Synthesis and spectral properties of fluorescent dithienylmaleimides

Article abstract of DOI:10.1246/bcsj.79.889

A convenient preparative method of the synthesis of dithienylethenes based on maleimides was proposed. Previously, difficult accessible dithienylethene derivatives, in which 2-thienyl substituents are attached to the double bond of maleimide, have been sy

Full text of DOI:10.1246/bcsj.79.889

Ó 2006 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 79, No. 6, 889–893 (2006)
889
Synthesis and Spectral Properties of Fluorescent Dithienylmaleimides
ꢀ
Ol’ga Yu. Kuznetsova, and Alexey A. Shimkin
Valerii Z. Shirinian, Mikhail M. Krayushkin, Boris V. Nabatov,
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
Leninsky prosp., 47, 119991 Moscow, Russian Federation
Received September 30, 2005; E-mail: shir@ioc.ac.ru
A convenient preparative method of the synthesis of dithienylethenes based on maleimides was proposed. Previ-
ously, difficult accessible dithienylethene derivatives, in which 2-thienyl substituents are attached to the double bond of
maleimide, have been synthesized. The spectral properties of the dithienylmaleimides were studied and it has been
shown that these compounds do not belong to photochromes but they possess fluorescent properties.
Diarylethenes have been extensively studied owing to their
potential as optoelectronic materials1–3 and precursors of med-
icines.4–6 The spectral properties of dithienylethenes depend
on the nature of the ethene bridge, substituents in the heterocy-
clic rings and the substitution position on the thiophene ring
with the double bond of the ethene moiety.7–15 So, although
most bis(2-thienyl)ethenes display photochromism,11,12 some
of them do not belong to photochromes.7 Therefore, it is diffi-
cult to predict the spectral properties of the diarylethenes
before their studies.
drous benzene in the presence of metallic sodium, with quan-
titative yields (Scheme 1).
The structures of the compounds obtained were proved by
1H and 13C NMR spectroscopy and mass spectrometry, and
were confirmed by elemental analysis. These compounds have
a reddish yellow color. The characteristic absorption of these
compounds is a broad band (3450 cmꢁ1) due to the hydrogen-
bonded –OH group. The 1H NMR spectra of these C-alkylation
products contain characteristic signals for the OH protons (ꢁH
10.05).
The promising compounds among of diarylethenes are the
dithienylmaleimides that have been considered as potential
photoswitching materials.7–9 The ethene bridge of most known
dithienylmaleimides is attached to the 3-position of the thio-
phene ring (structure I). There are only a few examples of
these kinds of compounds where the ethene moiety is linked
to the 2-position of the thiophene ring (structure II) and the
methods for the preparation of them are quite laborious and
of low efficiency (Chart 1). In this work, we present the syn-
thesis and spectral properties of new dithienylmaleimides
according to the structure II.
The O-alkylation (methyl iodide, ethyl 2-bromoacetate) of
the diols 2a–2c was found to also proceed smoothly at room
temperature in DMF in the presence of potassium carbonate
yielding the dithienylethenes 3a–3f. O-Acylation of the com-
pounds 2a–2c was carried out in an acetic anhydride–pyridine
mixture at 90–100 ꢂC (Scheme 2).
We have further studied some spectral properties of the
compounds obtained. Our investigations show that these com-
pounds do not belong to the photochromes but they possess
fluorescent properties. In Fig. 1, the absorption and fluores-
cence spectra for the compound 2a are shown. These spectra
are typical for the compounds 2a–2c and 3a–3f. The absorp-
tion maxima, the extinction coefficients, and fluorescence
intensities for some dithienylethenes are reported in Table 1.
