A novel analogue of Asinger reaction for the synthesis of thiazinoquinoline derivatives

Article abstract of DOI:10.1007/s00706-016-1755-1

Abstract: The unexpected synthesis of 2H-[1,3]thiazino[6,5-b]quinoline derivatives from domino cyclic condensation of 2-mercaptoquinoline-3-carbaldehyde and ammonium acetate at ambient temperature in EtOH was described. Graphical abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s00706-016-1755-1

Monatsh Chem
DOI 10.1007/s00706-016-1755-1
ORIGINAL PAPER
A novel analogue of Asinger reaction for the synthesis
of thiazinoquinoline derivatives
Zeinab Faghihi1 Hossein Abdi Oskooie1 Majid M. Heravi1
•
•
•
Mahmoud Tajbakhsh2 Morteza Shiri1
•
Received: 20 December 2015 / Accepted: 7 April 2016
Ó Springer-Verlag Wien 2016
Abstract The unexpected synthesis of 2H-[1,3]thi-
azino[6,5-b]quinoline derivatives from domino cyclic
condensation of 2-mercaptoquinoline-3-carbaldehyde and
ammonium acetate at ambient temperature in EtOH was
described.
Introduction
Natural and synthetic quinoline derivatives display inter-
esting biological activities [1–7]. For example, those
containing sulfur atom exhibit remarkable properties such
as antimicrobial activities and cytotoxicity [8, 9], radio-
protection, and antineoplastic activities [10]. At
physiological pH, the predominant protonated species,
HNO, can be detected by observing reaction products with
mercapto derivatives as they are well situated to produce
fluorescent sensors for important molecules. It indirectly
detects the NO concentrations whose over-production in
human is linked to cancer, chronic inflammatory diseases,
and neurodegenerative diseases [11].
Graphical abstract
The synthesis and biological evaluation of 1,3-thiazine
derivatives have been widely investigated thus far [12].
Asinger reported an interesting reaction for the synthesis of
3-thiazolines involving a-haloaldehydes or a-ketones,
ammonia, NaSH, and aldehydes or ketones [13, 14]. Ugi
et al., in a similar strategy, used 3-hydroxy-2,2-dimethyl-
propionaldehyde or 1,3-dihydroxyacetone along with
ammonia and aldehyde to generate 1,3-oxazines [15] as
well as 1,3-oxazoles, respectively [16]. Oxa- and thiazo-
lidine-containing polymers have lately been synthesized
via the Asinger four-component reaction [17]. Recently,
Martens group incorporated b-chlorovinyl aldehydes
instead of a-haloaldehydes in Asinger reaction to get target
molecules of 3,4-dihydro-2H-1,3-thiazines in good yields
[18, 19].
Keywords Cyclization Á Condensation Á
2-Mercaptoquinoline-3-carbaldehydes Á
Thiazinoquinoline Á Catalyst-free Á Asinger reaction
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-016-1755-1) contains supplementary
material, which is available to authorized users.
& Morteza Shiri
mshiri@alzahra.ac.ir
Although Asinger protocol is created to contribute to
mercapto or thiocarbonyl groups reacting with carbonyl
compounds to construct thiazoline scaffold, other advan-
tages of Asinger reaction still invite consideration.
Formation of four bonds in thiazoline produced simulta-
neously from simple reactants is an important advantage.
1
Department of Chemistry, Faculty of Physics and Chemistry,
Alzahra University, Vanak, Tehran 1993893973, Iran
2
Department of Chemistry, University of Mazandaran,
Babolsar, Iran
123

Z. Faghihi et al.
Very recently, this name reaction has been reviewed by Liu
as one of the neglected important reactions for the prepa-
ration of thiazolines [20].
thione 5a to dithiocine 6a (Scheme 2) by applying different
conditions such as basic catalysts of L-proline, DABCO, or
Et3N in ethanol and K2CO3 in DMF as well as acidic
catalysts such as AcOH as solvent or in ethanol have been
without any results. It indicated that 5a is stable and would
not convert to 6 under above-mentioned conditions. To the
best of our knowledge, synthesis of this type of thiazino-
quinoline has not been reported thus far in literature.
