One-pot synthesis of thiazolo[3,4-a]quinoxalines and the related heterocyclic systems using 4-hydroxy-4-alkoxycarbonyl-3,5-diaryl-2- aryliminothia(selena)zolidines as versatile reagents

Article abstract of DOI:10.1016/j.tet.2012.06.084

An efficient and versatile one-step method for the synthesis of thiazolo[3,4-a]quinoxalines and related new heterocyclic systems have been developed on the basis of a new strategy for the construction of the pyrazine ring system. The key step of the process involves the cascade annulation of the iminothiazolopyrazine system to benzene in the reaction of 4-hydroxy-3,5-diaryl- 2-phenyliminothiazolidines with 1,2-diaminobenzenes. The use of selenium analogues instead of thiazolidine derivatives in this reaction, leads to selenazolo[3,4-a]quinoxalines and the use of aza analogues instead of 1,2-diaminobenzenes gives aza analogues of thiazolo[3,4-a]quinoxalines.

Full text of DOI:10.1016/j.tet.2012.06.084

Tetrahedron 68 (2012) 7363e7373
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
One-pot synthesis of thiazolo[3,4-a]quinoxalines and the related heterocyclic
systems using 4-hydroxy-4-alkoxycarbonyl-3,5-diaryl-2-aryliminothia(selena)
zolidines as versatile reagents
*
Vakhid A. Mamedov , Nataliya A. Zhukova, Alsu A. Balandina, Sergey V. Kharlamov,
Tat’yana N. Beschastnova, Il’dar Kh. Rizvanov, Shamil K. Latypov
A.E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Research Center of the Russian Academy of Sciences, Arbuzov str. 8, 420088 Kazan, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 April 2012
Received in revised form 31 May 2012
Accepted 20 June 2012
Available online 29 June 2012
An efficient and versatile one-step method for the synthesis of thiazolo[3,4-a]quinoxalines and related
new heterocyclic systems have been developed on the basis of a new strategy for the construction of the
pyrazine ring system. The key step of the process involves the cascade annulation of the iminothiazo-
lopyrazine system to benzene in the reaction of 4-hydroxy-3,5-diaryl-2-phenyliminothiazolidines with
1,2-diaminobenzenes. The use of selenium analogues instead of thiazolidine derivatives in this reaction,
leads to selenazolo[3,4-a]quinoxalines and the use of aza analogues instead of 1,2-diaminobenzenes
gives aza analogues of thiazolo[3,4-a]quinoxalines.
Keywords:
Methyl phenylchloropyruvate
N,N0-Diphenylthiourea
N,N0-Diphenylselenourea
4-Hydroxythiazolidines
4-Hydroxyselenazolidines
Diastereomers
Ó 2012 Elsevier Ltd. All rights reserved.
Open chain tautomers
One-pot synthesis
Ring formation
Thiazolo[3,4-a]quinoxalines
Selenazolo[3,4-a]quinoxalines
Aza analogues of thiazolo[3,4-a]
quinoxalines
NMR data
1. Introduction
[3,4-a]quinoxalines.3bee The second approach to the design of the
thiazolo[3,4-a]quinoxaline system employs thiazole derivatives as
Azolo[a]quinoxalines and their 4,5-dihydro derivatives have
attracted considerable interest in recent years because they display
valuable pharmacological activities1aei and are also used in the
synthesis of many biologically important compounds and
drugs.2aee However, in contrast to the well studied synthesis and
properties of the imidazo[1,5-a]quinoxaline system, methods for
the synthesis of thiazolo[3,4-a]quinoxalines first obtained3a remain
poorly investigated. A variety of methodologies have emerged for
the synthesis of this type compounds and are based on three dif-
ferent approaches.2d,3aef The first approach involves the intra-
starting materials, involving intramolecular reductive cyclization of
4-carboxy- or 4-methoxycarbonyl-3-(2-nitrophenyl)thiazolines3a
and amine initiated intermolecular cyclization of 4-chloromethyl-
3-(2,3,4-trifluorophenyl)thiazolidine-2-thione.2d,3f These methods
are not widely used because these the quinoxaline and thiazolidine
derivatives are difficult to synthesize.
In this paper unlike the first two approaches, according to which
a thiazole molecule is annulated with the already existing qui-
noxaline system or vice versa, a novel approach, discovered by us, is
proposed. This approach involves cascade annulation of the imi-
nothiazolopyrazine system to benzene in reactions of 4-hydroxy-4-
methoxycarbonyl-3,5-diphenyl-2-phenyliminothiazolidine4a,b 1a
with 1,2-diaminobenzene 2a in boiling acetic acid (Scheme 1). This
condensation affords, thiazolo[3,4-a]quinoxalines 3a in high yields
through the elimination of methanol, aniline and water (Scheme 1).
molecular acid-catalyzed cyclization of 3-(a-isothioureido-
thiocyanato- and xanthahenato)quinoxalin-2-ones into thiazolo
* Corresponding author. E-mail addresses: mamedov@iopc.knc.ru, mamedov@
iopc.ru (V.A. Mamedov).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.06.084

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V.A. Mamedov et al. / Tetrahedron 68 (2012) 7363e7373
Scheme 1. The interaction of 4-hydroxythiazolidine with the 1,2-diaminobenzene as
a new method of synthesizing thiazolo[3,4-a]quinoxaline explored in this work.
Scheme 3. Synthesis of 4-hydroxyselenazolidines by interaction of methyl phenyl-
chloropyruvate 4a and methyl phenylethylchloropyruvate 4b with N,N0-diphenylsele-
nourea 6.
Since this new reaction provides an attractive one-pot
route from readily available 4-hydroxy-4-methoxycarbonyl-3,5-
diphenyl-2-phenyliminothiazolidines to thiazolo[3,4-a]quinoxa-
lines, we have now explored the reagents and reaction
conditions in more detail and extended it to the 4-hydroxy-4-
methoxycarbonylphenyliminothiazolidines containing various
aryl and heteroaryl groups in isothioureido fragment and
1,2-diaminobenzenes 2, to include electron-withdrawing and
electron-releasing functional groups and 2,3- and 3,4-
diaminopyridines.
Scheme 4. Synthesis of 4-hydroxythiazolidine by interaction of ethyl bromopyruvate
4c with N,N0-diphenylthiourea 5a.
2. Results and discussion
5-diaryl-2-phenyliminothiazolidines were due to the structural
features of the latter, in this work we consider it appropriate to
examine their behaviour in solution by NMR and GIAO DFT
calculations.
When synthesizing thiazolo[3,4-a]quinoxalines with various sub-
stituents and related tri-cyclic systems, we examined the reactions of
4-hydroxy-4-methoxycarbonylaryliminothiazolidines 1aed, 10bed
and 4-hydroxy-4-methoxycarbonylaryliminoselenazolidines 7a,b
obtained from methyl phenylchloropyruvate 4a or phenyl-
ethylchloropyruvate 4b with various types of N,N0-diphenyl-5a, N-
pyridin-2-yl-3-phenyl-5b, N-(3-methylpyridin-2-yl)-N0-phenyl-5c,
N-thiazol-2-yl-N0-phenyl-5d thioureas (Scheme 2) and N,N0-diphe-
nylselenourea 6 (Scheme 3). A 4-hydroxy-4-ethoxycarbonylary-
liminothiazolidine 1e was obtained by the interaction of ethyl bro-
mopyruvate 4c with N,N0-diphenylthiourea 5a (Scheme 4).
Unlike 4-hydroxythiazolidine 1a and 4-hydroxyselenazolidine
7a, obtained from symmetrical N,N0-diphenylthiourea 5a and
N,N0-diphenylselenourea 6, 4-hydroxythiazolidines obtained
from N-pyridin-2-yl-N0-phenyl-5b, N-(3-methylpyridin-2-yl)-N0-
phenyl-5c, N-thiazol-2-yl-N0-phenyl-5d thioureas can actually be
formed in two regioisomeric forms 1bed and 10bed (Scheme 2).
According to the 1H NMR and IR spectroscopic data, the component
ratio of these mixtures substantially depends on the nature of the
aromatic substituents and the heteroatom in the ring, medium
(solvent and temperature) and time.
1H NMR spectra of 1aed/7aeb in DMSO-d6 correspond to
a mixture of components the populations of which evolve in time
and reach the steady state after ca. 24 h (Fig. 1a,b, Table 1). While in
the case of 1a and 7a,b only two components in equilibrium are
observed for compounds 1bed and 10bed the picture is essentially
complicated due to additional forms presented in solution.
In principle, these 1H NMR spectra and their evolution in time
can be ascribed to the existence of the 4-hydroxythiazolidine 1a
and 4-hydroxyselenazolidine 7a,b in solution as a mixture of the
a
and b diastereomers (due to C4/C5 chirality), which can convert
into each other through open chain forms (OF) 8a, 9a,b (Scheme 5).
Moreover, there may be additional isomers/conformers due to the
different orientation around the C]N and CeC(O) bonds. Thus, the
observed spectra can be ascribed to all these structures in slow
exchange in the NMR timescale.
