1-Alkylpyrazoles and 1-alkyl-5-chloropyrazoles from halovinyl ketones and 1,1-dialkylhydrazines

Article abstract of DOI:10.1134/S1070428008080150

Regioselective heterocyclization of alkyl 2-chloro-and 2,2-dichlorovinyl ketones with 1,1-dialkyl-hydrazines to 1,3-dialkyl-1H-pyrazoles and 1,3-dialkyl-5-chloro-1H-pyrazoles involves intermediate formation of the corresponding dialkylhydrazones. Fragment

Full text of DOI:10.1134/S1070428008080150

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2008, Vol. 44, No. 8, pp. 1194–1199. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © G.V. Bozhenkov, V.A. Savosik, L.V. Klyba, E.R. Zhanchipova, A.N. Mirskova, G.G. Levkovskaya, 2008, published in Zhurnal
Organicheskoi Khimii, 2008, Vol. 44, No. 8, pp. 1207–1212.
1-Alkylpyrazoles and 1-Alkyl-5-chloropyrazoles from Halovinyl
Ketones and 1,1-Dialkylhydrazines
G. V. Bozhenkov, V. A. Savosik, L. V. Klyba, E. R. Zhanchipova,
A. N. Mirskova, and G. G. Levkovskaya
Favorskii Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
e-mail: ggl@irioch.irk.ru
Received January 5, 2008
Abstract—Regioselective heterocyclization of alkyl 2-chloro- and 2,2-dichlorovinyl ketones with 1,1-dialkyl-
hydrazines to 1,3-dialkyl-1H-pyrazoles and 1,3-dialkyl-5-chloro-1H-pyrazoles involves intermediate formation
of the corresponding dialkylhydrazones. Fragmentation pattern of chlorine-containing pyrazoles, 3-chloro-
methyl-1-methyl-1H-pyrazole and 5-chloro-1-methyl-3-propyl-1H-pyrazole, depends on the position of the
halogen atom.
DOI: 10.1134/S1070428008080150
Development of the chemistry of pyrazoles on the
whole and specifically of halogen-containing pyrazoles
is stimulated by broad spectrum of useful properties of
these compounds. For example, they are used as inter-
mediate products in the synthesis of dyes, materials for
optoelectronics, pesticides, medicines, etc.; in addition,
they attract interest due to diversity of their chemical
transformations [1–8].
zine [11]. The proposed mechanism of this reaction
involved initial formation of the corresponding halo
enone dimethyl- and alkylhydrazones, followed by
intramolecular nucleophilic attack by the dimethyl-
(alkyl)amino group on the β-carbon atom of the vinyl
group [9–11]. An alternative mechanism with initial
formation of quaternary 1-(1-halo-2-acylvinyl)-1-di-
methylhydrazinium halides and subsequent hetero-
cyclization seemed to be improbable, for quaternary
salts obtained from 1,1-dimethylhydrazine and bromo-
acetylenic ketones, 1-[1-bromo-2-benzoyl(2-thenoyl)-
vinyl]-1,1-dimethylhydrazinium bromides (their struc-
ture was determined by X-ray analysis), failed to
undergo cyclization to pyrazoles [12]. It should be
emphasized that neither dialkylhydrazones nor dihy-
dropyrazolium salts were isolated or detected in the
Systematic studies in the field of reactivity of halo-
vinyl ketones showed that 1,3-dialkyl- and 1-alkyl-5-
chloro(bromo)-3-alkyl(aryl, chloroalkyl, perfluoroal-
kyl)pyrazoles are formed by reactions of the corre-
sponding methyl, ethyl, and chloromethyl 2-chloro-
vinyl ketones with 1,1-dimethyl-, 1,1-diethyl-, and
1,1-dibutylhydrazines [9, 10], as well as from 2,2-di-
chloro(bromo)vinyl ketones and 1,1-dimethylhydra-
Scheme 1.
