Synthesis of 2-arylhydrazono-4-chloro-3-oxobutanoates existing as (E)/(Z)-hydrazone isomers in solution: Correlation between equilibrium constants and substituent constants

Article abstract of DOI:10.1016/j.molstruc.2019.126960

Various 2-arylhydrazono-4-chloro-3-oxobutanoates 10a-i synthesized by the reaction of ethyl 4-chloro-3-oxobutanoate with the 4-substituted benzenediazonium chlorides were found to exist as two isomers between the (E)- and (Z)-hydrazone forms in DMSO?d

Full text of DOI:10.1016/j.molstruc.2019.126960

Journal of Molecular Structure 1199 (2020) 126960
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Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Synthesis of 2-arylhydrazono-4-chloro-3-oxobutanoates existing as
(E)/(Z)-hydrazone isomers in solution: Correlation between
equilibrium constants and substituent constants
,
Chihaya Kawamura a, Kiminari Yoshida b *, Naoki Yamazaki a, Noriko Sato c,
Kenichiro Nagai c, Eisuke Kaji c, Yoshihisa Kurasawa a
a School of Pharmacy, Iwaki Meisei University, Iino, Chuodai, Iwaki, 970-8551, Fukushima, Japan
b School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, Horinouchi, Hachioji, 192-0392, Tokyo, Japan
c Graduate School of Pharmaceutical Sciences, Kitasato University, Shirokane, Minato-ku, 108-8641, Tokyo, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Various 2-arylhydrazono-4-chloro-3-oxobutanoates 10a-i synthesized by the reaction of ethyl 4-chloro-
3-oxobutanoate with the 4-substituted benzenediazonium chlorides were found to exist as two isomers
between the (E)- and (Z)-hydrazone forms in DMSO‑d6 solution. The equilibrium constants {K ¼ [(Z)-
Received 24 April 2019
Received in revised form
31 July 2019
Accepted 19 August 2019
Available online 20 August 2019
form]/[(E)-form]: (8.0e3.4) at 30 ꢀC} were clarified to correlate with the substituent constants of R (sp
:
0.78 to ꢁ0.27) in the aryl group of compounds 10a-i, wherein the correlation coefficient was 0.99. The
preponderance of the (Z)-hydrazone isomers in compounds 10a-i was assumed to be directed by the 4-
chloro substituent, while the ratios of less stable (E)-hydrazone isomers gradually increased with
decrease in sp values and rise in temperature.
Keywords:
2-Arylhydrazonobutanoates
(E)/(Z)-Hydrazone isomers
Equilibrium constant
Substituent constant
© 2019 Elsevier B.V. All rights reserved.
1. Introduction
electron withdrawing R1 (CH2Cl) exhibited different result from
compound 7, which is presumably due to the presence of the 20,60-
dimethyl substituents (R2) in the arylhydrazono group. That is,
compound 8 was clarified to occur as the (E)-hydrazone isomer in
solid state (Fig. 1), suggesting that the substituents in the arylhy-
drazono group also play an important role for the equilibria be-
tween the (E)/(Z)-hydrazone isomers. Compound 9 [6] with the 2-
(2,6-dimethylphenylhydrazono) group was also confirmed as the
(E)-hydrazone isomer (Fig. 1). The above published information
[1e6] exhibits that the balance of the substituents R1 and R2 with
the electron donating or withdrawing nature seems to control the
(E)/(Z)-hydrazone isomer ratios. In the present investigation, we
studied the influence of the benzene ring substituent R on the (E)/
(Z)-hydrazone isomer ratios for the 2-arylhydrazono-4-chloro-3-
oxobutanoates 10a-i (Scheme 2) in solution.
