Synthesis, spectral, crystal and theoretical studies of some novel 4-heterocyclic substituted pyrazolones

Article abstract of DOI:10.1016/j.molstruc.2013.10.018

Reactions of pyrazolone ketene dithioacetals with various binucleophiles afforded 4-heterocyclic substituted pyrazolone compounds as ketene N,N-, N,O-acetals in the absence of any acid/base catalyst in good yields. The products 3a-i formed by the direct d

Full text of DOI:10.1016/j.molstruc.2013.10.018

Journal of Molecular Structure 1056–1057 (2014) 70–78
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, spectral, crystal and theoretical studies of some novel
4-heterocyclic substituted pyrazolones
Kuppusamy Narayanan a, Mani Shanmugam a, Gnanasambandam Vasuki b, Senthamaraikannan Kabilan a,
⇑
a Department of Chemistry, Annamalai University, Annamalainagar 608002, Tamil Nadu, India
b Department of Chemistry, Pondicherry University, Kalapet, Puducherry 605014, Tamil Nadu, India
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
ꢀ
Pyrazolone ketene dithioacetals were
synthesised by mild/PTC/strong
bases.
ꢀ
Regioselective products were
obtained from dithioacetals reacting
with 1,2-binuclephiles.
ꢀ
ꢀ
Biologically potent imidazole/oxazole
fused pyrazolones were synthesized.
Compounds 3a-i were characterized
by IR, NMR and X-ray diffraction
techniques.
ꢀ
Theoretical data of 3e by B3LYP/6-
31G⁄⁄ method gives best fit with X-
ray data.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 July 2013
Received in revised form 8 October 2013
Accepted 8 October 2013
Available online 15 October 2013
Reactions of pyrazolone ketene dithioacetals with various binucleophiles afforded 4-heterocyclic
substituted pyrazolone compounds as ketene N,N-, N,O-acetals in the absence of any acid/base catalyst
in good yields. The products 3a–i formed by the direct displacement of dithioacetals exhibited high
regioselectivity towards binucleophiles. All the synthesized compounds were characterized by IR, 1H,
13C, 2D NMR and X-ray diffraction techniques. Optimized geometry of compound 3e has been computed
by Density Functional Theory (DFT) method in B3LYP 6-31Gꢁꢁ level basis set. The title compounds 3d–f
were crystallized in monoclinic space group Pc, P21/n, P21/c with cell parameters: a = 7.6647(3),
Keywords:
Pyrazolone
Oxoketene dithioacetals
Conjugate addition–elimination
1,3-Azoles
0
0
b = 26.7020(8), c = 12.8364(5) ÅA, b = 102.842(4)°, V = 2561.42(16) ÅA3, Z = 9 (for 3d), a = 13.448(5),
0
0
b = 7.539(5), c = 14.832(5) ÅA, b = 94.747(5)°, V = 1498.6(12) ÅA3, Z = 4 (for 3e) and a = 13.6468(17),
0
0
b = 15.905(2), c = 7.9029(9) ÅA, b = 100.774(9)°, V = 1685.1(4) ÅA3, Z = 4 (for 3f) respectively. The spectral
and crystal studies revealed that the compounds 3a–i exist in amine-one tautomeric form in solid state
and the optimized structure T5 of the compound 3e exhibit good agreement with X-ray diffraction data.
Ó 2013 Elsevier B.V. All rights reserved.
1,3-Oxazoles
Density Functional Theory
1. Introduction
agents used in the treatment of arthritis and other musculoskeletal
and joint disorders. The term of pyrazolone is sometimes used to
Pyrazolone is
a
five membered lactum ring compound
refer anti-inflammatory agents [1,2]. The structures of a few drugs
with pyrazolone as one of the component [3] are shown in (Fig. 1).
NH-substituted 3-pyrazolin-5-ones are important targets as a
consequence of their prevalence in numerous pharmaceuticals,
agrochemicals, dyes and pigments as well as chelating and
extracting agents [4,5]. Moreover pyrazolones with a heterocycle
containing two nitrogens which is an active ingredient of many
drugs, especially in the class of nonsteroidal anti-inflammatory
⇑
Corresponding author. Tel.: +91 9443924629.
E-mail address: kabilan60@sify.com (S. Kabilan).
0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2013.10.018

K. Narayanan et al. / Journal of Molecular Structure 1056–1057 (2014) 70–78
71
Fig. 1. Structures of a few drugs with pyrazolone moiety.
Fig. 2. Crystal structure of the compound 3d.
Fig. 3. Crystal structure of the compound 3e.
substituent either at C-4 or C-3 are behave as kinase inhibitors
[6,7]. Particularly, they are found to inhibit a class of enzymes that
function in the catalysis of phosphoryl transfer reactions.
Therefore, heterocycle substituted pyrazolones can be effective
against targets in central nervous system disorders (Alzheimer dis-
ease), inflammatory disorders (psoriasis), bone diseases (osteopo-
rosis), cardiac diseases (atherosclerosis, restenosis and
thrombosis), metabolic disorders (diabetes) and infectious diseases
such as viral and fungal infections. A few heterocycle substituted
pyrazolones that are inhibitors of protein kinases such as vascular
endothelial growth factor receptor (VEGFR) kinase, trkA tyrosine
kinase (trkA), mixed lineage kinase (MLK) or fibroplast growth fac-
tor receptor kinase.
Pyrazolones are readily synthesized by condensation between
b-ketoester and hydrazine hydrate. The physical and chemical
properties of pyrazolones are modulated by their tautomeric prop-
erty. In the case of 3-phenyl-5-pyrazolones, the nucleophilic char-
acter and the basicity of the nitrogen atoms change from tautomer
to tautomer [8]. The hydrogen on C-4 can be readily deprotonated,
generating a carbon nucleophile. Ketene dithioacetals have become
an important synthon in organic chemistry and it can be readily
prepared by reaction between a carbon nucleophile and carbon
disulphide. The sulphur atom exercises the stabilizing effect on
neighboring positive as well as negative species. This makes the
double bond in ketene dithioacetals responsive towards both
nucleophilic as well as electrophilic attack; an extremely useful
feature for organic synthetic purposes. The synthesis of ketene
dithioacetals and their applications in manipulation of the func-
tionality or in the synthesis of heterocyclic system has been exten-
sively investigated and reviewed [9–17].
