One-pot syntheses of 2-pyrazoline derivatives

Article abstract of DOI:10.1016/S0040-4020(03)00338-7

Hydrazinediium dithiocyanate and α,β-unsaturated ketones give in one-pot reactions 1-thiocarbamoyl-2-pyrazolines and 1-formyl-2-pyrazolines. The syntheses of pyridine-2-thiones, pyrimidine-2-thiones and bicyclo[2.2.2]octan-2-ones from ammonium thiocyanates and ketones by analogous procedures are reviewed. The mechanisms of the ring formations are discussed. Crystal structure analyses of a 1-thiocarbamoyl- and a 1-formyl-2-pyrazoline are given.

Full text of DOI:10.1016/S0040-4020(03)00338-7

Tetrahedron 59 (2003) 2811–2819
One-pot syntheses of 2-pyrazoline derivatives
b
c
d
e
Werner Seebacher,a Gunther Michl, Ferdinand Belaj, Reto Brun, Robert Saf
,
*
¨
and Robert Weisa
,
*
aInstitute of Pharmaceutical Chemistry and Pharmaceutical Technology, Karl-Franzens-University,
¨
Universitatsplatz 1, A-8010 Graz, Austria
¨
b
Schering A.G., Mullerstrasse 170-178, D-13342 Berlin, Germany
¨
c
Institute of Chemistry, Karl-Franzens-University, Universitatsplatz 1, A-8010 Graz, Austria
dSwiss Tropical Institute, Socinstrasse 57, CH-4002 Basel, Switzerland
eInstitute of Chemical Technology of Organic Materials, Erzherzog-Johann University, Stremayrgasse 26/1, A-8010 Graz, Austria
Received 6 November 2002; revised 6 February 2003; accepted 4 March 2003
Abstract—Hydrazinediium dithiocyanate and a,b-unsaturated ketones give in one-pot reactions 1-thiocarbamoyl-2-pyrazolines and
1-formyl-2-pyrazolines. The syntheses of pyridine-2-thiones, pyrimidine-2-thiones and bicyclo[2.2.2]octan-2-ones from ammonium
thiocyanates and ketones by analogous procedures are reviewed. The mechanisms of the ring formations are discussed. Crystal structure
analyses of a 1-thiocarbamoyl- and a 1-formyl-2-pyrazoline are given. q 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
ever, ammonia or methylamine are added preferably to the
isothiocyanato group of 8 giving thioureas 12 which cyclize
to the pyrimidine-2(1H)-thiones 4.9
Ammonium thiocyanates and a,b-unsaturated ketones have
already been cyclized to products having pyridine-2-thione,
pyrimidine-2-thione or bicyclo[2.2.2]octan-2-one structure.
This paper reports the reaction of a,b-unsaturated ketones
with hydrazinediium dithiocyanate giving 1-thiocarbamoyl-
or 1-formyl-2-pyrazolines depending on the structure of the
ketone.
The reaction between benzylidene acetone (1c) and
dialkylammonium rhodanides 7 proceeds in a completely
different way. Most likely the formation of enamines 10
becomes the first step followed by a Diels-Alder addition
of unchanged 1c giving 4-acetylcyclohex-1-en-1-ylammo-
niumsalts 11. Those cyclize to the bicyclo[2.2.2]octan-2-
1
ones 3 (Scheme 2). In H NMR spectra, the discrimination
between the two similar chains (C-5/C-6 and C-7/C-8) was
achieved by the correlation of NOE spectra and w-couplings
as reported in Ref. 3.
2. Results and discussion
The reaction of the b-alkyl ketones 1a,b with dialkyl-
ammonium thiocyanates gives the 4-dialkylamino-5,6-di-
hydropyridinethiones 2a–c.1,2 However, from the corre-
sponding b-phenylketone 1c the bicyclo[2.2.2]octan-2-ones
3a–d have been formed under the same reaction con-
ditions.3,4 The dihydropyrimidine-2-thiones 4a–d5–8 were
yielded upon heating of alkylammonium or ammonium thio-
cyanates with a,b-unsaturated ketones 1a,c,d (Scheme 1).
But no formation of bicyclo-octanone was observed, when
1c was treated with diethylammonium thiocyanate 7e.
Surprisingly we were able to isolate a small amount of the
dihydropyridine-2(1H)-thione 2d from the reaction mixture
by means of column chromatography. This indicates that the
above cyclizations are competitive reactions. Accordingly
the structure of the ketone only favours the formation of a
certain cyclic product but does not rule out the generation of
another.
The following mechanisms (Scheme 2) have been proposed
for the above-mentioned reactions. When the thiocyanate
ion is added in b-position of the b-alkyl ketones 1a,b,d
isothiocyanates 8 are formed. The latter react with
secondary amines giving enamines 9 which cyclize to the
dihydropyridine-2(1H)-thiones 2 in good yields.1,2 How-
We refluxed a,b-unsaturated ketones with hydrazinediium
dithiocyanate. Recently, we reported the formation of 1,2,4-
triazepine-3-thiones from a,b-unsaturated ketones 1c,e–h
and hydrazinediium dithiocyanate 13.10 Their structural
elucidation was based on the comparison of the chemical
shifts in their 13C NMR spectra with reported data of
formerly prepared 1,2,4-triazepine-3-thiones.11 With the aid
of a single crystal structure analysis we found out recently
Keywords: a,b-unsaturated ketones; cyclization; hydrazinediium
dithiocyanate; pyrazolines.
*
Corresponding authors. Tel.: þ433163805379; fax: þ433163809846;
e-mail: robert.weis@uni-graz.at
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00338-7

2812
W. Seebacher et al. / Tetrahedron 59 (2003) 2811–2819
Scheme 1.
that these products are not 1,2,4-triazepine-3-thiones but
1-thiocarbamoyl-2-pyrazolines 5a–e which have the same
elemental composition. We assume the following reaction
mechanism for the pyrazoline formation: first the imines 14
are formed which cyclize to the pyrazolines 15. The latter
are added to the thiocyanato group giving 1-thiocarbamoyl-
2-pyrazolines 5a–e (Scheme 2).