2.1. The synthesis of thiazolo[3,4-a]quinoxalines
It should be noted that before the discovery of the
reaction for synthesizing thiazolo[3,4-a]quinoxalines the
synthetic possibilities of the 4-hydroxythiazolidine derivatives
considered here were mainly limited to the dehydration
into corresponding thiazolines,5aeg although the first repre-
sentatives of 4-hydroxythiazolidines were obtained over
Table 2 showsthatavarietyof4-hydroxy-4-methoxycarbonyl-3,5-
diphenyl-2-aryliminothiazolidines 1aed with 1,2-diaminobenzenes
2aee is compatible with these reaction conditions producing di-
verse, variously substituted thiazolo[3,4-a]quinoxalines in high
yields.
a
hundred years ago.5a Since many of the reactions of
1,2-diaminobenzenes 2, with 4-hydroxy-4-methoxycarbonyl-3,
The reactions of ‘symmetrical’6 4-hydroxythiazolidine 1a with
symmetrically substituted 1,2-diaminobenzene 2d proceed
Scheme 2. Synthesis of isomeric 4-hydroxythiazolidines by interaction of methyl phenylchloropyruvate 4a with various types of N-hetaryl-N0-phenylthioureas 5aed.

V.A. Mamedov et al. / Tetrahedron 68 (2012) 7363e7373
7365
Fig. 1. 1H NMR spectra in DMSO-d6 after period of time t: (a) 1a, t¼0, (b) 1a, t¼24 h, (c) 1a (t¼24 h)þD2O (0.5 mM), t¼24 h, (d) 1b, t¼0, (e) 1b, t¼24 h, (f) 1b (t¼24 h)þD2O (0.5 mM),
t¼24 h.
O
R
NHPh
NPh
Table 1
The time dependence of the ratio of isomers (Irel)
a of 4-hydroxythiazolidine 1a and
MeO
Z
4-hydroxyselenazolidines 7a,b in the DMSO-d6 solution at room temperature and
after heating
O
MeO
H
O
Z
OH
R
a
Z
8a, 9a,b
H
O
Product
Isomer dH (ppm)
Irel (%)
NPh
NPh
MeO
OMe CH(R) w2 min 30 min 24 h 10 minb
N
N
HO
R
Ph
a
a
a
-1aþ8aþ
-7aþ9aþ
b
-1a
-7a
1
2
1
2
1
2
3.17 5.06
3.61 5.47
3.13 5.13
3.57 5.58
3.59 4.38
3.84 4.22
0
100
0
100
100
0
19
81
8
92
86
14
33
67
18
82
d
d
26
74
14
41
d
d
Ph
β−1a, 7a,b
α−1a, 7a,b
1a, 8a R = Ph, Z = S
7a, 9a R = Ph, Z = Se
b
-7bþ9bþ
b-7b
7b, 9b R = (CH2)2Ph, Z = Se
a Only one OF is shown. In fact several open forms may bepresented in solution.
a
Calculated by averaging the relative integral intensities of methoxy and meth-
ene protons.
Scheme 5. The possible transformations of the and diastereomers of
4-hydroxythiazolidine 1a and 4-hydroxyselenazolidines 7a,b in solution.
a
b
b
Immediately after heating the samples for 10 min at 100 ꢀC.

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V.A. Mamedov et al. / Tetrahedron 68 (2012) 7363e7373
Table 2
A novel one-pot synthesis of thiazolo[3,4-a]quinoxalines by interaction of 4-hydroxythiazolidines with 1,2-diaminobenzenes
ArN
S
O
OH
AcOH,
reflux
Ph
NH2
NH2
N
Ph
MeO
Ph
N
+
- MeOH,
- PhNH2,
- H2O
NAr
S
1a
N
H
10-12
O
R1
R1
2
Entry
1
Substrate
Time, h
Product (yield)
10a (48%) + 11a (31%)
10bb + 11b (74%)
NH2
a
-1aþ8aþ
b
-1a
3
Me
NH2
2b
NH2
NH2
2
3
a
a
-1aþ8aþ
-1aþ8aþ
b
-1a
-1a
6
3
O2N
2c
Me
Me
NH2
NH2
b
2d
10c (84%)
F
NH2
NH2
N
N
4
a
-1aþ8aþ
b-1a
3
Me
2e
10d (58%) + 11d (20%)
NH2
5
6
(
a
,
,
b
)-1bþ8bþ(
a
,
b
)-10b
2
2
NH2
2а
12a(77%)
NH2
NH2
(a
b
)-1cþ8cþ(
a
,
b
)-10c
2a
2d
12b(80%)
Me
Me
NH2
NH2
7
(a
,
b
)-1dþ8dþ(
a
,
b
)-10d
2
10c (27%) + 12c (38%)
aThe structures of 4-hydroxythiazolidines and 4-hydroxyselenazolidine were given both in this case (Table 1) and hereafter (Tables 3 and 4) established for the crystalline states.
bThe formation of the thiazoloquinoxaline 10b was confirmed by 1H NMR spectrum.
with the formation of only one product, but in the reactions
with mono-2b, 2c and ‘nonsymmetrically’ di-substituted 2e
1,2-diaminobenzenes a mixture of regioisomers is formed. In this
case it should be pointed out that one or another regioisomer
dominates depending on the nature of the substituent.
The structures of compounds 10e12 were unequivocally
established by
a
variety of NMR correlation methods
(1He1H/13C/15N). Good agreement of experimental versus theo-
retical (GIAO DFT) chemical shifts for the corresponding com-
pounds provided an additional support to structural conclusions.

V.A. Mamedov et al. / Tetrahedron 68 (2012) 7363e7373
7367
The condensation of pyridyl-containing ‘nonsymmetrical’
4-hydroxythiazolidines 1b,cþ10b,c with 1,2-diaminobenzene 2a, as
in the case with 4-hydroxydiphenylthiazolidine 1a, results in the
expected thiazolo[3,4-a]quinoxalines 12a,b. Condensation is ac-
companied by the elimination of aniline but not of 2-aminopyridine
or 2-aminopicoline. However, unlike 4-hydroxythiazolidine
1b,cþ10b,c 4-hydroxythiazolidine 1dþ10d, obtained from other
nonsymmetrical N,N0-di-substituted thiourea 5d produce mixtures
of isomeric thiazolo[3,4-a]quinoxalines 10c and 12c.
Scheme 7. The reaction of 4-hydroxythiazolidine 1e with 1,2-diaminobenzene 2a.
On the basis of the conventional chemistry of 1,2-
diaminobenzenes7 and 4-hydroxythiazolidines4a,b,5a,g (considered
hereinacyclicforminthecrystallinephaseandintheopenchainform
in solvents)4a it is reasonable to assume that the formation of thiazolo
[3,4-a]quinoxalines involves the intermediate formation of the type A
compound as a result of interactions of 1,2-diaminobenzene with the
open chain ketone 8. The above type A compound is further subjected
tointramolecularamidation and the bindingof the amino group of the
aminal system to the amidine atom of carbon. The thiazolo[3,4-a]
quinoxaline system B, containing geminal amino-phenyl and amino-
aryl substituents in position 1 is formed. Then, the acid-catalyzed
eliminationofanilinefromintermediateBleadstocovalenthydrate30,
which, when subjected to dehydration under reaction conditions,
gives the final products (Scheme 6).
Table 3
A
novel one-pot synthesis of selenazolo[3,4-a]quinoxalines by interaction of
4-hydroxyselenazolidines 7a,b with 1,2-diaminobenzenes 2a,c
ArN
Se
O
OH
AcOH,
reflux
Ph
NH2
NH2
N
R
MeO
N
+
- MeOH,
- PhNH2,
- H2O
R
NAr
Se
N
H
O
R1
R1
7
2
14
The condensation of 4-hydroxythiazolidine 1e with non-
substituted 1,2-diaminobenzene 2a yielded 15% thiazolo[3,4-a]
quinoxaline 10e with no substituent in position 3 (Scheme 7, all
NMR data are in SD). The major product 13 is formed as a result of
the dehydration of 4-hydroxythiazolidine 1e in the following re-
action conditions (boiling acetic acid). This is apparently due to the
fact that one of the geminal hydrogen atoms at C(5), unlike the
hydrogen atom at the same carbon atom in 5-arylsubstituted 4-
hydroxythiazolidines 1aed, is in a favourable position for de-
hydration trans- in relation to the OH-group. This has been well
documented5aed with the examples of the dehydration of other 4-
hydroxythiazolidines containing geminal protons in acidic medium
in position 5.
Entry
1
Substrate
Time
Product (yield)
PhN
Se
N
Ph
a
a
a
-7aþ9aþ
b
-7a
2a
2 h
N
H
O
14a (14%)
PhN
Se
Ph
N
2
3
-7bþ9bþ
-7bþ9bþ
b
-7b
-7b
2a
2c
1 min
N
H
O
14b (56%)
PhN
Se
Ph
2.2. The synthesis of selenazolo[3,4-a]quinoxalines
O2N
N
b
4.5 h
N
H
O
It is necessary to stress that, if their selenium analogues 7a,b are
used instead of thiourea derivatives in this reaction, it is possible to
synthesize a novel heterocyclic system, i.e., selenazolo[3,4-a]qui-
noxalines 14 (Table 3).
14c (43%)
MeO
H
O
PhHN
S
NPh
S
HO
PhN
NH
N
O
Ph NHPh
Ph
OH
OMe
2a, H+
Ph Ph
α-1a
MeO
S
NPh
NH2
A
O
O
8a
OH
H
S
H+
- MeOH
MeO
NPh
N
PhHN
PhHN
O
PhN
Ph
Ph
β-1a
S
S
Ph
Ph
N
N
H+
- H2O
H+
H
H
3
OH
OH
- PhNH2
N
H
O
N
H
O
3'
B
Scheme 6. A plausible mechanism for the formation of thiazolo[3,4-a]quinoxalines.