In our present investigation various new heterocycle
substituted pyrazolones have been synthesized with the reported
[18–21] synthons and with 1,2-binucleophiles. Especially,
dithioacetals in 3-methyl-1H-phenylpyrazolone derivative, we im-
proved the synthesis of ketene dithioacetals in the absence of
strong bases. Moreover the reported reactions were carried out
only with 3-methyl-1H-phenylpyrazol-5-one. However the
reaction of 4-(bis(methylthio)methylene)-3-methyl-1H-pyrazol-
5-one/4-(bis(methylthio)methylene)-1,3-diphenyl-1H-pyrazol-
5(4H)-one with aliphatic 1,2-binucleophile are not reported.
Similar reactions with 3-methyl-1H and 3-phenyl-1H-phen-
ylpyrazolone isomers are not also known. Hence in the present
work it was proposed to synthesize heterocyclic substituted
pyrazolones using ketene dithioacetals and to investigate their
preferred tautomeric existence by the crystal structure.

72
K. Narayanan et al. / Journal of Molecular Structure 1056–1057 (2014) 70–78
precipitate was filtered and washed with cold ethanol. The com-
2. Experimental
pound was purified by recrystallization with methanol. Yield:
38%. m.p: 248 °C. IR (cmꢂ1): 3461 (NH), 3166, 3062 (C–H), 1578,
1515 (C@C/C@N), 1657 (C@O). 1H NMR d (ppm) (400 MHz):
(DMSO-d6 + CDCl3): 2.65 (3H, s), 4.25 (NH), 7.64 (1H, d), 7.55
(1H, d), 7.32 (2H, t). 13C NMR d (ppm) (100 MHz): 159.93, 91.24,
160.86, 11.5, 148.65, 140.45, 140.05, 123.74, 123.08, 117.74, and
109.51.
2.1. Synthesis of pyrazolone ketene dithioacetals
2.1.1. Preparation of 4-(1,3-dithiepan-2-ylidene)-3-methylpyrazol-5-
one (2a)
In a 100 mL round bottom flask fitted with air condenser, a
suspension of 3-methyl-1H-pyrazol-5-one (1b) (0.01 mol), anhy-
drous potassium carbonate (0.02 mol), tetrabutylammonium
bromide (TBAB) (0.003 mol) and carbon disulfide (10 mL) in dry
acetonitrile (50 mL) was efficiently stirred at room temperature
for 30 min. To the reaction mixture dibromobutane (0.03 mol)
was added, stirred constantly at 25 °C. The reaction progress was
monitored by TLC over the entire reaction period. After completion
of the reaction, the residue obtained was filtered and washed with
50 mL of ice-cold water. The pH of the solution was checked and
neutralized with 10% diluted hydrochloric acid. The yellow solid
thus obtained was purified by recrystallization with ethanol. Yield:
55%; m.p: 198 °C; lit m.p: 195–196 °C [20].
2.4. synthesis of imidazole substituted pyrazolone
2.4.1. Synthesis of 4-(4,5-dihydro-1H-imidazol-2-yl)-5-methyl-
1H-pyrazol-3(2H)-one (3c)
A mixture of 4-(1,3-dithiepan-2-ylidene)-3-methyl-1H-pyra-
zol-5(4H)-one (2a) (0.114 g, 0.5 mmol) and ethylenediamine
(0.031 g, 0.5 mmol) was refluxed in ethanol (7 mL) for an hour.
After cooling, solvent was evaporated in a rotary evaporator. The
crude precipitate obtained was purified by crystallization in
ethanol. Yield: 49%, m.p: >300 °C. IR (cmꢂ1): 3304 (NH), 3123,
2946 (C–H), 1594 (C@C/C@N), 1641 (C@O). 1H NMR d (ppm)
(400 MHz): (D2O): 2.23 (3H, s), 2.25 (NH), 3.78 (4H, s). 13C NMR
d (ppm) (100 MHz): 137.66, 85.18, 160.71, 14.04, 148.62 and 42.87.
2.1.2. Preparation of 4-(bis(methylthio)methylene)-3-methyl-1-
phenyl -1H-pyrazol-5(4H)-one (2b & 2C)
3-Methyl-1H-phenylpyrazol-5-one (1b) (0.036 mol) and trieth-
ylamine (0.072 mol) were dissolved in 15 mL of dimethyl sulfoxide
in a 250 mL round bottom flask. Carbon disulfide (0.036 mol) was
added drop wise slowly through a pressure-equalizing funnel to
the mixture at room temperature with vigorous stirring. After
10 min, methyl iodide (0.072 mol) was added and the reaction
mixture was maintained at 0 °C and stirred for 30 min. Yellow solid
(hemithioacetals) was formed and filtered. The remaining filtrate
was separated by chloroform–water mixture and the organic layer
was dried using anhydrous sodium sulphate. Solvent was removed
and the crude was purified by column chromatography (Silica gel,
hexane/ethyl acetate 8:2). Two products were isolated from the
mixture that was found to be yellow solid as hemithioacetal
(m.p: 92–95 °C, Yield: 55%) and red colored syrupy semisolid as
dithioacetal (m.p: 62–65 °C, Yield: 29%). For compound 2c prepara-
tion, 1c with sodium hydride (NaH) base in dry tetrahydrofuran
(THF) sovent medium was used and the above same procedure
was followed. (Note: pyrazolone hemithioacetal further converted
into dithioacetal by methylation in DMF/triethylamine/MeI re-
agent; Yield: 84%) [21].
2.4.2. Synthesis of 4-(imidazolidin-2-ylidene)-3-methyl-1-phenyl-
1H-pyrazol-5(4H)-one (3d)
A mixture of 4-(bis(methylthio)methylene)-3-methyl-1-phe-
nyl-1H-pyrazol-5(4H)-one (2b) (0.278 g, 1 mmol) and ethylenedia-
mine (0.06 g, 1 mmol) was vigorously stirred in ethanol at room
temperature for 10 min. The colorless precipitate was filtered
and crystallized from methanol. Yield: 41%. m.p: 138–140 °C. IR
(cmꢂ1): 3410 (NH), 2971 (C–H), 1500 (C@C/C@N), 1656 (C@O).
