Synthesis and characterization of new helically chiral heptacyclic systems

Article abstract of DOI:10.1016/j.tetlet.2015.10.025

New helically chiral heptacyclic systems with cyano groups at selected positions have been synthesized in good yields, via a four-step sequence, from readily available materials. The optical properties of the target helicenes were investigated by UV-visible absorption and photoluminescence spectroscopy and an emission in the visible region was observed. The energy levels of these organic materials were determined by cyclic voltammetry and showed a relatively high electronic affinity, indicating that they may be good candidates for electron-injection hole blocking layer in organic light-emitting diodes.

Full text of DOI:10.1016/j.tetlet.2015.10.025

Accepted Manuscript
Synthesis and characterization of new helically chiral heptacyclic systems
Mourad Ben Braiek, Faouzi Aloui, Souad Moussa, Béchir Ben Hassine
PII:
S0040-4039(15)30222-7
DOI:
http://dx.doi.org/10.1016/j.tetlet.2015.10.025
TETL 46854
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
9 May 2015
15 September 2015
6 October 2015
Please cite this article as: Braiek, M.B., Aloui, F., Moussa, S., Hassine, B.B., Synthesis and characterization of new
helically chiral heptacyclic systems, Tetrahedron Letters (2015), doi: http://dx.doi.org/10.1016/j.tetlet.2015.10.025
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Synthesis and characterization of new helically chiral heptacyclic systems
Mourad Ben Braiek, Faouzi Aloui, Souad Moussa, Béchir Ben Hassine*
Laboratory of Asymmetric Organic Synthesis and Homogenous Catalysis (UR11ES56), Faculty of Sciences,
Avenue of Environment, Monastir 5019-Tunisia
* Corresponding author: Tel.: +21673500279; fax: +21673500278.
e-mail address: bechirbenhassine@yahoo.fr
Abstract- New helically chiral heptacyclic systems with cyano groups at selected positions have
been synthesized in good yields, via a four-step sequence, from readily available materials. The
optical properties of the target helicenes were investigated by UV-visible absorption and
photoluminescence spectroscopy and an emission in the visible region was observed. The energy
levels of these organic materials were determined by cyclic voltammetry and showed a relatively
high electronic affinity, indicating that they may be good candidates for electron-injection
holeblocking layer in organic light-emitting diodes.
Keywords: Helicenes, Heck coupling, Photocyclization, Optical properties, Visible emission.
Carbohelicenes, represent an intriguing class of polycyclic aromatic hydrocarbons (PAHs)
and are composed of ortho-fused aromatic rings with a fully conjugated system and a non-planar
topology.1 They have attracted great interest owing to their unique structural features and
widespread potential applications as chiral luminescent materials,2,3 or as building blocks for
helical conjugated polymers.4 They are also considered useful for wave guides,5 non-linear
optics,6 biomolecular recognition7 and asymmetric synthesis.8 Helicenes were shown to be
effective in the development of materials with chiroptical properties which are useful for
molecular-based electronic applications.9
For instance, heptahelicene is a particularly interesting [n]helicene containing one complete
turn of the helix and high optical stability (racemization barrier 40.5 kcal mol-1).10 Such
heptacyclic structures have seen interest for their silver-binding interactions via the central
cavity.11 In addition, theoretical studies for alkali metal cations and transition metals have been
established12 and their deposition onto metal surfaces have also been investigated.13
Since Newman and Lednicer reported the first helicene in 1956,14 various methods for the
synthesis of helicenes including successive silylenol ether coupling with benzoquinone,15
1

