Efficient synthesis of novel azo compounds based on pyrimido[4,5-e][1,3,4] thiadiazine

Article abstract of DOI:10.4314/bcse.v26i1.12

Some new 5-bromo-2,4-dichloro-6-alkylpyrimidines were prepared by sequential treatment of 6- alkyl-pyrimidin-2,4(1H,3H)-diones with bromine and phosphoryl chloride. Condensation of the dithizone with 5- bromo-2,4-dichloro-6- alkylpyrimidines in alkaline a

Full text of DOI:10.4314/bcse.v26i1.12

Bull. Chem. Soc. Ethiop. 2012, 26(1), 115-120.
Printed in Ethiopia
DOI: http://dx.doi.org/10.4314/bcse.v26i1.12
ISSN 1011-3924
 2012 Chemical Society of Ethiopia
EFFICIENT SYNTHESIS OF NOVEL AZO COMPOUNDS BASED ON PYRIMIDO[4,5-
E][1,3,4]THIADIAZINE
Mohsen Nikpour1*, Soroush Zarinabadi2 and Sattar Saberi2
1Department of Chemistry, School of Sciences, Ahvaz Branch, Islamic Azad University, Ahvaz
6134968875, Iran
2Department of Chemistry, School of Sciences, Shushtar Branch, Islamic Azad University,
Shushtar, Iran
3Department of Chemistry, School of Sciences, Ferdowsi University of Mashhad, Mashhad
91775-1436, Iran
(Received April 21, 2011; revised August 19, 2011)
ABSTRACT. Some new 5-bromo-2,4-dichloro-6-alkylpyrimidines were prepared by sequential treatment of 6-
alkyl-pyrimidin-2,4(1H,3H)-diones with bromine and phosphoryl chloride. Condensation of the dithizone with 5-
bromo-2,4-dichloro-6-alkylpyrimidines in alkaline acetonitrile achieved 5-alkyl-7-chloro-3-phenylazo-1-phenyl-
1H-pyrimido[4,5-e][1,3,4] thiadiazines. 7-chlorine atom of these compounds was replaced by secondary amines
in boiling ethanol to afford their 7-amino derivatives.
KEY WORDS: Azo dyes, 5-Bromo-2,4-dichloro-6-alkyllpyrimidines, Dithizone, Cyclocondensation,
Pyrimido[4,5- e][1,3,4]thiadiazine
INTRODUCTION
A variety of biological activities of pyrimido[4,5-e][1,3,4]thiadiazines is a strong motive to
search for more efficient synthetic methods for this class of heterocyclic compounds. These
compounds have been described as anti-inflammatory, hypotensive, diuretic [1, 2],
phosphodiesterase inhibitor [2] and nucleoside analogues [3] agents. A patent literature
disclosed that pyrimido[4,5-e][1,3,4]thiadiazines are good candidates for dyeing of polyesters
[4]. Condensation of dithizone with 2,4-dichloro-6-methyl-5-nitro-pyrimidine via the smile’s
rearrangement, is an efficient rout for the preparation of this heterocyclic system [5]. In a
previous communication [6] we had described a new approach for the formation of
pyrimido[4,5-e][1,3,4]thiadiazines by condensation of alkyl-2-phenylhydrazinecarbodithioates
with 5-bromo-2,4-dichloro-6- methylpyrimidine. This strategy was extended in the present
research for preparing of novel group of coloring azo compounds.
RESULTS AND DISCUSSION
In this research we exhibit the synthesis of new 1-(5-alkyl-7-chloro- 1-phenyl-1H-pyrimido[4,5-
e][1,3,4]thiadiazin-3-yl)-2-phenyldiazenes by condensation of 5-bromo-2,4-dichloro-6-alkyl-
(phenyl)pyrimidines 3a-e with dithizone 4 as shown in Scheme 1. One of the key starting
materials 3a was prepared earlier [7] and compounds 3b-e were synthesized by treatment of 5-
bromo-6-alkyl-pyrimidin-2,4(1H,3H)-diones 2b-e with phosphoryl chloride. The latter
compounds were prepared via bromination of 6-alkyl-pyrimidin-2,4(1H,3H)-diones 1b-e in
water as shown in Scheme 2.