7368
V.A. Mamedov et al. / Tetrahedron 68 (2012) 7363e7373
The structures of the new ring system e selenazolo[3,4-a]qui-
However, as shown in Table 4, the yields of tri-cyclic systems
15 and 16 in these cases are lower than in the reactions of
4-hydroxythiazolidine 1a with the common 1,2-diaminobenzenes
2aec. The reason for reducing the yields of tri-cyclic systems in
the investigated condensation of the diamines 2f,g observed is the
deactivating effect of the nitrogen atom of pyridine rings on the
amino group located in the second position of 2,3-diamino- and the
noxalines were established ‘directly’ by a variety of hetero-
correlation NMR experiments. 1D TOCSY spectra allow to
distinguish proton sub-spin systems in a simple way. Particularly
useful were applications of 1He77Se HMBC experiments that
allowed the total correlation of all the nuclei in molecular 14b
(Fig. 2) and thus enabled the direct structure elucidation.
Fig. 2. Structure of 14b and principal TOCSY (coloured bonds and 1D spectra), 1H-15N HMBC (brown arrows from 1H to 15N), 1He77Se HMBC (lilac arrows from 1H to 77Se) and ROE
(black arrow) correlations.
2.3. The synthesis of aza analogues of thiazolo[3,4-a]
quinoxalines
fourth position of 3,4-diaminopyridines. This effect is further am-
plified due to the protonation of the nitrogen atom of pyridine rings
by acetic acid as a solvent. Therefore, in both cases, the competitive
reaction is the dehydration of 4-hydroxythiazolidine 1a with the
formation of thiazoline derivative 17.
This reaction appeared to be the best method for synthesizing
not only thiazolo- and selenazoloquinoxalines, but also other new
heterocyclic systems. For instance, if aza analogues, i.e., various
diaminopyridines are used instead of 1,2-diaminobenzene 2a in
this reaction, aza analogues of thiazoloquinoxalines are obtained
(Table 4).
Structures of all compounds were unequivocally established by
NMR methods. An application of the 1He15N correlation experi-
ments allow a safe determination of any either position of nitrogen
in the quinoxaline ring (Fig. 3). It is particularly important that such
a NMR approach can be safely and easily made towards regioiso-
meric structure8 as there is no need to obtain monocrystal of good
quality due to the availability of NMR equipment.
Table 4
A novel one-pot synthesis of aza analogues of thiazolo[3,4-a]quinoxalines by in-
teraction of 4-hydroxythiazolidine 1a with 1,2-diaminobenzenes 2f,g
Besides, the GIAO DFT calculations of 15N CSs an additionally
strong support is rendered for the structural conclusion (Fig. 3),
which demonstrates the power of this combined approach in the
fine structure determination of the systems in which nitrogen
atoms may be in different positions.
3. Conclusion
To summarize, we have reported an efficient and versatile one-
step method for the preparation of a series of thiazolo[3,4-a]
quinoxalines as well as other pyridine-, thiazolo- and piperazine-
containing ring systems. This was accomplished by the cascade
annulation of the iminothiazolopyrazine system to benzene
in reactions of 4-hydroxy-4-methoxycarbonyl-3,5-diphenyl-2-
phenyliminothiazolidine 1a with 1,2-diaminobenzenes 2 in boil-
ing acetic acid. This method makes it possible to synthesize im-
ino- as well as benzo-substituted thiazolo[3,4-a]quinoxalines, and
if instead of thiourea derivatives their selenium analogues are
used in this reaction, it is possible to construct a novel hetero-
cyclic system, i.e., selenazolo[3,4-a]quinoxalines. The reaction is
readily applicable to large-scale synthesis. Application of this
Entry
1
Substrate
Time, h
12
Product (yield)
NH2
NH2
a
a
-1aþ8aþ
-1aþ8aþ
b
-1a
-1a
15 (25%)þ17 (68%)
N
2f
NH2
NH2
N
2
b
4
16 (23%)þ17 (72%)
2g

V.A. Mamedov et al. / Tetrahedron 68 (2012) 7363e7373
7369
(a)
(b)
Fig. 3. Experimentally determined structures of 15 and 16 (above); Mismatch of experimental and calculated 15N shifts (ad15, bd16) for possible structures with different po-
sitions of nitrogen in quinoxaline ring (below).
methodology to the synthesis of other heterocyclic ring systems is
currently under investigation and the results will be published in
due time.
Mass polyisotopic (Se) molecular ions have been selected with
bold letters.
4.2. Preparation of 4-hydroxy-4-alkoxycarbonyl-2-
aryliminothiazolidines 1
4. Experimental section
4.1. General methods
4-Hydroxy-4-methoxycarbonyl-3,5-diphenyl-2-phenylimino-
thiazolidine1a has been synthesized according to a procedure
described by us.4a The 4-hydroxy-4-methoxycarbonyl-2-aryylimino-
thiazolidines 1bed, 10bed and 1e were synthesized by the same
procedure starting from the methyl phenylchloropyruvate 4a or
NMR investigation was carried out in the NMR department of
the federal collective spectral analysis center for physical and
chemical investigations of structure, properties and composition
of matter and materials. All NMR experiments were performed
with a Bruker AVANCE-600 (600 MHz for 1H, 150 MHz for 13C,
114 MHz for 77Se, 60 MHz for 15N) or AVANCE-400 (400 MHz for
1H, 110 MHz for 13C, 40 MHz for 15N) spectrometers equipped
with a 5 mm diameter gradient inverse broad band probe head
and a pulsed gradient unit capable of producing magnetic field
pulse gradients in the z-direction of 53.5 G cmꢁ1. Chemical shifts
ethyl bromopyruvate 4c and
a
corresponding N,N0-diary-
lsubstituted thiourea derivative 5. The following products were
obtained.
4.2.1. 4-Hydroxy-4-methoxycarbonyl-3,5-diphenyl-2-(pyridin-2-
ylimino)thiazolidine (1b) and 4-hydroxy-4-methoxycarbonyl-5-
phenyl-2-phenylimino-3-(pyridin-2-yl)thiazolidine (10b). Sodium
acetate (3.6 g, 43.8 mmol) was added to the solution N-(pyrid-2-
yl)-N0-phenylthiourea 5b (4 g,17.5 mmol) in 150 mL of dry CH2Cl2
then cooled to the temperature from ꢁ15 to ꢁ20 ꢀC, methyl
chloro(phenyl)pyruvate10 4a (3.7 g, 17.5 mmol) was added
dropwise. The reaction mixture was stirred for 5 h at w20 ꢀC and
poured into water (150 mL). The organic layer was separated, and
the aqueous layer was extracted with CHCl3 (2ꢂ20 mL). The
organic layer and the extract were combined and dried
with MgSO4, and the solvent was removed in vacuo. A crude
(
(
(
d
d
d
in parts per million) are referenced to the solvents DMSO-d6
¼2.50 ppm for 1H and 40.45 ppm for 13C NMR) and CDCl3
¼7.27 ppm for 1H and 77.0 ppm for 13C NMR) and to external
CH3CN (235.50 ppm) for 15N NMR spectra. 77Se chemical shifts
were referred to the signal of Se(Ph)2 (d 402). The quantum
chemical calculations were performed using Gaussian 98.9
Chemical shifts were determined by the GIAO method within
the DFT framework using a hybrid exchange-correlation func-
tional, B3LYP, at the 6-31G(d) level. Full geometry optimizations
were performed at the ab initio RHF/6-31G(d) level. All data were
referred to TMS (0.00 ppm) and to CH3CN (235.50 ppm) for
1H/13C and 15N chemical shifts, respectively. Infrared (IR) spectra
were recorded on a Bruker Vector-22 FT-IR spectrometer using
potassium bromide pellets and Nujol. Melting points were de-
termined on a Boetius hot-stage apparatus. Elemental analysis
was performed on a PerkineElmer analyzer. Flash chromatogra-
phy was performed on silica gel (100e200 mesh). Mass spectra
electronic ionization (EI) was measured on a ThermoQuest/Fin-
nigan TRACE MS quadrupole mass spectrometer, inlet of the
sample was performed through the system of the direct injection
with water cooling. In the description of mass-spectra no mass
peaks of ions with a relative intensity less than 5% are given.
yellow oil was obtained and
a mixture of 4-hydroxy-4-
methoxycarbonylthiazolidines (1bþ10b) was obtained after re-
crystallization from i-PrOH in a yield 3.4 g (50%). White solid, mp
137e139 ꢀC; IR (KBr): nmax 3462, 3217, 3172, 3101, 3028, 2947,
2922, 2852, 1738, 1628, 1595, 1551, 1532, 1494, 1472, 1462, 1430,
1349, 1314, 1257, 1188, 1142, 1106, 772, 743, 733, 694, 655, 640,
511 cmꢁ1; 1H NMR (600 MHz, DMSO-d6):
d 3.17 (s, 3H, OMe), 3.18
(s, 3H, OMe), 3.19 (s, 3H, OMe), 3.58 (s, 3H, OMe), 3.60 (s, 3H,
OMe), 3.61 (s, 3H, OMe), 4.99 (s, 1H, CH), 5.02 (s, 1H, CH), 5.06
(s, 1H, CH), 5.20 (s, 1H, CH), 5.32 (s, 1H, CH), 5.47 (s, 1H, CH),
6.63e8.51 (m, 6ꢂ 15H, 6ꢂ 2Phþ6ꢂ (H2eH5) pyridinesþ6ꢂ OH).
