Interaction of aminoazoles with Meldrum's acid and dialkyl ketones or cyclohexanone

Article abstract of DOI:10.1007/s10593-007-0071-4

Interaction of 3-amino-5-methylpyrazole, 3-amino-5-methylthio-, and 3,5-diamino-1,2,4-triazole with Meldrum's acid, acetone, ethyl methyl ketone, and cyclohexanone leads to alkyl-substituted pyrazolo[3,4-b]pyridin-6-ones and 1,2,4-triazolo[1,5-a]pyrimidin-7-ones respectively. The structure of 5,5-dimethyl-2-methylthio-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-a] pyrimidin-7-one was demonstrated by an X-ray structural investigation.

Full text of DOI:10.1007/s10593-007-0071-4

Chemistry of Heterocyclic Compounds, Vol. 43, No. 4, 2007
INTERACTION OF AMINOAZOLES WITH MELDRUM'S ACID
AND DIALKYL KETONES OR CYCLOHEXANONE
V. V. Lipson1, V. V. Borodina1, M. G. Shirobokova1,
S. M. Desenko2, O. V. Shishkin2, and R. I. Zubatyuk2
Interaction of 3-amino-5-methylpyrazole, 3-amino-5-methylthio-, and 3,5-diamino-1,2,4-triazole with
Meldrum's acid, acetone, ethyl methyl ketone, and cyclohexanone leads to alkyl-substituted
pyrazolo[3,4-b]pyridin-6-ones and 1,2,4-triazolo[1,5-a]pyrimidin-7-ones respectively. The structure of
5,5-dimethyl-2-methylthio-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-a]pyrimidin-7-one was demonstrated by
an X-ray structural investigation.
Keywords: 3-amino-5-methylpyrazole, 3-amino-5-methylthio-1,2,4-triazole, dialkyl ketones, 3,5-diamino-
1,2,4-triazole, Meldrum's acid, pyrazolo[3,4-b]pyridin-6-ones, 1,2,4-triazolo[1,5-a]pyrimidin-7-ones, X-ray
structural analysis.
The cyclocondensation of nitrogen-containing binucleophiles with arylmethylidene derivatives of Meldrum's
acid or their synthetic precursors has given a broad scope to the synthesis of heterocycles [1-3]. Previously by the
interaction of the indicated acid, aromatic aldehydes, 3-amino-1,2,4-triazole and 2-amino-benzimidazole, we obtained
partially hydrogenated derivatives of 1,2,4-triazolo[1,5-a]pyrimidin-5-one [4] or pyrimido[1,2-a]benzimidazol-2- or -
4-one respectively [5]. It is known that ketones of the aliphatic and aromatic series are also capable of condensing
with Meldrum’s acid as carbonyl components [1, 6]. The alkylmethylidene and arylalkylmethylidene derivatives of
isopropylidenemalonates, formed as a result of such an interaction, in their turn are of interest as synthons in the
synthesis of azoloazine systems. The aim of the present investigation is to clarify the direction of formation of the
azine ring in reactions of 3-amino-5-methylpyrazole (1), 3-amino-5-methylthio- (2) and 3,5-diamino-1,2,4-tetrazole
(3) with Meldrum's acid (4) acetone (5a), ethyl methyl ketone (5b), and cyclohexanone (5c).
It was established that on boiling aminopyrazole 1 with an equimolar amount of 2,2-dimethyl-1,3-dioxane-
4,6-dione (4) and ketones 5a-c, both in methanol and in DMF, only the corresponding pyrazolo[3,4-b]pyridin-
6-ones 6a-c were formed. Products of the isomeric structure 7-9a-c were not isolated.
The composition and structure of the obtained compounds 6a-c were confirmed by the results of elemental analysis
and spectral characteristics (see Experimental). In the IR spectra of compounds 6a-c there was a set of absorption
bands characteristic of cyclic amides in the regions 3400-2850 (ν NH), 1656-1652 (amide I), and 1524-1508 cm-1
(amide II). However these data do not permit an assignment to be made for structures to one of the two types of
positional isomers 6 (7) or 8 (9).