__________
*Corresponding author. E-mail: nikpour@iauahvaz.ac.ir

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Mohsen Nikpour et al.
Ph
Cl
N
Cl
N=NPh
Cl
N
R
N
S
Acetonitrile, heat
Triethylamine
N
+
N
NH
N
Br HN
Ph
S
N=NPh
R
3a-e
4
5a-e
R= a: methyl, b: ethyl, c: propyl, d:isopropyl, e: phenyl
Ph
Ph
Cl
N
R
N
S
R2N
N
R
N
N
N
EtOH, R2NH, heat
N
N
S
N=NPh
N=NPh
5a, c
5f-k
f: R= methyl, R2NH= piperidine
g: R= methyl, R2NH= morpholine
h: R= methyl, R2NH= 4-methylpiperazine
i: R= propyl, R2NH= piperidine
j: R= propyl, R2NH= morpholine
k: R= propyl, R2NH= 4-methylpiperazine
Scheme 1. Preparation of compounds 5a-k.
Structure assignments of compounds 2b-e and 3b-e are based upon spectral and
microanalytical data. 1H NMR spectrum of the compounds 2b-e lacked the signal of vinyl
proton of number 5 position. This result was confirmed by mass spectra, when it showed the
1
two molecular ions, by 78 and 80 m/z more than the molecular ion of each precursor 1b-e. H
NMR and IR spectra of compounds 3b-e do not show the signals and vibration bands of NH
moieties, which has been regarded to compounds 2b-e and their mass spectra confirmed the
existence of two chlorines and a bromine by exhibition of M, M+2, M+4 and M+6 molecular
ions with the ratio of 9, 15, 7, 1, respectively.
H
N
H
N
N
O
O
Cl
Br
O
O
Cl
POCl3
Br2, H2O
HN
HN
N
Br
R
R
R
1b-e
2b-e
3b-e
R= b:ethyl, c: propyl, d:isopropyl, e: phenyl
Scheme 2. Preparation of precursor 2b-e.
The structures assigned to compounds 5a-e are verified by their spectral and microanalytical
1
data. The H NMR spectrum of compound 4 presented the signals around δ 6.0 and 9.0 ppm
1
belonging to NH moieties, which were devoided in the H NMR spectra of products 5a-e. This
result also amplified by appearance of signals of aromatic protons and signals at δ 1-2.8 ppm for
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Efficient synthesis of novel azo compounds based on pyrimido[4,5-e][1,3,4]thiadiazine
117
alkyl group of precursor 3a-e. IR spectra of compounds 5a-e lacked the stretching vibration
bands at around 3350 cm-1 regarding to N-H bonds of the precursor 4, but showed some bands
at 2900-3000 cm-1 due to symmetric and asymmetric stretching vibration of C-H bonds of alkyl
groups belonged to precursor 3a-e. These results plus the observation of M and M+2 ions in the
mass spectra of compounds 5a-e by the ratio 3:1, indicates the situation of [1,3,4]thiadiazine
ring around positions 4 and 5 of the pyrimidine ring.
In the earlier communications 3D molecular structure of the condensed product of dithizone
analogs with 5-bromo-2,4-dichloro-6-methylpyrimidine 3a was strongly evidenced by X-ray
crystallography [6, 8].
Microanalytical data of compounds 5a-e have no significant difference with the expected
data. We also found that the chlorine atom in the number 7 position of products is easily
replaced by secondary amines in boiling ethanol and C-Cl stretching band disappeared in IR
spectra of compounds 5f-k.
In conclusion the condensation of 5-bromo-2,4-dichloro-6-alkyl(and phenyl)pyrimidine with
dithizone afforded novel 3-phenylazo-1-phenyl-1H-pyrimido[4,5-e][1,3,4]thiadiazines with the
magenta color. Further replacement of chlorine with secondary amines is also a general
procedure for preparation of 7-amino-3-phenylazo-1-phenyl-1H-pyrimido[4,5-e][1,3,4]thia-
diazine derivatives with blue color.
