Convenient synthesis of photochromic symmetrical or unsymmetrical bis(heteroaryl)maleimides via the Suzuki-Miyaura cross-coupling reaction

Article abstract of DOI:10.1016/j.tet.2007.06.088

A general method for the synthesis of symmetrical or unsymmetrical bis(heteroaryl)maleimides by a one-pot procedure involving Suzuki-Miyaura cross-coupling sequence was developed on the basis of the reaction of 3,4-diiodo-1-benzyl-1H-pyrrole-2,5-dione wit

Full text of DOI:10.1016/j.tet.2007.06.088

Tetrahedron 63 (2007) 9482–9487
Convenient synthesis of photochromic symmetrical
or unsymmetrical bis(heteroaryl)maleimides via the
Suzuki–Miyaura cross-coupling reaction
*
ꢀ
A. El Yahyaoui, G. Felix, A. Heynderickx, C. Moustrou and A. Samat
´
Universite de la Mediterranee, Groupe de Chimie Organique et Materiaux Moleculaire, UMR 6114 CNRS Case 901,
´
´
´
´
13288 Marseille Cedex 9, France
Received 4 April 2007; revised 26 June 2007; accepted 27 June 2007
Available online 4 July 2007
Abstract—A general method for the synthesis of symmetrical or unsymmetrical bis(heteroaryl)maleimides by a one-pot procedure involving
Suzuki–Miyaura cross-coupling sequence was developed on the basis of the reaction of 3,4-diiodo-1-benzyl-1H-pyrrole-2,5-dione with cyclic
boronate esters using PdCl2(dppf) as the catalyst. Photochromic properties of the products were examined.
Ó 2007 Published by Elsevier Ltd.
1. Introduction
These processes fall short of the ideal for several reasons: (1)
Perkin condensation of aryl acetic acid with glyoxylic
acids13 (or their derivatives14), which are relatively expen-
sive complexes and of limited availability, have been
plagued with a poor overall yield; (2) same limitation can
be noted with base hydrolysis of diheteroarylmaleonitrile
(or fumaronitrile), followed by imidization with alkylamine
leading to symmetrical and unsymmetrical structures;15 (3)
Friedel–Crafts reaction of thiophene and thieno[3,2-b]thio-
phene derivatives with squaric acid16 derivative, which is
not readily available and of high cost, followed by subse-
quent oxidation and imidization is limited to symmetrical
maleimides.17 It is worth noting too that accessibility to 2,4,5-
trimethylthiophene or 2-methylbenzo[b]thiophene analogs
was not allowed.
In recent years, organic photochromic compounds have re-
ceived increasing attention due to their potential applications
for optoelectronic devices.1 So far, various photochromic
families, such as spiropyranes,2 spirooxazines,3 azobenz-
enes,4 fulgides,5 and diarylethenes6 have been developed
so as to satisfy the specific needs of each new device. 1,2-Di-
heteroarylethenes exhibit reversible variations in their phys-
ical and chemical characteristics, between their ring-open
and ring-closed forms, such as fluorescence emission,7 infra-
red absorption,8 optical rotation,9 redox potential,10 and
magnetism11 are considered as promising carriers of three-
dimensional optical memory.12
In this work, we attempt to prepare symmetrical or unsym-
metrical bis(heteroaryl)maleimides by treating of 3,4-
diiodo-1-benzyl-1H-pyrrole-2,5-dione with cyclic boronate
esters using PdCl2(dppf) as catalyst, in a one-pot process.
The accessibility of new compounds of this class is a steadily
growing field due to new possible applications.
Besides the above classical methods, few examples of palla-
dium-catalyzed reactions, which are one of the most reliable
tools to obtain symmetrical or unsymmetrical biaryls, have
also been reported.
Correia and co-workers have used an ingenious Heck aryla-
tion of maleic anhydrides starting from arenediazonium tet-
rafluoroborates to perform the synthesis of symmetrical and
unsymmetrical arylated maleic anhydrides.18 To the best of
our knowledge, this methodology could not be extended to
heteroarylated maleic anhydride due to the difficulty of
heteroarenediazonium tetrafluoroborates synthesis.
2. Results and discussion
This paper describes total synthesis of symmetrical or un-
symmetrical substituted diheteroarylmaleimides as having
a number of advantages over existing processes and the
potential to increase the rate of production.
