Heterocyclization of 3-(R-amino)-3-methylthio-1-phenylpropenones and 5-benzoyl-6-methylthio-1,2-dihydropyridin-2-ones with 1,2- and 1,3-dinucleophilic reagents

Article abstract of DOI:10.1007/s10593-011-0862-5

The interaction of 3-(R-amino)-3-methylthio-1-phenylpropenones and 1-alkyl-5-benzoyl-3-ethoxy-carbonyl-6-methylthio-1,2-dihydropyridin-2-ones with N,N- and N,C-1,2- and 1,3-dinucleophiles proceeded regioselectively by [3+2] and [3+3] cyclocondensation with the formation of derivatives of pyrazole, benzimidazo[1,2-a]-pyridine, benzimidazo[1,2-a]pyrimidine, imidazo[1,2-a] pyrimidine, [1,2,4]triazolo[4,3-b]pyridazine, and 6,7-dihydro-2H-pyrazolo[3,4-b] pyridine. The regioselectivity of the reactions carried out was analyzed.

Full text of DOI:10.1007/s10593-011-0862-5

Chemistry of Heterocyclic Compounds, Vol. 47, No. 8, November, 2011 (Russian Original Vol. 47, No. 8, August, 2011)
HETEROCYCLIZATION OF 3-(R-AMINO)-3-METHYLTHIO-
1-PHENYLPROPENONES AND 5-BENZOYL-6-METHYLTHIO-
1,2-DIHYDROPYRIDIN-2-ONES WITH 1,2- AND
1,3-DINUCLEOPHILIC REAGENTS
V. N. Britsun1**, N. V. Pikun1, A. B. Ryabitskii1, and M. O. Lozinskii1*
The interaction of 3-(R-amino)-3-methylthio-1-phenylpropenones and 1-alkyl-5-benzoyl-3-ethoxy-
carbonyl-6-methylthio-1,2-dihydropyridin-2-ones with N,N- and N,C-1,2- and 1,3-dinucleophiles
proceeded regioselectively by [3+2] and [3+3] cyclocondensation with the formation of derivatives of
pyrazole, benzimidazo[1,2-a]-pyridine, benzimidazo[1,2-a]pyrimidine, imidazo[1,2-a]pyrimidine,
[1,2,4]triazolo[4,3-b]pyridazine, and 6,7-dihydro-2H-pyrazolo[3,4-b]pyridine. The regioselectivity of
the reactions carried out was analyzed.
Keywords: 1-alkyl-5-benzoyl-3-ethoxycarbonyl-6-methylthio-1,2-dihydropyridin-2-ones, 6-amino-
5-benzoyl-3-ethoxycarbonyl-1-methyl-1,2-dihydropyridin-2-one, 3-(R-amino)-3-methylthio-1-phenyl-
propenones, 1-R1-5-(R-amino)-3-phenylpyrazoles, benzimidazo[1,2-a]pyridines, benzimidazo[1,2-a]-
pyrimidines, 6,7-dihydro-2H-pyrazolo[3,4-b]pyridines, 1,2,4-triazole, [1,2,4]triazolo[4,3-b]pyridazines,
heterocyclization, [3+2] and [3+3] cyclocondensations.
3-Alkylthio-3-(R-amino)-1-arylpropenones may react both with electrophilic and with nucleophilic and
polycentered reagents. As a result of this they are desirable starting materials for the synthesis of nitrogen-
containing heterocycles, derivatives of pyrimidine, pyrrole, pyridine, isoxazole, and quinoline [1-5]. In reactions
with nucleophiles these substrates react at two reaction centers, at the carbonyl group and at C-3 [5]. The
relative ease of carrying out such heterocyclizations is caused by the good nucleofugicity of the alkylthio group
of 3-alkylthio-3-(R-amino)-1-aryl-propenones. In addition the presence of competing reaction centers may lead
to nonselectivity in the execution of reactions of 3-alkylthio-3-(R-amino)-1-aryl-propenones with
unsymmetrical dinucleophiles. It should be mentioned that, with the exception of [5], no investigations have
been carried out in this area.
_______
*Deceased.
**To whom correspondence should be addressed, e-mail: ioch@ioch.kiev.ua.
1Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanska St., Kyiv 02094,
Ukraine.
