One-pot, pseudo-five-component synthesis of bis[2-(arylimino)-1,3- thiazolidin-4-ones]

Article abstract of DOI:10.1002/hlca.200900402

Synthesis and characterization of bis[2-(arylimino)-1,3-thiazolidin-4-ones] are described. The onepot, pseudo-five-component reaction of an aliphatic diamine, isothiocyanatobenzene, and dialkyl but-2-ynedioate at room temperature in anhydrous CH₂Cl₂ gives the title compound in relatively high yield. Under the same conditions, aromatic 1,2-diamines yield 2-(arylimino)-N-(enaminoaryl)-1,3-thiazolidin-4-ones in a pseudo-four-component reaction. Their structures were corroborated spectroscopically (IR, ¹H- and ¹³C-NMR, and EI-MS) and by elemental analyses. A plausible mechanism for this type of cyclization is proposed (Scheme 3).

Full text of DOI:10.1002/hlca.200900402

Helvetica Chimica Acta – Vol. 93 (2010)
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One-Pot, Pseudo-Five-Component Synthesis of Bis[2-(arylimino)-1,3-
thiazolidin-4-ones]
by Abdolali Alizadeh*, Zohreh Noaparast, Hamideh Sabahno, and Nasrin Zohreh
Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran
(phone: þ 98-21-88006631; fax: þ 98-21-88006544; e-mail: abdol_alizad@yahoo.com,
aalizadeh@modares.ac.ir)
Synthesis and characterization of bis[2-(arylimino)-1,3-thiazolidin-4-ones] are described. The one-
pot, pseudo-five-component reaction of an aliphatic diamine, isothiocyanatobenzene, and dialkyl but-2-
ynedioate at room temperature in anhydrous CH2Cl2 gives the title compound in relatively high yield.
Under the same conditions, aromatic 1,2-diamines yield 2-(arylimino)-N-(enaminoaryl)-1,3-thiazolidin-
4-ones in a pseudo-four-component reaction. Their structures were corroborated spectroscopically (IR,
1H- and 13C-NMR, and EI-MS) and by elemental analyses. A plausible mechanism for this type of
cyclization is proposed (Scheme 3).
1. Introduction. – The multi-component coupling reactions are emerging as a useful
tool for synthesizing small, drug-like molecules with several levels of structural
diversity [1]. They are also welcome in the context of economic and practical
considerations. Moreover, multicomponent coupling strategies offer significant advan-
tages over conventional linear-type syntheses [2].
Among small-molecule heterocyclic compounds, thiazolidine is a recognized
scaffold for potential drugs and drug candidates. Anticonvulsant, sedative, antidepres-
sant, anti-inflammatory, antihypertensive, antihistaminic, and antiarthritic activities are
a few among many biological responses shown by this scaffold [3]. In particular, 2-
imino-1,3-thiazolidin-4-ones are known to possess remarkable hypnotic, antitubercular,
and cardiovascular activities [4 – 6]. For example, 5-(4-methoxycyclohexa-2,4-dien-1-
ylidene)-2-(phenylimino)-3-propyl-1,3-thiazolidin-4-one (1) is known to have potent
anti-inflammatory (COX inhibitor) activity [7]. This diversity in the biological
response profiles of thiazolidine derivatives has attracted the attention of many
researchers to explore this skeleton.
ꢀ 2010 Verlag Helvetica Chimica Acta AG, Zꢁrich

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Helvetica Chimica Acta – Vol. 93 (2010)
2. Results and Discussion. – Some of our previous works included the use of
aliphatic and aromatic diamines to synthesize important heterocycles of potential
synthetic and pharmacological interest [8]. In continuation, we investigated the
synthesis of bis(2-arylimino-1,3-thiazolidin-4-ones) and 2-(arylimino)-N-(enami-
noaryl)-1,3-thiazolidin-4-ones from various diamines. Thus, the reaction of aliphatic
diamines 2 and isothiocyanatobenzene in the presence of dialkyl but-2-ynedioate 3
proceeded spontaneously at 258 in anhydrous CH2Cl2 and furnished bis(2-arylimino-
1,3-thiazolidin-4-ones) 4 within 3 h in 80 – 85% yields (Scheme 1).
