Efficient regioselective synthesis of novel water-soluble 2h,3h-[1,4]thiazino[2,3,4-ij]quinolin-4-ium derivatives by annulation reactions of 8-quinolinesulfenyl halides

Article abstract of DOI:10.3390/molecules26041116

Regioselective synthesis of novel 2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium derivatives has been developed by annulation reactions of 8-quinolinesulfenyl halides with vinyl chalcogenides (vinyl ethers, divinyl sulfide, divinyl selenide and phenyl vinyl

Full text of DOI:10.3390/molecules26041116

molecules
Article
Efficient Regioselective Synthesis of Novel Water-Soluble
2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium Derivatives by
Annulation Reactions of 8-quinolinesulfenyl Halides
Vladimir A. Potapov * , Roman S. Ishigeev and Svetlana V. Amosova
A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of The Russian Academy of Sciences,
1 Favorsky Str., 664033 Irkutsk, Russia; ishigeev@irioch.irk.ru (R.S.I.); amosova@irioch.irk.ru (S.V.A.)
* Correspondence: v.a.potapov@mail.ru
Abstract: Regioselective synthesis of novel 2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium derivatives
has been developed by annulation reactions of 8-quinolinesulfenyl halides with vinyl chalcogenides
(vinyl ethers, divinyl sulfide, divinyl selenide and phenyl vinyl sulfide) and tetravinyl silane. The
novel reagent 8-quinolinesulfenyl bromide was used in the annulation reactions. The influence of the
substrate structure and the nature of heteroatoms on the direction of the reactions and on product
yields has been studied. The opposite regiochemistry was observed in the reactions with vinyl
chalcogenides and tetravinyl silane. The obtained condensed heterocycles are novel water-soluble
functionalized compounds with promising biological activity.
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
Keywords: 2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium derivatives; annulation reactions; 8-quinolines-
ꢀꢁꢂꢃꢄꢅꢆ
ulfenyl halides; vinyl ethers; divinyl sulfide; divinyl selenide; phenyl vinyl sulfide; tetravinyl silane
Citation: Potapov, V.A.; Ishigeev,
R.S.; Amosova, S.V. Efficient
Regioselective Synthesis of Novel
Water-Soluble 2H,3H-[1,4]thiazino
[2,3,4-ij]quinolin-4-ium Derivatives
by Annulation Reactions of
1. Introduction
The quinoline ring continues to occupy an important place in medicinal chemistry as
a valuable scaffold, presenting in many natural and biologically active compounds [1–6].
The quinoline scaffold is an integral part of a variety of drugs, including antimalarial
medications (chloroquine, hydroxychloroquine, amodiaquine and primaquine) and fluoro-
quinolone antibiotics (ciprofloxacin, levofloxacin, gatifloxacin and moxifloxacin). Hydroxy-
chloroquine in combination with other medications was recently used for the treatment of
COVID-19 [7].
The sulfur-containing heterocycles are a structural part of many medications. Combi-
nations of nitrogen heterocycles with condensed sulfur-containing rings have often played
an important role in the discovery of new drugs [8]. Penicillin and cephalosporin scaf-
8-quinolinesulfenyl Halides.
Molecules 2021, 26, 1116. https://
doi.org/10.3390/molecules26041116
Academic Editor: Jacek Nycz
Received: 2 February 2021
Accepted: 16 February 2021
Published: 20 February 2021
folds are examples of useful combinations of condensed nitrogen and sulfur-containing
heterocycles in the structure of antibiotics.
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
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iations.
The combination of a quinoline heterocycle with a thiazine ring into a single fused
molecule provides a very promising scaffold for medicinal chemistry [
[1,4]thiazino [2,3,4-ij]quinolin-4-ium derivatives represent an important family of com-
pounds exhibiting various types of biological activity [12 20], including anticancer [18],
8–11]. The 2H,3H-
–
antibacterial [19] and antituberculosis [20] action (Figure 1). The fluoroquinolone antibiotic
rufloxacin is also a derivative of the 2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium scaffold.
The laboratory of organochalcogen compounds of the A. E. Favorsky Irkutsk Institute
of Chemistry develops effective approaches to novel chalcogen heterocycles by regioselec-
tive cyclization and annulation reactions of chalcogen-containing reagents [21–26].
