Synthesis, spectroscopic studies and X-ray crystal structures of new pyrazoline and pyrazole derivatives

Article abstract of DOI:10.1007/s10870-010-9896-2

The synthesis and characterization of some pyrazoline compounds of 1,3-diketones with hydrazine derivatives, namely, 1-(S-benzyldithiocarbazate)-3- methyl-5-phenyl-5-hydroxypyrazoline (1); 1-(2-thiophenecarboxylic)-3-methyl-5- phenyl-5-hydroxypyrazoline (

Full text of DOI:10.1007/s10870-010-9896-2

J Chem Crystallogr (2011) 41:401–408
DOI 10.1007/s10870-010-9896-2
ORIGINAL PAPER
Synthesis, Spectroscopic Studies and X-ray Crystal Structures
of New Pyrazoline and Pyrazole Derivatives
•
Gerimario F. de Sousa Claudia C. Gatto
•
´
Ines S. Resck Victor M. Deflon
•
ˆ
Received: 21 January 2010 / Accepted: 4 September 2010 / Published online: 26 September 2010
Ó Springer Science+Business Media, LLC 2010
˚
˚
Abstract The synthesis and characterization of some
pyrazoline compounds of 1,3-diketones with hydrazine
derivatives, namely, 1-(S-benzyldithiocarbazate)-3-methyl-
5-phenyl-5-hydroxypyrazoline (1); 1-(2-thiophenecarboxy-
lic)-3-methyl-5-phenyl-5-hydroxypyrazoline (2); 1-(2-thio-
phenecarboxylic)-3,5-dimethyl-5-hydroxypyrazoline (3);
1-(S-benzyldithiocarbazato)-3-methyl-5-phenylpyrazole (4);
1-(2-thiophenecarboxylic)-3-methyl-5-phenylpyrazole (5)
and 1-(S-benzyldithiocarbazate)-3,5-dimethylpyrazole (6)
are reported. Studies by IR, (1H, 13C)-NMR spectroscopies
and single crystal X-ray diffraction revealed that compounds
(1), (2) and (3) are formed as pyrazoline, whereas (4) and (5)
are formed as pyrazole derivatives only under acidic condi-
tions. Compound (1) crystallizes in orthorhombic P212121,
b = 9.3766(3) A, c = 16.6910(5) A and b = 113.825(2)°,
˚
(4) crystallizes in monoclinic, P21/c, a = 15.228(4) A,
˚
˚
b = 5.5714(13) A, c = 19.956(5) A and b = 91.575(7)°
and (6) crystallizes in orthorhombic, P212121, a =
˚
˚
˚
5.3920(2) A, b = 11.2074(5) A, c = 21.885(1) A. The (3)
derivative represents the first pyrazoline compound prepared
from 2,4-pentanedione and characterized crystallograph-
ically.
Keywords 1,3-Diketones Á Pyrazoline Á Pyrazole
derivatives Á Crystal structures
Introduction
˚
a = 6.38960(10) A, b = 12.9176(3) A, c = 21.2552(5) A,
˚
˚
˚
(2) crystallizes in monoclinic, P21/n, a = 11.3617(2) A,
1,3-Diketones and related derivatives constitute an impor-
tant class of organic compounds because they have the
potential of binding to a great number of transition metal
ions, as well as to main group metal centers. Furthermore,
metal complexes containing pyrazole ligands have drawn
considerable interest, owing to their unusual coordination
chemistry and their biological and biochemical importance
[1, 2].
˚
˚
b = 8.4988(2) A, c = 92.8900(10) A and b = 92.8900
˚
(5)°, (3) crystallizes in monoclinic, C2/c, a = 15.9500(5) A,
Joshi and collaborators [3] have reported that benzoic
acid hydrazide derivatives of 1,3-diketones can exist in
several distinct isomeric forms. Some tautomeric possi-
bilities for this class of compounds are shown ahead.