__________________________________________________________________________________________
1V. Ya. Danilevsky Institute of Endocrine Pathology Problems, Academy of Medical Sciences of Ukraine,
2
Kharkiv 61002; e-mail: lipson@ukr.net. Institute of Single Crystals, National Academy of Sciences of Ukraine,
Kharkiv 61001; e-mail: desenko@isc.kharkov.com. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4,
pp. 595-601, April, 2007. Original article submitted March 1, 2006; revision submitted July 4, 2006.
490
0009-3122/07/4304-0490©2007 Springer Science+Business Media, Inc.

O
O
R1
R2
H
N
O
O
4
1. –H2O; 2. –CO2, –Me2CO
MeOH/DMF
N
+
+
O
Me
NH2
1
5a–c
N
HN
NH
Me
R1
2
O
R
6a–c
O
R1 R2
HN
O
N
N
N
N
N
NH
Me
R1
R2
R2
Me
N
Me
N
O
R1
H
H
8a–c
9a–c
7a–c
5–9 а R1 = R2 = Me, b R1 = Me, R2 = Et, с R1 + R2 = −(CH2)5−
1
In the H NMR spectra of compounds 6a-c signals were present for protons of two NH groups, alkyl
substituents, and a methylene group of a partially hydrogenated pyridine ring. In favor of assigning the obtained
products to a pyrazolopyridine (6 or 7) and not a pyrimidine series (8 or 9) is the presence of two broadened singlet
signals of NH groups at 11.71-11.69 and 10.65-10.10 ppm and the absence of a signal for the methine proton of a
pyrazole ring. The choice in favor of isomers 6 was made on the basis of a nuclear Overhauser experiment carried out
for compound 6c. Irradiation of the protons of the CH3 group at position 3 (2.20 ppm) causes a response at the proton
of the NH group of the pyrazole ring (11.64 ppm) and at the protons of the spiro-linked cyclohexane fragment, which
indicates their close spatial disposition.
The interaction of 3-amino-5-methylpyrazole (1) with 2,2-dimethyl-1,3-dioxane-4,6-dione (4) and ketones
5a-c is therefore characterized by high regioselectivity and leads exclusively to the formation of the pyrazolo[3,4-b]-
pyridin-6-one system 6. Such a direction for the process corresponds to the interaction of the β-carbon atom of
intermediates 10 or 11, formed at the first stage from Meldrum’s acid 4 and ketone 5 with the carbon nucleophilic
center in the aminoazole molecule and the carbon atom of the C=O group with the exocyclic amino group.
O
R1
R2
O
O
R1
O
O
O
O
β
α
R2
β
O
O
O
O
O
10
11
The three-component condensation of 3-amino-5-methylthio-1,2,4-triazole (2) with 2,2-dimethyl-1,3-dioxane-
4,6-dione (4) and acetone (5a) or cyclohexanone (5c) was carried out by us in ethyl acetate in the presence of
catalytic amounts of pyridine. An excess of the appropriate ketone was used as solvent for the analogous reactions
involving 3,5-diamino-1,2,4-triazole (3). In all cases tetrahydro-1,2,4-triazolo[1,5-a]pyrimidin-7-ones 12a,b and
13a,b were obtained. In the reaction of diamine 3, triazolylacetamide 14 was isolated together with products
13a,b [7].
491

O
H
O
O
N
N
5a,c
+
+
NH2
R
N
1. –H2O; 2. –CO2 , –Me2CO
O
O
2,3
4
Ac
N
N
N
N
R2
+
H2N
N
NH2
R
N
N
H
R1
12,13a,b
R1 R 2
14 (from diamine 3)
N
N
N
N
NH
R
N
N
N
NH
R
N
R1
R2
O
R
N
O
N
O
R2
19,20a,b
R1
17,18a,b
H
15,16a,b
The composition and structure of the previously undescribed compounds 12 and 13 were confirmed by
results of elemental analysis and spectral characteristics (see experimental). In the IR spectra of products 12a,b and
13a,b there were absorption bands for a carbonyl group at 1712-1756 cm-1, the position of which is typical of the
similar 7-oxo isomers [8], but the amide I and amide II absorption bands characteristic of structures 15 (16) or 19 (20)
were absent (see IR spectra of compounds 6a,c). However the data presented do not permit a choice to be made
between isomers 12 (13) and 17 (18).