EXPERIMENTAL
The melting points were recorded on an Electrothermal type 9100 melting point apparatus. The
1
IR spectra were obtained on a 4300 Shimadzu Spectrometer. The H NMR (100 MHz) spectra
were recorded on a Bruker AC 100 spectrometer. The mass spectra were scanned on a Varian
Mat CH-7 instrument at 70 eV. Elemental analysis was obtained on a Thermo Finnigan Flash
EA microanalyzer. The purity of either synthetic compound was tested by TLC using
chloroform as mobile phase. Alkyl-2-phenylhydrazinecarbodithioates were prepared according
to the earlier procedure [9, 10].
General procedure for the preparation of 5-bromo-6-alkyl-pyrimidin-2,4(1H,3H)-diones 2b-e.
To a suspension of either 6-alkyl-pyrimidine-2,4(1H,3H)-dione 1b-e (20 mmol) in water (40
mL), bromine (3.2 g, 20 mmol) was added with vigorous stirring. Stirring was continued for
further 30 min and then the mixture was heated to boil and then kept for overnight to give a
white precipitate. The precipitate was filtered off, washed with warm water and dried at 80 oC.
5-Bromo-6-ethylpyrimidine-2,4(1H,3H)-dione (2b). This compound was obtained as a white
o
powder in 70% yield, m.p. 265-267 C (dec), IR: 3170 cm-1 (NH), 1580 cm-1 (C=O); 1H NMR:
(DMSO-d6) δ, 1.15 (t, 3H, CH3, J = 7.5 Hz ), 2.37 (q, 2H, 5-CH2, J = 7.5 Hz ), 11.35 (s, 1H,
N1H), 11.45 (s, 1H, N3H); ms: m/z, 218 (80%), 220 (80%).
5-Bromo-6-propylpyrimidine-2,4(1H,3H)-dione (2c). This compound was obtained as a white
o
powder in 80% yield, m.p. 260-261 C (dec), IR: 3200 cm-1 (NH), 1550 cm-1 (C=O); 1H NMR:
(DMSO-d6) δ, 1.05 (t, 3H, CH3, J = 7.3 Hz), 1.57 (sextet, 2H, CH2), 2.45 (t, 2H, 5-CH2, J = 7.6
Hz ), 11.35 (s, 1H, N1H), 11.45 (s, 1H, N3H); ms: m/z, 232 (80%), 234 (80%).
5-Bromo-6-(1-methylethyl)pyrimidine-2,4(1H,3H)-dione (2d). This compound was obtained as a
o
white powder in 75% yield, m.p. 252-253 C (dec), IR: 3250 cm-1 (NH), 1600 cm-1 (C=O); 1H
NMR: (DMSO-d6) δ, 0.95 (d, 6H, 2CH3, J = 7.2 Hz), 2.55 (m, 1H, 5-CH), 11.30 (s, 1H, N1H),
11.40 (s, 1H, N3H); ms: m/z, 232 (90%), 234 (90%).
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Mohsen Nikpour et al.
5-Bromo-6-phenylpyrimidine-2,4(1H,3H)-dione (2e). This compound was obtained as a white
o
powder in 85% yield, m.p. 243-244 C (dec), IR: 3200 cm-1 (NH), 1570 cm-1 (C=O); 1H NMR:
(DMSO-d6) δ, 7.1-7.4 (m, 5H, aromatic), 11.50 (s, 1H, N1H), 11.65 (s, 1H, N3H); ms: m/z, 266
(60%), 268 (60%).
General procedure for the preparation of 5-bromo-2,4-dichloro-6-alkylpyrimidine (3b-e). A
mixture of 5-bromo-6-alkyl-pyrimidine-2,4(1H,3H)-dione 2b-e (10 mmol) in phosphoryl-
chloride (10 mL) was heated under reflux for 3 h. The excess phosphorylchloride was removed
in vacuo and the residue was added to ice. The precipitate was extracted by chloroform (2 x 10
mL), dried by sodium sulfate and then evaporated under an efficient hood.
