Application of 9-ethyl[1,2,5]selenadiazolo[3,4-h]quinolones in the synthesis of tricyclic azoloquinolones

Article abstract of DOI:10.1016/j.tet.2014.04.097

A series of tricyclic azoloquinolones was prepared by a novel approach based on the protection of a benzene-1,2-diamine moiety as 2,1,3- benzoselenadiazole ring. A new reductive deselenation of 9-ethylselenadiazolo[3, 4-h]quinolones using zinc powder in acetic acid afforded 7,8-diamino-1- ethylquinolones in high yields. The obtained diaminoquinolones were employed as useful substrates in cyclocondensation reactions leading to azoloquinolone derivatives.

Full text of DOI:10.1016/j.tet.2014.04.097

Accepted Manuscript
Application of 9-ethyl[1,2,5]selenadiazolo[3,4-h]quinolones in the synthesis of tricyclic
azoloquinolones
Maroš Bella, Viktor Milata
PII:
S0040-4020(14)00643-7
10.1016/j.tet.2014.04.097
TET 25547
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 13 January 2014
Revised Date: 14 April 2014
Accepted Date: 29 April 2014
Please cite this article as: Bella M, Milata V, Application of 9-ethyl[1,2,5]selenadiazolo[3,4-h]quinolones
in the synthesis of tricyclic azoloquinolones, Tetrahedron (2014), doi: 10.1016/j.tet.2014.04.097.
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Graphical Abstract
Application of 9-
Leave this area blank for abstract info.
ethyl[1,2,5]selenadiazolo[3,4-h]quinolones in
the synthesis of tricyclic azoloquinolones
Maroš Bellaa,b,* and Viktor Milatab
aInstitute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-845 38 Bratislava, Slovakia
bDepartment of Organic Chemistry, Faculty of Chemical and Food Technology, Slovak University of
Technology, Radlinského 9, SK-812 37 Bratislava, Slovakia

1
ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
Application of 9-ethyl[1,2,5]selenadiazolo[3,4-h]quinolones in the synthesis of
tricyclic azoloquinolones
Maroš Bellaa,b, and Viktor Milatab
a Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-845 38 Bratislava, Slovakia
b Department of Organic Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinského 9, SK-812 37 Bratislava, Slovakia
ARTICLE INFO
ABSTRACT
Article history:
Received
A series of tricyclic azoloquinolones was prepared by a novel approach based on the protection
of
a benzene-1,2-diamine moiety as 2,1,3-benzoselenadiazole ring. A new reductive
Received in revised form
Accepted
Available online
deselenation of 9-ethylselenadiazolo[3,4-h]quinolones using zinc powder in acetic acid afforded
7,8-diamino-1-ethylquinolones in high yields. The obtained diaminoquinolones were employed
as useful substrates in cyclocondensation reactions leading to azoloquinolone derivatives.
2014 Elsevier Ltd. All rights reserved
.
Keywords:
Azoloquinolones
2,1,3-Benzoselenadiazoles
Cyclocondensation
Ethylselenadiazoloquinolones
Reductive deselenation
1. Introduction
3-substituted benzene-1,2-diamines which can be further
transformed into various nitrogen heterocycles (Scheme 1).
3-Substituted benzene-1,2-diamines, in particular 3-
nitrobenzene-1,2-diamines, represent valuable intermediates in
the synthesis of heterocyclic compounds.1 However, their
preparation is often laborious and time consuming multistage
synthesis. Although, it is very convenient to base their
preparation on benzene-1,2-diamine itself, an electrophilic
aromatic substitution on benzene-1,2-diamine usually leads to
the 4-substituted and/or 4,5-disubstituted products. For
example, nitration or bromination of N,N’-bis(p-
toluenesulfonyl)benzene-1,2-diamine followed by deprotection
gave 4,5-dinitrobenzene-1,2-diamine and 4,5-dibromobenzene-
1,2-diamine, respectively.2 This obstacle was overcome by the
Scheme 1.
application
of
2,1,3-benzoselenadiazoles
as
useful
intermediates in the synthesis of 3-substituted benzene-1,2-
diamines.1 The 2,1,3-benzoselenadiazole skeleton serves as a
protecting group for a benzene-1,2-diamine moiety and
simultaneously directs the electrophile in the electrophilic
The 2,1,3-benzoselenadiazole skeleton is extremely stable to
acidic, basic and thermal conditions.6,7 On the other hand, its
sensitivity to reductive conditions is successfully used in the
recovery of the benzene-1,2-diamine moiety (deprotection).
The reductive deselenation is achieved with classical reducing
agents commonly employed in organic synthesis such as
NH4HS (NH3/H2S),8,9-11 HI,12-14 SnCl2ꢀ2H2O,4,15,16 Fe/AcOH,17
aromatic
substitutions
(nitration,3
bromination,4
(chloro)sulfonation4,5) to the position 4 or 7, if the position 4 is
already occupied. Subsequent reductive deselenation provides
———
Corresponding author. Tel.: +421 2 59410231; fax: +421 2 59410222; e-mail: maros.bella@savba.sk

2
Tetrahedron
ACCEPTED MANUSCRIPT
Scheme 2.
2. Results and discussion
Zn/HCl,3,4 Raney Ni/N2H4ꢀH2O18,19 and BH3ꢀSMe2.20 The first
two reducing agents (NH4HS, HI) mentioned above reduce
2,1,3-benzoselenadiazole ring selectively leaving the nitro
group untouched thus making 2,1,3-benzoselenadiazoles
precious intermediates in the heterocyclic synthesis. In
addition, the protection of the benzene-1,2-diamine moiety as
the 2,1,3-benzoselenadiazole skeleton was applied in the
synthesis of o-diaminoindoles18,19 and o-diaminoquinolines16
which were obtained after the deselenation of
9-Ethylselenadiazoloquinolones 1, prepared as detailed in
our previous paper,20 serve as the masked form of
azoloquinolones derivatives. The reductive deselenation of 9-
ethylselenadiazoloquinolone 1a with SnCl2ꢀ2H2O in
concentrated HCl afforded 7,8-diamino-1-ethylquinolone 2a in
85% yield (Scheme 2). The amount of concentrated HCl was
reduced by using MeOH as the co-solvent. However, these
reduction conditions are not suitable for the deselenation of 9-
ethylselenadiazoloquinolone 1b due to ethyl ester hydrolysis or
its transesterification to methyl ester, therefore reductive
deselenation of 9-ethylselenadiazoloquinolones 1 was carried
out with zinc powder in acetic acid to give 7,8-diamino-1-
ethylquinolones 2 in excellent yields without ethyl ester
hydrolysis (Scheme 2). The diamines 2 were isolated as stable
yellow solids which can be stored in the air for a long time.