Scheme 1. Synthesis of the Bis(2-arylimino-1,3-thiazolidin-4-ones) 4
When benzene-1,2-diamines 5 and isothiocyanatobenzene in dry CH2Cl2 were
allowed to react in the presence of 3 at room temperature, compound 6, as a yellow
powder, was formed in nearly quantitative yield (Scheme 2). This product was
identified as dimethyl 2-({2-[5-(2-methoxy-2-oxoethylidene)-4-oxo-2-(phenylimino)-
1,3-thiazolidin-3-yl]phenyl}amino)but-2-enedioate.
Scheme 2. Synthesis of 2-(Arylimino)-N-(enaminoaryl)-1,3-thiazolidin-4-ones 6

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The structures of compounds 4a – 4f, 6a, and 6b were deduced from their elemental
analysis, IR, and 1H- and 13C-NMR spectra.
The mass spectrum of the symmetric 4a displayed the molecular-ion peak at m/z
550. Two fragment-ion peaks at m/z 288 ([M ꢀ 262]þ) and 263 ([M ꢀ 287]þ) are in
agreement with two important structural parts of 4a. The fragment-ion peak at m/z 288
resulted from dissociation of the CH2ꢀN bond along with a transfer of an H-atom
between the two fragments (m/z 261 and 289). The fragment-ion peak at m/z 263
([M ꢀ 288 þ 1]þ) is related to the protonation of the fragment with the mass 262. The
IR spectrum of 4a showed four sharp adsorptions at 1709, 1691, 1635, and 1608 cmꢀ1
1
which are ascribed to NC¼O, CO2R, C¼N, and C¼C, respectively. The H-NMR
spectrum of 4a exhibited three sharp singlets arising from MeO groups (3.81 ppm),
CH2 groups of the diamine (4.45 ppm), and the ¼CH group (6.89 ppm). The Ph moiety
1
gave rise to characteristic signals in the aromatic region of the spectrum. The H-
decoupled 13C-NMR spectrum of 4a showed eleven distinct resonances in agreement
with the symmetric structure. The characteristic C-atom signals of the 2-(arylimino)-
1,3-thiazolidin-4-one ring are attributed to NC¼O, NC¼N, and SC¼C, and they
appeared at 165.20, 151.22, and 141.18 ppm, respectively. It is important to note that the
molecular structures of product 4a – 4d are symmetric.
1
The H-NMR spectrum of 6a showed six singlets at 3.60, 3.73, 3.84, 5.55, 7.03, and
9.54 ppm arising from three MeO groups, two CH groups (NC¼CH and SC¼CH), and
a NH group. The 13C-NMR spectrum of 6a showed 22 prominent peaks assigned to the
proposed structure. Signals for NC¼O, NC¼N, and SC¼CH appeared at 164.07,
150.82, and 148.06 ppm, respectively, indicating the presence of the thiazolidine ring.
The enaminone moiety gave rise to characteristic signals at 95.73 (NC¼CH), 138.66
(NC¼CH), and 164.22, 166.29 ppm (2 CO2Me).
Although we have not established the mechanism of the reaction in an
experimental manner, an explanation is proposed in Scheme 3. First, the aliphatic
diamine 2 readily reacts with 2 equiv. of isothiocyanatobenzene to produce bis-thiourea
7, which is converted to the intermediate 8 in the presence of dialkyl but-2-ynedioate 3.
Finally, product 4 is obtained via an intramolecular cyclocondensation [9] in 80 – 85%
yields. On the other hand, benzene-1,2-diamine 5 reacts with only 1 equiv. of
isothiocyanatobenzene to produce thiourea 9 (in a separate reaction, 9 was isolated and
characterized). In the presence of 2 equiv. of dialkyl but-2-ynedioate 3, 9 is converted
to intermediate 10 that finally afforded 2-(arylimino)-N-(enaminoaryl)-1,3-thiazolidin-
4-one 6 via an intramolecular cyclocondensation in 70 – 75% yield.