5-Bromo-2,4-dichloro-6-ethylpyrimidine (3b). This compound was obtained as a viscose liquid
1
in 60% yield, H NMR: (CDCl3) δ, 1.25 (t, 3H, CH3, J = 7 Hz), 2.62 (q, 2H, 5-CH2, J = 7 Hz);
ms: m/z, 254 (54%), 256 (89%), 258 (42%), 260 (6%).
5-Bromo-2,4-dichloro-6-propylpyrimidine (3c). This compound was obtained as a viscose
liquid in 70% yield, 1H NMR: (CDCl3) δ, 1.15 (t, 3H, CH3, J = 7.2 Hz), 1.80 (sextet, 2H, CH2),
2.72 (t, 2H, 5-CH2, J = 7.2 Hz ); ms: m/z, 268 (56%), 270 (91%), 272 (43%), 274 (6%).
5-Bromo-2,4-dichloro-6-(1- methylethyl)pyrimidine (3d). This compound was obtained as a
viscose liquid in 50% yield, 1H NMR: (CDCl3) δ, 1.10 (d, 6H, 2CH3, J = 7.5 Hz ), 2.83 (m, 1H,
5-CH ); ms: m/z, 268 (64%), 270 (97%), 272 (50%), 274 (7%).
5-Bromo-2,4-dichloro-6-phenylpyrimidine (3e). This compound was obtained as a viscose
1
liquid in 70% yield, H NMR: (CDCl3) δ, 7.5-7.8 (m, aromatic ); ms: m/z, 302 (36%), 304
(60%), 306 (28%), 308 (4%).
General procedure for the preparation of pyrimido [4,5-e][1,3,4]thiadiazines 5a-e. A mixture
of either 5-bromo2,4-dichloro-6-alkyl(and phenyl)pyrimidine 3a-e (2.5 mmol), dithizone 4 (2.5
mmol) and triethylamine (1 mL) in acetonitrile (20 mL) was boiled under reflux for 15 min.
After the reaction was completed, the mixture was cooled to room temperature, and then
evaporated under reduced pressure. The residue was washed with water and crystallized with
ethanol to give products 5a-e.
1-(7-Chloro-5-methyl-1-phenyl-1H-pyrimido[4,5-e][1,3,4]thiadiazin-3-yl)-2-phenyldiazene
o
(5a). This compound was obtained as a magenta powder in 90% yield, m.p. 271-273 C (dec);
IR (KBr disk) ν: 950 cm-1, 1700 cm-1, 2950 cm-1; 1H NMR: (CDCl3) δ, 2.31 (s, 3H, 5-CH3 ), 7.5-
8 (m, 10H); m/z, 382, 380, 277, 275. Anal. calcd. for C18H13ClN6S: C, 56.77; H, 3.44; N, 22.07;
S, 8.42. Found: C, 56.52; H, 3.5; N, 22.20; S, 8.13.
1-(7-Chloro-5-ethyl-1-phenyl-1H-pyrimido[4,5-e][1,3,4]thiadiazin-3-yl)-2-phenyldiazene (5b).
o
This compound was obtained as a magenta powder in 85% yield, m.p. 262-264 C (dec); IR
1
(KBr disk) ν: 940 cm-1 1730 cm-1, 2970 cm-1; H NMR: (CDCl3) δ, 1.23 (t, 3H, CH3, J = 7.3
,
Hz), 2.52 (q, 2H, 5-CH2, J = 7.3 Hz ), 7.5-8 (m, 10H); m/z, 396, 394, 291, 289. Anal. calcd. for
C19H15ClN6S: C, 57.79; H, 3.83; N, 21.28; S, 8.12. Found: C, 58.06; H, 3.96; N, 21.04; S, 7.82.
