Stereoselective electrocatalytic oxidative coupling of phenylacetonitriles: Facile and convenient way to trans-α,β-dicyanostilbenes

Article abstract of DOI:10.1002/ejoc.200601108

Electrolysis of phenylacetonitriles in methanol in an undivided cell in the presence of sodium halides as mediators induces a stereoselective oxidative coupling process that results in the formation of trans-α,β- dicyanostilbenes in 60-85% yield with 40-70% current efficiency. The application of this efficient stereoselective electrocatalytic method to the formation of trans-α,β-dicyanostilbenes represents an environmentally benign synthetic strategy and is valuable from the viewpoint of large-scale processes. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejoc.200601108

FULL PAPER
DOI: 10.1002/ejoc.200601108
Stereoselective Electrocatalytic Oxidative Coupling of Phenylacetonitriles:
Facile and Convenient Way to trans-α,β-Dicyanostilbenes
Michail N. Elinson,*[a] Alexander S. Dorofeev,*[a] Sergey K. Feducovich,[a]
Pavel A. Belyakov,[a] and Gennady I. Nikishin[a]
Keywords: Stilbenes / Electrochemistry / Homogeneous catalysis / Stereoselectivity / Dimerization
Electrolysis of phenylacetonitriles in methanol in an un-
divided cell in the presence of sodium halides as mediators
induces a stereoselective oxidative coupling process that re-
sults in the formation of trans-α,β-dicyanostilbenes in 60–
85% yield with 40–70% current efficiency. The application
of this efficient stereoselective electrocatalytic method to the
formation of trans-α,β-dicyanostilbenes represents an envi-
ronmentally benign synthetic strategy and is valuable from
the viewpoint of large-scale processes.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
less than 20% to as high as 80%. Moreover, differences in
the resulting stereoselectivities are observed even under the
same experimental conditions.[1,3–5] This indicates that the
reaction is highly sensitive to the reaction conditions and
to the chemical structures of the substrates. According to
the literature procedures, the essential conditions that are
necessary to obtain α,β-dicyanostilbenes in a stereoselective
manner with a preparative yield are the careful control of
the temperature and the concentrations of the base and
halogen components; the need for a free halogen constitutes
a major industrial drawback as well as scale-up limitations.
By considering the unique synthetic and biomedical poten-
tial of cyanostilbenes, as well as the large amount of mate-
rial demanded in the optoelectronic industry, a facile and
environmentally benign stereoselective approach to α,β-di-
cyanostilbenes, which is convenient to perform and suitable
for large-scale preparations, is welcome.
The advances in electrosynthesis in the last few decades
has provided organic chemists with a new and versatile syn-
thetic device of great promise.[6] One of the most fascinating
methods available in organic electrochemistry today is elec-
trocatalytic oxidation that takes place in the presence of me-
diators or mediatory systems. These mediators allow the use
of undivided cells and generally simplify the conduction of
the electrochemical process. Among a variety of mediators,
the redox system halide anion/halogen is one of the most
useful for organic synthesis and large-scale processes.[7] This
type of mediatory system was already successfully employed
by us in a number of electrocatalytic transformations of cy-
ano-functionalized C–H acids that contained the oxidative
coupling process as an intermediate step.[8] The electrolysis
in an undivided cell in the presence of an alcohol as a sol-
vent and alkali metal halides affords the simultaneous gen-
eration of catalytic quantities of strong base (alkoxide
Introduction
In recent years, functionally substituted α,β-dicyanostil-
benes (or bisarylmaleonitriles and bisarylfumaronitiles de-
pending on the configuration of the double bond) have
played an increasing role in the synthetic approach to prom-
ising compounds in the field of materials and biomedical
sciences. α,β-Dicyanostilbenes are convenient precursors for
the synthesis of nonsymmetrical phthalocyanines and tet-
raazaporphyrines, and their metal complexes exhibit a wide
range of unique properties[1] that allows their usage not
only in practical industrial areas, but also in the fields of
nonlinear optics and photodynamic cancer therapy.[2]
Furthermore, tetraazaporphyrines are analogous to por-
phyrins, which play significant roles in different biological
systems.[2c,2d] Functionally substituted α,β-dicyanostilbenes
are valuable synthetic precursors for unusual nondoped
host emitters for red organic light-emitting diodes (OLEDs)
and appear as basic structural units in novel types of photo-
luminescent and electrochemically active soluble π-conju-
gated polymers.[3] The recent result shows that there is con-
siderable binding affinity and selectivity of nonsteroidal 2,3-
bisarylpropionitriles to estrogen receptors and accentuates
the biomedical interest of the cyanostilbene moiety.[4]
The preparation of α,β-dicyanostilbenes from phenylace-
tonitrile derivatives in either Br2- or I2-containing alcoholic
alkoxide or aqueous hydroxide by an oxidative coupling re-
action has been known since the late 19th century.[5] How-
ever, the reaction has been performed somewhat differently
in many cases, and the reaction yields widely varied from
[a] N. D. Zelinsky Institute of Organic Chemistry,
Leninsky prospect 47, 119991 Moscow, Russia
Fax: +7-495-135-53-28
E-mail: elinson@ioc.ac.ru
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M. N. Elinson, A. S. Dorofeev et al.