R1
NH2NR22
Δ, H+
O
X
NNR22
X
N
X
–R2Cl
N
R1
Cl
R1
Cl
R2
I–III, IX
IV–VIII, X, XI
NH2NR22, Δ, H+ or base
O
X
IV–VIII, X, XI
–R2Cl
R1
Cl
Base = NH2NR22, NEt3; I–VIII, X = H; IX–XI, X = Cl; VI, IV, R1 = Me, R2 = Bu; II, V, XI, R1 = Pr, R2 = Me; III, VI, IX, X, R1 =
Pr, R2 = Bu; VII, R1 = R2 = Me; VIII, R1 = ClCH2, R2 = Me.
1194

1-ALKYLPYRAZOLES AND 1-ALKYL-5-CHLOROPYRAZOLES
1195
reactions of halo enones with 1,1-dimethylhydrazine
[9–11].
corresponding pyrazoles IV–VIII and X on heating in
organic solvents in the presence of acids or in acetic
acid. When hydrazones I–III and IX were heated in
the absence of acid the reaction was accompanied by
decomposition, and pyrazoles IV–VI and X were
formed in a poor yield.
In the present work we continued our studies on
reactions of 1-chloro- and 2,2-dichlorovinyl ketones
with 1,1-dialkylhydrazines with a view to obtain new
1-alkyl-substituted pyrazoles and refine the mechanism
of their formation. We were the first to find conditions
for the synthesis of 2-chlorovinyl ketone dimethyl-
(butyl)hydrazones I–III and isolate them as individual
substances. The reactions were carried out by mixing
equimolar amounts of the reactants in an organic sol-
vent at –40 to 0°C (reaction time 1–3 h). Hydrazone
III was also obtained by reaction of 1,1-dibutylhydra-
zine with an equimolar amount of 2-chlorovinyl propyl
ketone in diethyl ether at room temperature. By re-
acting 2,2-dichlorovinyl propyl ketone with 1,1-di-
butylhydrazine at –10 to 0°C we succeeded in obtain-
ing the corresponding hydrazone IX containing no
more than 5% of pyrazole X (Scheme 1). Presumably,
the different conditions for the synthesis of 2-chloro-
and 2,2-dichlorovinyl ketone dimethyl- and dibutylhy-
drazones are determined by steric factors.
Presumably, the role of acid in the cyclization of
hydrazones to pyrazoles IV–VIII and X is not only
promotion of isomerization of the E-s-trans-hydrazine
conformer into Z-s-cis whose configuration is favor-
able for heterocyclization (as with halo enone dinitro-
phenylhydrazones [13]) but also electrophilic assis-
tance to nucleophilic attack on the double bond by the
amino nitrogen atom of the hydrazone fragment. Acid
protonates the C=N nitrogen atom in the hydrazone,
and electron-withdrawing effect of the C=N+H group is
transmitted through the conjugated bond system to
enhance electrophilicity of the β-carbon atom at the
double C=C bond thus facilitating nucleophilic attack
at that atom.
Pyrazoles IV–VIII and 5-chloropyrazole X can
also be obtained in good yields by exothermic reaction
of 2-chloro- and 2,2-dichlorovinyl ketones with
2 equiv of 1,1-dialkylhydrazine or in the presence of
a base which is required to bind methyl or butyl
chloride liberated during the heterocyclization process;
as a result, the yield of the target pyrazoles increases.
In the reactions of 1,1-dimethylhydrazine with
2-chloro- and 2,2-dichlorovinyl ketones (reactant ratio
1:1) in alcohol, diethyl ether, and other solvents with-
out cooling, the corresponding dimethylhydrazones
were not isolated, and the products were 1-methyl-
pyrazoles IV–VIII, X, and XI, while the conversion of
the initial halo enone was not complete. No dimethyl-
hydrazone was formed in the reaction of 2,2-dichloro-
vinyl propyl ketone with 1,1-dimethylhydrazine at
–40°C; in this case, we isolated 5-chloro-1-methyl-3-
propyl-1H-pyrazole (XI) in no more than 35% yield
and the initial ketone.