The ratio of the amounts of the integral intensities of peaks of CH,
OMe and Ar groups remains equal to 1:3:14; 13C NMR (600 MHz,
DMSO-d6, data for dominant component): d 52.9 (CH3), 55.0 (C5),

7370
V.A. Mamedov et al. / Tetrahedron 68 (2012) 7363e7373
92.8 (C4), 121.7 (o-C(Pyr)-d), 116.0e136.0 (m, Ph), 133.1 (i-
C(Ph000)), 137.7 (i-C(Ph00), 146.3 (NC (Pyr)), 158.6 (i-C(Pyr)), 159.6
(C2), 169.2 (CO). Anal. Calcd for C22H19N3O3S: C, 65.17; H, 4.72; N,
10.36; S, 7.91. Found: C, 65.01; H, 4.64; N, 10.29; S, 8.05.
chromatography (CHCl3/n-C6H14, 2:1) gave 0.41 g (48%) an analyt-
ically pure sample of 10a and 0.26 g (31%) 11a. Compound 10a:
Rf 0.68 (CHCl3/n-C6H14/MeOH, 1:3:2), yellow crystals, mp
280e283 ꢀC; IR (KBr): nmax 3195, 3020, 2921, 2871, 1674, 1614, 1587,
1575, 1485, 1397, 1332, 1209, 813, 761, 694 cmꢁ1
;
1H NMR
4.2.2. 4-Hydroxy-4-methoxycarbonyl-3,5-diphenyl-2-(3-
methylpyridin-2-ylimino)thiazolidine (1c) and 4-hydroxy-4-
methoxycarbonyl-5-phenyl-2-phenylimino-3-(3-methylpyridin-2-yl)
thiazolidine (10c). A mixture of 4-hydroxy-4-methoxycarbonylth-
iazolidines (1cþ10c) was obtained as white crystals in a 46% yield,
mp 130e134 ꢀC (from i-PrOH); IR (KBr): nmax 3472, 3056, 3026,
2958, 2922,1757,1737,1624,1574,1515,1494,1451,1418,1364,1343,
1269, 1253, 1191, 1164, 1138, 1100, 1025, 959, 834, 785, 762, 725,
(600 MHz, DMSO-d6): d 2.30 (s, 3H, Me), 6.93e6.95 (m, 2H,
H6þH8), 7.06 (d, 2H, J¼7.6 Hz, 2o-H phenylimines), 7.13 (dd, 1H,
J¼7.6, 7.1 Hz, p-H phenylimine), 7.35e7.37 (m, 3H, 2o-HPhþp-HPh),
7.40 (dd, 2H, J¼7.3, 7.3 Hz, 2m-H phenylimines), 7.45e7.47 (m, 2H,
2m-HPh), 9.27 (d, 1H, J¼8.9 Hz, H9), 11.15 (s, 1H, NH); 13C NMR
(600 MHz, DMSO-d6):
d 20.4, 115.9, 117.7, 120.7, 121.7, 122.2, 122.8,
123.8, 127.5, 128.2, 129.8, 130.0, 131.2, 134.3, 150.8, 154.0, 154.4.
Anal. Calcd for C23H17N3OS: C, 72.04; H, 4.47; N, 10.96; S, 8.36.
Found: C, 72.12; H, 4.37; N, 10.91; S, 8.21. Compound 11a: Rf 0.56
(CHCl3/n-C6H14/MeOH, 1:3:2), yellow crystals, mp 317e320 ꢀC; IR
(KBr): nmax 3180, 3026, 2923, 2854, 1671, 1614, 1587, 1488, 1399,
693 cmꢁ1; 1H NMR (600 MHz, DMSO-d6):
d 2.00 (s, 6H, 2Me), 3.14
(s, 3H, OMe), 3.56 (s, 3H, OMe), 4.97 (s, 1H, CH), 5.30 (s, 1H, CH),
6.90e8.15 (m, 23 14H, 23 2Phþ23 H2eH5 pyridinesþ23 OH). The
ratio of the amounts of the integral intensities of peaks of CH, OMe
and Ar groups remains equal to 1:3:13. 13C NMR (600 MHz, DMSO-
695, 616 cmꢁ1 1H NMR (600 MHz, DMSO-d6):
; d 2.31 (s, 3H, Me),
7.02e7.04 (m, 2H, H6þH7), 7.07 (d, 2H, J¼7.1 Hz, 2o-H phenyl-
imines), 7.14 (dd, 1H, J¼7.1, 7.1 Hz, p-H phenylimine), 7.33e7.35
(m, 3H, 2o-HPhþp-HPh), 7.42 (dd, 2H, J¼7.8, 7.1 Hz, 2m-H phenyl-
imines), 7.43e7.47 (m, 2H, 2m-HPh), 9.25 (s, 1H, H9), 11.14 (s, 1H,
d6):
d 53.0, 55.1, 93.0, 118.4, 119.3, 127.4, 128.2, 128.3, 128.6, 128.9,
129.2, 129.9, 133.2, 137.8, 138.8, 146.3, 158.7, 159.7, 169.2. Anal. Calcd
for C23H21N3O3S: C, 65.85; H, 5.05; N,10.02; S, 7.64. Found: C, 65.66;
H, 5.01; N, 9.96; S, 7.59.
NH); 13C NMR (600 MHz, DMSO-d6):
d 21.1, 114.9, 117.3, 117.8, 120.7,
121.8, 122.9, 123.9, 126.5, 127.6, 127.8, 129.9, 130.0, 131.4, 134.6,
150.8, 153.6, 153.9. Anal. Calcd for C23H17N3OS: C, 72.04; H, 4.47; N,
10.96; S, 8.36. Found: C, 72.25; H, 4.52; N, 11.05; S, 8.28.
4.2.3. 4-Hydroxy-4-methoxycarbonyl-3,5-diphenyl-2-(thiazol-2-
ylimino)thiazolidine (1d) and 4-hydroxy-4-methoxycarbonyl-5-
phenyl-2-phenylimino-3-(thiazol-2-yl)thiazolidine (10d). A mixture
of 4-hydroxy-4-methoxycarbonylthiazolidines (1dþ10d) was
obtained as white powder in a 52% yield, mp 150e155 ꢀC (from
i-PrOH); IR (Nujol): nmax 3500, 3189, 3111, 3088, 1763, 1737, 1630,
1597, 1564, 1492, 1451, 1358, 1313, 1216, 1151, 1132, 1095, 1049, 722,
4.3.2. 7-Nitro-3-phenyl-1-phenyliminothiazolo[3,4-a]quinoxalin-
4(5H)-one (10b) and 8-nitro-3-phenyl-1-phenyliminothiazolo[3,4-a]
quinoxalin-4(5H)-one (11b) (the mixture of isomers 10bþ11b in a 10
to 90 ratio on a percentage basis). A mixture of thiazolo[3,4-a]
quinoxalines (10bþ11b) was obtained in 74% yield as orange crys-
693 cmꢁ1; 1H NMR (600 MHz, CDCl3):
d 3.32 (s, 3H, OMe), 3.41 (s, 3H,
OMe), 3.49 (s, 3H, OMe), 3.72 (s, 3H, OMe), 3.73 (s, 3H, OMe), 3.87 (s,
3H, OMe), 5.23 (br s, 3H, 3CH), 5.30 (s,1H, CH), 5.43 (s,1H, CH), 5.46 (s,
1H, CH), 6.89e7.65 (m, 6ꢂ 13H, 6ꢂ 2Phþ6ꢂ H4 and 6ꢂ H5
thiazolesþ6ꢂ OH). The ratio of the amounts of the integral intensities
of peaks of CH, OMe and Ar groups remains equal to 1:3:12. 13C NMR
tals, mp 320e326 ꢀC; 1H NMR (600 MHz, DMSO-d6):
d 7.11e8.16
(m, 24H, 4Phþ2H6, H7, H8), 8.04 (d, 1H, J¼9.2 Hz, H8), 8.15 (d, 1H,
J¼8.9 Hz, H7), 9.62 (d, 1H, J¼8.9, H9), 10.42 (d, 1H, J¼2.1, H9), 11.50,
11.75 (both s, 1H, NH). An analytical sample of compound 11b was
obtained by recrystallization from DMF in a yield of 59%. Orange
crystals, mp 344e346 ꢀC; IR (KBr): nmax 3094, 3043, 2922, 2853,
1678, 1628, 1590, 1573, 1529, 1485, 1416, 1394, 1330 cmꢁ1; 1H NMR
(600 MHz, DMSO-d6):
d 52.4, 53.4, 53.5, 55.5, 57.4, 94.2, 97.1, 115.3,
115.5, 121.5, 128.0, 128.2, 128.5, 128.6, 128.7, 128.8, 128.9, 129.0, 129.1,
129.14,129.3,129.6,129.7,130.2,133.0,134.4,137.1,138.2,139.6,162.2,
169.0, 171.2. Anal. Calcd for C20H17N3O3S2: C, 58.38; H, 4.16; N, 10.21;
S, 15.58. Found: C, 58.44; H, 4.20; N, 10.15; S, 15.46.