Figure 1, two molecules of 5b are held together by two
˚
N–H· · ·S hydrogen bonds [N· · ·S 3.355(3) A, N–H· · ·S
169(4)8]. The 2-pyrazoline ring adopts an envelope
˚
conformation [C5 has a deviation of 0.231(16) A from the
least-squares plane through the atoms N1 to C4]. The phenyl
ring bonded to C5 encloses an angle of 86.68(15)8 with the
least-squares plane of the 2-pyrazoline ring. The thio-
carbamoyl group is almost co-planar to the bond N1–N2
[N7–C7–N1–N2¼22.1(4)8].
2.1. X-Ray crystal structure of 5b
The crystal structure analysis of 5b established the
compound as a 2-pyrazoline derivative. A search in the
Cambridge Structural Database12 resulted in no structural
data for 1-thiocarbamoyl-2-pyrazolines. As shown in
Because substances with thiosemicarbazide partial structure
have been reported to exhibit antimalarial14 as well as anti-
mycobacterial15 activities the 1-thiocarbamoyl-2-pyrazoline
5a has been screened for its activity against causative

W. Seebacher et al. / Tetrahedron 59 (2003) 2811–2819
2813
Scheme 2.

2814
W. Seebacher et al. / Tetrahedron 59 (2003) 2811–2819
Figure 1. Stereoscopic ORTEP13 plot of two molecules of 5b showing the atomic numbering scheme. The probability ellipsoids are drawn at the 50%
probability level.
organisms of tropical diseases including Plasmodium
falciparum K1, Trypanosoma cruzi and Trypanosoma b.
rhodesiense. However, 5a which has formerly been
prepared in a two-step procedure16 showed no antiprotozoal
activity (Table 1).
revealing the formation of products 5 and 6 as competitive
reactions.
The substitution of N-1 of the 2-pyrazolines 5 and 6 was
established by long-range couplings. Crosspeaks from 5-H
to CvS were observed in the HMBC spectra of compounds
5. The formyl protons of compounds 6 resonating at 9 ppm
When the chalcone derivatives 1i–l were heated with
hydrazinediium dithiocyanate 13 high amounts of the
1-formyl-2-pyrazolines 6a–d were formed. The formyl-
ation of the pyrazoline intermediates 15 proceeds via a
transamidation reaction of DMF which was used as solvent.
in their 1H NMR spectra show correlations to C-5. In the 13
C
NMR spectra of 5 the signals for the formyl carbons
typically appear at 160 ppm, whereas the CvS carbons of
compounds 5 resonate at 176 ppm. The signals for the C-3
carbons of the 2-pyrazolines 5 and 6 were observed at ca.
157 ppm. The structures of compounds 6a–d were
established by a single crystal structure analysis.
Both pyrazoline derivatives 5a and 6a were formed by
the reaction of the 1-unsubstituted pyrazolines 15 with
hydrazinediium dithiocyanate 13 under the same conditions
verifying the reaction mechanisms.
2.2. X-Ray crystal structure of 6a
With the aid of 1H NMR spectroscopy 1-formyl and 1-thio-
carbamoyl pyrazolines were detected in all mother liquors
The molecular structure and labelling scheme of 6a are
shown in Figure 2. The 2-pyrazoline ring is almost planar
Table 1. Antiprotozoal activities of compound 5a, expressed as IC50 (mg/ml)
Compound
P. falciparum K1
T.b.rhodesiense
T. cruci
Cytotoxicity. L6
5a
Standarda
.5000
0.0018
9.36
0.000849
49.0
1.25
.90.0
4.3
Values represent the average of four determinations (two determinations of two independent experiments).
a
Substances used as standard are mentioned in Section 4.

W. Seebacher et al. / Tetrahedron 59 (2003) 2811–2819
2815
Figure 2. Stereoscopic ORTEP13 plot of 6a showing the atomic numbering scheme. The probability ellipsoids are drawn at the 50% probability level.
[the max. deviation from the least-squares plane is
˚
0.055(9) A] and the phenyl ring bonded to C3 is almost
not active against Plasmodium falciparum K1, Trypanosoma
cruzi and Trypanosoma b. rhodesiense.
co-planar to it [5.06(13)8] whereas the phenyl ring bonded to
C5 encloses an angle of 77.67(13)8 with the least-squares
plane of the 2-pyrazoline ring. The carboxaldehyde group is
trans oriented to N2 [O11–C11–N1–N2¼2178.5(2)8] as
observed in all the other crystal structure determinations of
1-carbonyl-2-pyrazolines found in the Cambridge Structural
Database.12
4. Experimental
4.1. General
Melting points were obtained on a digital melting point
apparatus Electrothermal IA 9200 and are uncorrected.
IR spectra: infrared spectrometer system 2000 FT (Perkin–
Elmer). UV/VIS: Lambda 17 UV/VIS-spectrometer
(Perkin–Elmer). NMR spectra: Varian Inova 400 (300 K)
Substances 6a and 6d have already been prepared from
the corresponding pyrazoline with formic acid.17,18 The
2-hydroxyphenyl analogue 6e of compound 6a showed the
highest antifungal activity in an assay against Alternaria
alternata, Macrophomina phaseoli, Colletotrichum
falcatum and Fusarium oxysporum.19
1
5 mm tubes, TMS resonance as internal standard. H- and
1
1
13C-resonances were assigned using H,1H- and H,13C-
correlation spectra. HMBC spectra were optimized for 8 Hz.
For NOE measurements oxygen was carefully removed by
1
bubbling Ar through the solutions. H- and 13C-resonances
3. Conclusion
are numbered as given in the formulae. Assignments
marked with an asterisk are interchangeable. MS: Varian
MAT 711 spectrometer 70 eV electron impact, Kratos
profile spectrometer 70 eV electron impact, Micromass
Tofspec (MALDI). Microanalyses: EA 1108 CHNS-O
apparatus (Carlo Erba), Microanalytical Laboratory at the
Institute of Physical Chemistry, Vienna. Materials: Column-
chromatography (CC): silica gel 60 (Merck, 70–230 mesh),
When a,b-unsaturated ketones are cyclized with
ammonium thiocyanates or hydrazinediium dithiocyanates
the mainly formed product is predictable from the struc-
tures of both reactants. Reactions with alkylammonium or
ammonium thiocyanates give dihydropyrimidine-2-thiones.