The reductive deselenation of 2,1,3-benzoselenadiazole ring
with zinc in acetic acid was in part employed in our previous
paper.16 This method of reductive deselenation is advantegeous
due to stability, cheapness and availability of reagents,
moreover it does not require strong acidic reagents and
solvents (HI, HCl) or elevated reaction temperatures.
selenadiazoloindoles
respectively.
and
selenadiazoloquinolines,
To date, a large number of 9-substituted imidazo-21,22 and
triazolo[4,5-h]quinolone derivatives23-25 have been prepared
and their antibacterial activity against pathogenic bacteria has
been evaluated. In general, 4-quinolone derivatives bearing a
small alkyl group (ethyl, cyclopropyl) at the nitrogen of the
pyridone ring show stronger antibacterial effects than their N-
dealkylated analogues.26 However, the ethylation of 4-
quinolones with an annelated azole ring can be troublesome
with low yields due to the ethylation of the azole ring.23 To
avoid the ethylation of the azole ring, the ethyl group should be
introduced prior to the azole ring formation. Concerning this
strategy, 9-ethyl[1,2,5]selena-diazolo[3,4-h]quinolones 1,20
which already bear the ethyl group at the N-9 position, were
employed as the precursors of azoloquinolone derivatives.
Within the structure of 9-ethylselenadiazoloquinolones 1, the
2,1,3-benzoselenadiazole skeleton represents protected
benzene-1,2-diamine moiety, which followed by deprotection,
can be further transformed into nitrogen heterocycles. In this
paper, the reductive deselenation of 9-ethyl[1,2,5]selena-
diazolo[3,4-h]quinolones 1 with zinc powder in acetic acid
yielding 7,8-diamino-1-ethylquinolones 2 is described. The
cyclocondensation reactions of 7,8-diamino-1-ethylquinolones
2 into various azoloquinolone derivatives ethylated at the
nitrogen of the pyridone ring are discussed in detail.
Next, the cyclocondensation of diaminoquinolones 2 with
various reagents was examined. Simple heating of 7,8-
diamino-1-ethylquinolones 2 in formic acid smoothly afforded
imidazo[4,5-h]quinolones 3 in excellent yields (Scheme 3).
Both derivatives 3 were isolated as hemihydrates as comfirmed
by the elemental analyses. This is in accordance with well-
known fact that benzimidazole derivatives form hemihydrates27
or hydrates.28 A treatment of diamines 2 with cyanogen
bromide in MeOH or dioxane at room temperature or under
reflux did not lead to desired 2-aminoimidazoquinolones.
Heating of diamines 2 with carbonyldiimidazole (CDI) in dry
DMF to access imidazoquinolin-2,6-diones was also
unsuccessful.
Scheme 3.

3
4. Experimental section
The diazotation of diamines 2 in dilute acetic acid with
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NaNO2 led to the formation of triazolo[4,5-h]quinolones 4 in
good yields (Scheme 3). Ethyl 9-ethyltriazolo[4,5-h]quinoline-7-
carboxylate 4b was already prepared by ethylation of ethyl
triazolo[4,5-h]quinoline-7-carboxylate in a very low yield (3.2
%) as reported by Carta et. al.23 However, comparing the values
of chemical shifts published for derivative 4b with our observed
values, significant differences were found. For example, the
chemical shift for methylene hydrogens of the ethyl group
attached to the nitrogen of the pyridone ring (5.0-5.2 ppm),
which is characteristic for 9-ethylselenadiazoloquinolones 1 and
Thin-layer chromatography (TLC) was performed on
aluminium plates pre-coated with 0.2 mm silicagel (25 ꢁm)
containing fluorescent indicator 254 nm (Fluka) and stains were
visualised by UV light (254 nm or 366 nm). Flash liquid
chromatography (FLC) was performed on silica gel [Normasil 60
(43-60 ꢁm)]. Melting points were measured on a Koffler block
and are uncorrected. 1H NMR and 13C NMR spectra were
recorded on a Varian Mercury 300-MHz spectrometer at 25 °C.
1
The operating frequencies were 300 MHz for H and 75.5 MHz
for 13C nuclei. Chemical shifts (δ) are reported in ppm and
coupling constants (J) are given in Hz. IR spectra were recorded
on a Nicolet model NEXUS 470 FT-IR spectrometer using KBr
technique at 25 °C. Elemental analyses were performed using a
Thermo Finnigan Flash EA 1112 instrument.
1
azoloquinolones 3-5, is not present in the H NMR spectrum
published for derivative 4b. Moreover, the values of all the
chemical shifts as well as the melting points were different.
Because the ethylation of [1,2,3]triazolo[4,5-h]quinoline-7-
carboxylate can provide several products, we assume that Carta
et al.23 isolated one of the possible products of the triazole ring
ethylation.
4.1. Synthesis of 7,8-diamino-1-ethylquinolones 2
The cyclocondensation of diamines 2 with symmetric α-
dicarbonyl compounds (benzil, biacetyl, glyoxal) readily
provided quinoxaline derivatives 5 in high yields (Scheme 3). In
the case of cyclocondensation of the diamine 2a with aqueous
solution of glyoxal, the complex reaction mixture was formed
and desired product 5c was isolated in 52% yield only. Because
of the low yield, the aqueous solution of glyoxal was replaced by
(N,N’-dicyclohexyl)-1,2-ethanediimine (6)29 according to Grivas
et. al.11 However, in this literature, the procedure for the
cyclocondensation of benzene-1,2-diamines with diimine 6 to
corresponding quinoxalines is not described. Treatment of
diamines 2 with a stoichiometric amount of diimine 6 in ethanol
led to the extremely slow formation of pyrazine ring. However,
when a small amount of acetic acid was added to the reaction
mixture, the ring closure proceeded rapidly to access
pyridoquinoxalines 5c and 5f in excellent yields (Scheme 3).
