Cyclocondensation of 5-benzoyl-3-ethoxycarbonyl-6-methylthio-1-R-1,2- dihydropyrid-2-ones with heterocyclic N,N-and N,C-1,3-dinucleophiles

Article abstract of DOI:10.1007/s10593-008-0142-1

[3+3] Cyclocondensation of 5-benzoyl-3-ethoxycarbonyl-6-methylthio-1-R-1,2- dihydropyrid-2-ones with heterocyclic N,N-and N,C-1,3-dinucleophiles proceeds regioselectively to give a series of new tri-and tetracyclic heterosystems, viz. derivatives of 5,6-d

Full text of DOI:10.1007/s10593-008-0142-1

Chemistry of Heterocyclic Compounds, Vol. 44, No. 8, 2008
CYCLOCONDENSATION OF 5-BENZOYL-
3-ETHOXYCARBONYL-6-METHYLTHIO-
1-R-1,2-DIHYDROPYRID-2-ONES WITH
HETEROCYCLIC N,N- AND N,C-
1,3-DINUCLEOPHILES
V. N. Britsun, A. N. Esipenko, V. V. Piroghenko, and M. O. Lozinskii
[3+3] Cyclocondensation of 5-benzoyl-3-ethoxycarbonyl-6-methylthio-1-R-1,2-dihydropyrid-2-ones
with heterocyclic N,N- and N,C-1,3-dinucleophiles proceeds regioselectively to give a series of new tri-
and tetracyclic heterosystems, viz. derivatives of 5,6-dihydropyrazolo[1,5-a]pyrido[2,3-d]pyrimidin-
6-one, 1,2-dihydropyrido[2,3-d]pyrido[2′,3′:3,4]pyrazolo[1,5-a]pyrimidin-2-one, 8,9-dihydro-5H-pyrido-
[2,3-d]thiazolo[3,2-a]pyrimidin-8-one, 1,2-dihydrobenzo[4,5]imidazo[1,2-a]pyrido[2,3-d]pyrimidin-
2-one, and 1,2-dihydrobenzo[4,5]imidazo[1,2-g][1,6]naphthyridin-2-one.
Keywords: 2-aminobenzimidazole, 3-amino-2H-pyrazolo[3,4-b]pyridine, 5-amino-3-R1-4-R2-pyrazoles,
2-amino-5-R-thiazoles, 5-benzoyl-3-ethoxycarbonyl-6-methylthio-1-R-1,2-dihydropyridin-2-ones, 7-ethoxy-
carbonyl-5-hydroxy-9-methyl-5-phenyl-2-R-8,9-dihydro-5H-pyrido[2,3-d]thiazolo[3,2-a]pyrimidin-8-ones,
3-ethoxycarbonyl-5-phenyl-1-R-1,2-dihydrobenzo[4,5]imidazo[1,2-a]pyrido[2,3-d]pyrimidin-2-ones,
7-ethoxycarbonyl-9-phenyl-5-R1-3-R2-2-R3-5,6-dihydropyrazolo[1,5-a]pyrido[2,3-d]pyrimidin-6-ones,
3-ethoxycarbonyl-5-phenyl-1-R-1,2-dihydropyrido[2,3-d]pyrido[2',3':3,4]pyrazolo[1,5-a]pyrimidin-
2-ones, 12-cyano-3-ethoxycarbonyl-5-phenyl-1-R-1,2-dihydrobenzo[4,5]imidazo[1,2-g][1,6]naphthyridin-
2-ones, 2-(cyanomethyl)benzimidazole, heterocyclization, [3+3] cyclocondensation.
Derivatives of 3-aroyl-2-(methylthio)pyridine are valuable starting materials for obtaining condensed
nitrogen-containing heterosystems. In spite of the significant number of studies devoted to the synthesis of these
compounds [1-7] their further conversions have not been studied. This is probably explained both by the
nonselectivity of the reactions obtaining them [1-3] and the difficulty of availability of the initial reactants [4-7].
Ph
O
1.
2.