Dialkylammonium thiocyanates and b-alkyl substituted
a,b-unsaturated ketones afford dihydropyridine-2-thiones
whereas bicyclo[2.2.2]octan-2-ones are obtained from their
b-phenyl analogues.
˚
pore-diameter 60 A, thin-layer chromatography (TLC):
TLC plates (Merck, silica gel 60 F254, 0.2 mm, 200£
200 mm2); the substances were detected in UV light at
254 nm.
Hydrazinediium dithiocyanates and b-aryl substituted
a,b-unsaturated ketones give 2-pyrazoline derivatives.
From methylketones 1-thiocarbamoyl-2-pyrazolines are
formed in moderate yields. However, phenylketones give
1-formyl-2-pyrazolines in good yields. The 1-thiocarba-
moyl-2-pyrazoline 5a was investigated for its activity
against causative organisms of tropical deseases. 5a was
General procedure for the synthesis of thiocyanates 7d,e
and 13. Equivalent amounts of the amino component and
ammonium thiocyanate were dissolved in the required
volume of water and stirred for 1 h at room temperature.
The solvent was evaporated and the residue was triturated

2816
W. Seebacher et al. / Tetrahedron 59 (2003) 2811–2819
with ethanol or benzene, filtered with suction and dried over
phosphorus pentaoxide.
6.69, S 7.66; found: C 74.45, H 7.43, N 6.77, S 7.44; HRMS
(MALDI) calcd (C25H29NO): 359.2249; found: 359.2251.
4.1.1. (RS-(6)-4-Diethylamino-5,6-dihydro-6-phenyl-
pyridine-2(1H)-thione (2d). 82 g (0.56 mol) Benzylidene
acetone 1c and 37.1 g (0.28 mol) diethylammonium thio-
cyanate 7e were suspended in 110 ml of dimethylformamide
and refluxed for 4 h at 1508C at a water separator. After
cooling to room temperature, the solvent was removed in
vacuo and the residue purified by means of CC using a
mixture of toluene/chloroform/ethanol (4:4:1) as eluent.
The solvent of the fraction containing the product was
removed in vacuo and the residue triturated with ethanol.
The solid was filtered off and recrystallized from ethanol,
giving 100 mg of 2c as yellow crystals. Mp: 1538C
4.1.3. 5-Aryl-3-methyl-1-thiocarbamoyl-2-pyrazolines
(5) and 3-aryl-1-formyl-5-phenyl-2-pyrazolines (6).
General procedure. Hydrazinediium dithiocyanate 13 and
the a,b unsaturated ketones 1c, 1e–l were dissolved in
dimethyl formamide and refluxed at a water separator for
4 h. The solvent was evaporated in vacuo and the residue
triturated with ethanol. Products 6a–d crystallized over
night, were filtered and recrystallized from ethanol. Only a
part of compounds 5a–e crystallized. The solid was treated
with charcoal in ethanol, filtered and crystallized twice from
ethanol. The filtrate has to be purified by CC over silica gel
(eluent: CH2Cl2 for 5a and CH2Cl2/MeOH (20:1) for 5b–e).
(ethanol); IR (KBr): n¼3179 (m), 2973 (w), 1563 (s),
~
1521 (s), 1491 (w), 1473 (m), 1424 (m), 1414 (m), 1362 (m),
1336 (w), 1141 (s), 1079 (m), 1057 (m), 705 (w) cm21; UV
4.1.4. (RS)-(6)-3-Methyl-5-phenyl-1-thiocarbamoyl-2-
pyrazoline (5a). 12.7 g (84.5 mmol) Hydrazinediium
dithiocyanate (13) and 14 g (95.8 mmol) benzylidene
acetone (1c) in 200 ml of dimethylformamide gave yellow-
ish plates. Yield: 5.0 g (27.0%); mp: 2378C (ethanol);
1
(CH2Cl2): l (log 1)¼346 (4.602) nm; H NMR (CDCl3, d,
400 MHz): 1.67 (t, J¼7.0 Hz, 6H, (CH3CH2)2), 2.59–2.71
(m, 2H, 5-H), 3.24–3.33 (m, 4H, (NCH2)2), 4.65 (dd,
J¼12.3, 6.0 Hz, 1H, 6-H), 5.72 (s, 1H, 3-H), 6.72 (s, 1H,
NH), 7.29–7.41 (m, 5H, aromatic H) ppm; 13C NMR
(CDCl3, d, 100 MHz): 12.91 ((CH3CH2)2), 33.66 (C-5),
44.35 (N(CH2)2), 57.27 (C-6), 97.64 (C-3), 126.72, 128.64,
128.99 (aromatic C), 139.79 (aromatic Cq), 152.50 (C-4),
191.70 (C-2) ppm; MS (EIþ): m/z (%)¼260 (100.0) [Mþ],
227 (17.8), 188 (14.0), 154 (7.8), 124 (8.5), 100 (8.5), 83
(9.3), 70 (8.9). Anal. calcd for C15H20N2Sþ0.125H2O
(262.65): C 68.59, H 7.77, N 10.67, S 12.21; found: C 68.52,
H 7.78, N 10.77, S 12.03; HRMS (MALDI) calcd
(C15H20N2S): 260.1347; found: 260.1348.
