3-Cyano-4,6-dimethyl-5-R-pyridine-2-sulfonyl chlorides and N-substituted sulfonylamides based on them

Article abstract of DOI:10.1007/s10593-009-0386-4

3-Cyanopyridine-2-sulfonyl chlorides were synthesized by the oxidative chlorination of the respective 3-cyanopyridine-2(1H)-2-thiones. It was established that 3-cyano-4,6-dimethylpyridine-2-sulfonyl chloride eliminates a SO₂ molecule at the iso

Full text of DOI:10.1007/s10593-009-0386-4

Chemistry of Heterocyclic Compounds, Vol. 45, No. 9, 2009
3-CYANO-4,6-DIMETHYL-5-R-PYRIDINE-
2-SULFONYL CHLORIDES AND N-SUBSTITUTED
SULFONYLAMIDES BASED ON THEM
I. G. Dmitrieva1*, L. V. Dyadyuchenko1, V. D. Strelkov2,and E. A. Kaigorodova3
3-Cyanopyridine-2-sulfonyl chlorides were synthesized by the oxidative chlorination of the respective
3-cyanopyridine-2(1H)-2-thiones. It was established that 3-cyano-4,6-dimethylpyridine-2-sulfonyl
chloride eliminates a SO2 molecule at the isolation stage. N-Substituted sulfonylamides based on the
latter were obtained by the reaction of the crude sulfonyl chloride with amines in an aqueous medium.
Keywords: sulfonylamides, sulfonyl chlorides, oxidative chlorination, synthesis, elimination.
Aryl- and heterylsulfonylamides have various types of biological activity, including pharmacological
[1, 2], herbicidal [3], and fungicidal [4]. In order to extend the range of biologically active substances we made
an attempt at the synthesis of new pyridyl-2-sulfonyl chlorides and N-substituted sulfonylamides based on them.
One of the widely used methods for the production of aromatic sulfonyl chlorides is oxidative chlorination of
the corresponding mercapto derivatives [5]. As starting compounds we used 3-cyanopyridine-2(1H)-thiones
1a,b, the synthesis of which was described in [6].
Oxidative chlorination was realized in a 2 N solution of HCl in the range between -3 and 0°C. Here
5-chloro-4,6-dimethyl-2(1H)-pyridinethione (1a) gives the corresponding pyridine-2-sulfonyl chloride 2a
smoothly and with a good yield (85% theor.). 4,6-Dimethyl-2(1H)-pyridinethione (1b) also forms the required
sulfonyl chloride 2b in the reaction process. However, its subsequent behavior is unusual; at the drying stage
(room temperature, atmospheric pressure or 5-10 mm Hg; distillation of the solvent from the dried extract of the
product) the latter eliminates a molecule of SO2, just as if it were "boiling". As a result 2-chloro-4,6-dimethyl-
nicotinonitrile (3) is formed.
In order to avoid decomposition of the sulfonyl chloride 2b the crude product was used straight away in
the reactions with the amines. For this purpose a solution of the corresponding amine in acetone was added
dropwise to an aqueous suspension of 2b at 8-10°C, and after stirring for 2-4 h the sulfonylamides 4h-l were
isolated with fairly high yields (64-74%). The sulfonyl chloride 2b was consequently unable to be hydrolyzed
under the given conditions.
_______
* To whom correspondence should be addressed, e-mail: chem._dmitrieva@mail.ru.
1Kuban State Agrarian University, Krasnodar 350044, Russia.
2All-Russia Research Institute of Biological Plants Protection, Krasnodar 350039, Russia; e-mail:
vladstrelkov@yandex.ru.
3Kuban State University of Technology, Krasnodar 350072, Russia; e-mail: e_kaigorodova@mail.ru.
__________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1311-1318, September, 2009.
Original article submitted April 21, 2006. Revision submitted June 10, 2008.
0009-3122/09/4509-1047©2009 Springer Science+Business Media, Inc.