There have been many papers concerning the (E)/(Z)-hydrazone
isomers of the 2-arylhydrazono-3-oxocarboxylates in solution [1]
and solid state [2e6]. In our literature survey, the substituent R1 of
the 2-arylhydrazono-3-oxocarboxylates such as compounds 1e4
[1] (Scheme 1) were supposed to exert an influence on the (E)/(Z)-
hydrazone isomer ratios. Namely, Table 1 suggests that the (E)-
hydrazone isomer is predominant in chloroform or acetone when
the R1 is electron donating group (compound 1: R1 ¼ Me). On the
contrary, the (Z)-hydrazone isomers are preponderant in the same
solvent as the above when the R1 is electron withdrawing substit-
uent (compounds 2e4: R1 ¼ CF3, CHF2, CF2CHF2). In the solid state,
the (E)-2-arylhydrazono-3-oxobutanoates 5 [2], 6 [3] with the
electron donating R1 (Me) and the (Z)-2-arylhydrazono-4-chloro-3-
oxobutanoate 7 [4] with the electron withdrawing R1 (CH2Cl) were
also confirmed to exist as the (E)- and (Z)-hydrazone isomers,
respectively, by the X-ray crystallography (Fig. 1). However, the 2-
(2,6-dimethylphenylhydrazono)-3-oxobutanoate 8 [5] with the
2. Results and discussion
2.1. Synthesis and NMR spectral data for 10a-i
The reaction of ethyl 4-chloro-3-oxobutanoate with various 4-
* Corresponding author. 1432-1 Horinouchi, Hachioji, 192-0392, Tokyo, Japan.
E-mail address: kyoshida@toyaku.ac.jp (K. Yoshida).
substituted
benzenediazonium
chlorides
gave
the
2-
https://doi.org/10.1016/j.molstruc.2019.126960
0022-2860/© 2019 Elsevier B.V. All rights reserved.

2
C. Kawamura et al. / Journal of Molecular Structure 1199 (2020) 126960
Scheme 2. Equilibria of 10a-i between (E)/(Z)-hydrazone isomers in DMSO‑d6 solution.
confirmed between the C4-methylene and NH protons or between
the C4-methylene and phenyl 20,60-CH protons. These results would
be due to the strong hydrogen bond between NH proton and keto
group in the (E)-hydrazone isomer, while the hydrogen bond be-
tween the NH and ester carbonyl group is not so tight in the (Z)-
hydrazone isomer [1]. Accordingly, the forementioned NOE spectral
data rationalize the assignment for the (E)/(Z)-hydrazone isomers
of 10a-i in solution [1] (Scheme 2). Based on the above NOE spectral
data specifying the (E)/(Z)-hydrazone isomers, the carbon chemical
shifts of compounds 10a-i were assigned by the gHSQC and gHMBC
spectral data (Table 3).
Scheme 1. Equilibria of 1e4 in solution.
Table 1
(E)/(Z)-Hydrazone isomer ratios of 1e4 in solution.
Compound
R1
R2
R3
Solvent
Isomer ratio (%)
(E)-Form
(Z)-Form
1
2
3
4
Me
Me
Et
CDCl3
(CD3)2CO
CDCl3
(CD3)2CO
CDCl3
90
62
0
0
0
10
38
CF3
OMe
Me
Et
100
100
100
90
100
100
In the above isomerism, there was not the diazenylenol (azoe-
nol) tautomer [8] (Fig. 2) in solution, which was supported by the
nitrogen NMR spectral data (Table 4). Namely, the NH protons of
compounds 10b (R ¼ CN) and 10c (R ¼ Ac) due to the (E)/(Z)-
hydrazone isomers were confirmed to bind to the sp3-nitrogens by
CHF2
CF2CHF2
Et
(CD3)2CO
CDCl3
10
0
OMe
Me
(CD3)2CO
0
the 15N-gHMBC spectra [(E)-form: NH (13.72), sp3-N (ꢁ209.1); (Z)-
form: NH, (11.99), sp3-N (ꢁ217.8)] (10b) and [(E)-form: NH (13.86),
sp3-N (ꢁ206.9); (Z)-form: NH, (12.03), sp3-N (ꢁ216.2)] (10c),
respectively (Table 4), wherein the sp2-nitrogens of compounds
10b,c were observed in
CH3NO2].
d
(ꢁ10.6 to ꢁ27.6) [
d (
15N) reference:
2.2. Correlation between equilibrium constants (K) and substituent
constants (sp
)
The equilibrium constants {K ¼ [(Z)-form]/[(E)-form]} were ob-
tained from the NMR spectral data of compounds 10a-i utilizing the
integral intensity of some CH and NH proton signals due to the (E)/
(Z)-hydrazone isomers, wherein the K value range was 8.0 to 3.4 at
30 ꢀC (Table 5). Fig. 3 shows a good correlation between the equi-
librium constants (K) and the substituent constants (sp: 0.78
to ꢁ0.27), wherein the correlation coefficient was 0.99.