(600 MHz, DMSO-d6):
d 2.75 (s, 3H, Me), 2.90 (s, 3H, Me), 7.13
(d, 2H, J¼7.9 Hz, 2o-H phenylimines), 7.20 (dd,1H, J¼7.3, 7.3 Hz, p-H
phenylimine), 7.28 (d, 1H, J¼8.6 Hz, H6), 7.39e7.41 (m, 3H,
2o-HPhþp-HPh), 7.46 (dd, 2H, J¼7.9, 7.6 Hz, 2m-H phenylimines),
7.49e7.51 (m, 2H, 2m-HPh), 8.14 (dd, 1H, J¼8.9, 2.1 Hz, H7), 10.42
(d, 1H, J¼2.1, H9), 11.77 (s, 1H, NH); 13C NMR (600 MHz, DMSO-d6):
4.2.4. 4-Hydroxy-4-ethoxycarbonyl-3-phenyl-5H-2-phenyl-
yliminothiazolidine (1e). Yellowish powder, yield 76%, mp
119e121 ꢀC (from i-PrOH); IR (KBr): nmax 3490, 3049, 3026, 2987,
2958, 2900, 1741, 1728, 1629, 1588, 1493, 1316, 1285, 1198, 1178,
d
109.6, 113.4, 115.2, 120.7, 121.1, 123.6, 124.5, 124.8, 127.9, 129.0,
130.0, 130.4, 134.5, 141.6, 150.2, 153.8, 154.1, 162.3. Anal. Calcd for
C22H14N4O3S$DMF: C, 56.18; H, 3.93; N, 13.11; S, 14.79. Found: C,
56.02; H, 3.89; N, 13.03; S, 14.68.
1158, 1116, 1058, 878, 776, 696, 563 cmꢁ1
DMSO-d6):
;
1H NMR (600 MHz,
0.97 (t, 3H, J¼7.3 Hz, CH3CH2OCO), 3.36 (d, 1H,
d
J¼11.7 Hz, CHAHB), 3.76 (d,1H, J¼11.7 Hz, CHAHB), 4.00e4.05 (m, 2H,
CH3CH2OCO), 6.82e7.41 (m, 11H, 2PhþOH); 13C NMR (600 MHz,
4.3.3. 7,8-Dimethyl-3-phenyl-1-phenyliminothiazolo[3,4-a]quinox-
DMSO-d6):
d
14.0 (CH3), 38.9 (C5), 62.4 (CH2), 92.5 (C4), 121.7
alin-4(5H)-one (10c). Yellow crystals, mp 352e355 ꢀC; IR (KBr):
(o-C(Ph0)), 123.5 (p-C(Ph0)), 127.1 (p-C(Ph00)), 128.5 (o-C(Ph00)), 128.8
(m-C(Ph00)), 129.4 (m-C(Ph0)), 139.1 (i-C(Ph00)), 151.7 (i-C(Ph0)), 157.6
(C2), 169.6 (CO). Anal. Calcd for C18H18N2O3S: C, 63.14; H, 5.30; N,
8.18; S, 9.36. Found: C, 63.07; H, 5.35; N, 8.14; S, 9.44.
nmax 3025, 2921, 2871, 1671, 1613, 1587, 1486, 1396, 692, 633 cmꢁ1
;
1H NMR (600 MHz, DMSO-d6):
d 2.21 (s, 6H, 2Me), 6.92 (s, 1H, H6),
7.07 (d, 2H, J¼7.8 Hz, 2o-H phenylimines), 7.13 (dd,1H, J¼7.8, 6.7 Hz,
p-H phenylimine), 7.34e7.36 (m, 3H, 2o-HPhþp-HPh), 7.41 (dd, 2H,
J¼7.8, 6.7 Hz, 2m-H phenylimines), 7.45e7.48 (m, 2H, 2m-HPh), 9.21
4.3. Preparation of thiazolo[3,4-a]quinoxalin-4(5H)-ones 10e12
(s, 1H, H9), 11.09 (s, 1H, NH); 13C NMR (600 MHz, DMSO-d6):
d 18.9,
19.4, 116.0, 118.8, 120.8, 121.6, 121.8, 122.9, 124.0, 125.7, 127.7, 128.5,
129.9, 130.0, 130.1, 131.1, 133.2, 150.9, 153.8, 153.9. Anal. Calcd for
C24H19N3OS: C, 72.52; H, 4.82; N, 10.57; S, 8.07. Found: C, 72.33; H,
4.73; N, 10.62; S, 8.01.
4.3.1. 7-Methyl-3-phenyl-1-phenyliminothiazolo[3,4-a]quinoxalin-
4(5H)-one (10a) and 8-methyl-3-phenyl-1-phenyliminothiazolo[3,4-
a]quinoxalin-4(5H)-one (11a) (the mixture of isomers 10aþ11a in
a
60 to 40 ratio on a percentage basis). A solution of 1,2-
diaminobenzene 2b (0.31 g, 2.6 mmol) and 4-hydroxythiazolidine
1a (1 g, 2.6 mmol) in AcOH (15 mL) was refluxed for 3 h. The yel-
low crystals that precipitated were filtered off. The yield of the
mixture (10aþ11a) was 0.85 g (85%), which after column
4.3.4. 3-Phenyl-1-(pyridin-2-yl)iminothiazolo[3,4-a]quinoxalin-
4(5H)-one (12a). Yellow powder, mp 346e347 ꢀC; IR (KBr): nmax
3029, 2962, 2919, 2854, 1682, 1610, 1586, 1568, 1532, 1461, 1429,
1403 cmꢁ1
;
1H NMR (600 MHz, DMSO-d6):
d
7.08 (ddd, 1H, J¼7.1,

V.A. Mamedov et al. / Tetrahedron 68 (2012) 7363e7373
7371
4.8, 0.8 Hz, H5 pyridine), 7.19 (dd, 1H, J¼7.5, 1.6 Hz, H6), 7.22 (ddd,
1H, J¼8.4, 7.5, 1.6 Hz, H8), 7.27 (ddd, 1H, J¼7.6, 7.6, 1.3 Hz, H7), 7.34
(d, 1H, J¼8.1 Hz, H3 pyridine), 7.41e7.43 (m, 3H, 3HPh), 7.55e7.57
(m, 2H, 2HPh), 7.82 (ddd, 1H, J¼8.1, 7.6, 2.0 Hz, H4 pyridine), 8.49
(dd, 1H, J¼5.0, 1.0 Hz, H6 pyridine), 10.00 (d, 1H, J¼8.4 Hz, H9), 11.27
phenyliminothiazoline 13. Beige crystals, mp 95e96 ꢀC; IR
(Nujol): nmax 1732, 1626, 1588, 1493, 1465, 1396, 1378, 1258, 1210,
1156, 1092, 713, 696 cmꢁ1; 1H NMR (600 MHz, CDCl3):
d 1.11 (t, 3H,
J¼7.1 Hz, CH3CH2OCO), 4.11 (q, 2H, J¼14.1, 7.1 Hz, CH3CH2OCO),
7.11e7.53 (m, 13H, 2PhþCH); 13C NMR (600 MHz, DMSO-d6):
(s, 1H, NH); 13C NMR (600 MHz, DMSO-d6):
d
115.3, 117.9, 119.8,
d 128.3, 129.0, 130.7, 138.8, 151.3, 157.8, 158.5. Anal. Calcd for
119.9, 120.3, 122.4, 125.2, 125.8, 127.7, 128.0, 128.4, 128.6, 130.2,
131.5,138.0, 145.6, 153.4, 153.9, 156.5. Anal. Calcd for C21H14N4OS: C,
68.09; H, 3.81; N, 15.12; S, 8.65. Found: C, 67.79; H, 3.75; N, 15.01; S
8.74. The filtrate was treated with a 5% NaHCO3 solution. The
aqueous layer was extracted with ethyl acetate (3ꢂ20 mL). Ethyl
acetate was evaporated, the residue was treated with diethyl ether
(20 mL) and after filtered off the yellow precipitate (85%) of acet-
anilide was obtained, mp 110e113 ꢀC (lit.11: 113 ꢀC).
C18H16N2O2S: C, 66.65; H, 4.97; N, 8.64; S, 9.88. Found: C, 66.54; H,
5.09; N, 8.51; S, 9.77.
4.3.8. 7-Fluoro-8-(4-methylpyperazin-2-yl)-3-phenyl-1-phenyl-
iminothiazolo[3,4-a]quinoxalin-4(5H)-one (10d) and 7-(4-
methylpyperazin-2-yl)-8-fluoro-3-phenyl-1-phenyliminothiazolo
[3,4-a]quinoxalin-4(5H)-one (11d) (the mixture of compounds
(10dþ11d) in a 74 to 26 ratio on a percentage basis). N2H4
(96%) (0.6 mL, 18.9 mmol) in absolute ethanol (40 mL) was
added to a solution of (0.5 g, 1.97 mmol) 1-amino-2-nitro-4-(4-
methylpiperazino)-5-fluorobenzene. The reaction mixture was
heated on a water bath until complete dissolution of the starting
compound and then cooled down to 30 ꢀC. The solution of Ni-Reney
catalyst (0.1 g) in absolute ethanol (20 mL) was added and then
heated under reflux for 3 h. The reaction mixture was cooled to
room temperature, the catalyst was filtered, and the solvent was
evaporated with a vacuum evaporator. 4-Hydroxythiazolidine 1a
(0.79 g, 1.95 mmol) in AcOH (30 mL) was added to the 10 mL acetic
acid solution of the diamine 2f obtained and heated under reflux
for 3 h. The solvent was evaporated and the ether (10 mL) was
added to the residue. The dark-green crystals that precipitated
were filtered off and dried in air. The yield of the mixture isomers
(10dþ11d) was 0.8 g (84%), which after column chromatography
(CHCl3/n-C6H14, 4:1) gave 0.46 g (58%), an analytically pure sample
of 10d and 0.16 g (20%) of 11d. Compound 10d: Rf 0.34 (CHCl3/n-
C6H14/MeOH, 1:1:6), yellow crystals, mp 275e280 ꢀC; IR (KBr): nmax
3047, 2924, 2851, 1681, 1614, 1582, 1513, 1406, 1372, 1306, 1260,
4.3.5. 3-Phenyl-1-(3-methylpyridin-2-yl)iminothiazolo[3,4-a]qui-
noxalin-4(5H)-one (12b). Yellow powder, mp 350e352 ꢀC; IR (KBr):
nmax 3029, 2958, 2921, 2853, 1681, 1606, 1573, 1532, 1436, 1418,
1400, 1318, 1215, 736, 688 cmꢁ1 1H NMR (600 MHz, DMSO-d6):
;
d
2.48 (s, 3H, Me), 7.01 (dd, 1H, J¼7.2, 4.8 Hz, H5 pyridine), 7.21 (dd,
1H, J¼7.6, 1.6 Hz, H6), 7.23 (ddd, 1H, J¼8.7, 7.3,1.8 Hz, H8), 7.28 (ddd,
1H, J¼7.6, 7.3, 1.3 Hz, H7), 7.42e7.45 (m, 3H, 3HPh), 7.55e7.57
(m, 2H, 2HPh), 7.70 (d, 1H, J¼7.2 Hz, H4 pyridine), 8.34 (d, 1H,
J¼4.8 Hz, H6 pyridine), 10.01 (d, 1H, J¼8.6 Hz, H9), 11.28 (s, 1H, NH);
13C NMR (600 MHz, DMSO-d6):
d 17.5,115.2,117.7,119.5,122.1,125.0,
125.6, 127.6, 128.2, 128.5, 129.8, 130.0, 131.5, 132.1, 137.9, 142.6,
153.0, 153.8, 155.2. Anal. Calcd for C22H16N4OS: C, 68.73; H, 4.19; N,
14.57; S, 8.34. Found: C, 68.99; H, 4.25; N, 14.45; S, 8.24.
