Synthesis of 2-aryl-5-oxo-4-[2-(phenylmethylidene)hydrazino]-2,5-dihydro- 1H-pyrrole-3-carboxylates by the reaction between hydrazones, acetylenedicarboxylates, and 1-aryl-N,N′-bis(arylmethylidene) methanediamines

Article abstract of DOI:10.1002/hlca.201300116

An efficient approach for the preparation of functionalized 2-aryl-2,5-dihydro-5-oxo-4-[2-(phenylmethylidene)hydrazino]-1H-pyrroles is described. The four-component reaction between aldehydes, NH₂NH ₂×H₂O, dialkyl acetylenedicarboxylates, and 1-aryl-N,N′-bis(arylmethylidene)methanediamines proceeds in EtOH under reflux in good-to-excellent yields (Scheme 1). The structures of 4 were corroborated spectroscopically (IR, ¹H- and ¹³C-NMR, and EI-MS, and, in the case of 4f, by X-ray crystallography). A plausible mechanism for this type of reaction is proposed (Scheme 2). Copyright

Full text of DOI:10.1002/hlca.201300116

Helvetica Chimica Acta – Vol. 96 (2013)
1991
Synthesis of 2-Aryl-5-oxo-4-[2-(phenylmethylidene)hydrazino]-2,5-
dihydro-1H-pyrrole-3-carboxylates by the Reaction between Hydrazones,
Acetylenedicarboxylates, and 1-Aryl-N,N’-
bis(arylmethylidene)methanediamines
by Abdolali Alizadeh*, Vahid Saberi, and Javad Mokhtari
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)
An efficient approach for the preparation of functionalized 2-aryl-2,5-dihydro-5-oxo-4-[2-(phenyl-
methylidene)hydrazino]-1H-pyrroles is described. The four-component reaction between aldehydes,
NH2NH2 · H2O, dialkyl acetylenedicarboxylates, and 1-aryl-N,N’-bis(arylmethylidene)methanediamines
proceeds in EtOH under reflux in good-to-excellent yields (Scheme 1). The structures of 4 were
corroborated spectroscopically (IR, 1H- and 13C-NMR, and EI-MS, and, in the case of 4f, by X-ray
crystallography). A plausible mechanism for this type of reaction is proposed (Scheme 2).
Introduction. – Multicomponent reactions (MCRs) are excellent strategies,
employed in the synthesis of many natural products. These MCRs are generally
defined as reactions where more than two starting materials react to form a product,
incorporating more or less atoms of all the starting materials [1].
Pyrrole and its derivatives such as dihydro-2-oxopyrroles and pyrrolidines are
important structural motifs that are found in natural and unnatural products [2]. 2-
Oxopyrroles show high versatility, and they are important substructures in a variety of
pharmaceutical drugs, including products active against viral infections (HIV,
influenza, cytomegalovirus), anticancer agents, and products active against micro-
biological diseases (bacterial or fungal) [3].
Hydrazones have also been demonstrated to possess, among others, antimicrobial,
anticonvulsant, analgesic, anti-inflammatory, antiplatelet, antitubercular, and antitu-
mor activities [4]. Also hydrazone-based coupling methods are used in medical
biotechnology to couple drugs to targeted antibodies, e.g., antibodies against a certain
type of cancer cell. The hydrazone-based bond is stable at neutral pH (in the blood),
but is rapidly destroyed in the acidic environment of lysosomes of the cell. The drug is
thereby released in the cell, where it exerts its function [5]. Inspired by the above
findings and in continuation of our ongoing research program in the field of synthesis of
medicinally relevant compounds [6], we herein report a synthesis of novel hydrazone
derivatives with 2-oxopyrrole building blocks.
We previously investigated the reactions of 1-aryl-N,N’-bis(arylmethylidene)me-
thanediamine 3 with heterocyclic ketene aminals and isocyanides in Ugi reaction,
respectively [7], for the synthesis of new heterocyclic compounds. Now, we have
ꢀ 2013 Verlag Helvetica Chimica Acta AG, Zꢁrich