cyclotrimerizations of acetylenes,16 carbenoid couplings,17 electrophilic aromatic cyclizations,18
radical cyclizations,19 olefin metathesis,20 transition metal catalyzed cycloisomerization21 and
Friedel-Crafts-type cyclisations22 have been described. However, in many cases, complicated
precursors, expensive and sensitive metallic catalysts or harsh reaction conditions were needed
and the helicenes were usually prepared on a small scale. Additionally, most of the strategies
adopted for the synthesis of these compounds suffer from a lack of general applicability.16,20,23
Our research group has previously reported the synthesis of enantiomerically 2-
cyanoheptahelicene (1), using a photochemical procedure, and described its use in the
epoxidation of olefins.24 Recently, Stöhr et al.25 prepared 6,13-dicyanohepahelicene (2) using the
same approach. More recently, Storch et al.26 reported the synthesis of racemic 9-
cyanoheptahelicene (3) from commercially available 9-bromoheptahelicene and proceeding via a
microwave assisted reaction. Helicene synthesis via photocyclodehydrogenation of stilbene
derivatives still represents a simple and efficient synthetic method, as it is well suited to the
laboratory scale.
In this paper, we report the synthesis of the helically chiral heptacyclic systems 3 and 4,
with cyano groups at selected positions on the aromatic rings. The synthetic approach makes use
of phenanthrene derivatives as suitable building blocks for the synthesis of appropriately
substituted 1,2-diarylethenes which can then be easily converted into helically chiral heptacyclic
systems under UV irradiation. The cyano groups in these chiral compounds serve as functional
groups for increasing the solubility of the helicenes in organic solvents and improving the optical
properties of the heptahelicene moiety.
Figure 1. Representative structures of heptahelicene carbonitriles.
2

Our strategy relies on a Mizoroki-Heck coupling reaction followed by oxidative
photocyclodehydrogenation to build the helical scaffold which has been proven to be a robust
and reliable methodology for the preparation of helicenes and their analogues.27-32 The synthesis
of target helicene 3 from commercially available 4-bromophenylacetonitrile 5 began with the
Knoevenagel reaction33 of 4-bromobenzaldehyde 6 to yield (Z)-2,3-bis(4-bromophenyl)-
acrylonitrile (7) in 94% yield.34 The latter was irradiated in toluene with a 150 W high-pressure
mercury lamp, on a 500 mg scale in the presence of catalytic iodine, to give 3,6-dibromo-9-
cyanophenanthrene (8) in 80% yield (Scheme 1).35
Having obtained key building block 8, we carried out the Mizoroki-Heck coupling reaction
with 3,6-dibromo-9-cyanophenanthrene (8) and styrene (3 equiv), in the presence of Herrmann’s
palladacycle {trans-di(μ-acetato)-bis[o-(di-o-tolylphosphino)benzyl]dipalladium} (2 mol%) as
catalyst and sodium acetate as base in N,N-dimethylacetamide (DMA), which provided 3,6-
bis(styryl)-9-cyanophenanthrene (9) in 74% yield (Scheme 1).36 The latter showed a greenish
fluorescence in solution. Diarylethene 9 underwent photocyclization in the presence of a
stoichiometric amount of iodine as the oxidizing agent and THF as a hydrogen iodide
scavenger.37 Photolysis was performed on a 200 mg scale per run, in a one litre reactor for
approximately two hours, to afford the desired helicene 3 in 61% yield (33% overall yield), after
purification by column chromatography.38
Scheme 1. Synthesis of the helically chiral heptacyclic system 3.
As a logical extension, we prepared the target dicyanohelicene 4 following the same
synthetic procedure as for helicene 3. The starting 4-bromophenylacetonitrile (5) was readily
dimerized in the presence of sodium methoxide and iodine to produce 2,3-bis(4-
bromophenyl)fumaronitrile (10) in 92% yield (Scheme 2).39 The latter underwent
3