In the IR spectra of hydrazones I–III and IX we
observed absorption bands due to vibrations of C=N,
C=C, and aliphatic C–H bonds. Hydrazone IX showed
1
in the H NMR spectrum signals from protons in the
alkyl groups and a singlet from the vinylic CH=CCl2
1
proton. The H NMR spectra of I–III contained two
doublets from protons in the CH=CHCl group with
a coupling constant J of 14.1 Hz, indicating trans
1,1-Dimethyl- and 1,1-dibutylhydrazones I–III and
IX readily undergo intramolecular cyclization to the
3
Scheme 2.
[C4H4]+
·
·
–CH3N2
m/z 52 (14%)
+·
CH2Cl
CH2
[C4H3]+
–CH4N2
m/z 51 (19%)
N
N
N
·
–Cl
N
N
N
[C2H3N2]+
Me
Me
Me
·
–C3H4
+
·
m/z 55 (28%)
[M] , m/z 130 (65%)
m/z 95 (100%)
VIII
[C2H4N]+
·
–C3H3N
m/z 42 (33%)
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 8 2008

BOZHENKOV et al.
1196
Scheme 3.
CH2
N
N
·
Cl
–H
Cl
N
N
Me
Me
m/z 129 (53%)
+·
+·
C3H7
CH3
N
N
N
[C4H6N]+
·
Cl
Cl
Cl
N
–C2H4
–CH3
N
N
m/z 68 (10%)
Me
Me
Me
+
·
[M] , m/z 158 (28%)
m/z 130 (100%)
m/z 115 (11%)
–HCN
XI
Me
Me
N
N
·
–Cl
N
NH
CH2
m/z 95 (8%)
[C3H3N]+
m/z 53 (17%)
configuration of the double bond. In the 13C NMR
spectra of hydrazones I–III and IX, the C=N carbon
signal appears in a very weak field, at δC 196–
199 ppm. The doublet signals from the olefinic protons
in the 1H NMR spectra of hydrazones I–III and IX are
also displaced downfield relative to the corresponding
signals of initial methyl and propyl 2-chloro(2,2-di-
chloro)vinyl ketones.
ring expansion as shown in Scheme 2. This process is
related to cleavage of benzylic bond [15]. The struc-
tures of the primary rearranged ions derived from N-
and C-methyl pyrazoles are different, and they deter-
mine further decomposition pattern with formation of
lighter ions.
It is known that halogen atom generally does not
leave stable molecular ions derived from 4-chloro-
(bromo)pyrazoles; these ions lose only two hydrogen
cyanide molecules [16]. In fact, the mass spectrum of
5-chloro-1-methyl-3-propyl-1H-pyrazole (XI) obtained
from 2,2-dichlorovinyl propyl ketone and 1,1-dimeth-
ylhydrazine according to the procedure described in
[10] contained no [M – Cl]+ ion peak. The base peak in
the mass spectrum of XI was that corresponding to
odd-electron 5-chloro-1,3-dimethyl-1H-pyrazolium ion
with m/z 130 (100%) and products of its subsequent
fragmentation (Scheme 3). Thus the fragmentation pat-
tern of chlorine-containing pyrazoles VIII and XI is
determined by the position of the halogen atom with
respect to the heteroatom.
Pyrazoles IV–VIII and X are characterized by IR
absorption at 3100–3130 cm–1, belonging to stretching
1
vibrations of the =C–H bonds. In the H NMR spectra
of IV–VIII, signals from 4-H and 5-H appear as two
doublets at δ 5.9 and 7.2 ppm, respectively, with a cou-
pling constant of 1.3–2.0 Hz. The 4-H proton in pyra-
zole X resonates as a singlet at δ 5.95 ppm.
