reduction wave on
Introduction
cyclic voltammetry (CV), in excellent yields.5
Tetrathiafulvalene (TTF) is well known as a powerful electron
donor to form charge-transfer (CT) complexes with a variety of
electron-deficient organic compounds because of the formation
of stable aromatic 1,3-dithiole rings by one- or two-electron oxi-
dation. Thus, TTF and its derivatives have attracted much atten-
tion as conductive components of molecular conductors.1
Hopf et al. reported the [2 + 2] cycloaddition reaction of TTF,
a strong electron donor, with electron-deficient acetylenes
bearing a dicyanoethylene substituent to afford 1,2-bis(1,3-
dithiol-2-ylidene)ethane derivatives with a dicyanoethylene sub-
stituent.2 As an extension of this study, Diederich et al. reported
the sequential [2 + 2] cycloaddition reaction of tetracyanoethy-
lene (TCNE) and TTF with dialkylamino- (DAA-) substituted
electron-rich butadiynes yielding multivalent CT chromophores,
tetracyanobutadiene (TCBD)/1,2-bis(1,3-dithiol-2-ylidene)ethane
derivatives, that are capable of taking up an exceptional number
of electrons under electrochemical conditions.3
Previously, Hafner et al. reported the preparation of 1-azul-
enylbutadiynes utilizing a Cu-meditated oxidative coupling under
Eglinton conditions.6 Although 1-azulenylbutadiynes are prom-
ising building blocks for the construction of novel CT chromo-
phores, reactivity of their derivatives has not been energetically
investigated so far. Similar to the DAA-substituent, the 1-posi-
tion of an azulene ring possesses strong electron-donating pro-
perties with high reactivity toward electrophilic substitution
reactions. Thus, butadiyne derivatives substituted by a 1-azulenyl
moiety should be expected to afford a new series of donor–
acceptor chromophores by sequential [2 + 2] cycloaddition reac-
tions with TCNE and TTF. Furthermore, azulene-substituted
donor–acceptor chromophores may exhibit multistage ampho-
teric redox behaviour with a redox reaction of the azulene core.
Herein, we report the synthesis of novel azulene-substituted
donor–acceptor chromophores by the sequential [2 + 2] cyclo-
addition of 1-azulenylbutadiynes with TCNE and TTF, as well
as the spectroscopic and electrochemical properties of the novel
donor–acceptor chromophores clarified by UV/Vis spectroscopy
and electrochemical analysis.
Azulene (C10H8) has attracted the interest of many research
groups owing to its unusual properties as well as its beautiful
blue color.4 Recently, we also reported the reaction of poly-
(1-azulenylethynyl)benzene and thiophene derivatives with
TCNE and TCNQ to give the corresponding intramolecular CT
Results and discussion
Synthesis
aDepartment of Chemistry, Faculty School of Science, Shinshu
University, Matsumoto 390-8621, Japan.
Preparation of azulene-substituted butadiene derivatives, i.e.,
methyl 7-isopropyl-3-(4-phenylbuta-1,3-diynyl)azulene-1-car-
boxylate (2), 1,4-bis(7-isopropyl-1-methoxycarbonylazulen-3-yl)-
buta-1,3-diyne (3), and methyl 7-isopropyl-3-(4-trimethylsilyl-
buta-1,3-diynyl)azulene-1-carboxylate (4), was investigated by
Cu-mediated Hay7 cross- and Glaser8 homo-coupling conditions,
respectively (Scheme 1). The cross-coupling reaction of methyl
7-isopropyl-3-ethynylazulene-1-carboxylate (1)5 with 5 equiv.
of ethynylbenzene, using CuI/tetramethylethylenediamine
E-mail: tshoji@shinshu-u.ac.jp; Fax: +81 263 2476; Tel: +81 263 2476
bGraduate School of Science and Technology, Hirosaki University,
Hirosaki 036-8561, Japan
cDepartment of Chemistry and Biology, Graduate School of Science and
Engineering, Ehime University, Matsuyama 790-8577, Japan
dDepartment of Chemistry, Graduate School of Science, Tohoku
University, Sendai 980-8578, Japan
†Electronic supplementary information (ESI) available: The experimen-
tal, UV/Vis spectra and cyclic voltammograms of reported compounds.