The difference of the two reactions is related to the reactivity of aliphatic and
aromatic diamines. Aliphatic diamines are more reactive than aromatic diamines, and,
at first step, the aliphatic diamine 2 readily reacts with 2 equiv. of isothiocyanatoben-
zene to produce bis-thiourea 7, whereas the benzene-1,2-diamine 5 reacts with only 1
equiv. of phenyl isothiocyanate to produce thiourea 9. Another reason can be a steric
factor.
In summary, we have described an efficient and simple one-pot multicomponent
reaction for the synthesis of bis(2-arylimino-1,3-thiazolidin-4-ones) from aliphatic
diamines, isothiocyanatobenzene, and dialkyl but-2-ynedioates. In addition, we have
shown that benzene-1,2-diamine produces a 2-(arylimino)-N-(enaminoaryl)-1,3-thia-
zolidin-4-one under the same conditions. The use of easily accessible starting materials,

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Helvetica Chimica Acta – Vol. 93 (2010)
Scheme 3. Proposed Mechanism for the Formation of Bis(2-arylimino-1,3-thiazolidin-4-ones) 4 and N-
(Enaminoaryl)-2-imino-1,3-thiazolidin-4-ones 6
the simple experimental procedure and purification, neutral conditions, using the
substrates in the reaction without any prior activation or modification, short reaction
times, and relatively good yields with both diamine types are the advantages of the
present method.
Experimental Part
General. Aliphatic diamines, benzene-1,2-diamines, dialkyl but-2-ynedioates, and isothiocyanato-
benzene were obtained from Merck (Germany) and Fluka (Switzerland). Column chromatography:
Merck silica gel (SiO2; 230 – 240 mesh). M.p.: Electrothermal 9100 apparatus. IR Spectra: Shimadzu IR-
460 spectrometer. 1H- and 13C-NMR spectra: in CDCl3, with a Bruker DRX-500 AVANCE spectrometer
at 500.13 and 125.75 MHz, resp. EI-MS: FINNIGAN-MAT 8430 mass spectrometer operating at an
ionization potential of 20 eV. Elemental analyses: Herpes CHNꢀOꢀRapid analyzer.
Preparation of Compounds 4a – 4f. General Procedure (exemplified for 4a). Dimethyl but-2-
ynedioate (3a; 2 mmol) was added slowly to a magnetically stirred 5-ml flat bottom flask containing a
mixture of diamine 2 (1 mmol) and isothiocyanatobenzene (2 mmol) in 3 ml of CH2Cl2 at r.t. The mixture
was stirred for 3 h to completion of the reaction (monitored by means of TLC). The solvent was
removed, and the product was separated by CC with hexane/AcOEt 6 :1.

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Dimethyl 2,2’-{Ethane-1,2-diylbis[4-oxo-2-(phenylimino)-1,3-thiazolidin-3-yl-5-ylidene]}diethanoate
(4a). Yield: 0.44 g (80%). Yellow powder. M.p. 135 – 1388 (dec.). IR (KBr): 1709 (2 CO2Me), 1635
(2 NCO), 1608 (2 C¼N), 1584 (2 C¼C), 1206, 1190 (2 CꢀO). 1H-NMR (500.1 MHz): 3.81 (s, 2 MeO);
4.45 (s, 2 CH2); 6.89 (s, 2 ¼CH); 6.93 (d, J ¼ 7.3, 4 H); 7.17 (t, J ¼ 7.5, 2 H); 7.33 (t, J ¼ 7.6, 4 H). 13C-NMR
(125.7 MHz): 40.46; 52.44; 116.34; 120.99; 125.25; 129.35; 141.18; 147.1; 151.22; 165.20; 166.17. EI-MS:
550 (8, Mþ), 518 (21), 491 (19), 458 (56), 288 (100), 275 (39), 263 (47), 201 (42), 117 (25), 104 (14), 91
(10), 77 (30). Anal. calc. for C26H22N4O6S2 (550.60): C 56.72, H 4.03, N 10.18; found: C 56.78, H 4.01, N
10.15.