The structure of pyrazoles VIII and XI was also
studied by mass spectrometry. The main fragmentation
pathway of 3-chloro-1-methyl-1H-pyrazole (VIII)
under electron impact involves cleavage of the C–Cl
bond in the molecular ion. Such behavior is typical of
aromatic halogen derivatives, for which elimination of
chlorine atom from the molecular ion is the main
decomposition process [14]. Six-membered cyclic ions
are known to be more stable than five-membered;
therefore, it is quite possible that the [M – Cl]+ ion
with m/z 95 (100%) undergoes rearrangement with
To conclude, the described procedure for selective
synthesis of 1-alkylpyrazoles and 1-alkyl-5-chloropyr-
azoles from halogenated enones and 1,1-dialkylhydra-
zines makes these compounds accessible for further
studies, while the use of 2-chloro- and 2,2-dichloro-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 8 2008

1-ALKYLPYRAZOLES AND 1-ALKYL-5-CHLOROPYRAZOLES
1197
vinylketones and dialkylhydrazines ensures variation
of the structure of the resulting pyrazoles and deter-
mines the presence of chlorine therein.
The solution was separated by decanting, and the
residue was dried under reduced pressure. Yield 0.8 g
(92%), oily substance. IR spectrum, ν, cm–1: 1630
1
(C=N, C=C); 2955, 2925, 2870 (C–HAlk). H NMR
EXPERIMENTAL
spectrum (DMSO-d6), δ, ppm: 0.83 t (3H, CH3, J =
7.1 Hz), 1.51 m (2H, CH2, J = 7.1 Hz), 2.65 t (2H,
CH2, J = 7.1 Hz), 3.56 s (6H, CH3), 6.86 d (1H, =CH,
J = 13.9 Hz), 7.66 d (1H, =CHCl, J = 13.9 Hz). Found,
%: C 54.95; H 8.86; Cl 20.27; N 16.09. C8H15ClN2.
Calculated, %: C 55.01; H 8.66; Cl 20.30; N 16.04.
The IR spectra were recorded in KBr or in thin
1
films on a Specord 75IR spectrometer. The H and 13C
NMR spectra were measured on Bruker DPX-400 and
1
Bruker AV-400 spectrometers at 400.13 MHz for H
13
and 100.62 MHz for C using tetramethylsilane as in-
1-Chlorohex-1-en-3-one dibutylhydrazone (III).
1,1-Dibutylhydrazine, 7.22 g (0.05 mol), was slowly
added dropwise to a solution of 6.6 g (0.05 mol) of
1-chlorohex-1-en-3-one in 30 ml of methanol, main-
taining the temperature below 20°C. The mixture was
stirred for 3 h at room temperature, the solvent was
removed under reduced pressure, and the dark red
viscous oily residue was dried in a vacuum. Yield 12 g
(93%). IR spectrum, ν, cm–1: 1610 (C=N, C=C); 2965,
2930, 2875 (C–HAlk); 3115 (=C–H). 1H NMR spectrum
(DMSO-d6), δ, ppm: 0.83 t (3H, CH3, J = 7.1 Hz);
0.86 t (6H, CH3, J = 7.7 Hz); 1.25 m, 1.50 m, and
1.70 m (10H, CH2); 1.25 m (8H, CH2); 2.32 t (2H,
CH2, J = 7.1 Hz); 3.68 t (4H, CH2, J = 7.7 Hz); 6.62 d
(1H, =CH, J = 13.9 Hz); 7.46 d (1H, =CH, J = 13.9
ternal reference; the chemical shifts were determined
with an accuracy of 0.01 and 0.02 ppm, respectively,
and the coupling constants JHH were determined with
an accuracy of 0.1 Hz. The mass spectra were obtained
on an LKB-2091 GC–MS system (SE-30 capillary col-
umn, 25 m; energy of ionizing electrons 60 eV; ion
source temperature 250°C, injector temperature 240°C,
oven temperature programming from 60 to 240°C at
a rate of 10 deg/min).