1
The H NMR spectra of the obtained products 12a,b 13a,b contain signals of all the protons proposed for
their structures. Finally a choice in favor of the latter was made on the basis of the results of X-ray structural analysis
of compound 12a (Fig. 1, Tables 1, 2).
Fig. 1. Structure of the compound 12a molecule.
492

TABLE 1. Bond Lengths (d) in Molecules A and B of Compound 12a
d, Å
d, Å
Bond
Bond
A
B
A
B
S(1)–C(1)
S(1)–C(6)
O(1)–C(5)
N(1)–C(2)
N(1)–C(5)
N(1)–N(2)
N(2)–C(1)
N(3)–C(2)
1.735(2)
1.781(3)
1.209(2)
1.375(3)
1.391(3)
1.401(2)
1.311(3)
1.322(3)
1.739(2)
1.786(3)
1.197(3)
1.373(3)
1.402(3)
1.397(2)
1.310(3)
1.317(3)
N(3)–C(1)
N(4)–C(2)
N(4)–C(3)
C(3)–C(7)
C(3)–C(8)
C(3)–C(4)
C(4)–C(5)
1.375(3)
1.325(3)
1.474(3)
1.521(3)
1.527(3)
1.533(3)
1.496(3)
1.377(3)
1.333(3)
1.465(3)
1.498(3)
1.542(4)
1.526(3)
1.493(3)
TABLE 2. Valence Angles (ω) in Molecules A and B of Compound 12a
ϕ, deg
ϕ, deg.
Angle
Angle
A
B
A
B
С(1)–S(1)–C(6)
C(2)–N(1)–C(5)
C(2)–N(1)–N(2)
C(5)–N(1)–N(2)
C(1)–N(2)–N(1)
C(2)–N(3)–C(1)
C(2)–N(4)–C(3)
N(2)–C(1)–N(3)
N(2)–C(1)–S(1)
N(3)–C(1)–S(1)
N(3)–C(2)–N(4)
N(3)–C(2)–N(1)
101.1(1)
124.6(2)
109.2(2)
124.5(2)
101.0(2)
102.5(2)
119.7(2)
117.2(2)
124.6(2)
118.3(2)
128.4(2)
110.1(2)
101.2(1)
125.0(2)
109.3(2)
124.5(2)
100.9(2)
102.3(2)
119.9(2)
117.2(2)
123.5(2)
119.3(2)
129.1(2)
120.6(2)
N(4)–C(2)–N(1)
N(4)–C(3)–C(7)
N(4)–C(3)–C(8)
C(7)–C(3)–C(8)
N(4)–C(3)–C(4)
C(7)–C(3)–C(4)
C(8)–C(3)–C(4)
C(5)–C(4)–C(3)
O(1)–C(5)–N(1)
O(1)–C(5)–C(4)
N(1)–C(5)–C(4)
121.5(2)
107.8(2)
109.5(2)
110.5(2)
108.0(2)
109.2(2)
111.7(2)
116.8(2)
121.5(2)
125.6(2)
112.7(2)
120.6(2)
108.3(2)
108.7(2)
110.2(2)
107.9(2)
111.9(2)
109.7(2)
115.3(2)
121.8(2)
126.2(2)
111.9(2)
In the symmetrically independent portion of the unit cell of the crystal of 5,5-dimethyl-2-methylthio-4,5,6,7-
tetrahydro-1,2,4-triazolo[1,5-a]pyrimidin-7-one 12a two molecules (A and B) were found which differed in the
conformation of the six-membered ring. The tetrahydropyrimidine fragment has the distorted half-chair conformation
(folding parameters S = 0.58 (A), 0.63 (B), θ = 50.03 (A), 48.47 (B), Ψ = 12.62 (A), 20.93 (B) [9]). The deviation of
the C(3) and C(4) atoms from the mean plane of the remaining ring atoms was 0.34 (A), 0.31 Å (B) and –0.25 (A) –
0.33 Å (B) respectively. The thiazole ring and the methylthio group atoms lie in one plane with a precision of 0.014
(A) and 0.028 Å (B). The configuration of the N(1) nitrogen atom was not absolutely planar, the sum of the valence
angles centered on the atom was 358.3° in molecule A and 358.7° in molecule B. The C(7) and C(8) atoms have
equatorial and axial orientations, respectively, relative to the six-membered ring [torsion angles C(7)-C(3)-C(4)-C(5)
162.6(2)o (A), -169.7(2)o (B), C(8)-C(3)-C(4)-C(5) –74.9(2) ° (A) and 67.7(3)o (B)],
Nonequivalence of the C(3)-C(7) and C(3)-C(8) bonds occurs in molecule B. The C(3)-C(7) bond at 1.498(3)
Å (mean value 1.530 Å) [10] is significantly shorter, but the C(3)-C(8) bond at 1.542(4) Å is significantly lengthened.