_________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1183-1190, August, 2011.
Original article submitted February 18, 2011.
970
0009-3122/11/4708-0970©2011 Springer Science+Business Media, Inc.

R2
N
Ph
H2N
R2
H
N
Ph
N
H
Me
R
R1NHNH2
N
O
S
N
4a,b
N
2a,b
R2
R
NH
R
N
R1
Ph
N
N
H
N
R2
5a–c
1a,b
N
3a–c
N
N
N
H
NC
H2N
R
R
NH
8
6
H
N
Ph
Ph
CN
N
N
N
N
N
N
7a,b
9
1a, 3а,b, 5b, 7a, 9 R = Me; 1b, 3c, 5a,c, 7b R = Ph; 2a, 3а R1 = Me; 2b, 3b,c R1 = Ph;
4a, 5a R2 = H; 4b, 5b,c R2 + R2 = benzo
TABLE 1. Characteristics of Compounds Synthesized
Found, %
——————
Calculated, %
Com-
pound
Empirical
formula
mp, C*
Yield, %
С
H
N
3a
3b
3с
C11H13N3
C16H15N3
C21H17N3
C18H14N4
C17H14N4
C22H16N4
C12H11N5
C17H13N5
C19H14N4
C17H17N3O3
C22H19N3O3
C23H21N3O3
C16H16N2O4
C2H3N3
70.34
70.56
7.19
7.00
22.13
22.44
54–57
57
61
68
66
60
52
45
49
37
73
79
53
51
29
77.09
77.08
6.11
6.06
17.08
16.85
101–103
106–108 [12]
80.88
81.00
5.78
5.50
13.25
13.49
150–153
272–278
297–300
328–331
268–270
307–309
305–308
161–164
170–172
131–133
295–298
5a
5b
5с
75.36
75.51
5.20
4.93
19.73
19.57
74.40
74.43
5.32
5.14
20.65
20.42
78.73
78.55
4.52
4.79
16.47
16.66
7а
7b
9
64.04
63.99
5.05
4.92
30.85
31.09
70.79
71.07
4.66
4.56
24.53
24.37
76.72
76.49
5.01
4.73
18.59
18.78
13a
13b
13c
15
16
65.67
65.58
5.38
5.50
13.72
13.50
71.03
70.76
5.28
5.13
11.26
11.25
71.46
71.30
5.47
5.46
11.13
10.85
64.15
63.99
5.08
5.37
9.36
9.33
35.04
34.78
4.24
4.38
61.11
60.84
116–118
119–121 [13]
_______
*Compounds 3a,b, 13a,c were recrystallized from 2-propanol, 3c, 13b, 16
from ethanol, and 5a-c, 7a,b, 9, and 15 from DMSO.
971

The 3-alkylthio-3-(R-amino)-1-arylpropenones form part of the structure of 1-alkyl-5-benzoyl-3-ethoxy-
carbonyl-6-methylthio-1,2-dihydropyridin-2-ones, the annelation of which by nitrogen-containing dinucleo-
philic reagents has been studied more recently [6, 7]. Howevever the data obtained are needed in addition and
reviews.
The aim of the present work was the investigation of the regioselectivity and clarification of the rules
for cyclocondensation of 3-(R-amino)-3-methylthio-1-phenylpropenones and 1-alkyl-5-benzoyl-3-ethoxy-
carbonyl-6-methylthio-1,2-dihydropyridin-2-ones with nitrogen-containing dinucleophilic reagents of unsym-
metrical structure.
The heterocyclization of 3-(R-amino)-3-methylthio-1-phenylpropenones 1a,b with nitrogen-containing
dinucleophiles was effected under fairly rigorous conditions, in boiling hexanol. We established that propenones
1a,b react with substituted hydrazines 2a,b, 2-aminoimidazole (4a), and 2-aminobenzimidazole (4b), 4-amino-
1,2,4-triazole (6), and 2-cyanomethylbenzimidazole (8), regiospecifically with the formation of only one
product in each case (Tables 1-3).
1
Since the H NMR spectra of compounds 3a-c (Table 2) are poorly informative and are incapable of
showing whether they are 1,3- or 1,5-disubstituted pyrazoles, the identification of these compounds was carried
out by counter synthesis.