4.3.6. 7,8-Dimethyl-3-phenyl-1-phenyliminothiazolo[3,4-a]quinox-
alin-4(5H)-one (10c) and 7,8-dimethyl-3-phenyl-1-(thiazol-2-yl)
iminothiazolo[3,4-a]quinoxalin-4(5H)-one (12c) (the mixture of
compounds (10cþ12c) in a 40 to 60 ratio on a percentage basis). A
mixture of thiazolo[3,4-a]quinoxalines (10cþ12c) was obtained in
a yield of 77%. An analytical sample of compound 12c was obtained
by recrystallization from DMF in a 38% yield of yellow crystals, mp
340e345 ꢀC; IR (KBr): nmax 3044, 2920, 2853, 1688, 1630, 1584,
1546, 1507, 1487, 1430, 1404, 1399, 1301, 1141, 1017, 685, 635, 493,
695 cmꢁ1; 1H NMR (600 MHz, CDCl3):
d 1.26 (s, 3H, Me), 2.58e3.30
(m, 8H, 4CH2), 6.53 (d, 1H, JHF¼12.0 Hz, H6), 7.09e7.44 (m, 10H,
2Ph), 9.47 (d, 1H, J¼8.8 Hz, H9), 10.33 (s, 1H, NH); 13C NMR
(600 MHz, DMSO-d6):
d 45.25 (CH3), 49.4 (C2, C6), 49.4 (C3, C5),
104.9 (C6), 106.3 (C9, 2JCF¼30.7 Hz), 118.2 (C9a, 3JCF¼11.1 Hz), 120.5
(o-C(NPh)), 120.8 (C3a), 121.70 (C3), 123.8 (p-C(NPh)), 124.6 (C5a),
127.4 (m-C(Ph)), 128.34 (p-C(Ph)), 129.63 (m-C(NPh)), 129.81
458 cmꢁ1 1H NMR (600 MHz, DMSO-d6):
; d 2.24 (s, 3H, Me), 2.30
(s, 3H, Me), 6.97 (s, 1H, H6), 7.32 (d, 1H, J¼3.5 Hz, H5 or H4 thia-
zoles), 7.42e7.44 (m, 3H, 2o-HPhþp-HPh), 7.56e7.58 (m, 2H,
2m-HPh), 7.61 (d, 1H, J¼3.5 Hz, H5 or H4 thiazoles), 9.49 (s, 1H, H9),
2
(o-C(Ph)), 130.5 (i-C(Ph)), 136.4 (C7, JCF¼11.2 Hz), 148.5 (C8,
1JCF¼223.6 Hz), 150.3 (i-C(NPh)), 153.3 (C4), 153.52 (C1). Anal. Calcd
11.26 (s, 1H, NH); 13C NMR (600 MHz, DMSO-d6):
d
18.5, 19.5, 113.2,
for C27H24FN5OS: C 66.79; H 4.98; N 14.42; S 6.60. Found: C, 66.82;
114.0, 115.6, 119.8, 122.0, 125.2, 127.4, 128.4, 129.8, 129.9, 130.5,
134.1, 138.6, 143.9, 146.5, 169.2. Anal. Calcd for C21H16N4OS2: C,
62.36; H, 3.99; N, 13.85; S, 15.85. Found: C, 62.26; H, 3.92; N, 13.72;
S, 15.70. H2O (5 mL) was added to the filtrate (DMSO) the yellow
solid that precipitated was filtered off, washed with water
(2ꢂ5 mL) and dried in air. Compound 10c was obtained in a 0.13 g
(27%) yield. Mp, IR and MMR spectral features of this sample were
identical to compound 10c obtained previously.
H, 4.92; N, 14.51; S, 6.50. Compound 11d: Rf 0.18 (CHCl3/n-C6H14/
MeOH, 1:1:6), yellow crystals, mp 309e310 ꢀC; IR (Nujol): nmax
3026, 2925, 2855, 1675, 1617, 1590, 1520, 1459, 1398, 1264,
696 cmꢁ1; 1H NMR (600 MHz, CDCl3):
d 1.25 (s, 3H, Me), 2.41e3.05
(m, 8H, 4CH2), 6.33 (d, 1H, J¼7.6 Hz, H6), 7.07e7.47 (m, 10H, 2Ph),
9.38 (d, 1H, JHF¼15.4 Hz, H9), 9.55 (s, 1H, NH); 13C NMR (600 MHz,
DMSO-d6):
d 45.28 (CH3), 50.0 (C2, C6), 54.3 (C3, C5), 102.6 (C6,
2JCF¼26.6), 109.8 (C9), 120.4 (o-C(NPh)), 121.0 (C3a), 121.3 (C9a,
4JCF¼2.4 Hz), 121.73 (C3), 122.9 (C5a, JCF¼10.5 Hz), 123.75
3
4.3.7. 3H-1-Phenyliminothiazolo[3,4-a]quinoxalin-4(5H)-one
(10e). Beige powder, yield 15%, mp 314e317 ꢀC; IR (KBr): nmax 3173,
3121, 3099, 3047, 3027, 2980, 2905, 2852, 1685, 1621, 1589, 1575,
(p-C(NPh)), 127.4 (m-C(Ph)), 128.33 (p-C(Ph)), 129.60 (m-C(NPh)),
2
129.82 (o-C(Ph)), 130.6 (i-C(Ph)), 133.7 (C8, JCF¼9.1 Hz), 150.0
1
(i-C(NPh)), 151.1 (C7, JCF¼244.7 Hz), 153.2 (C4), 153.45 (C1). Anal.
1431, 1413, 756, 694 cmꢁ1
;
1H NMR (600 MHz, DMSO-d6):
d
7.04
Calcd for C27H24FN5OS: C, 66.79; H, 4.98; N, 14.42; S, 6.60. Found: C,
66.77; H, 5.10; N, 14.31; S, 6.49.
(d, 2H, J¼8.1 Hz, 2o-HPh), 7.12e7.16 (m, 3H, H6eH8), 7.20 (dd, 1H,
J¼7.3, 7.3 Hz, p-HPh), 7.29 (s, 1H, CH), 7.42 (dd, 2H, J¼8.1, 7.3 Hz, 2m-
HPh), 9.38 (d, 1H, J¼8.8 Hz, H9), 11.36 (s, 1H, NH); 13C NMR
4.4. Preparation of 4-hydroxy-4-methoxycarbonyl-2-
phenyliminoselenazolidines 7
(600 MHz, DMSO-d6):
d 105.5 (C3), 115.4 (C6), 117.2 (C9), 120.6
(o-C(NPh)), 122.5 (C8), 123.8 (p-C(NPh)), 124.8 (C9a), 124.9 (C7),
127.6 (C5a), 128.5 (C3a), 129.8 (m-C(NPh)), 150.7 (i-C(NPh)), 153.5
(C1), 156.8 (C4). Anal. Calcd for C16H11N3OS: C, 65.51; H, 3.78;
N, 14.32; S, 10.93. Found: C, 65.49; H, 3.71; N, 14.43; S, 10.78.
