Substituted pyridopyrimidinones. Part IV. 2-Chloro-4H-pyrido[1,2-a]pyrimidin-4-one as a synthone of some new heterotricycles

Article abstract of DOI:10.2298/JSC1001011A

2-Chloro-4H-pyrido[1,2-a]pyrimidin-4-one (1) was utilized as a synthone precursor to prepare novel heterotricyclic systems. 2-Azido and 2-hydrazino derivatives (2 and 3) were obtained by nucleophilic replacement evolving compound 1. The hydrazine derivative 3 was transformed into the azido derivative 2 by nitrosation. Treatment of compound 3 with [bis(methylthio)methylene] malononitrile afforded 2-pyrazolylpyridopyrimidine 4. When compound 1 was reacted with 5-amino-3-(methylthio)-1H-pyrazole-4-carbonitrile, the same compound 4 was obtained with no evidence for the production of (pyrazolylamino) pyridopyrimidine 5 or pyrazolodipyridopyrimidine 6. Poly-functionalized dipyridopyrimidine 8 was obtained by reaction of compound 1 with 2-[(methylthio)-(phenylamino)methylene]propanedinitrile. Cyanoguanidine was reacted with compound 1 to afford N-pyridopyrimidinylguanidine 9, which was subjected to cyclization reaction, in presence of piperidinium acetate, to give pyridopyrimidopyrimidine 10. 2009 Copyright (CC) SCS.

Full text of DOI:10.2298/JSC1001011A

J. Serb. Chem. Soc. 75 (1) 11–17 (2010)
UDC 547.821+547.853:547.7/.8
JSCS–3936
Original scientific paper
Substituted pyridopyrimidinones. Part IV.
2-Chloro-4H-pyrido[1,2-a]pyrimidin-4-one as
a synthone of some new heterotricycles
*
MOHAMED ABASS , MOSTAFA M. ISMAIL, WAFAA R. ABDEL-MONEM
and AISHA S. MAYAS
Department of Chemistry, Faculty of Education, Ain Shams University,
Roxy, Cairo 11757, Egypt
(Received 27 November 2008, revised 9 June 2009)
Abstract: 2-Chloro-4H-pyrido[1,2-a]pyrimidin-4-one (1) was utilized as a syn-
thone precursor to prepare novel heterotricyclic systems. 2-Azido and 2-hyd-
razino derivatives (2 and 3) were obtained by nucleophilic replacement evolving
compound 1. The hydrazine derivative 3 was transformed into the azido deriva-
tive 2 by nitrosation. Treatment of compound 3 with [bis(methylthio)methyl-
ene]malononitrile afforded 2-pyrazolylpyridopyrimidine 4. When compound 1
was reacted with 5-amino-3-(methylthio)-1H-pyrazole-4-carbonitrile, the same
compound 4 was obtained with no evidence for the production of (pyrazolyl-
amino)pyridopyrimidine 5 or pyrazolodipyridopyrimidine 6. Poly-functionalized
dipyridopyrimidine 8 was obtained by reaction of compound 1 with 2-[(me-
thylthio)-(phenylamino)methylene]propanedinitrile. Cyanoguanidine was reacted
with compound 1 to afford N-pyridopyrimidinylguanidine 9, which was
subjected to cyclization reaction, in presence of piperidinium acetate, to give
pyridopyrimidopyrimidine 10.
Keywords: pyridopyrimidine; dipyridopyrimidine; pyridopyrimidopyrimidine.
INTRODUCTION
Recently, a convenient new synthesis of 2-chloro-4H-pyrido[1,2-a]pyrimi-
1
din-4-one (1) was described. It is well-known that this type of α-halohetero-
cyclic compounds are susceptible to synthetically important nucleophilic substi-
2–5
tutions.
Many hetero-fused pyrimidines exhibit attractive cancer chemothe-
6
rapy properties as antitumor agents. Risperidone, SSR6907, and ramastine are
derivatives of pyrido[1,2-a]pyrimidin-4-one, which show antipsychotic acti-
7–9
10
vity.
Dominguez et al. reported that some hetero-fused tricyclic systems
exhibited significant antimalarial activity. It was cited that the biological reac-
*Corresponding author. E-mail: m.abass@chemist.com
doi: 10.2298/JSC1001011A
11
Available online at www.shd.org.rs/JSCS/
___________________________________________________________________________________________________________________________
2009 Copyright (CC) SCS