See DOI: 10.1039/c2ob26028j
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Likewise, the reaction of butadiyne 3 with TCNE at room
temperature afforded TCBD 7 in 97% yield. Although the result-
ing 7 was treated with TTF, the corresponding TCNE/TTF
double-adduct could not be obtained, but resulted in the recovery
of the TCBD 7. Meanwhile, the subsequent [2 + 2] cyclo-
addition of 7 with TCNE was observed under reflux conditions
in 1,1,2,2-tetrachloroethane to afford the double TCNE-adduct 8
in 71% yield, along with the novel 6,6-dicyanofulvene derivative
9 in 22% yield (Scheme 3).
When compounds 7 and 8 were refluxed in 1,1,2,2-
tetrachloroethane without TCNE, 6,6-dicyanofulvene 9 could not
be obtained, but resulted in the recovery of the starting com-
pounds 7 and 8. Thus, TCNE has an important role in the for-
mation of the 6,6-dicyanofulvene derivative 9. The presumed
reaction mechanism for the formation of 8 and 9 is illustrated in
Scheme 4. This reaction involves two reaction pathways to
afford 8 and 9. Initially, TCNE exhibits coordination to 7 with
the electron-rich acetylene moiety attached to the 1-azulenyl
group. In one pathway, the TCNE molecule undergoes a [2 + 2]
Scheme 1 Synthesis of 1-azulenylbutadiynes 2, 3 and 4.
(TMEDA) as the catalysts, and subsequent chromatographic
purification on silica gel afforded the desired 2 in 74% yield,
along with the homo-coupling product 3 in 20% yield. Com-
pound 3 was also obtained in 91% yield as a sole product, by
the Glaser homo-coupling reaction of 1 under similar reaction
conditions. Similar to the synthesis of 2, butadiyne 4 was
obtained by the reaction of 1 with 5 equiv. trimethylsilylacety-
lene in 76% yield, along with 3 in 17% yield. These butadiyne
derivatives 2, 3 and 4 possess fair solubility in chloroform,
dichloromethane, and so on. Moreover, they are stable and show
no decomposition, even after several weeks at room temperature.
Thus, these butadiyne derivatives could be utilized in further
transformations for the synthesis of novel donor–acceptor chromo-
phores owing to their considerable stability and solubility.
The sequential [2 + 2] cycloaddition reaction of 2 and 3 with
TCNE and TTF was examined for the construction of novel
donor–acceptor chromophores. Thus, the reaction of 2 with
TCNE was examined in ethyl acetate at room temperature to
yield 5 in 95% yield.3,5,9 Subsequent [2 + 2] cycloaddition reac-
tion of the remaining ethynyl moiety of 5, contiguous to the
phenyl group, with excess TCNE did not proceed even under
reflux conditions in DMF. These results indicate the low reactiv-
ity of the CuC triple bond attached to the highly electron-with-
drawing TCBD moiety. The synthesis of the TCNE/TTF double
adduct 6 was achieved in 92% yield by the [2 + 2] cycloaddition
reaction of 5 with TTF (Scheme 2). The one-pot cascade reaction
of 2 with TCNE and TTF also gave 6 in 70% yield, which corre-
sponds to an 84% yield in each step. However, the cascade reac-
tion requires a tedious separation process.
Scheme 3
Scheme 2
Scheme 4 Presumed reaction mechanism for the formation of 8 and 9.
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Table 1 Absorption maxima [nm] and their coefficients (log ε) of
compounds 5–9, and 12 in dichloromethane and in 10% CH2Cl2–hexane
cycloaddition with the acetylene moiety of 7 to afford the cyclo-
butene intermediate. The subsequent ring-opening reaction of
the cyclobutene derivative gives the thermodynamically stable
TCBD derivative 8.10 As another mechanism, the dicyano-
methylidene group attached to the azulene ring in 7, which has
certain electronegativity due to conjugation with the 1-azulenyl
group, attacks the intramolecular acetylene moiety with a
decreased LUMO-level because of the TCNE coordination, to
form the five-membered ring of 9′. In the generated zwitterionic
species 9′, the migration of a cyano group results in the for-
mation of 6,6-dicyanofulvene derivative 9.11 Recently, Diederich
et al. reported the first synthesis of donor-substituted 6,6-dicyano-
fulvene derivatives with interesting optoelectronic properties.12
In the view point of azulene chemistry, compound 9 is the first
example of a 6,6′-dicyanofulvene derivative with an azulene ring
substituent.