The filtrate was evaporated, the residue was triturated with
i-PrOH to yield (79%) of 4-ethoxycarbonyl-3-phenyl-5H-2-
4.4.1. 4-Hydroxy-4-methoxycarbonyl-3,5-diphenyl-2-phenylimino
selenazolidine (7a). Methyl chloro(phenyl)pyruvate10 4a (3.9 g,
18.2 mmol) was added dropwise to the suspension of sodium ac-
etate (3.7 g, 45.5 mmol) and N,N0-diphenylselenourea12 (5 g,
18.2 mmol) in CH2Cl2 (150 mL) at room temperature with the

7372
V.A. Mamedov et al. / Tetrahedron 68 (2012) 7363e7373
stirring and continue for 9 h. The reaction mixture was boiled for
1 h. The precipitated during the cooling was filtrated. The organic
layer was separated, and the aqueous layer was extracted with
CHCl3 (3ꢂ50 mL). The organic layer and the extract were combined
and dried with MgSO4, the solvent was removed in vacuo. A crude
brown oil was obtained, which after recrystallization from i-PrOH
gave 7 g (72%) of an analytically pure sample of 7a as beige crystals,
mp 146e148 ꢀC; IR (KBr): nmax 3514, 3065, 3026, 3004, 2954, 2923,
2853, 1740, 1648, 1589, 1490, 1304, 1240, 1156, 1099, 692 cmꢁ1; 1H
d 114.8 (C6), 118.3 (C9), 119.8 (o-C(NPh)), 122.0 (C8), 122.7 (C3a),
124.37 (p-C(NPh)), 124.5 (C3), 124.9 (C7), 125.1 (C9a), 127.4
(m-C(Ph)), 127.8 (C5a), 127.9 (p-C(Ph)), 129.5 (o-C(Ph)), 129.9
(m-C(NPh)), 133.5 (i-C(Ph)), 152.1 (i-C(NPh)), 154.0 (C1), 154.4
(C4); MS: m/z 419 (6), 418 (7), 417 (30), 415 (15), 414 (6), 413 (6)
Mþ, 316 (9), 315 (8), 314 (50), 312 (25), 311 (7), 310 (9), 236 (7), 235
(40), 234 (100), 207 (8), 206 (31), 205 (33), 169 (25), 167 (14), 165
(5), 160 (10), 158 (6), 117 (10), 104 (7), 103 (7), 90 (5), 89 (15), 77
(19). Anal. Calcd for C22H15N3OSe: C, 63.47; H, 3.63; N, 10.09.
Found: C, 63.62; H, 3.60; N, 10.15.
NMR (600 MHz, DMSO-d6):
d 3.13 (s, 3H, OMe), 3.57 (s, 3H, OMe),
5.13 (s, 1H, CH), 5.58 (s, 1H, CH), 6.84e7.46 (m, 2ꢂ 16H, 2ꢂ 3Phþ2ꢂ
OH). The ratio of the amounts of the integral intensities of peaks of
CH, OMe and Ar groups remains equal to 1:3:15. 13C NMR
4.5.2. 3-(2-Phenylethyl)-1-phenyliminoselenazolo[3,4-a]quinoxalin-
4(5H)-one (14b). Grey solid, mp 273e275 ꢀC (from DMF); IR (KBr):
nmax 3187, 3060, 3024, 2923, 2850, 2766, 1669, 1621, 1590, 1497,
(600 MHz, DMSO-d6):
d 14.0 (CH3), 38.9 (C5), 62.4 (CH2), 92.3 (C4),
121.7 (o-C(Ph0)), 123.5 (p-C(Ph0)), 127.1 (p-C(Ph00)), 128.5 (o-C(Ph00)),
128.8 (m-C(Ph00)), 129.4 (m-C(Ph0)), 139.1 (i-C(Ph00)), 151.7 (i-C(Ph0)),
157.6 (C2), 169.6 (CO); MS: m/z 454 (6), 453 (10), 452 (30), 451 (10),
450 (16), 449 (9), 448 (6) Mþ, 393 (10), 391 (5), 274 (6), 273 (6), 211
(9), 210 (62), 196 (19), 195 (91), 194 (100), 182 (9), 180 (14), 179 (8),
171 (15), 170 (14), 169 (19), 168 (14), 167 (29), 166 (8), 165 (7), 149
(16), 147 (5), 137 (16), 136 (18), 135 (9), 132 (10), 123 (16), 122 (6),
121 (28), 120 (11), 119 (14), 118 (26), 117 (8), 109 (15), 107 (13), 105
(9), 104 (12), 103 (8), 95 (25), 94 (7), 93 (21), 92 (29), 91 (55), 90
(23), 89 (14), 82 (12), 81 (60), 79 (11), 78 (9), 77 (72). Anal. Calcd for
C23H20N2O3Se: C, 61.20; H, 4.47; N, 6.21. Found: C, 61.41; H, 4.39; N,
6.16.
1403, 1309, 757, 696 cmꢁ1 1H NMR (600 MHz, DMSO-d6):
;
d
2.82e2.86 (m, 2H, PhCH2CH2), 3.52e3.54 (M, 2H, PhCH2CH2),
6.99e7.45 (m, 13H, 2PhþH6eH8), 9.29 (d, 1H, J¼8.4 Hz, H9), 11.06
(s, 1H, NH); 13C NMR (600 MHz, DMSO-d6): 31.0 (C10), 36.3 (C20),
d
114.7 (C6), 118.16 (C9), 120.0 (o-C(NPh)), 122.1 (C8), 123.5 (C3a),
124.2 (p-C(NPh)), 124.7 (C7), 125.5 (C9a), 125.9 (p-C(Ph)), 127.9
(C5a), 128.0 (o-C(Ph)), 128.1 (m-C(Ph)), 129.2 (C3), 129.9
(m-C(NPh)), 140.4 (i-C(Ph)), 152.5 (i-C(NPh)), 154.8 (C1), 155.5 (C4).
Anal. Calcd for C24H19N3OSe: C, 64.87; H, 4.31; N, 9.46. Found: C,
64.66; H, 4.35; N, 9.40.
4.5.3. 8-Nitro-3-(2-phenylethyl)-1-phenyliminoselenazolo[3,4-a]qui-
noxalin-4(5H)-one (14c). Orange powder, mp >350 ꢀC; IR (KBr):
nmax 3169, 3085, 3056, 3023, 2919, 1697, 1675, 1617, 1592, 1527,
1488,1411,1386,1325,1071, 758, 743, 694 cmꢁ1; 1H NMR (600 MHz,
4.4.2. 4-Hydroxy-4-methoxycarbonyl-3-phenyl-5-(2-phenylethyl)-2-
phenyliminoselenazolidine (7b). Selenazolidine 7b was obtained by
following the same procedure as that described above for 7a with
using the methyl 2-oxo-3-chloro-5-phenylpentaoate.13 The re-
action mixture was poured into water (150 mL). The organic layer
was separated, and the aqueous layer was extracted with CHCl3
(3ꢂ50 mL). The organic layer and the extract were combined and
dried with MgSO4, the solvent was removed in vacuum. The residue
was treated with i-PrOH and filtrated. After the evaporation of fil-
trate a compound 7b was obtained in a 77% yield as orange oil; IR
(Nujol): nmax 3485, 3176, 3061, 3027, 2953, 2924, 2854, 1741, 1632,
DMSO-d6):
d
2.83e2.87 (m, 2H, PhCH2CH2), 3.51e3.55 (m, 2H, J¼8.1,
7.7 Hz, PhCH2CH2), 7.03e7.56 (m, 11H, 2PhþH6), 8.07 (dd,1H, J¼8.8,
2.6 Hz, H7), 10.35 (d, 1H, J¼2.6 Hz, H9), 11.64 (s, 1H, NH); 13C NMR
(600 MHz, DMSO-d6):
d 31.2, 36.3, 113.7, 115.2, 120.2, 120.9, 122.9,
124.6, 125.4, 126.0, 128.2, 128.3, 130.2, 130.5, 136.0, 140.5, 141.0,
152.3, 155.5, 156.0. Anal. Calcd for C24H18N4O3Se: C, 58.90; H, 3.71;
N, 11.45. Found: C, 58.79; H, 3.77; N, 11.3.
4.6. Preparation of aza analogues thiazolo[3,4-a]quinoxalin-
4(5H)-ones 15, 16
1588, 1493, 1453, 1309, 1260, 1153, 1110, 1027, 697 cmꢁ1
;
1H NMR
(600 MHz, CDCl3): 2.04e2.13 (m, 2H, PhCH2CH2), 2.26e2.36
d
(m, 2H, PhCH2CH2), 2.51e2.58 (m, 2H, PhCH2CH2), 2.66e2.75
(m, 2H, PhCH2CH2), 3.59 (s, 3H, OMe), 3.84 (s, 3H, OMe), 4.22e4.25
(m, X-part of ABX-system, 1H, JA,XþJB,X¼14.4 Hz, CH), 4.37e4.41
(m, X-part of ABX-system, 1H, JA,XþJB,X¼14.7 Hz, CH), 6.92e7.43
(m, 2ꢂ 16H, 2ꢂ 3Phþ2ꢂ OH). The ratio of the amounts of the in-
tegral intensities of peaks of CH, OMe and Ar groups remains equal
4.6.1. 3-Phenyl-1-phenyliminothiazolo[3,4-a]pyrido[2,3-e]pyrazin-
4(5H)-one (15). Compound 15 was obtained in the same way as
thiazolo[3,4-a]quinoxalin-4(5H)-ones using the 4-hydroxythiazolidine
1a and 2,3-diaminopyridine 2f in a yield of 25%. Dark powder, mp
323e324 ꢀC; IR (KBr): nmax 3130, 3048, 2968, 2897, 2851, 2771, 1697,
1616, 1589, 1574, 1563, 1515, 1486, 1466, 1442, 1359, 1278, 1201, 1166,
to 1:3:15. 13C NMR (600 MHz, DMSO-d6):
d
29.11, 29.2, 31.0, 31.4,
;
798, 765, 744, 695, 628, 619, 581, 534 cmꢁ1 1H NMR (600 MHz,
32.1, 34.6, 39.4, 46.6, 53.4, 54.0, 67.9, 86.0, 93.9, 121.0, 123.5, 123.7,
125.7, 125.9, 127.8, 127.85, 127.90, 127.94, 127.99, 128.04, 128.07,
128.1, 128.4, 128.7, 128.8, 129.0, 139.7, 140.5, 165.9, 170.1. Anal. Calcd
for C25H24N2O3Se: C, 62.63; H, 5.05; N, 5.84. Found: C, 62.35; H,
4.96; N, 5.76.
