β-Enamino esters in heterocyclic synthesis: Synthesis of pyrazolone and pyridinone derivatives

Article abstract of DOI:10.3390/molecules15064359

An efficient and convenient synthesis of pyrrolidinones and pyridinones utilizing enamino esters as starting material has been described. The structures of the compounds obtained were confirmed by spectral and elemental analyses.

Full text of DOI:10.3390/molecules15064359

Molecules 2010, 15, 4359-4368; doi:10.3390/molecules15064359
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
β-Enamino Esters in Heterocyclic Synthesis: Synthesis of
Pyrazolone and Pyridinone Derivatives
1
2,
Abdellatif Mohamed Salaheldin and Mariam Abdullah Al-Sheikh *
1
Department of Chemistry, Faculty of Science, Cairo University, Giza-12613, Egypt
2
Department of Chemistry, Girls College of Education, Jeddah, P. O. Box 138016, Jeddah 21323,
Saudi Arabia
* Author to whom correspondence should be addressed; E-Mail: r1425@hotmail.com;
Tel.: + 966 0505694706.
Received: 22 April 2010; in revised form: 22 May 2010 / Accepted: 26 May 2010 /
Published: 15 June 2010
Abstract: An efficient and convenient synthesis of pyrrolidinones and pyridinones
utilizing enamino esters as starting material has been described. The structures of the
compounds obtained were confirmed by spectral and elemental analyses.
Keywords: β-enamino esters; pyrazolone; pyridinone; phenylhydrazones
1. Introduction
β-Enamino esters are versatile intermediates for the synthesis of nitrogen containing compounds
[1–8]. Also, they are important subunits present in some biologically important natural products as
well as therapeutic agents [9–12]. Due to the importance of β-enamino ester derivatives as bioactive
leads and versatile building blocks, their synthesis and applications have long been an active topic in
organic synthesis [13–19].
As part of our ongoing studies on the synthesis of nitrogen-containing compounds and in
conjunction of our interest in the chemistry of enamines [20–25], we report herein the synthesis of the
starting enamino esters 2 and 3 and a study of their reactivity towards some selected nitrogen and
carbon nucleophiles as well as benzenediazonium salts to synthesize the new pyrazolone, pyridinone
and phenylhydrazone derivatives with the expectation that they would be of biological interest. In our

Molecules 2010, 15
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chemical reactivity studies described here, we principally employed the intermediates 2b and 3 due to
their easy preparation and good yield of the subsequent reactions.
2. Results and Discussion
Reaction of ethyl phenyl acetate and ethyl p-nitrophenyl acetate 1a,b with N,N-dimethylformamide
dimethyl acetal (DMFDMA) in DMF at 60 °C for 4h yielded the enamino esters 2a,b in good yields.
On the other hand, the enamino ester 3 was prepared by reacting compound 1b with triethyl
orthoformate and piperidine in DMF at reflux temperature for 24 h (Scheme 1). The structures of the
enamino esters 2a,b and 3 were confirmed by mass spectrometry, 1H- and 13C-NMR. For example, the
1H-NMR spectrum of compound 3 showed two broad signals for the piperidinyl protons at δ = 1.48
(3 CH2) and 3.01 (2 CH2) ppm and singlet signal at δ = 7.63 ppm for the olefinic proton, besides the
signals of ester and aromatic protons in their expected positions (see Experimental).
Scheme 1. Synthesis and reactivity of β-enamino esters.
NH2
O2N
X
OEt
X
O
O
DMFDMA
DM F
O
Y
OEt
OEt
H
N
Toluene/PTSA
N
a, X = H
1
2a, X = H
b, X = NO
2
b, X = NO
2
Y
PhN2Cl
2a or 3
4a, Y = H
b, Y = OMe
c, Y = Cl
CH(OEt)
3
DMF/Pip.
1b
Cl
O2N
TEA
or
DMF/K2CO3
O2N
O
N
N
O2N
H2O
N
N
CN
CO2Et
OEt
CO2Et
N
N
CHO
Ar
O
7
6
OH
O
CN
O2N
3
N
O2N
Cl
O
OEt
NH
CN
N
N
N
Y
TEA
or
DMF/K2CO3
CN
5
8
9
The reaction of enamino esters 2b or 3 with aromatic amines in refluxing toluene and in the
presence of p-toluenesulfonic acid (PTSA) afforded compounds 4a-c as the only reaction products.