According to the authors, literature data reveal conflicting
reports about which tautomeric forms predominate in
solution for such derivatives. Yakimovich et al. [4] from
(1H, 13C) NMR spectral studies, proposed that acylhydra-
zones of 1,3-diketones can participate in the cycle-chain
equilibrium between the hydrazonic (A, B), enhydrazinic
(C), and/or 5-hydroxypyrazoline (D) forms and pyrazole
(E) forms. Due to these observations, we decided to
G. F. de Sousa (&) Á C. C. Gatto Á I. S. Resck
´
Instituto de Quımica, Universidade de Brasılia,
Brasılia, DF 70919-970, Brazil
´
´
e-mail: gfreitas@unb.br
V. M. Deflon
Instituto de Quımica de Sa˜o Carlos, Universidade de Sa˜o Paulo,
´
Sa˜o Carlos, SP 1350-250, Brazil
123

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J Chem Crystallogr (2011) 41:401–408
R1
R2
N
R1
R2
N
R1
R2
N
evaporating the solvent from their MeOH solution at room
temperature. Single crystals for (4) and (5) were obtained
as reported in the synthesis section. The data collections
were performed with Mo Ka radiation (k = 71.073 pm) on
a NONIUS KAPPA CCD instrument for (1), (2) and (6)
and on a BRUKER KAPPA APEX II CCD diffractometer
for (3), (4) and (5) applying standard procedures. X-ray
crystal structures were solved by the heavy atom method
with SHELXS-97 [8] and refined with the SHELXL-97 [9].
Hydrogen atom positions were calculated at idealized
positions using the Riding model option of SHELXL-97
[9]. Additional crystal data and more information about the
X-ray structural analyses are shown in Table 1. All of the
structures of the pyrazoline and pyrazole derivatives are
shown in Scheme 1 and their ORTEP plots are depicted in
Figs. 1, 2, 3, 4, and 5. All relevant crystallographic infor-
mation is presented in Table 1, and selected bond distances
and angles in Table 2.
H
O
N
O
H
H
O
N
OH
N
O
H
R3
O
R3
R3
(A)
(B)
(C)
R1
R2
R1
R2
HO
R3
N
N
N
N
O
R3
O
(E)
(D)
R1, R2 , R3 alkyl or aryl
investigate, in detail, the preparation and the structural
aspects of pyrazoline derivatives obtained from the cycli-
zation of 1,3-diketones RCOCH2COCH3 (R = Me and Ph)
with S-benzyldithiocarbazate and 2-thiophenecarboxylic
hydrazine compounds. Moreover, this paper is an extension
of research programs devoted to the investigation of the
coordination modes of hydrazones and thiohydrazones with
organotin(VI) compounds [5, 6]. Our studies demonstrated
that the isomeric form is determined by the nature of the
1,3-diketone, by the structure of the hydrazine derivative,
by the pH of the reaction medium and, to a certain extent,
by the polarity of the solvent used in the condensation
reactions.
Synthesis
Compounds (1), (2), and (3) were prepared as follows: a
solution of 1,3-diketone, RCOCH2COMe (4.0 mmol),
where R is a methyl or a phenyl group, in 10 mL of MeOH
was added to a solution of the appropriate hydrazide
derivative (4.0 mmol) in 10 mL of MeOH. The mixture
was refluxed for 1 h, obtaining yellow solutions for (1) and
(2), and a colorless solution for (3). The clear solutions
were slowly evaporated, leading appearance of colorless
crystalline products, which were filtered, washed with
hexane and dried in air. Compounds (1) and (3) pyrazoline
derivatives can easily be obtained as single crystals by
using CH2Cl2 as the reaction solvent.
Experimental
Materials and Methods
Solvents were purified and dried according to standard
procedures. The reagents, 2,4-pentanedione, 4-phenyl-2,
4-butanedione, 2-thiophenecarboxylic hydrazide, were of
the highest commercially available quality and the starting
material, S-benzyldithiocarbazate, was prepared by a lit-
erature method [7]. IR spectra were recorded on a BOMEM
MB100 FT-IR spectrophotometer in the 4000–400 cm-1
range using KBr pellets and microanalyses were performed
using a FISSONS CHNS, mod. EA 108 microanalizer.
NMR spectra were recorded on a VARIAN MERCURY
Compounds (4), (5), and (6) were prepared as follows:
pyrazole derivative compounds (4) and (5) were prepared
employing an acid-catalyzed conversion by adding two
drops of concentrated HCl in equimolar mixture of
4-phenyl-2,4-butanedione and the appropriate hydrazone in
20 mL of MeOH (Scheme 1). After about 2 h under reflux
and slow evaporation of the solvent, deep yellow and
colorless crystals precipitated from solutions of (4) and (5),
respectively. Crystals suitable for X-ray diffraction studies
for (4) were acquired by a slow evaporation technique from
a hot hexane/CH2Cl2 (3:1, v/v) solution and (5) was
obtained as a pure material. Equimolar mixture of
2,4-pentanedione and S-benzyldithiocarbazate in 20 mL of
MeOH for 1 h, under the same conditions as described
above, gave pyrazole (6) as yellow needles. However,
similar treatment of 4-phenyl-2,4-butanedione with
S-benzyldithiocarbazate afforded 5-hydroxy-4,5-dihydro-
pyrazoline derivative (1) in excellent yield. It is noteworthy
to mention that the presence of a strong electron-with-
drawing substituent at 1- or 5-position of the 5-hydroxy-4,
1
PLUS spectrometer (7.05 T) operating at 300 MHz for H
and at 75.46 MHz for 13C. The compound was dissolved in
CDCl3 or DMSO-d6 containing TMS as internal reference
(see Fig. 6 for atom numbering). Chemical shifts were
expressed in d (ppm) and coupling constants as J (Hz). The
homonuclear and heteronuclear two-dimensional experi-
ments (COSY, HMQC and HMBC) were completed using
the field gradient mode.