FULL PAPER
anion) at the cathode and halogen at the anode, which then
First, to evaluate the synthetic potential of the proposed
go through a chemical oxidative cycle in solution that al- procedure and to optimize the electrolytic conditions, the
lows them to return back to the electrodes as initial halide electrocatalytic oxidative coupling of (4-chlorophenyl)ace-
anion and alcohol. The mild catalytic nature of the media- tonitrile (1a) was studied (Table 1, Entries 1–6).
tory oxidative process enables low current concentrations of
The electrolysis of (4-chlorophenyl)acetonitrile (1a) in
base and halogen along with a neutral pH of the reaction methanol in an undivided cell in the presence of sodium
solution, which seems to be a key factor for the selective iodide as the mediator under the constant current density
oxidative coupling of C–H acids bearing a nitrile function- of 100 mAcm–2 at 30 °C led to the stereoselective formation
ality. Therefore, the application of the described electrocata- of bis(4-chlorophenyl)fumaronitrile (2a) in 51% yield
lytic methodology to the base–halogen-promoted oxidative (Table 1, Entry 1). The decrease in the temperature of elec-
coupling process of phenylacetonitriles is highly promising trolysis from 30 to 0 °C increased the yield of 2a to 68%
as it allows the combination of the synthetic virtues of a (Table 1, Entries 2 and 3). Excellent conversions (98–99%)
mild catalytic oxidation protocol with the benefits and con- of starting material were obtained in all experiments for a
venience of a cheap and environmentally responsible chemi- 30 to 0 °C temperature interval after passing 2.5 Fmol–1 of
cal reagent Ϫ electricity.
electricity (Table 1, Entries 1–3). The reaction product was
isolated from the reaction mixture by direct filtration after
electrolysis. According to NMR spectroscopic and GC
analysis, the filtrate of the reaction mixture contained oligo-
meric by products, which may be a result of undesired ad-
dition processes that are possible for anions of cyano-func-
tionalized C–H acids (Table 1, Entries 1–3). An electrolysis
temperature of 0 °C was found to be optimal and gave 68%
yield of 2a with 98–99% conversion (Table 1, Entry 3). Fur-
ther decrease in the temperature to –30 °C suppressed the
formation of undesirable oligomeric species, but the conver-
sion of 2a in latter cases did not exceed 70–75% (Table 1,
Entries 4 and 5).
Results and Discussion
In the present study we report our results on the stereose-
lective electrocatalytic oxidation of phenylacetonitriles 1a–e
into trans-α,β-dicyanostilbenes 2a–e in methanol in an un-
divided cell in the presence of sodium halides as mediators
(Scheme 1, Table 1).
Sodium bromide is a more efficient mediator than so-
dium iodide for the process studied. The bromine formed at
the anode during the electrolysis is a more effective oxidizer
compare to iodine, and its presence promotes the chemical
oxidation cycle in solution and the removal of the starting
material from the undesired oligomerization reaction. Thus,
electrocatalytic oxidation of (4-chlorophenyl)acetonitrile
(1a) in methanol in an undivided cell in the presence of
sodium bromide as the mediator at 0 °C leads to corre-
sponding fumaronitrile 2a in 85% yield (Table 1, Entry 6).
Scheme 1.