EtO CH
EtONa + MeI
C(COOEt)2
O
S
O
EtO
R
N
Ph
H
O
N
SMe
1a,b
R
2a,b
1, 2 a R = Me. b R = Et
__________________________________________________________________________________________
Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Kiev 2660; e-mail:
bvn1967@rambler.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1216-1222, August,
2008. Original article submitted February 5, 2008.
0009-3122/08/4408-0979©2008 Springer Science+Business Media, Inc.
979

Recently we have developed a preparative method of synthesizing 5-benzoyl-3-ethoxycarbonyl-
6-methylthio-1-R-1,2-dihydropyrid-2-ones from available starting materials and the possibility was shown of
using them for cyclocondensation with nitrogen-containing 1,3-dinucleophiles, particularly with the aim of
obtaining bi- and tricyclic heterosystems [8].
On continuing these investigations we improved the two-step procedure developed by us previously for
the synthesis of 5-benzoyl-3-ethoxycarbonyl-6-methylthio-1-R-1,2-dihydropyridin-2-ones 2a,b, by establishing
that these reactions may be carried out as a one-stage (one-pot) process accomplished without isolation of the
intermediate products.
In comparison with the two-stage method this approach enabled the yields of products 2a,b to be
increased from 45-52 to 65-73%.
Development of a preparative one-step method of synthesizing 1-R-1,2-dihydropyrid-2-ones 2a,b
enabled an investigation [8] of the regioselectivity of their cyclocondensations with heterocyclic N,N- and
N,C-1,3-dinucleophiles to be continued. As such were used 5-amino-3-R1-4-R2-pyrazoles 3a,b, 3-amino-
2H-pyrazolo[3,4-b]pyridine (5), 2-amino-5-R-thiazoles 7a,b, 2-aminobenzimidazole (9), and 2-(cyanomethyl)-
benzimidazole (11).
A special feature of the reaction of 1-R-1,2-dihydropyrid-2-ones 2a,b with N,C- and unsymmetrical
N,N-1,3-dinucleophiles is the possibility of forming two isomeric products, a linear and an angular. It turned out
that in all cases the interaction of substrates 2a,b with reactants 3a,b, 5, 7a,b, 9, and 11 was effected selectively
(Tables 1 and 2).
We showed previously [8] by X-ray structural analysis that the cyclocondensation of 1-R-1,2-
dihydropyrid-2-ones 2a,b with such an aminoazole as 3-amino-1,2,4-triazole (pKa 4.17 [9]) proceeds selectively
and is effected as a nucleophilic attack of the exocyclic and endocyclic amino groups of the reactant at the
methylthio and aroyl groups of the substrate respectively. On the basis of these data it may be concluded that the
products of the interaction of 1-R-1,2-dihydropyridin-2-ones 2a,b with derivatives of 3(5)-aminopyrazole (pKa
4.11 [9]) 3a,b, 5 and 2-aminothiazole (pKa 5.39 [10]) 7a,b have similar structures and are 7-ethoxycarbonyl-
9-phenyl-5-R1-3-R2-2-R3-5,6-dihydropyrazolo[1,5-a]pyrido[2,3-d]pyrimidin-6-ones 4a-c, 3-ethoxycarbonyl-
5-phenyl-1-R-1,2-dihydropyrido[2,3-d]pyrido[2',3':3,4]pyrazolo[1,5-a]pyrimidin-2-ones 6a,b and 7-ethoxycarbonyl-
5-hydroxy-9-methyl-5-phenyl-2-R-8,9-dihydro-5H-pyrido[2,3-d]thiazolo[3,2-a]pyrimidin-8-ones 8a,b.
Since the products of cyclocondensation of 1,2-dihydropyridin-2-one 2a with 2-amino-5-R-thiazoles
7a,b may have both an acyclic and a cyclic structure, then for the unequivocal determination of their structure
we recorded the 13C NMR spectrum of compound 8b.
13
The carbon signal of the phenylcarbonyl group (192.6-198.1 ppm [8]) was absent from the C NMR
spectrum of the reaction product of 1,2-dihydropyrid-2-one 2a with 2-amino-5-methylthiazole 7b, and a signal
was observed for the sp3-hybridized C–N carbon at 86.7 ppm [11], which may be assigned only to the C-5 atom
of pyrido[2,3-d]thiazolo[3,2-a]pyrimidin-8-one 8b.