Unlike 5-arylamino-1,3-disubstituted pyrazoles [8, 9], the 1,5-dialkyl-3-arylaminopyrazoles are less
accessible [10].
We have synthesized 1,3-disubstituted pyrazoles 3a-c by the reaction of 2-benzoylthioacetamides 10a,b
with hydrazines 2a,b by the procedure of [8]. The spectral and physical properties of compounds 3a,c obtained
from 1a,b and 10a,b proved to be identical. This permits us to assume that the products of heterocyclization of
3-(R-amino)-3-methylthio-1-phenylpropenones 1a,b with hydrazines 2a,b are pyrazoles 3a-c. It should be
mentioned that pyrazoles of such structure were synthesized previously by the cyclocondensation of 2-acyl-
acetamides with hydrazines and the Lawesson's reagent [11], albeit in lower yield.
Ph
NHR
2a,b
3a,c
S
O
AcOH
10a,b
10a R = Me, b R = Ph
The structures of the products of heterocyclization of 3-(R-amino)-3-methylthio-1-phenylpropenones
1
1a,b with 2-aminoimidazoles 4a,b and 2-(cyanomethyl)benzimidazole (8) were confirmed by data of H NMR
spectroscopy. The signals of the H-6 protons in the spectra of benzimidazo[1,2-a]pyrimidines 5b,c were found
in the range 7.03-7.31 ppm, while in the case of pyrido[1,2-a]benzimidazole 9 the signal of the H-9 proton was
shifted towards high field (6.14 ppm) as a result of shielding, caused by the effect of the π-electron ring currents
of the phenyl ring.
It may be concluded that the oxygen atom of the carbonyl group of substrates 1a,b reacts with the
exocyclic nitrogen atom of reactant 4a,b, or in its absence (benzimidazole 8) with the endocyclic nitrogen atom.
Proceeding from these data, it may be assumed that the products of the reaction of propenones 1a,b with
4-amino-1,2,4-triazole (6), to all appearances, are [1,2,4]triazolo[4,3-b]pyridazines 7a,b.
In [6, 7] we studied the regioselectivity of the heterocyclization of 1-alkyl-5-benzoyl-3-ethoxycarbonyl-
6-methylthio-1,2-dihydropyridin-2-ones 11a,b, containing fragments of 3-(R-amino)-3-methylthio-1-phenyl-
propenones 1a,b. With the aim of clarifying the differences and similarities of the reactions of the structurally
close compounds 1a,b and 11a,b, we investigated the cyclocondensation of compounds 11a,b with substituted
hydrazines 2a,b and 4-amino-1,2,4-triazole (6).
972

The rings formed in the reaction of 1,2-dihydropyridin-2-ones 11a,b with hydrazines 2a,b may be both
1-R1-7-alkyl-5-ethoxycarbonyl-3-phenyl-6,7-dihydro-1H-pyrazolo[3,4-b]pyridine-6-ones 12a-c and also 2-R1-
7-alkyl-5-ethoxycarbonyl-3-phenyl-6,7-dihydro-2H-pyrazolo[3,4-b]pyridine-6-ones 13a-c. It was clear that the
interaction occurs selectively with the formation of only compounds 13a-c.
Ph
Ph
EtO2C
EtO2C
O
N
N
O
NH
N
R1
O
N
R
2a,b
EtO2C
O
N
R
14a–c
N
6
Ph
SMe
12a–c
N
R
11a,b
6
2a,b
EtO2C
Ph
N
Ph
EtO2C
O
R1
N
O
+
N
N
H
HN
O
N
R
N
R
N
H
16
13a–c
15
11a, 12а,b, 13a,b, 14a,b, 15 R = Me; 11b, 12c, 13c, 14c R = Et; 12а, 13а R1 = Me;
12b,c, 13b,c R1 = Ph
The structures of the products obtained were determined by methods of 2D-spectroscopy (by NOESY
and HETCOR experiments). As the subject of the investigation a compound was taken to which the structure 12a or
13
13a may be assigned. In the HETCOR spectrum of long-range C–1H heteronuclear correlations a C(3)–NCH3
coupling appeared, effected through three bonds. The position of the C(3) atom signal (140.9 ppm)
demonstrated the presence of a long-range C(3)-H-2',6' correlation. Such an interaction is possible only for
isomer 13a.