Attempts to convert compounds 4 into the corresponding pyrrolidinone derivatives 5 either by heating
with chloroacetonitrile in triethylamine or in DMF/K2CO3 were unsuccessful (Scheme 1) [25,26].

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Coupling compound 2b or 3 with benzenediazonium chloride furnished the phenylhydrazone 8. It is
believed that nitrogen lone pair resonance increases the nucleophility of C-2 and that the diazonium
salts 6, which are initially formed, are hydrolyzed under the reaction conditions and then underwent a
Japp-Klingmann type of cleavage to yield 8, which could not be obtained by direct coupling with
benzenediazonium chloride. Compound 8 failed to react with chloroacetonitrile in triethylamine or in
DMF/K2CO3 to give the pyrazolone 9 (Scheme 1).
We envisaged that the reaction of 2a,b with o-phenylenediamine in refluxing toluene and in the
presence of PTSA might afford the 2-phenylacrylate derivatives 10a,b or diazepene derivative 11
(Scheme 2). The identity of compounds 10 was supported by a correct element analysis and spectral
data. Thus, IR spectrum of 10b relived a broad absorption bands at 3,448 (NH), 3,325 (NH2) cm-1,
1
corresponding to NH and NH2 stretching, and 1,664 for C=O absorption. The H-NMR spectrum
displayed the presence of broad signals at δ = 3.65 ppm and a doublet signal at δ = 10.41 ppm with J
coupling = 12.6 Hz, (D2O exchanged for both signals), assignable to a NH2 group and the NH. A
doublet signal at δ = 7.45 ppm with J coupling = 12.6 Hz, was assigned for H-3 (=CH), besides signals
due to the ester group and aromatic protons in their expected positions. Additionally, its structure was
13
fully confirmed by C-NMR, which was compatible with the suggested structure. Furthermore, in its
mass spectrum, this product has the molecular ion m/z = 327 (84%), also confirming its presumed
structure. Analytical data are thus all in accordance with the proposed structure for compound 10b.
Our efforts to synthesize the interesting diazepenes 11 via the intramoleculer condensation of
compound 10 failed (Scheme 2) [27,28].
Scheme 2. Reaction of β-enamino ester with hydrazines, amine and active methylen group.
NH2
X
X
O
X
O
NH2
RNHNH2.HCl
OEt
OEt
O
2 or 3
NH
13a
, R=H
b, R=C6H4-p-OMe
N
NH2
N
R
N
H
2a,b
14
X
R
H
X
COCH
3
a
10a,b
H
AcONH4/AcOH
b
c
NO
2
H
COCH
3
in case of 2b or 3
O
NO
2
4-OMeC6H4
X
N
O
R
O2N
N
O
X
A
NH
NH
N
H
OH
CH
COCH3
3
11
N
R
N
12
B
Next, we investigated the reaction of compounds 2a,b or 3 with acetylacetone in acetic acid in the
presence of ammonium acetate that afforded the pyridinone 12. This find is similar to the reported
synthesis of pyridines from the reaction of enaminones with acetylacetone under similar conditions
[29]. On the other hand, when compounds 2b or 3 reacted with substituted hydrazines 13a,b in ethanol
at reflux temperature for 3h they afforded the pyrazolone derivatives 14a-c [30]. Although pyrazolone

Molecules 2010, 15
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derivatives 14 can also exist as 14A or hydroxypyrroles 14B, the pyrazolone structure 14 is established
1
based on the presence of carbonyl absorption band in IR spectra and also the H-NMR spectra that
revealed pyrazolone H-5 and NH signals. Moreover, structure 14 was confirmed by the 13C-NMR
spectra which allowed an unambiguous assignment in the 1H- and 13C-NMR spectra (see
Experimental).