Recently, we described the annulation reactions of 2-pyridinesulfenyl and 2-pyri- dine-
selenenyl halides with functionalized alkenes to afford 2H,3H-[1,3]thiazino[3,2-a]pyridin-4-
ium and 2H,3H-[1,3]selenazolo[3,2-a]pyridin-4-ium derivatives in high yields [27–32].
Copyright:
© 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
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conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Molecules 2021, 26, 1116. https://doi.org/10.3390/molecules26041116
https://www.mdpi.com/journal/molecules

Molecules 2021, 26, 1116
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In spite of some progress in synthetic methods for the preparation of 2H,3H-[1,4]thi-
azino[2,3,4-ij]quinolin-4-ium derivatives [33–38], the annulation reactions of 8-quino- line-
sulfenyl halides with vinylic heteroatom compounds, including vinylic ethers, sulfides,
selenides and silanes, are hitherto unknown.
Figure 1. Known biologically active compounds containing 2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-
ium scaffold (anticancer [18], antibacterial [19] and antituberculosis [20] activity).
The creation of synthetic approaches to novel derivatives of the [1,4]thiazino[2,3,4-
ij]quinolin-4-ium scaffold based on functionalized alkenes remains an important task. The
goal of this research is the development of regioselective synthesis of novel condensed
[1,4]thiazino[2,3,4-ij]quinolin-4-ium derivatives with promising biological activity based on
the annulation reactions of 8-quinolinesulfenyl halides with vinylic heteroatom compounds
(vinyl ethers, sulfides, selenides and silanes). Studying the influence of the substrate
structure and the nature of the heteroatom in vinylic compounds on the direction of
reactions and the yields of products is also a task of this research.
Efficient methods for the preparation of vinyl chalcogenides, including divinyl sulfide,
divinyl selenide and divinyl telluride, have been previously developed in this institute [39–45].
2. Results and Discussion
Responding to the increasing demand for structurally diverse heterocyclic com-
pounds with promising biological activity, we developed the synthesis of a new family
of [1,4]thiazino[2,3,4-ij]quinolin-4-ium derivatives based on the annulation reactions of
8-quinolinesulfenyl chloride and bromide (2a
ethers, divinyl sulfide, divinyl selenide, phenyl vinyl sulfide and tetravinyl silane). Divinyl
telluride was also studied in the reactions of sulfenyl halides 2a . The latter compounds
were generated in situ from di(8-quinolinyl) disulfide ( ) by the action of sulfuryl chloride
or bromine and used in further reactions without isolation (Scheme 1).
,b) with vinylic heteroatom compounds (vinyl
,
b
1
Scheme 1. The generation of 8-quinolinesulfenyl halides 2a, b from di(8-quinolinyl) disulfide 1 by
the action of sulfuryl chloride or bromine.

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It should be emphasized that quinolinesulfenyl bromide 2b was used in the reactions
for the first time. There is no information about sulfenyl bromide 2b in the literature (the
SciFinder database).
The reaction of sulfenyl chloride 2a with divinyl sulfide and selenide resulted in the
annulation of the dihydrothiazine cycle to the quinoline ring, affording water-soluble 3-
(vinylsulfanyl)- and 3-(vinylselanyl)-2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium chlorides
3, 4 in 94% and 50% yields, respectively (Scheme 2).
Scheme 2. Synthesis of condensed compounds 3, 4 from sulfenyl chloride 2a and divinyl sulfide and selenide.
The reaction of sulfenyl chloride 2a with divinyl sulfide proceeded more easily than
with divinyl selenide. The reaction with divinyl sulfide was carried out at room temperature
for 24 h to give product
70 h in order to obtain product
refluxing the mixture of sulfenyl chloride 2a and divinyl selenide led to an increase in the
yield of compound to 71%; however, the procedure was accompanied by the formation
3
in 94% yield, whereas the process with divinyl selenide required
4
in 50% yield. Attempts to intensify the reaction by
4
of some by-products, and in this case, the purification of the target compound
with difficulties.
4
met
The presence of vinylsulfanyl and vinylselanyl groups in compounds 3 and 4
opens
new possibilities for functionalization reactions as well as polymerization and copoly-
merization. It is known that vinyl sulfides can be easily involved in radical addition,
polymerization and copolymerization due to their high reactivity in radical reactions [39].
For example, radical polymerization or oligomerization of compound 3 can afford water-
soluble oligomeric or polymeric products, which may exhibit antibacterial activity.