The characteristic property for these compounds is the intensi-
ty band of the absorption in the visible spectrum (400–
530 nm). The displacement of the hydroxy substituent in the
thiophene ring by the alkoxy or acetoxy group leads to a
Results and Discussion
Recently, we have found that the hydroxythiophene 1 in
benzene in the presence of metallic sodium smoothly reacts
with an equal mol amount of ꢀ-halo ketones exclusively yield-
ing C-alkylation products.16 For the purpose of the preparation
of the dithienylmaleimides, we have carried out the reaction of
the hydroxythiophene 1 with different 3,4-dichloromaleimides
under similar conditions. The reaction takes place in anhy-
Ar
N
COOEt
EtOOC
OH HO
O
O
R
N
R
N
OH
EtOOC
O
O
S
O
S
O
Cl
Cl
S
S
R1
R2
R1
R2
S
R1
R2
Na / C6H6
S
O
R1
O
N
1
Ar
R3
R3
R3
S
R3
R2
2a-c
Ar = C6H5 (2a), 4-Cl-C6H4 (2b), 4-MeO-C6H4 (2c)
I
II
Chart 1.
Scheme 1.
Published on the web June 6, 2006; doi:10.1246/bcsj.79.889

890 Bull. Chem. Soc. Jpn. Vol. 79, No. 6 (2006)
Synthesis of Fluorescent Dithienylmaleimides
O
O
O
R
O
R
O
EtOOC
EtOOC
COOEt
CH3
COOEt
CH3
O
2a-c
S
S
CH3
S
S
CH3
O
O
O
O
N
N
Ar
Ar
4 (a-c)
3 (a-f)
2, 4: a) Ar = C6H5; b) Ar = 4-Cl-C6H4; c) Ar = 4-MeO-C6H4;
3: a) Ar = C6H5, R = CH3; b) 4-Cl-C6H4, R = CH3;
c) 4-MeO-C6H4, R = CH3; d) Ar = C6H5, R = CH2COOEt;
e) 4-Cl-C6H4, R = CH2COOEt; f) 4-MeO-C6H4, R = CH2COOEt;
Scheme 2.
D
D
I, a.u.
I, a.u.
250
800
1,0
1,1
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
700
600
500
400
300
200
100
0
200
150
100
50
1
3
2
4
0
λ
, nm
λ, nm
300 350 400 450 500 550 600 650 700 750 800
300 350 400 450 500 550 600 650 700 750 800
Fig. 1. Absorption DðꢂÞ (——) and fluorescence IðꢂÞ
(– – –) spectra of the dithienylethene 2a in toluene at
298 K (1 ꢄ 10ꢁ4 mol Lꢁ1).
Fig. 2. Absorption DðꢂÞ (curves 1 and 3) and fluorescence
IðꢂÞ (curves 2 and 4) spectra of the dithienylethenes 2a
(——) and 2c (– – –) in acetonitrile at 298 K (1 ꢄ 10ꢁ4
mol Lꢁ1).
Table 1. Absorption Maxima, Extinction Coefficient, and Fluorescence Intensity for Compounds 2–4aÞ
ꢂAbs max
/nm
"
ꢂFluo max
/nm
IFluo max
/a.u.
max
/L molꢁ1 cmꢁ1
Compound
Solvent
ꢂ
Ex/nm
ꢀꢂ/nm
2a
3a
3d
4a
2a
2c
toluene
toluene
toluene
toluene
acetonitrile
acetonitrile
469
457
446
438
466
466
6800
9150
7150
9500
11600
7400
450
457
446
438
465
466
580
568
564
556
596
600
6740
530
790
24
226
3.8
111
111
118
118
130
134
a) The concentration of all samples was 1:0 ꢄ 10ꢁ4 mol Lꢁ1
.
hypsochromic shift of the absorption maximum. The dithienyl-
ethenes 2, 4a–4c, and 3a–3f possess fluorescence in the visible
spectrum and have fluorescence maxima at 562–596 nm. The
largest value of the fluorescence intensity is observed for the
compounds containing hydroxy groups; that value is approxi-
mately 8–13-fold more than the values of the fluorescence
intensity for the compounds alkylated (compare the value of
the fluorescence intensity for compounds 2a and 3a, Table 1).