3. Experimental
3.1. General
The melting points were determined on a Stuart melting point apparatus. The IR spectra were
1
recorded as KBr pellets using a FTIR Bruker-Vector 22 spectrophotometer. The H and 13C-NMR
spectra were recorded in DMSO-d6 or CDCl3 as solvent, on a Varian Gemini 300 MHz NMR
spectrometer using TMS as internal standard. Double resonance, HMQC and HMBC experiments were
1
carried out for complete assignment of H and 13C peaks in the NMR spectra, whenever possible.
Chemical shifts are reported in δ units (ppm). Mass spectra were measured on a Shimadzu GCMS-QP-
1000 EX mass spectrometer in EI (70 ev) mode. The elemental analyses were performed at the Micro
analytical Center, Cairo University, Egypt.
3.2. Synthesis of ethyl 3-(dimethylamino)-2-arylacrylates 2a,b
To a solution of ethyl phenylacetate 1a or ethyl 4-nitrophenylacetate 1b (0.01 mol) in DMF
(10 mL), DMFDMA (0.012 mol) was added. Then, the mixture was heated at 60 °C for 4 h. After
cooling to r.t., the mixture was left standing overnight, then the resulting solid product was collected
by filtration and washed with ethanol to give 2b. In case of compound 2a, brine (10 mL) was added to
the reaction mixture. After extraction with CH2Cl2 (3 × 10 mL), the combined organic fractions were
dried over MgSO4 and concentrated under vacuum to afford compound 2a as a brown oil.
1
Ethyl 3-(dimethylamino)-2-phenylacrylate (2a). Yield 86%, H-NMR (CDCl3): δ = 1.18 (t, 3H,
J = 7.5 Hz, CH3), 2.65 (s, 6H, 2CH3), 4.10 (q, 2H, J = 7.5 Hz, CH2), 7.17–7.29 (m, 5H, Ar-H), 7.57 (s,
1H, CH-olfeinic-H-3), MS (EI, 70eV): m/z = 219 (M+); Anal. Calcd. for C13H17NO2 (219.13): C, 71.21;
H, 7.81; N, 6.39. Found: C, 71.34; H, 7.69; N, 6.52.
Ethyl 3-(dimethylamino)-2-(4-nitrophenyl)acrylate (2b). Orange crystals (85%), mp 127–129 ºC; IR
(KBr) ν = 1,668 (C=O), 1,463, 1,376 (NO2) cm-1; 1H NMR (CDCl3): δ = 1.20 (t, 3H, J = 7.5 Hz, CH3),
2.73 (s, 6H, 2CH3), 4.14 (q, 2H, J = 7.5 Hz, CH2), 7.32 (d, 2H, J = 9.0 Hz, H-2´,6´), 7.65 (s, 1H, CH-
13
olfeinic- H-3), 8.14 (d, 2H, J = 9.0 Hz, H-3´,5´); C-NMR (CDCl3): δ = 14.46 (CH3), 43.64 (2CH3),
59.80 (CH2), 97.27 (C=CH,C-2), 122.36 (C-3´,5´), 132.39 (C-2´,6´), 144.45 (C-1´), 145.75 (C-4´),
150.50 (C=CH,C-3), 168.73 (CO). MS (EI, 70eV): m/z = 264 (M+). Anal.Calcd. for C13H16N2O4
(264.28) :C, 59.08; H, 6.10; N, 10.60. Found: C, 58.87; H, 6.21 ; N, 10.68.