Sample
λmax (log ε) in CH2Cl2
λmax (log ε) in hexane
5
6
7
8
388 (4.47), 530 (3.93)
471 (4.52)
394 (4.33), 545 (4.52)
450 (4.40), 510 sh (4.19)
513 (3.87)a
463 (4.48)a
392 (4.29), 515 (4.49)a
419 (4.25), 438 (4.24),
488 sh (4.17)a
9
542 sh (4.03), 583 (4.11),
808 (3.64)
443 (4.46), 544 sh (4.11)
530 sh (4.04), 570 (4.11),
755 (3.50)a
12
438 (4.46), 544 sh (4.04)b
a Dichloromethane (10%) was included to keep the solubility of these
compounds. b Dichloromethane (20%) was included to keep the
solubility of these compounds.
Compound 11 was prepared by the Pd-catalyzed alkynylation
of 1,4-diiodobenzene with butadiyne 10, which was prepared by
the desilylation of 4, under Sonogashira–Hagihara conditions
(Scheme 5). A solution of 4 in methanol was treated with a pota-
ssium carbonate solution to generate the corresponding buta-
diyne 10. The green solid 10 decomposed at room temperature,
but has certain stability in solution for employment in further
transformations. The cross-coupling reaction of 10 with 1,4-di-
iodobenzene using Pd(PPh3)4 as a catalyst, and the subsequent
chromatographic purification of the reaction mixture on silica
gel, afforded the desired 11 in 87% yield. Similar to the results
for the butadiynes 2 and 3, the reaction of 11 with TCNE
afforded the bis-adduct 12 in 95% yield. Regarding the synthesis
of the TCNE/TTF double adduct, the [2 + 2] cycloaddition reac-
tion of 12 with TTF was also examined under similar conditions
used for the preparation of 6. However, in contrast to the results
for the reaction of 6, the reaction of 12 with TTF formed an inso-
luble complex mixture. It should be attributed to instability of
the compound under the reaction conditions.
Fig. 1 UV/Vis spectra of 2 (red line), 5 (blue line) and 6 (green line)
in dichloromethane.
Spectroscopic properties
The structures of these novel compounds 2–12 were confirmed
1
by spectral data including H, 13C NMR, HMQC, HMBC and
NOE experiments, except for 10. The absorption maxima (λmax
)
and their coefficients (log ε) of the new compounds 5–9 and 12
are summarized in Table 1.
The UV/Vis spectra of butadiynes 2, 3, 4 and 11 show weak
characteristic absorption bands arising from the azulene moiety
in the visible region. As expected from their structures, TCBD
derivatives, the TCNE/TTF double-adduct 6 and 6,6-dicyano-
fulvene 9 show relatively strong CT absorption bands in the visible
region (Fig. 1–3). The spectrum of 5 in dichloromethane displays a
characteristic CT absorption band at λmax = 530 nm (log ε = 3.93).
The UV/Vis spectrum of 6 exhibits a strong and broad absorp-
tion band at λmax = 471 nm in dichloromethane, which might be
due to the overlapping of the CT absorption bands between the
two donor moieties [i.e., azulene and 1,2-bis(1,3-dithiol-2-
ylidene)ethane] and the TCBD-acceptor unit (Fig. 1).
Compound 7 exhibits two CT absorption bands at λmax
=
394 nm (weak) and λmax = 545 nm (strong) in dichloromethane
(Fig. 2). The longest absorption of 7 displays a bathochromic
shift of 15 nm compared with that of 5 (λmax = 530 nm). These
results indicate that the π-conjugation is efficiently expanded by
Scheme 5
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Fig. 2 UV/Vis spectra of 3 (blue line), 7 (red line) and 8 (green line)
in dichloromethane.
Fig. 4 Frontier Kohn–Sham orbitals of 9′′ at the B3LYP/6-31G**
level.
Table 2 Electronic transitions for 9′′ derived from the computed
values based on the B3LYP/6-31G** method and experimental values
from 9
Fig. 3 Solvent dependence of the UV/Vis spectra of 9 in dichloro-
methane (blue line) and 10% dichloromethane–hexane (red line).