TABLE 2. IR Spectra of Compounds Synthesized
Compound
, cm–1
3a
3b
3с
3400, 3100, 3000, 2900, 1590, 1520, 1500, 1460, 1370
3250, 3100, 3000, 2950, 1600, 1560, 1500, 1470, 1420, 1360
3200, 3100, 3000, 1605, 1550, 1490, 1460, 1410
3100, 3000, 1620, 1570, 1490, 1400
5a
5b
5с
3100, 2950, 1615, 1560, 1500
3100, 3000, 1610, 1580, 1500
7а
7b
9
3280, 3000, 2900, 1620, 1580, 1540, 1510
3100, 3000, 1610, 1580, 1550
3300, 3100, 3000, 2200, 1640, 1610, 1540
3000, 2900, 1710, 1650, 1630, 1560, 1520
3000, 2850, 1710, 1640, 1600, 1560
13a
13b
13c
15
3000, 2900, 1715, 1650, 1610, 1550
3350, 3200, 3000, 1720, 1660, 1580, 1500, 1390
973

1
We have determined the H-1H spatial correlations for the same compound 13a using the nuclear
1
Overhauser effect (NOESY experiment). In the H NMR spectrum, the signals of the phenyl group protons are
displayed as an unresolved multiplet (7.52-7.73 ppm), while in the NOESY spectrum a correlation peak is
observed demonstrating the interaction of the N(2)−CH3 group protons (3.94 ppm) with the phenyl group
protons through space. This is possible only for isomer 13a as a result of the proximity of the spatial disposition
of the corresponding molecular fragments. Consequently, the formation of pyrazolo[3,4-b]pyridin-6-ones 13a-c
is confirmed unequivocally by the methods of 2D-spectroscopy.
8.05
H
O
H
135.5
140.9
7.80
117.9
164.6
H3C
O
102.8
N
CH3
158.4
3.94
37.9
149.9
N
O
N
CH3
3.48
28.4
Fig. 1. Main correlations and assignment of signals in the 1H and 13C spectra of compound 13a.
On interacting 1,2-dihydropyridin-2-ones 11a,b with 4-amino-1,2,4-triazole (6), similarly to the
condensation with 2-aminoazoles [6,7], it is assumed that pyrido[3,2-e][1,2,4]triazolo[4,3-b]pyridazin-7-ones
14a-c are synthesized. But it is clear that it reacts by a different route, the reaction products are 6-amino-
1
5-benzoyl-3-ethoxycarbonyl-1-methyl-1,2-dihydropyridin-2-one (15) and 1,2,4-triazole (16). In the H NMR
spectrum of compound 15 the signals of the NH2 group were displayed as two broadened singlets, located fairly
remote from one another (8.53 and 10.33 ppm). Evidently, the proton of the primary amino group found at low
field forms a stable hydrogen bond with the oxygen atom of the benzoyl group.
In this conversion, 4-amino-1,2,4-triazole (6) is the carrier of the amino group. Concerning similar
reactions for derivatives of 4-amino-1,2,4-triazole it was reported in [13] that the formation of 1,2,4-triazole was
observed on thermolysis of 1-(1',2',4'-triazol-4'-yl)-2,4,6-trimethylpyridinium tetrafluoroborate.
The results obtained by us in this study and previously [6,7] have made it possible to a definite extent to
compare the reactivity and regioselectivity of reactions of 3-(R-amino)-3-methylthio-1-phenylpropenones 1a,b
and 1-alkyl-5-benzoyl-3-ethoxycarbonyl-6-methylthio-1,2-dihydropyridin-2-one 11a,b, containing the same
structural fragment, in relation to dinucleophilic reagents. Heterocyclizations of derivatives of 1,2-dihydro-
pyridin-2-one 11a,b were effected under more mild conditions than similar reactions of arylpropenones 1a,b,
and are characterized by different chemoselectivity. Cyclocondensations of nitrogen-containing 1,2- and 1,3-di-
nucleophilic reagents with 1,2-dihydropyridin-2-ones 11a,b proceed, respectively, as reactions of the exocyclic
and endocyclic amino groups of the dinucleophile at the C-6 atom of the pyridine ring and the benzoyl
fragment. A different direction of heterocyclization is observed for 3-(R-amino)-3-methylthio-1-phenyl-
propenones 1a,b. Reactions of the exocyclic and endocyclic amino groups of the dinucleophile are carried out at
the carbonyl group and C-3 atom of substrates 1a,b. This phenomenon is caused by the fact that in substituted
1,2-dihydropyridin-2-ones 11a,b the enamine fragment is a part of a π-deficient heterocycle. This further
reduces the electron density on the C-6 atom and assists attack of the exocyclic amino group of the nucleophile
at precisely this reaction center.