1047

Me
Me
Me
R
CN
R
CN
S
CN
Cl
Cl2
– SO2
2 N HCl
Me
N
2a,b
SO2Cl
Me
N
H
1a,b
Me
N
3
R1
R2NH2
NH
R2
Me
Me
Me
Cl
CN
NC
Cl
R2
R
CN
4
+
R1
R2
N
O
Me
N
N
Me
S
S
Me
N
SO2N
O
O
O
5a,b
4a–l
1, 2 а R = Cl, b R = H; 4 a–g R = Cl; a R1 = H, R2 = 2-ethylphenyl; b R1 = H,
R2 = 3-chloro-4-methylphenyl; c R1 = H, R2 = furfuryl; d R1 = H, R2 = 4-chlorobenzyl;
e R1 = Et, R2 = Ph; f R1R2 = (CH2CH2)2CHMe; g R1R2 = (CH2CH2)2O; h–l R = H, h R1 = H,
R2 = 2-ethylphenyl; i R1 = H, R2 = cyclohexyl; j R1 = H, R2 = isopropyl; k R1 = R2 = allyl;
l R1 = Me, R2 = Ph; 5 а R2 = 2-ethylphenyl, b R2 = 3-chloro-4-methylphenyl
TABLE 1. The Physicochemical Characteristics of the Synthesized Compounds
Found, %
Calculated, %
——————
Com-
pound
Empirical
formula
Yield,
%
mp, °C
С
Н
N
S
2a
3
C8H6Cl2N2O2S
C8H7ClN2
36.41
36.24
2.33
2.28
10.20
10.57
11.88
12.09
79-80
(hexane)
85
81
71
66
69
56
69
88
76
66
74
72
70
64
56
44
57.82
57.67
4.38
4.23
17.01
16.81
—
95-96
(hexane)
4a
4b
4c
4d
4e
4f
C16H16ClN3O2S
C15H13Cl2N3O2S
C13H12ClN3O3S
C15H13Cl2N3O2S
C16H16ClN3O2S
C14H18ClN3O2S
C12H14ClN3O3S
C16H17N3O2S
C14H19N3O2S
C11H15N3O2S
C14H17N3O2S
C15H15N3O2S
55.12
54.93
4.65
4.61
11.88
12.01
9.24
9.17
181-182
(EtOAc)
48.80
48.66
3.47
3.54
11.11
11.35
8.89
8.66
198-200
(EtOH)
48.59
47.93
3.86
3.71
13.01
12.90
10.03
9.84
138-139
(hexane + EtOAc)
48.41
48.66
3.31
3.54
11.18
11.35
8.74
8.66
179-180
(EtOAc)
54.68
54.93
4.39
4.61
12.29
12.01
8.93
9.17
129-131
(cyclohexane)
51.02
51.29
5.67
5.53
12.56
12.82
9.61
9.78
106-107
(hexane)
4g
4h
4i
45.83
45.64
4.26
4.47
13.12
13.31
10.22
10.15
154-156
(hexane + EtOAc)
61.17
60.93
5.62
5.43
13.18
13.32
10.34
10.17
147-148
(hexane + EtOAc)
57.12
57.31
6.41
6.53
14.17
14.32
11.08
10.93
151-152
(hexane + EtOAc)
4j
51.89
52.16
5.64
5.97
16.72
16.59
12.43
12.66
98-100
(hexane)
4k
4l
57.58
57.71
5.69
5.88
14.57
14.42
11.14
11.00
52-53
(hexane)
59.51
59.78
5.16
5.02
13.71
13.94
10.39
10.64
111-112
(cyclohexane)
5a
5b
C24H21Cl2N5O4S2 50.02
49.83
3.60
3.66
12.23
12.11
10.89
11.09
248-251
(EtOH + DMF)
C23H18Cl3N5O4S2 46.64
46.13
3.19
3.03
11.37
11.69
11.04
10.71
262-265
(EtOH + DMF)
1048

Unlike compound 2b the sulfonyl chloride 2a is fairly stable. After drying and purification it was
therefore reacted with amines under traditional conditions, i.e., the sulfonylamides 4a-g were synthesized in
anhydrous benzene in the presence of triethylamine. It was found that the reaction of 2a with primary amines
takes place in different ways. If the primary amine is added to a solution of the sulfonyl chloride 2a the
bissulfonylamides 5a,b are formed in addition to the required sulfonylamides 4a,b. Conditions were found that
make it possible to exclude the parallel competing reaction, and for this purpose a solution of the sulfonyl
chloride 2a was added dropwise to a solution of the primary amine at 10-15°C.
The results from elemental analysis are presented in Table 1. The structure of the synthesized
1
compounds was confirmed by a combination of IR, H NMR, and mass spectra (Tables 2 and 3, experimental
section).