Computed value
Experimental
Composition of banda,b/CI
λmax (log ε)
λmax
Strength
coefficientsc
the 1-azulenyl group substituent rather than the phenyl group
substituent. A broad CT absorption centered at λmax = 450 nm
and extending beyond λmax = 800 nm was also observed in 8
(Fig. 2). The UV/Vis spectrum of 9 displays two broad absorp-
tions centered at λmax = 583 nm and λmax = 808 nm in dichloro-
methane. When the solvent was changed to 10%
dichloromethane in hexane, which possesses a much lower
808 (3.64)
583 (4.11)
815
611
0.0853
0.5618
H → L/0.94
H − 2 → L/0.27
H − 1 → L/0.89
H → L + 2/0.62
H − 1 → L + 1/0.40
H → L + 1/0.55
H → L + 2/0.59
542 sh (4.03)
533
522
0.0062
0.0067
a H = HOMO. b L = LUMO. c CI = configuration interaction.
polarity, these bands showed an apparent blue-shift to λmax
=
572 nm and 753 nm, respectively. These results suggest the intra-
molecular CT character of these absorption bands (Fig. 3).13 The
bis-TCNE adduct 12 exhibits strong and broad CT absorption
bands at 443 nm and 544 (sh) nm in dichloromethane.
Electrochemistry
The time dependence density functional theory (TD-DFT) cal-
culation was performed for 9′′, in which the isopropyl groups
were replaced with H groups, in order to clarify the origin of the
broad absorption for 9.14 The frontier Kohn–Sham orbitals of 9′′
are shown in Fig. 4. The broad CT-absorption beyond the near-
infrared region for 9′′ originated from the overlap of the HOMO
located on the azulene-ring with the LUMO that was mainly
located on the 6,6-dicyanofulvene moiety. The broad absorption
of 9 centered at λmax = 583 nm was confirmed to arise from the
overlap of some transitions as shown in Table 2.
To clarify the electrochemical properties, the redox behavior of
5–9 and 12 was examined by CV and differential pulse voltam-
metry (DPV). The redox potentials (in volts vs. Ag/AgNO3) of
5–9 and 12 are summarized in Table 3. The cyclic voltammo-
grams of 6, 8 and 12 are shown in Fig. 5–7, respectively.
All the novel donor–acceptor chromophores 5–9 and 12
showed reversible reduction waves in CV. The TCBD derivative
5 exhibited a reversible two-step reduction wave, of which
potentials were identified at −0.39 V and −0.87 V by CV. These
results could be attributable to the generation of a dianionic
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Table 3 Redox potentialsa of the compounds 5–9 and 12
ox
red
red
red
red
Sample
Method
E1
E1
E2
E3
E4
5
CV
(DPV)
CV
(DPV)
CV
(DPV)
CV
(DPV)
CV
(DPV)
CV
−0.39
−0.87
(+1.87)
+0.57
(+0.56)
(−0.37)
−0.80
(−0.85)
−1.08
6
(−0.78)
−0.49
(−1.06)
−0.90
7
−1.76
(+1.21)
(+1.40)
(+0.98)
(+1.35)
(−0.47)
(−0.88)
−0.37
(−1.74)
−1.33
(−1.31)
8
+0.23
(+0.21)
−0.32
(−0.35)
−0.59
(−1.66)
9
(−0.30)
−0.44
(−0.57)
−0.62
(−1.75)
−0.99
(−0.97)
12
−1.08
(DPV)
(−0.42)
(−0.60)
(−1.06)b
a Redox potentials were measured by CV and DPV [V vs. Ag/AgNO3, 1 mM in benzonitrile containing Et4NClO4 (0.1 M), Pt electrode (internal
diameter: 1.6 mm), scan rate = 100 mV s−1, and Fc/Fc+ = +0.15 V]. In the case of reversible waves, redox potentials measured by CV are presented.
The peak potentials measured by DPVare shown in parentheses. b The E5red and E6red were observed at −1.88 Vand −1.96 V, respectively.
Fig. 5 Cyclic voltammogram of 6 (1 mM) in benzonitrile containing
Fig. 7 Cyclic voltammogram of 12 (1 mM) in benzonitrile containing
Et4NClO4 (0.1 M) as a supporting electrolyte; scan rate = 100 mV s−1
.
Et4NClO4 (0.1 M) as a supporting electrolyte; scan rate = 100 mV s−1
.
Scheme 6 Presumed electrochemical behavior of 5.
owing to the redox activities of the TCBD and 1,2-bis(1,3-
dithiol-2-ylidene)ethane units (Fig. 5). The first reduction poten-
tial of 6 (−0.80 V) was much more negative than that of
5 (−0.39 V). These results indicate that the 1,2-bis(1,3-dithiol-2-
ylidene)ethane substituent on 6 leads to an increase in the
LUMO-level of the molecule, due to the strong electron-donating
nature of the 1,2-bis(1,3-dithiol-2-ylidene)ethane moiety.