Single crystals of compounds (1), (2), (3), and (6),
suitable for X-ray data collection, were grown by slowly
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J Chem Crystallogr (2011) 41:401–408
403
Table 1 Crystallographic data for pyrazoline [(1), (2), (3)] and pyrazole [(4), (6)] derivatives
(1)
(2)
(3)
(4)
(6)
Formula
C18H18N2OS2
342.46
C15H14N2O2S
286.34
C10H12N2O2S
224.28
C18H16N2S2
324.45
C13H14N2S2
262.38
Formula weight
Crystal system
Space group
Crystal color
Z
Orthorhombic
P212121
Colorless
4
Monoclinic
P21/n
Monoclinic
C2/c
Monoclinic
P21/c
Orthorhombic
P212121
Yellow
4
Colorless
4
Colorless
8
Yellow
4
T (K)
˚
a (A)
293(2)
293(2)
293(2)
293(2)
293(2)
6.38960(10)
12.9176(3)
21.2552(5)
90
11.3617(2)
8.4988(2)
14.8959(3)
92.8900(10)
1436.53(5)
1.324
15.9500(5)
9.3766(3)
16.6910(5)
113.825(2)
2283.53
1.305
15.228(4)
5.5714(13)
19.956(5)
91.575(7)
1692.5(7)
1.273
5.3920(2)
11.2074(5)
21.885(1)
90
˚
b (A)
˚
c (A)
b (°)
3
˚
V (A )
1754.37(6)
1.297
1322.5(1)
1.318
qcalcd (g cm-3
)
Index ranges
-7 B h B 7
-15 B k B 15
-25 B l B 25
720
-14 B h B 14
-11 B k B 11
-19 B l B 19
600
-16 B h B 11
-9 B k B 9
-16 B l B 17
944
-21 B h B 21
-4 B k B 7
-25 B l B 28
680
-6 B h B 6
-13 B k B 13
-25 B l B 26
552
F(000)
l (mm-1
)
0.309
0.228
0.266
0.312
0.382
Refinement method
Reflections collected
Data/parameters
GOF on F2
i
i
i
i
i
23496
10533
5488
16132
11233
3090/211
1.234
3278/182
1.086
1317/136
1.098
4940/199
0.763
2594/157
1.075
R1 [I [ 2r(I)]ii
0.0590
0.0546
0.0548
0.0459
0.0482
wR2 [I [ 2r(I)]iii
0.1809
0.1699
0.1670
P
0.1036
0.1156
P
P
P
(i) Full-matrix least-squares on F2, (ii) R1 = ||Fo| - |Fc||/ |Fo|, (iii) wR2 = [ w(|Fo|2 - |Fc|2)2/ w|F2o|2]1/2
R1
CH3
HO
N
C
N
H2O
R1
CH3
X
X
R2
NH
C
H2N
(1), (2), (3)
O
O
R2
H+
CH3
R1
N
C
N
(1) X = S, R1 = Ph, R2 = -SCH2C6H5
(2) X = O, R1 = Ph, R2 = -(2-C4H3S)
(3) X = O, R1 = Me, R2 = -(2-C4H3S)
(4) X = S, R1 = Ph, R2 = -SCH2C6H5
(5) X = O, R1 = Ph, R2 = -(2-C4H3S)
2 H2O
X
R2
(4), (5)
Scheme 1 Condensation reactions on preparation of pyrazoline [(1), (2), (3)] and pyrazole [(4), (5)] derivatives
1
5-dihydropyrazoline ring is a necessary condition of their
stability.