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Helvetica Chimica Acta – Vol. 96 (2013)
developed a novel, one-pot synthesis of 2-aryl-2,5-dihydro-5-oxo-4-[2-(phenylmethy-
lidene)hydrazino]-1H-pyrroles using NH2NH2 · H2O, different aldehydes 1, dialkyl
acetylenedicarboxylates 2, and 1-aryl-N,N’-bis(arylmethylidene)methanediamines 3
(Scheme 1).
Scheme 1. Synthesis of 2-Aryl-2,5-dihydro-5-oxo-4-[2-(phenylmethylidene)hydrazino]-1H-pyrroles
Results and Discussion. – For this purpose, 1 equiv. of 1 was reacted with 1 equiv. of
2 and 1 equiv. 3 in presence of hydrazine hydrate in refluxing EtOH to yield 2-aryl-2,5-
dihydro-5-oxo-4-[2-(phenylmethylidene)hydrazino]-1H-pyrroles 4 in ca. 80% yield.
We have shown that the use of various substituted aldehydes 1 in this reaction makes it
possible the synthesis of libraries of 4 under the same conditions. The results are
compiled in the Table. Irrespective of the presence of a MeO substituent in the para-
positions of 3, the reactions proceeded fairly well and afforded the desired products in
good-to-excellent yields (Entries 4 and 5, Table). An electron withdrawing substituent
in meta-position of the aldehyde (3-NO2) afforded the desired products in a lower yield
(Entry 7, Table), and electron-releasing substituents in para-position afforded the
desired products in high yields (Entries 3 and 5, Table).
The structures of compounds 4a – 4h were deduced from their elemental analyses,
1
IR, and high-field H- and 13C-NMR spectra. The structure of product 4f was further
confirmed by X-ray crystallographic analysis (Fig.). The mass spectrum of 4a displayed
the molecular-ion peak at m/z 335, which is in agreement with the proposed structure.
The IR spectrum of this compound showed absorption bands due to the NH group at
Table. Synthesis of Functionalized 2-Aryl-2,5-dihydro-5-oxo-4-[2-(phenylmethylidene)hydrazino]-1H-
pyrroles 4. Time, 1 h.
Entry
4
R1
R2
Ar
Yield [%]
1
2
3
4
5
6
7
8
4a
4b
4c
4d
4e
4f
4g
4h
H
Me
Me
Me
Me
Me
Me
Me
Et
Ph
Ph
Ph
81
82
85
82
84
83
74
80
4-Cl
4-MeO
H
4-MeO
4-Me
3-NO2
H
4-MeOꢀC6H4
4-MeOꢀC6H4
Ph
Ph
Ph

Helvetica Chimica Acta – Vol. 96 (2013)
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3301 and 3036, COOMe group at 1709, C¼N group at 1650, and the Ph group at 1561
and 1445 cmꢀ1. The 1H-NMR spectrum of 4a showed three singlet signals for the MeO,
CH-NH, and N¼CH groups at d(H) 3.64, 5.30, and 7.85, respectively, and of two NH
groups at 6.44 and 9.90 ppm, and the aromatic moieties gave rise to multiplets in the
aromatic region of the spectrum (7.26 – 7.73 ppm). The 1H-decoupled 13C-NMR
spectrum of 4a displayed 15 distinct resonances in agreement with the suggested
structure.
Figure. X-Ray crystal structure of compound 4f
Although we have not established the mechanism of the reaction experimentally, a
proposal is outlined in Scheme 2.
Scheme 2. Proposed Mechanism for the Formation of Compound 4 (exemplified for 4a)