1H NMR d (ppm) (400 MHz): (DMSO-d6 + CDCl3): 2.32 (3H, s),
N-Ph 8.01 (2H, d), 7.31 (2H, t), 7.04 (1H, t) 8.20 (1H, s), 3.76 (4H,
s). 13C NMR d (ppm) (100 MHz): 159.62, 84.39, 164.84, 14.54,
N-Ph 139.10, 127.37, 122.19, 117.6, 144.79 and 42.13.
2.4.3. Synthesis of 4-(imidazolidin-2-ylidene)-1,3-diphenyl-1H-
pyrazol-5(4H)-one (3e)
4-(Bis(methylthio)methylene)-1,3-diphenyl-1H-pyrazol-5(4H)-
one (2c) (0.340 g, 1 mmol) and ethylenediamine (0.06 g, 1 mmol)
were vigorously stirred in ethanol at 60 °C for 5 min. The colorless
precipitate obtained was filtered and crystallized from ethanol.
Yield: 51%. m.p: 260–262 °C; IR (cmꢂ1): 3277 (NH), 2933 (C–H),
2.2. Synthesis of benzimidazole substituted pyrazolone
1599, 1478 (C@C/C@N), 1641 (C@O). 1H NMR
d
(ppm)
2.2.1. Synthesis of 4-(1H-benzo[d]imidazol-2-yl)-5-methyl-1H-
pyrazol -3(2H)-one (3a)
(400 MHz): (DMSO-d6): 3.61 (4H, s, NCH2CH2N), 8.03 (2H, s, NH);
Aryl protons: 7.10 (1H, t), 7.37 (2H, t), 7.46 (2H, t) 7.57 (2H, d),
8.08 (2H, d); 13C NMR d (ppm) (100 MHz): 43.07, 165.27, 148.36,
83.14, 159.87; Aryl carbons: 118.03, 123.29, 127.92, 128.41,
128.51, 128.67, 133.91, 140.04.
4-(1,3-Dithiepan-2-ylidene)-3-methyl-1H-pyrazol-5(4H)-one
(2a) (0.114 g, 0.5 mmol) and 1,2-phenylenediamine (0.054 g,
0.5 mmol) in ethanol (7 mL) were refluxed for 5 h. The colorless
solid thus obtained was filtered and washed with cold ethanol. Fur-
ther it was recrystalized from methanol. Yield: 33%, m.p:174–
175 °C. IR (cmꢂ1): 3402, 3262 (NH), 2978 (C–H), 1576, 1510
(C@C/C@N), 1634 (C@O) 1H NMR d (ppm) (400 MHz): (CDCl3):
2.48 (3H, s), 4.76 (3H, s), 7.12 (2H, dd), 7.53 (2H, dd). 13C NMR d
(ppm) (100 MHz): 12.88, 140.96, 90.5, 162.33, 90.94, 147.49,
135.96, 113.56, and 121.56.
2.4.4. Synthesisof4-(1H-benzo[d]imidazol-2(3H,3aH,4H,5H,6H,7H,7aH)
-ylidene)-3-methyl-1-phenyl-1H-pyrazol-5(4H)-one (3f)
4-(Bis(methylthio)methylene)-3-methyl-1-phenyl-1H-pyrazol-
5(4H)-one (2b) (0.278 g, 1 mmol) was treated with (1R, 2R)-diami-
nocyclohexane (0.114 g, 1 mmol) in ethanol (20 mL) for 5 h. The
solid obtained was filtered and recrystallized from ethyl acetate.
Yield: 54%. m.p: 130–132 °C; IR (cmꢂ1): 3410 (NH), 2971 (C–H),
1500 (C@C/C@N), 1656 (C@O). 1H NMR d (ppm) (400 MHz):
(CDCl3): 2.34 (3H, s), N-Ph 8.00 (2H, d), 7.35 (2H, t), 7.11 (1H, t),
9.09 & 5.66 (NH), 3.19 (2H, q, CH), 1.36 (2H, m), 1.54 (2H, m),
1.87 (2H, m), 1.87 (2H, m), 2.16 (2H, m). 13C NMR d (ppm)
(100 MHz): 145.06, 86.70, 162.04, 15.83, N-Ph 139.72, 128.57,
123.81, 119.07, 166.10, 62.35, 28.95, 23.86 and 15.83.
2.3. Synthesis of benzoxazole substituted pyrazolone
2.3.1. Synthesis of 4-(benzo[d]oxazol-2-yl)-5-methyl-1H-pyrazol-
3(2H) -one (3b)
A mixture of 4-(1,3-dithiepan-2-ylidene)-3-methyl-1H-pyra-
zol-5(4H)-one (2a) (0.114 g, 0.5 mmol), 2-aminophenol (0.054 g,
0.5 mmol) was refluxed in ethanol (7 mL) for 3 h. The colorless

K. Narayanan et al. / Journal of Molecular Structure 1056–1057 (2014) 70–78
73
2.4.5. Synthesis of 4-(1H-benzo[d]imidazol-2(3H,3aH,4H,5H,6H,
2.6. Spectral measurement
7H,7aH)-ylidene)-1,3-diphenyl-1H-pyrazol-5(4H)-one (3g)
4-(Bis(methylthio)methylene)-1,3-diphenyl-1H-pyrazol-5(4H)-
one (2c) (0.340 g, 1 mmol) was treated with (1R,2R)-diaminocyclo-
hexane (0.114 g, 1 mmol) in ethanol (20 mL) for 15 min. The solid
obtained was filtered and recrystallized from ethanol. Yield: 58%.
m.p: 262–264 °C; IR (cmꢂ1): 3425, 3230 (NH), 2931 (C–H), 1596,
All the reagents and solvents were purchased from Aldrich, E-
Merck or Sisco Chemicals, India. Melting points were recorded on
Gallemkamp melting point apparatus and were uncorrected. IR
spectra were recorded in a spectral range 4000–400 cmꢂ1 using
KBr pellets in Nicolet 6700 FT-IR and ABB Bomem MB 104 FT-IR
spectrometer. 1H NMR spectra were recorded on 400 MHz, Bruker
AVENCE 400 MHz spectrometer using CDCl3, DMSO-d6 and its mix-
ture as solvent with TMS as the internal standard. 13C NMR spectra
were recorded on 100 MHz, Bruker AVENCE 400 MHz spectrometer
using CDCl3, DMSO-d6 and its mixture as solvent with TMS as the
internal standard.