1
The H NMR spectrum of the sulfonyl chloride 2a only contains signals for the two methyl groups of
pyridine at 2.80 and 2.85 ppm. In the mass spectrum there is a group of molecular ion peaks with relative
intensity of 15%. Two primary fragmentation paths are observed, i.e., elimination of the SO2 group and loss of
the SO2Cl group, and the fraction of the last fragment is maximum in the total ion current. The secondary
dissociative ionization is characterized by loss of the CN, Cl, and other groups.
TABLE 2. The 1H NMR Spectra of Compounds 2-5
Com-
pound
Chemical shifts, δ, ppm (J, Hz)
2a
3
2.85 (3H, s, 6-CH3); 2.80 (3H, s, 4-CH3)
7.45 (1H, s, H-5); 2.62 (3H, s, 6-CH3); 2.55 (3H, s, 4-CH3)
4a
7.78 (1H, br. s, NH); 7.62-7.30 (4H, m, Ar); 3.00 (3H, s, 6-CH3); 2.85 (3H, s, 4-CH3);
2.62 (2H, q, J = 7.6, CH2CH3); 1.22 (3H, t, J = 7.6, CH2CH3)
4b
4c
8.02 (1H, br. s, NH); 7.89 (1H, s, Н-2 Ar); 7.64 (1H, d, J = 8.3, Н-5 Ar);
7.55 (1H, d, J = 8.3, Н-6 Ar); 2.94 (3H, s, 6-CH3 Py); 2.82 (3H, s, 4-CH3 Py);
2.35 (3H, s, 4-CH3 Ar)
8.85 (1H, s, NH), furane ring: 7.45 (1Н, d, J5,4 = 1.8, Н-5);
6.30 (1Н, dd, J3,4 = 3.5, J5,4 = 1.8, Н-4); 6.20 (1Н, d, J3,4= 3.5, Н-3); 4.27 (2H, s, CH2);
2.65 (3H, s, 6-CH3 Py); 2.60 (3H, s, 4-CH3 Py)
4d
4e
4f
8.70 (1H, br. s, NH); 7.32-7.21 (4H, m, Ar); 4.25 (2H, s, CH2); 2.85 (3H, s, 6-CH3 Py);
2.75 (3H, s, 4-CH3 Py)
7.41-7.30 (5H, m, Ar); 3.95 (2H, q, J = 7.2, CH2CH3); 2.80 (3H, s, 6-CH3 Py);
2.65 (3H, s, 4-CH3 Py); 1.15 (3H, t, J = 7.2, CH2CH3)
3.84 (1Н, m, СН2 piperidine); 3.01 (1Н, m, СН2 piperidine); 2.72 (3H, s, 6-CH3 Py);
2.62 (3H, s, 4-CH3 Py); 1.75 (1Н, m, СН2 piperidine); 1.62 (1Н, m, СН2 piperidine);
1.30 (1Н, m, СН piperidine); 1.02 (3Н, m, CH3)
4g
4h
3.73 (4Н, m, ОCH2); 3.43 (4Н, m, NCH2); 2.78 (3H, s, 6-CH3 Py); 2.70 (3H, s, 4-CH3 Py)
10.24 (1H, br. s, NH); 7.70 (1Н, s, Н-5 Py); 7.24-7.05 (4H, m, Ar);
2.66 (2H, q, J = 7.5, CH2CH3); 2.60 (3H, s, 6-CH3 Py); 2.55 (3H, s, 4-CH3 Py);
1.08 (3H, t, J = 7.5, CH2CH3)
4i
8.30 (1H, br. s, NH); 7.65 (1Н, s, Н-5), cyclohexane ring: 3.18 (1Н, m, СНN);
1.81 (2Н, m, Не-2,6); 1.75 (3Н, m, Не-3,4,5); 1.48 (2Н, m, На-2,6); 1.21 (1Н, m, На-4);
1.10 (2Н, m, На-3,5); 2.62 (3H, s, 6-CH3 Py); 2.55 (3H, s, 4-CH3 Py)
4j
8.18 (1H, d, J = 6.8, NH); 7.66 (1Н, s, Н-5); 3.52 (1H, m, CH(CH3)2);
2.60 (3H, s, 6-CH3 Py); 2.55 (3H, s, 4-CH3 Py); 1.12 (6H, d, J = 6.8, CH(CH3)2)
4k
7.69 (1Н, s, Н-5); 5.77 (2H, ddd, J = 15.0, J = 11.0, J = 17.0, CH2CH=CH2);
5.26-5.15 (4H, m, CH2CH=CH2); 3.93 (4H, d, J = 4.8, CH2CH=CH2);
2.62 (3H, s, 6-CH3 Py); 2.57 (3H, s, 4-CH3 Py)
4l