5-Chloro-1-methyl-3-propyl-1H-pyrazole (XI) was
synthesized in 84% yield by reaction of 2,2-dichloro-
vinyl propyl ketone with 1,1-dimethylhydrazine in di-
ethyl ether as described in [10].
4-Chlorobut-3-en-2-one dibutylhydrazone (I).
1,1-Dibutylhydrazine, 7.22 g (0.05 mol), was slowly
added to a solution of 5.23 g (0.05 mol) of 4-chloro-
but-3-en-2-one in 20 ml of methanol or ethanol on
cooling to –10 to 0°C. The mixture was stirred for 3 h
at that temperature, allowed to warm up to room tem-
perature, and evaporated under reduced pressure. The
dark red viscous oily residue was dried under reduced
pressure until constant weight. Yield 10.9 g (95%). IR
spectrum, ν, cm–1: 1610 (C=N, C=C); 2965, 2930,
13
Hz). C NMR spectrum, δC, ppm: 13.57 (CH3), 19.03
(CH2), 19.48 (CH3), 23.93 (CH2), 67.59 (CH2), 127.91
(=CH), 146.88 (=CHCl), 196.45 (C=N). Found, %:
C 64.85; H 10.45; Cl 13.49; N 10.90. C14H27ClN2. Cal-
culated, %: C 64.97; H 10.51; Cl 13.70; N 10.82.
1-Butyl-3-methyl-1H-pyrazole (IV). A mixture of
0.92 g (4 mmol) of 4-chlorobut-3-en-2-one dibutylhy-
drazone (I), 20 ml of methanol, and 0.5 ml of acetic
acid was heated for 5 h under reflux. The mixture was
cooled and poured into water, the aqueous solution was
neutralized with a solution of Na2CO3 and treated with
diethyl ether. The extract was dried over CaCl2 and
evaporated under reduced pressure, and the oily
residue was dried in a vacuum. Yield 0.25 g (45%).
IR spectrum, ν, cm–1: 1510 (C=C); 2945, 2920, 2855
1
2875 (C–HAlk), 3115 (=C–H). H NMR spectrum
(DMSO-d6), δ, ppm: 0.86 t (6H, CH3, J = 7.7 Hz),
1.70 m and 1.25 m (8H, CH2), 2.32 s (3H, CH3), 3.68 t
(4H, CH2, J = 7.7 Hz), 6.62 d (1H, =CH, J = 13.9 Hz),
7.46 d (1H, =CH, J = 13.9 Hz). 13C NMR spectrum,
δC, ppm: 13.57 (CH3), 19.03 (CH2), 19.48 (CH3), 23.93
(CH2), 67.59 (CH2), 127.91 (=CH), 146.88 (=CHCl),
196.45 (C=N). Found, %: C 62.25; H 10.15; Cl 15.29;
N 12.04. C12H23ClN2. Calculated, %: C 62.45; H 10.05;
Cl 15.36; N 12.14.
1
(C–HAlk), 3100 (=CH). H NMR spectrum (CDCl3), δ,
ppm: 0.87 t (3H, CH3, J = 7.3 Hz), 1.24 m (2H, CH2,
J = 7.3 Hz), 1.75 m (2H, CH2, J = 7.3 Hz), 2.22 s (3H,
CH3), 3.96 t (2H, CH2, J = 7.3 Hz), 5.91 d (1H, 4-H,
J = 2.0 Hz), 7.17 d (1H, 5-H, J = 2.0 Hz). Found, %:
C 69.50; H 10.24; N 20.30. C8H14N2. Calculated, %:
C 69.52; H 10.21; N 20.27.
1-Chlorohex-1-en-3-one dimethylhydrazone (II).
1,1-Dimethylhydrazine, 0.3 g (5 mmol), was slowly
added dropwise under stirring to a solution of 0.66 g
(5 mmol) of 1-chlorohex-1-en-3-one in 30 ml of
carbon tetrachloride, maintaining the temperature at
–30 to –40°C. The mixture was allowed to gradually
warm up to room temperature and was stirred for 1 h.