photocyclization, using a 150 W high-pressure mercury lamp, to give 3,6-dibromo-9,10-
dicyanophenanthrene (11) in 88% yield.35
The key building block dibromophenanthrene 11 was then subjected to the Mizoroki-Heck
coupling, with styrene (3 equiv), in the presence of sodium acetate and Herrmann’s catalyst (2
mol%), to furnish (E,E)-3,6-distyryl-9,10-dicyanophenanthrene (12) in 78% yield (Scheme 2).36
To complete the synthesis of the helicene skeleton, olefin 12 underwent photocyclization on
a 250 mg scale, in a one litre reactor for approximately two hours, to afford the target helicene 4
in 64% yield, after purification by column chromatography (Scheme 2).38 No other regioisomer
was isolated from the reaction mixture, indicating that ring closure of the diarylethene 12 had
occurred at the opposite side of the tricyclic moiety.
Scheme 2. Synthesis of the helically chiral heptacyclic system 4.
The optical properties of the parent unsubstituted carboheptahelicene32 and the obtained
cyanoheptahelicene derivatives 3 and 4 were investigated using UV-Vis absorption and
photoluminescence (PL) spectroscopies at room temperature and the results summarized in Table
1. The UV-Vis absorption spectra were recorded as dilute solutions in dichloromethane (5.0x10-5
M). As shown in Figure 2, all compounds exhibited similar main absorption bands at 270 nm and
absorbance bands in the range of 280-375 nm which could be assigned to π-π* and n-π*
electronic transitions. As expected, we observed that the absorption of helicenes 3 and 4 were
red-shifted in comparison to the parent carboheptahelicene due to the electronic effect of the
nitrile groups. However, helicene 4, showed a broader absorption at longer wavelengths. It should
be noted that the UV-Vis absorption spectra of unsubstituted carboheptahelicene, tailed off at
approximately about 400 nm, whereas helicene derivatives 3 and 4 had significant absorption
4

bands in the range of 400-450 and 400-475 nm and tailed off at 450 and 485 nm respectively,
suggesting that the increase of the electron withdrawing group (EWG) led to more significant
red-shifts and the spectral differences were due to the presence of the nitrile functional groups.
Table 1. Physical properties of cyanohelicenes 3-4 and the unsubstituted carboheptahelicene.
Absorption
Photoluminescence
λems (nm)c FWHM (nm)d
Compound
λmaxabs (nm)a
Eg-op (eV)b
Carboheptahelicene
270
267
268
3.15
3.00
2.62
466
494
508
77
116
127
3
4
a Absorption maxima, measured in CH2Cl2 solutions (5.0x10-5 mol) at rt.
b The optical gap (Eg-op) was estimated from the onset point of the absorption spectra: Eg-op = 1240/ λonset
.
c Emission maxima, measured in CH2Cl2 solutions (5.0x10-6 mol) at rt.
d
Spectrum full width at half maximum.
Carboheptahelicene
1.0
3
4
0.8
0.6
0.4
0.2
0.0
250
300
350
400
450
500
550
Wavelength (nm)
Figure 2. Normalized UV/vis absorption spectrum of carboheptahelicene and the
cyanohelicene derivatives 3-4 in CH2Cl2.
For the unsubstitued carboheptahelicene in solution, a blue emission was observed with a
long wavelength emission maximum at 466 nm and a shoulder band at 450 nm (Fig. 3). However,
for cyanohelicene derivatives 3 and 4, all emission spectra were largely bathochromically red-
shifted into the green region. Helicene 3 showed a main emission at 493 nm with two shoulder
5

peaks at 466 and 522 nm, while helicene 4 showed two main emissions at 507 and 540 nm with a
shoulder peak at 467 nm. The emission difference of helicenes 3 and 4 compared to that of
carboheptahelicene could be ascribed to the presence of the cyano group linkages that elongate
the conjugated skeleton and slightly expand the π-delocalized system. In addition, the emission
spectra of the cyanoheptahelicene derivatives 3 and 4 varied in agreement with the electronic
absorption spectra, implying that the energy gap between ground and excited states decreases in
the order of unsubstituted carboheptahelicene > 3 > 4 (Table 1).
Carboheptahelicene
3
1.0
4
0.8
0.6
0.4
0.2
0.0
350
400
450
500
550
600
650
700
750
Wavelength (nm)
Figure 3. Normalized emission spectrum of unsubstituted carboheptahelicene
and cyanohelicene derivatives 3-4 in CH2Cl2.
Next, we investigated the electrochemical characteristics of the parent carboheptahelicene
and cyanohelicenes 3 and 4 using cyclic voltammetry (CV). The helicenes were scanned both
positively and negatively, in solutions of tetrabutylammonium perchlorate (Bu4NClO4) in
anhydrous acetonitrile (0.10 M) with a scan rate of 50 mVs−1 at room temperature (Fig. 4). We
found that the oxidation and reduction processes of the helicenes were irreversible. The onset
potentials for oxidation were 1.42, 1.57 and 1.06 V (vs SCE) for cyanoheptahelicenes 3 and 4,
respectively, while the onset potentials for reduction were -1.81, -1.35 and -1.78 V (vs SCE),
respectively. From the onset potentials of the oxidation and reduction processes, the band gaps
(Eg) could be calculated as follows:40
6