Molecules 2010, 15
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3.3. Synthesis of ethyl 2-(4-nitrophenyl)-3-(piperidin-1-yl)acrylate (3)
A mixture of ethyl 4-nitrophenylacetate 1b (0.2 mol), triethylorthoformate (0.2 mol) and piperidine
(0.2 mol) in DMF (30 mL) was refluxed for 24 h. The reaction mixture was then cooled to r. t. and
poured into water. The solid product thus formed was collected by filtration and recrystallized from
1
ethanol. m.p. 94–95 °C. Yield: 75%. IR (KBr) ν= 1,665 (C=O), 1,463, 1,377 (NO2) cm-1; H-NMR
(CDCl3): δ = 1.19 (t, 3H, J = 7.5 Hz, CH3), 1.47–1.52 (m, 6H, 3CH2), 2.98–3.03 (m, 4H, 2CH2), 4.13
(q, 2H, J =7.5 Hz, CH2), 7.33 (d, 2H, J = 9Hz, H-2´,6´), 7.63 (s, 1H, CH-olfeinic- H-3), 8.15 (d, 2H,
13
J = 9 Hz, H-3´,5´); C-NMR (CDCl3): δ = 14.46 (CH3), 23.53 (2CH2), 25.62 (2CH2), 52.16 (CH2),
59.75 (OCH2), 96.15 (C=CH, C-2), 122.74 (C-3´,5´), 131.93 (C-2´,6´), 145.14 (C-1´), 145.80 (C-4'),
149.39 (C=CH,C-3), 168.89 (CO); MS (EI, 70 eV): m/z = 304 (M+); Anal. Calcd. for C16H20N2O4
(304.34) :C, 63.14; H, 6.62; N, 9.20. Found: C, 62.99; H, 6.80; N, 8.99.
3.4. General procedure for preparation of 3-arylamino-2-(4-nitrophenyl)acrylate derivatives 4a-c and
10a,b
Aromatic amines (0.01 mol) and p-toluenesulfonic acid (0.15 g) were added to a solution of
enamino esters 2a,b or 3 (0.01 mol) in toluene (25 mL). The reaction mixture was refluxed for 7 h.
After cooling to r.t., the precipitated solid product was collected by filtration and recrystallized from
the proper solvents to afford 4a-c and 10a,b, respectively.
Ethyl-2-(4-nitrophenyl)-3-(phenylamino)acrylate (4a). Colorless needles, 75% yield, mp 140–141 °C;
IR (KBr) ν = 3,448 (NH), 1,664.9 (C=O), 1,460, 1,370 (NO2) cm-1; 1H- NMR (CDCl3): δ= 1.33 (t, 3H,
J = 7.5 Hz, CH3), 4.29 (q, 2H, J = 7.5 Hz, CH2); 7.06-7.11 (m, 3H, H-4´´, 3´´,5´´); 7.33-7.38 (m, 2H,
H-2´´, 6´´), 7.51 (d, 2H, J = 9.2 Hz, H-2´,6´), 7.55 (d, 1H, J = 12.8 Hz, H-3), 8.19 (d, 2H, J = 9Hz, H-
3´,5´), 10.57 (d, 1H, J = 12.8 Hz, NH); 13C NMR (CDCl3): δ = 14.32 (CH3), 60.31 (CH2), 101.17 (C-
2), 116.13 (C-2´´, 6´´), 123.38 (C-3´, 5´), 123.71 (C-4´´), 129.38 (C-2´, 6´), 129.82 (C-3´´, 5´´), 140.05
(C-1´´), 144.77 (C-1´), 145.23 (C-3), 145.65 (C-4´), 169.36 (CO); MS (EI, 70eV): m/z = 312 (M+);
Anal. Calcd. for C17H16N2O4 (312.32): C, 65.38; H, 5.16; N, 8.97. Found: C, 65.52; H, 5.04; N, 8.90 %.
Ethyl-3-(4-methoxyphenylamino)-2-(4-nitrophenyl) acrylate (4b). Colorless needles, 75% yield, mp
1
102–104 °C; IR (KBr) ν= 3,446 (NH), 1,665 (C=O), 1,469, 1,372 (NO2) cm-1; H-NMR (CDCl3):
δ= 1.33 (t, 3H, J = 7.5 Hz, CH3), 3.81 (s, 3H, OCH3), 4.28 (q, 2H, J = 7.5 Hz, CH2); 6.88 (d, 2H,
J = 9.0 Hz, H-3´´,5´´); 7.03 (d, 2H, J = 9.0 Hz, H-2´´, 6´´), 7.43 (d, 1H, J = 12.9 Hz, H-3), 7.51 (d, 2H,
13
J = 9.0 Hz, H-2´,6´), 8.18 (d, 2H, J = 9.0 Hz, H-3´,5´), 10.52 (d, 1H, J = 12.9 Hz, NH); C-NMR
(CDCl3): δ = 14.35 (CH3), 55.54 (OCH3), 60.16 (CH2), 99.11 (C-2), 116.44 (C-3´´, 5´´), 118.80 (C-2´´,
6´´), 124.73 (C-3´, 5´), 130.37 (C-2´, 6´), 135.60 (C-1´´), 146.54 (C-1´), 147.77 (C-4´), 148.26 (C-3),
157.01 (C-4´´), 170.75 (CO); MS (EI, 70eV): m/z = 342 (M+); Anal. Calcd. for C18H18N2O5 (342.35):
C, 63.15; H, 5.30; N, 8.18. Found: C, 62.99; H, 5.11; N, 8.31 %.