1-(7-Chloro-1-phenyl-5-propyl-1H-pyrimido[4,5-e][1,3,4]thiadiazin-3-yl)-2-phenyldiazene
o
(5c). This compound was obtained as a magenta powder in 80% yield, m.p. 255-257 C (dec);
IR (KBr disk) ν: 960 cm-1, 1750 cm-1, 2930 cm-1; 1H NMR: (CDCl3) δ, 1.12 (t, 3H, CH3, J = 7.4
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Efficient synthesis of novel azo compounds based on pyrimido[4,5-e][1,3,4]thiadiazine
119
Hz), 1.74 (sextet, 2H, CH2), 2.63 (t, 2H, 5-CH2, J = 7.4 Hz), 7.5-8 (m, 10H); m/z, 410, 408, 305,
303. Anal. calcd. for C20H17ClN6S: C, 58.75; H, 4.19; N, 20.55; S, 7.84. Found: C, 59.06; H,
4.35; N, 20.32; S, 7.51.
1-(7-Chloro-5-(1-methylethyl)-1-phenyl-1H-pyrimido[4,5-e][1,3,4]thiadiazin-3-yl)-2-phenyldi-
o
azene (5d). This compound was obtained as a magenta powder in 85% yield, m.p. 249-251 C
1
(dec); IR (KBr disk) ν: 9300 cm-1, 1770 cm-1, 2960 cm-1; H NMR: (CDCl3) δ, 1.05 (d, 6H,
2CH3, J = 7.5 Hz), 2.75 (m, 1H, 5-CH ), 7.5-8 (m, 10H); m/z, 410, 408, 305, 303. Anal. calcd.
for C20H17ClN6S: C, 58.75; H, 4.19; N, 20.55; S, 7.84. Found: C, 58.91; H, 4.31; N, 20.28; S,
7.56.
1-(7-Chloro-1,5-diphenyl-1H-pyrimido[4,5-e][1,3,4]thiadiazin-3-yl)-2-phenyldiazene
o
(5e).
This compound was obtained as a magenta powder in 92% yield, m.p. 292-294 C (dec); IR
1
(KBr disk) ν: 930 cm-1 1770 cm-1; H NMR: (CDCl3) δ, 7.5-8.3 (m, aromatic); m/z, 444, 442,
,
339, 337. Anal. calcd. for C23H15ClN6S: C, 62.37; H, 3.41; N, 18.97; S, 7.24. Found: C, 62.58;
H, 3.62; N, 18.73; S, 6.95.
General procedure for the reaction of 5b,c,e with secondary amines. A mixture of either
compound 5a,c (5 mmol) in ethanol (20 mL) was heated under reflux with 2 mL of either
morpholine, piperidine or 1-methylpiprazine for 6 h. The solvent was removed and the residue
was washed with water and then crystallized from ethanol to give the products 5f-k.
1-(5-Methyl-1-phenyl-7-(piperidin-1-yl)-1H-pyrimido[4,5-e][1,3,4]thiadiazin-3-yl)-2-phenyldi-
azene (5f). This compound was obtained as a blue powder in 70% yield, m.p. 250-252 oC (dec);
1
IR (KBr disk) ν: 2950 cm-1; H NMR: (CDCl3) δ, 1.4-1.8 (m, 6H, ((CH2)3-CH2N), 2.27 (s, 3H,
5-CH3 ), 3.5 (t, 4H, 2(CH2N), J = 6 Hz), 7.5-8 (m, 10H); m/z, 429, 324. Anal. calcd. for
C23H23N7S : C, 64.31; H, 5.40; N, 22.83; S, 7.46. Found: C, 64.59; H, 5.67; N, 22.49; S, 7.22.
1-(5-Methyl-7-(morpholin-4-yl)-1-phenyl-1H-pyrimido[4,5-e][1,3,4]thiadiazin-3-yl)-2-phenyl-
o
diazene (5g). This compound was obtained as a blue powder in 75% yield, m.p. 255-257 C
(dec); IR (KBr disk) ν: 2920 cm-1; 1H NMR: (CDCl3) δ, 2.25 (s, 3H, 5-CH3 ), 3.6 (s, 8H, CH2-(O
and N)), 7.5-8 (m, 10H); m/z, 431, 326. Anal. calcd. for C22H21N7OS: C, 61.23; H, 4.91; N,
22.72; S, 7.43. Found: C, 61.32; H, 5.12; N, 22.51; S, 7.22.