DMSO-d6):
d
7.12 (dd, 2H, J¼8.5, 1.0 Hz, 2o-H phenylimines), 7.17 (ddd
1H, J¼8.5, 7.5,1.0 Hz, p-H phenylimine), 7.21 (dd,1H, J¼8.5, 5.0 Hz, H8),
7.38e7.40 (m, 3H, p-HPhþ2o-HPh), 7.45 (ddd, 2H, J¼8.5, 7.5, 1.0 Hz, 2m-
H phenylimines), 7.49e7.51 (m, 2H, 2m-HPh), 8.15 (dd, 1H, J¼5.0,
1.3 Hz, H7), 9.67 (dd, 1H, J¼8.5, 1.3 Hz, H9), 11.70 (s, 1H, NH); 13C NMR
(600 MHz, DMSO-d6): d 119.3 (C8), 121.8 (o-C(NPh)), 122.3 (C3a), 122.6
4.5. Preparation of selenazolo[3,4-a]quinoxalin-4(5H)-ones 14
(C9a), 123.5 (C3), 125.4 (p-C(NPh)), 126.0 (C9), 128.9 (m-C(Ph)), 129.9
(p-C(Ph)), 131.1 (m-C(NPh)), 131.2 (o-C(Ph)), 131.7 (i-C(Ph)), 142.5 (C5a),
144.4 (C7), 151.5 (i-C(NPh)), 155.1 (C1), 155.3 (C4). Anal. Calcd for
C21H14N4OS: C, 68.09; H, 3.81; N, 15.12; S, 8.65. Found: C, 67.84; H,
3.89; N, 14.97; S, 8.59. The reaction mixture after the separation of
compound 15 was treated with a 5% water solution of NaHCO3, the
precipitate of dark brown colour was filtered, washed with water
(2ꢂ10 mL), dried in air, recrystallized (from i-PrOH) to yield 68% of
4-methoxycarbonylthiazoline 17 as white crystals, mp 105e106 ꢀC. IR
(KBr): nmax 3054, 2949, 1732, 1622, 1584, 1491, 1358, 1200, 1169, 762,
4.5.1. 3-Phenyl-1-phenyliminoselenazolo[3,4-a]quinoxalin-4(5H)-
one (14a). A solution of 1,2-diaminobenzene 2a (0.2 g, 1.85 mmol)
and 4-hydroxyselenazolidine 7a (0.84 g, 1.85 mmol) in AcOH
(10 mL) was refluxed for 2 h. 75 mg of Selenium were decanted
from the hot reaction mixture as grey crystals. The crystals pre-
cipitated from the filtrate after cooling was filtered the compound
14a with the 14% yield as yellow crystals, mp 290e293 ꢀC; IR
(KBr): nmax 3182, 3117, 3025, 2982, 2913, 2861, 2767, 1674, 1619,
1605, 1586, 1488, 1394, 1201, 756, 737 cmꢁ1
;
1H NMR (600 MHz,
694 cmꢁ1 1H NMR (600 MHz, DMSO-d6):
; d 3.43 (s, 3H, OMe);
DMSO-d6):
d
7.07e7.46 (m, 13H, 2PhþH6eH8), 9.29 (d, 1H,
6.93e7.53 (m,15H, 3Ph). Anal. Calcd for C23H18N2O2S: C, 71.48; H, 4.69;
N, 7.25; S, 8.30. Found: C, 71.16; H, 4.62; N, 7.09; S, 8.16. The aqueous
J¼8.6 Hz, H9), 11.09 (s, 1H, NH); 13C NMR (600 MHz, DMSO-d6):

V.A. Mamedov et al. / Tetrahedron 68 (2012) 7363e7373
7373
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2. (a) TenBrink, R. E.; Jacobsen, E. J.; Gammill, R. B. U.S. Patent 5,541,324, 1996;
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layer was extracted with ethyl acetate (3ꢂ20 mL). Ethyl acetate was
evaporated, the residue was treated with diethyl ether (20 mL) and
after filtration a yellow precipitate (23%) of acetanilide was obtained,
mp 111e113 ꢀC.
4.6.2. 3-Phenyl-1-phenyliminothiazolo[3,4-a]pyrido[3,4-e]pyrazin-
4(5H)-one (16). A solution of 3,4-diaminopyridine 2 g (0.25 g,
2.3 mmol) and 4-hydroxythiazolidine 1a (1.85 g, 4.6 mmol) in
AcOH (10 mL) was refluxed for 4 h. The solvent was evaporated
and the ether (10 mL) was added to the residue. The yellow crys-
tals that precipitated were filtered off and recrystallized from
i-PrOH to yield 0.19 g (23%) of compound 16 as a yellow powder,
mp 306e308 ꢀC; IR (KBr): nmax 3027, 2919, 2893, 1677, 1620, 1587,
1575, 1425, 1383, 1206, 686, 670 cmꢁ1; 1H NMR (600 MHz, DMSO-
3. (a) Adegoke, E. A.; Alo, B. J. Heterocycl. Chem. 1983, 20, 1513; (b) Benchidmi, M.;
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2004, 40, 1510; (e) Kalinin, A. A.; Mamedov, V. A. Chem. Heterocycl. Compd.
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d6):
d
7.09 (d, 1H, J¼5.2 Hz, H6), 7.10 (d, 2H, J¼8.1 Hz, 2o-H phe-
nylimines), 7.15 (dd, 1H, J¼7.8, 7.6 Hz, p-H phenylimine), 7.38
(m, 3H, p-HPhþ2o-HPh), 7.42 (dd, 2H, J¼7.8, 7.6 Hz, 2m-H phenyl-
imines), 7.47e7.48 (m, 2H, 2m-HPh), 8.28 (d, 1H, J¼5.2 Hz, H7),
10.40 (s, 1H, H9), 11.50 (s, 1H, NH); 13C NMR (600 MHz, DMSO-d6):
4. (a) Mamedov, V. A.; Nurkhametova, I. Z.; Shagidullin, R. R.; Chernova, A. V.; Levin,
Y. A. Chem. Heterocycl. Compd.1999, 35, 855; (b) Mamedov, V. A.; Nurkhametova,
I. Z.; Rizvanov, I. K.; Efremov, Y. Y.; Levin, Y. A. Chem. Heterocycl. Compd. 1999, 35,
1364.
d
110.5 (C6), 121.8 (o-C(NPh)), 122.1 (C3a), 123.7 (C9a), 124.5
(C3), 125.4 (p-C(NPh)), 128.9 (m-C(Ph)), 130.0 (p-C(Ph)), 131.1
(m-C(NPh)), 131.2 (o-C(Ph)), 131.7 (i-C(Ph)), 135.8 (C5a), 139.9 (C9),
147.0 (C7), 151.5 (i-C(NPh)), 154.6 (C1), 155.2 (C4). Anal. Calcd for
C21H14N4OS: C, 68.09; H, 3.81; N, 15.12; S, 8.65. Found: C, 68.31; H,
3.77; N, 14.99; S, 8.69. The reaction mixture after separation of
compound 15 was treated with 5% water solution of NaHCO3, the
precipitate of dark brown colour was filtered, washed with water
(2ꢂ10 mL), dried in air and recrystallized (from i-PrOH) to yield
72% of 4-methoxycarbonylthiazoline 17 as white crystals, mp
105e106 ꢀC.
5. (a) Metzger, J. V. In The Chemistry of Heterocyclic Compounds; Wessberger, A.,
Taylor, E. C., Eds.; John Wiley & Sons: New$York-Chicheater-Brisbane-Toronto,
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29, 2146; (c) Humplett, W. J.; Lamon, R. W. J. Org. Chem. 1964, 29, 2148; (d)
Hanefeld, W.; Wurtz, S. J. Prakt. Chem. 2000, 342, 355; (e) Ge, Z.-M.; Cui, J.-L.;
ꢀ
Wang, Y.-L.; Cheng, T.-M.; Li, R.-T. Synthesis 2004, 1257; (f) Muraveva, K. M.;
Shchukina, M. N. Zh. Obshchei Khim. 1960, 30, 1327; (g) Tanaka, K.; Nomura, K.;
Oda, H.; Yoshida, S.; Mitsuhashi, K. J. Heterocycl. Chem. 1991, 28, 907.
6. 4-Hydroxythiazolidine 1a obtained in this paper with the use of symmetri-
cally substituted thiourea derivative we named ‘symmetrical’ 4-
hydroxythiazolidine, and we named 4-hydroxythiazolidines 1bed obtained
with the use of nonsymmetrically substituted thiourea derivatives ‘non-
symmetrical’ 4-hydroxythiazolidines.
7. Lindsey, R. J. In Comprehensive Organic Chemistry. The Synthesis and Reactions of
Organic Compounds; Barton, D., Ollis, W. D., Sutherland, I. O., Eds.; Pergamon:
1979; Vol. 2, Chapter 6.3.
Acknowledgements
This work was financially supported by the Russian Foundation
8. Chimichi, S.; Boccalini, M.; Matteucci, A.; Kharlamov, S. V.; Latypov, S. K.;
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Supplementary data
1D and 2D NMR spectra for all new compounds. Supplementary
data associated with this article can be found in the online version,
at http://dx.doi.org/10.1016/j.tet.2012.06.084. These data include
MOL files and InChiKeys of the most important compounds de-
scribed in this article.
References and notes
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