Fig. 6 Cyclic voltammogram of 8 (1 mM) in benzonitrile containing
Et4NClO4 (0.1 M) as a supporting electrolyte; scan rate = 100 mV s−1
.
species owing to electron acceptance by the TCBD moiety, as
illustrated in Scheme 6.
In the case of the electrochemical analysis of 6, a reversible
one-stage two-electron oxidation wave (+0.57 V) and two-step
reduction wave (−0.80 V and −1.08 V) was observed in CV,
The electrochemical reduction of 7 showed a reversible three-
stage wave in CV (−0.49 V, −0.90 V and −1.76 V) by the for-
mation of up to a trianionic species, which may include the
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reduction of an azulene ring. The electrochemical reduction of 8
exhibited a reversible three-step reduction wave, whose poten-
tials were identified at +0.21 V, −0.35 V and −1.31 V by DPV,
in which the second reduction wave could be concluded to be a
two-electron transfer in one step to form a tetraanionic species
(Fig. 6). The first reduction of 8 (+0.23 V) showed rather less
negativity, compared with those of 5 (−0.39 V) and 7 (−0.49 V).
Furthermore, the first reduction potential of 8 exhibited the least
negative value, compared with those previously reported for
TCBD and dicyanoquinodimethane (DCNQ) derivatives.15
These results indicate that the combined two TCBD units in 8
fairly reduce the LUMO-level resulting in the increase of the
π-accepting property.
A reversible two-stage wave was also observed in 9 in CV
(−0.32 V and −0.59 V), owing to the formation of a dianionic
species. The electrochemical reduction of 12 exhibited a reversi-
ble four-step reduction wave, the potentials of which were
identified at −0.42, −0.60, −0.97 and −1.06 V by DPV, which
were attributed to the formation of up to a tetraanionic species
due to the reduction of the two TCBD moieties (Fig. 7).
Ministry of Education, Culture, Sports, Science, and Technology,
Japan.
Notes and references
1 Special Issue on Molecular Conductors: Chem. Rev., 2004, 104,
4887–5782, edited by P. Batail.
2 H. Hopf, M. Kreutzer and M. P. G. Jones, Angew. Chem., Int. Ed. Engl.,
1991, 30, 1127–1128.
3 (a) M. Kivala, C. Boudon, J.-P. Gisselbrecht, P. Seiler, M. Gross and
F. Diederich, Angew. Chem., Int. Ed., 2007, 46, 6357–6360;
(b) B. B. Frank, M. Kivala, B. C. Blanco, B. Breiten, W. B. Schweizer,
P. R. Laporta, I. Biaggio, E. Jahnke, R. R. Tykwinski, C. Boudon,
J.-P. Gisselbrecht and F. Diederich, Eur. J. Org. Chem., 2010,
2487–2503.
4 K.-P. Zeller, Azulene in Methoden der Organischen Chemie (Houben-
Weyl), ed. H. Kropf, Thieme, Stuttgart, Germany, 4th edn, 1985, vol. V,
part 2c, pp. 127–418.
5 (a) T. Shoji, S. Ito, K. Toyota, M. Yasunami and N. Morita, Chem.–Eur.
J., 2008, 14, 8398–8408; (b) T. Shoji, S. Ito, K. Toyota, T. Iwamoto,
M. Yasunami and N. Morita, Eur. J. Org. Chem., 2009, 4316–4324;
(c) T. Shoji, M. Maruyama, S. Ito and N. Morita, Bull. Chem. Soc. Jpn.,
2012, 85, 761–773.
6 (a) A. H. M. Elwahy and K. Hafner, Tetrahedron Lett., 2000, 41,
2859–2862; (b) K. H. H. Fabian, A. H. M. Elwahy and K. Hafner,
Eur. J. Org. Chem., 2006, 791–802; (c) A. H. M. Elwahy and K. Hafner,
Eur. J. Org. Chem., 2006, 3910–3916.
Conclusions
7 A. S. Hay, J. Org. Chem., 1962, 27, 3320–3321.
In conclusion, azulene-substituted butadiynes 2, 3 and 4 were
prepared by Hay and Glaser reactions, respectively. A series of
azulene-substituted TCBD chromophores possessing an acety-
lene moiety, 5 and 7, were synthesized by the [2 + 2] cyclo-
addition reaction of 2 and 3, respectively, with TCNE. The
[2 + 2] cycloaddition of 5 with TTF gave the novel donor–acceptor
chromophore 6. The reaction of 7 with TCNE gave the product 8
with two TCBD moieties and the 6,6-dicyanofulvene derivative
9. Compound 11 was prepared by the Pd-catalyzed alkynylation
of 1,4-diiodobenzene with butadiyne 10, which was prepared by
the desilylation of 4, under Sonogashira–Hagihara conditions.