1566, 1498 (C@C/C@N), 1642 (C@O). 1H NMR
d
(ppm)
(500 MHz): (DMSO d6): 8.280(NH), All aryl protons: 7.10 (1H,t),
7.38 (2H, t), 7.48 (3H, m), 7.59 (2H, d), 8.09 (2H, d); Alkyl protons:
3.10 (2H, q), 2.15 (2H, d), 1.73 (2H, d), 1.40 (2H, m), 1.28 (2H, m);
13C NMR d (ppm) (125.7 MHz): 24.05, 29.16, 62.94, 148.91, 84.71,
162.30, 165.83; Aryl Carbons: 118.53, 123.84, 128.42, 129.01,
129.16, 134.41 and 140.47.
2.7. X-ray determination
2.5. Synthesis of oxazole substituted pyrazolone
Single crystals were obtained by the slow evaporation of com-
pound 3d–f in ethanol. The colorless crystals of the compound
with appropriate dimensions were mounted on a glass fiber with
epoxy cement for the X-ray crystallographic study. Table 2 lists
the crystallographic data and data collection parameters of the
compounds 3e–f which were collected at 293 K in Oxford Diffrac-
tion Xcalibur CCD Eos diffractometer (for 3d) and Bruker axs kappa
apex2 CCD diffractometer (for 3e & 3f) equipped with graphite
2.5.1. Synthesis of 3-methyl-4-(oxazolidin-2-ylidene)-1-phenyl-1H-
pyrazol-5(4H)-one (3h)
A mixture of 4-(bis(methylthio)methylene)-3-methyl-1-phe-
nyl-1H-pyrazol-5(4H)-one (2b) (0.278 g, 1 mmol) and ethanol-
amine (0.061 g, 1 mmol) was vigorously stirred in ethanol at RT
for 30 min. The colorless solid obtained was purified by recrystal-
lization from ethyl acetate. Yield: 48%. m.p: 182–185 °C; IR
(cmꢂ1): 3300, 3261 (NH), 2972 (C–H), 1535, 1490 (C@C/C@N),
1673 (C@O). 1H NMR d (ppm) (400 MHz): (CDCl3): 2.30 (3H, s), Aryl
protons: 8.01 (2H, d), 7.36 (2H, t), 7.11 (1H, t), 6.90 (NH), 3.76 (2H,
t), 4.59 (2H, t). 13C NMR d (ppm) (100 MHz): 146.99, 85.86, 166.39,
15.24, Aryl carbons: 139.63, 128.59, 123.93, 119.10, 166.0, 69.30
and 42.66.
monochromated Mo Ka (k = 0.71073 Å) radiation source was used
for the measurement of data. Data collection, cell refinements and
data reduction were performed using the CRYSALISPRO [22] (for
3d) and SAINT [23] (for 3e & 3f) softwares. Molecular graphics em-
ployed include ORTEP [24] and PLATON [25] programs. The struc-
tures of all the compounds (3d–f) were solved by the direct
method and Full-matrix least-squares refinement on F2 with
anisotropic thermal parameters was carried out by (SHELXL-97)
[26]. Positional and anisotropic atomic displacement parameters
were refined for all non-hydrogen atoms. Hydrogen atoms were
placed geometrically and the positional parameters were refined
using riding model.
2.5.2. Synthesis of 4-(oxazolidin-2-ylidene)-1,3-diphenyl-1H-pyrazol-
5(4H)-one (3i)
A mixture of 4-(bis(methylthio)methylene)-1,3-diphenyl-1H-
pyrazol-5(4H)-one (2c) (0.340 g, 1 mmol), ethanolamine (0.061 g,
1 mmol) was refluxed in ethanol at 60 °C for 10 min. Solvent was
removed under vacuum and the solid separated was washed with
cold ethanol. The colorless solid obtained was purified by recrystal-
lization from ethanol. Yield 68%.m.p: 218–220 °C. IR (cmꢂ1): 3420
(NH), 2923 (C–H), 1593, 1540 (C@C/C@N), 1653 (C@O). 1H NMR d
(ppm) (400 MHz): (CDCl3 + DMSOd6): 4.65 (4H, s, OCH2CH2N), Aryl
protons: 7.10 (2H, t), 7.63 (4H, s), 8.01 (4H, d), 8.06 (NH); 13C NMR
d (ppm) (100 MHz): 42.74, 69.86, 148.23, 83.26, 165.31, 165.74;
Aryl Carbons: 118.45, 123.88, 127.73, 128.24, 128.35, 128.48,
133.10, 139.31 and 148.23.
2.8. Computational details
Theoretical calculations were performed at DFT levels on a Xeon
processor E3-1225, V2 quardcore, 3.20 GHz personal computer
using Jaguar software package, version 8.0, Schrodinger, LLC, New
York. The geometry of 4-(imidazolidin-2-ylidene)-1,3-diphenyl-
1H-pyrazol-5(4H)-one (3e) was optimized by Density Functional
Theory (DFT) method (B3LYP) with standard 6-31Gꢁꢁ basis set.
The resulting geometry, bond length and bond angles were
compared with the existing experimental data. Also HOMO,
The synthesis of the all the compounds (3a–i) can be summa-
rized in Scheme 1 and their product formations from their respec-
tive ketene dithioacetals are listed in Table 1.
Scheme 1.

74
K. Narayanan et al. / Journal of Molecular Structure 1056–1057 (2014) 70–78
Table 1
Illustration of the product formation (3a–i) from the respective reactants.