Subsequently, the generality of reaction with substituted
2-mercaptoquinoline-3-carbaldehydes was examined.
Table 1 summarizes results of examination. The electron
donor groups such as methyl and methoxy produced the
corresponding products 5b–5d in high yield; however, with
electron-withdrawing groups such as Cl and Br the reaction
fails to proceed (Table 1). Negative results would arise
because of reduced nucleophilic property of sulfur atom in
cyclization step.
As shown in Scheme 1, the synthesis of dithiocins 3
which is a product of the reaction of 2-mercaptoarylalde-
hydes 1 and ammonium acetate via 1,3-thiazine formation
of 2 was reported (Scheme 1) [21, 22]. Structure 3 belongs
to an interesting class of conformationally rigid molecules
which are well-defined molecules with V-shaped molecular
clefts.
To explore this remarkable and neglected reaction by
replacing more complex mercapto compounds, and con-
tinue our line of research toward the chemistry of quinoline
derivatives [23–29], we found enough motivation to
examine the condensation of 2-mercaptoquinoline-3-carb-
aldehydes and amines.
Drawing upon the reports on salicylaldehyde reaction
with various imines to form 1,5-dibenzodioxocins [21, 22],
we worked out the replacement of 2-hydroxyquinoline-3-
carbaldehyde with salicylaldehyde so that it reacts with
ammonium acetate. Replacing oxygen by a sulfur atom
afforded no product in reflux of ethanol even after 24 h. It
is accounted for by the fact that keto conformer of quino-
line aldehyde is far dominant conformer.
Results and discussion
In the initial setup after step-by-step synthesizing of
2-mercaptoquinoline-3-carbaldehydes [30], Scheme 2
shows the model reaction. The reaction started using
aldehyde 4a, with no substituent, and ammonium acetate in
EtOH at room temperature. It was completed in 24 h of
stirring without any catalyst and unexpected compound 5a
was isolated in 95 % yield (Scheme 2).
As long as an SH group of the quinoline aldehyde failed
to participate in the second step (Scheme 2), it seemed that
replacing any other aldehyde could lead to a similar
derivative product. Thus, replacing one mole ratio of
mercaptoquinolinecarbaldehyde by another aldehyde
would be interesting. To do this, the three-component
reactions of 2-mercaptoquinoline-3-carbaldehyde, ammo-
nium acetate, and aldehyde such as 4-methylbenzaldehyde,
4-methoxybenzaldehyde, 4-(dimethylamino)benzaldehyde
and 2-nitrobenzaldehyde were performed under different
conditions (Scheme 4). No satisfactory product resulted in
the cases of electron-donating groups under applied con-
To examine the effect of heating on reaction rate, the
temperature was raised to reflux condition. The findings
indicated that the time required for completion of reaction
was decreased to 3 h at this condition. Apart from the main
product 5a in 63 %, the by-product 7 was produced in
30 % yield (Scheme 3). It is assumed that the new and
considerable disulfide 7 was a result of the self-coupling of
2-mercaptoquinoline-3-carbaldehydes.
The effect of ammonium source demonstrated that
NH4OAc has slightly yielded better results than NH4Cl,
(NH4)2CO3, and (NH4)2SO4. Other sources of amines such
as 4-methylaniline and butylamine did not yield satisfac-
tory results, and the reaction was stopped in imine
formation step. Further attempts in the cyclization of
3-(2H-[1,3]thiazino[6,5-b]quinolin-2-yl)quinoline-2(1H)-
ditions
whatsoever.
Surprisingly,
when
2-nitrobenzaldehyde was used, compound 8 as well as
disulfide 7 isolated everyone in 30 % yield. Most probably,
2-(4-nitrophenyl)-4H-[1,3]thiazino[6,5-b]quinolone
was a result of the [1,3]-hydride shift of 80 (Scheme 4).