Phenyl vinyl sulfide was involved in the reaction with sulfenyl chloride 2a. The
reaction was carried out at room temperature in methylene chloride to afford the condensed
product, 3-(phenylsulfanyl)-2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium chloride 5, in 97%
yield (Scheme 3). Like the reaction with divinyl sulfide, the annulation process proceeded in
a regioselective mode, and the addition of the sulfur atom of sulfenyl chloride 2a occurred
exclusively at the β-position of the vinylsulfanyl group.
Scheme 3. The reaction of sulfenyl chloride 2a with phenyl vinyl sulfide.
The reactions of sulfenyl bromide 2b with divinyl sulfide, divinyl selenide and phenyl
vinyl sulfide proceeded with low selectivity, and complex mixtures of products were
obtained in each case.

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The addition to the double bond was not observed in the reaction of sulfenyl halides
2a, b with divinyl telluride. This reaction proceeded as halogenation of the tellurium atom
with the formation of divinyltellurium dichloride and dibromide (6a
of sulfenyl halide 2a and divinyl telluride was used, divinyltellurium dihalides 6a
were obtained in 73% and 90% yields, respectively (Scheme 4).
,
b
). When a 2:1 ratio
,
b
,
b
Scheme 4. The formation of divinyltellurium dihalides 6a, b in the reaction of sulfenyl halides 2a, b
with divinyl telluride.
We suppose that the high affinity of the tellurium atom for halogens determines the
course of this reaction. It is known that organic tellurides can be used as dehalogenation
reagents. Previously, the formation of divinyltellurium dihalides 6a, b in high yields was
observed in the reactions of divinyl tellurides with bromine [46] as well as with selenium
dichloride [47].
Tetravinyl silane was chosen as a representative of vinyl silanes, reactive compounds
in the electrophilic addition due to the electron donating effect of the silicon atom, and
studied in the reactions with sulfenyl halides 2a, b. A 3-fold molar excess of tetravinyl
silane with respect to sulfenyl halides 2a
to only one vinyl group of tetravinyl silane.
The reaction of sulfenyl halides 2a
,
b
was used in order to realize selective addition
,
b with tetravinyl silane was found to proceed with
opposite regiochemistry compared to the annulation with divinyl sulfide, divinyl selenide
and phenyl vinyl sulfide. The products containing the sulfur atom attached to the -carbon
α
atom of the vinyl group, 2-trivinylsilyl-2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium halides
7a and 7b, were obtained in 98% and quantitative yields, respectively (Scheme 5).
Scheme 5. Synthesis of condensed compounds 7a, b from sulfenyl halides 2a, b and tetravinyl silane.
Vinyl ethers are among the most reactive compounds in electrophilic addition and
are promising substrates for annulation reactions. From vinyl ethers, isobutyl vinyl and
2-chloroethyl vinyl ethers were available, and we studied these compounds in the reactions
with sulfenyl halides 2a, b.
The reactions smoothly proceeded at room temperature in methylene chloride or
chloroform in a regioselective mode to afford the annulation products, 3-(2-methylpropoxy)-
and 3-(2-chloroethyl)-2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium chlorides (8a
bromides (8b, 9b), in 95–98% yields (Scheme 6).
, 9a) and

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Scheme 6. Synthesis of condensed products 8a
,
b
and 9a
,
b
from sulfenyl halides 2a
,
b
and isobutyl
vinyl and 2-chloroethyl vinyl ethers.
Cyclic vinyl ether, 2,3-dihydrofuran, was also involved in the reactions with sulfenyl
halides 2a, b. The reaction was carried out at room temperature in methylene chlo-
ride, leading to the condensed tetracyclic products, 7aH,8H,9H,10aH-furo[20,30:5,6]-2H,3H-
[1,4]thiazino[2,3,4-ij]quinolin-11-ium halides 10a and 10b, in 95% and 97% yields, respec-
tively (Scheme 7). Like the reaction with isobutyl vinyl and 2-chloroethyl vinyl ethers, the
annulation process proceeded in a regioselective manner, giving only one isomer. The
addition of the sulfur atom of sulfenyl halides 2a, b occurred exclusively at the β-position
of the vinyloxy moiety of 2,3-dihydrofuran.
Scheme 7. Synthesis of condensed products 10a, b from sulfenyl halides 2a, b and 2,3-dihydrofuran.