Diethyl 2,2’-{Ethane-1,2-diylbis[4-oxo-2-(phenylimino)-1,3-thiazolidin-3-yl-5-ylidene]}diethanoate
(4b). Yield: 0.47 g (82%). Yellow powder. M.p. 160 – 1628. IR (KBr): 1721 (2 CO2Et), 1697 (2 NCO),
1
1647 (2 C¼N), 1610 (2 C¼C), 1189, 1147 (2 CꢀO). H-NMR (500.1 MHz): 1.31 (t, J ¼ 7.1, 2 MeCH2);
4.23 (q, J ¼ 7.1, 2 MeCH2O); 4.45 (s, 2 CH2N); 6.88 (s, 2 ¼CH); 6.94 (d, J ¼ 7.4, 4 H); 7.15 (t, J ¼ 7.4, 2 H);
7.31 (t, J ¼ 7.6, 4 H). 13C-NMR (125.7 MHz): 14.14; 40.43; 61.66; 116.81; 121.01; 125.2; 129.32; 140.93;
147.14; 151.4; 165.25; 165.78. EI-MS: 579 (2, [M þ 1]þ), 578 (2, Mþ), 532 (24), 505 (44), 486 (32), 301
(100), 289 (38), 276 (76), 201 (48), 117 (13), 104 (61), 91 (32), 77 (30). Anal. calc. for C28H26N4O6S2
(578.65): C 58.12, H 4.53, N 9.68; found: C 58.15, H 4.50, N 9.70.
Dimethyl 2,2’-{Propane-1,3-diylbis[4-oxo-2-(phenylimino)-1,3-thiazolidin-3-yl-5-ylidene]}dietha-
noate (4c). Yield: 0.46 g (82%). Yellow powder. M.p. 160 – 1628. IR (KBr): 1727 (2 CO2Me), 1693
1
(2 NCO), 1648 (2 C¼N), 1616 (2 C¼C), 1203, 1155 (2 CꢀO). H-NMR (500.1 MHz): 2.31 – 2.34 (m,
CH2); 3.79 (s, 2 MeO); 4.11 (t, J ¼ 7.1, 2 CH2N); 6.89 (s, 2 ¼CH); 6.96 (d, J ¼ 7.3, 4 H); 7.17 (t, J ¼ 7.4,
2 H); 7.34 (t, J ¼ 7.7, 4 H ) . 13C-NMR (125.7 MHz): 25.75; 40.57; 52.44; 116.15; 121.08; 125.24; 129.34;
141.51; 147.14; 150.79; 164.84; 166.20. EI-MS: 564 (7, Mþ), 532 (6), 505 (1), 472 (35), 302 (100), 287 (35),
263 (6), 117 (16), 104 (6), 91 (5), 77 (27). Anal. calc. for C27H24N4O6S2 (564.63): C 57.44, H 4.28, N 9.92;
found: C 57.46, H 4.25, N 9.95.
Diethyl 2,2’-{Propane-1,3-diylbis[4-oxo-2-(phenylimino)-1,3-thiazolidin-3-yl-5-ylidene]}diethanoate
(4d). Yield: 0.47 g (80%). Yellow powder. M.p. 147 – 1508. IR (KBr): 1721 (2 CO2Me), 1688
1
(2 NCO), 1642 (2 C¼N), 1612 (2 C¼C), 1193, 1152 (2 CꢀO). H-NMR (500.1 MHz): 1.30 (t, J ¼ 7.1,
2 MeCH2); 2.32 – 2.34 (m, CH2); 4.12 (t, J ¼ 7.1, 2 CH2N); 4.26 (q, J ¼ 7.1, 2 MeCH2O); 6.89 (s, 2 ¼CH);
6.98 (d, J ¼ 7.4, 4 H); 7.18 (t, J ¼ 7.4, 2 H); 7.35 (t, J ¼ 7.9, 4 H). 13C-NMR (125.7 MHz): 14.13; 25.78; 40.55;
61.64; 116.63; 121.08; 125.20; 129.32; 141.24; 147.17; 150.94; 164.92; 165.84. EI-MS: 592 (10, Mþ), 546 (6),
519 (1), 501 (35), 316 (100), 301 (24), 277 (18), 117 (14), 104 (27), 91 (31), 77 (49), 59 (11), 41 (7). Anal.