IR (KBr): n¼3397 (s), 3252 (s), 3149 (s), 1592 (s), 1498 (s),
~
1421 (m), 1380 (s), 1364 (s), 1326 (m), 828 (m), 756 (m),
699 (s) cm21; UV (CH2Cl2): l (log 1)¼276 (4.235), 235
1
(3.890) nm; H NMR (400 MHz, d, CDCl3): 2.07 (s, 3H,
CH3), 2.73 (dd, J¼18.3, 3.4 Hz, 1H, 4-H), 3.46 (dd, J¼18.3,
11.3 Hz, 1H, 4-H), 5.87 (dd, J¼11.3, 3.4 Hz, 1H, 5-H), 5.95
(br, s, 1H, NH), 6.87 (br, s, 1H, NH), 7.15–7.35 (m, 5H,
aromatic H) ppm; 13C NMR (100 MHz, d, CDCl3): 16.14
(CH3), 47.09 (C-4), 63.08 (C-5), 125.21, 127.48, 128.84
(aromatic C), 141.80 (aromatic Cq), 158.11 (C-3), 176.40
(CSNH2) ppm; MS (EIþ): m/z (%)¼220 (12.9) [MþHþ],
219 (93.9) [Mþ], 186 (39.3), 178 (41.0), 177 (65.1), 163
(39.3), 159 (33.6), 145 (21.3), 137 (61.0), 119 (19.0), 115
(16.6), 104 (90.2), 103 (100.0), 91 (24.7), 83 (60.3), 77
(43.1), 69 (13.6), 65 (11.5), 60 (34.6), 56 (14.2), 51 (23.7),
42 (29.5). Anal. calcd for C11H13N3S (219.31): C 60.24, H
5.97, N 19.16, S 14.62; found: C 59.96, H 6.03, N 19.14, S
14.02.
4.1.2. (6RS,7RS)-(6)-6,7-Diphenyl-4-piperidinobicyclo-
[2.2.2]octan-2-one3HNCS (3d). 67.4 g (0.46 mol) Benzyl-
idene acetone 1c and 39.0 g (0.27 mol) piperidinium
thiocyanate 7d were suspended in 250 ml of dimethyl-
formamide and refluxed for 4 h at 2208C at a water
separator. After cooling to room temperature, the solvent
was removed in vacuo and the residue crystallized from
ethanol over night. After recrystallization from ethanol,
15.9 g (16.7%) of 3d were obtained as beige crystals. Mp:
4.1.5. (RS)-(6)-5-(4-Methoxyphenyl)-3-methyl-1-thio-
carbamoyl-2-pyrazoline (5b). 7.6 g (50 mmol) Hydrazine-
diium dithiocyanate (13) and 14 g (50 mmol) 4-methoxy-
benzylidene acetone (1e) in 80 ml of dimethylformamide
gave yellowish prisms. Yield: 4.9 g (40%); mp: 1828C
2648C (ethanol); IR (KBr): n¼2958 (s), 2877 (m), 2601 (w),
~
2444 (s), 1725 (s), 1497 (s), 1452 (m), 1361 (m), 1330 (m),
755 (s), 698 (s) cm21; UV (CH3OH): l (log 1)¼212
1
(4.005) nm; H NMR (DMSO-d6, d, 400 MHz): 1.40–1.54
(ethanol); IR (KBr): n¼3419 (s), 3254 (s), 3149 (s), 1596
~
(m, 1H, CH2), 1.64–1.80 (m, 3H, CH2, (CH2)2), 1.82–1.96
(m, 3H, 8-H, (CH2)2), 2.35 (dd, J¼12.5, 9.3 Hz, 1H, 5-H),
2.53 (s, 1H, 1-H), 2.57 (ddd, J¼12.5, 9.3, 2.3 Hz, 1H, 5-H),
2.80 (ddd, J¼13.7, 9.4, 3.3 Hz, 1H, 8-H), 2.83 (dd, J¼17.4,
2.2 Hz, 1H, 3-H), 3.01 (dd, J¼17.7, 3.2 Hz, 1H, 3-H), 2.90–
3.34 (m, 2H, N(CH2)2), 3.40 (t, J¼9.4 Hz, 1H, 7-H), 3.54 (t,
J¼9.3 Hz, 1H, 6-H), 3.64 (br, d, J¼10.2 Hz, 1H, N(CH2)2),
3.77 (br, d, J¼10.5 Hz, 1H, N(CH2)2), 7.08–7.49 (m, 10H,
aromatic H), 9.24 (br, s, 1H, NH) ppm; 13C NMR (DMSO-
d6, d, 100 MHz): 21.63 (CH2), 23.62 ((CH2)2), 29.60 (C-5),
34.35 (C-8), 34.58 (C-7), 36.41 (C-6), 43.46 (C-3), 47.50,
48.01 (N(CH2)2), 53.61 (C-1), 64.40 (C-4), 126.95, 127.18,
127.76, 128.83, 128.94 (aromatic C), 140.39, 142.91
(aromatic Cq), 207.83 (C-2) ppm; MS (base, EIþ): m/z
(%)¼359 (100.0) [Mþ], 316 (11.6), 268 (24.8), 255 (66.7),
227 (36.4), 213 (23.3), 178 (12.0), 136 (14.0), 91 (10.9).
Anal. calcd for C26H30N2OS (418.60): C 74.60, H 7.22, N
(s), 1514 (s), 1491 (s), 1455 (m), 1385 (s), 1361 (s), 1324
(m), 1252 (s), 1184 (s), 1034 (s), 823 (s) cm21; UV
(CH2Cl2): l (log 1)¼273 (4.257), 235 (4.065) nm; 1H NMR
(400 MHz, d, DMSO-d6): 2.02 (s, 3H, CH3), 2.60 (dd,
J¼18.3, 3.1 Hz, 1H, 4-H), 3.50 (dd, J¼18.4, 11.4 Hz, 1H,
4-H), 3.72 (s, 3H, OCH3), 5.68 (dd, J¼11.3, 3.3 Hz, 1H,
5-H), 6.86 (d, J¼8.7 Hz, 2H, m-aromatic H), 7.02 (d, J¼
8.7 Hz, 2H, o-aromatic H), 7.37 (br, s, 1H, NH), 7.70 (br, s,
1H, NH) ppm; 13C NMR (100 MHz, d, DMSO-d6): 15.96
(CH3), 46.59 (C-4), 55.22 (OCH3), 61.93 (C-5), 113.88
(m-aromatic C), 126.80 (o-aromatic C), 135.33 (aromatic
Cq), 158.27 (p-aromatic C), 158.55 (C-3), 175.75 (CSNH2)
ppm; MS (EIþ): m/z (%)¼250 (8.8) [MþHþ], 249 (54.1)
[Mþ], 233 (9.1), 216 (32.4), 207 (57.4), 193 (26.4), 189
(13.5), 175 (19.6), 167 (37.2), 166 (16.9), 149 (10.8), 135
(11.5), 134 (100.0), 133 (64.2), 119 (14.9), 91 (25.0), 77
(17.6), 75 (8.8), 65 (15.5), 60 (18.9), 42 (16.2). Anal. calcd

W. Seebacher et al. / Tetrahedron 59 (2003) 2811–2819
2817
for C12H15N3OS (249.34): C 57.81, H 6.06, N 16.85, S
12.86; found: C 57.71, H 6.10, N 16.89, S 12.38.