The acylation of the hydroxy groups leads to a drastic decrease
in the fluorescence intensity. A significant decrease (60-fold)
in the fluorescence intensity was also observed by displace-
ment of the benzene ring in the maleimide fragment by a more
donor substituent, 4-methoxyphenyl (compare the value of the
fluorescence intensity for the compounds 2a and 2c, Fig. 2 and
Table 1). It should be noted that the displacement of the sub-
stituents in the dithienylethenes 2–4 changes in fluorescence
intensity but does not influence the spectrum form. These re-
sults show that both substituents in the thiophene rings and
in the maleimide fragment influence the fluorescence intensity.
It is significant that the observed Stokes shift for these com-
pounds was quite large (ꢃ110{120 nm).
Furthermore, we have studied the influence of medium ba-
sicity on the spectral properties of these compounds using as
a sample the dithienylethene 2a. The investigations were car-

V. Z. Shirinian et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 6 (2006)
891
spectrofluorimeter (the maximum value of fluorescence intensity
is 1000 arbitrary units for this spectrofluorimeter). Commercially
available (Merck) anhydrous acetonitrile and toluene were used
for the spectral studies.
D
I, a.u.
250
1,3
1,2
1,1
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
200
150
100
50
General Procedure for the C-Alkylation of Ethyl 4-
Hydroxy-2-methylthiophene-3-carboxylate with 3,4-Dichloro-
maleimides. Metallic sodium (0.01 mol) was added to a solution
of compound 1 (0.01 mol) in 5 mL of anhydrous benzene. Then, a
solution of the corresponding 3,4-dichloromaleimide (0.005 mol)
in 5 mL of anhydrous benzene was added dropwise with stirring
at 10–15 ꢂC. The reaction mixture was stirred at 20 ꢂC for 5 h
and refluxed until the starting hydroxythiophene disappeared com-
pletely. After the reaction was completed (TLC), the solvent was
removed and the residue was chromatographed on silica gel in
light petroleum (60–80 ꢂC)–ethyl acetate (3:1).
5
1
2
6
3
4
0
λ
, nm
250 300 350 400 450 500 550 600 650 700 750 800
Fig. 3. Absorption DðꢂÞ and fluorescence IðꢂÞ spectra of
the dithienylethene 2a in acetonitrile at 298 K before
(curves 1 and 2) and after adding DBU (curves 3 and 4)
and pyridine (curves 5 and 6); the concentrations of the di-
3,4-Bis(4-ethoxycarbonyl-3-hydroxy-5-methyl-2-thienyl)-1-
phenyl-1H-pyrrol-2,5-dione (2a): Dark-orange crystal. Yield:
78%. mp 193–195 ꢂC (ethanol). IR (KBr) 3060 (OH), 1756
(C=O), 1592, 1588, 1504, 1332 cmꢁ1. 1H NMR (CDCl3) ꢁ 1.42 (t,
6H, J ¼ 7:2 Hz), 2.75 (s, 6H), 4.4 (q, 4H, J ¼ 7:2 Hz), 7.45 (m,
5H), 10.05 (s, 2H). 13C NMR (CDCl3) ꢁ 170.51, 166.70, 157.92,
153.92, 131.90, 129.03, 127.61, 126.11, 123.09, 114.08, 104.11,
61.42, 17.80, 14.31. MS: m=z 541 [Mþ]. Found: C, 57.92; H,
4.27; N, 2.65; S, 11.53%. Calcd for C26H23NO8S2: C, 57.66; H,
4.28; N, 2.59; S, 11.84%.
thienylethene 2a, DBU and pyridine are 1 ꢄ 10ꢁ4 mol Lꢁ1
.