4.1.1. 7,8-Diamino-1-ethylquinolin-4(1H)-one (2a)
Method
A (reduction with SnCl2·2H2O). To a stirred
suspension of selenadiazoloquinolone 1a (0.80 g, 2.87 mmol) in
MeOH (18 mL), concentrated HCl (12 mL) was added while
cooling in an ice bath. Then the ice bath was removed and the
resulting suspension was allowed to reach the room temperature.
Subsequently, SnCl2·2H2O (3.24 g, 12.15 mmol) was added in
small portions within 20-25 min. and the reaction mixture was
stirred for 6 hours at room temperature. Then it was diluted with
MeOH (30 mL), the insoluble material was separated by suction
and the filter cake was washed thoroughly with MeOH (30 mL).
The filtrate was alkalised with 10% MeONa in MeOH, followed
by the addition of silica gel (10 g) to the resulting suspension and
evaporation of the solvent under reduced pressure. The residue
was loaded on a silica gel column and was eluted with a mixture
of CHCl3/MeOH = 9:1 (Rf = 0.14) to afford compound 2a as
The carboxylic acids 7 were obtained by the basic hydrolysis
of the corresponding ethyl esters 3b, 4b and 5d-f in good yields
(Scheme 4).
1
yellow crystals. Yield 0.49 g (85%); mp 233–237 °C; H NMR
(300 MHz, DMSO-d6): δ 1.06 (t, 3H, J = 6.9 Hz, NCH2CH3),
4.20 (br s, 2H, NH2), 4.50 (q, 2H, J = 6.9 Hz, NCH2CH3), 5.42
(br s, 2H, NH2), 5.81 (d, 1H, J = 7.6 Hz, H-3), 6.72 (d, 1H, J =
8.4 Hz, H-6), 7.47 (d, 1H, J = 8.4 Hz, H-5), 7.65 (d, 1H, J = 7.6
Hz, H-2); 13C NMR (75 MHz, DMSO-d6): δ 15.3 (NCH2CH3),
48.6 (NCH2CH3), 108.1, 112.9, 117.3, 120.2, 120.7, 132.8, 141.6,
146.1, 176.5 (CO). IR (KBr): 3200, 1597, 1557, 1537, 1440 cm-1.
Anal. Calcd for C11H13N3O (203.24): C, 65.01; H, 6.45; N, 20.68.
Found: C, 65.23; H, 6.57; N, 20.58.
Method B (reduction with Zn in AcOH). To a stirred solution
of selenadiazoloquinolone 1a (0.70 g, 2.51 mmol) in AcOH (14
mL), Zn powder (0.82 g, 12.58 mmol) was added at room
temperature. After 3 h of stirring, the same amount of Zn powder
was added and stirring was continued overnight. Once the
reaction was complete, it was diluted with MeOH (20 mL), the
insoluble material was separated by suction and the filter cake
was washed thoroughly with MeOH (30 mL). The filtrate was
evaporated under reduced pressure, the residue was dissolved in
MeOH (40 mL) and the resulting solution was alkalised with 10
% MeONa in MeOH. To this solution silica gel (8 g) was added
and the solvent was evaporated under reduced pressure. The
residue was loaded on a silica gel column and was eluted with a
mixture of CHCl3/MeOH = 9:1 (Rf = 0.14) to give compound 2a
as yellow crystals. Yield 0.45 g (88%); mp 234–237 °C. The
NMR spectra characteristics were in accordance with those of
diaminoquinolone 2a prepared by the reduction with
SnCl2·2H2O.
Scheme 4.
3. Conclusions
Novel tricyclic azoloquinolones 3-5 and 7 as potential
biological active compounds were synthesized by an unusual
approach. A new method of reductive deselenation applied to 9-
ethylselenadiazoloquinolones 1 using zinc powder in acetic acid
afforded 7,8-diamino-1-ethylquinolones 2 as versatile building
blocks for preparation of tricyclic azoloquinolones. In addition,
by this synthetic method, the structure of triazoloquinolones 4b
and 7b was revised. It should be noted that diaminoquinolones 2
could be used in the cyclocondensation reactions without
isolation and purification, and could be prepared in situ.

4
Tetrahedron
4.1.2. Ethyl 7,8-diamino-1-ethyl-4-oxo-1,4-
7), 7.64 (d, 1H, J = 8.8 Hz, H-4), 8.07 (d, 1H, J = 7.6 Hz, H-8),
ACCEPTED MANUSCRIPT
8.24 (d, 1H, J = 8.8 Hz, H-5); 13C NMR (75 MHz, DMSO): δ
dihydroquinoline-3-carboxylate (2b)
15.6 (NCH2CH3), 50.4 (NCH2CH3), 107.4, 112.0, 122.4, 125.4,
132.7, 135.1, 136.9, 143.7, 175.3 (CO). IR (KBr): 1627, 1587,
1558, 1554 cm-1. Anal. Calcd for C11H10N4 O (214.22): C, 61.67;
H, 4.71; N, 26.15. Found: C, 61.63; H, 4.76; N, 26.16.
To a stirred solution of selenadiazoloquinolone 2b (1.0 g, 2.85
mmol) in AcOH (20 mL), Zn powder (0.74 g, 11.31 mmol) was
added at room temperature and after 1 h of stirring the same
amount of Zn powder was added and stirring was continued for
an additional hour. Once the reaction was complete, the insoluble
material was separated by suction, the filter cake was washed
thoroughly with AcOH (50 mL) and the filtrate was evaporated
under reduced pressure (bath 30 °C). The residue was dissolved
in EtOH (20 mL), alkalised with conc. NH4OH, followed by the
addition of silica gel (8 g) and evaporation of the solvent under
reduced pressure. The residue was loaded on a silica gel column
and was eluted with a mixture of CHCl3/MeOH = 9:1 (Rf = 0.15)
to afford compound 2b as an yellow solid. Yield 0.74 g (95%);
mp 199–206 °C; 1H NMR (300 MHz, DMSO-d6): δ 1.11 (t, 3H, J
= 6.8 Hz, NCH2CH3), 1.26 (t, 3H, J = 7.0 Hz, OCH2CH3), 4.17
(q, 2H, J = 7.0 Hz, OCH2CH3), 4.34 (s, 2H, NH2), 4.66 (q, 2H, J
= 6.8 Hz, NCH2CH3), 5.58 ( s, 2H, NH2), 6.78 (d, 1H, J = 8.4 Hz,
H-6), 7.53 (d, 1H, J = 8.4 Hz, H-5), 8.36 (s, 1H, H-2); 13C NMR
(75 MHz, DMSO-d6): δ 14.3 (OCH2CH3), 15.4 (NCH2CH3), 50.0
(NCH2CH3), 59.2 (OCH2CH3), 108.8, 113.3, 118.0, 120.7, 121.4,
130.8, 142.7, 151.1, 164.9 (COOEt), 172.8 (CO). IR (KBr):
3232, 1569, 1547, 1478, 1437 cm-1. Anal. Calcd for C14H17N3O3
(275.30): C, 61.08; H, 6.22; N, 15.26. Found: C, 61.23; H, 6.29;
N, 15.30.