calc. for C29H28N4O6S2 (592.68): C 58.77, H 4.76, N 9.45; found: C 58.75, H 4.79, N 9.44.
Dimethyl 2,2’-{Propane-1,2-diylbis[4-oxo-2-(phenylimino)-1,3-thiazolidin-3-yl-5-ylidene]}dietha-
noate (4e). Yield: 0.48 g (85%). Yellow powder. M.p. 140 – 1428. IR (KBr): 1729 (2 CO2Me), 1696
1
(2 NCO), 1640 (2 C¼N), 1611 (2 C¼C), 1199, 1116 (2 CꢀO). H-NMR (500.1 MHz): 1.78 (d, J ¼ 7.1,
MeCH); 3.79 (s, MeO); 3.81 (s, MeO); 4.08 (dd, J ¼ 13.6, 3.0, 1 H); 4.97 – 5.07 (m, 1 H); 5.38 – 5.47 (m,
1 H); 6.85 (s, ¼CH); 6.89 (s, ¼CH); 6.91 – 6.92 (m, 4 H); 7.12 – 7.18 (m, 2 H); 7.31 (t, J ¼ 7.7, 4 H ) .
13C-NMR (125.7 MHz): 15.41; 44.18; 49.84; 52.36; 52.45; 115.95; 116.46; 120.88; 120.94; 125.12; 125.20;
129.34; 129.39; 141.05; 141.27; 147.10; 147.44; 150.87; 151.20; 164.94; 165.20; 166.18; 166.26. EI-MS: 564
(8, Mþ), 550 (9), 532 (10), 505 (13), 472 (36), 302 (100), 287 (48), 263 (19), 117 (14), 104 (11), 91 (39), 77
(75), 59 (16), 41 (7). Anal. calc. for C27H24N4O6S2 (564.63): C 57.44, H 4.28, N 9.92; found: C 57.41, H
4.30, N 9.90.
Diethyl 2,2’-{Propane-1,2-diylbis[4-oxo-2-(phenylimino)-1,3-thiazolidin-3-yl-5-ylidene]}diethanoate
(4f). Yield: 0.47 g (80%). Yellow powder. M.p. 141 – 1438. IR (KBr): 1719 (2 CO2Et), 1695 (2 NCO),
1
1640 (2 C¼N), 1610 (2 C¼C), 1200, 1117 (2 CꢀO). H-NMR (500.1 MHz): 1.32 (t, J ¼ 7.1, 2 MeCH2);
1.77 (d, J ¼ 7.2, MeCH); 4.07 (dd, J ¼ 14.0, 3.0, 1 H); 4.23 (q, J ¼ 7.1, 2 MeCH2O); 4.98 – 5.08 (m, 1 H);
5.37 – 5.48 (m, 1 H); 6.84 (s, ¼CH); 6.88 (s, ¼CH); 6.91 (d, J ¼ 7.8, 4 H); 7.15 (t, J ¼ 7.2, 2 H); 7.31 (t, J ¼
7.4, 4 H). 13C-NMR (125.7 MHz): 14.14; 15.42; 44.14; 49.79; 61.55; 61.68; 116.41; 116.93; 120.90; 120.96;
125.08; 125.17; 129.28; 129.33; 140.79; 141.02; 147.16; 147.40; 151.05; 151.45; 164.99; 165.27; 165.81;
165.90. EI-MS: 592 (7, Mþ), 577 (15), 546 (17), 519 (22), 500 (58), 316 (100), 301 (62), 277 (19), 117 (26),
104 (18), 91 (13), 77 (37). Anal. calc. for C29H28N4O6S2 (592.68): C 58.77, H 4.74, N 9.45; found: C 58.75,
H 4.71, N 9.43.