It should be noted that 5,6-dihydropyrazolo[1,5-a]pyrido[2,3-d]pyrimidin-6-ones 4a-c, 1,2-dihydro-
pyrido[2,3-d]pyrido[2',3':3,4]pyrazolo[1,5-a]pyrimidin-2-ones 6a,b, and 8,9-dihydro-5H-pyrido[2,3-d]thiazolo-
[3,2-a]pyrimidin-8-ones 8a,b are new, previously undescribed heterosystems.
The structures of the products of reaction of 1,2-dihydropyridin-2-ones 2a,b with such highly basic
aminoazines as 3-aminobenzimidazole 9 (pKa 7.39, [9]) and 2-(cyanomethyl)benzimidazole 11, were confirmed
by 1H NMR spectroscopy.
1
The signal of the H-7 proton in the H NMR spectra of compounds 10a,b and 12a,b was displayed at
fairly high fields, at 5.97-6.08 ppm. Such values for proton chemical shifts are not characteristic of
benzimidazole and its derivatives, for which, as shown by analysis of literature data, the chemical shifts of
protons in positions 4-7 lie in the range 7.20-7.80 ppm [12].
980

O
Ph
N
O
Ph
N
EtO
N
N
HN
H2N
N
R3
H
EtO
N
N
N
N
N
R2
3a,b
O
N
R3
O
N
R1
R1
N
H2N
R2
6a,b
5
4a–c
N
R4
2a,b
H2N
7a,b
S
O
Ph
OH
N
HN
NC-CH2
EtO
R4
HN
N
S
N
O
N
R1
11
8a,b
N
H2N
9
Ph
O
Ph
O
N
EtO
N
EtO
N
O
N
N
N
O
N
R1
R1
12a,b
CN
10a,b
2a, 4a,c, 6a, 8a,b 10a, 12a R1 = Me, 2b, 4b, 6b, 10b, 12b R1 = Et; 3a, 4a,b R2 = H,
3b, 4c R2 = CN; 3a, 4a,b R3 = Me, 3b, 4c R3 = H; 7a, 8a R4 = H, 7b, 8b R4 = Me
The anomalous value of the H-7 proton chemical shift in compounds 10a,b and 12a,b act, in our opinion,
as fair confirmation of the linear structure of these polycyclic compounds. In reality, analysis of spatial models
shows that in 1,2-dihydrobenzo[4,5]imidazo[1,2-a]pyrido[2,3-d]pyrimidin-2-ones 10a,b and 1,2-dihydro-
benzo[4,5]imidazo[1,2-g][1,6]naphthyridin-2-ones 12a,b as a result of the steric difficulties the phenyl ring must
be twisted from the planarity of the heterocyclic fragment. An estimate of the size of this dihedral angle for
compound 12a by molecular mechanics methods (MM2) gives a value of ~103o. The position of the phenyl ring
causes the H-7 proton to fall in the shielding region of its π-electron ring currents [13], which also leads to a
displacement of its signal in the 1H NMR spectra into the stronger field region. Calculation of the contribution of
the ring currents of the phenyl ring [14] to the shielding of this proton predicts a displacement of the H-7 proton
signal for compound 12a of 1.9 ppm towards high field, which is in fairly good agreement with the experimental
data.
H
H
O
7
EtO
N
H
N
X
O
N
R
H
10a,b, 12a,b
10, 12 a R = Me, b R = Et; 10a,b X = N, 12a,b X = C–CN
981

TABLE 1. Characteristics of the Synthesized Compounds
Found, %
——————
Calculated, %
Com-
pound
Empirical
formula
mp, °С*
Yield, %
С
H
N
4a
C20H18N4O3
66.54
66.29
66.89
67.01
64.39
64.34
66.38
66.16
66.84
66.82
59.74
59.52
60.27
60.44
69.52
69.34
5.18
5.01
5.57
5.36
4.16
4.05
4.37
4.29
4.38
4.63
4.40
4.47
5.03
4.82
4.67
4.55
15.33
15.46
15.06
14.88
19.02
18.76
17.55
17.53
17.03
16.94
11.19
10.96
10.63
10.57
13.83
14.06
223-225
231-233
300-303
368-370
320-324
350-354
240-242
325-328
306-309
370-375
355-359
62
57
53
47
43
27
24
48
45
56
51
4b
C21H20N4O3
C20H15N5O3
C22H17N5O3
C23H19N5O3
C19H17N3O4S
C20H19N3O4S
C23H18N4O3
C24H20N4O3
C25H18N4O3
C26H20N4O3
4с
6a
6b
8а
8b
10a
10b
12a
12b
70.02
69.89
70.85
71.08
71.29
71.55
5.16
4.89
4.07
4.29
4.68
4.62
13.34
13.58
13.35
13.26
12.71
12.84
_______
*All compounds were recrystallized from DMSO.