Thus, the annulation reactions with vinyl chalcogen compounds (vinyl ethers, divinyl
sulfide, divinyl selenide and phenyl vinyl sulfide) proceeded with the attachment of the
sulfur atom of sulfenyl halides 2a
group (“Markovnikov direction”), whereas the addition of the sulfur atom occurred at the
-carbon atom of the vinylsilyl moiety in the case of tetravinyl silane (“anti-Markovnikov
, b exclusively at the β-position of the vinylchacogenyl
α
direction”). Possible intermediates
to explain these trends.
A and B of these reactions (Scheme 8) can be considered
Scheme 8. Directions of the reactions of sulfenyl halides 2a, b with vinyl chalcogenides and tetravinyl silane.

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It is known that the chalcogen atoms (oxygen, sulfur, selenium) stabilize well the
adjacent carbocation as in intermediate
cation at the -position of the vinylchalcogenyl group (Scheme 8). On the other hand, it
is known that electrophilic attack on the vinylsilyl moiety usually occurs at the -carbon
atom of the double bond, placing the developing carbocation at the -position ( -effect,
intermediate ) [48]. The -effect of silicon is a special type of hyperconjugation that
describes the stabilizing influence of the silicon atom on the development of positive
charge at the -carbon atom [49]. This effect manifests itself in the addition reaction of
A, which is formed by the addition of the sulfenyl
β
α
β
β
B
β
β
arenesulfenyl chlorides to vinyl silanes, leading to anti-Markovnikov adducts [48], whereas
the reactions of arenesulfenyl chlorides with vinyl ethers and vinyl sulfides proceed with
the opposite regiochemistry [50].
The structural assignments of synthesized compounds were made using 1H and 13C-
NMR spectroscopy (Supplementary Materials containing examples of 1H- and 13C-NMR
spectra are available online), including two-dimensional experiments, and were confirmed
by elemental analysis. The products of opposite regiochemistry have characteristic signals
of the carbon atoms bonded with charged nitrogen (N+): CH2N+ (~60 ppm) in 13C-NMR
spectra of products 7a, b
(obtained from tetravinyl silane), SCHN+ (~73 and ~75 ppm)
in 13C-NMR spectra of products (obtained from vinyl sulfides) and OCHN+ (~93–
3,5
97 ppm) in 13C-NMR spectra of products 8a
, b–10a, b (obtained from vinyl ethers and
2,3-dihydrofuran).
3. Experimental Section
3.1. General Information
1H (400.1 MHz), 13C (100.6 MHz) and 29Si (79.5 MHz) NMR spectra were recorded
on a Bruker DPX-400 spectrometer (Bruker BioSpin GmbH, Rheinstetten, Germany) in
2–5% solution in D2O. 1H, 13C and 29Si chemical shifts (
δ
) are reported in parts per million
(ppm), relative to tetramethylsilane (external) or to the residual solvent peaks of D2O
= 4.79). Elemental analysis was performed on a Thermo Scientific FLASH 2000 Organic
(δ
Elemental Analyzer (Thermo Fisher Scientific Inc., Milan, Italy). Analytical determination
of silicon was made by the gravimetric method [51]. Melting points were determined on a
Kofler Hot-Stage Microscope PolyTherm A apparatus (Wagner & Munz GmbH, München,
Germany). Absolute solvents were used in the reactions.
3.2. Synthesis of Compounds 3–10a,b
3-(Vinylsulfanyl)-2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium chloride (3). A solution of sulfuryl
chloride (0.079 g, 0.59 mmol) in chloroform (10 mL) was added dropwise to a solution of
di(8-quinolinyl) disulfide (0.188 g, 0.59 mmol) in chloroform (10 mL), and the mixture was
stirred for 10 min at room temperature. A solution of divinyl sulfide (0.101 g, 1.18 mmol)
in chloroform (10 mL) was added dropwise, and the reaction mixture was stirred for 24 h
at room temperature. The solvent was removed by rotary evaporator. The residue was
washed with hexane and dried in vacuum, giving product
3 (0.311 g, 94% yield) as a light
1
yellow oil. H-NMR (400 MHz, D2O):
δ 3.86 (dd, J 14.4, 3.0 Hz, 1H, SCH2), 4.09 (dd, J 14.4,
2.3 Hz, 1H, SCH2), 5.39 (d, J 16.4 Hz, 1H, =CH2,), 5.68 (d, J 9.0 Hz, 1H, =CH2), 6.71 (s,
1H, NCH), 6.78 (dd, J 16.4, 9.0 Hz, 1H, SCH=), 7.88–7.92 (m, 1H, Cquino), 8.01–8.04 (m, 1H,
Cquino), 8.11–8.16 (m, 2H, Cquino), 9.13–9.17 (m, 2H, Cquino). 13C-NMR (101 MHz, D2O):
δ
28.95 (SCH2), 73.19 (NCH), 121.15 (=CH2), 125.47 (Cquino), 126.47 (Cquino), 127.96 (Cquino),
129.57 (=CH), 131.62 (Cquino), 131.80 (Cquino), 133.49 (Cquino), 134.35(Cquino), 147.28 (Cquino),
150.39 (Cquino). Anal. Calcd for C13H12ClNS2): C 55.40, H 4.29, Cl 12.58, N 4.97, S 22.76.