(8)
Scheme 1
123

A novel analogue of Asinger reaction for the synthesis of thiazinoquinoline derivatives
Scheme 2
Scheme 3
Table 1 Condensation of 2-mercaptoquinoline-3-carbaldehyde and
ammonium acetate
Conclusion
We reported a novel Asinger-type reaction involving cyclic
condensation of 2-mercaptoquinoline-3-carbaldehydes and
ammonium acetate. During the reaction, a type of thiazino-
quinoline derivatives was prepared in ethanol without
using any additive. The yield of products was high and
purified simply without using column chromatography.
This new scaffold bears quinoline and thiazine rings as
well as sulfur atom which make them highly interesting
cases for biological examination.
Entry
R1
R2
Product
Yield/%
1
2
3
4
5
6
H
H
5a
95
90
93
89
–
Me
MeO
H
H
5b
5c
H
MeO
H
5d
NR
NR
Cl
Br
H
–
Aldehyde (1 mmol), NH4OAc (1.2 mmol), EtOH (10 cm3), room
temperature
Experimental
The proposed mechanism consists of formation of
unstable imine A first. As ammonium acetate produces an
acidic environment by releasing AcOH, it activates formyl
group to react with SH to form B. Intramolecular attack of
Chemicals were purchased from Fluka, Merck, and Aldrich
chemical companies. IR spectra were recorded on a Shi-
madzu Infrared Spectroscopy IR-435. Nuclear magnetic
resonance (NMR) spectra were recorded on a Bruker
Avance 400 MHz Spectrometers on DMSO-d6 and CDCl3
as solvents. A Leco CHNS model 932 was used for
NH in
B via dehydrative cyclization produced 5
(Scheme 5). Further activation of thio-atom in 5 toward
imine would possibly give 6 which, however, did not
happen under above-mentioned conditions.
123

Z. Faghihi et al.
Scheme 4
Scheme 5
1586, 1489, 1154 cm-1; H NMR (400 MHz, DMSO-d6):
elemental analysis. Mass spectra were recorded on Agilent
Technology (HP) 5973 Network Mass Selective Detector
operating at an ionization potential of 70 eV.
4
d = 7.27 (1H, d, JHH = 2.0 Hz, CH2), 7.37 (1H, td,
3JHH = 8.0 Hz, 4JHH = 1.6 Hz, CH of Ar), 7.60 (1H, ddd,
3
4
3JHH = 8.0 Hz, JHH = 5.6 Hz, JHH = 2.4 Hz, CH of
Synthesis of thiazinoquinoline derivatives 5a–5d
3
Ar), 7.67 (1H, t, JHH = 8.0 Hz, CH of Ar), 7.68 (1H, d,
3JHH = 6.8 Hz, CH of Ar), 7.81 (1H, d, JHH = 6.0 Hz,
2-Mercaptoquinoline-3-carbaldehydes (1 mmol) and NH4-
OAc (1.2 mmol) in ethanol were stirred for 24 h at room
temperature. The reaction was filtered and washed with
excess ethanol and water to get pure product. The yellow
powders were afforded in 89–95 % yields.