1-(5-Methyl-7-(4-methylpiperazin-1-yl)-1-phenyl-1H-pyrimido[4,5-e][1,3,4]thiadiazin-3-yl)-2-
phenyldiazene (5h). This compound was obtained as a blue powder in 60% yield, m.p. 240-242
oC (dec); IR (KBr disk) ν: 2980 cm-1; 1H NMR: (CDCl3) δ, 2.3-2.6 (m, 10H, CH3N(CH2)2 and 5-
CH3), 3.6 (t, 4H, 2(CH2N), J = 6.1 Hz), 7.5-8 (m, 10H); m/z, 444, 339. Anal. calcd. for
C23H24N8S: C, 62.14; H, 5.44; N, 25.21; S, 7.21. Found: C, 62.33; H, 5.63; N, 24.96; S, 7.03.
2-Phenyl-1-(1-phenyl-7-(piperidin-1-yl)-5-propyl-1H-pyrimido[4,5-e][1,3,4]thiadiazin-3-yl)di-
azene (5i). This compound was obtained as a blue powder in 65% yield, m.p. 241-243 oC (dec);
IR (KBr disk) ν: 2950 cm-1; 1H NMR: (CDCl3) δ, 1.12 (t, 3H, CH3, J = 7.2 Hz), 1.4-1.8 (m, 8H,
((CH2)3-CH2N, CH2), 2.63 (t, 2H, 5-CH2, J = 7.2 Hz), 3.5 (t, 4H, 2(CH2N), J = 6 Hz), 7.5-8 (m,
10H); m/z, 457, 352. Anal. calcd. for C25H27N7S: C, 65.62; H, 5.95; N, 21.43; S, 7.01. Found:
C, 65.51; H, 5.72; N, 21.28; S, 6.79.
1-(7-(Morpholin-4-yl)-1-phenyl-5-propyl-1H-pyrimido[4,5-e][1,3,4]thiadiazin-3-yl)-2-phenyl-
o
diazene (5j). This compound was obtained as a blue powder in 70% yield, m.p. 235-237 C
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Mohsen Nikpour et al.
1
(dec); IR (KBr disk) ν: 2900 cm-1; H NMR: (CDCl3) δ, 1.12 (t, 3H, CH3, J = 7.4 Hz ), 172
(sextet, 2H, CH2), 2.63 (t, 2H, 5-CH2, J = 7.2 Hz ), 3.6 (s, 8H, CH2-(O and N)), 7.5-8 (m, 10H);
m/z, 459, 354. Anal. calcd. for C24H25N7OS: C, 62.72; H, 5.48; N, 21.33; S, 6.98. Found: C,
67.56; H, 5.55; N, 21.52; S, 6.72.
1-(7-(4-Methylpiperazin-1-yl)-1-phenyl-5-propyl-1H-pyrimido[4,5-e][1,3,4]thiadiazin-3-yl)-2-
phenyldiazene (5k). This compound was obtained as a blue powder in 55% yield, m.p. 229-231
1
oC (dec); IR (KBr disk) ν: 2980 cm-1; H NMR: (CDCl3) δ, 1.12 (t, 3H, CH3, J = 7.1 Hz), 1.74
(sextet, 2H, CH2), 2.3-2.6 (m, 9H, CH3N(CH2)2 and 5-CH2), 3.6 (t, 4H, 2(CH2N), J = 6 Hz), 7.5-
8 (m, 10H); m/z, 472, 367. Anal. calcd. for C25H28N8S: C, 63.53; H, 5.97; N, 23.71; S, 6.78.
Found: C, 65.34; H, 6.17; N, 23.93; S, 6.54.
ACKNOWLEDGEMENT
Financial support of this research by Ahvaz Branch, Islamic Azad University is gratefully
acknowledged.
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