Microwave-assisted synthesis of furo[3,2-c]-1,8-naphthyridines

Article abstract of DOI:10.1080/00397911.2010.493264

Microwave-assisted ring-conversion reactions of some pyrido[1,2-a] pyrimidine derivatives to 1,8-naphthyridines have been investigated. Novel furo[3,2-c]-1,8-naphthyridine compounds were synthesized in good yields under thermal reaction conditions. Both microwave and classical heating methods have been found to be satisfactory for the synthesis of new 1,8-naphthyridines.

Full text of DOI:10.1080/00397911.2010.493264

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Microwave-Assisted Synthesis of
Furo[3,2-c]-1,8-naphthyridines
Mustafa Güllü a & Deniz Yiğit a
a Faculty of Science, Department of Chemistry , Ankara University ,
Ankara, Turkey
Published online: 02 May 2011.
To cite this article: Mustafa Güllü & Deniz Yiğit (2011) Microwave-Assisted Synthesis of Furo[3,2-
c]-1,8-naphthyridines, Synthetic Communications: An International Journal for Rapid Communication
of Synthetic Organic Chemistry, 41:13, 1881-1888, DOI: 10.1080/00397911.2010.493264
To link to this article: http://dx.doi.org/10.1080/00397911.2010.493264
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Synthetic Communications1, 41: 1881–1888, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.493264
MICROWAVE-ASSISTED SYNTHESIS OF
FURO[3,2-c]-1,8-NAPHTHYRIDINES
˘
Mustafa Gu¨llu¨ and Deniz Yigit
Faculty of Science, Department of Chemistry, Ankara University,
Ankara, Turkey
GRAPHICAL ABSTRACT
Abstract Microwave-assisted ring-conversion reactions of some pyrido[1,2-a]pyrimidine
derivatives to 1,8-naphthyridines have been investigated. Novel furo[3,2-c]-1,8-naphthyri-
dine compounds were synthesized in good yields under thermal reaction conditions. Both
microwave and classical heating methods have been found to be satisfactory for the
synthesis of new 1,8-naphthyridines.
Keywords Furo[3,2-c]-1,8-naphthyridines; microwave synthesis; pyrido[1,2-a]pyrimi-
dines; thermal rearrangement
1,8-Naphthyridines are bicyclic pyridine derivatives well known for their spectacular
drug activities. Some of these compounds are synthetic antibacterial drugs,[1–3] namely
quinolone antibiotics. 1,8-Naphthyridine derivatives show a variety of biological
activities, such as antihypertensive,[4,5] antiallergic,[6] and anti-inflammatory[7]
properties in addition to their remarkable antibacterial effect. These compounds
are always the focus of attention from many researchers due to their valuable phar-
maceutical properties. Because of increasing bacterial resistance to antibiotics,
including some quinolone-type compounds, synthesis of new derivatives of 1,8-
naphthyridine and development of newer methods for the synthesis of these
compounds are very important.
Generally, 1,8-naphthyridines are synthesized through multistep reactions by
reacting 2-aminopyridine derivatives, usually 3-substituted ones, with 1,3-dicarbonyl
compounds or with suitable ketones.[7–9] These synthetic methods generally require a
costly 2-aminopyridine derivative as a starting material, which has a substituent like
Received March 9, 2010.
Address correspondence to Mustafa Gullu, Faculty of Science, Department of Chemistry, Ankara
¨
¨
University, 06100 Tandog˘an, Ankara, Turkey. E-mail: gullu@science.ankara.edu.tr
1881