7.77 (br, s, 1H, NH) ppm; 13C NMR (100 MHz, d, DMSO-
d6): 15.86 (CH3), 42.82 (C-4), 56.30 (C-5), 107.22 (C-30),
110.50 (C-40), 142.02 (C-50), 153.46 (C-20), 158.52 (C-3),
175.80 (CSNH2) ppm; MS (EIþ): m/z (%)¼210 (13.5)
[MþHþ], 209 (100.0) [Mþ], 192 (10.1), 180 (27.0), 176
(10.8), 168 (56.8), 167 (16.9), 153 (35.8), 151 (15.5), 140
(26.4), 139 (12.1), 135 (10.1), 126 (13.5), 121 (28.4), 114
(64.9), 97 (13.5), 94 (82.4), 91 (25.0), 83 (22.3), 81 (65.5),
77 (19.6), 69 (30.4), 65 (48.0), 60 (55.4), 53 (25.0), 51
(18.9), 42 (39.2). Anal. calcd for C9H11N3OS (209.27): C
51.66, H 5.30, N 20.08, S 15.32; found: C 51.64, H 5.33, N
20.04, S 15.18.
X-Ray diffraction data of 5b. All the measurements were
performed using graphite-monochromatized Mo Ka radia-
tion at 97 K: C12H15N3OS, Mr 249.33, monoclinic, space
˚
˚
group P21=c; a¼6.264(2) A, b¼15.212(3) A, c¼
3
˚
˚
12.990(4) A, b¼95.06(2)8, V¼1233.0(6) A , Z¼4, dcalc
¼
1.343 g cm23, m¼0.250 mm21. A total of 3109 reflections
were collected (Qmax¼268), from which 2428 were unique
(Rint¼0.0443), with 1685 having I.2s(I). The structure was
solved by direct methods (SHELXS-97)20 and refined by
full-matrix least-squares techniques against F 2 (SHELXL-
97)21. The non-hydrogen atoms were refined with aniso-
tropic displacement parameters without any constraints. The
H-atoms of the NH2 group were refined without any
positional constraints but with common isotropic displace-
ment parameters. The H atoms bonded to C atoms were
refined with common isotropic displacement parameters for
the H atoms bonded to the same C atom and with idealized
geometries of approximately tetrahedral angles. The C–H
4.1.8. (RS)-(6)-3-Methyl-5-(2-thienyl)-1-thiocarbamoyl-
2-pyrazoline (5e). 5.2 g (35 mmol) Hydrazinediium dithio-
cyanate (13) and 7 g (35 mmol) thenylidene acetone (1h) in
60 ml of dimethyl formamide gave yellow needles. Yield:
2.3 g (29%); mp: 2208C (ethanol); IR (KBr): n¼3389 (s),
~
3251 (s), 3150 (s), 1592 (s), 1494 (s), 1420 (m), 1367 (s),
1326 (m), 1305 (m), 1235 (w), 1222 (w), 1197 (w), 1072
(w), 825 (s), 705 (s), 634 (w), 570 (m) cm21; UV (CH2Cl2):
distances were fixed to 0.98, 0.99, 1.00, and 0.95 A for the
l
(log 1)¼279 (3.714), 237 (3.576) nm; 1H NMR
˚
methyl, secondary, tertiary, and phenyl H atoms, respec-
tively. For 167 parameters final R indices of R¼0.0514 and
wR 2¼0.1501 (GOF¼1.046) were obtained. The largest
(400 MHz, d, CDCl3): 2.11 (s, 3H, CH3), 2.90 (dd, J¼
18.2, 2.7 Hz, 1H, 4-H), 3.43 (dd, J¼18.2, 10.7 Hz, 1H, 4-H),
6.01 (br, s, 1H, NH), 6.19 (dd, J¼10.7, 2.7 Hz, 1H, 5-H),
6.81 (br, s, 1H, NH), 6.930(dd, J¼5.0, 3.7 Hz, 1H, 40-H),
7.02 (d, J¼3.5 Hz, 1H, 5 -Hp), 7.19 (d, J¼5.0 Hz, 1H,
30-Hp) ppm; 13C NMR (100 MHz, d, CDCl3): 16.15 (CH3),
46.77 (C-4), 58.82 (C-5), 1240.36 (C-30p), 124.74 (C-50p),
126.70 (C-40), 144.23 (C-2 ), 158.25 (C-3), 176.30
(CSNH2) ppm; MS (ESþ): m/z (%)¼226 (11.5) [MþHþ],
225 (77.7) [Mþ], 184 (20.2), 183 (38.5), 171 (10.1), 169
(100.0), 165 (18.9), 151 (36.5), 143 (14.9), 133 (12.2), 111
(11.5), 110 (79.7), 109 (73.6), 97 (21.6), 83 (18.2), 74
(10.1), 69 (23.6), 65 (13.5), 60 (29.7), 45 (21.6). Anal. calcd
for C9H11N3S2 (225.33): C 47.97, H 4.92, N 18.65, S 28.64;
found: C 48.10, H 4.95, N 18.44, S 28.50.
peak in a difference Fourier map was 0.348 e A23. The final
˚
atomic parameters, as well as bond lengths and angles are
deposited at the Cambridge Crystallographic Data Centre
(CCDC202863).