TABLE 2. IR Spectra of the Synthesized Compounds
Com-
pound
Com
pound
IR spectrum, ν, cm-1
IR spectrum, ν, cm-1
4a
4b
4c
6a
6b
8a
3100, 3000, 1720, 1660, 1610, 1530,
1490, 1470, 1440, 1390, 1370
8b
3400, 3100, 3000, 1710, 1690, 1620,
1580, 1550, 1530, 1490, 1370
3070, 3000, 1700, 1675, 1600, 1550,
1530, 1490, 1480, 1370
10a
10b
12a
12b
3100, 3000, 1730, 1670, 1620, 1580,
1560, 1520, 1490, 1450, 1370
3100, 3000, 2230, 1730, 1660, 1610,
1540, 1500, 1450, 1370
3090, 3000, 1725, 1660, 1620, 1580,
1520, 1490, 1455, 1380, 1360
3100, 3000, 1730, 1670, 1620, 1580,
1530, 1500, 1470, 1400, 1375
3100, 3000, 2220, 1730, 1680, 1620,
1570, 1530, 1490, 1450, 1370
3060, 3000, 1730, 1660, 1620, 1580
1530, 1490, 1470, 1400, 1380
3080, 3000, 2230, 1730, 1670, 1620,
1570, 1530, 1480, 1460, 1380
3400, 3100, 3000, 1700, 1620, 1550,
1470, 1380
The interaction of 5-benzoyl-3-ethoxycarbonyl-6-methylthio-1-R-1,2-dihydropyrid-2-ones with hetero-
cyclic N,N- and N,C-1,3-dinucleophiles, independent of their basicity, therefore proceeds selectively as a
nucleophilic attack of an exocyclic amino (or cyanomethyl) and endocyclic amino group of a dinucleophile at
the methylthio and aroyl group of the substrate respectively. This cyclocondensation is a method of synthesis of
tri- and tetracyclic heterosystems, including those previously unknown.
EXPERIMENTAL
The 1H and 13C NMR spectra were recorded on a Varian-300 instrument (300 and 75 MHz respectively),
internal standard was TMS. The IR spectra were recorded on a UR-20 instrument in KBr disks.
982

TABLE 3. 1H and 13C NMR Spectra of the Synthesized Compounds
Com-
pound
Chemical shifts, δ, ppm (J, Hz)*
4a
1.22 (3Н, t, J = 6.6, OCH2CH3); 2.35 (1H, s, 2-CH3); 3.60 (3Н, s, 5-CH3);
4.20 (2Н, q, J = 6.6, ОСН2СН3); 6.43 (1H, H-3); 7.70 (5Н, m, C6H5); 7.87 (1Н, s, Н-8)
4b
1.25 (6Н, m, 2 CH2CH3); 2.37 (1H, s, 2-CH3); 4.19 (2Н, q, J = 6.3, ОСН2СН3);
4.38 (2Н, q, J = 4.8, NСН2СН3); 6.48 (1H, H-3); 7.69 (5Н, m, C6H5); 7.88 (1Н, s, Н-8)
4c