4.2.3. 10-Ethyl-2,3-diphenyl-7H,10H-pyrido[2,3-
f]quinoxalin-7-one (5a)
To a stirred solution of diamine 2a (50 mg, 0.24 mmol) in a
mixture of EtOH (2 mL) and AcOH (5 mL), benzil (52 mg, 0.24
mmol) was added at room temperature. After 1 h of stirring, the
reaction mixture was treated with water (10 mL), the precipitated
solid was collected by suction, washed with water and dried to
give compound 5a as a white solid. Yield 84 mg (90%); mp 255–
1
259 °C; H NMR (300 MHz, CDCl3): δ 1.57 (t, 3H, J = 6.9 Hz,
NCH2CH3), 5.19 (q, 2H, J = 6.9 Hz, NCH2CH3), 6.62 (d, 1H, J =
7.6 Hz, H-8), 7.38 (m, 6H, 2 × Ph), 7.52 (dd, 2H, J = 7.8, 1.8 Hz,
2 × Ph), 7.60 (dd, 2H, J = 7.9, 1.7 Hz, 2 × Ph), 7.68 (d, 1H, J =
7.6 Hz, H-9), 7.99 (d, 1H, J = 8.9 Hz, H-5), 8.76 (d, 1H, J = 8.9
Hz, H-6); 13C NMR (75 MHz, CDCl3): δ 16.5 (NCH2CH3), 53.7
(NCH2CH3), 113.6, 124.7, 127.5, 128.0, 128.4, 129.0, 129.3,
129.6, 129.8, 133.9, 136.9, 138.0, 138.5, 143.4, 145.3, 149.8,
153.2, 176.7 (CO). IR (KBr): 1632, 1585, 1543, 1444 cm-1. Anal.
Calcd for C25H19N3O (377.44): C, 79.55; H, 5.07; N, 11.13.
Found: C, 79.64; H, 5.10; N, 11.15.
4.2. Synthesis of 9-ethylazoloquinolones 3a, 4a and 10-
ethylpyridoquinoxalines 5a-c
4.2.4. 10-Ethyl-2,3-dimethyl-7H,10H-pyrido[2,3-
f]quinoxalin-7-one (5b)
4.2.1. 9-Ethyl-6H,9H-imidazo[4,5-h]quinolin-6-one
To a stirred suspension of diamine 2a (50 mg, 0.24 mmol) in
EtOH (3 mL), biacetyl (0.06 mL, 59 mg, 0.69 mmol) was added
at 0 °C. After 15 min. of stirring, the reaction mixture was
allowed to reach room temperature and the stirring was continued
for 3 h. Thereafter, the volatiles were evaporated under reduced
pressure and the residue was purified by FLC (SiO2,
CHCl3/MeOH = 25:1, Rf = 0.20) to yield compound 5b as a white
hemihydrate (3a)
A mixture of diamine 2b (50 mg, 0.24 mmol) and HCOOH (1
mL) was heated at 100 °C for 10 min. in an oil bath. After
cooling to room temperature, HCOOH was evaporated under
reduced pressure. The residue was dissolved in MeOH (4 mL)
and the resulting solution was alkalised with 10% MeONa in
MeOH. To this solution silica gel (0.9 g) was added and the
solvent was evaporated under reduced pressure. The residue was
loaded on a silica gel column and eluted with a mixture of
CHCl3/MeOH = 9:1 (Rf = 0.14) to give compound 3b as a white
1
solid. Yield 58 mg (93%); mp 223–225 °C; H NMR (300 MHz,
CDCl3): δ 1.53 (t, 3H, J = 6.8 Hz, NCH2CH3), 2.74 (s, 6H, 2 ×
CH3), 5.07 (q, 2H, J = 6.8 Hz, NCH2CH3), 6.52 (d, 1H, J = 7.5
Hz, H-8), 7.61 (d, 1H, J = 7.5 Hz, H-9), 7.78 (d, 1H, J = 8.9 Hz,
H-5), 8.64 (d, 1H, J = 8.9 Hz, H-6); 13C NMR (75 MHz, CDCl3):
δ 16.3 (NCH2CH3), 22.7 (CH3), 22.8 (CH3), 53.8 (NCH2CH3),
113.0, 124.1, 126.7, 126.9, 133.7, 136.7, 143.5, 145.3, 150.1,
153.8, 176.8 (CO). IR (KBr): 1620, 1574, 1464, 1405 cm-1. Anal.
Calcd for C15H15N3O (253.30): C, 71.13; H, 5.97; N, 15.59.
Found: C, 71.10; H, 5.94; N, 15.54.
1
solid. Yield 53 mg (89%); mp 220–224 °C; H NMR (300 MHz,
DMSO-d6): δ 1.38 (t, 3H, J = 6.8 Hz, NCH2CH3), 5.06 (q, 2H, J
= 6.8 Hz, NCH2CH3), 6.13 (d, 1H, J = 7.6 Hz, H-7), 7.52 (d, 1H,
J = 8.6 Hz, H-4), 7.94 (d, 1H, J = 7.6 Hz, H-8), 8.09 (d, 1H, J =
8.6 Hz, H-5), 8.38 (s, 1H, H-2), 13.08 (br s, 1H, NH); 13C NMR
(75 MHz, DMSO-d6): δ 16.2 (NCH2CH3), 49.7 (NCH2CH3),
108.8, 109.9, 120.5, 121.9, 131.4, 133.0, 136.0, 140.6 (C-2),
143.6, 175.9 (CO). IR (KBr): 3300, 1623, 1583, 1558 cm-1. Anal.