At the same time both bonds in molecule A have equal length [C(3)-C(7) 1.527(3) Å, C(3)-C(8) 1.521(3) Å]. Also
observed was a shortening of the C(5)-N(2) bond at 1.391(3) (A), 1.402(3) Å (B) (1.346 Å) and of the C(2)-N(4) at
1.325(3) (A), 1.333(3) Å (B) (1.339 Å). In the crystal of the compound 12a molecule dimers of the AA and BB type
are formed as a result of hydrogen bonds N(4)-H(4)…N(3') (-x, 1-y, 1-z for AA, -x, 1-y, -z for BB), [H…N 2.23 Å
(AA), 2.16 Å (BB), N-H…N 146o (AA), 172o (BB)]. Furthermore, there were also dimers of the AB type as a result
of stacking interactions between the thiazole rings (distance between ring centers was 3.53 Å, angle between the
planes of rings 8.4°).
493

The considered examples of the interaction of 3-amino-5-methylthio- and 3,5-diamino-1,2,4-triazole with
Meldrum's acid and ketones 5a-c indicate that the process proceeds regioselectively in all cases and leads to the
formation of only one of the possible isomers, viz. 5-alkyl-substituted tetrahydro-1,2,4-triazolo[1,5-a]pyrimidin-
7-one.
EXPERIMENTAL
1
The H NMR spectra were recorded on a Varian 200 spectrometer (200 MHz) for solutions in DMSO-d6.
internal standard was SiMe4. The IR spectra were described on a Specord M 82 instrument (KBr disks). Mass spectra
of compounds 6b,c, 12a,c, and 13a,c were obtained on a Finnigan MAT INCOS 50 instrument (70 eV) and of
compound 6a on a MSBC SELMI spectrometer (source was 10 µCi 252Cf) for positive and negative ions with an
accelerating voltage of ±20 kV. A check on the composition of reaction mixtures and the purity of the compounds
obtained was effected by TLC on Silufol UV 254 plates, eluent was methanol–chloroform–dioxane, 3 : 3 : 4. Melting
points were determined on a Kofler block.
3,4,4-Trimethyl-4,5,6,7-tetrahydropyrazolo[3,4-b]pyridin-6-one (6a). A. A mixture of pyrazole 1 (0.19 g,
2 mmol), Meldrum's acid (4) (0.28 g, 2 mmol), and acetone (5a) (0.170 ml, 2 mmol) in methanol (5 ml) was boiled
for 20-25 min. The reaction mixture was cooled, compound 6a (0.14 g, 40%) was filtered off, and was purified by
1
recrystallization from 2-propanol. Mp 245-247°C. IR spectrum, ν, cm-1: 3400-2650, 1652, 1556, 1520. H NMR
spectrum, δ, ppm: 11.71 (1H, br. s, NH); 10.10 (1H, br. s, NH); 2,26 (2H, s, CH2); 2.20 (3H, s, CH3); 1.19 (6H, s,
CH3). Mass spectrum, m/z (Irel, %): 180 [M+H], 178 [M-H]. Found, %: C 60.04; H 7.33; N 23.31. C9H13N3O.