4.1.6. (RS)-(6)-5-(4-Dimethylaminophenyl)-3-methyl-1-
thiocarbamoyl-2-pyrazoline (5c). 1.6 g (11 mmol) Hydra-
zinediium dithiocyanate (13) and 2.0 g (11 mmol) 4-di-
methylaminobenzylidene acetone (1f) in 100 ml of dimethyl-
formamide gave white needles. Yield: 1.6 g (57%); mp:
2388C (ethanol); IR (KBr): n¼3427 (m), 3261 (m), 3153
~
(m), 1621 (m), 1592 (s), 1529 (s), 1488 (s), 1381 (m), 1363
(s), 810 (m) cm21
;
UV (CH2Cl2):
l
(log 1)¼266
1
(4.458) nm; H NMR (400 MHz, d, DMSO-d6): 2.02 (s,
3H, CH3), 2.58 (dd, J¼18.2, 3.1 Hz, 1H, 4-H), 2.85 (s, 6H,
(NCH3)2), 3.48 (dd, J¼18.2, 11.1 Hz, 1H, 4-H), 5.62 (dd,
J¼11.1, 3.1 Hz, 1H, 5-H), 6.64 (d, J¼8.7 Hz, 2H, m-aro-
matic H), 6.92 (d, J¼8.5 Hz, 2H, o-aromatic H), 7.31 (br, s,
1H, NH), 7.63 (br, s, 1H, NH) ppm; 13C NMR (100 MHz, d,
DMSO-d6): 16.00 (CH3), 40.42 (N(CH3)2), 46.58 (C-4),
62.00 (C-5), 112.50 (m-aromatic C), 126.37 (o-aromatic C),
130.93 (aromatic Cq), 149.64 (p-aromatic C), 158.59 (C-3),
175.65 (CSNH2) ppm. Anal. calcd for C13H18N4S (262.38):
C 59.51, H 6.92, N 21.35, S 12.22; found: C 59.50, H 6.98,
N 21.38, S 11.94.
4.1.9. (RS)-(6)-1-Formyl-3,5-diphenyl-2-pyrazoline (6a).
7.2 g (48 mmol) Hydrazinediium dithiocyanate (13) and
10 g (48 mmol) chalcone (1i) in 85 ml of dimethylforma-
mide gave 9.8 g (81%) of 6a. Mp: 1588C (ethanol), (mp20
1538C); IR (KBr): n¼1655 (s), 1594 (m), 1425 (m), 1379
~
(m), 1327 (m), 1139 (m), 763 (s), 695 (m) cm21; UV
(CH2Cl2): l (log 1)¼282 (4.319), 233 (3.824) nm; 1H NMR
(400 MHz, d, DMSO-d6): 3.20 (dd, J¼18.1, 4.8 Hz, 1H,
4-H), 3.92 (dd, J¼18.1, 11.6 Hz, 1H, 4-H), 5.54 (dd,
J¼12.0, 4.8 Hz, 1H, 5-H), 7.23–7.49 (m, 8H, aromatic H),
7.78–7.81 (m, 2H, aromatic H), 8.92 (s, 1H, HCvO) ppm;
13C NMR (100 MHz, d, DMSO-d6): 42.50 (C-4), 58.68
(C-5), 125.84, 126.88, 127.65, 128.90, 128.99, 130.71
(aromatic C), 130.90, 141.49 (aromatic Cq), 156.25 (C-3),
159.82 (HCvO) ppm; MS (ESþ): m/z (%)¼251 (19.6)
[MþHþ], 250 (100.0) [Mþ], 222 (16.2), 221 (40.5), 145
(82.4), 119 (35.5), 118 (14.9), 104 (59.1), 103 (14.9), 91
(26.3), 77 (36.5); HRMS (MALDI) calcd (C16H14N2O):
250.1106, found: 250.1127. Anal. calcd for (250.30); calcd:
C 76.78, H 5.64, N 11.19; found: C 76.34, H 5.58, N 11.34.
4.1.7. (RS)-(6)-5-Furyl-3-methyl-1-thiocarbamoyl-2-
pyrazoline (5d). 7.7 g (51 mmol) Hydrazinediium dithio-
cyanate (13) and 7 g (51 mmol) furfurylidene acetone (1g)
in 85 ml of dimethylformamide gave grey plates. Yield:
2.7 g (25%); mp: 220–2228C (ethanol); IR (KBr): n¼3406
~
(s), 3263 (s), 3153 (s), 1593 (s), 1489 (s), 1432 (w), 1368 (s),
815 (m), 763 (s) cm21; UV (CH2Cl2): l (log 1)¼269
1
(4.222), 236 (3.985) nm; H NMR (400 MHz, d, DMSO-
d6): 2.04 (s, 3H, CH3), 2.82 (dd, J¼18.1, 3.4 Hz, 1H, 4-H),
3.42 (dd, J¼18.1, 11.4 Hz, 1H, 4-H), 50.81 (dd, J¼11.4,
3.4 Hz, 1H, 5-H), 6.23 (d, J¼3.4 Hz, 1H, 3 -H), 6.37 (m, 1H,
40-H), 7.36 (br, s, 1H, NH), 7.53 (d, J¼0.8 Hz, 1H, 50-H),
X-Ray diffraction data of 6a. All the measurements were
performed using graphite-monochromatized Mo Ka radia-
tion at 90 K: C16H14N2O, Mr 250.29, monoclinic,
space group P21=c; a¼10.469(2) A, b¼16.227(4) A, c¼
˚
˚

2818
W. Seebacher et al. / Tetrahedron 59 (2003) 2811–2819
3
1
˚
˚
7.506(2) A, b¼97.38(2)8, V¼1264.6(5) A , Z¼4, dcalc
¼
(log 1)¼292 (4.308), 234 (3.946) nm; H NMR (400 MHz,
1.315 g cm23, m¼0.084 mm21. A total of 2966 reflections
were collected (Qmax¼258), from which 2221 were unique
(Rint¼0.0446), with 1638 having I.2s(I). The structure was
solved by direct methods (SHELXS-97)20 and refined by
full-matrix least-squares techniques against F 2 (SHELXL-
97).21 The non-hydrogen atoms were refined with aniso-
tropic displacement parameters. The H-atoms were included
at calculated positions with their isotropic displacement
parameters fixed to 1.2 times Ueq of the C atom they are
bonded to. The C–H distances were fixed to 0.99, 1.00, and
d, DMSO-d6): 3.17 (dd, J¼18.1, 4.8 Hz, 1H, 4-H), 3.81 (s,
3H, OCH3), 3.89 (dd, J¼17.9, 11.8 Hz, 1H, 4-H), 5.50 (dd,
J¼11.8, 4.6 Hz, 1H, 5-H), 7.02 (d, J¼8.9 Hz, 2H, aromatic
H), 7.21–7.37 (m, 5H, aromatic H), 7.74 (d, J¼8.9 Hz, 2H,
aromatic H), 8.87 (s, 1H, HCvO) ppm; 13C NMR
(100 MHz, d, DMSO-d6): 42.59 (C-4), 55.53 (OCH3),
58.51 (C-5), 114.43, 125.81, 127.60, 128.60, 128.89
(aromatic C), 123.39, 141.60, 161.27 (aromatic Cq),
155.99 (C-3), 159.55 (HCvO) ppm. Anal. calcd for
C17H16N2O2 (280.33): C 72.84, H 5.75, N 9.99; found: C
72.60, H 6.00, N 9.86.