˘
M. GULLU AND D. YIGIT
¨
¨
1882
Scheme 1. Synthesis of some 3-allyl-2-hydroxy-4H-pyrido[1,2-a]pyrimidin-4-ones.
CHO, CN, or COOR at the 3-position of the pyridine ring. An attractive but less
investigated synthetic procedure for the synthesis of 1,8-naphthyridines is thermal
conversion of pyrido[1,2-a]pyrimidines. This synthetic method has been studied by
Schober and Kappe[10] with a series of pyrido[1,2-a]pyrimidin-4-one derivatives
under thermal conditions and produced various 1,8-naphthyridines. In spite of some
advantages, there are only a few examples in the literature dealing with this method
for the synthesis of new 1,8-naphthyridine derivatives.[10,11]
In this study, synthesis of new furo derivatives of 1,8-naphthyridines from easily
accessible pyrido[1,2-a]pyrimidines has been investigated. The results of the thermal
ring-conversion reactions of several 6-substituted and 6-unsubstituted 3-allyl-4H-
pyrido[1,2-a]pyrimidin-4-ones tocyclic 1,8-naphthyridinederivatives are reported here.
Initially, several 3-allyl-2-hydroxy-4H-pyrido[1,2-a]pyrimidin-4-ones have been
prepared in good yields by cyclization of bis(2,4,6-trichlorophenyl) allylmalonate (2)
with some derivatives of 2-aminopyridines (1a–e) (Scheme 1). The results of these
reactions are given in Table 1.
Following the successful synthesis of 3-allyl-2-hydroxy-4H-pyrido[1,2-a]-
pyrimidine-4-ones (3a–e) (Table 1), ring-conversion reaction of these compounds
to 1,8-naphthyridines has been investigated using both microwave and classical heat-
ing methods.[10] First, thermal conversion of 3-allyl-2-hydroxy-6-methyl-4H-
pyrido[1,2-a]pyrimidin-4-one (3a) was attempted by heating it in diphenyl ether at
200 ꢀC. At the end of this reaction, pyrido[1,2-a] pyrimidine derivative was converted
not only to a 1,8-naphthyridine compound but also to its novel cyclic derivative.
Structural analysis of the isolated product by spectroscopic methods revealed that
following the ring conversion of 3-allyl-2-hydroxy-6-methyl-4H-pyrido[1,2-a]
pyrimidin-4-one (3a) to a 3-allyl-1,8-naphthyridine derivative, surprisingly a furo-
cyclization reaction occurred spontaneously under these conditions. A novel tricyclic
Scheme 2. Ring conversion and cyclization of 3-allyl-2-hydroxy-4H-pyrido[1,2-a]pyrimidin-4-ones.

FURO[3,2-c]-1,8-NAPHTHYRIDINES
1883
Table 1. 3-Allyl-2-hydroxy-4H-pyrido[1,2-a]pyrimidines (3a–3e)
Entry
1
2-Aminopyridine
Methoda
Product
Yield (%)b
81
A
R¼6-CH3 (1a)
2
3
4
B
A
B
80
87
85
R¼6-NH2 (1b)
5
6
A
B
A
B
A
B
85
83
70
70
76
70
R¼6-NHAc (1c)
R¼4-CH3 (1d)
R¼H (1e)
7
8
9
10
aMethod A: Room temperature, with Et3N as catalyst; Method B: Refluxing temperature without Et3N.
bIsolated product yields.
naphthyridine derivative, namely 2,7-dimethyl-2,3-dihydro-furo[3,2-c][1,8]naphthyr-
idin-4(5H)-one (4a), has been synthesized in one step for the first time.
This result prompted us to apply this synthetic method to other available
6-substituted-3-allyl-2-hydroxy-4H-pyrido[1,2-a]pyrimidine-4-ones (3b and 3c). Under
similar thermal conditions, ring-conversion reactions of other 3-allylpyrido[1,2-a]-
pyrimidines gave corresponding furo[3,2-c]-1,8-naphthyridine derivatives (4b and 4c).
All spectral data [infrared (IR), NMR, and mass (MS)] and elemental analysis results
of pure products supported the structural analysis of these novel furo[3,2-c]-1,8-
naphthyridine derivatives. Optimization of reaction parameters (temperature, reaction
period, catalysts) have been carried out for each pyrido[1,2-a]pyrimidine, and the results
are given in Table 2.
In addition to classical heating methods, this conversion reaction of 6-
substituted-3-allyl-2-hydroxy-4H-pyrido[1,2-a]pyrimidin-4-one derivatives (3a–3c)
has also been studied at different temperatures and periods by controlled microwave
heating using a single-mode microwave instrument (CEM Discover S-class, CEM