Found: C 55.65, H 4.53, Cl 12.29, N 5.15, S 23.01.
3-(Vinylselanyl)-2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium chloride (4). A solution of sulfuryl
chloride (0.095 g, 0.7 mmol) in chloroform (10 mL) was added dropwise to a solution of
di(8-quinolinyl) disulfide (0.224 g, 0.7 mmol) in chloroform (10 mL), and the mixture was
stirred for 10 min at room temperature. A solution of divinyl selenide (0.186 g, 1.4 mmol)
in chloroform (10 mL) was added dropwise, and the reaction mixture was stirred for 70 h

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at room temperature. The solvent was removed by rotary evaporator. The residue was
washed with hexane and dried in vacuum, giving product
4 (0.23 g, 50% yield) as a light
yellow oil. 1H-NMR (400 MHz, D2O):
δ
3.83 (dd, J 14.3, 3.2 Hz, 1H, SeCH2), 4.09 (dd,
J 14.3, 2.3 Hz, 1H, SeCH2), 5.49 (d, J 16.7 Hz, 1H, =CH2), 5.99 (d, J 9.0 Hz, 1H, =CH2), 6.77
(m, 1H, NCH), 7.03 (dd, J 16.7, 9.0 Hz, 1H, SeCH=), 7.77–7.81 (m, 1H, Cquino), 7.92–7.95
(m, 1H, Cquino), 8.00–8.05 (m, 2H, Cquino), 9.04–9.08 (m, 2H, Cquino). 13C-NMR (101 MHz,
D2O): δ 30.09 (SeCH2), 66.78 (NCH), 121.39 (=CH2), 121.56 (Cquino), 125.50 (=CH), 128.06
(Cquino), 129.65 (Cquino), 129.95 (Cquino), 130.29 (Cquino), 131.79 (Cquino), 133.59 (Cquino),
146.91 (Cquino), 150.12 (CN+,Cquino). Anal. Calcd for C13H12ClNSSe: C 47.50, H 3.68, Cl
10.79, N 4.26, S 9.75. Found: C 47.35, H 3.83, Cl 10.61, N 4.45, S 10.02.
3-(Phenylsulfanyl)-2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium chloride (5). A solution of sul-
furyl chloride (0.081 g, 0.6 mmol) in methylene chloride (5 mL) was added dropwise to a
solution of di(8-quinolinyl) disulfide (0.192 g, 0.6 mmol) in methylene chloride (10 mL), and
the mixture was stirred for 10 min at room temperature. A solution of phenyl vinyl sulfide
(0.163 g, 1.2 mmol) in methylene chloride (10 mL) was added dropwise, and the reaction
mixture was stirred for 24 h at room temperature. The solvent was removed by rotary
evaporator. The residue was washed with hexane and dried in vacuum, giving product
1
5
(0.386 g, 97% yield) as a light yellow oil. H-NMR (400 MHz, D2O):
δ
3.92 (dd, J 14.4,
2.9 Hz, 1H, SCH2), 4.10 (dd, J 14.4, 2.0 Hz, 1H, SCH2), 6.52 (s, 1H, NCH), 7.09–7.11 (m, 2H,
Ar), 7.33–7.37 (m, 2H, Ar), 7.50–7.57 (m, 2H, Cquino), 7.85–7.89 (m, 1H, Ar), 8.07–8.10 (m,
3H, Cquino), 9.02–9.04 (m, 1H, Cquino). 13C-NMR (101 MHz, D2O):
δ 28.24 (SCH2), 75.21
(NCH), 120.30 (Ar), 125.16 (Cquino), 126.99 (Cquino), 127.64 (Cquino), 129.31 (Cquino), 129.94
(Ar), 130.82 (Cquino), 131.23 (Ar), 132.96 (Cquino), 135.50 (Ar), 146.41 (Cquino), 150.04 (Cquino).