12
ABASS et al.
tivity of this category of compounds is essentially due to presence of the pyri-
11
do[1,2-a]pyrimidinone moiety in their molecular structure. In this study, it was
planned to utilize the readily available chloro derivative to obtain novel polycyc-
lic compounds, which could be expected to possess antimalarial activity.
RESULTS AND DISCUSSION
Analytical and spectral characterization of the prepared compounds
2-Azido-4H-pyrido[1,2-a]pyrimidin-4-one (2). Anal. Calcd. for C H N O (FW
8
5 5
187.16): C, 51.34; H, 2.69; N, 37.42 %; Found: C, 50.96; H, 2.54; N, 37.40 %. IR
–1
(KBr, cm ): 3073, 3042, 2129 (N ), 1718 (C=O), 1634 (C=N), 1565, 1517,
3
1
1455, 1412, 1110, 930, 839, 782, 760. H-NMR (200 MHz, DMSO-d , δ / ppm):
6
5.85 (1H, s, C –H), 7.55 (1H, dd, J = 7.5, 3.6 Hz, C –H), 7.63 (1H, d, J = 7.4 Hz,
3
7
C –H), 8.08 (1H, dd, J = 7.4, 3.4 Hz, C –H), 8.99 (1H, d, J = 7.5 Hz, C –H). MS
9
8
6
+
(m/z (I / %)): M 187 (34).
2-Hydrazino-4H-pyrido[1,2-a]pyrimidin-4-one (3). Anal. Calcd. for C H N O
8
8 4
(FW 176.18): C, 54.54; H, 4.58; N, 31.80 %; Found: C, 54.42; H, 4.42; N, 31.77 %.
–1
IR (KBr, cm ): 3428, 3340, 3328, 3270 (NHNH ), 3072, 1690 (C=O), 1636
2
1
(C=N), 1610, 1570, 1518, 1445, 1352, 1080, 776. H-NMR (200 MHz, DMSO-d ,
6
δ / ppm): 4.30 (2H, b, NH ), 5.62 (1H, s, C –H), 7.31 (dd, 1H, J = 7.4, 3.6 Hz,
2
3
C –H), 7.56 (1H, d, J = 7.2 Hz, C –H), 7.95 (1H, dd, J = 7.2, 3.5 Hz, C –H),
7
9
8
+
8.12 (1H, b, NH), 8.93 (1H, d, J = 7.4 Hz, C –H). MS (m/z (I / %)): M 176 (80).
6
5-Amino-3-(methylthio)-1-(4-oxo-4H-pyrido[1,2-a]pyrimidin-2-yl)-1H-pyra-
zole-4-carbonitrile (4). Anal. Calcd. for C H N OS (FW 298.33): C, 52.34; H,
13 10
6
3.38; N, 28.17; S, 10.75 %; Found: C, 52.33; H, 3.38; N, 28.10; S, 10.50 %. IR
–1
(KBr, cm ): 3360, 3265 (NH), 3115, 3071, 3043, 2924, 2210 (CN), 1676 (C=O),
1
1614 (C=N), 1549, 1501, 1457, 819, 762. H-NMR (200 MHz, DMSO-d ,
6
δ / ppm): 2.56 (3H, s, SCH ), 6.59 (1H, s, C –H), 7.43 (1H, m, C –H), 8.08 (2H,
3
3
7
13
m, C –H + C –H), 8.38 (2H, s, NH ), 8.99 (1H, d, J = 7.4 Hz, C –H). C-NMR
9
8
2
6
(70 MHz, DMSO-d , δ / ppm): 38.5, 93.7, 100.1, 116.4, 118.0, 121.3, 124.2,
6
130.6, 133.8, 148.7, 149.7, 154.4, 158.9.
4-Imino-2-(methylthio)-5-oxo-1-phenyl-1,5-dihydro-4H-dipyrido-[1,2-a:2',3'-
-d]-pyrimidine-3-carbonitrile (8). Anal. Calcd. for C H N OS (FW 359.41): C,
19 13
5
63.50; H, 3.65; N, 19.49; S, 8.92 %; Found: C, 6.40; H, 3.30; N, 19.20; S, 8.60
–1
%. IR (KBr, cm ): 3292 (NH), 3065, 3039, 3001, 2928, 2202 (CN), 1671
1
(C=O), 1621 (C=N), 1596, 1524, 1492, 1261, 759; H-NMR (200 MHz, DMSO-d ,
6
δ / ppm): 2.08 (3H, s, SCH ), 7.05–8.29 (8H, m, 5H
.+ C –H + C –H + C –H),
3
arom
13
7 9 8
8.85 (1H, d, J = 7.5 Hz, C –H), 10.19 (1H, s, NH). C-NMR (70 MHz, DMSO-d ,
6
6
δ / ppm): 35.5, 89.3, 96.4, 115.3, 117.7, 122.4, 112.9, 125.2, 129.7, 136.2, 139.0,
140.5, 142.1, 151.2, 156.0, 160.3, 165.9.
N-Cyano-N’-(4-oxo-4H-pyrido[1,2-a]pyrimidin-2-yl)guanidine (9). Anal.
Calcd. for C H N O (FW 228.21): C, 52.63; H, 3.53; N, 36.83 %; Found: C,
10
8 6
Available online at www.shd.org.rs/JSCS/
___________________________________________________________________________________________________________________________
2009 Copyright (CC) SCS