(1). Anal. Calcd for C18H18N2OS2: (342.47 g mol-1): C,
63.13; H, 5.30; N, 8.18; S, 18.72. Found: C, 62.99; H, 5.61;
N, 8.27; S, 19.67%; color: colorless; yield: 81%; m.p.:
125–127 °C. H NMR (300 MHz, CDCl3): d 2.09 (d, 3H,
–CH3); 3.21 (dd, J 18.8 Hz, 2H, –CH2–); 4.35 (dd,
J 13.2 Hz, 2H, –CH2–); 6.47 (s, 1H, –OH). 13C NMR
(300 MHz, CDCl3): d 16.0 (1C), 158.4 (2C), 54.6(3C),
97.3(4C); 142.3 (5C); 191.2 (9C); 39.2 (10C). IR (KBr):
123

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J Chem Crystallogr (2011) 41:401–408
Fig. 1 ORTEP plot of (1) with the displacement parameters drawn at
the 30% probability level. The dashed line indicates an intramolecular
hydrogen bonding
Fig. 3 ORTEP plot of (3) with the displacement parameters drawn at
the 30% probability level. The dashed line indicates an intramolecular
hydrogen bonding
Fig. 2 ORTEP plot of (2) with the displacement parameters drawn at
the 30% probability level
m
max./cm-1: 3356 (O–H), 1629 (C=N), 1494, 1461 (C=C),
1377 (C–N), 1320 (C–O), 1252, 854 (C = S), 981 (C–S–S).
(2). Anal. Calcd for C15H14N2SO2: (286.35 g mol-1):
C, 62.92; H, 4.93; N, 9.78; S, 11.20. Found: C, 61.99; H,
4.85; N, 9.75; S, 12.27%; color: colorless; yield: 75%;
1
m.p.: 161–163 °C. H NMR (300 MHz, CDCl3): d 2.15
(d, 3H, –CH3); 3.23 (dd, J 18.0 Hz, 2H, –CH2–); 5.29
(s, 1H, –OH). 13C NMR (300 MHz, CDCl3): d 16.1 (1C),
155.0 (2C), 53.5 (3C), 94.5 (4C); 143.5 (5C); 160.2 (9C);
135.0 (10C). IR (KBr): mmax./cm-1: 3411 (O–H), 1610 (C=O),
1630 (C=N), 1513, 1445 (C=C), 1313 (C–O), 1378 (C–N).
(3). Anal. Calcd for C10H12N2OS2: (224.28 g mol-1):
C, 53.55; H, 5.39; N, 12.49; S, 14.29. Found: C, 53.04; H,
5.62; N, 12.40; S, 15.94%; color: colorless; yield: 65%;
Fig. 4 ORTEP plot of (4) with the displacement parameters drawn at
the 30% probability level
(O–H), 1600 (C=O), 1638 (C=N), 1512, 1445 (C=C), 1378
(C–N), 1322 (C–O).
1
m.p.: 102–105 °C. H NMR (300 MHz, CDCl3): d 1.85
(4). Anal. Calcd for C18H16N2S2: (324.46 g mol-1): C,
66.63; H, 4.97; N, 8.63; S, 19.76. Found: C, 64.47; H, 5.14;
N, 8.65; S, 21.16%; color: deep yellow; yield: 76%; m.p.:
(s, 3H, –CH3); 2.99 (dd, J 18.0 Hz, 2H, –CH2–); 2.04
(s, 3H, –CH3); 5.06 (s, 1H, –OH). 13C NMR (300 MHz,
CDCl3): d 16.2 (1C), 155.4 (2C), 50.8 (3C), 92.7 (4C); 26.9
(5C); 160.4 (9C); 135.4 (10C). IR (KBr): mmax./cm-1: 3414
1
101–103 °C. H NMR (300 MHz, CDCl3): d 2.34 (d, 3H,
–CH3); 6.27 (s, 1H, = CH–); 4.35 (s, 2H, –CH2–). 13C
123

J Chem Crystallogr (2011) 41:401–408
405
145.5 (5C); 160.6 (9C); 137.5 (10C). IR (KBr): mmax./cm-1
:
1681 (C=O), 1574 (C=N), 1502, 1468 (C=C), 1355 (C–N).
(6). Anal. Calcd for C13H14N2S: (262.39 g mol-1): C,
59.51; H, 5.38; N, 10.68; S, 24.44. Found: C, 57.83; H,
5.44; N, 10.46; S, 25.56%; color: deep yellow; yield: 75%;
1
m.p.: 90–92 °C. H NMR (300 MHz, CDCl3): d 2.08 (s,
3H, –CH3); 5.90 (q, 3H, –CH3); 2.55 (d, 3H, –CH3); 4.23
(s, 2H, –CH2–). 13C NMR (300 MHz, CDCl3): d 13.6 (1C),
145.5 (2C), 113.2 (3C), 151.7 (4C); 17.3 (5C); 200.3 (9C);
41.3 (10C). IR (KBr): mmax./cm-1: 1580 (C=N), 1489, 1454
(C=C), 1367 (C–N), 1274, 863 (C=S), 963 (C–S–S).
