The Mannich reaction in the synthesis of N,S-containing heterocycles 3. Unexpected direction of the aminomethylation reaction of N-methylmorpholinium 1-amino-2,4-dicyano-4-ethoxycarbonyl-1,3-butadienethiolate. One stage cascade synthesis of new derivatives of pyrido[1,2-a][1,3,5]triazine

Article abstract of DOI:10.1007/s10593-007-0143-5

The interaction of N-methylmorpholinium 1-amino-2,4-dicyano-4- ethoxycarbonyl-1,3-butadienethiolate with primary amines and formaldehyde leads to the formation of ethyl esters of 7-cyano-6-thioxo-1,3,4,6-2H-pyrido[1,2-a][1, 3,5]triazine-9-carboxylic acid in place of the expected derivatives of pyrido[2,1-b][1,3,5]thiadiazine. The structure of the ethyl ester of 7-cyano-3-phenyl-6-thioxo-1,3,4,6-2H-pyrido[1,2-a][1,3,5]triazine-9-carboxylic acid was demonstrated by X-ray structural analysis.

Full text of DOI:10.1007/s10593-007-0143-5

Chemistry of Heterocyclic Compounds, Vol. 43, No. 7, 2007
THE MANNICH REACTION IN THE SYNTHESIS
OF N,S-CONTAINING HETEROCYCLES
3*. UNEXPECTED DIRECTION OF THE
AMINOMETHYLATION REACTION OF
N-METHYLMORPHOLINIUM 1-AMINO-
2,4-DICYANO-4-ETHOXYCARBONYL-
1,3-BUTADIENETHIOLATE. ONE STAGE
CASCADE SYNTHESIS OF NEW DERIVATIVES
OF PYRIDO[1,2-a][1,3,5]TRIAZINE
V. V. Dotsenko1, S. G. Krivokolysko1, E. B. Rusanov2,
A. V. Gutov2, and V. P. Litvinov3
The interaction of N-methylmorpholinium 1-amino-2,4-dicyano-4-ethoxycarbonyl-1,3-butadienethiolate
with primary amines and formaldehyde leads to the formation of ethyl esters of 7-cyano-6-thioxo-
1,3,4,6-2H-pyrido[1,2-a][1,3,5]triazine-9-carboxylic acid in place of the expected derivatives of
pyrido[2,1-b][1,3,5]thiadiazine. The structure of the ethyl ester of 7-cyano-3-phenyl-6-thioxo-1,3,4,6-
2H-pyrido[1,2-a][1,3,5]triazine-9-carboxylic acid was demonstrated by X-ray structural analysis.
Keywords: N-methylmorpholinium 1-amino-2,4-dicyano-4-ethoxycarbonyl-1,3-butadienethiolate, pyrido-
[1,2-a][1,3,5]triazines, cascade heterocyclization, Mannich reaction, X-ray structural analysis.
It is known from numerous literature data that the three-component Mannich cyclocondensation of a
series of mercaptoazoles and -azines, formaldehyde, and primary amines serves as a convenient method of
obtaining various heterocyclic systems annelated with the 1,3,5-thiadiazine ring [2-11]. Recently
heterocyclization of a similar type was used successfully by us to obtain derivatives of pyrido-
[2,1-b][1,3,5]thiadiazine [12, 13]. Continuing investigations of polycomponent cascade reactions [14], we turned
our attention to N-methylmorpholinium 1-amino-2,4-dicyano-4-ethoxycarbonyl-1,3-butadienethiolate (1) [15] as
a promising subject for carrying out cascade heterocyclization under the conditions of the Mannich reaction.
This diene is readily available and fairly stable. Even on boiling for 3 h it crystallizes out from
_______
* For Part 2 see [1].
__________________________________________________________________________________________
1ChemEx Laboratory, East-Ukrainian Vladimir Dal National University, Lugansk 91034, Ukraine;
e-mail: ksg@lep.lg.ua. 2Institute of Organic Chemistry, National Academy of Sciences of Ukraine; Kiev 02094;
3
e-mail: iochkiev@ukrpack.net. N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
Moscow 117913; e-mail: vpl@mail.ioc.ac.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7,
pp. 1075-1081, July, 2007. Original article submitted April 3, 2006.
906
0009-3122/07/4307-0906©2007 Springer Science+Business Media, Inc.