3
3
CH of Ar), 7.82 (1H, t, JHH = 7.0 Hz, CH of Ar), 7.86
(1H, d, 3JHH = 8.0 Hz, CH of Ar), 8.00 (1H, s, CH of Ar),
8.05 (1H, d, 3JHH = 8.4 Hz, CH of Ar), 8.57 (1H, s, CH of
Ar), 8.84 (1H, d, J = 2.4 Hz, CH of Ar), 14 (1H, s, NH)
ppm; 13C NMR (100 MHz, DMSO-d6): d = 63.05 (CH2),
116.34 (C-5a), 116.42 (CH of Ar), 119.31 (C-4a), 122.61
(C-40), 125.02 (C-30), 126.63 (CH of Ar), 127.11 (CH of
Ar), 127.88 (CH of Ar), 128.86 (CH of Ar), 129.93 (CH of
3-(2H-[1,3]Thiazino[6,5-b]quinolin-2-yl)quinoline-2(1H)-
thione (5a, C20H13N3S2)
Yellow powder; yield 171 mg (95 %); m.p.: 270–272 °C;
FT-IR (KBr): v = 3250, 3121, 3000, 2928, 1685, 1621,
123

A novel analogue of Asinger reaction for the synthesis of thiazinoquinoline derivatives
Ar, C-80a), 132.30 (CH of Ar), 132.86 (C-9a), 134.29 (CH
of Ar), 139.04 (CH of Ar), 139.10 (CH of Ar), 149.32 (CH
of Ar), 156.94 (C-10a), 160.74 (CH of Ar), 179.09 (C=S)
ppm; MS (EI, 70 eV): m/z (%) = 359 (M?, 15), 325 (19),
282 (37), 204 (32), 172 (42), 153 (100), 128 (82), 101 (51),
43 (88).
7-Methoxy-3-(8-methoxy-2H-[1,3]thiazino[6,5-b]quinolin-
2-yl)quinoline-2(1H)-thione (5d, C22H17N3O2S2)
Yellow powder; yield 186 mg (93 %); m.p.: 253–258 °C;
FT-IR (KBr): v = 3252, 3105, 2920, 1650, 1500,
1230 cm-1; H NMR (400 MHz, DMSO-d6): d = 3.86
(3H, s, CH3), 3.90 (3H, s, CH3), 7.01 (1H, dd,
4
3JHH = 8.8 Hz, JHH = 2, CH of Ar), 7.19 (1H, s, CH of
6-Methyl-3-(7-methyl-2H-[1,3]thiazino[6,5-b]quinolin-2-
yl)quinoline-2(1H)-thione (5b, C22H17N3S2)
Ar), 7.23 (3H, m, CHs of Ar), 7.79 (1H, d, 3JHH = 8.8 Hz,
3
CH of Ar), 7.93 (1H, d, JHH = 12 Hz, CH of Ar), 7.95
Yellow powder; yield 173 mg (90 %); m.p.: 265–267 °C;
FT-IR (KBr): v = 3250, 3120, 2920, 1649, 1622, 1588,
1486, 1162, 1074 cm-1; H NMR (400 MHz, DMSO-d6):
d = 2.33 (3H, s, CH3), 2.48 (3H, s, CH3), 7.24 (1H, d,
(1H, s, CH of Ar), 8.43 (1H, s, CH of Ar), 8.71 (1H, s, CH
of Ar), 13.83 (1H, s, NH) ppm; 13C NMR (100 MHz,
DMSO-d6): d = 56.10 (CH3), 56.21 (CH3), 63.08 (CH2),
107.00 (CH of Ar), 115.06 (CH of Ar), 117.31 (CH of Ar),
117.63 (C-4a’), 119.41 (C-5a), 121.49 (CH of Ar), 130.36
(C-4a), 131.11 (CH of Ar), 134.47 (CH of Ar), 136.48 (C-
30), 138.52 (CH of Ar), 141.00 (C-80a), 151.32 (C-8),
157.58 (C-9a), 160.53 (C-70), 162.50 (CH of Ar), 163.04
(CH of Ar), 165.00 (C-10a), 178.00 (C=S) ppm; MS (EI,
70 eV): m/z (%) = 419 (M?, 20), 387 (60), 261 (35), 203
(10), 173 (30), 127 (20), 75 (10), 43 (20).