Reactant
Binucleophile
Compound
R
R’
Structure
3a
H
CH3
H2N
H
N
S
S
N
HN
N
HN
H2N
N
H
O
O
3b
3c
H
H
CH3
CH3
H2N
HO
S
S
O
N
N
HN
HN
N
H
O
O
H2N
H2N
H
S
N
N
N
HN
HN
S
N
H
O
O
3d
3e
Ph
Ph
CH3
Ph
H2N
H2N
N
N
N
N
H
N
S
HN
S
O
O
H2N
H2N
N
N
H
N
N
N
S
HN
S
O
O
3f
Ph
Ph
CH3
Ph
H2N
H2N
N
N
N
H
S
N
N
HN
S
O
O
3g
H2N
H2N
N
N
H
N
N
S
N
HN
O
S
S
O
3h
3i
Ph
Ph
CH3
Ph
HO
N
N
N
N
O
H2N
S
S
HN
O
O
HO
N
N
H2N
N
N
O
S
HN
O
O
LUMO energies were calculated for various tautomeric form of
compound 3e.
absence of OH stretching frequency around 3450–3650 cmꢂ1) re-
veals that pyrazolone amide carbonyl which is preferable in
amine-one form [27,28] rather than imine-ol form and involves
in the intramolecular hydrogen bonding with NH of the
newly formed heterocycles [29]. Aromatic C–H stretching bands
appear in the region 2971–3123 cmꢂ1. In addition, the C@N and
C@C stretching frequencies appear at 1576–1598 cmꢂ1 and
1495–1515 cmꢂ1 respectively.
3. Results and discussion
All the synthesized compounds were characterized by IR, 1H
NMR and 13C NMR spectra.
3.1. IR spectral studies
3.2. 1H NMR spectral studies of compounds 3a–i
IR spectral data indicate the presence of characteristic func-
tional groups present in the title compounds. For all the com-
pounds (3a–i), stretching frequency around 3261–3461 cmꢂ1 and
1631–1673 cmꢂ1 are assigned for NH of the newly formed hetero-
cycle at C4 carbon and pyrazolone amide C@O functional groups,
respectively. The above NH and C@O stretching frequency (the
The compound 3a–c were obtained from 4-(1,3-dithiepan-2-
ylidene)-3-methylpyrazol-5-one react with 1,2-diaminobenzene,
2-aminophenol and 1,2-diaminoethane, respectively in good yield.
The above three compounds only differ by their N,N-acetal and
N,O-acetal from the parent NH pyrazolone ring. 1H NMR spectra

K. Narayanan et al. / Journal of Molecular Structure 1056–1057 (2014) 70–78
75
Table 2
Summary of crystallographic data of 3d–f.
Compound
3d
3e
3f
Emprical formula
C13 H14 N4
242.28
O
C18 H16 N4
304.34
O
C17 H20 N4
296.37
O
Formula weight (g molꢂ1
)
Crystal system (space group)
P c, monoclinic
0.71073
P21/n, monoclinic
0.71073
P 21/c, monoclinic
0.71073
0
Wave length (AÅ)
0
7.6647(3)
26.7020(8)
12.8364(5)
13.448(5)
7.539(5)
14.832(5)
13.6468(17)
15.905(2)
7.9029(9)
a (AÅ)
0
b (AÅ)
0
c (AÅ)
a
(°)
90.00
90.000(5)
90.00
b (°)
102.842(4)
94.747(5)
100.774(9)
c
(°)
90.00
2561.42(16)
9, 1.414
0.095
90.000(5)
1498.6(12)
4, 1.344
0.087
90.00
1685.1(4)
4, 1.168
0.076
Volume (A3)
Z, Dcalc (Mg/mꢂ3
)
Absorption coefficient (mmꢂ1
)
F(000)
1152
636
632
Theta range for data collection (°)
Reflection collected/unique
Goodness of fit
2.73–25.00
22961/8825 [R(int) = 0.0608]
0.738
1.00–24.99
13721/2630 [R(int) = 0.0425 ]
1.093
1.99–25.00
16711/2964 [R(int) = 0.0591]
0.886
Data/restraints/parameter
Completeness to theta = 25.00°
Refinement method
R indices (all data)
Final R indices [I > 2 sigma(I)]
8825/14/709
99.9%
2630/0/272
99.9%
2964/0/232
99.9%
Full-matrix least squares on F^2
R1 = 0.1077, wR2 = 0.2137
R1 = 0.0608, wR2 = 0.1615
ꢂ8 6 h 6 9, ꢂ31 6 k 6 31, ꢂ15 6 l 6 15
0.309 and ꢂ0.473
Full-matrix least squares on F^2
R1 = 0.0498, wR2 = 0.1106
R1 = 0.0425, wR2 = 0.1044
ꢂ15 6 h 6 15, ꢂ8 6 k 6 6, ꢂ17 6 l 6 17
0.219 and ꢂ0.350
Full-matrix least squares on F^2
R1 = 0.1996, wR2 = 0.1671
R1 = 0.0591, wR2 = 0.1248
ꢂ13 6 h 6 16, ꢂ18 6 k 6 18 ꢂ9 6 l 6 9
0.166 and ꢂ0.244
Limiting indices
Largest diff. peak and hole (e ÅAꢂ3
0
)
of the compound 3a–c show a signal in the shielded region with
three protons integral at 2.48 ppm, 2.65 ppm and 2.23 ppm as a
sharp singlet, are respectively assigned for pyrazolone C3-methyl
group. For compounds 3a and 3b, NH protons are appeared at
4.71 ppm and 4.25 ppm with three protons integral. However NH
signals are not observed for 3c, since the NH protons are exchange-
able with D2O solvent. Moreover in compound 3a two signals in
the aromatic region at 7.12 ppm (J = 6.0 Hz; 3.2 Hz) and 7.53 ppm
(J = 5.6 Hz; 2.4 Hz) as doublet of doublet with two protons integral
each suggest that they are chemical shift equivalent and magneti-
cally non-equivalent protons. Whereas 3b, a benzoxazole deriva-
tive, shows three peaks at 7.65 ppm (1H), 7.55 ppm (1H) and
7.32 ppm (2H) in the aromatic region which are due to the two dif-
ferent hetero atoms persist in the C4 benzoxazole aryl ring. In 3c,
imidazolyl heterocycle shows an intense signal at 3.78 ppm with
four protons integral confirms the formation of –N–CH2–CH2–N–
at C4 of the pyrazolone ring. Whereas introduction of an aryl group
at N1 in 3d and two aryl groups at N1 and C3 in 3e show a singlet
for –N–CH2–CH2–N– protons at 3.76 ppm and 3.61 ppm respec-
tively, do not have much variation (3.78 ppm) with 3c. Hence a
singlet with four protons integral suggests that compound 3c–e
have two equivalent CH2 groups adjacent to two NH protons
(–HNCH2CH2NH–) on C4 heterocycle (Figs. 2 and 3). For compound
3f & 3g formation, 1R,2R-cyclohexyldiamine was used for the
cyclization, thus resulted structures exhibit the diequatorial sub-
stitution on C4 pyrazolone (Fig. 4). Cyclohexyl group shows 5 sets
of protons each with two integrals show that cyclohexyl ring
adopts chair conformation with diequatorial amino substitution.