A method for preparing 3,4-diaryl(or heteroaryl)maleimides
by reacting aryl(or heteroaryl)boronic acid with N-
substituted dibromomaleimides19 was reported recently by
Krayushkin et al. The authors used a wide variety of bases
Keywords: Diheteroarylmaleimides; Suzuki–Miyaura cross-coupling reac-
tion; Palladium; Photochromism.
* Corresponding author. Tel.: +33 4 91 82 93 41; fax: +33 4 91 82 93 01;
e-mail: heynderi@luminy.univ-mrs.fr
0040–4020/$ - see front matter Ó 2007 Published by Elsevier Ltd.
doi:10.1016/j.tet.2007.06.088

A. El Yahyaoui et al. / Tetrahedron 63 (2007) 9482–9487
9483
and cesium fluoride seemed to be the most efficient for
Suzuki–Miyaura cross-coupling reactions starting from a
dibromomaleimide (Table 1, entries 1 and 2).
Optimization of the cross-coupling reaction was performed
on 3,4-diiodo-1-benzyl-1H-pyrrole-2,5-dione with arylbor-
onic acid derivatives using PdCl2(dppf) as catalyst. 5,5-
Dimethyl-2-(aryl or heteroaryl)-1,3,2-dioxaborinane has
often been used as a substitute of arylboronic acids to
circumvent protodeboronation22 and to efficiently couple
with aryl halides or aryl triflates in the presence of Pd
catalyst.
The application of this protocol (Table 1, entry 3), employ-
ing inexpensive and commercial 3-(thiophenyl)boronic acid
with 3,4-dibromo-1-benzyl-1H-pyrrole-2,5-dione,20 did not
supply the amounts of the desired product, while no starting
material was recovered. Therefore, this reaction does not
work with a wide range of substrates. The reaction has
been performed differently with a variety of solvents
(DME, MeOH) and bases (K3PO4, Na2CO3). So far, none
of the used experimental conditions has resulted into a signif-
icant yield improvement. Indeed, the poor stability of the
maleimide species and protodeboronation process would
be accountable for that observed result.
We applied this strategy to synthesize new bis(heteroaryl)-
maleimides as described in Scheme 1.
The protection of commercial 3-thienylboronic acid was
carried out by esterification with 2,2-dimethylpropane-1,3-
diol, according to literature procedure,23 leading to 5,5-
dimethyl-2-(thien-3-yl)-1,3,2-dioxaborinane 2a in excellent
yield. Phenylboronate ester 2b is commercially available.24
Synthesis of substituted bis(fur-2-yl), bis(fur-3-yl), and bis-
(thien-2-yl) maleimides20 has been described as involving,
as a key step, a one-pot Pd/C21 catalyzed Suzuki cross-
coupling between various boron derivatives and the dibromo
or diiodomaleimides. These catalysis conditions were not
able to promote coupling of 3-thiopheneboronic acid with
halogenated maleimides (Table 1, entries 4 and 5).
Heteroarylboronic esters 2c and 2d have been prepared by
a one-pot procedure as shown in Scheme 2. The initial bro-
mide–lithium exchange step on to 2,5-dimethyl-3-bromo-
thiophene25 and 3-bromo-2-methylbenzo[b]thiophene26
was easily carried out at ꢀ40 ꢁC in ethereal solution on a
multigram scale in excellent yield (97%). At ꢀ78 ꢁC, an
excess amount (2.5 equiv) of tributyl borate was added
into the solution of heteroaryl lithium reagents formed.
The reaction mixture was allowed to return to room temper-
ature and the solvent was removed by a rotary evaporator.
Transesterification of boronate esters intermediates occurred
cleanly with 2,2-dimethylpropane-1,3-diol to generate cyclic
boronate esters very efficiently (Scheme 2).
Table 1. Suzuki–Miyaura cross-coupling of 3,4-dihalogeno-1-(alkyl)-1H-
pyrrole-2,5-dione and arylboronic acid ester
R
N
R
N
O
O
2.5 eq.