˘
¨ ¨
M. GULLU AND D. YIGIT
1884
Table 2. Results of synthesis reactions and optimization experiments of furo[3,2-c][1,8]naphthyridines
(4a–4c)
Temp
(ꢀC)
Time
(min)
Yield
(%)b
Entry
Starting material
Product
Methoda
A
c
—
1
2
150
200
200
250
250
150
150
200
250
200
200
250
200
200
250
200
200
250
30
30
60
30
60
10
20
20
20
10
20
20
30
60
60
10
20
20
c
—
3
21
38
49
4
5
c
6
B
—
c
—
7
8
46
75
24
33
35
50
62
70
47
65
90
9
10
11
12
13
14
15
16
17
18
C
A
B
19
C
A
250
20
25
20
21
22
23
24
25
26
200
250
250
200
200
250
250
60
30
60
10
20
10
20
55
64
76
54
60
68
94
B
C
27
250
20
38
Note: Microwave power was 250 W.
aMethod A: Heating in diphenyl ether; method B: Controlled microwave heating in the presence of a
few drops of sulfolane; method C: Controlled microwave heating without any solvent.
bIsolated product yields.
cStarting material was recovered unchanged.
Corporation). These reactions were carried out without a solvent or in the presence of a
few drops of a suitable polar solvent [e.g., dimethylsulfoxide (DMSO), sulfolane,
dimethylformamide (DMF)]. Moreover, some Lewis acid catalysts such as Al2O3,
AlCl3, ZnCl2, and FeCl3 have also been used under microwave conditions. Microwave-
assisted reactions of 3a, 3b and 3c gave expected furo[3,2-c]-1,8-naphthyridine deriva-
tives (4a–4c) in better yields under optimized conditions than normal heating in
diphenyl ether (Table 2). Syntheses of furo[3,2-c][1,8]naphthyridines has been
possible under both classical and microwave-assisted heating conditions.
This rearrangement–cyclization reaction gave greater yields of furo[3,2-c]-
1,8-naphthyridine derivatives by refluxing in diphenyl ether at 250 ꢀC than lower
temperatures, as seen in Table 2. Under these conditions, a 1-hour reaction per-
iod has been enough to obtain maximum yields. Microwave-assisted synthesis of

FURO[3,2-c]-1,8-NAPHTHYRIDINES
1885
these novel compounds was also possible in the presence of a polar solvent.
Usually, sulfolane has been better than other polar solvents such as DMSO or
DMF. A Lewis acid catalyst did not improve the yield nor shorten the reaction
period, and caused the decomposition of reaction mixture. Microwave heating has
been found to be more successful in producing these compounds than heating in
diphenyl ether because of shorter reaction periods and less solvent consumption.
In a similar manner, ring conversion of 6-unsubstituted 3-allyl-2-hydroxy-4H-
pyrido[1,2-a]pyrimidin-4-ones (3d–3e) to 1,8-naphthyridine compounds has been
investigated using both microwave and classical heating methods. Unfortunately,
no expected conversion product, a 1,8-naphthyridine derivative, has been observed.
No attempt produced any 1,8-naphthyridine derivative by heating in diphenyl ether
or by microwave heating at different temperatures. In most high-temperature experi-
ments (230–260 ꢀC), decomposition of starting materials and formation of a tar-like
mass have been observed.
In conclusion, a highly efficient and simple synthetic method was developed for
the synthesis of novel furo[3,2-c]-1,8-naphthyridines in one step with good yields
from easily accessible 6-substituted 3-allyl-2-hydroxy-4H-pyrido[1,2-a]pyrimidin-4-
ones. The presence of a substituent at the 6-position of the pyrido[1,2-a]pyrimidin
ring system seems to be necessary for the ring conversion to 1,8-naphthyridines. This
thermal ring-conversion reaction can be realized in excellent yields within shorter
reaction periods by controlled microwave heating with or without a few drops of
polar solvent such as sulfolane. This reaction may also be successfully performed
by classical heating in diphenyl ether, though moderate yields are observed. The
scope of this reaction with different pyrido[1,2-a]pyrimidines having an allylic
substituent at the 3- or 2-position is currently being studied in detail.
EXPERIMENTAL
1H NMR spectra were recorded at room temperature on Varian-Mercury
400-MHz high-performance digital Fourier transform (FT)–NMR spectrometer
with tetramethylsilane (TMS) as an internal standard. IR spectra were recorded
on a Perkin-Elmer Spectrum 100 spectrometer. Mass spectra were recorded with a
Shimadzu GC-MS QP2010 mass spectrometer operating at an inoization potential
(EI) of 70 eV. Samples were injected using a DI-2010 direct inlet probe. Melting
points were determined using an Electrothermal 9300 instrument. Elemental analyses
for C, H, and N were performed using an EuroVector CHNS-O elemental analyzer.
Microwave-assisted reactions were performed in a CEM Discover S-class single-
mode microwave synthesis instrument.
Synthesis
Bis(2,4,6-trichlorophenyl) allylmalonate (2). Diethyl allylmalonate was
first hydrolyzed to allylmalonic acid in potassium hydroxide (KOH)=ethanol solution
almost quantitatively. Then, to a mixture of allylmalonic acid (3.9 g, 27 mmol) and
2,4,6-trichlorophenol (11.2 g, 57 mmol) was added POCl3 (40 mL). This mixture was
heated at 90 ꢀC until hydrochloric acid evolution stopped. Then, excess of POCl3
was distilled under reduced pressure. The cooled dark residue was added to an ice–
water mixture to destroy excess POCl3. The acidic aqueous phase was neutralized with