1.22 (3Н, t, J = 6.6, OCH2CH3); 3.65 (3Н, s, 5-CH3); 4.22 (2Н, q, J = 6.6, ОСН2СН3);
7.74 (5Н, m, C6H5); 7.96 (1Н, s, Н-8); 8.81 (1H, s, H-2)
6a*2
6b
1.44 (3Н, t, J = 7.2, OCH2CH3); 4.24 (3Н, s, 1-CH3); 4.54 (2Н, q, J = 7.7, ОСН2СН3);
7.77–7.97 (6Н, m, НAr); 8.67 (1Н, s, Н-4); 9.08 (1Н, m, Н-10); 9.57 (1Н, d, J = 6.9, Н-9)
1.24 (3Н, t, J = 6.6, OCH2CH3); 1.39 (3Н, t, J = 6.3, NCH2CH3);
4.26 (2Н, q, J = 6.6, ОСН2СН3); 4.59 (2Н, q, J = 6.3, NСН2СН3); 7.23 (1H, m, HAr);
7.75 (3Н, m, HAr); 7.82 (2Н, m, HAr ); 8.03 (1Н, s, Н-4); 8.67 (1Н, m, Н-10);
8.84 (1Н, d, J = 7.0, Н-9)
8a
1.50 (3Н, t, J = 4.2, OCH2CH3); 4.26 (3Н, s, 9-CH3); 4.61 (2Н, q, J = 4.2, ОСН2СН3);
7.59 (1Н, m, НAr), 7.86 (6Н, m, НAr); 9.13 (1Н, br. s, Н-3)
8b*3
1.15 (3Н, t, J = 6.3, OCH2CH3); 2.17 (3Н, s, 2-CH3); 3.50 (3Н, s, 9-CH3);
4.08 (2Н, q, J = 6.3, ОСН2СН3); 6.77 (1Н, s, ОН); 7.48 (5Н, m, C6H5);7.60 (1Н, s, Н-6);
8.22 (1Н, s, Н-3)
10a
10b
1.21 (3Н, t, J = 6.9, OCH2CH3); 3.58 (3Н, s, 1-CH3); 4.20 (2Н, q, J = 6.9, ОСН2СН3);
6.07 (1Н, d, J = 8.1, Н-7); 7.00 (1Н, m, Н-8); 7.39 (1Н, m, Н-9);
7.69 (1Н, d, J = 8.1, Н-10); 7.73 (1Н, s, Н-4); 7.85 (5Н, m, C6H5)
1.21 (3Н, t, J = 6.3, OCH2CH3); 1.34 (3Н, t, J = 6.9, NCH2CH3);
4.20 (2Н, q, J = 6.3, ОСН2СН3); 4.43 (2Н, q, J = 6.9, NСН2СН3);
6.08 (1Н, d, J = 7.2, Н-7); 7.02 (1Н, m, Н-8); 7.46 (1Н, m, Н-9);
7.60 (1Н, d, J = 6.6, Н-10); 7.76 (1Н, s, Н-4); 7.85 (5Н, m, C6H5)
12a
12b
1.55 (3Н, t, J = 3.9, OCH2CH3); 4.58 (3Н, s, 1-CH3); 4.64 (2Н, q, J = 3.9, ОСН2СН3);
6.55 (1Н, d, J = 5.1, Н-7); 7.59 (1Н, m, Н-8); 7.88 (2H, m, C6H5); 8.04 (1Н, m, Н-9);
8.16 (3H, m, C6H5); 8.26 (1Н, d, J = 4.2, Н-10); 8.63 (1Н, s, Н-4)
1.19 (3Н, t, J = 6.0, OCH2CH3); 1.47 (3Н, t, J = 6.3, NCH2CH3);
4.19 (2Н, q, J = 6.0, ОСН2СН3); 4.67 (2Н, q, J = 6.3, NСН2СН3);
5.97 (1Н, d, J = 7.0, Н-7); 7.05 (1Н, m, Н-8); 7.49 (1Н, m, Н-9);
7.60 (1Н, d, J = 6.8, Н-10); 7.72 (1Н, s, Н-4); 7.88 (5Н, m, C6H5)
_______
1
* H NMR spectra were recorded in DMSO-d6 (compounds 4a-c, 6b, 8b,
10a,b, and 12b) and CF3COOD (compounds 6a, 8a, and 12a).