Anal. Calcd for C17H14ClNS2: C 61.52, H 4.25, N 4.22, Cl 10.68, S 19.32. Found: C 61.94,
H 4.52, N 4.42, Cl 10.93, S 19.13.
2-(Trivinylsilyl)-2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium chloride (7a). A solution of sulfuryl
chloride (87 mg, 0.64 mmol) in methylene chloride (5 mL) was added dropwise to a
solution of di(8-quinolinyl) disulfide (206 mg, 0.64 mmol) in methylene chloride (10 mL),
and the mixture was stirred for 10 min at room temperature. The obtained solution of
8-quinolinesulfenyl chloride was added dropwise to a solution of tetravinylsilane (500 mg,
3.68 mmol) in methylene chloride (10 mL), and the reaction mixture was stirred for 72 h
at room temperature. The solvent was removed by rotary evaporator. The residue was
washed with hexane and dried in vacuum, giving product 7a (416 mg, 98% yield) as a
1
dark yellow oil. H-NMR (400 MHz, D2O):
δ 3.42 (m, 1H, SCH), 5.07–5.11 (m, 1H, NCH2),
5.34 (m, 1H, NCH2), 6.04 (m, 3H, SiCH=), 6.20–6.35 (m, 6H, =CH2), 7.75–7.80 (m, 1H,
Cquino), 7.95–8.06 (m, 3H, Cquino), 9.05–9.09 (m, 2H, Cquino). 13C-NMR (101 MHz, D2O):
δ
22.42 (SCH), 60.91 (NCH2), 121.60 (Cquino), 127.18 (Cquino), 129.30 (SiCH=CH2), 131.18
(Cquino), 132.65 (Cquino), 134.08 (Cquino), 135.36 (Cquino), 139.03 (SiCH=CH2), 148.38 (Cquino),
149.12 (Cquino), 182.44 (Cquino). 29Si-NMR (400 MHz, D2O):
–21.78. Anal. Calcd for
δ
C17H18ClNSSi: C 61.51, H 5.47, Cl 10.68, N 4.22, S 9.66, Si 8.46. Found: C 61.87; H 5.65; Cl
10.76, N 4.09, S 9.93, Si 8.25.
2-(Trivinylsilyl)-2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium bromide (7b). A solution of bromine
(45 mg, 0.28 mmol) in methylene chloride (2 mL) was added dropwise to a solution of di(8-
quinolinyl) disulfide (90 mg, 0.28 mmol) in methylene chloride (10 mL), and the mixture
was stirred for 10 min at room temperature. The obtained solution of 8-quinolinesulfenyl
bromide was added dropwise to a solution of tetravinylsilane (230 mg, 1.69 mmol) in
methylene chloride (10 mL), and the reaction mixture was stirred for 72 h at room tem-
perature. The solvent was removed by rotary evaporator, and the residue was dried in
1
vacuum, giving product 7b (211 mg, quantitative yield) as a dark yellow oil. H-NMR
(400 MHz, D2O):
6.02–6.08 (m, 3H, SiCH=), 6.21–6.34 (m, 6H, =CH2), 7.80–7.84 (m, 1H, Cquino), 7.95–8.07
(m, 3H, Cquino), 9.05–9.10 (m, 2H, Cquino). 13C-NMR (101 MHz, D2O):
22.78 (SCH), 61.35
(NCH2), 121.94 (Cquino), 127.58 (Cquino), 129.79 (SiCH=CH2), 131.64 (Cquino), 133.09 (Cquino),
δ 3.46 (m, 1H, SCH), 5.12–5.19 (m, 1H, NCH2), 5.35 (m, 1H, NCH2),
δ

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134.12 (Cquino), 135.41 (Cquino), 139.37 (SiCH=CH2), 148.76 (Cquino), 149.51 (Cquino), 188.91
(Cquino). 29Si-NMR (400 MHz, D2O):
δ
–21.83. Anal. Calcd for C17H18BrNSSi: C 54.25, H
4.82, Br 21.23, N 3.72, S 8.52, Si 7.46. Found: C 54.67, H 5.01, Br 21.05, N 3.91, S 8.32, Si 7.28.