Ethyl-3-(4-chlorophenylamino)-2-(4-nitrophenyl) acrylate (4c). Yellow crystals, 82% yield,
1
mp 119–120 °C; IR (KBr) ν= 3,447 (NH), 1,665 (C=O), 1,459, 1,371 (NO2) cm-1; H-NMR (DMSO-

Molecules 2010, 15
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d6): δ= 1.24 (t, 3H, J = 7.5 Hz, CH3), 4.22 (q, 2H, J = 7.5 Hz, CH2); 7.26 (d, 2H, J = 8.8 Hz, H-2´´,6´´),
7.55 (d, 2H, J = 8.8 Hz, H-3´´,5´´), 7.68 (d, 2H, J = 8.8 Hz, H-2´,6´), 7.86 (d, 1H, J = 12.8 Hz, H-3),
8.16 (d, 2H, J = 9Hz, H-3´,5´), 10.49 (d, 1H, J = 12.8 Hz, NH); 13C-NMR (DMSO-d6): δ = 14.75
(CH3), 60.44 (CH2), 101.32 (C-2), 118.38 (C-2´´, 6´´), 123.49 (C-3´, 5´), 129.77 (C-3´´, 5´´), 130.29
(C-2´, 6´), 132.56 (C-4´´), 139.78 (C-1´´), 141.80 (C-1´), 144.20 (C-4´), 145.73 (C-3), 167.89 (CO);
35
37
MS (EI, 70 eV): m/z = 346 (M+, Cl). 348 (M+, Cl); Anal. Calcd. for C17H15ClN2O4 (346.76): C,
58.88; H, 4.36; N, 8.08. Found: C, 58.59; H, 4.18; N, 8.14%.
Ethyl 3-(2-aminophenylamino)-2-phenylacrylate (10a). Colorless needles, 75% yield, mp 156–158 °C;
1
IR (KBr) ν = 3,440 (NH), 3,317 (NH2), 1,670 (C=O) cm-1; H-NMR (DMSO-d6): δ= 1.37 (t, 3H,
J = 7.5 Hz, CH3), 3.80 (brs, 2H, NH2), 4.27 (q, 2H, J = 7.5 Hz, CH2); 6.90-6.96 (m, 2H, Ar-H),
6.98–7.06 (m, 2H, Ar-H), 7.14–7.22 (m, 5H, Ar-H), 7.42 (d, 1H, J = 12.6 Hz, H-3), 10.41 (d, 1H,
J = 12.6 Hz, NH); MS (EI, 70 eV): m/z = 282 (M+); Anal. Calcd. for C17H18N2O2 (282.34): C, 72.32;
H, 6.43; N, 9.92;. Found: C, 72.26; H, 6.79; N, 10.22.