Fig. 1. (E)/(Z)-Hydrazone isomers of 5e9 confirmed by X-ray crystallography.
arylhydrazono-4-chloro-3-oxobutanoates 10a-i [7], which were
also found to exist as the (E)/(Z)-hydrazone isomers in the DMSO‑d6
solution, as described below (Scheme 2).
2.3. Influence of temperature on the equilibrium constants (K)
In the NMR spectral data for the (Z)-hydrazone isomers of
compounds 10a-i, the NOE was observed among the ester methy-
The NMR spectra of compounds 10c (R ¼ Ac) and 10h (R ¼ Me)
were measured in DMSO‑d6 with the range of 30e90 ꢀC, wherein
the ratios of less stable (E)-hydrazone isomers increased with
elevation of temperature (Table 6). The change in the equilibrium
constants (K) was 7.4 to 5.8 in compound 10c and 4.2 to 3.4 in
compound 10h, respectively. The signals due to the 4-CH2 and aryl
20,60-CH protons of the (E)/(Z)-hydrazone isomers slightly shifted
towards higher magnetic fields.
lene (
7.64 to 7.40) protons and between the C4-methylene (
and phenyl 20,60-CH protons (
7.64 to 7.40) (Table 2, Scheme 2). On
the other hand, only NOE between the NH ( 14.37 to 13.67) and
phenyl 20,60-CH (
7.74 to 7.48) protons was observed in the (E)-
hydrazone isomers (Table 2, Scheme 2), whereas the NOE was not
d 4.34 to 4.28), NH (d d
12.66 to 11.99), and phenyl 20,60-CH (
d
5.03 to 4.90)
d
d
d

C. Kawamura et al. / Journal of Molecular Structure 1199 (2020) 126960
3
Table 2
Proton chemical shifts for 10a-i.
Substituent
Isomer
NH
4-CH2
Phenyl
20, 60
Ester
CH2
Others
30, 50
Me
a
b
c
d
e
f
NO2
CN
Ac
Cl
E
Z
E
Z
E
Z
E
Z
E
Z
E
Z
E
Z
E
Z
E
Z
13.67
12.05
13.72
11.99
13.86
12.03
13.97
12.66
13.96
12.04
14.11
12.16
14.11
12.12
14.23
12.19
14.37
12.33
5.02
5.03
4.97
5.00
4.97
5.00
4.95
4.95
4.95
4.95
4.95
4.94
4.94
4.93
4.94
4.92
4.93
4.90
7.74
7.64
7.72
7.62
7.68
7.58
7.61
7.53
7.55
7.46
7.64
7.56
7.57
7.50
7.48
7.40
7.55
7.48
8.25
8.22
7.85
7.81
8.00
7.97
7.47
7.42
7.60
7.54
7.27
7.22
7.41
7.37
7.23
7.19
7.00
6.96
4.26
4.34
4.25
4.32
4.52
4.32
4.24
4.30
4.23
4.30
4.23
4.30
4.22
4.29
4.23
4.29
4.22
4.28
1.18
1.28
1.31
1.28
1.30
1.28
1.29
1.27
1.28
1.27
1.28
1.27
1.28
1.26
1.28
1.27
1.28
1.27
2.53 (Ac)
2.54 (Ac)
Br
F
g
h
i
H
7.19 (Phenyl-40)
7.12 (Phenyl-40)
2.28 (40-Me)
2.27 (40-Me)
3.75 (OMe)
Me
OMe
3.74 (OMe)
Table 3
Carbon chemical shifts for 10a-i.