7.72 (1Н, s, Н-5); 7.40-7.25 (5H, m, Ar); 3.48 (3H, s, N-CH3); 2.68 (3H, s, 6-CH3 Py);
2.57 (3H, s, 4-CH3 Py)
5a
5b
7.55-7.25 (4H, m, Ar); 2.92 (2H, q, J = 7.6, CH2CH3); 2.75 (6H, s, 6-CH3 Py);
2.70 (6H, s, 4-CH3 Py); 1.22 (3H, t, J = 7.6, CH2CH3)
7.82 (1H, s, Н-2 Ar); 7.60 (1H, d, J = 8.3, Н-5 Ar); 7.51 (1H, d, J = 8.3, Н-6 Ar);
7.82-7.51 (3H, m, Ar); 2.82 (6H, s, 6-CH3 Py); 2.72 (6H, s, 4-CH3 Py);
2.41 (3H, s, 4-CH3 Ar)
1049

TABLE 3. The Electron-Impact Mass Spectra of Compounds 2a, 3, 4a-l, 5a,b
Com-
pound
m/z (Irel,%)
2а
264 [М]+ (15), 200 [М–SO2]+ (18), 165 [М–SO2С1]+ (100),
138 [165–НCN]+ (34), 130 [165–Сl]+ (25), 102 [138–HCl]+ (55)
3
166 [М]+ (100), 130 [M–HCl]+ (30), 104 [130–CN]+ (24), 103 [130–HCN]+ (26)
4а
349 [М]+ (10), 320 [М–С2Н5]+ (22), 285 [F1]+ (14), 270 [285–CH3] + (30),
256 [320–SO2]+ (19), 165 [F2]+ (11), 120 [F3]+ (100)
4b
4c
305 [F1]+ (8), 270 [305–Сl]+ (24), 165 [F2]+ (51), 140 [F3]+ (100),
105 [140–Сl]+ (44)
261 [F1]+ (10), 232 [M–СN, –furyl]+ (17), 165 [F2]+ (100), 138 [165–HСN]+ (18), 96 [F3]+
(56)
4d
4e
4f
369 [М]+ (2), 305 [F1]+ (6), 165 [F2]+ (51), 140 [F3] ]+ (100), 125 [F3–NH]+ (23)
349 [М]+ (2), 334 [M–CH3]+ (4), 285 [F1]+ (4), 165 [F2]+ (11), 120 [F3] + (100)
327 [М]+ (2), 263 [F1]+ (5), 165 [F2]+ (23), 98 [F3] + (100)
4g
4h
251 [F1]+ (3), 165 [F2]+ (14), 130 [165–Cl]+ (10), 86 [F3]+ (100)
315 [М]+ (23), 251 [F1]+ (16), 236 [251–CH3] + (23), 222 [251–C2H5]+ (27),
131 [F2]+ (11), 120 [F3]+ (100)
4i
293 [М]+ (2), 250 [М–С3Н7]+ (57), 186 [F1]+ (28), 159 [186–HCN] + (38),
131 [F2]+ (49), 98 [F3]+ (100)
4j
4k
4l
238 [М–CH3]+ (61), 174 [F1]+ (42), 131 [F2]+ (84), 104 [131–HCN]+ (37),
58 [F3]+ (100)
186 [М–SO2, –CH2CH=CH2]+ (8), 171 [186–CH3]+ (5), 131 [F2]+ (23),
96 [F3]+ (100)
301 [М]+ (5), 237 [F1]+ (27), 222 [237–CH3] + (11), 131 [F2]+ (16),
106 [F3]+ (100), 77 [C6H5]+ (87)
5a
5b
449 [M–2SO2]+ (3), 348 [M–2SO2–Het]+ (45), 284 [M–HetSO2] + (100),
165 [Het]+ (20), 129 [Het–HCl]+ (10), 119 [M–2HetSO2]+ (80)
469 [M–2SO2]+ (3), 368 [M–2SO2–Het]+ (18), 304 [M–HetSO2] + (10),
269 [M–HetSO2–Cl]+ (18), 165 [Het]+ (32), 139 [M–2HetSO2]+ ( (100)
The sulfonyl chloride 2b was identified by the N-substituted sulfonylamides 4h,l produced from it. In
the IR spectra of the sulfonylamides 4a-l there are two characteristic absorption bands in the regions of
1134-1157 and 1358-1377 cm−1, corresponding to the symmetrical and asymmetrical vibrations of the SO2
1
group, and also an absorption band for the cyano group at 2222-2231 cm−1 [7]. The H NMR spectra of
compounds 4a-l contain all the necessary signals (Table 2).