Ethyl-3-(2-aminophenylamino)-2-(4-nitrophenyl) acrylate (10b). Colorless needles, 75% yield, mp
186–188 °C; IR (KBr) ν = 3,448 (NH), 3,325 (NH2), 1,664 (C=O), 1,465, 1,378 (NO2) cm-1; 1H-NMR
(DMSO-d6): δ= 1.33 (t, 3H, J = 7.5 Hz, CH3), 3.65 (brs, 2H, NH2), 4.32 (q, 2H, J = 7.5 Hz, CH2);
6.82-6.88 (m, 2H, Ar-H), 6.98–7.06 (m, 2H, Ar-H), 7.45 (d, 1H, J = 12.6 Hz, H-3),, 7.50 (d, 2H,
13
J = 9.0 Hz, H-2´,6´), 8.17 (d, 2H, J = 9.0 Hz, H-3´,5´), 10.36 (d, 1H, J = 12.6 Hz, NH); C-NMR
(DMSO-d6): δ = 14.49 (CH3), 59.77 (CH2), 96.86 (C-2), 115.07 (C-3"), 121.29 (C-4"), 122.50 (C-3´,
5´), 122.74 (C-5"), 123.17 (C-6''), 132.06 (C-1"), 132.46 (C-2´, 6´), 136.04 (C-2"), 145.20 (C-1´),
145.97 (C-4´), 149.40 (C-3), 169.70 (CO); MS (EI, 70 eV): m/z = 327 (M+); Anal. Calcd. for
C17H17N3O4 (327.33): C, 62.38; H, 5.23; N, 12.84. Found: C, 62.26; H, 5.08; N, 12.77.
3.5. General procedure for preparation of ethyl (4-nitrophenyl)phenylhydrazono acetate (8)
A solution of benzenediazonium chloride salt (10 mmol), prepared by adding sodium nitrite
solution (0.7 g in 10 mL of H2O) to a chilled solution of aniline hydrochloride (10 mmol of aniline in
5 mL of conc. HC1) with stirring, was added to a cold solution of ethyl 3-substituted-2-(4-
nitrophenyl)acrylates 2b or 3 in ethanol (50 mL) containing sodium acetate (10 mmol). The reaction
mixture was stirred for 1 h. The solid product formed was collected by filtration, washed well with
water and recrystallized from ethanol. The title compound was obtained in 90% yield as yellow
1
crystals, mp 145–146 °C, IR (KBr) v= 3,220 (NH); 1,669 (C=O) cm¯1; H-NMR (DMSO-d6):
δ=1.16 (t, 3H, J = 7.5 Hz, CH3), 4.25 (q, 2H, J = 7.5 Hz, CH2); 7.11–7.25 (m, 3H, Ar-H), 7.30–7.40 (m,
4H, Ar-H); 7.62 (d, 2H, J = 8.5 Hz, Ar-H), 11.78 (bs, 1H, NH), MS (EI, 70eV): m/z = 313 (M+); Anal.
Calcd. for C16H15N3O4 (313.31): C, 61.34; H, 4.83; N, 13.41. Found: C, 61.42; H, 4.88; N, 13.38 %.
3.6. Synthesis of 5-acetyl-6-methyl-3-(4-nitrophenyl)pyridin-2(1H)-one (12)
To a mixture of enamino ester 2b or 3 (4 mmol) and the acetylacetone (4 mmol) in acetic acid
(10 mL), ammonium acetate (6 mmol) was added, then the reaction mixture was refluxed for 6 h. After
cooling to r.t., the precipitated solid product was collected by filtration and recrystallized from

Molecules 2010, 15
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DMF/EtOH (1:3) to give compound 12 as brown crystals, yield (70%), mp 260–262 °C; IR (KBr)
ν = 3,225 (NH); 1,680 (C=O); 1,660 (C=O), 1,469, 1,374 (NO2) cm-1; 1H-NMR (DMSO-d6): δ = 2.21
(s, 3H, CH3), 2.65 (s, 3H, CH3), 7.28 (d, 2H, J = 8.8 Hz, Ar-H), 7.79–7.88 (m, 3H, Ar-H), 8.01 (s, 1H,
NH); MS (EI, 70 eV): m/z = 272 (M+); Anal. Calcd. for C14H12N2O4 (272.26): C, 61.76; H, 4.44; N,
10.29. Found: C, 61.81; H, 4.32; N, 10.35 %.
3.7. General procedure for preparation of 4-aryl pyrazolo-3-one (14)
A mixture of enamino esters 2a,b or 3 (0.01 mol) and substituted hydrazine hydrochlorides 13a,b
(0.01 mol) in ethanol (25 mL) was refluxed for 3h. After cooling to r.t., the reaction mixture was
poured into cold water. The resulting solid was collected by filtration and washed with ethanol.