Calculated, %: C 60.34; H 7.26; N 23.46.
B. DMF (1 ml) was used in place of methanol. The reaction mixture was boiled for 5-7 min, then cooled,
2-propanol (10 ml) was added, and compound 6a (0.12 g, 34%) was filtered off, and was purified by recrystallization
from 2-propanol. A mixing test with a sample obtained by method A gave no depression of melting point.
4-Ethyl-3,4-dimethyl-4,5,6,7-tetrahydropyrazolo[3,4-b]pyridin-6-one (6b) was obtained analogously to
compound 6a from ethyl methyl ketone 5b. Yield was 46% (method A), 43% (method B); mp 226-228°C (from
2-propanol). IR spectrum, ν, cm-1: 3200-2850, 1652, 1612, 1524. 1H NMR spectrum, δ, ppm (J, Hz): 11.64 (1H, br. s,
NH); 10.05 (1H, br. s, NH); 2.22 (2H, s, CH2); 2.15 (3H, s, CH3); 1.45 (2H, m, CH2); 1.15 (3H, s, CH3); 0.72 (3H, t, J
= 8.0, CH3). Mass spectrum (EI, 70 eV), m/z (Irel, %): 193 (42), 164 (100), 146 (32), 136 (23). Found, %: C 61.90; H
7.53; N 21.83. C10H15N3O. Calculated, %: C 62.18; H 7.77; N 21.76.
3-Methyl-4,5,6,7-tetrahydropyrazolo[3,4-b]pyridin-6-one-4-spirocyclohexane (6c) was obtained
analogously to compound 6a from cyclohexanone (5c). Yield was 52% (method A), 50% (method B); mp 272-275°C
(from 2-propanol). IR spectrum, ν, cm-1: 3400-2900, 1656, 1612, 1508. 1H NMR spectrum, δ, ppm: 11.64 (1H, br. s,
NH); 10.67 (1H, br. s, NH); 2.43 (2H, s, CH2); 2.20 (3H, s, CH3); 1.62-1.36 (10H, m, CH2); Mass spectrum, m/z (Irel,
%): 219 (93), 176 (100), 164 (86), 150 (40), 134 (56). Found, %: C 66.02; H 7.63; N 19.21. C12H17N3O. Calculated,
%: C 65.75; H 7.76; N 19.18.
5,5-Dimethyl-2-methylthio-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-a]pyrimidin-7-one (12a). A mixture of
amine 2 (0.2 g, 1.5 mmol), Meldrum's acid (0.22 g, 1.5 mmol), and acetone (5a) (0.13 ml, 1.5 mmol) in ethyl acetate
(5 ml) was boiled for 2 h in the presence of a catalytic amount of pyridine. The reaction mixture was cooled,
compound 12a (0.17 g, 54%) was filtered off, and was recrystallized from acetone, mp 222-224°C. IR spectrum, ν,
1
cm-1: 3180-2892, 1752, 1636. H NMR spectrum, δ, ppm: 8.50 (1H, br. s, NH); 2.75 (2H, s, CH2); 2.46 (3H, s,
CH3S); 1.26 (6H, s, CH3). Mass spectrum, m/z (Irel, %): 212 (100), 197 (21), 170 (87), 83 (83), 42 (30). Found, %: C
45.40; H 5.74; N 26.37; S 14.89. C8H12N4OS. Calculated, %: C 45.28; H 5.66; N 26.42; S 15.09.
2-Methylthio-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-a]pyrimidin-7-one-5-spirocyclohexane (12b) was
obtained analogously to compound 12a, using cyclohexanone in place of acetone. Yield was 48%; mp 228-231°C
(from 2-propanol). IR spectrum, ν, cm-1: 3252-2812, 1756, 1640. 1H NMR spectrum, δ, ppm: 8.50 (1H, br. s, NH);
494

2.79 (2H, s, CH2); 2.46 (3H, s, CH3S); 1.26-1.58 (10H, m, 5CH2). Mass spectrum, m/z (Irel, %): 252 (95), 209 (53),
123 (100), 85 (39), 55 (36). Found, %: C 53.00; H 6.28; N 22.32; S 12.75. C11H16N4OS. Calculated, %: C 52.80;
H 6.40; N 22.40; S 12.80.