Ar B(OH)2
A or B
O
O
X
X
Ar
Ar
O
1) n-BuLi, Et20, -40 °C, 1h
Entry
R
X
Boronic acid
Reaction
conditions
Coupling
reaction
Het
B
Het Br
2) B(On-Bu)3, -78 to rt
O
yielda [%]
3) , THF, 1h
boronic ester
Yield [%]
1
2
n-Bu
n-Bu
Br
Br
A
A
98a
76a
H3CO
OH OH
2c
90
H3C
CH3
S
S
CH3
S
S
S
S
2d
87
CH3
3
4
5
Bz
Bz
Bz
Br
Br
I
A
B
B
0
0
0
Scheme 2. Synthesis of cyclic boronate esters 2c and d.
Cross-coupling reaction of dibromomaleimide 1a with an
excess of 5,5-dimethyl-2-(thien-3-yl)-1,3,2-dioxaborinane
2a was first performed in polar solvent (DMF), in presence
of base (Na2CO3) and catalytic amount of PdCl2(dppf). The
desired product 3a was isolated, for the first time, in moder-
ate yield (48%) as illustrated in Table 2 (entry 1).
A: CsF, Pd(PPh3)4, dioxane, reflux, 4 h; B: Pd/C, Et3N, EtOH, 24 h, reflux.
Ref. 19.
a
PdCl2(dppf), 2 M aq. Na2CO3
N
N
O
O
O
O
O
O
DMF, 80 °C/ 2 hours
Ar
B
Ar
Ar
(2 eq.)
X
X
1a X = Br
1b X = I
2 a-d
3 a-d
Scheme 1.

9484
A. El Yahyaoui et al. / Tetrahedron 63 (2007) 9482–9487
Table 2. Optimized conditions of Suzuki–Miyaura cross-coupling reaction
one-pot procedure, by adding simultaneous the two different
cyclic boronate esters 2c and 2d. After purification by
HPLC, the target unsymmetrical bis(heteroaryl)male-
imide 4 was isolated as major product (50%). Symmetric
maleimides 3c and 3d were separated too (7 and 3%,
respectively).
Entry
X
Boronate ester
Coupling
reaction product
(yield %)
1
Br
3a (48)
2a
S
The photocyclisation of new di(heteroaryl)ethenes (3d
and 4) was achieved, by irradiation of toluene solution
(3ꢂ10ꢀ5 M) in presence of air, at wavelengths correspond-
ing to the absorption band of the open-ring isomer (Scheme
4, Table 3). Both closed isomers are thermally stable for 3
days at 20 ꢁC. Colored forms are also sensitive to visible
light, leading to the initial open form.
2
3
I
I
3a (64)
3b (75)
2a
2b
S
H3C
4
5
I
I
3c (68)
3d (43)
2c
H3C
CH3
CH3
S
S
2d
N
λ1 (UV)
λ2 (Vis)
O
O
N
O
S
O
When instead of 1a, diiodomaleimide 1b was used, a 16%
yield increase was observed (entry 2). With the same
cross-coupling methodology, the synthesis of 1-benzyl-3,4-
bis(4-methylphenyl)-pyrrole-2,5-dione 3b, 1-benzyl-3,4-
bis(2,5-dimethyl-3-thienyl)-pyrrole-2,5-dione 3c and its
2-methylbenzo[b]thiophene analogous 3d was carried out in
moderate to good yield (entries 3–5). Synthesis of 3c has
previously been described, in 3 steps starting from 2,5-di-
methylthiophene and expensive 3,4-dichlorocyclobutane-
1,2-dione in 40 % overall yields.27
S
S
S
4
closed-ring isomer
open-ring isomer
Scheme 4.
An example of photochromic behavior is given for com-
pound 4 (Fig. 1).
The fatigue resistance of toluene solution of 4, determined
by the decrease of absorption maximum at 510 nm (where
the closed form has an absorption maximum), was observed
at room temperature for 7 optical switching cycles upon al-
ternatively irradiation with 404 nm and 510 nm light in pres-
ence of air, see Figure 2. An absorbance decrease of 11%
The possibility of preparing monoiodo heteroarylated male-
imides has been investigated aiming at adding flexibility to
this Suzuki–Miyaura cross-coupling methodology and to ex-
tend its applicability to the conversion of monoheteroary-
lated maleimides into the unsymmetrical diheteroarylated
compounds (Scheme 3). Treatment of diiodomaleimide 1b
with stochiometric amount of 5,5-dimethyl-2-(2,5-di-
methylthien-3-yl)-1,3,2-dioxaborinane 2c, heating for 1 h in
DMF instead of 2 h, furnished only 3c in 40% yield. The
presence of starting material and mono cross-coupling prod-
uct have not been detected.