Substituent
Isomer
C1
C2
C3
C4
C10
C20,60
C30,50
C40
Ester
CH2
Others
Me
a
b
c
d
e
f
NO2
CN
Ac
Cl
E
Z
E
Z
E
Z
E
Z
E
Z
E
Z
E
Z
E
Z
E
Z
163.6
161.5
163.3
161.2
163.5
161.4
163.7
161.6
163.7
161.6
163.8
161.7
163.9
161.8
163.9
161.9
164.1
162.1
132.1
132.2
125.9
130.5
129.8
125.4
124.1
127.9
124.2
128.0
123.6
126.9
127.0
127.0
123.2
129.2
122.6
125.3
189.3
187.3
188.7
186.8
186.6
186.7
188.3
186.3
188.3
186.3
188.1
186.2
188.2
186.3
188.1
186.0
187.7
185.9
50.5
47.2
50.1
46.9
50.1
46.8
50.0
46.9
50.0
46.9
49.9
47.0
49.9
47.0
49.8
47.0
49.8
47.1
149.1
116.0
116.9
116.8
116.1
116.1
115.3
118.2
117.5
118.5
117.9
118.4
117.8
116.6
115.9
116.6
115.9
118.2
117.5
126.2
126.0
133.9
133.8
130.0
130.0
129.5
129.3
132.3
132.1
116.4
116.1
129.6
129.4
130.0
129.8
114.8
114.7
144.0
143.1
106.9
105.5
133.4
132.4
128.2
128.2
117.7
116.3
159.9
159.2
125.8
124.6
135.4
134.0
157.7
156.8
61.5
62.2
60.9
61.6
60.8
61.5
60.6
61.3
60.6
61.3
60.5
61.1
60.5
61.1
60.4
61.0
60.4
60.9
14.5
14.3
14.1
13.9
14.1
13.9
14.2
13.9
14.2
13.9
14.2
13.9
14.2
13.9
14.2
13.9
14.2
14.0
148.1
145.7
145.8
145.6
145.8
140.8
141.0
141.2
141.4
138.4
138.5
141.7
141.9
139.3
139.6
135.0
135.4
118.9 (CN)
119.0 (CN)
196.6 (Acetyl CO), 26.6 (Acetyl Me)
196.5 (Acetyl CO), 26.3 (Acetyl Me)
Br
F
g
h
i
H
Me
OMe
20.5 (40-Me)
20.4 (40-Me)
55.4 (OMe)
55.4 (OMe)
Table 4
NH proton and nitrogen chemical shifts for 10b,c.
Compound
Chemical shift (
NH
d)
sp3-Na
sp2-Na
(E)-Form
(Z)-Form
(E)-Form
(Z)-Form
(E)-Form
(Z)-Form
10b (R ¼ CN)
10c (R ¼ Ac)
13.72
11.99
13.86
12.03
ꢁ209.1
ꢁ217.8
ꢁ206.9
ꢁ216.2
ꢁ13.4
ꢁ27.6
ꢁ10.6
ꢁ25.5
a
Reference of
d (
15N): CH3NO2.
Fig. 2. Diazenylenol tautomer absent in solution.
substituent of compounds 10a-i, as already reported for the 2-
arylhydrazono-3-oxocarboxylates 2, 3, 4, and 7 having the elec-
tron withdrawing substituents R1 (Table 1, Fig. 1). Moreover, the
electron donating substituent R in the 2-arylhydrazono group of
compounds 10a-i (Scheme 2) elevated the ratios of the (E)-hydra-
zone isomers, and the equilibrium constants (K) were elucidated to
correlate with the substituent constants of R (sp: 0.78 to ꢁ0.27) in
the arylhydrazono group of compounds 10a-i (correlation
3. Conclusion
We found that the 2-arylhydrazono-4-chloro-3-oxobutanoates
10a-i existed as the (E)/(Z)-hydrazone isomers in DMSO‑d6 solu-
tion, wherein the equilibrium constants {K ¼ [(Z)-form]/[(E)-form]}
were 8.0 to 3.4 at 30 ꢀC. The predominance of the (Z)-hydrazone
isomers would be controlled by the electron withdrawing 4-chloro

4
C. Kawamura et al. / Journal of Molecular Structure 1199 (2020) 126960
Table 5
Equilibrium constants (K)a and substituent constants (sp) for 10a-i.
Substituent
Substituent constant (sp
)
Isomer ratio (%)
Equilibrium constant (K)b
(E)-Form
(Z)-Form
a
b
c
d
e
f
g
h
i
NO2
CN
Ac
Cl
Br
F
H
Me
OMe
0.78
0.66
0.56
0.23
0.23
0.06
0
11.1
11.2
11.9
13.9
13.9
15.9
17.4
19.4
22.5
88.9
88.8
88.1
86.1
86.1
84.1
82.6
80.6
77.5
8.0
7.9
7.4
6.2
6.2
5.3
4.8
4.2
3.4
ꢁ0.17
ꢁ0.27
a
K ¼ [(Z)-Form]/[(E)-Form].
b
At 30 ꢀC.