1-Methyl-3-propyl-1H-pyrazole (V) was synthe-
sized in a similar way from 1.75 g (0.01 mol) of
1-chlorohex-1-en-3-one dimethylhydrazone (II). Yield
0.77 g (62%), bp 125–130°C (12 mm). IR spectrum, ν,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 8 2008

BOZHENKOV et al.
1198
cm–1: 1515 (C=C); 2940, 2920, 2855 (C–HAlk); 3110
(=C–H). H NMR spectrum (CDCl3), δ, ppm: 0.97 t
and the residue was purified by passing through
a column charged with silica gel or by distillation.
Yield 0.91 (70%), bp 146–148°C, nD20 = 1.5275.
1H NMR spectrum (CDCl3), δ, ppm: 3.86 (NCH3),
4.58 (CH2Cl), 6.278 and 6.274 (4-H), 7.324 and 7.319
(5-H). 13C NMR spectrum, δC, ppm: 38.62 (CH3N),
76.838 (CH2Cl), 105.084 (C4), 130.97 (C3), 148.37
(C5). Found, %: C 45.78; H 5.24; N 21.47. C5H7ClN2.
Calculated, %: C 45.99; H 5.40; N 21.45. The physical
properties of the product were consistent with pub-
lished data [10].
1,1-Dichlorohex-1-en-3-one dibutylhydrazone
(IX). 1,1-Dichlorohex-1-en-3-one, 4.17 g (0.025 mol),
was added dropwise to a solution of 3.60 g (0.025 mol)
of dibutylhydrazine in 15 ml of ethanol on cooling to
–10 to 0°C. The mixture was stirred for 3 h on cooling,
allowed to warm up to room temperature, and evapo-
rated under reduced pressure. Yield 5.57g (95%), dark
red oily substance containing 5% of 1-butyl-5-chloro-
3-propyl-1H-pyrazole (X). IR spectrum, ν, cm–1: 1610
(C=N); 2965, 2930, 2875 (C–HAlk); 3100 (=C–H).
1H NMR spectrum (CDCl3), δ, ppm: 0.91 t, 0.92 t, and
0.93 t (3H each, CH3); 1.35 m and 1.65 m (10H, CH2);
2.20 t (2H, CH2, J = 7.2 Hz); 3.00 t (4H, CH2, J =
7.4 Hz); 6.64 s (1H, =CH). Found, %: C 57.30; H 8.79;
Cl 24.17; N 9.53. C14H26Cl2N2. Calculated, %: C 57.34;
H 8.94; Cl 24.18; N 9.55.
1-Butyl-5-chloro-3-propyl-1H-pyrazole (X). A so-
lution of 5.86 g (0.02 mol) of 1,1-dichlorohex-1-en-3-
one dibutylhydrazone (IX) in 30 ml of ethanol con-
taining 0.5 ml of acetic acid was heated for 5 h under
reflux. The solution was cooled, neutralized with a so-
lution of sodium carbonate, and extracted with diethyl
ether. The extract was dried over CaCl2 and evap-
orated, and the residue was distilled in a vacuum. Yield
2.40 g (60%) [11]. IR spectrum, ν, cm–1: 1610 (C=N,
C=C); 2945, 2920, 2855 (C–HAlk); 3130 (=C–H).
1H NMR spectrum (CDCl3), δ, ppm: 0.89 m (3H, CH3,
J = 7.3 Hz), 0.94 t (3H, CH3, J = 7.5 Hz), 1.25 m (2H,
CH2, J = 7.3 Hz), 1.66 m (2H, CH2, J = 7.5 Hz), 1.76 m
(2H, CH2, J = 7.3 Hz), 2.58 t (2H, CH2, J = 7.5 Hz),
4.05 t (2H, CH2, J = 7.3 Hz), 5.95 (1H, =CH). Found,
%: C 59.82; H 8.51; Cl 17.63; N 13.94. C10H17ClN2.