Table 1. Stereoselective indirect electrochemical oxidative coupling of phenylacetonitriles 1a–e.[a]
Entry
Phenylacetonitrile
X
Mediator
Temperature
Electricity passed
Product yield
[%][b]
Current yield
[%]
[°C]
[Fmol–1
]
1
2
3
1a
1a
1a
1a
1a
1a
1a
1a
1b
1b
1c
1c
1d
1d
1e
1e
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
H
H
4-F
4-F
4-Br
4-Br
2-CN
2-CN
NaI
NaI
NaI
NaI
NaI
NaBr
NaBr
NaBr
NaI
NaBr
NaI
NaBr
NaI
NaBr
NaI
30
10
0
–10
–30
0
0
0
0
0
0
0
0
0
0
0
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.8
2.8
2a, 51
2a, 63
2a, 68
2a, 55
2a, 50
2a, 85
2a, 81
2a, 78
2b, 59
2b, 61
2c, 58
2c, 65
2d, 74
2d, 86
2e, 53
2e, 56
41
51
54
44
40
68
65
63
47
49
46
52
59
69
36
40
4[c]
5[c]
6
7[d]
8[e]
9
10
11
12
13
14
15
16
NaBr
[a] Phenylacetonitrile (10 mmol), mediator (5 mmol), MeOH (20 mL), iron cathode, graphite anode, undivided cell, current density
100 mAcm–2, 98–99% conversion of starting material. [b] Yields of isolated compounds based on starting 1. [c] 70–75% conversion of
starting material. [d] 2.5 mmol of mediator were used. [e] 2 mmol of mediator were used.
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Oxidative Coupling of Phenylacetonitriles to give trans-α,β-Dicyanostilbenes
FULL PAPER
The effect of a varied phenylacetonitrile/mediator ratio
was experimentally studied next. The electrolyses of
10 mmol of (4-chlorophenyl)acetonitrile (1a) in the presence
of 5, 2.5 or 2 mmol of sodium bromide under the condi-
tions indicated in Table 1 proceeded with the same conver-
sions of starting material and led to similar reaction yields
Scheme 2.
The formation of either bromine or iodine at the anode
of 85–78% (Table 1, Entries 6–8). These results confirm the is visually observed by the corresponding colour of the
requirement for only a catalytic quantity of sodium halide solution when the electrolysis proceeds without stirring.
and underscore the catalytic mediatory nature of the elec- The cathodic process leads to the formation of methoxide
trochemical process. The whole quantity of mediator could anions and liberation of hydrogen gas. In solution, meth-
be easily isolated from the reaction mixture after electroly- oxide anions can deprotonate phenylacetonitrile 1 to give
sis.
rise to phenylacetonitrile anion 3 (Scheme 3). The subse-
Under the optimal conditions (sodium halide as media- quent halogenation of initially formed carbanion 3 leads to
tor, 0 °C reaction temperature, 2.5–2.8 Fmol–1 electricity α-halobenzylcyanide 4. Then, two pathways are possible for
passed) the electrolysis of phenylacetonitriles 1a–e in meth- the following steps. α-Halobenzylcyanide 4 could be either
anol in an undivided cell afforded corresponding bisarylfu- attacked by carbanion 3 with formation of corresponding
maronitriles 2a–e in 60–85% substance yields and 40–70% succinonitrile 5 (pathway A), or it can undergo deproton-
current yields. Products 2a–e can be isolated by direct fil- ation by methoxide anions to give rise to anion 7 (pathway
tration of the reaction mixture after electrolysis and they B). Both pathways A and B do lead to corresponding halo-
do not need any further purification.
succinonitrile 8 either by halogenation of intermediate suc-
This electrocatalytic process proceeds with excellent ster- cinonitrile 5 or by the coupling of anion 7 with α-haloben-
eoselectivity. In all experiments, only a single isomer of α,β- zylcyanide 4, respectively. According to kinetic studies of
dicyanostilbenes was detected both in the reaction mixture the chemical oxidative coupling of phenylacetonitrile, path-
and in the solid product isolated after electrolysis. The trans way A was found to be slower than pathway B because of
configuration of the double bond in obtained α,β-dicya- the rate-determining halogenation step of succinonitrile
nostilbenes 2a,b,d was established by comparison of the anion 6.[10] However, in the case of excess base and small
NMR spectral characteristics (for 2b,d) and melting point quantities of halogen, pathway A could be preferable in
values (for 2a,b,d) with the literature data.[9] We presume which case the reaction mainly leads to the formation of
that the structures of α,β-dicyanostilbenes 2c,e also possess succinonitrile 5.[10] As for the electrocatalytic oxidation of
a trans configuration of the double bond.