ried out in an acetonitrile solution, and pyridine and DBU (1,8-
diazabicyclo[5.4.0]undec-7-ene) were used as bases. The stud-
ies show that using pyridine as a base does not lead to a signif-
icant change in the absorption spectrum, while using DBU
results in a 1.5-fold increase of the absorption density (D)
and shifts the absorbance maximum from ꢂAbs max ¼ 466 nm
to ꢂAbs max ¼ 583 nm (Fig. 3). The base influence on the fluo-
rescence, spectrum is as follows: a strong base (DBU) leads to
the disappearance of the fluorescence, while pyridine decreas-
es the fluorescence intensity in comparison to the initial value,
but keeps the absorption spectrum form invariable. Marked
facts could be explained by comparative stability of the result-
ing complex amine-fluorophore in the case of the stronger base
(DBU) and pyridine.17 Such a shift in the absorbance maxi-
mum in the case of DBU occurs due to the strong removal
of a proton of the hydroxy group of thiophene and the locali-
zation of the negative charge on the oxygen atoms.
3,4-Bis(4-ethoxycarbonyl-3-hydroxy-5-methyl-2-thienyl)-1-
(4-chlorophenyl)-1H-pyrrol-2,5-dione (2b):
crystal. Yield: 92%. mp 224–226 ꢂC. IR (KBr) 3208 (OH), 1768
(C=O), 1592, 1496, 1336 cmꢁ1 1H NMR (CDCl3) ꢁ 1.45 (t,
Reddish yellow
.
6H, J ¼ 7:2 Hz), 2.79 (s, 6H), 4.45 (q, 4H, J ¼ 7:2 Hz), 7.45 (m,
4H), 10.05 (s, 2H, OH). 13C NMR (CDCl3) ꢁ 170.20, 166.71,
158.12, 154.02, 133.19, 130.58, 129.21, 127.10, 123.22, 114.71,
104.14, 61.41, 17.68, 14.29. MS: m=z 575, 577 [Mþ]. Found: C,
54.65; H, 4.08; Cl, 5.65; N, 2.30; S, 11.3%. Calcd for C26H22-
ClNO8S2: C, 54.21; H, 3.85; Cl, 6.15; N, 2.43; S, 11.13%.
3,4-Bis(4-ethoxycarbonyl-3-hydroxy-5-methyl-2-thienyl)-1-
(4-methoxyphenyl)-1H-pyrrol-2,5-dione (2c): Reddish yellow
crystal. Yield: 84%. mp 207–209 ꢂC. IR (KBr) 3280 (OH), 1760
1
(C=O), 1580, 1516, 1328 cmꢁ1. H NMR (CDCl3) ꢁ 1.40 (t, 6H,
J ¼ 7:3 Hz), 2.78 (s, 6H), 3.85 (s, 3H, OCH3), 4.41 (q, 4H, J ¼
7:3 Hz), 6.96 (d, 2H, J ¼ 9:2 Hz), 7.35 (d, 2H, J ¼ 9:2 Hz), 10.05
(s, 2H). 13C NMR (CDCl3) ꢁ 170.71, 166.69, 159.03, 157.89,
153.88, 128.11, 127.62, 123.22, 114.80, 114.41, 104.21, 61.42,
55.61, 17.81, 14.30. MS: m=z 571 [Mþ]. Found: C, 56.38; H, 4.31;
N, 2.37; S, 11.18%. Calcd for C27H25NO9S2: C, 56.73; H, 4.41; N,
2.45; S, 11.22%.
General Procedure for the Synthesis of Dithienylmaleimides
3a–3f. To a solution of the hydroxythiophene 1 (0.01 mol) in
7 mL DMF was added (0.021 mol) K2CO3. Then, a solution of
the corresponding alkyl halide (0.025 mol) in 3 mL of the same
solvent was added dropwise with stirring at 10–25 ꢂC. The reac-
tion mixture was stirred at ꢃ20 ꢂC until the starting compound
disappeared completely. After the reaction was completed
(TLC), the mixture was poured into ice and the product was ex-
tracted with ethyl acetate, washed with saturated sodium hydrogen
carbonate and water, and dried. The solvent was removed and the
residue was chromatographed on silica gel in light petroleum (60–
80 ꢂC)–ethyl acetate (3:1).