Further compound 3h and 3i obtained from the cyclization with
2-aminoethanol, show two alkyl peaks in different chemical envi-
ronments. For compound 3h two triplets with two proton integrals
at 4.59 ppm and 3.76 ppm are assigned to methylene protons of C4
heterocycle which are adjacent to the O and N hetero atoms
respectively. Obviously, other aromatic protons of 3a–i are ob-
served in the region of 6.95–8.01 ppm with the respective
integrals.
Fig. 4. Crystal structure of the compound 3f.
3.3. 13C NMR spectral studies of compounds 3a-i
In all 3-methyl pyrazolone compounds (3a–f), C3-methyl car-
bon is observed in the region of 11.35–15.83 ppm and also pyraz-
olone amide carbonyl carbon is observed at 159.87–166.39 ppm in
the down field region. Mainly intense signals observed in the re-
gions at 42.87, 42.13 and 43.07 ppm are attributed to methylene
carbons (NH–CH2–CH2–NH) of C4 imidazole compounds 3c, 3d

76
K. Narayanan et al. / Journal of Molecular Structure 1056–1057 (2014) 70–78
and 3e, respectively. Whereas C4 oxazole methylene carbons
(O–CH2–CH2–NH) of compounds 3h & 3i exhibit, two signals at
42.66 & 42.74 ppm (O–CH2–CH2–NH) and 69.30 & 69.86 ppm (O–
CH2–CH2–NH) respectively, are due to the two different hetero
atoms adjacent to the methylene groups. Besides C4-cyclohexyl
imidazole derivatives, (3f & 3g) show three alkyl carbon peaks, in
the region of 23.86, 28.95 & 62.01 ppm and 24.05, 29.16 &
62.94 ppm, respectively illustrate the presence of cyclohexyl moi-
ety. Moreover, C4 benzimidazole (3a), benzoxazole (3b) are the
aromatic heterocycle, thus their respective carbon signals are ob-
served in the aromatic region at 118.03–129.16 ppm. Exclusively,
chemical shift value of ring junction carbon C2’ is varied by the
presence of alkyl and aryl moiety on the C4 heterocycle. Hence
C2’ of benzimidazole and benzoxazole heterocycle (147.4–
148.6 ppm) are slightly shielded (ꢃ10–15 ppm) than the aliphatic
C4 heterocycles (159.6–166.1 ppm).
3.4. 2D NMR spectral studies of compounds 3a & 3h
2D NMR spectra (HOMOCOSY, HSQC and HMBC) show the
structural skeleton of the compound and support the formation
of the compound 3a and 3h. HOMOCOSY spectra of compound
3a shows HOMO correlation with two proton peaks at 7.12 ppm
and 7.52 ppm, reveals that the above protons adjacent to one an-
other, and hence these peaks are attributed to the H4’,7’ and
H5’,6’, respectively. The chemical shift at 12.88 ppm is assigned
for methyl carbon of the pyrazolone moiety, which also exhibit
HSQC spectral correlation with methyl protons at 2.48 ppm. The
hydrogen attached imidazolyl carbons are assigned at
113.56 ppm for C4’,7’ and 121.56 ppm for C5’,6’ ring carbons, since
these peaks exhibit HSQC correlation with 7.12 ppm and 7.52 ppm,
respectively. In HMBC spectrum, a chemical shift at 140.96 ppm
Fig. 5. HMBC spectrum of compound 3h.
and 90.94 ppm show
a and b correlation with 3-Me protons at
2.48 ppm, hence these peaks are assigned to C3 and C4 of the pyr-
azolone ring, respectively. Also a peak at 135.96 ppm shows multi-
ple bond correlation with 7.12 ppm and 7.52 ppm, is attributed to
benzimidazole aryl ipso carbons (C8’,9’). The chemical shift values
162.33 and 147.49 ppm do not correlate with any hydrogen in
HMBC. So the most deshielded chemical shift value, 162.33 ppm
is assigned to pyrazolone carboxyl carbon and 147.49 ppm as-
signed to C2’ of benzimidazole ring junction carbon at C4 of the
pyrazolone ring. Similarly, for an oxazole compound 3h, a triplet
at 3.76 ppm shows HOMO cross peak with another triplet at
4.59 ppm, which implies that both set of protons are adjecent to
one another, hence these peaks are assignable to C4 oxazolidine
methylene protons. DEPT spectrum also confirms the C4 heterocy-
clic formation by the inverted carbon peaks at 42.67 and
69.29 ppm. A peak at 8.02 ppm shows intense HOMO correlation
with a triplet at 7.36 ppm and the later peak shows cross peak with
7.11 ppm, suggest that the peaks at 8.02, 7.36 & 7.11 ppm are as-
signed to ortho, meta and para protons, respectively. From the
HMBC spectrum, a peak in the deshielded region, at 166.00 ppm
shows intense b correlation with methylene protons at 3.76 and
4.59 ppm suggest that peak at 166.00 ppm is unambiguously as-
signed to C2’ of the oxazole ring. In addition two carbon peaks
146.99 ppm and 85.86 ppm shows HMBC correlation with methyl
protons at 2.303 ppm, suggest that the above peaks are respec-
tively assigned to C2(C@N) and C3(C@C) of the pyrazolone ring.
Fig. 6. Numbering of compounds 3a & 3h.
entropy by the free rotation between two heterocyclic systems
might have unfavored for a single tautomer. The stability decides
the reactivity improvement, in order that stable form of product
must be identified. For instance, compound 3e is taken into the
consideration and this tautomerise into various forms (T1–T5) is
shown in Fig. 7. The stable tautomer with lowest energy has been
identified (T5) by DFT/B3LYP calculation and the physical parame-
ters are compared with the structure obtained by the X-ray data.