phenylacetonitriles 1a–e, we were not able to determine the
With the above results taken into consideration, our pre- presence of succinonitrile 5 either in the reaction mixture
vious data on the mechanisms of electrochemically induced during the electrolysis (samples after 1, 1.5 and 2 Fmol–1)
oxidative coupling of C–H acids,[8] and previous kinetic or in the solid product collected after the process (Table 1,
studies on the chemical dehydrodimerization reaction of Entries 1–4 and 6–16). The presence of 9% of succinonitrile
phenylacetonitrile,[10] the following mechanism for the ster- 5a was detected only when the electrooxidation was con-
eoselective electrocatalytic transformation of phenylacetoni- ducted at –30 °C after 1 Fmol–1 passed (Table 1, Entry 5).
triles 1a–e into dicyanostilbenes 2a–e is proposed. To start, These results indicate that both mechanistic pathways are
the reactions that take place at each electrode during the involved in the oxidation coupling reaction, but owing to
process are shown in Scheme 2.
the low and equal current concentrations of base and halo-
Scheme 3.
Eur. J. Org. Chem. 2007, 3023–3027
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3025

M. N. Elinson, A. S. Dorofeev et al.
FULL PAPER
Scheme 4.
gen in the solution during the electrocatalytic process, path- due to its catalytic nature and the use of a cheap and envi-
way B is faster than pathway A and formation of succinon- ronmentally benign chemical reagent – electricity.
itrile 5 is not a preferential route under the conditions
studied.
Experimental Section
The reaction of halosuccinonitrile 8 with methoxide
leads to the formation of conjugated anion 9 (Scheme 4).
The steric hindrance between the two phenyl groups seems
to be the main reason for the subsequent stereoselective eli-
mination of halide anion from the thermodynamically fav-
oured conformation of 9, which gives rise to trans-α,β-dicy-
anostilbene 2.
The electrocatalytic oxidative conditions are a key feature
of this process; superior stereoselectivity along with good
yields in the coupling of phenylacetonitriles are observed.
Recently, it was noted that the double bond of α,β-dicya-
nostilbenes is sensitive to isomerization in the presence of
bases, including alkoxides.[11] It is conceivable that the base
acts as a nucleophile and transforms the double bond to a
rotary C–C single bond. The C–C double bond can then be
restored, but with a different configuration (from cis to
trans or from trans to cis), after elimination of the substi-
tuted base. In our case, the low current concentrations of
the methoxide anion and halogen during the electrocatalytic
process afford not only good substance yield in the oxidat-
ive chemistry of species bearing the base-sensitive nitrile
group, but the base-promoted isomerization of the formed
double bond is also avoided.
General Remarks: All melting points were measured with a Gallen-
kamp melting point apparatus and are uncorrected. GC analysis
was carried out with an LKhM–80 chromatograph with a flame-
ionization detector. Columns: (1) fused-silica capillary column HP–
1 (5 mϫ0.53 mmϫ2.65 µm), (2) glass column (3 mϫ3 mm) with
10% FFAP with a Chromaton N–Super (0.13–0.16 mm). 1H and
13C NMR spectra were recorded with a Bruker WM-250 spectrom-
eter at ambient temperature. Chemical shift values are relative to
Me4Si. IR spectra were registered with a SPECORD M82 spec-
trometer. Mass spectra (EI = 70 eV) were obtained directly with a
Finningan MAT INCOS 50 spectrometer.
Typical Electrolysis Procedure: A solution of phenylacetonitrile
(10 mmol) and sodium halide (5 mmol) in methanol (20 mL) was
electrolyzed in an undivided cell equipped with a magnetic stirrer,
a graphite anode and an iron cathode at 0 °C under a constant
current density of 100 mAcm–2 (I = 500 mA, electrodes square
5 cm2) until the quantity of electricity indicated in Table 1 was
passed. After the electrolysis was finished, the solution was filtered
to isolate the solid product, which was then rinsed with an ice-
cold methanol/water solution (9:1, 2 mL), and dried under reduced
pressure.