Fig. 5 ORTEP plot of (6) with the displacement parameters drawn at
the 30% probability level
NMR (300 MHz, CDCl3): d 13.7 (1C), 147.0 (2C), 114.4
(3C), 151.7 (4C); 131.9 (5C); 199.1 (9C); 41.7 (10C). IR
(KBr): mmax./cm-1: 1573 (C=N), 1490, 1453 (C=C), 1377
(C–N), 1275, 853 (C=S), 969 (C–S–S).
Results and Discussion
Crystal Structure of (1)
(5). Anal. Calcd for C15H12N2OS: (268.33 g mol-1): C,
67.14; H, 4.51; N, 10.44; S, 11.95. Found: C, 65.74; H,
4.72; N, 10.34; S, 13.27%; color: colorless; yield: 55%;
m.p.: 122–123 °C. 1H NMR (300 MHz, CDCl3): d 2.73 (s,
3H, –CH3); 6.58 (d, 1H, = CH–). 13C NMR (300 MHz,
CDCl3): d 14.7 (1C), 155.3 (2C), 108.1 (3C), 138.0 (4C);
The ORTEP plot of (1) is shown in Fig. 1 along with the
atom numbering scheme. Selected bond lengths and angles
with their estimated standard deviations are compiled in
Table 2. The structure obtained confirms the cyclization
reaction and formation of the 5-hydroxy-4,5-dihydropy-
razoline derivative. The compound crystallizes into an
˚
Table 2 Selected bond distances (A) and angles for pyrazoline [(1), (2), (3)] and pyrazole [(4), (6)] derivatives
(1)
(4)
(6)
(2)
(3)
S1–C7
1.810(5)
1.727(5)
1.679(5)
1.393(6)
1.353(6)
1.501(6)
1.407(6)
1.284(7)
1.487(2)
1.482(7)
1.540(7)
1.534(7)
102.6(2)
125.7(3)
120.6(4)
113.6(3)
118.4(4)
107.2(4)
128.2(4)
114.9(5)
104.5(4)
110.4(4)
111.7(4)
113.5(4)
99.7(4)
1.806(2)
1.812(3)
S–C4
1.704(2)
1.684(4)
1.478(5)
1.231(4)
1.407(4)
1.354(4)
1.494(4)
1.390(4)
1.273(5)
1.490(6)
1.462(6)
1.509(5)
1.502(5)
129.5(3)
120.2(3)
119.3(3)
120.5(3)
121.0(3)
107.8(3)
125.1(3)
114.0(5)
105.1(3)
113.7(3)
114.7(3)
111.1(3)
99.5(3)
S1–C8
1.736(2)
1.622(2)
1.745(3)
1.630(3)
C4–C5
1.475(2)
1.233(2)
S2–C8
O1–C5
O1–C12
O2– 9
1.404(2)
N1–C8
1.393(3)
1.386(3)
1.394(4)
1.403(4)
1.386(4)
1.315(4)
1.485(5)
1.422(5)
1.349(5)
1.483(5)
102.21(15)
125.26(19)
124.8(2)
109.99(19)
117.5(2)
105.1(2)
131.3(3)
111.0(3)
107.6(3)
125.7(3)
129.1(3)
N1–C5
1.355(2)
N1–C12
N1–C9
1.487(2)
N1–N2
1.384(2)
N1–N2
1.397(2)
N2–C9
1.311(3)
N2–C6
1.282(3)
C9–C10
1.488(3)
C6–C7
1.484(3)
C9–C11
1.409(3)
C6–C8
1.494(3)
C11–C12
C12–C13
C7–S1–C8
S1–C8–S2
S2–C8–N1
S1–C8–N1
C8–N1–N2
N1–N2–C9
C8–N1–C12
N2–C9–C11
C9–C11–C12
N1–C12–C13
C11–C12–C13
O1–C12–C13
N1–C12–C11
1.344(3)
C8–C9
1.542(2)
1.484(3)
C9–C10
1.524(3)
102.47(11)
125.12(15)
124.46(16)
110.43(15)
117.44(17)
105.57(18)
131.97(19)
110.4(2)
S–C4–C5
O1–C5–C4
O1–C5–N1
C4–C5–N1
C5–N1–N2
N1–N2–C6
C5–N1–C9
N2–C6–C8
C6–C8–C9
N1–C9–C10
C8–C9–C10
O2–C9–C10
N1–C9–C8
128.06(14)
120.59(15)
118.85(16)
120.52(15)
122.84(15)
107.73(16)
123.00(14)
114.43(16)
103.72(15)
109.64(14)
114.26(15)
113.64(15)
100.26(14)
107.8(2)
127.0(2)
127.4(2)
105.6(2)
105.2(2)
123

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J Chem Crystallogr (2011) 41:401–408