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Helvetica Chimica Acta – Vol. 96 (2013)
Compound 4a could result from the initial formation of hydrazone 5a and
subsequent attack on dimethyl acetylenedicarboxylate (2a) to yield hydrazino-
carboxylate 6a. Then, the reaction between 6a and compound 3a, which was obtained
from the reaction of aldehyde 1a with NH3 solution [8], gives the intermediate 8, which
undergoes successive intramolecular cyclization, followed by hydrolysis, to give
compound 4a. The solvent has an important effect on the configuration of compound
6. In a protic solvent, the (Z)/(E) ratio is 95 :5, and in an aprotic solvent, this ratio is
2 :98 [9].
In conclusion, we have developed a novel four-component reaction leading to 2-
aryl-2,5-dihydro-5-oxo-4-[2-(phenylmethylidene)hydrazino]-1H-pyrroles 4 from the
simple synthons NH2NH2 · H2O, aldehydes, NH3, and acetylenedicarboxylates. The
high yields, mild reaction conditions, the ease of purification, and commercial
availability of the synthons render this an ecologically friendly procedure for the
synthesis of 4. This protocol does not only provide a novel and effective methodology
for synthesis but also opens a new way for employing hydrazone intermediates to
design other similar multicomponent reactions. Further extension of the scope and
synthetic applications of this methodology are in progress in our laboratory.
Financial support of this work by the Tarbiat Modares University, Iran, is gratefully acknowl-
edged.
Experimental Part
General. The reagents and solvents were obtained from Fluka (CH-Buchs) and used without further
purification. M.p.: Electrothermal 9100 apparatus. IR Spectra: Shimadzu IR-460 spectrometer. 1H- and
13C-NMR spectra: at 500.1 and 125.7 MHz, resp., on a BRUKER DRX 500-AVANCE FT-NMR
instrument in CDCl3 as solvent. MS: FINNIGAN-MAT 8430 mass spectrometer, operating at an
ionization potential of 70 eV.
General Procedure (exemplified for 4a). A soln. of benzaldehyde (1a; 0.106 g, 1 mmol) and
NH2NH2 · H2O (0.32 g, 1 mmol) was magnetically stirred in 5 ml of EtOH for 10 min. Then, a soln. of
dimethyl acetylenedicarboxylate (2a; 0.142 g, 1 mmol) was added, and the mixture was stirred for 30 min
at r.t. Finally, 1-phenyl-N,N’-bis(phenylmethylidene)methanediamine (3a; 0.298 g, 1 mmol) was added,
and the mixture was stirred for 1 h under reflux, and the progress of the reaction was followed by TLC.
After completion, the mixture was cooled to r.t., and a pale-yellow solid precipitated. The precipitate was
filtered and washed with Et2O to give 4a in 81% yield. All products gave satisfactory spectroscopic data
in accordance with the assigned structures.
Methyl 4-[(2E)-2-Benzylidenehydrazinyl]-2,5-dihydro-5-oxo-2-phenyl-1H-pyrrole-3-carboxylate
(4a). Yield: 0.32 g (81%). Pale-yellow powder. M.p. 179 – 1828. IR: 3301 (NH), 3063 (NH), 1709
(COOMe), 1650 (C¼N), 1620 (NC¼O), 1260 (CꢀO of ester). 1H-NMR: 3.64 (s, 3 H); 5.30 (s, 1 H); 6.44
(s, 1 H); 7.26 – 7.34 (m, 5 H); 7.36 – 7.40 (m, 3 H); 7.73 (d, J ¼ 6.8, 2 H); 7.85 (s, 1 H); 9.90 (s, 1 H).
13C-NMR: 51.4; 57.8; 108.6; 127.2; 127.3; 128.4; 128.6; 128.69; 129.8; 134.0; 137.8; 142.6; 144.8; 165.3;
165.3. EI-MS (70 eV): 335 (36, Mþ), 276 (71), 232 (47), 173 (81), 129 (39), 104 (100), 77 (90), 55 (53).
Anal. calc. for C19H17N3O3 (335.36): C 68.05, H 5.11, N 12.53; found: C 68.10, H 5.19, N 12.59.
Methyl 4-[(2E)-2-(4-Chlorobenzylidene)hydrazinyl]-2,5-dihydro-5-oxo-2-phenyl-1H-pyrrole-3-car-
boxylate (4b). Yield: 0.33 g (79%). Pale-yellow powder. M.p. 178 – 1818. IR: 3182 (NH), 3030 (NH),
1720 (COOMe), 1612 (NC¼O), 1224 (CꢀO of ester). 1H-NMR: 3.69 (s, 3 H); 4.35 (s, 1 H); 6.58 (s, 1 H);
7.08 – 7.55 (m, 9 H); 7.86 (s, 1 H); 11.68 (s, 1 H). 13C-NMR: 51.1; 56.5; 105.6; 124.9; 127.7; 127.8, 128.1;
128.2, 129.6; 130.5; 133.8; 142.9; 147.3; 160.3; 164.0. EI-MS (70 eV): 369 (20, Mþ), 368 (50), 313 (16), 236
(32), 142 (20), 123 (27), 97 (65), 69 (100). Anal. calc. for C19H16ClN3O3 (369.80): C 61.71, H 4.36, N 11.36;
found: C 61.75, H 4.39, N 11.40.