Conclusion
We have proposed a new method of dithienylmaleimides
synthesis and studied their spectral properties. It has been
shown that these compounds do not belong to the photo-
chromes but they possess fluorescence properties. It has been
found that fluorescence intensity depends on both substituents
in the heterocyclic rings and on medium basicity.
Experimental
General. 1H and 13C NMR spectra were recorded on Bruker
AC-200, Bruker WM-250, and Bruker AM-300 radio spectrome-
ters in CDCl3. Mass spectra were recorded on a Kratos instrument
(EI, 70 eV, direct inlet probe). Melting points were determined on
a Boetius microscope stage and are given uncorrected. Reaction
completion was checked by TLC data (Silufol UV-254, light pe-
troleum (60–80 ꢂC)–ethyl acetate (3:1) as the eluent). Acros silica
gel (C.A.S.-7631-86-9) (0.060–0.200) was used for column chro-
matography. Ethyl 4-hydroxy-2-methylthiophene-3-carboxylates
(1)18 and 3,4-dichloromaleimides19 were prepared according to a
known procedure. The electronic absorption spectra were mea-
sured on a Varian ‘‘Cary 50 Bio’’ spectrophotometer. Fluorescence
measurements were performed using a Varian ‘‘Cary Eclipse’’
3,4-Bis(4-ethoxycarbonyl-3-methoxy-5-methyl-2-thienyl)-1-
phenyl-1H-pyrrol-2,5-dione (3a): Yellow crystal. Yield: 82%.
mp 142–144 ꢂC. IR (KBr) 2984, 1700 (C=O), 1532, 1504, 1444,
1
1396 cmꢁ1. H NMR (CDCl3) ꢁ 1.38 (t, 6H, J ¼ 7:2 Hz), 2.69 (s,

892 Bull. Chem. Soc. Jpn. Vol. 79, No. 6 (2006)
Synthesis of Fluorescent Dithienylmaleimides
6H), 3.49 (s, 6H, OCH3), 4.35 (q, 4H, J ¼ 7:2 Hz), 7.48 (m, 5H).
MS: m=z 569 [Mþ]. Found: C, 59.48; H, 4.92; N, 2.49; S, 11.08%.
Calcd for C28H27NO8S2: C, 59.04; H, 4.78; N, 2.46; S, 11.26%.
3,4-Bis(4-ethoxycarbonyl-3-methoxy-5-methyl-2-thienyl)-1-
3,4-Bis(3-acetoxy-4-ethoxycarbonyl-5-methyl-2-thienyl)-1-
(4-chlorophenyl)-1H-pyrrol-2,5-dione (4b): Yellowish green
crystal. Yield: 80%. mp 173–175 ꢂC. IR (KBr) 2988, 1772 (C=O),
1
1708, 1596, 1552, 1492, 1396 cmꢁ1. H NMR (CDCl3) ꢁ 1.35 (t,
(4-chlorophenyl)-1H-pyrrol-2,5-dione (3b):
Reddish yellow
6H, J ¼ 7:2 Hz), 1.81 (s, 6H), 2.78 (s, 6H), 4.31 (q, 4H, J ¼ 7:2
Hz), 7.45 (m, 4H). MS: m=z 659 [Mþ]. Found: C, 54.61; H,
4.11; Cl, 5.19; N, 2.13; S, 9.38%. Calcd for C30H26ClNO10S2:
C, 54.59; H, 3.97; Cl, 5.37; N, 2.12; S, 9.71%.
3,4-Bis(3-acetoxy-4-ethoxycarbonyl-5-methyl-2-thienyl)-1-
(4-methoxyphenyl)-1H-pyrrol-2,5-dione (4c): Yellow crystal.