EHOMO (ionization potential) = - (Vonset-ox-VFOC+4.8) eV
ELUMO (electron affinity) = - (Vonset-red-VFOC+4.8) eV
Eg-el = (ELUMO- EHOMO) eV
Where Vonset-ox and Vonset-red are the onset potentials for the oxidation and reduction of the
helicenes versus the reference electrode. The lowest unoccupied molecular orbital (LUMO) were
-2.27, -2.72 and -2.30 eV, while the highest occupied molecular orbital (HOMO) were -5.50, -
5.65 and -5.14 eV, giving electrochemical band gaps of 3.23, 2.93 and 2.84 eV for the
unsubstituted carboheptahelicene, compound 3 and compound 4, respectively, which were
consistent with the trend observed for the Eg values. Moreover, the calculated HOMO values of
carboheptahelicene, 3 and 4 vary slightly in the range of -5.65 to -5.14 eV, indicating that the
materials were suitable for application in OLED-like optoelectronic devices.41 All
electrochemical property data are summarized in Table 2.
0.08
0.06
Carboheptahelicene
3
4
0.04
0.02
0.00
-0.02
-0.04
-0.06
-0.08
-0.10
-0.12
-0.14
-2
-1
0
1
2
Potential (V)
Figure 4. Cyclic voltammograms of the parent carboheptahelicene and helicene derivatives 3-4
film coated onto ITO electrodes in 0.1 M (n-Bu)4NClO4/acetonitrile (scan rate = 50 mV/s).
Table 2. Electrochemical properties of helicenes 3 and 4 compared to those of the unsubstituted
heptahelicene.
Vonset-ox (V)
Compound
Vonset-red (V) EHOMO (eV)a ELUMO (eV)b Eg-el (eV)c
-1.81 -5.50 -2.27 3.23
Carboheptahelicene
1.42
7

1.57
1.06
-1.35
-1.78
-5.65
-5.14
-2.72
-2.30
2.93
2.84
3
4
a Calculated from the oxidation potential.
b Calculated from the reduction potential.
c Band gap was calculated from the difference of HOMO and LUMO.
In conclusion, we have developed a straightforward synthesis of 9-cyanoheptahelicene
and 9,10-dicyanoheptahelicene in good yields employing suitably functionalized phenanthrene
building blocks. The resolution of these helicenes is currently in progress for the examination of
these compounds as ligands or for broader application.
Acknowledgements
The authors are grateful to the DGRS (Direction Générale de la Recherche Scientifique)
of the Tunisian Ministry of Higher Education and Scientific Research for financial support.
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Lett. 2013, 54, 5421-5425.
28. Ben Braiek, M.; Aloui, F.; Ben Hassine, B. Tetrahedron Lett. 2013, 54, 424-426.
29. Aloui, F.; Moussa, S.; Ben Hassine, B. Tetrahedron Lett. 2011, 52, 572-575.
30. Aloui, F.; Ben Hassine, B. Tetrahedron Lett. 2009, 50, 4321-4323.
31. Aloui, F.; El Abed, R.; Ben Hassine, B. Tetrahedron Lett. 2008, 49,1455-1457.
32. Abed, R. El.; Ben Hassine, B.; Gorsane, M.; Genet, J.-P.; Marinetti, A.; Eur. J. Org. Chem.
2004, 1517-1522.
33. Wang, H. J.; Chen, Y. P.; Chen, Y. C.; Chen, C. P.; Lee, R. H.; Chan, L. H.; Jeng, R. J.
Polymer, 2012, 53, 4091-4103.
34. Experimental procedure and spectroscopic data for (Z)-2,3-bis(4-bromophenyl)acrylonitrile
(7): A mixture of 4-bromophenylacetonitrile (1 g, 5 mmol) and potassium tert-butoxide (0.85 g,
10 mmol) in THF (40 mL) was stirred at 0 °C for several minutes. Then 4-bromobenzaldehyde
(0.95 g, 10 mmol) was added and the solution stirred for 30 min at 0 °C followed by 12 hours at
room temperature. The reaction was quenched by the addition of ice water. The organic phase
was extracted with CH2Cl2 (3 x 30 mL), dried over MgSO4 and filtered. After evaporation of the
solvent, the residue was purified by silica gel column chromatography with
11