˚
hybridization. The structures of (2) and (3) show that the
angles between the mean planes of the two five-membered
rings are 7.7(1)° for (2) and 9.45(1)° for (3). The means
derivations from planarity for the pyrazoline and thiophene
˚
rings are 0.0225 and 0.0055 A for (2) and 0.0512 and
˚
0.0074 A for (3), respectively.
Table 3 Intramolecular hydrogen-bond parameters (A, °) for com-
pounds (1) and (3)
D–HÁÁÁA
d (D–H) d (HÁÁÁA) d (DÁÁÁA) \(DHA)
(1) O1–H1ÁÁÁS2
(3) O2–H2ÁÁÁO1
0.82
2.55
2.65
1.97
3.145
3.129
2.754
130.8
119.8
158.9
0.82
O2–H2ÁÁÁO1i 0.82
Crystal Structures of (4) and (6)
Symmetry code: (i) -x ? 3/2, -y ?1/2, –z
The ORTEP plots of (4) and (6) are shown in Figs. 4 and 5
and all relevant crystallographic information is given in
Table 1, while bond lengths and angles are summarized in
Table 2. The crystallographic data showed that (4) crys-
tallizes into a monoclinic lattice and (6) into an ortho-
rhombic one. The substitution of the methyl group in (6) by
the phenyl group in (4) leads to modifications in the crystal
packing of the molecules in each case (see Table 1). As
observed in 5-hydroxy-4,5-dihydropyrazoline derivatives
[(1), (2)], the pyrazole ring bond lengths of C9–C11 =
1.409(3), C11–C12 = 1.344(3), C12–N1 = 1.386(3),
orthorhombic crystal system and exhibits an intramolecular
˚
hydrogen bonding O1–H1ÁÁÁS2 = 2.55 A (Table 3), which
helps in stabilizing the crystal structure. The N2–C9 =
˚
1.284(7) A double bond length and the C9–C11 = 1.482(7),
C11–C12 = 1.540(7), N1–C12 = 1.501(6) and N1–N2 =
˚
1.407(6) A single bond lengths are very close to those
found in pyrazoline derivatives [(2), (3)] (Table 2). The
˚
S2–C8 = 1.727(5) and S1–C8 = 1.679(5) A bond lengths
indicate, respectively, single and double-bond nature. As
expected, the bond angles of O1–C12–C13 = 113.5(4)°,
C11–C12–N1 = 99.7(4)°, O1–C12–C11 = 109.8(4)° and
C13–C12–N1 = 110.4(4)° indicate that the C12 asymmetric
center is sp3 hybridized. The structure of (1) shows that each
ring is nearly planar, with the mean deviations from planarity
´
˚
N1–N2 = 1.384(2) and N2–C9 = 1.311(3) A, found in 4-
phenyl-2,4-butanedione derivative (4), are slightly longer
than the compared lengths observed in 2,4-pentanedione
derivative (6) (Table 2). However, these bond lengths are
shorter than the equivalent bond lengths found in pyrazoline
(1), due to its aromatization, with water elimination,
˚
forming (4). The bond lengths of N1–C8 = 1.393(3) A
observed in (4) is longer than the similar bond lengths of
˚
being 0.0227 and 0.0075 A for the pyrazoline and 5-phenyl
rings, respectively. The rings, however, are twisted with
respect to each other. The angle between the mean planes of
the rings is 87.6(2)°.
˚
N1–C8 = 1.353(3) A found in (1) indicating some degree
Crystal Structures of (2) and (3)
of overlap between the N1 lone pair of electrons and the
p-system of C=S bond, as expected. The bond angles of
C11–C12–C13 = 127.4(2)° and N1–C12–C13 = 127.0(2)°
observed in (4) are considerably larger than the equivalent
bond angles of C11–C12–C13 = 111.7(4)° and N1–C12–
C13 = 110.4(4)° found in (1), indicating rehybridization of
C11 and C12 atoms from sp3 to sp2 with water elimination
from (1). The bond lengths and the angles observed for (6)
are very close to those found for (4), so it is unnecessary to
compare one with the other (Table 2).