Table 3. Absorption characteristics of photochromic maleimides
Compound
lmax (nm) of the
open-ring isomer
(3ꢂ10ꢀ3 Mꢀ1 cmꢀ1
lmax (nm) of
the closed-ring
isomer
)
3c
3d
4
231, 277, 391 (5)
406 (2)
405 (3)
359, 504
510
511
Due to the instability of the monoiodo intermediate, un-
symmetrical maleimide synthesis has been carried out, in a
N
O
O
I
2d (2 eq)
2c (1eq.)
S
N
O
O
N
O
O
PdCl2(dppf), 2 M aq. Na2CO3
DMF, 80 °C/ 2 hours
2c
2d
3c
3d
I
I
S
S
1b
4 : 50 %
Scheme 3. Synthesis of unsymmetrical diheteroarylmaleimide 4.

A. El Yahyaoui et al. / Tetrahedron 63 (2007) 9482–9487
9485
4. Experimental section
0.28
0.21
0.14
0.07
0.00
4.1. General
All the reactions were conducted out under an atmosphere of
nitrogen in oven-dried glassware with magnetic stirring. All
solvents (Carlo Erba Company, France) for reactions were
purified before use and were dried if necessary. Et2O and
THF were distilled under nitrogen from sodium benzo-
phenone ketyl and used immediately. Metallations were
performed under an argon atmosphere and reagents were
handled with syringes through septa. Column liquid chroma-
tographies were carried out on Merck silica gel 60 (70–230
mesh). Analytical thin-layer chromatography (TLC) was
done on Merck 60F254 silica gel plates. Detection of TLC
components was accomplished using a 254/366 nm UV
lamp. Melting points were determined on a Buchi 510 appa-
ratus in open glass capillaries and were uncorrected.
d
c
b
a
300
400
500
600
Wavelengh / nm
Figure 1. Changes in the UV–vis absorption spectra of a toluene solution of
4 (3ꢂ10ꢀ5 M) upon irradiation with 404 nm light. Irradiation periods are 0 s
(a), 60 s (b), 120 s (c), and the photostationary state 180 s (d).
Reagents and starting materials were used as received with-
out further purification from Avocado, Aldrich or Acros.
Starting materials 2,5-dimethyl-3-bromothiophene,25 5,5-
dimethyl-2-(thien-3-yl)-1,3,2-dioxaborinane (2a),23 5,5-di-
methyl-2-(4-methylphenyl)-1,3,2-dioxaborinane (2b),24 and
3,4-diiodo-1-benzyl-1H-pyrrole-2,5-dione (1)20 were pre-
pared according to literature procedures.
0.05
0.04
0.03
0.02
0.01
0.00
The 1H NMR and 13C NMR spectra were recorded on
€
a Brucker AC 250 spectrometer (250 and 62.5 MHz, respec-
tively) in deuteriochloroform as solvent with tetramethyl-
silane as the internal standard. The electron impact mass
spectra (EIMS) were obtained on a spectrometer HP 5973
Masse Selective Detector. HPLC Analyses were performed
on a Shimadzu HPLC system using a Chromatorex C-18 col-
umn (250 mmꢂ4.6 mm i.d.), a Shimadzu LC-10AT solvent
delivery system, Shimadzu SPD-10A UV/VIS Detector,
with isocratic elution with acetonitrile/water (80:20, v/v),
0
10
20
30
40
50
at a flow rate of 1.0 mL minꢀ1
.
Time / min.
Figure 2. Fatigue resistance of 4 in toluene measured at 510 nm during
switching cycles.
Absorption spectra were measured on a Varian Cary
50 UV–vis spectrophotometer. Photoirradiation was carried
out by using a Xenon lamp (150 W) equipped with a mono-
chromator.
occurred. Similar results were obtained for toluene solutions
of 3c and 3d.
4.1.1. 5,5-Dimethyl-2-(2,5-dimethylthien-3-yl)-1,3,2-di-
oxaborinane (2c). n-BuLi (7.5 mL, 18.75 mmol, 2.5 M in
hexane) was added dropwise via syringe to a solution of
2,5-dimethyl-3-bromothiophene (3 g, 15.7 mmol) in dry
ether (30 mL) at ꢀ40 ꢁC under argon. After 1 h, at ꢀ78 ꢁC,
tributyl borate (12.5 mL, 47.1 mmol) was added dropwise.