cyclohexane/chloroform (10:1) as the eluent to give a white solid (1.69 g, 94%); m.p = 122-124
1
°C; H NMR (300 MHz, CDCl3): δ (ppm): 7.47 (s, 1H), 7.51-7.64 (m, 6H), 7.76 (d, J = 8.4 Hz,
2H); 13C NMR (75 MHz, CDCl3): δ (ppm): 110.86, 116.82, 123.24, 124.71, 126.98, 130.16,
131.82, 132.64, 140.54.
35. Experimental procedure and spectroscopic data for catalytic photocyclization: To a solution
of olefin 7 or 10 (1.3 mmol) in toluene (1.2 L) was added catalytic iodine (5 mg, 0.02 mmol).
Irradiation was performed using a 150 W high-pressure mercury lamp and the reaction monitored
by TLC. Following reaction completion, the solvent was removed under reduced pressure and the
resulting product purified by silica gel column chromatography with cyclohexane/EtOAc (90:10)
as the eluent. 3,6-Dibromo-9-cyanophenanthrene (8): 80% yield, white solid; m.p = 242-244 °C;
1H NMR (300 MHz, CDCl3): δ (ppm): 7,74-7.76 (m, 2H), 7.81 (dd, J1 = 8.7 Hz, J2 = 1.8 Hz, 1H),
8.10 (d, J = 8.7 Hz, 1H), 8.15 (s, 1H), 8.67 (m, 2H); 13C NMR (75 MHz, CDCl3): δ (ppm):
109.60, 117.13, 123.28, 125.09, 125.95, 126.07, 127.73, 127.81, 128.65, 130.34, 130.87, 131.73,
131.85, 132.06, 135.10. 3,6-Dibromo-9,10-dicyanophenanthrene (11): 88 % yield; white solid;
m.p = 297-299 °C; 1H NMR (300 MHz, CDCl3): δ (ppm): 8.01 (dd, J1 = 8.7 Hz, J2 = 1.6 Hz, 2H),
8.28 (d, J = 8.7 Hz, 2H), 8.84 (d, J = 1.6 Hz, 2H); 13C NMR (75 MHz, CDCl3 ): δ (ppm): 114.41,
116.69, 126.43, 126.81, 126.83, 128.80, 131.30, 133.32.
36. Experimental procedure and spectroscopic data for the Heck coupling: A solution of
phenanthrene derivative (8) or (11) (1.4 mmol) and dry NaOAc (234 mg, 2.86 mmol) in N,N-
dimethylacetamide (5 mL) was placed in a Schlenk tube and repeatedly degassed and purged
with argon five times. The styrene (3 equiv) was added and the mixture heated to 100 °C. Next, a
solution of Herrmann’s catalyst (24 mg, 2 mol%) in N,N-dimethylacetamide (2 mL) was added
and the mixture heated to 140 °C and maintained for 24 h. The product was worked up by the
addition of H2O and extraction of the organic phase with dichloromethane (3 × 30 mL). The
combined organic phases were dried over MgSO4. After removal of the solvent, the residue was
purified by silica gel column chromatography with cyclohexane/EtOAc (90:10) as the eluent.
(E,E)-3,6-Bis(styryl)-9-cyanophenanthrene (9): 74% yield; yellow solid; Rf = 0.31 (cyclohexane/
1
EtOAc, 90:10); m.p = 143-145 °C; H NMR (300 MHz, CDCl3): δ (ppm): 7.47-7.33 (m, 10 H),
7.64 (d, J = 7.5 Hz, 4H), 7.89 (s, 2H), 7.95 (d, J = 8.4 Hz, 1H), 8.14 (s, 1H), 8.24 (d, J = 8.4 Hz,
13
1H), 8.67 (d, J = 6.9 Hz, 2H); C NMR (75 MHz, CDCl3): δ (ppm): 108.71, 118.00, 121.41,
121.55, 125.18, 125.72, 126.49, 126.78, 126.84, 128.07, 128.17, 128.33, 128.71, 128.85, 128.87,
12