974

TABLE 3. 1H NMR Spectra of Compounds Synthesized
Com-
pound
Chemical shifts, , ppm (J, Hz)*
3a
3b
3с
2.72 (3Н, d, J = 2.9, NHCH3); 3.56 (3H, s, 1-CH3);
5.52 (1Н, br. s,, NHMe); 5.72 (1Н, s, H-4); 7.21 (1H, m, H Ph);
7.33 (2Н, m, H Ph); 7.67 (2Н, m, H Ph)
2.75 (3Н, d, J = 3.2, NHCH3); 5.53 (1Н, br. s, NHMe); 5.94 (1Н, s, H-4);
7.28 (4H, m, H Ph); 7.50 (2H, m, H Ph); 7.62 (2Н, m, H Ph);
7.78 (2Н, m, H Ph)
6.68 (1Н, s, H-4); 6.75 (1H, m, H Ph); 6.88 (2Н, m, H Ph);
7.16 (2H, m, H Ph); 7.32-7.49 (6H, m, H Ph); 7.67 (2Н, m, H Ph);
7.88 (2Н, m, H Ph); 8.08 (1Н, s, NHPh)
5a
5b
6.67 (1Н, s, H-6); 7.29-7.63 (9Н, m, H Ar); 7.95 (2Н, m, H Ar);
8.07 (1Н, d, J = 2.6, Н-3); 9.70 (1Н, br. s, NHPh)
3.21 (3Н, d, J = 3.6, NHCH3); 6.71 (1Н, s, Н-3); 7.31 (1Н, m, Н-6);
7.43-7.60 (5H, m, H Ar + NHMе); 7.73 (1Н, m, H Ar); 8.28 (2Н, m, H Ar);
8.45 (1H, m, H Ar)
5с
7а
7b
6.63 (1Н, s, H-3); 7.03 (3Н, m, H Ar); 7.27-7.46 (8Н, m, H Ar);
7.79 (2Н, m, H Ar); 8.77 (1Н, m, H Ar); 12.82 (1Н, br. s, NHPh)
2.86 (3Н, d, J = 3.5, NHCH3); 7.03 (1Н, s, Н-7); 7.27 (1Н, br. s, NHMе);
7.55 (3H, m, H Ph); 8.12 (2Н, m, H Ph); 9.11 (1Н, s, Н-3)
7.03 (1Н, m, H Ar); 7.30-7.38 (3H, m, H Ar); 7.59 (3Н, m, H Ar);
7.75 (2Н, m, H Ar); 8.26 (2Н, m, H Ar); 9.28 (1Н, s, Н-3);
9.62 (1Н, br. s, NHPh)
9
3.04 (3Н, d, J = 3.2, NHCH3); 6.14 (1Н, m, Н-9); 6.40 (1Н, s, Н-2);
6.78 (1Н, m, H Ar); 7.23 (1Н, m, H Ar); 7.57-7.71 (7Н, m, H Ar + NHMе)
13a*2
13b
13c
15
1.26 (3Н, t, J = 6.9, OCH2CH3); 3.49 (3Н, s, 7-CH3); 3.94 (3Н, s, 2-CH3);
4.19 (2Н, q, J = 6.9, ОСН2CH3); 7.52-7.73 (5Н, m, H Ph); 8.04 (1Н, s, Н-4)
1.28 (3Н, t, J = 6.8, OCH2CH3); 3.54 (3Н, s, 7-CH3);
4.22 (2Н, q, J = 6.8, ОСН2СН3); 7.30-7.52 (10Н, m, H Ph); 8.12 (1Н, s, Н-4)
1.28 (6Н, m, 2CH2CH3); 4.23 (4Н, m, 2СН2СН3);
7.32-7.53 (10Н, m, H Ph); 8.12 (1Н, s, Н-4)
1.16 (3Н, t, J = 6.4, OCH2CH3); 3.38 (3Н, s, 1-CH3);
4.07 (2Н, q, J = 6.4, ОСН2СН3); 7.46-7.52 (5Н, m, H Ph);
8.20 (1Н, s, Н-4); 8.53 (1H, br. s, NH); 10.33 (1Н, br. s, NH…O)
_______
*Centers are shown for narrow multiplets.