alcoholic solution in unchanged form. Aspects of the spatial structure of compound 1 were not considered in
[15], but it is entirely probable that its comparative stability towards cyclization is explained by the favorable
E,E-configuration, as was shown previously [16, 17] in the example of other functionally substituted butadienes
of similar type. In this connection it is of particular interest that on treatment with alkyl halides thiolate 1 is
spontaneously cyclized with the formation of 6-alkylthio-2-amino-5-cyanonicotinic acid esters [15, 18].
Butadienethiolate 1 was therefore considered by us as a convenient alicyclic synthon permitting, under Mannich
reaction conditions, one stage accomplishment of the cascade synthesis of bicyclic products, viz. derivatives of
pyrido[2,1-b][1,3,5]thiadiazine.
However the experiment gave an unexpected result. It turned out that the interaction of compound 1 with
primary amines 2 and an excess of formaldehyde in ethanol leads on brief heating to the formation of ethyl esters
of 7-cyano-6-thioxo-1,3,4,6-2H-pyrido[1,2-a][1,3,5]triazine-9-carboxylic acid 3a-e and not derivatives of
pyrido[2,1-b][1,3,5]thiadiazine 4.
RNH2
+
HCHO
RHN
OH
NH
2
COOEt
5
R
N
N
+
4
BH
S
S
RNH2 (2a-e), HCHO
COOEt
CN
H2N
S
EtOH,
– B
∆
CN CN
4
6
5
R
CN
1
3 N
N
7
8
1
2
N
9
H
– H2O
5
COOEt
3 a-e
NC
COOEt
NC
COOEt
NH
HCHO
_
..
CN
_
S
NH
S
N
– H2O,
– B
+
+
BH
BH
NHR
NHR
6
7
В = N-methylmorpholine; 2, 3 a R = Ph, b R = 3,4-Me2C6H3,
c R = furfuryl, d R = 4-FC6H4, e R = 2-EtOC6H4
Presumably, in the first stage of the process butadienethiolate 1 under the action of N-(hydroxy-
methyl)amine 5, formed as an intermediate, is converted into N-aminomethyl derivative 6. This is in agreement
with the data of [19], indicating the predominant aminomethylation of compounds with a thioamide fragment
just at the nitrogen atom. Then intermediate 6, existing in all appearances in the s-cissoid form, undergoes
selective cyclization with the formation of pyridine 7, which reacts with a second molecule of formaldehyde to
form the 1,3,5-triazine ring in the bicyclic molecule 3.
It is nessary to note that the number of methods of synthesizing derivatives of pyrido[1,2-a]-
[1,3,5]triazine is limited [20-25]. However, compounds of this class are of practical interest being strong
antagonists of the 5-hydroxytryptamine receptors 5-HT2 and 5-HT2a [26-28] and are active anthelmintic and
fungicidal agents [28, 29]. These data, the availability of the starting materials, and the simplicity of carrying out
the synthesis, in combination with the fairly high yields of the desired products (73-85%), indicate the promise
of the method developed by us for obtaining pyridotriazines.
907