SUBSTITUTED PYRIDOPYRIMIDINONES
13
–1
52.31; H, 3.40; N, 36.72 %; IR (KBr, cm ): 3429, 3383 (NH), 3334, 3249, 3194
(NH), 3151, 2920, 2207 (CN), 1669 (C=O), 1639 (C=N), 1571, 1506, 1434,
1
1357, 777, 721, 669. H-NMR (200 MHz, DMSO-d , δ / ppm): 5.40 (1H, s, NH,
6
disappeared with D O), 6.0 (1H, s, NH, disappeared with D O), 6.55 (1H, s, C –
2
2
3
–H), 7.40 (1H, dd, J = 7.5, 3.6 Hz, C –H), 7.49 (1H, d, J = 7.5 Hz, C –H), 7.82
7
9
(1H, dd, J = 7.5, 3.6 Hz, C –H), 7.95–8.08 (1H, bs, NH, disappeared with D O),
8
2
13
8.80 (1H, d, J = 7.5 Hz, C –H). C-NMR (70 MHz, DMSO-d , δ / ppm): 94.3,
6
6
115.5, 119.2, 122.6, 124.9, 138.0, 151.2, 157.3, 164.8, 165.8; MS (m/z (I / %)):
+
M 228 (28).
2,4-Diamino-5H-pyrido[1,2-a]pyrimido[4,5-d]pyrimidin-5-one (10). Anal.
Calcd. for C H N O (FW 228.21): C, 52.63; H, 3.53; N, 36.83 %; Found: C,
10
8 6
–1
52.50; H, 3.20; N, 36.50 %. IR (KBr, cm ): 3435, 3328 (NH ), 3221, 3172
2
(NH), 3075, 2936, 1668 (C=O), 1620 (C=N), 1585, 1535, 1440, 1330, 778, 725.
1
H-NMR (200 MHz, DMSO-d6, δ / ppm): 6.59 (2H, s, NH disappeared with
2
D O), 6.68 (2H, s, NH disappeared with D O), 7.44 (1H, dd, J = 7.6, 3.7 Hz,
2
2
2
C –H), 7.52 (1H, d, J = 7.5 Hz, C –H), 7.89 (1H, dd, J = 7.5, 3.6 Hz, C –H),
7
9
8
13
8.94 (1H, d, J = 7.6 Hz, C –H). C-NMR (70 MHz, DMSO-d6, δ / ppm): 98.5,
6
114.9, 125.4, 128.0, 136.2, 146.2, 154.6, 158.9, 165.5, 169.8; MS (m/z (I / %)):
+
M 228 (100).
Chemistry
Reaction of the chloro-compound 1 with sodium azide was performed in
12,13
DMF, leading to 2-azidopyridopyrimidinone (2).
product showed a sharp medium peak at ν
The IR spectrum of the
–1
2129 cm , which is characteristic
max
for the azide function. The same compound was afforded when 2-hydrazinopy-
ridopyrimidinone (3) was treated with in situ freshly obtained nitrous acid. This
12
hydrazine–azido conversion was previously described by Kovačič et al., albeit
they did not give any characterization for the structure of the azido product but
the same melting point was obtained. The hydrazine 3 was preliminary obtained
via refluxing the chloro compound 1 with hydrazine hydrate, according to the
14
method described by Oakes and Rydon, who did not give spectral characteri-
1
zation of the structure of the product. The IR and H-NMR spectra of the hyd-
razine 3 are given herein to fortify the proposed structure (Scheme 1).
Reaction of the chloro-compound 1 with 5-amino-3-(methylthio)-1H-pyra-
15
zole-4-carbonitrile, in boiling DMF, did not lead to the expected 5-(pyrido-
pyrimidinylamino)-1H-pyrazole-4-carbonitrile (5) or its targeted cyclized isomer
pyrazolo[3’,4’:1,6]pyrido-[2,3-d]pyrido[1,2-a]pyrimidinone (6). IR spectroscopy
–1
1
revealed the occurrence of the cyano function at ν
2210 cm . The H-NMR
max
spectrum showed the existence of NH at δ 8.38 ppm, which disappeared on ad-
2
dition of D O, besides δ 6.59 ppm, which is specific for position 3 of pyridopy-
2
rimidinone and the four proton set of the pyridine ring. These results suggested
Available online at www.shd.org.rs/JSCS/
___________________________________________________________________________________________________________________________
2009 Copyright (CC) SCS