4. Molecular structure determination from crystal data
The structural parameter of the compounds 3d–f were deter-
mined by using single crystal X-ray diffraction technique. ORTEP
diagram of compounds 3d–f with the atomic numbering is shown
in (Figs. 2–4). Theoretical study is computed and compared with
crystal structure of compound 3e. Compound 3e is crystallized in
a monoclinic system, with space group P21/n, Z = 4 and also with
0
lattice parameters a = 13.448(5), 0 b = 7.539(5), c = 14.832(5) ÅA,
b = 94.747(5)°, volume 1498.6(12) ÅA3. The selected bond length,
bond angles of 3e are also listed in (Table 3). The single crystal
structure analysis provides evidence that the molecular structure
of 3e is very close to the similar reports by Li-Nan Li [30].
Moreover, N1 ipso carbon is assigned by the intense HMBC (
a, b,
c)
correlation with respective ortho, meta and para protons
(Fig. 5). The structures of all the imidazoles as well as oxazoles
are proposed by the similar spectral pattern exerted by these (3a
& 3h) molecules (Fig. 6).
Obviously, pyrazolone heterocycle exhibits various tautomeric
forms in solution and hence its bond lengths are varied drastically.
The stabilization of the imidazole/oxazole moiety and the greater
The C(3)–O(1) distance is 1.245(2) Å which is shorter than that
for C–OH in some pyrazolone compounds 1.319(5) Å by Uzoukwu
[31] and 1.313(2) Å by Holzer [32], whereas it is closer to the dis-
tance of C@O in similar compounds: 1.248(3) Å by Jing Li [33] and
1.245(4) Å by Vyas [34]. The C(2)–C(16) (1.408(2) Å) is shorter than
the normal C–C bond length (1.53 Å), but close to C@C in some

K. Narayanan et al. / Journal of Molecular Structure 1056–1057 (2014) 70–78
77
Fig. 7. Various tautomeric form of compound 3e.
Table 3
Selected bond lengths, bond angles of compound 3d–f from XRD data.
Compound 3d Compound 3e Compound 3f
Bond distances (Å) with esd’s parentheses
C1–C2
C2–N2
C2–C3
C3–C11
C3–C4
C4–O1
C4–N1
C5–N1
C11–N3
C11–N4
N1–N2
1.525(11) C1–C10
1.330(10) C1–N2
1.420(11) C1–C2
1.380(12) C2–C16
1.391(11) C2–C3
1.4792(19) C3–C6
1.3187(18) C3–N2
1.4190(19) C3–C4
1.495(4)
1.314(4)
1.420(4)
1.402(5)
1.408(4)
1.267(4)
1.370(4)
1.427(4)
1.346(4)
1.354(4)
1.404(3)
1.408(2)
1.427(2)
C4–C13
C4–C5
1.276(7)
C3–O1
1.2447(17) C5–O1
1.3947(19) C5–N1
1.4107(18) C7–N1
1.3438(18) C13–N4
1.3187(18) C13–N3
1.3909(16) N1–N2
1.387(10) C3–N1
1.389(10) C4–N1
1.316(10) C16–N4
1.359(9)
1.438(8)
C16–N3
N1–N2
Bond angles (°) with esd’s parentheses
N2–C2–C3
N2–C2–C1
C3–C2–C1
C4–C3–C2
O1–C4–C3
112.7(7)
117.1(8)
130.2(8)
106.0(7)
128.7(8)
N2–C1–C2
N2–C1–C10 117.52(12) N2–C3–C6
C2–C1–C10 130.77(13) C4–C3–C6
C1–C2–C3
O1–C3–C2
C9–C4–N1
N1–C4–C5
111.63(12) N2–C3–C4
111.5(3)
118.5(3)
130.0(4)
106.2(3)
130.8(4)
106.33(12) C3–C4–C5
130.67(13) O1–C5–C4
120.87(13) C12–C7–N1 119.3(3)
119.90(14) N1–C7–C8 120.5(4)
C10–C5–N1 122.4(7)
N1–C5–C6 118.3(8)
N3–C11–N4 108.4(7)
N3–C11–C3 128.7(7)
N4–C11–C3 122.9(7)
N3–C16–N4 110.17(12) N3–C13–N4 109.1(4)
N4–C16–C2 126.48(12) N4–C13–C4 128.7(4)
N3–C16–C2 123.35(13) N3–C13–C4 122.2(4)
Fig. 8. The B3LYP/6-31Gꢁꢁ optimized structure (T5) of compound 3e.
relative compounds, 1.400(2) Å [30] and 1.392(8) Å [33]. From the
X-ray data, 1.319(2) Å and 1.344(2) Å, bond distances obtained for
C(16)–N(3), C(16)–N(4) respectively are compared with C@N value
(1.292 Å) reported by Peng et al. [35]. C(16)–N(3) with 1.319 Å has
partial double bond character than the C(16)–N(4), 1.344 Å. Fur-
ther the bond lengths N(2)–C(1) (1.319 Å) and C(1)–C(2)
(1.419 Å) are slightly differ from the normal C@N and C–C bond
length. This observation suggests that compound 3e involve in
the tautomerization through the delocalization of electrons around
N2–C1–C2–C16–N3 chain. Also from the X-ray structure analysis,
pyrazolone ring (C1–N2–N1–C3–C2) and the imidazolyl ring
(C16–N3–C18–C17–N4) of 3e virtually exhibit coplanarity with
the dihedral angle (15.18°) and the torsion angle for C1–C2–C16–
N3 is 175.85(14)°. These observations reveal that of electronic
delocalization about N2–C1–C2–C16–N3 chain and this extends
even up to C3 carbon, and not with N4 atom. In addition, the
N(3) atom is strongly hydrogen bonded with the O(1) atom, the
N(3)ꢄ ꢄ ꢄO(1) distances is 2.842 Å and the angle of N(3)–
H(3)ꢄ ꢄ ꢄO(1) is 126.08°. Therefore, the crystal study shows that
the compound exists in the amine-one form.
compared with X-ray diffraction data of 3e. Bond lengths, bond
angles and torsion angles obtained from X-ray diffraction study
and optimization by B3LYP/6-31Gꢁꢁ level study are listed in Tables
5 and S1 (supplementary). Based on the optimization data from
Table 5, the single bond distances of N1–N2, C16–N4 and C1–C2
are 1.384 Å, 1.368 Å and 1.430 Å respectively, while the double
bond distances of N2–C1, C3–O1 and C2–C16 are 1.315 Å, 1.248 Å
and 1.397 Å by B3LYP/6-31Gꢁꢁ level which are consistent with
XRD structure. But C16–N3 and C16–N4 with bond distances
1.348 Å, 1.368 Å differ from actual by 1.319 Å and 1.344 Å, respec-
tively; suggest that C16–N3 is much involving delocalization with
C2–C16 double bond.