The reaction mixture was allowed to warm to room temper-
ature and stirred for a further 8 h. The solvent was evapo-
rated in vacuo and the residue was dissolved in anhydrous
THF (30 mL). 2,2-Dimethylpropane-1,3-diol (8.17 g,
78.5 mmol) was added in one portion. The resulting mixture
was stirred for a further 1 h and concentrated. The obtained
crude product was dissolved in diethyl ether and washed sev-
eral times with water. The organic phase was then dried over
MgSO4, filtered and concentrated. The crude product was
purified by column chromatography with cyclohexane/ethyl
acetate (10:1) as eluant, yielding 3.16 g (90%) of the corre-
3. Conclusion
In summary, we have shown that the Suzuki–Miyaura cross-
coupling methodology can be fruitfully employed to synthe-
size, in a one-pot procedure, starting from available and low
cost starting materials, under mild conditions, symmetrical
or unsymmetrical bis(heteroaryl)maleimides, which are not
easily available by other routes.
The Suzuki reaction was chosen in part for the large number
of commercial boronic acids and esters available.
We have established that the cross-coupling reaction success
is highly dependent on the protection of unstable boronic
acids into cyclic boronate esters. In an effort to optimize
this reaction, the influence of different catalysts, solvents,
and bases are in progress.
1
sponding boronic ester as a white solid. Mp: 73–74 ꢁC; H
NMR d¼1.00 (s, 6H), 2.38 (s, 3H), 2.58 (s, 3H), 3.71 (s,

9486
A. El Yahyaoui et al. / Tetrahedron 63 (2007) 9482–9487
4H), 6.81 (s, 1H); 13C NMR d¼14.77, 15.53, 31.71, 72.01,
130.72, 35.39, 149.07, quaternary CthiopheneB not visible;
EIMS, m/z: 224 [M]+. Anal. Calcd for C11H17BO2S: C,
58.95; H, 7.65; S, 14.31. Found: C, 59.22; H, 7.88; S, 13.79.
organic layers were washed with water (15 mL), brine, and
dried over anhydrous MgSO4. Finally, purification by flash
chromatography on silica gel (eluant: cyclohexane/CH2Cl2
1:1) furnished bis(heteroaryl)maleimides below.
4.1.2. 3-Bromo-2-methylbenzo[b]thiophene.26 A solution
of bromine (0.34 mL, 6.75 mmol) in chloroform (10 mL)
was added to a stirring solution of 2-methyl-benzo[b]thio-
phene (1 g, 6.75 mmol) in chloroform (30 mL) at 0 ꢁC. After
2 h of stirring, the reaction was quenched by the successive
addition of the aqueous solutions of 10% Na2S2O3 and 10%
NaHCO3, and the reaction mixture was extracted with ethyl
acetate. The organic layer was washed with satd aq NaCl,
dried over anhydrous MgSO4, and filtered. After removing
the solvent in vacuo, the residue was purified by column
chromatography on silica gel using cyclohexane as eluant,
to give the title product (4.046 g, 99%) as a colorless oil.
1H NMR d¼2.56 (s, 3H), 7.35–7.44 (m, 2H), 7.70–7.74
(m, 2H); 13C NMR d¼138.48, 137.22, 135.23, 124.93,
124.79, 122.61, 122.21, 122.18, 106.66, 15.54; EIMS, m/z:
226, 227 [M]+.
4.2.1. 1-Benzyl-3,4-bis(thien-3-yl)-pyrrole-2,5-dione (3a).
This compound was prepared by general method, from 2a
(134 mg) in 64% (51 mg) yield as an orange solid after chro-
matography and recrystallization from pentane. Mp: 115 ꢁC;
1H NMR d¼4.73 (s, 2H, CH2N), 7.16 (dd, J¼5, 1.26 Hz,
2H), 7.20–7.29 (m, 5H, Harom), 7.36 (m, 2H), 7.91 (dd,
J¼3, 1.26 Hz, 2H); 13C NMR d¼41.94, 125.85, 127.58,
127.88, 128.69, 128.72, 129.19, 129.26, 129.59, 136.41,
170.69; EIMS, m/z: 351 [M]+. Anal. Calcd for
C19H13NO2S2: C, 64.93; H, 3.73; N, 3.99; S, 18.25. Found:
C, 64.92; H, 3.91; N, 3.79; S, 18.27.