14
ABASS et al.
that the obtained compound is 1-(pyridopyrimidin-2-yl)pyrazole (4). The produc-
tion of the pyrazole 4 can be attributed to the greater nucleophilicity character of
the ring nitrogen compared with the α-amino group, which backs to the meso-
meric effect. However, a clear-cut establishment of the structure was achieved
from the cyclization of the hydrazine 3 with [bis(methylthio)methylene]-
16,17
malononitrile.
This reaction was reported for the formation of 1-substituted
18
5-amino-3-(methylthio)-1H-pyrazole-4-carbonitriles starting from hydrazines
(Scheme 1).
Scheme 1.
2-[(Methylthio)(phenylamino)methylene]propanedinitrile was subjected to re-
action with the chloro compound 1 in refluxing DMF. Surprisingly, the intended
2-{(methylthio)[phenyl(4-oxo-4H-pyrido[1,2-a]pyrimidin-2-yl)amino]}propanedi-
nitrile (7) was not isolated. The spectra of the product showed the occurrence of
an imino function and at the same time the disappearance of the characteristic
signal due to C–H at position 3. This suggested that the obtained product was cy-
clized in a cascade nucleophilic reaction to yield dipyrido[1,2-a:2’,3’-d]pyri-
midine 8 (Scheme 2).
Available online at www.shd.org.rs/JSCS/
___________________________________________________________________________________________________________________________
2009 Copyright (CC) SCS

SUBSTITUTED PYRIDOPYRIMIDINONES
15
Scheme 2.
Reaction of the chloro compound 1 with cyanoguanidine in boiling DMF
gave the claimed N-cyano-N’-(pyridopyrimidinyl)guanidine 9. The IR spectrum
–1
exhibited a sharp absorbance peak at ν
2207 cm due to the CN function.
max
Trials for cyclization of this guanidine derivative met success by the action of
piperidinium acetate in boiling DMSO. It is thought that the relatively high boil-
ing temperature of DMSO is conditional for such a reaction because attempts to
perform the same reaction in THF, dioxane, and DMF were not successful. The
structure of the product was confirmed from its spectral data which suggested
10
that the product is pyrido[1,2-a]pyrimido[4,5-d]pyrimidinone 10 (Scheme 2).
EXPERIMENTAL
Melting points were determined in an open capillary tube on a digital Gallen-Kamp
MFB-595 apparatus. The IR spectra were taken on a Perkin-Elmer FT-IR 1650, using samples
1
in KBr disks. The H-NMR (200 MHz) and 13C-NMR (70 MHz) spectra were recorded on
Varian Gemini-200 spectrometer, using DMSO-d6 as the solvent and TMS as the internal
reference. The mass spectrum was determined on a HP-MS 5988 mass spectrometer by direct
inlet, operating at 70 eV. Elemental microanalysis was performed on a Perkin Elmer CHN-
-2400 Analyzer.
2-Azido-4H-pyrido[1,2-a]pyrimidin-4-one (2)
Method A. To a solution of the chloro-derivative 1 (10 mmol) in DMF (20 mL), sodium
azide (15 mmol) was added and the reaction mixture was heated on a boiling water bath for 2
Available online at www.shd.org.rs/JSCS/
___________________________________________________________________________________________________________________________
2009 Copyright (CC) SCS