Helvetica Chimica Acta – Vol. 96 (2013)
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Methyl 2,5-Dihydro-4-[(2E)-2-(4-methoxybenzylidene)hydrazinyl]-5-oxo-2-phenyl-1H-pyrrole-3-
carboxylate (4c). Yield: 0.32 g (75%). Pale-yellow powder. M.p. 178 – 1818. IR (KBr): 3304 (NH),
1707 (COOMe), 1649 (C¼N), 1613 (NC¼O), 1254 (CꢀO of ester). 1H-NMR: 3.62 (s, 3 H); 3.83 (s, 3 H);
5.26 (s, 1 H); 6.60 (s, 1 H); 6.90 (d, J ¼ 8.0, 2 H); 7.25 – 7.28 (m, 5 H); 7.66 (d, J ¼ 8.0, 2 H); 7.85 (s, 1 H);
9.91 (s, 1 H). 13C-NMR: 51.4; 55.4; 57.8; 107.6; 114.2; 127.3; 128.4; 128.6; 128.8; 129.9; 133.9; 137.9; 144.9;
161.1; 165.4; 165.4. EI-MS (70 eV): 365 (1, Mþ), 349 (61), 335 (19), 290 (100), 276 (36), 231 (32), 199
(22), 173 (86), 128 (32), 118 (49), 104 (77), 91 (45), 77 (45), 65 (20), 51 (16). Anal. calc. for C20H19N3O4
(365.38): C 65.74, H 5.24, N 11.50; found: C 65.80, H 5.32, N 11.62.
Methyl 4-[(2E)-2-Benzylidenehydrazinyl]-2,5-dihydro-2-(4-methoxyphenyl)-5-oxo-1H-pyrrole-3-
carboxylate (4d). Yield: 0.33 g (82%). Yellow powder. M.p. 167 – 1798. IR (KBr): 3340 (NH), 1708
(COOMe), 1640 (C¼N), 1621 (NC¼O), 1248 (CꢀO of ester). 1H-NMR: 3.64 (s, 3 H); 3.78 (s, 3 H); 5.23
(s, 1 H); 6.76 (s, 1 H); 6.83 (d, J ¼ 8.0, 2 H); 6.90 (d, J ¼ 8.3, 1 H); 7.19 (d, J ¼ 8.0, 2 H); 7.37 (d, J ¼ 7.0,
2 H); 7.66 (d, J ¼ 8.3, 1 H); 7.71 (d, J ¼ 7.0, 1 H); 7.85 (s, 1 H); 9.88 (s, 1 H). 13C-NMR: 51.3; 55.4; 57.44;
108.0; 114.2; 127.2; 128.4; 128.7; 128.9; 129.8; 134.0; 142.4; 144.7; 159.5; 165.4; 165.6. EI-MS (70 eV): 365
(1, Mþ), 257 (12), 149 (24), 137 (23), 123 (20), 109 (20), 95 (37), 81 (77), 69 (100), 55 (57). Anal. calc. for
C20H19N3O4 (365.38): C 65.74, H 5.24, N 11.50; found: C 65.81, H 5.32, N 11.58.
Methyl 2,5-Dihydro-4-[(2E)-2-(4-methoxybenzylidene)hydrazinyl]-2-(4-methoxyphenyl)-5-oxo-1H-
pyrrole-3-carboxylate (4e). Yield: 0.36 g (76%). Pale-yellow powder. M.p. 177 – 1798. IR: 3338 (NH),
1706 (COOMe), 1650 (C¼N), 1616 (C¼O), 1251 (CꢀO of ester). 1H-NMR: 3.63 (s, 3 H); 3.79 (s, 3 H);
3.83 (s, 3 H); 5.23 (s, 1 H); 6.32 (s, 1 H); 6.84 (d, J ¼ 8.4, 2 H); 6.90 (d, J ¼ 8.4, 2 H); 7.19 (d, J ¼ 8.4, 2 H);
7.66 (d, J ¼ 8.4, 2 H); 7.79 (s, 1 H); 9.79 (s, 1 H). 13C-NMR: 51.3; 55.3, 55.4; 57.3; 107.8; 114.0; 114.2; 126.7;
128.4; 128.8; 129.7; 137.9; 144.7; 159.5; 161.1; 161.1; 165.3. EI-MS (70 eV): 395 (16, Mþ), 368 (16), 336
(24), 303 (20), 288 (40), 268 (32), 203 (53), 161 (38), 134 (89), 97 (53), 83 (57), 69 (73), 57 (100). Anal.
calc. for C21H21N3O5 (395.40): C 63.79, H 5.35, N 10.63; found: C 63.85, H 5.39, N 10.68.
Methyl 2,5-Dihydro-4-[(2E)-2-(4-methylbenzylidene)hydrazinyl]-5-oxo-2-phenyl-1H-pyrrole-3-car-
boxylate (4f). Yield: 0.32 g (80%). Pale-yellow powder. M.p. 179 – 1828. IR: 3301 (NH), 1708 (COOMe),
1649 (C¼N), 1617 (C¼O), 1258 (CꢀO of ester). 1H-NMR: 2.37 (s, 3 H); 3.63 (s, 3 H); 5.26 (s, 1 H); 6.32