Calcd for C12H11N3Oꢀ½H2O (240.25): C, 64.85; H, 5.44; N,
18.91. Found: C, 64.78; H, 5.40; N, 18.74.
4.2.5. 10-Ethyl-7H,10H-pyrido[2,3-f]quinoxalin-7-
one (5c)
Method A (cyclocondensation with 40% aqueous solution of
glyoxal). To a stirred suspension of diamine 2a (50 mg, 0.24
mmol) in EtOH (2 mL), 40% aqueous solution of glyoxal (0.04
mL) was added at 0 °C. After 1 h of stirring at this temperature,
the mixture was treated with water (25 mL) and extracted with
CHCl3 (4 × 15 mL). The combined extracts were dried with
Na2SO4, filtered and evaporated under reduced pressure. The
residue was purified by FLC (SiO2, CHCl3/MeOH = 25:1, Rf =
0.21) to afford compound 5c as a pale yellow solid. Yield 29 mg
4.2.2. 9-Ethyl-6H,9H-[1,2,3]triazolo[4,5-
h]quinolin-6-one (4a)
To a stirred suspension of diamine 2a (50 mg, 0.24 mmol) in a
mixture of AcOH/H2O (1:5 (v/v), 1.2 mL), a solution of NaNO2
(17.3 mg, 0.25 mmol) in water (1 mL) was added dropwise at 0
°C. After 30 min. of stirring at this temperature, the mixture was
allowed to reach room temperature. Within a few minutes, white
crystals were formed. The precipitated crystals were separated by
suction, washed with water and dried to yield compound 4b as
white crystals. Yield 44 mg (83%); mp 300–305 °C; H NMR
(300 MHz, DMSO-d6): δ 1.42 (t, 3H, J = 6.8 Hz, NCH2CH3),
5.01 (q, 2H, J = 6.8 Hz, NCH2CH3), 6.28 (d, 1H, J = 7.6 Hz, H-
1
(52%); mp 190–193 °C; H NMR (300 MHz, CDCl3): δ 1.52 (t,
3H, J = 6.9 Hz, NCH2CH3), 5.11 (q, 2H, J = 6.9 Hz, NCH2CH3),
6.59 (d, 1H, J = 7.7 Hz, H-8), 7.68 (d, 1H, J = 7.7 Hz, H-9), 7.78
(d, 1H, J = 9.0 Hz, H-5), 8.77 (d, 1H, J = 9.0 Hz, H-6), 8.89 (d,
1

5
1H, J = 1.7 Hz, H-3), 8.95 (d, 1H, J = 1.7 Hz, H-2); 13C NMR (75
1583 cm-1. Anal. Calcd for C14H14N4O3 (286.29): C, 58.73; H,
4.93; N, 19.57. Found: C, 58.88; H, 4.98; N, 19.62.
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MHz, CDCl3): δ 16.4 (NCH2CH3), 54.0 (NCH2CH3), 113.6,
124.8, 127.5, 128.2, 129.6, 136.4, 137.1, 141.3, 145.2, 145.6,
176.6 (CO). IR (KBr): 1626, 1588, 1466, 1401 cm-1. Anal. Calcd
for C13H11N3O (225.25): C, 69.32; H, 4.92; N, 18.66. Found: C,
69.40; H, 4.96; N, 18.71.
4.3.3. Ethyl 10-ethyl-7-oxo-2,3-diphenyl-7H,10H-
pyrido[2,3-f]quinoxaline-8-carboxylate (5d)
To a stirred solution of diamine 2b (130 mg, 0.47 mmol) in a
mixture of EtOH (3 mL) and AcOH (6 mL), benzil (100 mg, 0.47
mmol) was added at room temperature. After 1 h of stirring, the
volatiles were evaporated under reduced pressure and the residue
was subjected to FLC (SiO2, CHCl3, Rf = 0.15) to afford
compound 5d as a pale yellow solid. Yield 198 mg (93%); mp
Method B (cyclocondensation with (N,N’-dicyclohexyl)-1,2-
ethanediimine (6)). To a stirred suspension of diamine 2a (150
mg, 0.74 mmol) and diimine 6 (163 mg, 0.74 mmol) in EtOH (8
mL), AcOH (0.25 mL) was added at room temperature. After 3 h
of stirring, the volatiles were evaporated under reduced pressure
and the residue was taken up into the CHCl3 (40 mL). The
organic phase was washed with water (2 × 40 mL), dried with
Na2SO4, filtered and evaporated under reduced pressure. The
residue was purified by FLC (SiO2, CHCl3/MeOH = 25:1, Rf =
0.21) to afford compound 5c as a pale yellow solid. The NMR
spectral characteristics were in accordance with those of
pyridoquinoxaline 5c prepared by the cyclocondensation with
40% aqueous solution of glyoxal.
1
247–249 °C; H NMR (300 MHz, CDCl3): δ 1.46 (t, 3H, J = 7.0
Hz, OCH2CH3), 1.61 (t, 3H, J = 6.7 Hz, NCH2CH3), 4.46 (q, 2H,
J = 7.0 Hz, OCH2CH3), 5.27 (q, 2H, J = 6.7 Hz, NCH2CH3),
7.34-7.44 (m, 6H, 2 × Ph), 7.52 (dd, 2H, J = 8.0, 1.8 Hz, 2 × Ph),
7.61 (dd, 2H, J = 8.0, 1.8 Hz, 2 × Ph), 8.07 (d, 1H, J = 8.9 Hz, H-
5), 8.58 (s, 1H, H-9), 8.86 (d, 1H, J = 8.9 Hz, H-6); 13C NMR (75
MHz, CDCl3): δ 14.4 (OCH2CH3), 16.7 (NCH2CH3), 54.7
(NCH2CH3), 61.2 (OCH2CH3), 114.0, 126.1, 128.3, 128.4, 129.2,
129.5, 129.6, 129.9, 130.2, 133.6, 136.1, 138.0, 138.4, 143.4,
150.5, 151.1, 153.7, 165.6 (COOEt), 173.2 (CO). IR (KBr):
1726, 1687, 1636, 1612 cm-1. Anal. Calcd for C28H23N3O3
(449.50): C, 74.82; H, 5.16; N, 9.35. Found: C, 74.94; H, 5.20;
N, 9.41.