Yield: 69%. mp 171–175 ꢂC. IR (KBr) 2980, 1780 (C=O), 1708,
1600, 1540, 1516, 1404 cmꢁ1. 1H NMR (CDCl3) ꢁ 1.36 (t, 6H, J ¼
7:2 Hz), 1.72 (s, 6H), 2.79 (s, 6H), 3.87 (s, 3H), 4.32 (q, 4H, J ¼
7:2 Hz), 7.02 (d, 2H, J ¼ 9:2 Hz), 7.32 (d, 2H, J ¼ 9:2 Hz). MS:
m=z 655 [Mþ]. Found: C, 56.37; H, 4.41; N, 2.26; S, 9.43%. Calcd
for C31H29NO11S2: C, 56.79; H, 4.46; N, 2.14; S, 9.78%.
crystal. Yield: 84%. mp 121–123 ꢂC. IR (KBr) 2936, 1704
1
(C=O), 1540, 1500, 1388 cmꢁ1. H NMR (CDCl3) ꢁ 1.39 (t, 6H,
J ¼ 7:2 Hz), 2.70 (s, 6H), 3.51 (s, 6H), 4.37 (q, 4H, J ¼ 7:2 Hz),
7.49 (m, 4H). MS: m=z 603, 605 [Mþ]. Found: C, 55.46; H, 4.54;
Cl, 5.66; N, 2.30; S, 10.24%. Calcd for C28H26ClNO8S2: C, 55.67;
H, 4.34; Cl, 5.87; N, 2.32; S, 10.62%.
3,4-Bis(4-ethoxycarbonyl-3-methoxy-5-methyl-2-thienyl)-1-
(4-methoxyphenyl)-1H-pyrrol-2,5-dione (3c): Brown crystal.
Yield: 72%. mp 133–135 ꢂC. IR (KBr) 2972, 1704 (C=O), 1584,
1
1516, 1448, 1396 cmꢁ1. H NMR (CDCl3) ꢁ 1.36 (t, 6H, J ¼ 7:2
Hz), 2.68 (s, 6H), 3.50 (s, 6H), 3.82 (s, 3H), 4.36 (q, 4H, J ¼ 7:2
Hz), 6.99 (d, 2H, J ¼ 9:2 Hz), 7.38 (d, 2H, J ¼ 9:2 Hz). MS: m=z
599 [Mþ]. Found: C, 56.82; H, 4.96; N, 2.31; S, 10.71%. Calcd for
C29H29NO9S2: C, 58.08; H, 4.87; N, 2.34; S, 10.69%.
This work was supported by the Russian Foundation for
Basic Research (Project No. 04-03-32878).
3,4-Bis(4-ethoxycarbonyl-3-ethoxycarbonylmethoxy-5-meth-
yl-2-thienyl)-1-phenyl-1H-pyrrol-2,5-dione (3d):
yellow crystal. Yield: 76%. mp 171–174 ꢂC. IR (KBr) 2984,
1704 (C=O), 1544, 1476, 1400 cmꢁ1 1H NMR (CDCl3) ꢁ 1.18
(t, 6H, J ¼ 7:5 Hz), 1.34 (t, 6H, J ¼ 7:2 Hz), 2.71 (s, 6H), 4.12
(q, 4H, J ¼ 7:5 Hz), 4.36 (q, 4H, J ¼ 7:2 Hz), 7.5 (m, 5H). MS:
m=z 713 [Mþ]. Found: C, 56.42; H, 4.98; N, 2.04; S, 8.46%. Calcd
for C34H35NO12S2: C, 57.21; H, 4.94; N, 1.96; S, 8.98%.
3,4-Bis(4-ethoxycarbonyl-3-ethoxycarbonylmethoxy-5-meth-
yl-2-thienyl)-1-(4-chlorophenyl)-1H-pyrrol-2,5-dione (3e): Yel-
low crystal. Yield: 86%. mp 181–183 ꢂC. IR (KBr) 2980, 1700
(C=O), 1540, 1472, 1440, 1400 cmꢁ1 1H NMR (CDCl3) ꢁ 1.20
.