4. Experimental
4.1. Instrumentation
All melting points were determined on a Yanako micro melting
point MP-J3 apparatus and are uncorrected. The IR spectra (po-
tassium bromide) were recorded with a JASCO FT/IR-410 spectro-
photometer. The 1H, 13C, and 15N NMR spectra were measured in
DMSO‑d6 with an Agilent Technologies DD2 400NB spectrometer at
400, 100, and 40 MHz, respectively. The chemical shifts are given in
the
d scale. The mass spectra (MS) were determined with JEOL
AX505-HA (for EI MS) and JEOL Accu TOF T100LP (for ESI MS)
spectrometers. Elemental analyses were performed on a J-Science
LAB JM10 instrument.
4.2. Synthesis and data for 10a-i
4.2.1. General procedure
The diazonium salts were prepared by adding a solution of so-
dium nitrite (0.55 g, 8.0 mmol) in H2O (10 mL) to a solution (or
suspension) of the appropriate aniline derivatives (8.0 mmol) in
AcOH (30 mL)/10% HCl (30 mL) with stirring in an ice water bath for
1 h. A solution of ethyl 4-chloro-3-oxobutanoate (1.0 g, 6.1 mmol) in
AcOH (4 mL) was added to the above appropriate diazonium salts
with stirring in an ice water bath for 5 h. After H2O (50 mL) was
added dropwise to the reaction mixture with stirring for 1 h, the
crystalline products were collected and recrystallized from appro-
priate solvent (EtOH or EtOH/H2O) to provide the analytically pure
samples.
Fig. 3. Correlation between equilibrium constants (K) and substituent constants (sp)
for 10a-i.
coefficient: 0.99). On the other hand, the ratios of the less stable (E)-
hydrazone isomers were confirmed to increase with elevation of
temperature (range: 30e90 ꢀC) in DMSO‑d6 media of compounds
10c and 10h.
4.2.2. Data for 10a-i
Ethyl 4-chloro-2-(4-nitrophenylhydrazono)-3-oxobutanoate
Table 6
Influence of temperature on equilibrium constants for 10c,h.
Compound
Temperature (oC)
Isomer ratio (%)
Equilibrium constant (K)
1H-Chemical shift (
4-CH2
d)
20,60-H
(E)-Form
(Z)-Form
(E)-Form
(Z)-Form
(E)-Form
(Z)-Form
10c (R ¼ Ac)
30
60
70
80
90
30
60
70
80
90
11.9
12.5
13.5
14.3
14.7
19.4
21.2
22.2
22.5
22.6
88.1
87.5
86.5
85.7
85.3
80.6
78.8
77.8
77.5
77.4
7.4
7.0
6.4
6.0
5.8
4.2
3.7
3.5
3.4
3.4
4.97
e
5.00
e
7.68
e
7.58
e
e
e
e
e
e
e
e
e
4.89
4.94
e
4.87
4.92
e
7.63
7.48
e
7.56
7.40
e
10h (R ¼ Me)
e
e
e
e
e
e
e
e
4.86
4.81
7.44
7.38

C. Kawamura et al. / Journal of Molecular Structure 1199 (2020) 126960
5
(10a): Yield: 95%, reddish brown crystals; IR: 1715, 1666,
1607 cmꢁ1; mp: 133 ꢀC; MS: 313 [M]þ, 315 [Mþ2]þ. Anal. Calcd for
MS: 268 [M]þ, 270 [Mþ2]þ. Anal. Calcd for C12H13ClN2O3: C, 53.64;
H, 4.88; N, 10.43. Found: C, 53.77; H, 4.84; N, 10.49.
C
12H12ClN3O5: C, 45.95; H, 3.86; N, 13.40. Found: C, 45.89; H, 3.92;
Ethyl 4-chloro-2-(4-methylphenylhydrazono)-3-oxobutanoate
(10h): Yield: 52%, yellow crystals; IR: 1701, 1663, 1635, cmꢁ1; mp:
95 ꢀC; MS: 305 [MþNa]þ, 307 [Mþ2 þ Na]þ. Anal. Calcd for
N, 13.52.