(s, 1 H); 7.20 – 7.37 (m, 9 H); 7.85 (s, 1 H); 9.89 (s, 1 H). 13C-NMR: 21.5; 51.4; 57.8; 106.0; 127.3; 128.6;
128.7; 129.4; 131.2; 137.7; 140.2; 144.9; 145.1; 165.0; 167.5. EI-MS (70 eV): 349 (8, Mþ), 335 (8), 290 (12),
276 (12), 232 (20), 173 (100), 118 (53), 104 (88), 91 (32), 77 (46), 57 (40). Anal. calc. for C20H19N3O3
(349.38): C 68.75, H 5.48, N 12.03; found: C 68.87, H 5.57, N 12.12. Crystal data for 4f C20H19N3O3
(CCDC-927914): Mr 349.38, a ¼ 6.1557(6) ꢂ, b ¼ 7.3821(7) ꢂ, c ¼ 19.4275(19) ꢂ, a ¼ 90.00 b ¼ 89.971(8),
g ¼ 90.008, V¼ 882.82(15) ꢂ3, Z ¼ 2, F (000) ¼ 368, radiation, MoKa (l ¼ 0.71073 ꢂ), 3.15 ꢁ 2q ꢁ 25.05,
intensity data were collected at 295(2) K with a Bruker APEX area-detector diffractometer, and
employing w/2q scanning technique, in the range of ꢀ 7 ꢁ h ꢁ 6, ꢀ 8 ꢁ k ꢁ 8, ꢀ 23 ꢁ l ꢁ 22; the structure
was solved by a direct method, all non-H-atoms were positioned, and anisotropic thermal parameters
were refined from 3831 observed reflections with R(into) ¼ 0.1055 by a full-matrix least-squares
technique converged to R ¼ 0.0752 and Rw ¼ 0.1834 [I > 2s(I)].
Methyl 2,5-Dihydro-4-[(2E)-2-(3-nitrobenzylidene)hydrazinyl]-5-oxo-2-phenyl-1H-pyrrole-3-car-
boxylate (4g). Yield: 0.32 g (83%). Pale-yellow powder. M.p. 170 – 1738. IR: 3419 (NH), 1719
(COOMe), 1626 (C¼O), 1529 (NO2) 1267 (CꢀO of ester). 1H-NMR: 3.68 (s, 3 H); 5.72 (s, 1 H); 6.57 (s,
1 H); 6.70 – 7.17 (m, 7 H); 7.79 (m, 1 H); 8.31 (m, 1 H); 8.69 (s, 1 H); 11.61 (s, 1 H). 13C-NMR: 51.1; 56.5;
105.6; 123.1; 124.8; 126.3; 127.7; 128.1; 128.8; 131.1; 134.9; 135.7; 147.3; 148.7; 161.0; 164.3; 164.3. EI-MS
(70 eV): 368 (5), 298 (81), 281 (32), 252 (44), 234 (28), 176 (100), 149 (26), 130 (61), 103 (69), 89 (67), 76
(90), 63 (40), 50 (35). Anal. calc. for C19H16N4O5 (380.35): C 60.00, H 4.24, N 14.73; found: C 60.12, H
4.33, N 14.84.
Ethyl 4-[(2E)-2-Benzylidenehydrazinyl]-2,5-dihydro-5-oxo-2-phenyl-1H-pyrrole-3-carboxylate
(4h). Yield: 0.33 g (80%). Pale-yellow powder. M.p. 190 – 1938. IR: 3413 (NH), 3309 (NH), 1702
(CO2Et), 1635 (C¼N), 1620 (NC¼O), 1253 (CꢀO of ester). 1H-NMR: 1.07 (t, J ¼ 7.2, 3 H); 4.06 (q, J ¼
7.2, 2 H); 5.26 (s, 1 H); 6.70 (s, 1 H); 7.28 – 7.38 (m, 8 H); 7.71 (d, J ¼ 7.5, 2 H); 7.83 (s, 1 H); 9.99 (s, 1 H).
13C-NMR: 14.0; 57.8; 60.3; 108.8; 127.3; 127.4; 128.3; 128.5; 128.7; 129.8; 134.0; 137.8; 142.9; 144.7; 165.1;
165.5. EI-MS (70 eV): 349 (31, Mþ), 276 (72), 256 (15), 236 (23), 173 (43), 149 (65), 137 (32), 123 (32),

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Helvetica Chimica Acta – Vol. 96 (2013)
111 (32), 97 (57), 81 (97), 69 (100), 57 (73). Anal. calc. for C20H19N3O3 (349.39): C 68.75, H 5.48, N 12.03;
found: C 68.86, H 5.56, N 12.14.
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Received March 9, 2013