4.3. Synthesis of 9-ethylazoloquinoline-7-carboxylates 3b, 4b and
10-ethylpyridoquinoxaline-8-carboxylates 5d-f
4.3.1. Ethyl 9-ethyl-6-oxo-6H,9H-imidazo[4,5-
h]quinoline-7-carboxylate hemihydrate (3b)
A mixture of diamine 2b (200 mg, 0.72 mmol) and HCOOH
(3 mL) was heated at 80 °C for 30 min. in an oil bath. After
cooling to room temperature, HCOOH was evaporated under
reduced pressure. The residue was dissolved in EtOH (6 mL) and
the resulting solution was alkalised with conc. NH4OH. To a
suspension formed, silica gel (1.0 g) was added and the solvent
was evaporated under reduced pressure. The residue was loaded
on a silica gel column and eluted with a mixture of CHCl3/MeOH
= 20:1 (Rf = 0.10) to give compound 3b as a white solid. Yield
202 mg (94%); mp 282–290 °C; 1H NMR (300 MHz, DMSO-d6):
δ 1.29 (t, 3H, J = 7.0 Hz, OCH2CH3), 1.42 (t, 3H, J = 6.9 Hz,
NCH2CH3), 4.24 (q, 2H, J = 7.0 Hz, OCH2CH3), 5.16 (q, 2H, J =
6.9 Hz, NCH2CH3), 7.63 (d, 1H, J = 8.7 Hz, H-4), 8.16 (d, 1H, J
= 8.7 Hz, H-5), 8.45 (s, 1H, H-8), 8.62 (s, 1H, H-2), 13.17 (br s,
1H, NH); 13C NMR (75 MHz, DMSO-d6): δ 14.2 (OCH2CH3),
16.2 (NCH2CH3), 50.8 (NCH2CH3), 59.6 (OCH2CH3), 110.1,
110.9, 120.8, 123.5, 131.6, 131.9, 136.7, 141.5, 148.4, 164.7
(COOEt), 172.5 (CO). IR (KBr): 3420, 1724, 1623, 1568, 1493
cm-1. Anal. Calcd for C15H15N3O3ꢀ½H2O (294.31): C, 61.22; H,
5.48; N, 14.28. Found: C, 61.33; H, 5.44; N, 14.39.
4.3.4. Ethyl 10-ethyl-7-oxo-2,3-dimethyl-7H,10H-
pyrido[2,3-f]quinoxaline-8-carboxylate (5e)
To a stirred suspension of diamine 2b (150 mg, 0.54 mmol) in
EtOH (9 mL), biacetyl (0.10 mL, 99 mg, 1.15 mmol) was added
at room temperature. After 3 h of stirring, the volatiles were
evaporated under reduced pressure and the residue was subjected
to FLC (SiO2, CHCl3/MeOH = 50:1, Rf = 0.16) to yield
compound 5e as a pale yellow solid. Yield 154 mg (87%); mp
1
215–218 °C; H NMR (300 MHz, CDCl3): δ 1.42 (t, 3H, J = 7.1
Hz, OCH2CH3), 1.56 (t, 3H, J = 6.8 Hz, NCH2CH3), 2.75 (s, 6H,
2 × CH3), 4.42 (q, 2H, J = 7.1 Hz, OCH2CH3), 5.16 (q, 2H, J =
6.8 Hz, NCH2CH3), 7.86 (d, 1H, J = 8.9 Hz, H-5), 8.51 (s, 1H, H-
9), 8.72 (d, 1H, J = 8.9 Hz, H-6); 13C NMR (75 MHz, CDCl3): δ
14.4 (OCH2CH3), 16.4 (NCH2CH3), 22.7 (CH3), 22.9 (CH3), 54.8
(NCH2CH3), 61.0 (OCH2CH3), 113.3, 125.5, 127.0, 129.4, 133.4,
135.7, 143.4, 150.9, 151.0, 154.4, 165.5 (COOEt), 173.2 (CO).
IR (KBr): 1726, 1695, 1623, 1592 cm-1. Anal. Calcd for
C18H19N3O3 (325.36): C, 66.45; H, 5.89; N, 12.91. Found: C,
66.52; H, 5.84; N, 13.00.
4.3.2. Ethyl 9-ethyl-6-oxo-6H,9H-
[1,2,3] triazolo[4,5-h]quinoline-7-carboxylate (4b)
4.3.5. Ethyl 10-ethyl-7-oxo-7H,10H-pyrido[2,3-
f]quinoxaline-8-carboxylate (5f)
To a stirred solution of diamine 2b (230 mg, 0.83 mmol) in a
mixture of AcOH/H2O (1:2 (v/v), 30 mL), a solution of NaNO2
(59 mg, 0.85 mmol) in water (2 mL) was added dropwise at room
temperature. After 30 min. of stirring, the beige solid was
separated by suction, washed with water and dried. Purification
by FLC (SiO2, CHCl3/MeOH = 10:1, Rf = 0.22) gave compound
4b as a pale yellow solid. Yield 184 mg (77%); mp 274–280 °C
To a stirred suspension of diamine 2b (0.35 g, 1.27 mmol) and
diimine 6 (0.28 g, 1.27 mmol) in EtOH (15 mL), AcOH (0.5 mL)
was added at room temperature. After 4 h of stirring, the volatiles
were evaporated under reduced pressure and the residue was
taken up into the CHCl3 (50 mL). The organic phase was washed
with water (40 mL), dried with Na2SO4, filtered and evaporated
under reduced pressure. Purification by FLC (SiO2,
CHCl3/MeOH = 100:1, Rf = 0.16) gave compound 5f as a pale
yellow solid. Yield 0.34 g (91%); mp 192–193 °C; 1H NMR (300
MHz, CDCl3): δ 1.43 (t, 3H, J = 7.1 Hz, OCH2CH3), 1.55 (t, 3H,
J = 6.9 Hz, NCH2CH3), 4.43 (q, 2H, J = 7.1 Hz, OCH2CH3), 5.18
(q, 2H, J = 6.9 Hz, NCH2CH3), 8.00 (d, 1H, J = 9.0 Hz, H-5),
8.55 (s, 1H, H-9), 8.86 (d, 1H, J = 9.0 Hz, H-6), 8.92 (d, 1H, J =
1.7 Hz, H-3), 8.98 (d, 1H, J = 1.7 Hz, H-2); 13C NMR (75 MHz,
CDCl3): δ 14.4 (OCH2CH3), 16.4 (NCH2CH3), 54.9 (NCH2CH3),
1
(ref.23 178–180 °C); H NMR (300 MHz, DMSO-d6): δ 1.30 (t,
3H, J = 7,0 Hz, OCH2CH3), 1.46 (t, 3H, J = 6.9 Hz, NCH2CH3),
4.25 (q, 2H, J = 7.0 Hz, OCH2CH3), 5.13 (q, 2H, J = 6.9 Hz,
NCH2CH3), 7.77 (d, 1H, J = 8.8 Hz, H-4), 8.32 (d, 1H, J = 8.8
Hz, H-5), 8.73 (s, 1H, H-8); 13C NMR (75 MHz, DMSO): δ 14.2
(OCH2CH3), 15.6 (NCH2CH3), 51.3 (NCH2CH3), 59.9
(OCH2CH3), 108.8, 113.0, 124.2, 125.4, 131.8, 135.1, 137.2,
148.3, 164.4 (COOEt), 171.8 (CO). IR (KBr): 1720, 1694, 1623,

6
Tetrahedron
4.4.5. 10-Ethyl-7-oxo-7H,10H-pyrido[2,3-
61.1 (OCH2CH3), 114.0, 126.3, 128.5, 130.3, 136.0, 136.2,
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f]quinoxaline-8-carboxylic acid (7e)
141.8, 145.4, 145.5, 151.2, 165.4 (COOEt), 173.0 (CO). IR
(KBr): 1724, 1623, 1462, 1411 cm-1. Anal. Calcd for C16H15N3O3
(297.31): C, 64.64; H, 5.09; N, 12.13. Found: C, 64.76; H, 5.04;
N, 12.04.