The structure of [1,2-a][1,3,5]triazines 3a-e was confirmed by data of spectral investigations. In the IR
spectra of the synthesized compounds absorption bands were detected for stretching vibrations in the ranges
ν = 3175-3210, 2217-2230, and 1675-1690 cm-1, indicating the presence of imino group, a conjugated nitrile
function, and ester groups respectively. Of the number of the most characteristic signals observed in the 1H NMR
spectra of pyrido[1,2-a][1,3.5]triazines, it is necessary to mention the sharp singlet of the proton H-8 of the
pyridine ring (δ = 7.95-8.03) and the broadened peak of the NH proton resonating in a narrow range (δ 9.93-9.96
ppm) for compounds 3a,b,d,e, while in the case of compound 3c, bearing a furfuryl substituent in position 3, the
signal of the imino group was displaced somewhat towards higher field (δ = 9.74 ppm). The protons of the
1,3,5-triazine ring were detected in the region δ = 5.39-6.08 (H2-4) and δ = 4.54-5.19 ppm (H2-2) and are
multiplets, which are resolved at 200 MHz as broadened peaks. It is necessary to note that since it is impossible
to characterize the fine structure and coupling constants for clearly multiplet signals of NH and H2-2, presumably
due to the low values of the corresponding JNH-H constant, the isomeric structures 3 and 4 are difficult to
1
distinguish on the basis of data of IR and H NMR spectra. We therefore investigated the structure of the
compound with the proposed structure 3a by the X-ray structural method.
Fig. 1. General shape of the 3a molecule.
In the compound 3a molecule (Fig. 1) the central pyridine ring C(1-5)N(1) is somewhat distorted, the
maximum deviation of an atom from the mean square plane is 0.047(1) Å. The bicyclic system N(1-3)C(1-7) is
not planar, the mean square deviation is 0.181 Å. The N(1-3)C(5-7) heterocycle has an envelope conformation,
N(1-2)C(5-7) atoms form a mean square plane with maximum deviation 0.043(1), but the C(6-7)N(3) atoms
form with it a corner of 51.79(14)°. The dihedral angle between the N(1-2)C(5-7) fragment of the heterocycle
and the N(1)C(1-5) pyridine ring is 7.16(1)°. The C=S bond length (1.677(2) Å) is within the limits
characteristic of pyridine-2-thiones [31]. The O(1), C(9), and O(2) of the ester group are unfolded relative to the
mean square plane of the pyridine fragment by 4.88(1)o. The N(3) atom has a pyramidal configuration, the sum
of the valence angles is 347.29(17)°, the bond lengths at the N(3) atom are within the limits 1.424-1.439(3) Å. A
special feature of the molecular structure of the compound is the formation of intramolecular hydrogen bonds
N(2)–H···O(1) (N(2)–H(2N) 0.83(3), N(2)···O(1) 2.675(3) Å, N(2)–H(2N)–O(1) 137(2)°), closing a five-
membered ring at O(1)C(9)C(4)C(5)N(2)H(2). This same hydrogen atom participates in the formation of a
908

series of intermolecular bonds with the nitrile group N(2)–(H)···N(4): N(2)–H(2N) 0.83(3), N(2)···N(4) 2.959(3)
Å, N(2)–H(2N)···N(4) 131(2)o (the underlined atoms are linked with the initial by a variation of the symmetry x,
y + 1, z), directed along the y crystallographic axis (Fig. 2).
Fig. 2. Crystal packing of compound 3a.
EXPERIMENTAL
1
The H NMR spectra were taken on a Varian Gemini 200 instrument (200 MHz) in DMSO-d6, internal
standard was TMS. The IR spectra were obtained on an IKS-29 spectrophotometer (in nujol), elemental analysis
was carried out on a Perkin-Elmer CHN analyzer. A check on the purity of the obtained substances was effected
by TLC on Silufol UV-254 plates, eluent was acetone–heptane, 1 : 1, visualization with iodine vapor, UV
detector. The melting points of substances were determined on a Kofler stage and are not corrected.
X-Ray Structural Investigation of a monocrystal of compound 3a (grown in acetone–DMF, 1 : 1) of
size 0.5 x 0.32 x 0.25 mm was carried out at room temperature on an Enraf-Nonius CAD-4 automatic four-circle
diffractometer (MoKα radiation, λ = 0.71073 Å, ratio of scanning rates 2θ/ω 1.2, θmax = 25°, segment of sphere
0 ≤ h ≤ 11, -11 ≤ k ≤ 11, -11 ≤ l ≤ 11). In all 2745 reflections were collected. The crystals of compound 3a were
triclinic, a = 9.282(3), b = 9.411(2), c = 9.867(2) Å, α = 96.49(2), β = 106.59(3), γ = 98.40(3)°, V = 806.3(4) Å3,
M = 340.40, Z = 2, dcalc = 1.402 g/cm3, µ = 0.219 mm-1, F(000) = 356, space group P , (N 2). The structure was
1
interpreted by the direct method and refined by the least squares method in a full matrix anisotropic
approximation using the SHELXL97 and SHELXS97 set of programs [31, 32]. In the refinement 2086
reflections with I >2σ(I) were used (281 refined parameters, number of reflections per parameter 7.4). The
positions of the hydrogen atoms were calculated geometrically and refined isotropically. The weighting scheme
calculated from the following equation was used in the refinement w = 1/[σ2(Fo2)+(0.0545P)2 + 0.0871P], where
P = (Fo2+2Fc2)/3. The final values of the divergence factors were R = 0.0353 and Rw = 0.0951, GOOF = 1.033.
The residual electron density from the Fourier difference synthesis was -0.18 and 0.17 e/Å2. Calculation of
absorption in the crystal was carried out by the azimuthal scanning method. The complete set of X-ray structural
data for compound 3a is deposited in the Cambridge Structure Data Bank (No. CCDC 601358).
909