The molecular ions of the sulfonylamides 4a-l are extremely unstable. In most of the compounds the
intensities of the molecular ion peaks amount to 2-5%, and only in individual cases are they 10 (4a) and 23%
(4i). There are no molecular ion peaks in the mass spectra of the sulfonylamides 4b,c,g,j and 4k. The subsequent
fragmentation has much in common and can be represented by the following scheme:
R1
R2
.
.
R1
R2
+
+
–SO2
Het
N
Het SO2
N
.
+
M
F1
– SO2NR1R2
– NR1R2
–Het
+
NR1R2
F3
+
Het
F2
In the IR spectra of compounds 5a,b the absorption band of the NH group disappears compared with the
spectra of 4a,b.
1050

The mass spectra of compounds 5a,b do not contain molecular ion peaks but do contain peaks of the
[M−SO2]+ fragments. The fragmentation paths are presented in Table 3.
Compounds with antidote and growth-regulating activity are found among the newly synthesized
sulfonylamides 4a-l.
EXPERIMENTAL
The IR spectra were recorded for suspensions in vaseline oil on a Specord-71 UR-20 spectrophotometer.
The H NMR spectra were obtained for solutions of the substances in DMSO-d6 on a Bruker WM-500
1
radiospectrometer (500 MHz) with TMS as internal standard. The electron-impact mass spectra were recorded
on a Finnigan MAT INCOS 50 instrument (ionization energy 70 eV). Elemental analysis of the synthesized
compounds for C, H, N, and S was performed on a Carlo-Erba analyzer (model 1106). The reactions and the
purity of the products were monitored by TLC on Silufol UV-254 plates in the 1:1 hexane–acetone system with
iodine vapor as developer.
The benzene used as solvent in the synthesis was purified from impurities and made absolute by known
methods [8].
The initial 3-cyanopyridine-2-thiones 1a,b were prepared by the method in [6] from the corresponding
2-chloronicotinonitriles, the synthesis of which was described in [9].
5-Chloro-3-cyano-4,6-dimethylpyridine-2-sulfonyl Chloride (2a). Chlorine was bubbled into a
suspension of the thione 1a (2.0 g, 10 mmol) in 2 N HCl (20 ml) with stirring for 1 h while the temperature of
the reaction mixture was kept in the range between -2 and 0°C. After the flow of chlorine had stopped the
mixture was stirred at the same temperature for a further 20 min. The precipitate was filtered off, washed on the
filter with iced water to a neutral reaction, pressed, and dried in a vacuum desiccator at 5-10 mm Hg. After
recrystallization from anhydrous hexane we obtained 2.27 g (85%) of the product in the form of light-yellow
shiny crystals; mp 79-80°C.
3-Cyano-4,6-dimethylpyridine-2-sulfonyl Chloride (2b). This compound was obtained similarly to
2a, but the drying stage was omitted, and the product was used straight away in the reaction with the amine.
2-Chloro-4,6-dimethylnicotinonitrile (3). A. The product 2b after washing with iced water was dried
in a vacuum desiccator at 5-10 mm Hg, and the nitrile 3 was obtained with a yield of 81%.
B. The product 2b after washing with iced water was extracted with benzene, the extract was dried with
Na2SO4, the solvent was distilled on a rotary evaporator, and the nitrile 3 was obtained with a yield of 73%.
All the physicochemical characteristics of the product 3 were identical with those of the compound
described in [9].