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Dimethyl 2-({2-[5-(2-Methoxy-2-oxoethylidene)-4-oxo-2-(phenylimino)-1,3-thiazolidin-3-yl]phenyl}-
amino)but-2-enedioate (6a). Yield: 0.37 g (75%). Yellow powder. M.p. 159 – 1618. IR (KBr): 1734,
1697 (3 CO2Me), 1673 (NCO), 1641 (C¼N), 1612, 1600 (2 C¼C), 1275, 1208 (2 CꢀO). 1H-NMR
(500.1 MHz): 3.60 (s, MeO); 3.73 (s, MeO); 3.84 (s, MeO); 5.55 (s, NC¼CH); 7.03 (s, ¼CH); 7.09 – 7.11
(m, 3 H); 7.18 (t, J ¼ 7.5, 1 H); 7.34 – 7.37 (m, 3 H); 7.39 – 7.44 (m, 2 H); 9.54 (s, NH). 13C-NMR
(125.7 MHz): 51.26; 52.52; 52.63; 95.73; 116.77; 121.25; 124.42; 125.25; 126.03; 128.20; 129.15; 129.44;
130.22; 138.66; 141.43; 147.33; 148.06; 150.82; 164.07; 164.22; 166.29; 169.27. EI-MS: 495 (5, Mþ), 462 (6),
436 (9), 403 (100), 351 (4), 337 (21), 292 (26), 261 (7), 240 (41), 157 (12), 121 (11), 93 (11), 77 (22). Anal.
calc. for C24H21N3O7S (495.50): C 58.18, H 4.27, N 8.48; found: C 58.15, H 4.29, N 8.51.
Diethyl 2-({2-[5-(2-Ethoxy-2-oxoethylidene)-4-oxo-2-(phenylimino)-1,3-thiazolidin-3-yl]-4-methyl-
phenyl}amino)but-2-enedioate (6b). Yield: 0.39 g (70%). Red liquid. IR (KBr): 1730, 1710 (3 CO2Me),
1668 (NCO), 1642 (C¼N), 1611 (NC¼C), 1605 (SC¼C), 1267, 1195 (2 CꢀO). 1H-NMR (500.1 MHz):
0.97 (t, J ¼ 7.0, MeCH2O); 1.27 (t, J ¼ 7.0, MeCH2O); 1.30 (t, J ¼ 7.0, MeCH2O); 2.34 (s, Me); 4.04 (q, J ¼
7.0, MeCH2O); 4.16 (q, J ¼ 7.0, MeCH2O); 4.25 (q, J ¼ 7.1, MeCH2O); 5.53 (s, NC¼CH); 6.89 (s, 1 H);
6.98 (s, ¼CH); 7.07 – 7.17 (m, 2 H); 7.24 – 7.32 (m, 5 H); 9.50 (s, NH). 13C-NMR (125.7 MHz): 13.99;
14.12; 14.30; 21.17; 59.92; 61.66; 61.86; 95.78; 117.06; 120.99; 125.08; 126.62; 128.14; 128.95; 129.04;
130.83; 138.41; 140.46; 141.26; 147.47; 148.50; 151.18; 163.88; 164.08; 165.89; 168.90. EI-MS: 551 (8, Mþ),
504 (7), 478 (10), 459 (100), 393 (5), 365 (20), 308 (25), 275 (8), 254 (40), 185 (14), 135 (10), 108 (10), 77
(20). Anal. calc. for C28H29N3O7S (551.61): C 60.97, H 5.30, N 7.62; found: C 60.95, H 5.32, N 7.65.
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Received November 13, 2009