129.54, 129.86, 130.20, 130.77, 131.26, 131.98, 134.64, 136.82, 136.92, 137.20, 138.79; HRMS
(MALDI-TOF) Calcd for C31H21N [M]+: 407.1674. Found: 407.1669. (E,E)-3,6-Bis(styryl)-9,10-
dicyanophenanthrene (12): 78% yield; yellow solid; Rf = 0.25 (cyclohexane/ EtOAc, 90:10); m.p
1
= 221-223 °C; H NMR (300 MHz, CDCl3): δ (ppm): 7.36-7.44 (m, 6H), 7.47 (d, J = 6.9 Hz,
4H), 7.66 (d, J = 6.9 Hz, 4H), 8.06 (d, J = 8.4 Hz, 2H), 8.32 (d, J = 8.4 Hz, 2H), 8.72 (s, 2H); 13C
NMR (75 MHz, CDCl3): δ (ppm): 115.15, 115.38, 121.48, 126.72, 127.01, 127.30, 127.55,
127.66, 128.76, 128.95, 131.51, 132.79, 136.43, 140.13; HRMS (MALDI-TOF) Calcd for
C32H20N2 [M]+: 432.1626. Found: 432.1631.
37. Talele, H. R.; Gohil, M. J.; Bedekar, A. V. Bull. Chem. Soc. Jpn. 2009, 82, 1182-1186.
38. Experimental procedure and spectroscopic data for the stoichiometric photocyclization: To a
solution of olefin 8 or 11 (0.5 mmol) in toluene (1.2 L) was added iodine (280 mg, 2.2 equiv).
The solution was degassed for 15-30 min, then excess THF (30 mL) was added. Irradiation was
performed using a 150 W high-pressure mercury lamp. A flow of argon was maintained
throughout the irradiation and the reaction monitored by TLC. Following reaction completion,
the solvent was removed under reduced pressure and the crude residue was purified by silica gel
column chromatography using cyclohexane/CH2Cl2 (90:10) as the eluent. 9-Cyanoheptahelicene
(3): 61% yield, yellow solid; Rf = 0.35 (cyclohexane/DCM, 90:10); m.p = 288-290 °C; 1H NMR
(300 MHz, CDCl3): δ (ppm): 6.44 (m, 2H), 6.93-6.98 (m, 2H), 7.00 (d, J = 8.7 Hz, 2H), 7.33 (d, J
= 8.1 Hz, 2H), 7.55 (d, J = 8.7 Hz, 1H), 7.57 (d, J = 8.7 Hz, 1H), 7.74 (d, J = 8.4 Hz, 1H), 7.76
(d, J = 8.4 Hz, 1H), 7.95- 8.01 (m, 2H), 8.08 (d, J = 8.4 Hz, 1H), 8.40 (d, J = 8.4 Hz, 1H), 8.46 (s,
1H); 13C NMR (75 MHz, CDCl3): δ (ppm): 107.97, 117.73, 122.85, 123.34, 123.50, 123.69,
124.90, 124.93, 125.02, 125.83, 126.31, 126.34, 127.06, 127.39, 127.63, 127.91, 128.17, 128.52,
128.62, 128.78, 129.19, 129.50, 130.83, 131.28, 131.37, 131.99, 133.31; HRMS (MALDI-TOF)
Calcd for C31H17N [M]+:403.2144. Found: 403.2136. 9,10-Dicyanoheptahelicene (4): 64% yield;
yellow solid; Rf = 0.29 (cyclohexane/DCM, 90:10); m.p > 300 °C; 1H NMR (300 MHz, CDCl3):
δ (ppm): 6.49 (dd, J1 = 8.1 Hz, J2, = 7.2 Hz, 2H), 6.89 (d, J = 8.4 Hz, 2H), 7.00 (dd, J1 = 7.5 Hz,
J2 = 7.2 Hz, 2H), 7.35 (d, J = 7.1 Hz, 2H), 7.62 (d, J = 8.4 Hz, 2H), 7.77 (d, J = 8.4 Hz, 2H), 8.17
13
(d, J = 8.4 Hz, 2H), 8.43 (d, J = 8.4 Hz, 2H); C NMR (75 MHz, CDCl3): δ (ppm): 114.27,
115.45, 123.37, 123.70, 124.78, 125.22, 126.01, 127.10, 127.36, 127.71 (C), 128.72 (C),
128.90 (C), 130.16, 130.62, 132.00, 132.88; HRMS (MALDI-TOF) Calcd for C32H16N2
[M]+:428.1307. Found: 428.1312.
13