4-Phenyl-1,2-dihydropyrazol-3-one (14a). Orange crystals, 80% yield, mp 199–200 °C; IR (KBr)
1
ν = 3,430 (NH), 1,666 (C=O) cm¯1; H-NMR (DMSO-d6): δ = 7.06 (t, 1H, J = 8.2 Hz, H-4´), 7.29 (t,
2H, J = 8.2 Hz, H-3´, 5´), 7.66 (d, 2H, J = 8.2 Hz, H-2´, 6´), 7.88 (s, 1H, H-5), 10.76 (bs, 1H, NH),
11.14 (br s, 1H, NH); 13C-NMR (DMSO-d6): δ = 104.68 (C-4), 125.22 (C-4´), 125.49 (C-3´, 5´),
127.94 (C-5), 128.89 (C-2´, 6´), 133.83 (C-1´), 158.94 (C=O); MS (EI, 70 eV): m/z = 160 (M+); Anal.
Calcd. for C9H8N2O (160.17): C,67.49; H,5.03; N,17.49. Found:C,67.52; H,4.98; N, 17.60.
4-(4-Nitrophenyl)-1, 2-dihydropyrazol-3-one (14b). Yellow crystals, 85% yield, mp 170–172 °C from
dilute ethanol; IR (KBr) ν= 3,500 (NH), 1,670 (C=O), 1,468, 1,380 (NO2) cm¯1; 1H-NMR (DMSO-d6):
δ = 7.39 (d, 2H, J = 9.0 Hz, H-2´,6´), 8.15 (d, 2H, J = 9.0 Hz, H-3´,5´), 8.19 (s, 1H, H-5) 11.06 (bs,
13
1H, NH), 11.88 (bs, 1H, NH); C-NMR (DMSO-d6): δ = 102.74 (C-4), 124.03 (C-3´, 5´), 124.86 (C-
2´, 6´), 129.33 (C-5), 141.0 (C-1´), 143.83 (C-4´), 159.18 (C=O); MS (EI, 70 eV): m/z = 205 (M+);
Anal. Calcd. for C9H7N3O3 (205.17): C, 52.69; H, 3.44; N, 20.48. Found: C, 52.74; H, 3.55; N, 20.59 %.
4-(4-Nitrophenyl)-2-(4-methoxyphenyl)-1,2-dihydropyrazol-3-one (14c). Orange crystals, 85% yield,
mp 176–178 °C from dilute ethanol; IR (KBr) ν = 3,300 (NH), 1,660 (C=O), 1,466, 1,374 (NO2) cm¯1;
1H-NMR (CDCl3): δ = 3.84 (s, 3H, OCH3), 6.90 (d, 2H, J = 9.0 Hz, Ar-H), 7.10 (d, 2H, J = 9.0 Hz, Ar-
H), 7.45 (s, 1H, H-5), 7.59 (d, 2H, J = 9.0 Hz, Ar-H), 8.15 (d, 2H, J = 9.0 Hz, Ar-H), 8.90 (s, 1H, NH);
13C-NMR (CDCl3): δ = 55.57 (OCH3), 100.01 (C-4), 115.04 (C-3´´, 5´´), 117.82 (C-2´´, 6´´), 123.33
(C-3´, 5´), 129.17 (C-2´, 6´), 133.62 (C-1´´), 145.40 (C-1´), 145.47 (C-4´), 146.11 (C-5), 156.33 (C-
4´´), 168.45 (CO); MS (EI, 70 eV): m/z = 311 (M+); Anal. Calcd. for C16H13N3O4 (311.29): C, 61.73;
H, 4.21; N, 13.50. Found: C, 61.94; H, 3.95; N, 13.88 %.
4. Conclusions
β-Enamino esters could be easily obtained by reaction of ethyl phenylacetate derivatives with
DMFDMA or with triethylorthoformate and piperidine in the presence of DMF. β-enamino esters are
versatile intermediates for the synthesis of pyrrolidinones and pyridinones.
Acknowledgements
We are grateful to E.A. Hafez for continued help and critical comments on our research progress.

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Sample Availability: Samples of all the compounds are available from the authors.
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