16
ABASS et al.
h. Then the reaction mixture was diluted with ice-water (20 mL) and left to stand for 1 h. The
product was filtered and crystallized from DMF/H2O (1:1). Yield 80 %, m.p. 160–161 °C.
Method B. To a stirred cold (0–5 °C) solution of the hydrazino derivative 3 (10 mmol), in
2 M hydrochloric acid (10 mL), an aqueous 1 M sodium nitrite solution (10 mL,) was added
dropwise. Then, stirring was continued at room temperature for 1 h and the obtained preci-
pitate was filtered and crystallized from DMF/H2O (1:1) to give the azido derivative 2. Yield:
72 %, m.p. 160–161 °C (m.p. 160–163 °C12).
2-Hydrazino-4H-pyrido[1,2-a]pyrimidin-4-one (3)
A mixture of the chloro-compound 1 (10 mmol) and hydrazine hydrate (15 mmol) in
DMF (10 mL) was refluxed for 1 h. Then the reaction mixture was poured onto crushed ice
and the solid deposits were filtered and crystallized from ethanol to give the hydrazine com-
pound 3. Yield: 69 %, m.p. 240–242 °C (m.p. 245 °C14).
5-Amino-3-(methylthio)-1-(4-oxo-4H-pyrido[1,2-a]pyrimidin-2-yl)-1H-pyrazole-4-carbonitrile (4)
Method A. To a solution of the hydrazino compound 3 (5 mmol) in DMF (20 mL), [bis-
(methylthio)methylene]malononitrile (5 mmol) was added and the reaction mixture was re-
fluxed for 2 h. The solid product, which separated after cooling, was filtered using a suction
pump, washed thoroughly with ethanol and crystallized from DMF. Yield: 89 %, m.p. > 300 °C.
Method B. A mixture of the chloro-compound 1 (5 mmol) and 5-amino-(3-methylthio)-
-1H-pyrazole-4-carbonitrile15 (5 mmol) in DMF (20 mL) was boiled under reflux for 2 h. Af-
terwards, the reaction mixture was left to cool to room temperature. The so-obtained crys-
talline deposit was filtered and recrystallized from DMF to give pyridopyrimidylpyrazole 4.
Yield: 77 %.
4-Imino-2-(methylthio)-5-oxo-1-phenyl-1,5-dihydro-4H-dipyrido-[1,2-a:2’,3’-d]pyrimidine-3-
-carbonitrile (8)
A mixture of the chloro-compound 1 (10 mmol) and 2-[(methylthio)(phenylamino)-
methylene]propanedinitrile (10 mmol) in DMF (25 mL) was heated under reflux for 4 h. Sub-
sequently, the reaction mixture was left to cool to room temperature. The obtained yellow
crystalline material was filtered off and recrystallized from DMF to give compound 8. Yield:
73 %, m.p. 257–258 °C.
N-Cyano-N’-(4-oxo-4H-pyrido[1,2-a]pyrimidin-2-yl)guanidine (9)
A mixture of the chloro compound 1 (5 mmol) and cyanoguanidine (5 mmol) in DMF
(20mL) was heated under reflux for 4 h. After cooling to room temperature, the mixture was
diluted with cold water and the solid that deposited was collected by filtration and crystallized
from acetone to give the guanidine derivative 9. Yield: 80 %, m.p. 178–180 °C.
2,4-Diamino-5H-pyrido[1,2-a]pyrimido[4,5-d]pyrimidin-5-one (10)
A solution of the guanidine derivative 9 (5 mmol) and piperidinium acetate (from 0.15 g
piperidine and 0.1 g acetic acid, 1.5 mmol) in DMSO (25 mL) was heated under reflux for 4 h.
The reaction mixture was left to cool to room temperature. The so-formed precipitate was fil-
tered off and washed several times with absolute ethanol. The product was crystallized from
DMF to give the yellowish orange diamine 10. Yield 85 %, m.p.> 300 °C (Lit.10 data is not
available).
Available online at www.shd.org.rs/JSCS/
___________________________________________________________________________________________________________________________
2009 Copyright (CC) SCS