N-Methylmorpholinium 1-Amino-2,4-dicyano-4-ethoxycarbonyl-1,3-butadienethiolate (1) was
obtained by a modification of the procedure of [15]. N-Methylmorpholine (6.5 ml, 60 mmol) was added to a
suspension of the ethyl ester of E-2-cyano-3-ethoxyacrylic acid [33] (10 g, 59 mmol) and cyanothioacetamide
[34] (5.9 g, 59 mmol) in EtOH (25 ml). The resulting dark-red solution was stirred for 5 h at ~20°C, left
overnight, then an equal volume of ether was added to the obtained suspension, and the mixture stirred for 1 h at
~20°C. The orange crystalline solid butadienethiolate 1 was filtered off, washed with cold EtOH, and with ether.
Yield 82%; mp 127-130°C (dec.) (Lit. 113-117°C [15]). IR spectrum, ν, cm-1: 1629 (δ NH2), 1689 (C=O), 2193
1
and 2217 (2 C≡N), 3300 and 3420 (NH2). H NMR spectrum, δ, ppm (J, Hz): 8.61 (1H, s, H-3); 8.05 and 7.18
(both 1H, br. s, NH2); 4.10 (2H, q, J = 7.0, CH2CH3); 3.78 (4H, m, CH2OCH2); 3.21 (4H, m, CH2NCH2); 2.82
(3H, s, NCH3); 1.25 (3H, t, J = 7.0, CH2CH3).
Pyrido[1,2-a][1,3,5]triazines 3a-e (General Method). A mixture of butadienethiolate 1 (1 g,
3.1 mmol), the appropriate amine 2a-e (3.1 mmol), and 37% HCHO (5 ml) in EtOH (15-20 ml) was brought to
boiling with stirring, and from the initially formed light-red solution a finely crystalline solid separated after
several seconds. The reaction mixture was boiled for 3 min further with vigorous stirring, the obtained
suspension was stirred for 2 h at ~20°C, the solid pyrido[1,2-a][1,3,5]triazine 3a-e was filtered off, and washed
with EtOH. For analytical purposes the product was recrystallized from a suitable solvent.
7-Cyano-3-phenyl-6-thioxo-1,3,4,6-2H-pyrido[1,2-a][1,3,5]triazine-9-carboxylic Acid Ethyl Ester
(3a). Light-yellow crystals, yield 81%; mp 227-230°C (dec.) (Me2CO : DMF, 1 : 1). IR spectrum, ν, cm-1: 1685
(C=O), 2223 (C≡N), 3190 (NH). 1H NMR spectrum, δ, ppm (J, Hz): 9.96 (1H, br. s, NH); 7.97 (1H, s, H-8);
7.32 (2H, m, C6H5, H-2,6); 7.00 (3H, m, C6H5, H-3-5); 6.08 (2H, br. s, 2H-4); 5.19 (2H, br. s, 2H-2); 4.25 (2H,
q, J = 7.0, CH2CH3); 1.36 (3H, t, J = 7.0, CH2CH3). Found, %: C 59.30; H 4.78; N 16.60. C17H16N4O2S.
Calculated, %: C 59.98; H 4.74; N 16.46.
7-Cyano-3-(3,4-dimethylphenyl)-6-thioxo-1,3,4,6-2H-pyrido[1,2-a][1,3,5]triazine-9-carboxylic Acid
Ethyl Ester (3b). Yellow crystals, yield 73%; mp 207-209°C (Me2CO : DMF, 4 : 1). IR spectrum, ν, cm-1: 1675
1