(t, 6H, J ¼ 7:5 Hz), 1.38 (t, 6H, J ¼ 7:2 Hz), 2.68 (s, 6H), 4.16
(q, 4H, J ¼ 7:5 Hz), 4.34 (q, 4H, J ¼ 7:2 Hz), 4.48 (s, 4H), 7.5
(m, 4H). MS: m=z 747, 749 [Mþ]. Found: C, 53.87; H, 4.69; Cl,
4.79; N, 1.84; S, 9.59%. Calcd for C34H34ClNO12S2: C, 54.58;
H, 4.58; Cl, 4.74; N, 1.87; S, 8.57%.
Brownish
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Dark-orange crystal. Yield: 73%. mp 136–140 ꢂC. IR (KBr) 2924,
8
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1704 (C=O), 1600, 1544, 1444, 1408, 1340 cmꢁ1
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(CDCl3) ꢁ 1.21 (t, 6H, J ¼ 7:2 Hz), 1.34 (t, 6H, J ¼ 7:2 Hz), 2.67
(s, 6H), 3.84 (s, 2H), 4.10 (q, 4H, J ¼ 7:2 Hz), 4.32 (q, 4H, J ¼ 7:2
Hz), 4.4 (s, 3H), 7.0 (d, 2H, J ¼ 9:1 Hz), 7.34 (d, 2H, J ¼ 9:1 Hz).
MS: m=z 743 [Mþ]. Found: C, 55.95; H, 5.03; N, 1.98; S, 7.11%.
Calcd for C35H37NO13S2: C, 56.52; H, 5.01; N, 1.88; S, 8.62%.
General Procedure for the Synthesis of Compounds 4a–4c.
Pyridine (0.002 mol) was added dropwise with stirring at 10–
25 ꢂC to a solution of the compounds 2a–2c (0.001 mol) in
10 mL acetic anhydrate, and then the reaction mixture was heated
to 100 ꢂC until the starting compound disappeared completely. Af-
ter the reaction was completed (TLC), the mixture was poured into
ice and the product was extracted with ethyl acetate, washed with
3% hydrochloric acid and water, and dried (MgSO4). The solvent
was removed and the residue was recrystallized from ethanol.
3,4-Bis(3-acetoxy-4-ethoxycarbonyl-5-methyl-2-thienyl)-1-
phenyl-1H-pyrrol-2,5-dione (4a): Bright yellow crystal. Yield:
72%. mp 226–228 ꢂC. IR (KBr) 2988, 1780 (C=O), 1712, 1600,
9
V. Z. Shirinian, M. M. Krayushkin, D. M. Nikalin, A. A.
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2005, 3921.
15 A. Goldberg, A. Murakami, K. Kanda, T. Kobayashi, S.
Nakamura, K. Uchida, H. Sekiya, T. Fukaminato, T. Kawai, S.
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16 M. M. Krayushkin, V. Z. Shirinian, D. M. Nikalin,
A. A. Shimkin, Izv. Akad. Nauk, Ser. Khim. 2004, 602; M. M.
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1552, 1492, 1396 cmꢁ1
.
1H NMR (CDCl3) ꢁ 1.35 (t, 6H, J ¼
7:2 Hz), 1.85 (s, 6H), 2.79 (s, 6H), 4.31 (q, 4H, J ¼ 7:2 Hz), 7.49
(m, 5H). MS: m=z 625 [Mþ]. Found: C, 57.37; H, 4.53; N, 2.24; S,
9.82%. Calcd for C30H27NO10S2: C, 57.59; H, 4.35; N, 2.24; S,
10.25%.
17 J. Lakovich, Principles of Fluorescence Spectroscopy,

V. Z. Shirinian et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 6 (2006)
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