2-Amino-5,5-dimethyl-4,5,6,7-tetrahydrotriazolo[1,5-a]pyrimidin-7-one
(13a)
and
1-Acetyl-
3,5-diamino-1,2,4-triazole (14). A mixture of diamine 3 (0.2 g, 2 mmol) and Meldrum’s acid 4 (0.28 g, 2 mmol) in
acetone (5 ml) was boiled for 2 h in the presence of a catalytic amount of pyridine, then cooled, and compound 13a
(0.08 g, 22%) was filtered off, and recrystallized from methanol, mp 248-250°C. IR spectrum, ν, cm-1: 3360-2800,
1716, 1636. 1H NMR spectrum, δ, ppm: 8.07 (1H, br. s, NH); 5.70 (2H, br s, NH2); 2.60 (2H, s, CH2); 1.21 (6H, s,
CH3). Mass spectrum, m/z (Irel, %): 181 (100). 166 (26), 139 (53), 99 (73), 83 (86), 42 (52). Found, %: C 46.50; H
6.08; N 38.75. C7H11N5O. Calculated, %: C 46.41; H 6.08; N 38.67.
The filtrate was evaporated to dryness, 2-propanol (3 ml) was added to the residue, and diamine 14 (0.11 g,
1
39%) was filtered off, mp 198-200°C. IR spectrum, ν, cm-1: 3392, 3296, 3228, 3140, 1712, 1644, 1572. H NMR
spectrum, δ, ppm: 7.32 (2H, br. s, NH2); 5.62 (2H, br. s, NH2); 2.32 (3H, s, CH3) [7].
2-Amino-4,5,6,7-tetrahydrotriazolo[1,5-a]pyrimidin-7-one-5-spirocyclohexane
(13b)
was
obtained
analogously to compound 13a using cyclohexanone 5c in place of acetone. The product 13b was purified from amide
14 by recrystallization from a DMF–2-propanol (1 : 2) mixture. Yield was 23%; mp 258-259°C. IR spectrum, ν, cm-
1: 3352-2848, 1720, 1628. 1H NMR spectrum, δ, ppm: 8.17 (1H, br. s, NH); 5.72 (2H, br. s, NH2); 2.66 (2H, s, CH2);
1.54-1.22 (10H, s, CH2). Mass spectrum, m/z, (Irel, %): 221 (100), 178 (34), 123 (81), 99 (26), 83 (34). Found, %: C
54.51; H 7.00; N 31.58. C10H15N5O. Calculated, %: C 54.30; H 6.79; N 31.67.
X-ray Structural Investigation of Compound 12a. Crystals of compound 12a were triclinic, C8H12N4OS,
at 20°C a = 8.371(2), b = 9.810(2), c = 13.520(4) Å, α = 70.41(2), β = 82.51(2), γ = 81.93(2)°, V = 1031.4(5) Å3, Mr
= 212.28, Z = 4, space group P1, dcalc = 1.367 g/cm3, µ(MoKα) = 0.288 mm-1, F(000) = 448. The parameters of the
unit cell and the intensities of 3901 reflections (3632 independent, Rint = 0.035) were measured on a Siemens P3/PC
automatic four-circle diffractometer (MoKα, graphite monochromator, 2θ/θ scanning, 2θmax = 50°).
The structure was solved by the direct method with the SHELXTL set of programs [11]. The positions of the
hydrogen atoms were made apparent from an electron density difference synthesis and were refined by the rider
model with nonfixed Uiso. The structure was refined on F2 by the full matrix least squares method in an anisotropic
approximation for the nonhydrogen atoms to wR2 = 0.073 for 3632 reflections [R1 = 0.042 for 2650 reflections with F
>4σ(F), S = 1.18].
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