(C=O), 2225 (C≡N), 3210 (NH). H NMR spectrum, δ, ppm (J, Hz): 9.94 (1H, br. s, NH); 7.95 (1H, s, H-8);
6.98 (1H, d, J = 7.9, Ar, H-6); 6.78 (1H, br. s, Ar, H-2); 6.65 (1H, d, J = 7.9, Ar, H-5); 6.00 (2H, br. s, 2H-4);
5.12 (2H, br. s, 2H-2); 4.24 (2H, q, J = 7.1, CH2CH3); 2.21 and 2.14 (both 3H, s, 2CH3); 1.34 (3H, t, J = 7.1,
CH2CH3). Found, %: C 61.88; H 5.49; N 15.28. C19H20N4O2S. Calculated, %: C 61.94; H 5.47; N 15.21.
7-Cyano-3-(2-furylmethyl)-6-thioxo-1,3,4,6-2H-pyrido[1,2-a][1,3,5]triazine-9-carboxylic
Acid
Ethyl Ester (3c). Yellow needle-shaped crystals, yield 85%; mp 211-213°C (DMF : EtOH, 1 : 1). IR spectrum,
1
ν, cm-1: 1675 (C=O), 2220 (C≡N), 3200 (NH). H NMR spectrum, δ, ppm (J, Hz): 9.74 (1H, br. s, NH); 8.01
(1H, s, H-8); 7.47, 6.34, and 6.27 (all 1H, m, furyl); 5.39 (2H, br. s, 2H-4); 4.54 (2H, br. s, 2H-2); 4.28 (2H, q,
J = 7.2, CH2CH3); 2.84 (2H, s, NCH2-C3H4O); 1.34 (3H, t, J = 7.2, CH2CH3). Found, %: C 56.03; H 4.71;
N 16.13. C16H16N4O3S. Calculated, %: C 55.80; H 4.68; N 16.27.
7-Cyano-3-(4-fluorophenyl)-6-thioxo-1,3,4,6-2H-pyrido[1,2-a][1,3,5]triazine-9-carboxylic Acid
Ethyl Ester (3d). Light-yellow crystals, yield 74%: mp 226-230oC (dec.) (DMF : EtOH, 1 : 1). IR spectrum, ν,
cm-1: 1676 (C=O), 2217 (C≡N), 3210 (NH). 1H NMR spectrum, δ, ppm (J, Hz): 9.95 (1H, br. s, NH); 8.00 (1H,
s, H-8); 7.02 (4H, m, 4-FC6H4); 6.05 (2H, br. s, H2-4); 5.14 (2H, br. s, H2-2); 4.25 (2H, q, J = 7.1, CH2CH3); 1.34
(3H, t, J = 7.1, CH2CH3). Found, %: C 56.30; H 4.28; N 15.40. C17H15FN4O2S. Calculated, %: C 56.97; H 4.22;
N 15.63.
7-Cyano-3-(2-ethoxyphenyl)-6-thioxo-1,3,4,6-2H-pyrido[1,2-a][1,3,5]thiazine-9-carboxylic Acid
Ethyl Ester (3e). Yellow crystals, yield 83%; mp 225-227°C (decomp.) (from DMF : aqueous HCHO, 10 : 1).
IR spectrum, ν, cm-1: 1690 (C=O), 2230 (C≡N), 3175 (NH). 1H NMR spectrum, δ, ppm (J, Hz): 9.93 (1H, br. s,
NH); 8.03 (1H, s, H-8); 6.90 (2H, m, Ar, H-3,6); 6.72 (2H, m, Ar, H-4,5); 5.97 (2H, br. s, 2H-4); 5.06 (2H, br. s,
2H-2); 4.25 (2H, q, J = 7.1, COOCH2CH3); 4.09 (2H, q, J = 6.9, OCH2CH3); 1.45 (3H, t, J = 6.9, OCH2CH3);
1.32 (3H, t, J = 7.1, COOCH2CH3). Found, %: C 58.90; H 5.27; N 14.68. C19H20N4O3S. Calculated, %: C 59.36;
H 5.24; N 14.57.
910

The work was carried out with the financial support of the Russian Fund for Fundamental Investigations
(RFFI) (project 05-03-32031).
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