2
*
13C NMR spectrum of compound 6a (CF3COOD), δ, ppm: 12.1 (OCH2CH3); 29.4
(1-CH3); 64.7 (OCH2CH3); 110.1, 124.7, 125.6, 129.0, 129.6, 130.1, 133.2, 133,7, 140.5,
144.5, 145.2, 145.5, 151.2, 151.4, 152.3 (CAr); 161.3 (C-2); 165.3 (COOEt).
3
*
13C NMR spectrum of compound 8b (DMSO-d6), δ, ppm: 12.7 (2-CH3); 14.8
(OCH2CH3); 29.17 (9-CH3); 60.0 (OCH2CH3); 86.7 (C-5); 101.3 (C-6), 109.5 (C-5a);
120.3, 123.3, 126.8, 129.0 (C6H5); 130.4 (C-2); 132.7 (C-3); 143.4 (C-7); 144.6 (C-9a);
150.1 (C-10a); 159.0 (C-8); 165.4 (COOEt).
5-Benzoyl-3-ethoxycarbonyl-6-methylthio-1-R-1,2-dihydropyrid-2-ones 2a,b. A solution of sodium
ethylate (50 mmol), thioamide 1a,b (50 mmol), and diethyl ethoxymethylenemalonate (10.80 g, 50 mmol) in
anhydrous ethanol (50 ml) was boiled for 1 h, cooled, and methyl iodide (9.23 g, 65 mmol) was added. The
mixture was maintained for 2 h at 30oC, cooled, and water (100 ml) was added to the reaction mixture. The solid
was filtered off, dried, and recrystallized from 2-propanol. Yield of compound 2a was 12.08 g (73%), and of 2b
11,21 g (65%). The melting points and 1H NMR and IR spectra of products 2a,b were identical to those given in
[8].
13
Compound 2a. C NMR spectrum (DMSO-d6), δ, ppm: 14.6 (OCH2CH3); 19.2 (SCH3); 34.7 (1-CH3);
61.1 (OCH2CH3); 119.0 (C-4); 122.3 (C-5); 129.3, 130.0, 134.1, 137.6 (C6H5); 141.3 (C-3); 151.9 (C-6); 159.2
(C-2); 164.5 (O=C−OEt); 193.2 (C6H5–C=O).
983

7-Ethoxycarbonyl-9-phenyl-5-R1-3-R2-2-R3-5,6-dihydropyrazolo[1,5-a]pyrido[2,3-d]pyrimidin-6-ones
4a-c, 3-Ethoxycarbonyl-5-phenyl-1-R1-1,2-dihydropyrido[2,3-d]pyrido[2′,3′:3,4]pyrazolo[1,5-a]pyrimidin-
2-ones 6a,b, 7-Ethoxycarbonyl-5-hydroxy-9-methyl-5-phenyl-2-R4-8,9-dihydro-5H-pyrido[2,3-d]thiazolo-
[3,2-a]pyrimidin-8-ones 8a,b, and 12-Cyano-3-ethoxycarbonyl-5-phenyl-1-R1-1,2-dihydrobenzo[4,5]imid-
azo[1,2-g]naphthyridin-2-ones 12a,b. A solution of 5-benzoyl-3-ethoxycarbonyl-6-methylthio-1-R-1,2-
dihydropyridin-2-one 1a,b (1 mmol) and 5-amino-3-R1-4-R2-pyrazole 3a,b, (or 3-amino-2H-pyrazolo[3,4-b]pyri-
dine 5, 2-amino-5-R-thiazole 7a,b, 2-(cyanomethyl)benzimidazole 11) (1 mmol), in 1-hexanol (4 ml) was boiled
for 4 h, cooled, and solid compound 4a-c (or 6a,b, 8a,b, 12a,b) was filtered off. The physicochemical and
spectral data are given in Tables 1-3.
3-Ethoxycarbonyl-5-phenyl-1-R1-1,2-dihydrobenzo[4,5]imidazo[1,2-a]pyrido[2,3-d]pyrimidin-2-ones
10a,b. A solution of 5-benzoyl-3-ethoxycarbonyl-6-methyl-1-R-1,2-dihydropyridin-2-one 1a,b (1 mmol) and 2-
aminobenzimidazole 9 (1 mmol) in 2-propanol (5 ml) was boiled for 7 h, cooled, and solid compound 10a,b was
filtered off.
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