Calculated, %: C 59.84; H 8.54; Cl 17.66; N 13.96.
1
(3H, CH3, J = 7.7 Hz), 1.31 m (2H, CH2, J = 7.7 Hz),
2.56 t (2H, CH2, J = 7.7 Hz), 3.80 s (3H, CH3), 5.99 d
(1H, 4-H, J = 1.6 Hz), 7.21 d (1H, 5-H, J = 1.6 Hz).
13C NMR spectrum, δC, ppm: 13.72, 22.95, 38.23,
45.84, 103.86, 130.31, 153.15. Found, %: C 67.30;
H 9.68; N 22.49. C7H12N2. Calculated, %: C 67.70;
H 9.74; N 22.56.
1-Butyl-3-propyl-1H-pyrazole (VI). 1-Chlorohex-
1-en-3-one, 1.33 g (0.01 mol), and triethylamine,
1.01 g (0.01 mol), were slowly added dropwise to
a solution of 1.44 g (0.01 mol) of 1,1-dibutilhydrazine
in 15 ml of ethanol. The mixture was heated for 5 h
under reflux, cooled, poured into water, and extracted
with diethyl ether. The extract was dried over CaCl2,
the solvent was distilled off, and the residue was
distilled in a vacuum. Yield 1 g (60%), bp 83–85°C
(12 mm), nD20 = 1.4710. IR spectrum, ν, cm–1: 1525,
1515 (C=C, C=N); 2950, 2925, 2870 (C–HAlk); 3100
1
(=C–H). H NMR spectrum (CDCl3), δ, ppm: 0.89 t
(3H, CH3, J = 7.3 Hz), 0.97 t (3H, CH3, J = 7.7 Hz),
1.31 m (2H, CH2, J = 7.7 Hz), 1.65 m (2H, CH2, J =
7.3 Hz), 1.76 m (2H, CH2, J = 7.3 Hz), 2.56 t (2H,
CH2, J = 7.7 Hz), 4.00 t (2H, CH2, J = 7.3 Hz), 5.96 d
(1H, 4-H, J = 1.8 Hz), 7.37 d (1H, 5-H, J = 1.8 Hz).
Found, %: C 72.28; H 11.07; N 16.78. C10H18N2. Cal-
culated, %: C 72.24; H 10.91; N 16.85.
1,3-Dimethyl-1H-pyrazole (VII). 1,1-Dimethyl-
hydrazine, 1.2 g (0.02 mol), was added under stirring
to a solution of 1.04 g (0.01 mol) of 4-chlorobut-3-en-
2-one in 35 ml of anhydrous diethyl ether. The mixture
was stirred for 5 h at room temperature and poured into
water, the organic layer was separated, and the aqueous
phase was extracted with diethyl ether, The extracts
were combined with the organic phase, dried over
CaCl2, and evaporated, and the residue was distilled
under reduced pressure. Yield 0.84 g (64%), bp 136°C,
nD20 = 1.4674. Found, %: C 62.30; H 8.37; N 29.12.
C5H8N2. Calculated, %: C 62.47; H 8.39; N 29.14.
The product was identical in physical properties to
a sample described in [9, 11].
3-Chloromethyl-1-methyl-1H-pyrazole (VIII).
1,4-Dichlorobut-3-en-2-one, 1.39 g (0.01 mol), was
slowly added in small portions to a solution of 1.20 g
(0.02 mol) of 1,1-dimethylhydrazine in 30 ml of
anhydrous diethyl ether so that to avoid boiling of the
mixture. When the exothermic reaction was over, the
mixture was stirred for 0.5–2 h, and the precipitate of
trimethylhydrazinium chloride, 0.96 g (89%, mp 261–
262°C), was filtered off. The filtrate was evaporated,
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 05-03-97202).
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