3
4JHH = 2.4 Hz, CH2), 7.50 (1H, dd, JHH = 8.0 Hz,
3
4JHH = 2.0 Hz, CH of Ar), 7.60 (1H, d, JHH = 8.8 Hz,
CH of Ar), 7.64 (1H, s, CH of Ar), 7.66 (1H, d,
3
3JHH = 1.6 Hz, CH of Ar), 7.73 (1H, d, JHH = 8.4 Hz,
CH of Ar), 7.81 (1H, s, CH of Ar), 7.90 (1H, s, CH of Ar),
8.48 (1H, s, CH of Ar), 8.82 (1H, d, 3JHH = 2.4 Hz, CH of
Ar), 14.0 (1H, s, NH) ppm; 13C NMR (100 MHz, DMSO-
d6): d = 21.09 (CH3), 21.42 (CH3), 62.95 (CH2), 116.25
(C-5a), 119.47, 122.62 (C-4a), 126.63 (CH of Ar), 127.68
(CH of Ar), 127.99 (CH of Ar), 128.53 (CH of Ar), 133.79
(CH of Ar), 133.84 (C-60), 134.46 (C-40a), 134.90 (C-80a),
136.72 (C-7), 137.20 (C-30), 138.44 (CH of Ar), 138.77
(CH of Ar), 147.94 (C-9a), 155.69 (C-10a), 160.89 (CH of
Ar), 178.08 (C=S) ppm; MS (EI, 70 eV): m/z (%) = 387
(M?, 64), 353 (100), 322 (8), 260 (13), 218 (13), 188 (40),
143 (25), 115 (21), 77 (12), 45 (15).
Synthesis of 2-(2-nitrophenyl)-4H-[1,3]thiazino[6,5-b]qui-
nolones 7 and 8
L-Proline (1 mmol) was added to the solution of 2-mer-
captoquinoline-3-carbaldehydes
(1 mmol),
NH4OAc
(2 mmol), and 2-nitrobenzaldehyde (1 mmol). The reaction
mixture was stirred for 6 h at refluxed conditions. The
solvent was evaporated, and the remaining solid was
washed with water. The residue was purified by column
chromatography (petroleum ether/ethyl acetate 8:2 as
eluent).
6-Methoxy-3-(7-methoxy-2H-[1,3]thiazino[6,5-b]quinolin-
2-yl)quinoline-2(1H)-thione (5c, C22H17N3O2S2)
Yellow powder; yield 195 mg (93 %); m.p.: 258–263 °C;
FT-IR (KBr): v = 3245, 2918, 3100, 2900, 2800, 1641,
1586, 1490, 1224 cm-1; H NMR (400 MHz, DMSO-d6):
d = 3.90 (3H, s, CH3), 3.95 (3H, s, CH3), 7.24 (1H, d,
2-[2-(3-Formylquinolin-2-yl)disulfanyl]quinoline-
3-carbaldehyde (7, C20H12N2O2S2)
Pale yellow crystals; yield 112 mg (30 %); m.p.:
158–160 °C; FT-IR (KBr): v = 3200, 3087, 2926, 1624,
1505, 1428, 1266, 1151 cm-1; H NMR (400 MHz,
3
4JHH = 2.4 Hz, CH2), 7.33 (1H, dd, JHH = 8.8 Hz,
3
3JHH = 2.6 Hz, CH of Ar), 7.39 (1H, d, JHH = 2.6 Hz,
CDCl3):
d = 7.61
(2H,
ddd,
3JHH = 8.0 Hz,
4
CH of Ar), 7.44 (1H, s, CH of Ar), 7.46 (1H, m, CH of Ar),
3
7.64 (1H, d, JHH = 9.2 Hz, CH of Ar), 7.75 (1H, d,
3JHH = 6.8 Hz, JHH = 1.2 Hz, CH of Ar), 7.93 (2H,
3
3
ddd, JHH = 8.4 Hz, JHH = 6.4 Hz, JHH = 1.2 Hz, CH
4
3JHH = 9.3 Hz, CH of Ar), 7.94 (1H, s, CH of Ar), 8.45
of Ar), 8.10 (2H, ddd, JHH = 8.4 Hz, JHH = 1.6 Hz,
4JHH = 0.8 Hz, CH of Ar), 8.24 (2H, ddd, 3JHH = 8.8 Hz,
3JHH = 1.6 Hz, JHH = 0.8 Hz, CH of Ar), 8.93 (2H, s,
3
3
4
(1H, s, CH of Ar), 8.82 (1H, d, JHH = 2.4 Hz CH of Ar),
14.0 (1H, s, NH) ppm; 13C NMR (100 MHz, DMSO-d6):
d = 56.02 (CH3), 56.17 (CH3), 62.94 (CH2), 107.74 (CH
of Ar), 108.72 (CH of Ar), 119.61 (CH of Ar), 122.71 (CH
of Ar), 123.68 (C-5a), 124.84 (CH of Ar), 126.7 (C-4a),
127.73 (C-80a), 129.41 (CH of Ar), 133.79 (C-40a), 136.94
(C-30), 137.91 (CH of Ar), 139.14 (CH of Ar), 145.45 (C-
9a), 153.61 (C-7), 156.39 (C-10a), 157.70 (C-60), 160.89
(CH of Ar), 179.17 (C=S) ppm; MS (EI, 70 eV): m/z
(%) = 419 (M?, 36), 388 (67), 345 (16), 260 (52), 234
(25), 203 (100), 173 (46), 129 (38), 102 (29), 76 (14), 43
(33).