˘
¨ ¨
M. GULLU AND D. YIGIT
1886
saturated sodium carbonate to pH 7–8. Afterwards, the oily product was extracted
with chloroform (150 mL), which was dried with Na2SO4, filtered, and removed on a
rotary evaporator. Residual light-brown solid product was purified by recrystallization
from acetone (94.5%). Mp 80–85 ꢀC. IR (KBr): nmax 3082, 3010, 2984, 2822, 1770, 1662,
1631, 1569, 1515, 1450, 1384, 1336, 1230, 1178, 1097, 972, 920, 858, 814, 741, 685 cmꢁ1
.
1H NMR (400 MHz, CDCl3) d 3.0 (t, J ¼ 7.2 Hz, 2H, -CH2-), 4.15 (t, J ¼ 7.2 Hz, 1H, -
=
CH), 5.23 (dd, J ¼ 10.4 Hz-cis and J ¼ 1.2 Hz, 1H, -CH C-), 5.32 (dd, J ¼ 14.8 Hz-
=
=
trans and J ¼ 1.2 Hz, 1H, CH C-), 5.95 (m, 1H, C CH-), 7.84 (s, 4H, Ph-H).
General Procedure for the Synthesis of 6-Substituted 3-Allyl-
2-hydroxy-4H-pyrido[1,2-a]pyrimidin-4-ones (3a–e)
2-Aminopyridine derivative (1a–c, 2.0 mmol) and bis(2,4,6-trichlorophenyl)
allylmalonate (2, 2.0 mmol) were dissolved in 10 mL acetone containing triethylamine
(0.4 mL). After stirring 1 h at room temperature, the reaction was complete. The solid
product was filtered under a vacuum and recrystallized from EtOH=H2O (1:3).
Selected Data for 3a–3c
2-Hydroxy-6-methyl-3-(prop-2-en-1-yl)-4H-pyrido[1,2-a]pyrimidin-4-one
(3a). Yellow solid (81%). Mp 226–230 ꢀC. IR (ATR): nmax 3073, 3034, 2878–2284,
2990, 2874, 1683, 1648, 1621, 1592, 1502, 1446, 1352, 1371, 1257, 1180, 982, 899,
1
800 cmꢁ1. H NMR (400 MHz, CDCl3) d 3,1 (s, 3H, 6-CH3), 3.25 (d, J ¼ 6 Hz,
=
2H, -CH2-), 5.0 (dd, J ¼ 11. 0 Hz-cis, 1H, -C CH-), 5.4 (dd, J ¼ 18.0 Hz-trans, 1H,
=
=
-C CH), 6.0 (m, 1H, -CH C-), 6.82 (d, J ¼ 6.8 Hz, 1H, 7-CH), 7.42 (d, J ¼ 8.0 Hz,
Hz, 1H, 9-CH), 7.66 (t, J ¼ 8.0 Hz, 1H, 8-CH). MS (EI) m=z calcd. for C12H12N2O2
216.2; found 216 (Mþ, 50), 201 (5), 188 (25), 173 (10), 159 (10), 149 (10), 135 (100),
119 (5), 108 (20), 92 (55). Elemental analysis: anal. calcd. for C12H12N2O2 (216.23):
C,65.65; H, 5.59; N, 12.96. Found: C, 66.30; H, 5.52; N, 12.82.
6-Amino-2-hydroxy-3-(prop-2-en-1-yl)-4H-pyrido[1,2-a]pyrimidin-4-one
(3b). Light green solid (87%). Mp 286–290 ꢀC (dec). IR (ATR): nmax 3317, 3259,
3184, 3130, 3028, 2880–2388, 2972, 2911, 2851, 1671, 1617, 1574, 1511, 1448,
1
1386, 1336, 1151, 1082, 995, 908, 843, 770 cmꢁ1. H NMR (400 MHz, DMSO-d6)
d 2.96 (d, J ¼ 6.4 Hz, 2H), 3.4 (broad signal, 2H, -NH2), 4.84 (dd, J ¼ 11.0 Hz-cis,
=
=
=
1H, -C CH-), 4.98 (dd, J ¼ 18.0 Hz-trans, 1H, -C CH-), 5.56 (m, 1H, -CH C-),
6.2 (d, J ¼ 8.0 Hz, 1H, 7-CH), 6.25 (d, J ¼ 8.0 Hz, 1H, 9-CH), 7,5 (t, J ¼ 8.0 Hz,
1H, 8-CH). MS (EI) m=z calcd. for C11H11N3O2 217.2; found 217 (Mþ, 100), 202
(100), 188 (5), 170 (20), 147 (5), 118 (5), 109 (5), 94 (5), 77 (5). Elemental analysis:
anal. calcd. for C11H11N3O2 (217.22): C, 60.82; H, 5.10; N, 19.34. Found: C,
60.45; H, 5.08; N, 19.30.
6-Acetylamino-2-hydroxy-3-(prop-2-en-1-yl)-4H-pyrido[1,2-a]pyrimidin-
4-one (3c). Green solid (85%). Mp 250–252 ꢀC (dec). IR (ATR): nmax 3192–2162,
3131, 3079, 3130, 2999, 2973, 2909, 1699, 1641, 1628, 1587, 1386, 1371, 1270,
1
1235, 1174, 1034, 997, 902, 794 cmꢁ1. H NMR (400 MHz, DMSO-d6) d 2.28 (s,
=
3H, -CH3), 3.28 (d, J ¼ 6.4 Hz, 2H, CH2-), 5.05 (dd, J ¼ 11,0 Hz-cis, 1H, -C CH-),
=
=
5.18 (dd, J ¼ 18,0 Hz-trans, 1H, -C CH-), 6.0 (m, 1H, -CH C-), 7,12 (d, J ¼ 8.0 Hz,