N-(2-Ethylphenyl)-5-chloro-3-cyano-4,6-dimethylpyridine-2-sulfonylamide (4a). To a solution of
2-ethylaniline (0.47 g, 4.0 mmol) and triethylamine (0.38 g, 3.8 mmol) in anhydrous benzene (15 ml) with
stirring we added dropwise a solution of the sulfonyl chloride 2a (1.0 g, 3.8 mmol) while keeping the
temperature of the mixture in the range of 10-15°C. The mixture was then stirred at the same temperature for 0.5
h and then at room temperature for a further 2-3 h. The precipitate was filtered off, washed from the Et3N·HCl
on the filter with water, combined with the residue obtained after evaporation of the mother solution, and
recrystallized from ethyl acetate. We obtained 0.94 g (71%) of the required sulfonylamide 4a; mp 181-182°C.
IR spectrum, ν, cm−1: 1144, 1362 (SO2), 1482, 1548, 1589 (C=C, C=N arom.), 2227 (С≡N), 3348 (N–H).
Compounds 4b-d were obtained similarly.
5-Chloro-3-cyano-4,6-dimethylpyridine-2-sulfonylmorpholine (4g). Into a solution of compound 2a
(0.90 g, 3.4 mmol) in anhydrous benzene (15 ml) we poured a solution of morpholine (0.31 g, 3.57 mmol) and
triethylamine (0.34 g, 3.4 mmol) in anhydrous benzene (10 ml). The mixture was left at room temperature
1051

for 3-4 h. The reaction mass was then filtered from the precipitate (Et3N·HCl), the solution was evaporated, the
residue was recrystallized from a 1:1 mixture of hexane and ethyl acetate, and 0.81 g (76%) of the
sulfonylamide 4g was obtained in the form of white crystals; mp 154-156°C. IR spectrum, ν, cm−1: 1162, 1373
(SO2), 1562, 1558 (C=C, C=N arom.), 2230 (С≡N).
Compounds 4e,f were obtained similarly.
N-Methyl-N-phenyl-3-cyano-4,6-dimethylpyridine-2-sulfonylamide (4l). To a suspension of moist
sulfonyl chloride 2b (1.0 g, 4.3 mmol) in water (6 ml) at 8-10°C we added dropwise a solution of N-methyl-
aniline (0.50 g, 4.3 mmol) and triethylamine (0.43 g, 4.3 mmol) in acetone (2 ml) while keeping the temperature
constant. When all the amines had been added the mixture was stirred at the same temperature for 1.5-2 h. The
temperature was then raised gradually to room temperature, and the mixture was stirred for a further 1.5-2 h.
The reaction mass was acidified to pH 3-4 with concentrated hydrochloric acid, and the precipitate was filtered
off, washed with water, and dried. After recrystallization from cyclohexane we obtained 0.84 g (64%) of the
product (4l); mp 111-112°C. IR spectrum, ν, cm−1: 1134, 1377 (SO2), 1458, 1527, 1591 (C=C, C=N arom.),
2226 (С≡N).
Compounds 4h-k were obtained similarly.
N-(2-Ethylphenyl)-5-chloro-3-cyano-4,6-dimethylpyridine-2-sulfonylamide (4a) and N-(2-Ethyl-
phenyl)-N,N-bis(4,6-dimethyl-5-chloro-3-cyanopyridine-2-sulfonyl)amine (5a). To a solution of the sulfonyl
chloride 2a (1.20 g, 4.5 mmol) in anhydrous benzene (15 ml) at 10-15°C we added dropwise a solution of
2-ethylaniline (0.57 g, 4.7 mmol) and triethylamine (0.48 g, 4.5 mmol) in anhydrous benzene (10 ml). When all
the amines had been added the mixture was stirred at the same temperature for 0.5 h and then at room
temperature for a further 2-3 h. The precipitate was filtered off, washed copiously with water, and dried. We
obtained a mixture of products with Rf 0.46 (4a) and 0.21 (5a) by TLC. The precipitate was heated to boiling
with ethyl acetate (15 ml) and filtered from the undissolved part. The extract was combined with the residue
obtained after evaporation of the mother solution and recrystallized twice from ethyl acetate. We obtained 0.38 g
(29%) of the product 4a; mp 181-182°C. The residue undissolved in ethyl acetate was recrystallized from a 1:1
mixture of ethanol and DMF, and 0.55 g (56%) of the product 5a was obtained in the form of white crystals; mp
248-251°C. IR spectrum, ν, cm−1: 1138, 1360 (SO2), 1464, 1541, 1580 (C=C, C=N arom.), 2226 (С≡N).
Compound 5b was obtained similarly.
REFERENCES
1.
2.
3.
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