3-(2-Methylpropoxy)-2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium chloride (8a A solution of
).
sulfuryl chloride (46 mg, 0.34 mmol) in methylene chloride (2 mL) was added dropwise to
a solution of di(8-quinolinyl) disulfide (109 mg, 0.34 mmol) in methylene chloride (8 mL),
and the mixture was stirred for 10 min at room temperature. The obtained solution of
8-quinolinesulfenyl chloride was added dropwise to a solution of isobutyl vinyl ether
(80 mg, 0.8 mmol) in methylene chloride (10 mL), and the reaction mixture was stirred for
20 h at room temperature. The solvent was removed by rotary evaporator. The residue was
washed with hexane and dried in vacuum, giving product 8a (193 mg, 96% yield) as a light
1
yellow powder, mp 138–139 ◦C (decomp). H-NMR (400 MHz, D2O):
δ 0.68 (d, J 6.7 Hz,
3H, CH3), 0.80 (d, J 6.7 Hz, 3H, CH3), 1.74–1.81 (m, 1H, CH), 3.29–3.33 (m, 1H, SCH2),
3.71–3.84 (m, 3H, OCH2, SCH2), 6.49 (m, 1H, NCH), 7.86–7.90 (m, 1H, Cquino), 8.08–8.15 (m,
3H, Cquino), 9.22–9.24 (m, 1H, Cquino), 9.34–9.36 (m, 1H, Cquino). 13C-NMR (101 MHz, D2O):
δ
18.01 (CH3), 27.46 (CH), 28.48 (SCH2), 76.50 (OCH2), 91.67 (NCH), 121.13 (Cquino), 122.41
(Cquino), 127.43 (Cquino), 129.49 (Cquino), 133.11 (Cquino), 134.24 (Cquino), 148.12 (Cquino),
149.11 (Cquino), 151.09 (Cquino). Anal. Calcd for C15H18ClNOS: C 60.90, H 6.13, Cl 11.98,
N 4.73, S 10.84. Found: C 61.18, H 6.29, Cl 12.17, N 4.56, S 11.05.
3-(2-Methylpropoxy)-2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium bromide (8b). A solution of
bromine (42 mg, 0.26 mmol) in methylene chloride (2 mL) was added dropwise to a
solution of di(8-quinolinyl) disulfide (84 mg, 0.26 mmol) in methylene chloride (8 mL),
and the mixture was stirred for 10 min at room temperature. The obtained solution of
8-quinolinesulfenyl bromide was added dropwise to a solution of isobutyl vinyl ether
(60 mg, 0.6 mmol) in methylene chloride (10 mL), and the reaction mixture was stirred for
20 h at room temperature. The solvent was removed by rotary evaporator. The residue was
washed with hexane and dried in vacuum, giving product 8a (172 mg, 97% yield) as a light
1
yellow powder, mp 135–137 ◦C (decomp). H-NMR (400 MHz, D2O):
δ
0.68 (d, J 6.6 Hz,
3H, CH3), 0.80 (d, J 6.6 Hz, 3H, CH3), 1.74–1.81 (m, 1H, CH), 3.31 (m, 1H, SCH2), 3.70–3.74
(m, 2H, OCH2), 3.82 (m, 1H, SCH2), 6.49 (m, 1H, NCH), 7.86–7.90 (m, 1H, Cquino), 8.07–8.15
(m, 3H, Cquino), 9.20–9.24 (m, 1H, Cquino), 9.33–9.36 (m, 1H, Cquino). 13C-NMR (101 MHz,
D2O):
δ 17.82, 17.88 (CH3), 27.32 (CH), 28.32 (SCH2), 76.35 (OCH2), 91.51 (NCH), 120.97
(Cquino), 122.34 (Cquino), 127.25 (Cquino), 129.30 (Cquino), 132.93 (Cquino), 134.18 (Cquino),
148.01 (Cquino), 149.01 (Cquino), 150.92 (Cquino). Anal. Calcd for C15H18NBrOS: C 52.94,
H 5.33, Br 23.48, N 4.12, S 9.42. Found: C 53.11, H 5.51, Br 23.65, N 3.98, S 9.23.
3-(2-Chloroethoxy)-2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium chloride (9a) was obtained as
a light yellow oil in 95% yield under similar conditions to the synthesis of compound 8a
.