SUBSTITUTED PYRIDOPYRIMIDINONES
17
И З В О Д
СУПСТИТУИСАНИ ПИРИДОПИРИМИДИНОНИ. ДЕО IV.
2-ХЛОРО-4H-ПИРИДО[1,2-a]ПИРИМИДИН-4-ОН КАО СИНТОН
НЕКИХ НОВИХ ХЕТЕРОЦИКЛИЧНИХ ЈЕДИЊЕЊА
MOHAMED ABASS, MOSTAFA M. ISMAIL, WAFAA R. ABDEL-MONEM и AISHA S. MAYAS
Department of Chemistry, Faculty of Education, Ain Shams University, Roxy, Cairo 11757, Egypt
2-Хлоро-4H-пиридо[1,2-а]пиримидин-4-он (1) је коришћен као синтон-прекурсор за
синтезу нових хетеротрицикличних система. 2-Азидо- и 2-хидразино-деривати (2 и 3) доби-
јени су нуклеофилном супституцијом из једињења 1. Хидразино-дериват 3 трансформисан је
нитрозовањем у азидо-дериват 2. Третирањем једињења 3 са [бис(метилтио)метилен]мало-
нонитрилом добијен је 2-пиразолилпиридопиримидин (4). Реакцијом једињења 1 са 5-амино-
-3-(метилтио)-1H-пиразол-4-карбонитрилом добијено је исто једињење 4 без грађења пира-
золиламино)пиридопиримидино 5 или пиразолодипиридопиримидина 6. Поли-функционали-
зован дипиридопиримидин 8 добивен је реакцијом једињења 1 са 2-[(метилтио)-фенилами-
но)метилен]пропандинитрилом. Цијаногванидин је третиран са једињењем 1 градећи N-пи-
ридопиримидинилгванидин 9, који реакцијом циклизације у присуству пиперидинијум-аце-
тата, даје пиридопиримидопиримидин 10.
(Примљено 27. новембра 2008, ревидирано 9. јуна 2009)
REFERENCES
1. M. Abass, A. S. Mayas, Heteroatom Chem. 18 (2007) 19
2. H. R. Snyder, M. M. Robison, J. Am. Chem. Soc. 74 (1952) 4910
3. A. R. Katritzky, A. J. Waring, J. Chem. Soc. (1962) 1544
4. M. di Braccio, G. Roma, M. Mazzei, A. Balbi, P. Schiantarelli, S. Cadel, S. Bongrani,
Farmaco 43 (1988) 705
5. C. Plug, W. Frank, C. Wentrup, J. Chem. Soc., Perkin Trans 2 (1999) 1087
6. S. Wang, A. Folkes, I. Chuckowree, X. Cockcroft, S. Sohal, W. Miller, J. Milton, S. P.
Wren, N. Vicker, P. Depledge, J. Scott, L. Smith, H. Jones, P. Mistry, R. Faint, D.
Thompson, S. Cocks, J. Med. Chem. 47 (2004) 1329
7. O. Bruno, C. Brullo, S. Schenone, F. Bondavalli, A. Ranise, M. Tognolini, M. Impic-
ciatore, V. Ballabeni, E. Barocelli, Bioorg. Med. Chem. 14 (2006) 121
8. K. L. E. Josephine, P. S. M. Aloysius, B. F. Paul, PCT Int. Appl. WO 2000020422 A1
20000413, 2000; Chem. Abstr. CA 265 188t
9. K. L. E. Josephine, V. D. Keybus, F. M. Alfons, M. J. Carolus, PCT Int. Appl. WO
2000020421 A2 20000413, 2000; Chem. Abstr. CA 265187c
10. J. Dominguez, J. Charris, L. Iarrusso, S. Lopez, G. Lobo, F. Riggione, Farmaco 51
(1996) 781
11. A. R. Katritzky, J. W. Rogers, R. M. Witek, S. K. Nair, Arkivoc 8 (2004) 52
12. M. Kovačič, S. Polanc, B. Stanovnik, M. Tišler, J. Heterocycl. Chem. 11 (1974) 949
13. S. Polanc, B. Stanovnik, M. Tišler, J. Org. Chem. 41 (1976) 3152
14. V. Oakes, H. N. Rydon, J. Chem. Soc. (1958) 209
15. J. S. Larsen, M. A. Zahran, E. B. Pedersen, C. Nielsen, Monatsh. Chem. 130 (1999) 1167
16. M. Abass, Phosphorus, Sulfur Silicon Relat. Elem. 170 (2003) 1413
17. K. A. Jensen, L. Hendriksen, Acta Chem. Scand. 22 (1968) 1107
18. Y. Tominaga, Y. Honkawa, M. Hara, A. Hosomi, J. Heterocycl. Chem. 27 (1990) 775.
Available online at www.shd.org.rs/JSCS/
___________________________________________________________________________________________________________________________
2009 Copyright (CC) SCS

Copyright of Journal of the Serbian Chemical Society is the property of National Library of Serbia and its
content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's
express written permission. However, users may print, download, or email articles for individual use.