˚
0.95 A for the secondary, tertiary, and phenyl hydrogen
atoms, respectively. For 174 parameters final R indices of
R¼0.0584 and wR 2¼0.1448 (GOF¼1.068) were
obtained. The largest peak in a difference Fourier map
was 0.258 e A23. The final atomic parameters, as well as
˚
4.2. Biology
IC50 values are given in Table 1.
bond lengths and angles are deposited at the Cambridge
Crystallographic Data Centre (CCDC192916).
Antimalarial activity of 5a. Antiplasmodial activity was
determined using the K1 strain of P. falciparum (resistant to
chloroquine and pyrimethamine). A modification of the
[3H]-hypoxanthine incorporation assay was used.23
Briefly, infected human red blood cells in RPMI 1640
medium with 5% Albumax were exposed to serial drug
dilutions in microtiter plates for 48 h. Viability was assessed
by measuring the incorporation of [3H]-hypoxanthine
by liquid scintillation counting 24 h after the addition of
the radiolabel. The counts were expressed as percentage
of the control cultures, sigmoidal inhibition curves were
drawn and IC50 values calculated. Standard was
artemisinine.
4.1.10. (RS)-(6)-3-(4-Chlorophenyl)-1-formyl-5-phenyl-
2-pyrazoline (6b). 5.6 g (37 mmol) Hydrazinediium dithio-
cyanate (13) and 9 g (37 mmol) 40-chlorochalcone (1j) in
100 ml of dimethylformamide gave 7.5 g (71%) of 6b. Mp:
1798C (ethanol); IR (KBr): n¼1652 (s), 1596 (m), 1426 (s),
~
1403 (m), 1356 (m), 1321 (m), 762 (m), 701 (m) cm21; UV
(CH2Cl2): l (log 1)¼290 (4.402), 233 (3.995) nm; 1H NMR
(400 MHz, d, DMSO-d6): 3.21 (dd, J¼18.3, 4.8 Hz, 1H,
4-H), 3.91 (dd, J¼18.3, 11.8 Hz, 1H, 4-H), 5.54 (dd, J¼
12.0, 4.8 Hz, 1H, 5-H), 7.22–7.37 (m, 5H, aromatic H), 7.54
(d, J¼8.5 Hz, 2H, aromatic H), 7.80 (d, J¼8.6 Hz,
2H, aromatic H), 8.91 (s, 1H, HCvO) ppm; 13C NMR
(100 MHz, d, DMSO-d6): 42.41 (C-4), 58.88 (C-5), 125.88,
127.59, 127.69, 128.63, 128.91, 129.08 (aromatic C),
129.81, 135.31, 141.37 (aromatic Cq), 155.31 (C-3),
159.90 (HCvO) ppm. Anal. calcd for C16H13N2OCl
(284.75): C 67.49, H 4.60, N 9.84, Cl 12.45; found: C
67.27, H 4.52, N 9.83, Cl 12.31.
Activity of 5a against Trypanosoma cruzi. Rat skeletal
myoblasts (L-6 cells) were seeded in 96-well microtiter
plates at 2000 cells/well/100 ml in RPMI 1640 medium with
10% FBS and 2 mM L-glutamine. After 24 hours 5000
trypomastigotes of T. cruzi (Tulahuen strain C2C4 contain-
ing the galactosidase (Lac Z) gene) were added in 100 ml
per well with 2£ of a serial drug dilution. The plates were
incubated at 378C in 5% CO2 for 4 days. After 96 h the
minimum inhibitory concentration (MIC) was determined
microscopically. For measurement of the IC50 the substrate
CPRG/Nonidet was added to the wells. The colour reaction
which developed during the following 2–4 h was read
photometrically at 540 nm. From the sigmoidal inhibition
curve IC50 values were calculated. Benznidazole was used
as standard.
4.1.11. (RS)-(6)-1-Formyl-3-(4-methylphenyl)-5-phenyl-
2-pyrazoline (6c). 5.6 g (37 mmol) Hydrazinediium dithio-
cyanate (13) and 7.7 g (35 mmol) 40-methylchalcone (1k) in
100 ml of dimethylformamide gave 6.5 g (70%) of 6c. Mp:
1688C (ethanol); IR (KBr): n¼1655 (s), 1597 (m), 1428 (s),
~
1360 (m), 1328 (m), 827 (m), 756 (m), 700 (m) cm21; UV
(CH2Cl2): l (log 1)¼287 (4.409), 232 (3.967) nm; 1H NMR
(400 MHz, d, DMSO-d6): 2.35 (s, 3H, CH3), 3.25 (dd,
J¼18.2, 4.8 Hz, 1H, 4-H), 3.90 (dd, J¼18.0, 11.8 Hz, 1H,
4-H), 5.52 (dd, J¼11.6, 4.8 Hz, 1H, 5-H), 7.21–7.37 (m,
7H, aromatic H), 7.68 (d, J¼8.4 Hz, 2H, aromatic H), 8.90
(s, 1H, HCvO) ppm; 13C NMR (100 MHz, d, DMSO-d6):
21.19 (CH3), 42.53 (C-4), 58.57 (C-5), 125.82, 126.86,
127.63, 128.90, 129.57 (aromatic C), 128.17, 140.62,
141.55 (aromatic Cq), 156.23 (C-3), 159.70 (HCvO) ppm.