The ORTEP plots of (2) and (3) are illustrated in Figs. 2
and 3, respectively, and all relevant crystallographic
information is given in Table 1, while bond lengths and
angles are summarized in Table 2. The crystallographic
data showed that both compounds crystallize into a
monoclinic lattice and the molecules are formed as five-
membered diazo ring corresponding to non-aromatic
5-hydroxy-4,5-dihydropyrazoline derivatives. In (3), an
˚
intramolecular hydrogen bond O2–H2ÁÁÁO1 = 2.65 A
(Table 3) stabilizes the conformation of the molecule about
the C9–N1, N1–C5 and C5–C4 single bonds. The five
cyclic N1–N2 = 1.397(2), N2–C6 = 1.282(3), C6–C8 =
Infrared Spectroscopy
The IR spectra of the pyrazoline [(2), (3)] and pyrazole
[(4), (5), (6)] derivatives are consistent with the formation
of hydrazones but are not useful for distinguishing the
tautomers (A), (B), (C), and (D) [3]. However, this tech-
nique is important to distinguish between pyrazoline and
pyrazole derivatives. The IR spectra of (1), (2) and (3)
show broad bands in the 3411–3356 cm-1 range, attributed
to m(O–H) stretching vibrations. Strong bands at 1610,
1600 and 1681 cm-1 found in the spectra of (2), (3) and
(5), respectively, are assigned to acyl m(C=O) absorptions.
The highest absorption, at 1681 cm-1, observed in (5), is
´
˚
1.494(3), C8–C9 = 1.542(2) and C9–N1 = 1.487(2) A
bond lengths found in 4-phenyl-2,4-butanedione derivative
(2) are slightly longer than the compared distances observed
in 2,4-pentanedione derivative (3) (Table 2). This obser-
vation may be attributed to the fact that the phenyl group is
a more electron-withdrawing group than the methyl group.
A similar effect was also observed in the structures of (4)
and (6) pirazole derivatives (Table 2). In both compounds
(2) and (3), the angles around the C9 asymmetric center are
in the range of 99.5(3)°–113.64(15)°, indicating a sp3
123

J Chem Crystallogr (2011) 41:401–408
407
consistent with overlap reduction between the N1 lone pair
of electrons and the p-system of C=O bond due to the
aromatic nature of the pyrazole ring. On the other hand, the
intramolecular hydrogen bonding (C=OÁÁÁH–O), observed
in (3) contributes to lengthen the C=O bond and conse-
quently shifts the m(C=O) absorption to lower frequencies.
The azomethine m(C=N) stretching mode overlapping with
other possible absorptions appears as a strong band in the
region around 1630 cm-1 in the spectra of (1), (2) and (3),
whereas this same stretching mode appears at about
1575 cm-1 in the spectra of (4), (5) and (6), indicating that
these compounds are aromatic. The m(C=S) absorptions
observed for (4) and (6) appear at higher frequencies
compared to (1) and corroborate with the reduction of
overlap between the N1 lone pair of electrons after aro-
matization takes place.
two doublets due to geminal coupling (2JHH = 13.2 Hz).
The signal of the –OH group appear as a broad singlet at 6.47,
5.29 and at 6.51 ppm in (1), (2) and (3), respectively. The
dissolution of compound (1) in DMSO-d6, which is a basic
dipolar solvent, results in the appearing of a yellow solution,
indicating that its pyrazoline (form D) may be transformed
into possible linear tautomers (A), (B), (C) or pyrazole form
(E). Concerning this, only signals of pyrazoline, form (D),
are observed in the spectrum of (1), obtained from CDCl3,
showing that the proportion of its linear tautomer (A or C)
[10], in DMSO-d6 solution, is less than 3%. Indeed, this is
1
observed for other molecules [10, 11]. The H NMR spec-
trum in CDCl3 solution at room temperature shows that the
5-hydroxypyrazoline (3) derivative quickly suffers aroma-
ticity, implying in water elimination, forming the conden-
sation product 1-(2-thyophenecarboxylic)-3,5-dimethylpyr-
1
azole. In the H NMR spectrum of (3) there are signals of
(1H, 13C) NMR Spectroscopy
non-equivalent 3CH2 methylene hydrogens at 2.99 ppm and
3CH aromatic hydrogen at 6.06 ppm due to the presence of 5-
hydroxypyrazoline (D form) and pyrazole (E form),
respectively. The (D)/(E) ratio is approximately equal to 3:1.
On the other hand, this same compound in DMSO-d6 solu-
tion exists exclusively as in the solid state, i.e., 5-hydrox-
ypyrazoline (form D). The D form is probably stabilized by
the formation of an intramolecular hydrogen bond between
OH group and molecules of the solvent.