4.2.2. 1-Benzyl-3,4-bis(4-methylphenyl)-pyrrole-2,5-di-
one (3b). This compound was prepared by general method,
from 2b (139 mg) in 75% (61 mg) yield as a yellow solid
after chromatography and recrystallization from pentane.
1
Mp: 131 ꢁC; H NMR d¼2.33 s (6H), 4.77 (s, 2H, CH2N),
4.1.3. 5,5-Dimethyl-2-(2-methylbenzo[b]thiophen-3-yl)-
1,3,2-dioxaborinane (2d). n-BuLi (4 mL, 9.9 mmol,
2.5 M in hexane) was added dropwiseviasyringeto a solution
of 3-bromo-2-methylbenzo[b]thiophene (1.5 g, 6.6 mmol)
in dry ether (45 mL) at ꢀ40 ꢁC under argon. After 1 h, at
ꢀ78 ꢁC, tributyl borate (5.25 mL, 19.8 mmol) was added
dropwise. The reaction mixture was allowed to warm to
room temperature and stirred for a further 8 h. The solvent
was evaporated in vacuo and the residue was dissolved in
anhydrous THF (45 mL). 2,2-Dimethylpropane-1,3-diol
(3.43 g, 33 mmol) was added in one portion. The resulting
mixture was stirred for a further 1 h and concentrated. The
obtained crude product was dissolved in diethyl ether and
washed several times with water. The organic phase was
then dried over MgSO4, filtered and concentrated. The crude
product was purified by column chromatography with cyclo-
hexane/ethyl acetate (10/1) as eluant, yielding 1.5 g (87%)
of the corresponding boronic ester as a white solid. Mp:
7.11–7.46 (m, 13H, Harom); 13C NMR d¼21.49, 41.89,
125.84, 127.80, 128.65, 128.83, 129.25, 129.73, 135.40,
136.54, 140.04, 170.72; EIMS, m/z: 367 [M]+, 353
[MꢀMe]+. Anal. Calcd for C25H21NO2: C, 81.72; H, 5.76;
N, 3.81. Found: C, 81.68; H, 5.91; N, 3.69.
4.2.3. 1-Benzyl-3,4-bis(2,5-dimethylthien-3-yl)-pyrrole-
2,5-dione (3c).27 This compound was prepared by general
method, from 2c (153 mg) in 68% (63 mg) yield as an or-
ange solid after chromatography and recrystallization from
1
isopropylic alcohol. Mp: 161 ꢁC; H NMR d¼1.86 (s, 6H,
5-CH3, 50-CH3), 2.41 (s, 6H, 2-CH3, 20-CH3), 4.78 (s, 2H,
CH2N), 6.75 (s, 2H, 4-H, 40-H), 7.30–7.40 (m, 3H, Harom),
7.41–7.51 (m, 2H, Harom); 13C NMR d¼14.72, 15.16,
41.94, 126.26, 126.53, 127.80, 128.64, 128.94, 132.60,
136.51, 136.75, 139.50, 170.74; EIMS, m/z: 407 [M]+, 392
[MꢀMe]+. Anal. Calcd for C23H21NO2S2: C, 67.78; H,
5.19; N, 3.44; S, 15.74. Found: C, 67.48; H, 4.97; N, 3.32;
S, 15.83.
1
76–77 ꢁC; H NMR d¼1.00 (s, 6H), 2.71 (s, 3H), 3.76 (s,
4H), 7.13–7.28 (m, 2H), 7.68 (d, J¼7.9 Hz, 1H), 8.21 (d,
J¼7.74 Hz, 1H); 13C NMR d¼16.75, 21.87, 31.71, 72.07,
121.20, 123.01, 123.84, 124.77, 139.26, 144.69, 152.98,
quaternary CthiopheneB not visible; EIMS, m/z: 260 [M]+.
Anal. Calcd for C14H17BO2S: C, 64.63; H, 6.59; S, 12.33.
Found: C, 64.94; H, 6.78; S, 11.82.