Bis(4-chlorophenyl)fumaronitrile (2a): White solid. Yield: 2.54 g
(85%). M.p. 193–194 °C (ref.[12] 188 °C). H NMR (250.13 MHz,
l
3
3
CDCl3): δ = 7.53 (d, JH,H = 8.7 Hz, 4 H, Ar), 7.79 (d, JH,H
=
8.7 Hz, 4 H, Ar) ppm. 13C NMR (62.53 MHz, CDCl3): δ = 116.2
(2 C), 124.6 (2 C), 129.7 (4 C), 130.0 (4 C), 130.2 (2 C), 138.4 (2
Conclusions
C) ppm. IR (KBr): ν = 3092, 2224, 1592, 1492, 1404, 1256, 1092,
˜
1012, 828, 824 cm–1. MS: m/z (%) = 299 (15) [M]+, 298 (71), 263
(72), 228 (100), 201 (35), 114 (27), 100 (41), 87 (24), 75 (54), 50
(42). C16H8Cl2N2 (299.16): calcd. C 64.24, H 2.70, Cl 23.70, N 9.36;
found C 64.20, H 2.74, Cl 23.71, N 9.30.
The simple electrocatalytic system presented here can
produce, under neutral and mild conditions, a stereoselec-
tive and efficient transformation of phenylacetonitriles into
the corresponding trans-α,β-dicyanostilbenes in 60–85%
yield with 40–70% current efficiency. This electrocatalytic
process offers a facile and convenient way to generate trans-
α,β-dicyanostilbenes, which are valuable precursors for a
variety of optoelectronic materials and biologically relevant
systems. The mild catalytic nature of the developed media-
tory oxidation process is the key feature that allows supe-
rior stereoselectivities and good product yields in such a
reagent-sensitive reaction. The electrocatalytic procedure
utilizes simple equipment and an undivided cell; it is easily
Diphenylfumaronitrile (2b): White solid. Yield: 1.41 g (61%). M.p.
l
156–157 °C (ref.[13] 155 °C). H NMR (250.13 MHz, CDCl3): δ =
7.50–7.57 (m, 6 H, Ar), 7.80–7.86 (m, 4 H, Ar) ppm.[1b]
Bis(4-fluorophenyl)fumaronitrile (2c): White solid. Yield: 1.73 g
(65%). M.p. 192 °C. lH NMR (250.13 MHz, CDCl3): δ = 7.23–7.26
(m, 4 H, Ar), 7.83–7.87 (m, 4 H, Ar) ppm. 13C NMR (62.53 MHz,
2
CDCl3): δ = 116.5 (d, JC,F = 22.3 Hz, 4 C), 124.1 (2 C), 127.6 (2
3
1
C), 127.8 (2 C), 130.8 (d, JC,F = 9.1 Hz, 4 C), 164.3 (d, JC,F
=
253.5 Hz, 2 C) ppm. IR (KBr): ν = 3080, 2224, 1600, 1516, 1416,
˜
1256, 1160, 1016, 840, 784 cm–1. MS: m/z (%) = 266 (100) [M]+,
carried out and is valuable from an industrial point of view 265 (56), 246 (30), 239 (29), 145 (20), 119 (25), 106 (22), 94 (21),
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Oxidative Coupling of Phenylacetonitriles to give trans-α,β-Dicyanostilbenes
FULL PAPER
York, 2000; d) K. M. Kadish, R. M. Smith, R. Guilard (Eds.),
The Porphyrin Handbook, 11–20, Academic Press, New York,
2003.
75 (49), 50 (23). C16H8F2N2 (266.25): calcd. C 72.18, H 3.03, N
10.52; found C 72.10, H 3.09, N 10.45.
Bis(4-bromophenyl)fumaronitrile (2d): White solid. Yield: 3.33 g
[3] a) H.-C. Yeh, S.-J. Yeh, C.-T. Chen, Chem. Commun. 2003,
2632–2633; b) Q. Fang, B. Jiang, B. Xu, W. Wang, F. Yu, X.
Wu, Macromol. Rapid Commun. 2004, 25, 1429–1432; c) W.-C.
Wu, H.-C. Yeh, L.-H. Chan, C.-T. Chen, Adv. Mater. 2002, 14,
1072–1075.
[4] M. J. Meyers, J. Sun, K. E. Carlson, G. A. Marriner, B. S. Katz-
enellenbogen, J. A. Katzenellenbogen, J. Med. Chem. 2001, 44,
4230–4251.
[5] For example, see: a) L. Chalanay, E. Knoevenagel, Ber. Dtsch.
Chem. Ges. 1892, 25, 285–288; b) G. Heller, Justus Liebigs Ann.