1
White solid, 83 mg (92%); mp 291–294 °C; H NMR (300
MHz, TFA-d): δ 1.84 (br t, 3H, J = 6.7 Hz, NCH2CH3), 5.86 (br
q, 2H, J = 6.9 Hz, NCH2CH3), 8.68 (d, 1H, J = 9.3 Hz, H-5), 9.10
(d, 1H, J = 9.3 Hz, H-6), 9.43 (s, 1H, H-9), 9.64 (s, 2H, H-2, H-
3); 13C NMR (75 MHz, TFA-d): δ 15.1 (NCH2CH3), 60.7
(NCH2CH3), 108.7, 124.4, 127.5, 127.57, 137.5, 139.0, 142.0,
144.1, 146.2, 152.8, 168.7 (COOH), 172.1 (CO). IR (KBr): 1720,
1619, 1485, 1465 cm-1. Anal. Calcd for C14H11N3O3 (297.31): C,
62.45; H, 4.12; N, 15.61. Found: C, 62.39; H, 4.10; N, 15.67.
4.4. Genaral method for hydrolysis of ethyl esters 3b, 4b and 5d-f
to acids 7
A mixture of ethyl ester 3b, 4b or 5d-f (100 mg) and NaOH
(3–4 eq.) in EtOH (2.5–3 mL) was heated at 65 °C for 1–2.5 h.
After cooling down, the mixture was diluted with water (2–3
mL), cooled to 0 °C in an ice bath and acidified with 20% HCl.
The resulting white precipitate was collected by suction, washed
with water and dried to give acids 7.
Acknowledgments
The authors wish to express their gratitude to the Scientific
Grant Agency (VEGA project 1/0829/14) and to the Slovak
Research and Development Agency (contracts nos. APVV-0339-
10 and APVV-0038-11) for the financial support received.
4.4.1. 9-Ethyl-6-oxo-6H,9H-imidazo[4,5-
h]quinoline-7-carboxylic acid (7a)
1
White solid, 70 mg (80%); mp 335–343 °C; H NMR (300
Supplementary data
MHz, TFA-d): δ 1.91 (t, 3H, J = 6.9 Hz, NCH2CH3), 5.29 (q, 2H,
J = 6.9 Hz, NCH2CH3), 8.46 (d, 1H, J = 9.1 Hz, H-4), 8.96 (d,
1H, J = 9.1 Hz, H-5), 9.58 (s, 1H, H-8), 9.72 (s, 1H, H-2); 13C
NMR (75 MHz, TFA-d): δ 12.8 (NCH2CH3), 55.2 (NCH2CH3),
106.1, 117.1, 119.0, 120.5, 125.0, 131.0, 137.0, 142.4, 149.7,
168.6 (COOH), 172.6 (CO). IR (KBr): 3114, 1696, 1622, 1584
cm-1. Anal. Calcd for C13H11N3O3 (257.24): C, 60.71; H, 4.31; N,
16.33. Found: C, 60.61; H, 4.24; N, 16.29.
Supplementary data related to this article can be found at …
These data include copies of 1H and 13C NMR spectra of all the
compounds described in this article.
References and notes
1. Grivas, S. Curr. Org. Chem. 2000, 4, 707.
2. Cheeseman, G. W. H. J. Chem. Soc. 1962, 1170.
3. Sawicki, E.; Carr, A. J. Org. Chem. 1957, 22, 503.
4. Bird, C. W.; Cheeseman, G. W. H.; Sarsfield, A. A. J. Chem. Soc.
1963, 4767.
5. Saimuru, H.; Masuda, M.; Toruimi, C.; Santa, T.; Ichikawa, E.;
Takamura, N.; Imai, K. J. Mater. Chem. 2005, 15, 2865.
6. Bella, M.; Schultz, M.; Milata, V.; Koňariková, K.; Breza, M.
Tetrahedron 2010, 66, 8169.
7. Bella, M.; Schultz, M.; V. Milata, ARKIVOC 2012, (iv), 242.
8. Brizzi, C.; Dal Monte, D.; Sandri, E. Ann. Chim. (Rome) 1964, 54,
476.
9. Nyhammar, T.; Grivas, S. Acta Chem. Scand. 1986, B40, 583.
10. Grivas, S.; Tian, W. Acta Chem. Scand. 1992, 46, 1109.
11. Grivas, S.; Tian, W.; Ronne, E.; Lindström, S.; Olsson, K. Acta
Chem. Scand. 1993, 47, 521.
12. Elvidge, J. A.; Newbold, G. T.; Percival, A.; Sencial, I. R. J.
Chem. Soc. 1965, 5119.
13. Tian, W.; Grivas, S. J. Heterocycl. Chem. 1992, 29, 1305.
14. Wright, S. W.; McClure, L. D. J. Heterocycl. Chem. 2004, 41,
1023.
15. Tsubata, Y.; Suzuki, T.; Miyashi, T. J. Org. Chem. 1992, 57,
6749.