Moreover, the bond angles C2–C16–N3, N3–C16–N4, C2–C3–O1
and C2–C1–C10 are 122.0°, 109.0°, 129.1° and 130.3°, respectively
are also consistent with actual values of 123.35(13)°, 110.17(12)°,
130.67(13)° and 130.77(13)° respectively. Torsion angles of stable
T5 at C16–C2–C3–O1, C3–C2–C16–N3 are 6.2° and ꢂ1.1° also exhi-
bit good agreement with the crystal structure of 3e. Consequently,
we suggest that O1–C3–C2–C16–N3–H3 are lying in a plane, in-
volves the intra molecular hydrogen bonding as well as coplanarity
exists in the planes of pyrazolone with C4 heterocycles.
The geometrical optimizations of compound 3e and its different
tautomeric forms were performed by B3LYP/6-31Gꢁꢁ method
(Fig. 8 and S2). Total energy and the HOMO, LUMO energies of
the all the isomers were assigned and listed in Table 4. HOMO,
LUMO diagram of T1–T5 was also predicted, is shown in Fig. S1.
5. Conclusion
Accordingly, calculated total energy of the tautomer
5 (T5)
(ꢂ620909.36 kcal/mol) is comparably lower than the tautomer 1
(T1) (ꢂ620882.31 kcal/mol) and the other tautomers (T2–T4) en-
ergy are lying in between the above two (T1 & T5). Hence T5 is
identified as the stable form of tautomer with 1.1726 eV than T1,
hence the physical parameters of more reliable form of T5 is
A general procedure for the synthesis of heterocycle substituted
pyrazolones from the simple starting materials like pyrazolone ke-
tene dithioacetal synthon has been developed. 1,3-azoles/oxazoles
and benzannulated azoles/oxazoles are readily constructed on pyr-
azolone moiety in the absence of any catalyst. All the synthesized

78
K. Narayanan et al. / Journal of Molecular Structure 1056–1057 (2014) 70–78
Table 4
Theoretically computed energies for structures T1–T5.
S. No.
Parameters
T1
T2
T3
T4
T5
1
2
3
4
HOMO energy (kcal/mol)
LUMO energy (kcal/mol)
Zero point energy (kcal/mol)
Total energy (kcal/mol)
ꢂ128.94
ꢂ35.39
ꢂ123.70
ꢂ38.50
ꢂ126.59
ꢂ21.43
ꢂ132.42
ꢂ18.31
ꢂ115.96
ꢂ21.70
195.91
196.52
195.98
196.15
196.84
ꢂ620882.31
ꢂ620886.85
ꢂ620893.03
ꢂ620902.59
ꢂ620909.36
Table 5
Selected bond distances (Å), bond angles (°) and dihedral angles (°) of 3e by crystal study with optimization.
Parameters
Experimental
XRD
Theoretical
B3LYP (T5)
Parameters
Experimental
XRD
Theoretical
B3LYP (T5)
N1–N2
N2–C1
C1–C2
C2–C3
C3–O1
C2–C16
C16–N3
C16–N4
C1–C10
1.3909(16)
1.3187(18)
1.4190(19)
1.427(2)
1.2447(17)
1.408(2)
1.3187(18)
1.3438(18)
1.4792(19)
1.4107(18)
1.3947(19)
105.90(11)
106.33(12)
130.67(13)
123.35(13)
126.48(12)
110.17(12)
1.384
1.315
1.430
1.451
1.248
1.397
1.348
1.368
1.477
1.416
1.397
107.3
105.6
129.1
122.0
129.0
109.0
C2–C1–C10
N2–C1–C10
C3–N1–C4
N2–N1–C4
130.77(13)
117.52(12)
128.47(12)
119.26(11)
122.8(12)
ꢂ22.3(2)
ꢂ1.28(15)
1.73(15)
130.3
118.7
128.9
118.8
117.2
ꢂ6.2
ꢂ3.1
0.6
C16–N3–H3
C3–N1–C4–C5
N2–N1–C4–C9
C1–C2–C3–N1
C16–C2–C3–O1
C3–C2–C16–N3
C1–C2–C16–N4
C10–C1–C2–C16
C10–C1–N2–N1
N2–C1–C10–C15
N2–C1–C10–C11
C2–C1–C10–C15
N3–C18–C17–N4
8.6(2)
6.2
N1–C4
N1–C3
ꢂ1.3(2)
ꢂ1.1
ꢂ3.8(2)
8.1
N1–N2–C1
C1–C2–C3
C2–C3–O1
C2–C16–N3
C2–C16–N4
N3–C16–N4
ꢂ11.6(3)
ꢂ178.54(11)
131.54(15)
ꢂ44.67(19)
ꢂ45.1(2)
4.7(2)
ꢂ7.9
ꢂ180.0
138.8
ꢂ38.9
ꢂ41.7
25.6
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compounds 3a–i in the present project were characterized by IR,
1H NMR, 13C NMR, 2D NMR and XRD techniques. Compounds
3d–f were crystallized as monoclinic system and their structural
parameters were evaluated. For compound 3e, stable form of the
tautomer, (T5) was identified by the DFT calculation with B3LYP,
6-31Gꢁꢁ basis set level and the physical parameters of T5 were
compared with X-ray data, which exhibit good consistency with
the proposed structure was obtained.
Acknowledgements
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The authors are thankful to Professor A. Manimekalai, Head,
Department of Chemistry, Annamalai University and Professor P.
Sambasiva Rao, former Head, Department of Chemistry, Pondicher-
ry University for providing necessary facilities required to carry out
this work.
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Crystallographic data for the structures reported in this paper
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CCDC 945144 (3e) and CCDC 916999 (3f). Copies of the data can
be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
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033: or e-mail: deposit@ccdc.cam.ac.uk. Frontier orbitals for T1–
T5 of compound 3e and spectral data of all the compounds 3a–i
are given in supplementary figures S1–S25. Supplementary data
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