4
CH of Ar), 9.15 (2H, s, CHO) ppm; 13C NMR (100 MHz,
CDCl3): d = 125.00 (C-4a), 126.29 (CH of Ar), 127.10 (C-
3), 128.78 (CH of Ar), 129.32 (CH of Ar), 132.15 (CH of
Ar), 133.01 (CH of Ar), 148.68 (C-8a), 154.45 (C-2),
170.29 (C=O) ppm; MS (EI, 70 eV): m/z (%) = 376 (M?,
20), 37 (4), 37 (10), 37 (76), 36 (31).
2-(2-Nitrophenyl)-4H-[1,3]thiazino[6,5-b]quinolone
(8, C17H11N3O2S)
Yellow crystals; yield 96 mg (30 %); m.p.: 160–162 °C;
FT-IR (KBr): v = 2955, 2923, 2852, 1524, 1351,
123

Z. Faghihi et al.
699 cm-1; NMR (400 MHz, CDCl3): d = 5.07 (2H, d,
7. Solomon VR, Haq W, Srivastava K, Puri SK, Katti SB (2007) J
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3
2JHH = 0.8 Hz, CH2), 7.58 (1H, ddd, JHH = 8.0 Hz,
4
3JHH = 7.2 Hz, JHH = 1.6 Hz, CH of Ar), 7.62-7.66
3
(1H, m, CH of Ar), 7.71 (1H, td, JHH = 7.6 Hz,
4JHH = 1.6 Hz, CH of Ar), 7.74–7.78 (2H, m, CH of
3
3
Ar), 7.87 (1H, dd, JHH = 8.0 Hz, JHH = 0.8 Hz, CH of
´
10. O’Connor NA, Lopez GE, Cruz A (2014) Curr Chem Lett 3:189
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3
3
Ar), 8.03 (1H, dd, JHH = 8.0 Hz, JHH = 1.2 Hz, CH of
Ar), 8.06–8.08 (2H, m, CH of Ar) ppm; 13C NMR
(100 MHz, CDCl3): d = 56.17 (CH42), 122.96 (CH of
benzene), 124.71 (C-4a), 126.78 (C-5a), 127.71 (CH of
quinoline), 127.83 (CH of quinoline), 128.40 (CH of
quinoline), 130.23 (CH of quinoline), 130.52 (CH of
benzene), 130.91 (CH of benzene), 133.01 (CH of
benzene), 133.11 (C-10 of benzene), 133.69 (CH of
quinoline), 147.61 (C-9a), 153.84 (C-20 of benzene),
158.90 (C-2), 174.71 (C-10a) ppm; MS (EI, 70 eV): m/z
(%) = 321 (M?, 19), 17(10), 14(1), 12(2), 84(11), 57(17).
¨
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Acknowledgments We thank Alzahra University and Iran National
Science Foundation (INSF) for financial support of our research
group.
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