The synthesis of the TCNE/TTF double adduct of 10 was also
examined, but the [2 + 2] cycloaddition reaction of 12 with TTF
did not afford the presumed double adduct. An analysis by CV
and DPV showed that compound 6 exhibited attractive ampho-
teric redox properties, owing to the electrochemical oxidation of
1,2-bis(1,3-dithiol-2-ylidene)ethane and the reduction of TCBD
moieties. It is noteworthy that the first reduction potential of 8
with two TCBD moieties exhibited the least negative value,
compared with those of TCBD and DCNQ derivatives pre-
viously reported. Construction of reversible multistage redox
systems based on the donor–acceptor system is currently being
examined in our laboratory.
8 (a) C. Glaser, Ber. Dtsch. Chem. Ges., 1869, 2, 422–424; (b) P. Siemsen,
R. C. Livingstone and F. Diederich, Angew. Chem., Int. Ed., 2000, 39,
2632–2657.
9 (a) J. Xu, X. Liu, J. Lv, M. Zhu, C. Huang, W. Zhou, X. Yin, H. Liu,
Y. Li and J. Ye, Langmuir, 2008, 24, 4231–4237; (b) W. Zhou, J. Xu,
H. Zheng, H. Liu, Y. Li and D. Zhu, J. Org. Chem., 2008, 73,
7702–7709; (c) W. Zhou, J. Xu, H. Zheng, X. Yin, Z. Zuo, H. Liu and
Y. Li, Adv. Funct. Mater., 2009, 19, 141–149; (d) H. Liu, J. Xu, Y. Li and
Y. Li, Acc. Chem. Res., 2010, 43, 1496–1508; (e) S. Chen, Y. Li, C. Liu,
W. Yang and Y. Li, Eur. J. Org. Chem., 2011, 6445–6451.
10 A detailed reaction mechanism was recently reported: Y.-L. Wu,
P. D. Jarowski, W. B. Schweizer and F. Diederich, Chem.–Eur. J., 2010,
16, 202–211.
11 Intramolecular migration of cyano group was recently reported:
M. Yamada, W. B. Schweizer, F. Schoenebeck and F. Diederich, Chem.
Commun., 2010, 46, 5334–5336.
12 G. Jayamurugan, J.-P. Gisselbrecht, C. Boudon, F. Schoenebeck,
W. B. Schweizer, B. Berneta and F. Diederich, Chem. Commun., 2011,
47, 4520–4522.
13 (a) P. Suppan and N. Ghoneim, Solvatochromism, Royal Society of
Chemistry, Cambridge, 1997; (b) P. Suppan, J. Photochem. Photobiol., A,
1990, 50, 293–330; (c) C. Reichardt, Solvent and Solvent Effects in
Organic Chemistry, Wiley-VCH, New York, 2004.
14 The B3LYP/6-31G** time-dependence density functional calculation was
performed with Spartan’10, Wavefunction, Irvine, CA.
15 (a) S. Kato and F. Diederich, Chem. Commun., 2010, 46, 1994–2006;
(b) B. Breiten, Y.-L. Wu, P. D. Jarowski, J.-P. Gisselbrecht, C. Boudon,
M. Griesser, C. Onitsch, G. Gescheidt, W. B. Schweizer, N. Langer,
C. Lennartz and F. Diederich, Chem. Sci., 2011, 2, 88–93;
(c) T. Michinobu, Chem. Soc. Rev., 2011, 40, 2306–2316;
(d) M. Morimoto, K. Murata and T. Michinobu, Chem. Commun., 2011,
47, 9819–9821; (e) T. Shoji, J. Higashi, S. Ito, T. Okujima, M. Yasunami
and N. Morita, Chem.–Eur. J., 2011, 17, 5116–5129; (f) T. Shoji, S. Ito,
T. Okujima and N. Morita, Eur. J. Org. Chem., 2011, 5134–5140;
(g) T. Shoji, J. Higashi, S. Ito, T. Okujima, M. Yasunami and N. Morita,
Org. Biomol. Chem., 2012, 10, 2431–2438.
Acknowledgements
This work was partially supported by a Grant-in-Aid for
Research Activity Start-up (Grant 22850007 to T.S.) from the
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 8308–8313 | 8313