16. Bella, M.; Milata, V. Beilstein J. Org. Chem. 2013, 9, 2669.
17. Efros, L. S.; Todres-Selektor, Z. V. Zh. Obshch. Khim. 1957, 27,
983.
18. Edin, M.; Grivas, S. ARKIVOC 2000, (i), 1.
19. Okwakol, J.; Grivas, S. Heterocycles 2005, 65, 1939.
20. Bella, M.; Milata, V. ARKIVOC 2014, submitted
21. Reddy, G. V.; Kanth, S. R.; Maitraie, D.; Narsaiah, B.; Rao, P. S.;
Kishore, K. H.; Murthy, U. S. N.; Ravi, B.; Kumar, B. A.;
Parthasarathy, T. Eur. J. Med. Chem. 2009, 44, 1570.
22. Reddy, G. V.; Shekhar, A. C.; Kumar, A. R.; Sathaiah, G.;
Narsaiah, B.; Rao, P. S. J. Heterocycl. Chem. 2012, 49, 687.
23. Sanna, P.; Carta, A.; Paglietti, G.; Zanetti, S.; Fadda, G. Farmaco
1992, 47, 1001.
24. Carta, A.; Palomba, M.; Paglietti, G.; Molicotti, P.; Paglietti, B.;
Canna, S.; Zanetti, S. Bioorg. Med. Chem. Lett. 2007, 17, 4791.
25. Carta, A.; Palomba, M.; Briguglio, I.; Corona, P.; Piras, S.; Jabes,
D.; Guglierame, P.; Molicotti, P.; Zanetti, S. Eur. J. Med. Chem.
2011, 46, 320.
4.4.2. 9-Ethyl-6-oxo-6H,9H-[1,2,3]triazolo[4,5-
h]quinoline-7-carboxylic acid (7b)
White solid, 80 mg (88%); mp 315–320 °C (ref.23 287–291
1
°C); H NMR (300 MHz, TFA-d): δ 1.87 (t, 3H, J = 6.9 Hz,
NCH2CH3), 5.77 (q, 2H, J = 6.8 Hz, NCH2CH3), 8.37 (d, 1H, J =
8.9 Hz, H-4), 8.81 (d, 1H, J = 8.9 Hz, H-5), 9.56 (s, 1H, H-8); 13
C
NMR (75 MHz, TFA-d): δ 14.3 (NCH2CH3), 57.5 (NCH2CH3),
106.9, 115.6, 119.5, 125.0, 134.7, 135.4, 139.5, 149.4, 169.4
(COOH), 171.7 (CO). IR (KBr): 1691, 1632, 1473, 1444 cm-1.
Anal. Calcd for C12H10N4O3 (258.23): C, 55.81; H, 3.90; N,
21.70. Found: C 55.94; H, 3.84; N, 21.78.
4.4.3. 10-Ethyl-7-oxo-2,3-diphenyl-7H,10H-
pyrido[2,3-f]quinoxaline-8-carboxylic acid (7c)
1
White solid, 85 mg (90%); mp 317–320 °C; H NMR (300
MHz, TFA-d): δ 1.72 (br s, 3H, NCH2CH3), 5.75 (br q, 2H, J =
6.0 Hz, NCH2CH3), 7.40-7.60 (m, 10H, 2 × Ph), 8.65 (d, 1H, J =
9.0 Hz, H-5), 9.07 (d, 1H, J = 9.0 Hz, H-6), 9.58 (s, 1H, H-9); 13
C
NMR (75 MHz, TFA-d): δ 15.1 (NCH2CH3), 60.1 (NCH2CH3),
109.1, 122.5, 124.6, 128.6, 129.1, 129.4, 129.6, 129.7, 130.2,
132.1, 134.0, 134.8, 134.9, 136.2, 138.1, 151.9, 153.4, 158.4,
168.4 (COOH), 172.4 (CO). IR (KBr): 1724, 1620, 1473, 1458
cm-1. Anal. Calcd for C26H19N3O3 (421.45): C, 74.10; H, 4.54; N,
9.97. Found: C, 74.15; H, 4.60; N, 10.08.
4.4.4. 10-Ethyl-7-oxo-2,3-dimethyl-7H,10H-
pyrido[2,3-f]quinoxaline-8-carboxylic acid (7d)
1
White solid, 83 mg (91%); mp 312–315 °C; H NMR (300
MHz, TFA-d): δ 1.71 (br s, 3H, NCH2CH3), 3.03 (s, 3H, CH3),
3.09 (s, 3H, CH3), 5.64 (br q, 2H, J = 5.7 Hz, NCH2CH3), 8.45 (d,
1H, J = 8.9 Hz, H-5), 8.98 (d, 1H, J = 8.9 Hz, H-6), 9.51 (s, 1H,
H-9); 13C NMR (75 MHz, TFA-d): δ 14.8 (NCH2CH3), 21.5 (2 ×
CH3), 60.4 (NCH2CH3), 109.1, 121.8, 124.5, 139.3, 134.1, 135.6,
137.8, 153.6, 154.8, 159.5, 168.4 (COOH), 172.4 (CO). IR
(KBr): 1733, 1621, 1443, 1375 cm-1. Anal. Calcd for C16H15N3O3
(297.31): C, 64.64; H, 5.09; N, 12.13. Found: C, 64.56; H, 5.12;
N, 12.18.
26. Boteva, A.; Krasnykh, O. Chem. Heterocycl. Compd. 2009, 45,
757.
27. Berg, S. S.; Parnell, E. W. J. Chem. Soc. 1961, 5275.
28. Kada, R.; Jurášek, A.; Kováč, J.; Králik, P. Chem. Pap. 1974, 28,
391.

7
29. Carson, J. F. J. Am. Chem. Soc. 1953, 75, 4337.
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Supplementary data
Application of 9-ethyl[1,2,5]selenadiazolo[3,4-h]quinolones in the
synthesis of tricyclic azoloquinolones
Maroš Bellaa,b, and Viktor Milatab
a Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-845 38 Bratislava, Slovakia
b Department of Organic Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinského 9, SK-812 37
Bratislava, Slovakia
Copies of 1H and 13C NMR spectra of 7,8-diamino-1-ethylquinolones 2 and
azoloquinolones 3-5 and 7
Corresponding author. Tel.: +421 2 59410231; fax: +421 2 59410222; e-mail: maros.bella@savba.sk

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