39. Experimental procedure and spectroscopic data for 2,3-bis(4-bromophenyl)fumaronitrile
(10): A mixture of 4-bromophenylacetonitrile 5 (2.50 g, 12.5 mmol) and iodine (3.20 g, 12.5
mmol) was purged with N2 and dry Et2O (80 mL) was added via syringe. A solution was cooled
to -78 °C. Sodium methoxide (1.40 g, 25 mmol) and methanol (10 mL) were slowly added over a
period of 30 min and stirred for another 30 min. The solution was then placed in an ice-water
bath with vigorous stirring at 0 °C for a further 5 h, before 5% hydrochloric acid (50 mL) was
added dropwise at a temperature lower than 10 °C. The solution was filtered to isolate the
precipitate, which was rinsed with a cold methanol/water solution (50/50) to give a white solid in
13
92% yield; m.p = 213-215 °C; 1H NMR (300 MHz, CDCl3), δ (ppm): 7.68-7.75 (m, 8H); C
NMR (75 MHz, CDCl3): δ (ppm): 115.59, 124.14, 126.30, 129.59, 130.08, 132.19.
40. Bredas, J. L; Silbey, R.; Boudreaux, D. S.; Chance, R. R. J. Am. Chem. Soc. 1983, 105, 6555-
6559.
41. (a) Chow, J. Org. Lett. 2007, 9, 5215-5218; (b) Sonar, P.; Son, M. S.; Cheng, Y. H.; Henssler,
J. T.; Sellinger,A. Org. Lett. 2010, 12, 3292-3295; (c) Sahasithiwat, S.; Mophuang, T.;
Menbangpung, L.; Kamtonwong, S.; Sooksimuang, T. Synth. Met. 2010, 160, 1148-1152; (d) Shi,
L.; Liu, Z.; Dong, G.; Duan, L.; Qiu, Y.; Jia, J.; Guo, W.; Zhao, D.; Cui, D.; Tao, X. Chem. Eur.
J. 2012, 18, 8092-8099; (e) Hua, W.; Liu, Z.; Duan, L.; Dong, G.; Qiu, Y.; Zhang, B.; Cui, D.;
Tao, X.; Cheng, N.; Liu, Y. RSC Adv. 2015, 5, 75-84.
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Graphical abstract
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