1
The H NMR spectra (Fig. 6 for atom numbering) of the
pyrazoline derivatives (1), (2) and (3) measured in CDCl3
show that they exist exclusively in the cyclic tautomeric form
1
(D). The signal of the terminal CH3 appears at 2.09 ppm
for (1), at 2.15 ppm for (2) and at 1.85 ppm for (3), whereas
the magnetically and chemically nonequivalent 3CH2
methylene hydrogens appear as two doublets at 3.21 ppm
(2JHH = 18.8 Hz) for (1), 3.23 ppm (2JHH = 18.0 Hz) for
(2) and at 2.99 ppm (2JHH = 18.0 Hz) for (3). The spectrum
of (1) also showed 10CH2 methylene signal at 4.35 ppm as
According to the 13C NMR spectroscopy, compounds
(1), (2) (prepared from 4-phenyl-2,4-butanedione) and (3)
(synthesized from 2,4-pentanedione) have structures
7
7
5
8
6
8
6
5
3
1
H3C
1
CH3
3
1
3
4
2
5
CH3
CH3
2
4
2
4
HO
N
N
HO
HO
N
N
N
N
C 9
10
C9
S
C9
12
O
11
10
S
S
13
14
O
13
10
S
13
11
11
12
12
(1)
(2)
(3)
CH3
CH3
H3C
CH3
N
C
N
S
N
N
N
C
N
C
S
S
O
S
S
(4)
(5)
(6)
Fig. 6 Structural formulas of the 5-hydroxypyrazoline [(1), (2), (3)] forms and pyrazole [(4), (5), (6)] derivatives synthesized in this work and
numbering scheme for NMR assignments
123

408
J Chem Crystallogr (2011) 41:401–408
corresponding the 5-hydroxypyrazoline (D form). Their
3
spectra showed singlet arising from C atoms at 54.6, 53.5
697461 (1), 697618 (2), 697462 (3), 697619 (4), 697463
(6). Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge
CB21EZ, United Kingdom; Fax: ?44 1223 336033 or e-
mail: deposit@ccdc.cam.ac.uk.
4
and 50.8 ppm, whereas the asymmetrical C atom signals
were observed at 97.3, 94.5 and 92.7 ppm for (1), (2) and
(3), respectively. The X-ray diffraction study of compound
(3) showed conclusively that this derivative has the
5-hydroxypyrazoline structure in the solid state. It is
noteworthy to mention that the reactions of carbonylhyd-
razides with 2,4-pentanedione can be used as routes for the
synthesis of the corresponding 5-hydroxypyrazoline form.
Some authors [5] have postulated, however, that it is
difficult to isolate stable compounds like this from
2,4-pentanedione. The 13C NMR spectra of (4), (5) and (6)
Acknowledgments This work was sponsored by Grants from
CNPq, FAPESP, FINEP (CT-INFRA 0970/01). GFS also gratefully
acknowledges the financial support of the Conselho Nacional de
´
Desenvolvimento Cientıfico e Tecnologico-CNPq (Edital Universal-
2007, Processo 307412/2008-3).
´
References
3
4
showed peaks of C and C atoms in the aromatic region
(108–152 ppm), obviously due to the formation of pyrazole
derivatives with water elimination from the 5-hydroxypy-
razoline form.
´
´
1. Evans IR, Howard JAK, Szecsenyi KM, Leovac VM, Jacimovic
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According to the reported results in this field, the presence
of a strong electron-withdrawing substituent at the 1- or
5-positions of the pyrazole ring is a very important condition
for preparing stable (5-hydroxypyrazoline) derivatives.
However, the preparation of the 5-hydroxypyrazoline
derivative (3) from 2,4-pentanedione contrasts with that.
Pyrazole instead of pyrazoline are obtained as main product
only under acidic conditions and it is noteworthy to mention
that the (3) pyrazoline derivative is the first compound pre-
pared from 2,4-pentanodione, which was crystallographi-
cally characterized.
8. Sheldrich GM (1997) SHELXS97, program for automatic solu-
¨
tion of crystal structures. University of Gottingen, Germany
9. Sheldrich GM (1997) SHELXL97, program for crystal structure
¨
refinement. University of Gottingen, Germany
10. Zelenin KN, Alekseyev VV, Kuzneysova OB, Saminskaya AG,
Yakimovich SI, Zerova LV (1999) Russ J Org Chem 35:357
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51:11256
Supporting Information Available
Crystallographic data for the structural analysis of the
compounds have been deposited at the Cambridge Crys-
tallographic Data Center (CCDC). The CCDC numbers are
123