4.2.4. 1-Benzyl-3,4-bis(2-methylbenzo[b]thiophen-3-yl)-
pyrrole-2,5-dione (3d). This compound was prepared by
general method, from 2d (178 mg) in 43 % (47 mg) yield
as an yellow solid after chromatography and recrystalliza-
1
tion from pentane. Mp: 181 ꢁC; H NMR d¼1.98 (s, 3H),
2.24 (s, 3H), 4.89 (s, 2H, CH2N), 7.04–7.69 (m, 13H, Harom);
13C NMR d¼15.46, 15.51, 42.27, 121.80, 121.86, 121.98,
122.19, 122.33, 124.13, 124.24, 124.38, 124.50, 127.93,
128.72, 128.81, 135.57, 136.04, 136.36, 137.61, 138.09,
138.14, 143.02, 143.49, 169.57; EIMS, m/z: 479 [M]+.
Anal. Calcd for C29H21NO2S2: C, 72.62; H, 4.41; N, 2.92;
S, 13.37. Found: C, 72.51; H, 4.61; N, 3.11; S, 13.08.
4.2. Suzuki–Miyaura cross-coupling reaction of
3,4-diiodo-1-benzyl-1H-pyrrole-2,5-dione (1) with
cyclic boronate ester (2a–c). General procedure for
preparation of compounds (3 and 4)
A mixture of the required cyclic boronate ester 2a–d
(0.684 mmol), 3,4-diiodo-1-benzyl-1H-pyrrole-2,5-dione
1b (100 mg, 0.228 mmol), and 2 M Na2CO3 (0.34 mL,
0.68 mmol) was degassed and flushed with a nitrogen flow
for 30 min. Then, the catalyst [1,10-bis(diphenylphosphino)-
ferrocene]dichloropalladium(II) (10 mg, 1.36ꢂ10ꢀ5 mol)
was added, and the mixture was stirred at 80 ꢁC, under nitro-
gen and tested by TLC to check the completion of the reac-
tion (2 h). The solution was cooled to room temperature and
was extracted with ethyl acetate (15 mL). The combined
4.2.5. 1-Benzyl-3-(2-methylbenzo[b]thiophen-3-yl)-4-
(2,5-dimethyl-3-thienyl)-pyrrole-2,5-dione (4). This com-
pound was prepared by general method, from a mixture of 2c
(50 mg, 0.228 mmol) and 2d (71 mg, 0.274 mmol) in 50%
(50 mg) yield as an orange solid after HPLC. Mp: 176 ꢁC;
1H NMR d¼1.64 (s, 3H), 2.21 (s, 3H), 2.37 (s, 3H), 4.82
(s, 2H, CH2N), 6.77 (s, 1H, Hthiophene), 7.22–7.49 (m, 8H,
Harom), 7.69–7.73 (m, 1H, Harom); 13C NMR d¼14.72,

A. El Yahyaoui et al. / Tetrahedron 63 (2007) 9482–9487
9487
7195–7210; (d) Matsuda, K.; Irie, M. J. Am. Chem. Soc.
2000, 122, 8309–8310; (e) Matsuda, K.; Irie, M. Chem.—
Eur. J. 2001, 16, 3466–3473; (f) Matsuda, K.; Irie, M. J. Am.
Chem. Soc. 2001, 123, 9896–9897.
15.09, 15.48, 121.83, 122.47, 122.54, 124.15, 124.38,
126.13, 126.20, 127.85, 128.72, 128.84, 131.76, 136.16,
136.46, 136.92, 138.08, 138.15, 140.58, 142.42, 169.86,
170.48; EIMS, m/z: 443 [M]+, 428 [MꢀMe]+. Anal. Calcd
for C26H21NO2S2: C, 70.40; H, 4.77; N, 3.16; S, 14.46.
Found: C, 70.18; H, 4.54; N, 3.01; S, 14.57.
12. (a) Irie, M. Hikari Araiansu 2006, 17, 6–9; (b) Belfield, K. D.
Adv. Mater. 2006, 18, 2910–2914; (c) Satoshi, K.; Yoshimasa,
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Acknowledgements
We thank Mr. Daniel Campese for valuable discussions and
for his technical support.
14. Yamaguchi, T.; Matsuo, M.; Irie, M. Bull. Chem. Soc. Jpn.
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