Anal. calcd for C17H16N2O (264.33): C 77.25, H 6.10, N
10.60; found: C 76.98, H 6.15, N 10.72.
Activity of 5a against Trypanosoma b. rhodesiense and
cytotoxicity. Minimum essential medium (50 ml) supple-
mented according to Baltz et al.24 with 2-mercaptoethanol
and 15% heat-inactivated horse serum was added to each
well of a 96-well microtiter plate. Serial drug dilutions were
added to the wells. Then 50 ml of trypanosome suspension
(T.b.rhodesiense STIB 900) was added to each well and the
plate incubated at 378C under a 5% CO2 atmosphere for
72 h. Alamar Blue (10 ml) was then added to each well and
incubation continued for a further 2–4 h. The plate was then
read with a Millipore Cytofluor 2300 using an excitation
wavelength of 530 nm and emission wavelength of
590 nm.25 Fluorescence development was expressed as
percentage of the control, and IC50 values determined.
Melarsoprol served as standard giving an IC50 of
0.000849 mg/ml whereas 5a exhibits an IC50 of 9.36 mg/ml.
4.1.12. (RS)-(6)-1-Formyl-3-(4-methoxyphenyl)-5-phenyl-
2-pyrazoline (6d). 2.6 g (17 mmol) Hydrazinediium dithio-
cyanate (13) and 4.1 g (17 mmol) 40-methoxychalcone (1l)
in 50 ml of dimethylformamide gave 3.2 g (68%) of 6d. Mp:
1458C (ethanol); (mp22 125–1268C); IR (KBr): n¼1680 (s),
~
1608 (m), 1519 (m), 1426 (s), 1325 (m), 1260 (s), 1174 (m),
828 (m), 773 (m), 700 (m) cm21; UV (CH2Cl2): l

W. Seebacher et al. / Tetrahedron 59 (2003) 2811–2819
2819
13. Johnson, C. K. ORTEP; Report ORNL-3794; Oak Ridge
National Laboratory: Tennessee, USA, 1965.
14. Prakash, O.; Tanwar, M. P.; Moriarty, R. M. J. Indian Chem.
Sect. B. 1992, 31, 470–471.
Cytotoxicity was assessed using the same assay and L-6 cells
using mefloquine as standard.
15. Desai, N. C.; Parekh, B. R.; Thaker, K. A. J. Indian Chem. Soc.
1987, 64, 491–493.
References
16. Nishimura, T. Bull. Chem. Soc. Jpn 1955, 28, 197–200.
17. Dovgilevich, A. V.; Pinson, V. V.; Torochesnikov, B. N.;
Zelenin, K. N.; Sviridova, L. A.; Golubeva, G. A. Khim.
Geterotsikl. Soedin. 1987, 7, 928–932.
1. Zigeuner, G.; Schweiger, K. Monatsh. Chem. 1976, 107,
1361–1367.
2. Weis, R.; Kungl, A. J.; Seebacher, W. Tetrahedron 2003, 59,
1403–1411.
18. Sayed, G. H.; Kjoesen, H. J. Prakt. Chem. 1980, 322,
716–722.
3. Weis, R.; Schweiger, K.; Seebacher, W.; Belaj, F. Tetrahedron
1998, 54, 14015–14022.
4. Weis, R.; Brun, R.; Saf, R.; Seebacher, W. Monatsh. Chem.
2003, 134. in press.
19. Sing, N.; Sangwan, N. K.; Dhindsa, K. S. Pest Manag. Sci.
2000, 56, 284–288.
20. Sheldrick, G. M. SHELXS-97: Program for the Solution of
5. Zigeuner, G.; Galatik, W.; Lintschinger, W. B.; Wede, F.
Monatsh. Chem. 1975, 106, 1219–1233.
6. Zigeuner, G.; Brunetti, H.; Ziegler, H.; Bayer, M. Monatsh.
Chem. 1970, 101, 1767–1787.
¨
Crystal Structures; University of Gottingen: Germany, 1997.
21. Sheldrick, G. M. SHELXL-97: Program for the Refinement of
¨
Crystal Structures; University of Gottingen: Germany, 1997.
7. Robbins, T. E. (Koppers Co.,Inc.). US 2539480, 1951; Chem.
Abstr. 1951, 45, 5726e.
22. Aubagnac, J. L.; Bouchet, P.; Elguero, J.; Jacquier, R.; Marzir,
C. J. Chim. Phys. 1967, 64, 11–12.
8. Zigeuner, G.; Bayer, M.; Paltauf, F.; Fuchs, E. Monatsh.
Chem. 1967, 98, 22–33.
23. Matile, H.; Pink, J. R. L. In Immunological Methods;
Lefkovits, I., Pernis, B., Eds.; Academic: San Diego, 1990;
pp 221–234.
9. Mathes, R. A. J. Am. Chem. Soc. 1953, 75, 1747–1748.
10. Seebacher, W.; Michl, G.; Weis, R. Tetrahedron Lett. 2002,
43, 7481–7483.
24. Baltz, T.; Baltz, D.; Giroud, C.; Crockett, J. EMBO J. 1985, 4,
1273–1277.
¨
¨
25. Raz, B.; Iten, M.; Grether-Buhler, Y.; Kaminsky, R.; Brun, R.
11. Rezessy, B.; Zubovics, Z.; Kovacs, J.; Toth, G. Tetrahedron
1999, 55, 5909–5922.
Acta Trop. 1997, 68, 139–147.
12. Allen, F. H.; Kennard, O. Chem. Des. Autom. News 1993, 8,
31–37.