FURO[3,2-c]-1,8-NAPHTHYRIDINES
1887
1H, 9-CH), 7.8 (t, J ¼ 8.0 Hz, 1H, 8-CH), 8.35 (d, J ¼ 8.0 Hz, 1H, 7-CH), 14.83
(broad signal, 1H, NH). MS (EI) m=z calcd. for C13H13N3O3 259.2; found 259
(Mþ, 100), 231 (25), 217 (35), 189 (20), 178 (50), 160 (50), 136 (95), 119 (10), 109
(50), 93 (60), 66 (20), 43 (80). Elemental analysis: anal. calcd. for C13H13N3O3
(259.26): C, 60.22; H, 5.05; N, 16.21. Found: C, 59.85; H, 4.93; N, 15,95.
General Procedure for the Synthesis of Furo[3,2-c]-1,8-naphthyridine
Derivatives (4a–c)
Method A. 6-Substituted-3-allyl-pyrido[1,2-a]pyrimidin-4-one (3a–3c, 1 mmol)
in 10 mL diphenyl ether was refluxed for 1 h. The solid product was diluted with
diethyl ether, filtered, and washed with diethyl ether several times. The crude solid
product was recrystallized from MeOH=H2O (1:3).
Method B. 6-Substituted-3-allyl-pyrido[1,2-a]pyrimidine-4-one derivative (3a–
3c, 1mmol) was placed in a microwave reaction vessel (10 mL), and a few drops of
sulfolane were added. Then, the starting material was heated at 250ꢀC under microwave
irradiation for 20 min. Diethyl ether was added to the reaction vessel. The solid product
was filtered and washed with diethyl ether. It was recrystallised from MeOH=H2O (1:3).
Selected Data for 4a–4c
2,7-Dimethyl-2,3-dihydro-furo[3,2-c][1,8]naphthyridin-4(5H)-one (4a).
Brown solid (49%, method A, and 75%, method B). Mp 120 ꢀC. IR (ATR): nmax
3065, 2960, 2927, 2861, 1645, 1562, 1556, 1452, 1404, 1378, 1163, 1137, 1090,
1
1033, 781 cmꢁ1. H NMR (400 MHz, CDCl3) d 1.56 (d, J ¼ 6.0 Hz, 3H, 2-CH3),
2.8 (s, 3H, 7-CH3), 2.83 (dd, J ¼ 15.2 Hz and J ¼ 6.0 Hz, 1H, furo-CH2), 3.35 (dd,
J ¼ 15.2 Hz and J ¼ 6.0 Hz, 1H, furo-CH2), 5.24 (m, 1H, furo-CH), 7,0 (d, J ¼ 8.0 Hz,
1H, 8-CH), 7.85 (d, J ¼ 8.0 Hz, 1H, 9-CH), 9.5 (broad signal, 1H, -NH-). MS (EI) m=z
calcd. for C12H12N2O2 216.2; found 216 (Mþ, 60), 201 (95), 187 (5), 173 (3), 159 (1),
135 (4), 120 (1), 107 (4), 77 (1), 64 (1), 44 (76). Elemental analysis: anal. calcd. for
C12H12N2O2 (216.23): C, 66.65; H, 5.59; N, 12.96. Found: C, 66.54; H, 5.20; N, 12.60.
7-Amino-2-methyl-2,3-dihydro-furo[3,2-c][1,8]naphthyridin-4(5H)-one
(4b). Light brown solid (70%, method A, and 90%, method B). Mp 325 ꢀC (dec.). IR
(ATR): nmax 3327, 3148, 2995, 2965, 1637, 1612, 1513, 1485, 1421, 1388, 1348, 1186,
1082, 972, 854 cmꢁ1
.
1H NMR (400 MHz, DMSO-d6) d 1.44 (d, J ¼ 6 Hz, 3H,
2-CH3), 2.45 (dd, J ¼ 14.4 Hz and J ¼ 7.6 Hz, 1H, furo-CH2), 3.10 (dd, J ¼ 14.4 Hz
and J ¼ 7.6 Hz, 1H, furo-CH2), 5.14 (m, 1H, furo-CH), 6.3 (d, J ¼ 8.8 Hz, 1H,
8-CH), 6.84 (broad signal, 2H, -NH2), 7.55 (d, J ¼ 8.8 Hz, 1H, 9-CH), 11.1 (broad
signal, 1H, -NH-). MS (EI) m=z calcd. for C11H11N3O2 217.2; found 217 (Mþ,
100), 202 (100), 188 (10), 174 (20), 162 (5), 146 (10), 136 (10), 118 (5), 107 (5), 94
(5), 81 (5). Elemental analysis: calcd. for C11H11N3O2 (217.22): C, 60.82; H, 5.10;
N, 19.34. Found: C, 60.50; H, 4.89; N, 19.20.
7-Acetylamino-2-methyl-2,3-dihydro-furo[3,2-c][1,8]naphthyridin-4(5H)-
one (4c). Light brown solid (76%, method A, and 94%, method B). Mp 265–270ꢀC
(dec.). IR (ATR): nmax 3274, 3145, 3072, 2973, 2947, 2844, 1678, 1644, 1620, 1607,