Chem. 1904, 332, 247–304; c) A. H. Cook, R. P. Linstead, J.
Chem. Soc. 1937, 929–933; d) C. F. Koelsch, S. Wawzonek, J.
Org. Chem. 1941, 6, 684–689; e) J. Niederl, A. Ziering, J. Am.
Chem. Soc. 1942, 64, 2486–2487; f) M. Wiezmann, S. Patai, J.
Am. Chem. Soc. 1949, 71, 2587; g) D. G. Coe, M. M. Gale,
R. P. Linstead, C. J. Timmons, J. Chem. Soc. 1957, 123–130.
[6] a) H. Lund (Ed.), Organic Electrochemistry, 4th ed., Marcel
Dekker Inc., New York, 2000; b) S. Torii (Ed.), Novel Trends
in Electroorganic Synthesis, Springer, Berlin, 1998.
l
(86%). M.p. 216–217 °C (ref.[5f] 214 °C). H NMR (250.13 MHz,
CDCl3): δ = 7.68–7.71 (m, 8 H, Ar) ppm.[14]
Bis(2-cyanophenyl)fumaronitrile (2e): White solid. Yield: 1.57 g
(56%). M.p. 239 °C. lH NMR (250.13 MHz, [D6]DMSO): δ = 7.88
3
3
(t, J1H,H = 7.5 Hz, J2H,H = 7.5 Hz, 2 H, Ar), 7.98–8.12 (m, 4 H,
Ar), 8.19 (d, 3JH,H = 7.6 Hz, 2 H, Ar) ppm. 13C NMR (62.53 MHz,
[D6]DMSO): δ = 111.0 (2 C), 113.9 (2 C), 115.9 (2 C), 127.6 (2 C),
130.9 (2 C), 132.7 (2 C), 133.1 (2 C), 134.6 (2 C), 134.7 (2 C) ppm.
IR (KBr): ν = 3076, 2232, 1592, 1572, 1484, 1444, 1288, 1248, 1188,
˜
764 cm–1. MS: m/z (%) = 280 (100) [M]+, 279 (55), 253 (60), 226
(22), 200 (13), 126 (22), 100 (20), 87 (16), 75 (40), 50 (33). C18H8N4
(280.29): calcd. C 77.13, H 2.88, N 19.99; found C 77.11, H 2.94,
N 19.92.
Acknowledgments
[7] T. Shono, Electroorganic Chemistry as a New Tool in Organic
Synthesis, Springer, Berlin, 1994.
The authors gratefully acknowledge the financial support of the
Russian Foundation for Basic Research (project no. 06-03-32181a)
and the Presidential Scholarship Program for State Support of
Leading Science Schools of Russian Federation (project no.
5022.2006.3). A. S. D. is indebted to the Russian Science Support
Foundation for a postgraduate fellowship in 2007.
[8] For recent publications, see: a) M. N. Elinson, S. K. Feducov-
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Nikishin, Tetrahedron Lett. 2006, 47, 9129–9133; b) M. N. Elin-
son, S. K. Feducovich, Z. A. Starikova, A. N. Vereshchagin,
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A. N. Vereshchagin, S. V. Gorbunov, G. I. Nikishin, Tetrahe-
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[9] cis and trans Isomers of α,β-dicyanostilbenes are distinctive by
1
their characteristic signals in the H NMR aromatic region of
the spectra (for example, see ref.[1b]), and by melting points.
References on melting point values and NMR spectroscopic
data for known trans-α,β-dicyanostilbenes are given in the Ex-
perimental Section.
[10] Y. Ogata, K. Nagura, J. Org. Chem. 1974, 39, 394–399.
[11] R. Huisgen, X. Li, H. Giera, E. Langhals, Helv. Chim. Acta
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[2] For reviews on practical applications and physicochemical
properties of phthalocyanine and tetraazoporphyrine deriva-
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1992, 1993, 1996; b) N. B. McKeown, Phthalocyanine Materials [14] H.-C. Yeh, L.-H. Chan, W.-C. Wu, C.-T. Chen, J. Mater. Chem.
Synthesis Structure and Function, Cambridge University Press,
Cambridge, 1998; c) K. M. Kadish, R. M. Smith, R. Guilard
(Eds.), The Porphyrin Handbook, 1–10, Academic Press, New
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Received: December 21, 2006
Published Online: April 30, 2007
Eur. J. Org. Chem. 2007, 3023–3027
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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