*
2 13C NMR spectrum (DMSO-d6) δ, ppm: 14.1 (ОCH2СH3); 28.4 (7-СH3);
37.9 (2-СH3); 60.3 (ОCH2СH3); 102.8 (С-4); 117.9 (С-5); 126.8, 129.2,
129.3, 129.8 (С Ph); 135.5 (С-3а); 140.9 (С-3); 149.9 (С-7а); 158.4 (C-6);
164.6 (C=O).
EXPERIMENTAL
1
13
The IR spectra were recorded on a UR 20 instrument in KBr disks. The H and C NMR spectra were
recorded on a Varian Gemini 2000 instrument (at 400 and 100 MHz respectively) in DMSO-d6 solution, internal
standard was TMS. 2D-experiments were carried out by the procedures of [14, 15] using standard settings. In
the NOESY spectrum the displacement time was 0.7 sec, in the HETCOR spectra the coupling constant values
were 1JCH = 140 and nJCH = 8 Hz.
1-R1-5-(R-amino)-3-phenylpyrazoles 3a-c, 4-(R-amino)-2-phenylbenzimidazo[1,2-a]pyrimidines
5b,c, 8-(R-amino)-6-phenyl[1,2,4]triazolo[4,3-b]pyridazines 7a,b, 3-Methylamino-1-phenyl-3,4-dihydro-
pyrido[1,2-a]benzimidazole-4-carbonitrile (9). A solution of 3-(R-amino)-3-methylthio-1-phenylpropenone
975

1a,b (2 mmol) and the corresponding reagent 2a,b, 4a,b, 6, or 8 (2 mmol) in 1-hexanol (15 ml) was boiled
under reflux for 3 h. 1-Hexanol (12 ml) was distilled off and the remainder cooled. The solid was filtered off
and dried.
Counter Synthesis of 1-Methyl-5-methylamino-3-phenylpyrazole (3a) and 1,3-Diphenyl-5-phenyl-
aminopyrazole (3c). Compounds 3a,c were obtained by the reaction of thioacetamides 10a,b with hydrazines
2a,b in AcOH by the procedure of [8].
N,7-Diphenylimidazo[1,2-a]pyrimidine-5-amine (5a). A solution of 3-methylthio-1-phenyl-3-phenyl-
aminopropenone (1b) (0.538 g, 2 mmol), 2-aminoimidazole sulfate (4a) (0.264 g, 1 mmol), and sodium ethylate
(0.136 g, 2 mmol) in anhydrous ethanol (5 ml) was boiled for 6 h. The mixture was cooled, the solid compound
5a was filtered off, washed with water (2x5 ml), and dried.
7-R-2-R1-5-Ethoxycarbonyl-3-phenyl-6,7-dihydro-2H-pyrazolo[3,4-b]pyridin-6-ones 13a-c were
obtained by the heterocyclization of 1-alkyl-5-benzoyl-3-ethoxycarbonyl-6-methylthio-1,2-dihydropyridin-
2-ones 11a,b with hydrazines 2a,b by the procedure of [7].
Reaction of 5-Benzoyl-3-ethoxycarbonyl-1-methyl-6-methylthio-1,2-dihydropyridin-2-one (11a)
with 4-amino-1,2,4-triazole (6). A solution of compound 11a (0.662 g, 2 mmol) and aminotriazole 6 (0.168 g,
2 mmol) in 1-hexanol (5 ml) was boiled for 3 h. The mixture was cooled and the solid filtered off, dried, and
6-amino-5-benzoyl-3-ethoxycarbonyl-1-methyl-1,2-dihydropyridin-2-one (15) was obtained. The filtrate was
evaporated and extracted with hot (50-60oC) water (25 ml). The aqueous extract was evaporated to a volume of
1 ml, cooled, and solid 1,2,4-triazole (16) (0.039 g) was filtered off.
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