˘
¨ ¨
M. GULLU AND D. YIGIT
1888
1578, 1544, 1491, 1344, 1317, 1254, 1231, 1191, 1112, 999, 834, 812, 789 cmꢁ1. 1H NMR
(400 MHz, DMSO-d6) d 1.47 (d, J ¼ 6.2 Hz, 3H, 2-CH3), 2.62 (dd, J¼ 16.0 Hz
and J ¼ 7.2Hz, 1H, furo-CH2), 3,19 (dd, J ¼ 16.0 Hz and J ¼ 7.2 Hz, 1H, furo-CH2),
5.22 (m, 1H, furo-CH), 7.96 (d, J ¼ 8.8Hz, 1H, 8-CH), 8,2 (d, J ¼ 8.8 Hz, 1H, 9-CH),
10.6 (broad signal, 1H, -NH-), 11,48 (broad signal, 1H, -ring-NH-). MS (EI) m=z calcd.
for C13H13N3O3 259.2; found 259 (Mþ, 50), 244 (50), 226 (5), 216 (20), 202 (100), 170 (5),
146 (5), 136 (10), 119 (5), 107 (5), 93 (5), 81 (5). Elemental analysis: anal. calcd. for
C13H13N3O3 (259.26): C, 60.22; H, 5.05; N, 16.21. Found: C, 60.63; H, 5.15; N, 15.85.
ACKNOWLEDGMENTS
We are grateful to the Scientific and Technological Research Council of
¨
Turkey-TUBITAK for financial support for our research project (TBAG-106T066).
¨
Deniz Yig˘it also thanks TUBITAK for a scholarship throughout this project.
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