Ethyl 4-chloro-2-(4-cyanophenylhydrazono)-3-oxobutanoate
(10b): Yield: 89%, light reddish brown crystþals; IR: 2222, 1707,
1671, 1606 cmꢁ1; mp: 127e129 ꢀC, MS: 293 [M] , 295 [Mþ2]þ. Anal.
Calcd for C13H12 ClN3O3: C, 53.16; H, 4.12; N, 14.31. Found: C, 53.50;
H, 4.15; N, 14.63.
C13H15ClN2O3: C, 55.23; H, 5.35; N, 9.91. Found: C, 55.11; H, 5.43; N,
9.89.
Ethyl 4-chloro-2-(4-methoxyphenylhdrazono)-3-oxobutanoate
(10i): Yield: 31%, yellow crystals; IR: 1686, 1604 cmꢁ1; mp: 99 ꢀC; MS:
298 [M]þ, 300 [Mþ2]þ. Anal. Calcd for C13H15ClN2O4･1/4H2O: C,
51.49; H, 5.15; N, 9.24. Found: C, 51.47; H, 4.98; N, 9.49.
Ethyl 2-(4-acetylphenylhydrazono)-4-chloro-3-oxobutanoate
(10c): Yield: 95%, reddish brown crystals; IR: 1698, 1672,
1601 cmꢁ1; mp: 128 ꢀC; MS: 308 [M]þ, 310 [Mþ2]þ. Anal. Calcd for
C14H15ClN2O4: C, 54.11; H, 4.87; N, 9.02. Found: C, 54.10; H, 4.87; N,
9.07.
References
Ethyl 4-chloro-2-(4-chlorophenylhydrazono)-3-oxobutanoate
(10d): Yield: 89%, orange crystals; IR: 1701, 1662,þ1634, 1614 cmꢁ1
,
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[5] G. Alpaslan, O. Oezdamar, M. Odabasoglu, O. Bueyuekguengoer, A. Erdoenmez,
Acta Crystallogr. E62 (2006) o2850eo2851.
[6] H.-K. Fun, S.R. Jebas, M. Padaki, C. Hegde, A.M. Isloor, Acta Crystallogr. E65
(2009) o1541eo1542.
[7] The literature for the 2-(4-acetylhydrazono) derivative (10c): (a) G. Alpaslan,
O. Oezdamar, M. Odabasoglu, N.O. Iskeleli, A. Erdoenmez, Acta Crystallogr. E63
(2007) o2746;
(b) M. Odabasoglu, O. Oezdamar, O. Bueyuekguengoer, Acta Crystallogr. E61
(2005) o2065eo2067.
[8] Z. Ma, A.M. Maharramov, I.A. Aliyev, I.N. Aliyeva, M.N. Kopylovich,
G.I. Amanullayeva, K.T. Mahmudov, A.J.L. Pombeiro, J. Mol. Struct. 1019 (2012)
16e20.
mp: 88 ꢀC; MS: 325 [MþNa]þ, 327 [Mþ2 þ Na] . Anal. Calcd for
C12H12Cl2N2O3: C, 47.54; H, 3.99; N, 9.24. Found: C, 47.62; H, 3.96; N,
9.39.
Ethyl 2-(4-bromophenylhydrazono)-4-chloro-3-oxobutanoate
(10e): Yield: 90%, orange crystals; IR: 1700, 1676, 1663 cmꢁþ1; mp:
89 ꢀC; MS: 368 [MþNa]þ, 370 [Mþ2 þ Na]þ, 372 [Mþ4 þ Na] . Anal.
Calcd for C12H12BrClN2O3: C, 41.46; H, 3.48; N, 8.06. Found: C, 41.30;
H, 3.46; N, 8.27.
Ethyl 4-chloro-2-(4-fluorophenylhydrazono)-3-oxobutanoate
(10f): Yield: 86%, yellow crystals; IR: 1694, 1635, 1608, cmꢁ1; mp:
107e108 ꢀC; MS: 286 [M]þ, 288 [Mþ2]þ. Anal. Calcd for
C12H12ClFN2O3: C, 50.27; H, 4.22; N, 9.77. Found: C, 50.29; H, 4.20; N,
9.66.
Ethyl 4-chloro-2-(phenylhydrazono)-3-oxobutanoate (10g):
Yield: 71%, yellow crystals; IR: 1699, 1661, 1637 cmꢁ1; mp: 85 ꢀC;