1H-NMR (400 MHz, D2O):
δ
3.66–3.70 (m, 2H, CH2Cl), 3.78–3.85 (m, 2H, SCH2), 3.90–3.95
(m, 1H, OCH2), 4.27–4.32 (m, 1H, OCH2), 6.50 (d, J 1.5 Hz, 1H, NCH), 7.86–7.90 (m, 1H,
Cquino), 8.09–8.15 (m, 3H, Cquino), 9.22–9.24 (m, 1H, Cquino), 9.39–9.40 (m, 1H, Cquino). 13C-
NMR (101 MHz, D2O): δ 28.30 (SCH2), 42.60 (CH2Cl), 70.06 (OCH2), 91.39 (NCH), 121.30
(Cquino), 125.55 (Cquino), 127.55 (Cquino), 129.53 (Cquino), 131.68 (Cquino), 133.26 (Cquino),
148.29 (Cquino), 151.33 (Cquino). Anal. Calcd for C13H13NCl2OS: C 51.66, H 4.34, N 4.63,
Cl 23.46, S 10.61. Found: C 51.95, H 4.66, N 4.89, Cl 23.31, S 10.39.
3-(2-Chloroethoxy)-2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium bromide (9b) was obtained as
a light yellow oil in 98% yield under similar conditions to the synthesis of compound 8b
.
1H-NMR (400 MHz, D2O):
δ
3.64–3.69 (m, 2H, CH2Cl), 3.76–3.84 (m, 2H, SCH2), 3.89–3.95
(m, 1H, OCH2), 4.25–4.31 (m, 1H, OCH2), 6.49 (d, J 1.5 Hz, 1H, NCH), 7.85–7.91 (m, 1H,
Cquino), 8.09–8.17 (m, 3H, Cquino), 9.23–9.26 (m, 1H, Cquino), 9.41–9.46 (m, 1H, Cquino). 13C-
NMR (101 MHz, D2O):
δ 28.38 (SCH2), 42.67 (CH2Cl), 70.13 (OCH2), 91.42 (NCH), 121.35
(Cquino), 125.59 (Cquino), 127.60 (Cquino), 129.57 (Cquino), 131.76 (Cquino), 133.32 (Cquino),

Molecules 2021, 26, 1116
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148.33 (Cquino), 151.42 (Cquino). Anal. Calcd for C13H13BrClNOS: C 45.04, H 3.78, N 4.04,
S 9.25. Found: C 44.79, H 3.96, N 3.98, S 9.45.
7aH,8H,9H,10aH-Furo[20,30:5,6]-2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-11-ium chloride (10a).
A
solution of sulfuryl chloride (60 mg, 0.44 mmol) in methylene chloride (5 mL) was added
dropwise to a solution of di(8-quinolinyl) disulfide (141 mg, 0.44 mmol) in methylene
chloride (10 mL), and the mixture was stirred for 10 min at room temperature. The
obtained solution of 8-quinolinesulfenyl chloride was added dropwise to a solution of 2,3-
dihydrofuran (63 mg, 0.9 mmol) in methylene chloride (10 mL), and the reaction mixture
was stirred for 24 h at room temperature. The solvent was removed by rotary evaporator.
The residue was washed with hexane and dried in vacuum, giving product 10a (222 mg,
95% yield) as a light yellow oil. 1H-NMR (400 MHz, D2O):
δ 1.90–2.01 (m, 1H, CH2),
2.62–2.70 (m, 1H, CH2), 4.14–4.19 (m, 1H, SCH), 4.31–4.35 (m, 1H, CH2O), 6.51 (d, 1H,
3
OCHN+, J = 4.6 Hz), 7.86–7.90 (m, 1H, Cquino), 8.12–8.18 (m, 3H, Cquino), 9.16–9.18 (m,
1H, Cquino), 9.57–9.59 (m, 1H, N+Cquino). 13C-NMR (101 MHz, D2O):
δ 28.08 (CH2), 37.55
(SCH), 69.30 (CH2O), 91.63 (OCHN+), 121.41 (Cquino), 121.86 (Cquino), 127.60 (Cquino), 129.15
(Cquino), 129.19 (Cquino), 130.60 (Cquino), 133.76 (Cquino), 146.08 (Cquino), 149.45 (CN+,Cquino).
Anal. Calcd for C13H12ClNOS: C 58.75, H 4.55, Cl 13.34, N 5.27, S 12.07. Found: C 59.02,
H 4.38, Cl 13.61, N 5.47, S 11.93.
7aH,8H,9H,10aH-Furo[20,30:5,6]-2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-11-ium bromide (10b).
A
solution of bromine (70 mg, 0.44 mmol) in methylene chloride (10 mL) was added dropwise
to a solution of di(8-quinolinyl) disulfide (141 mg, 0.44 mmol) in methylene chloride
(10 mL), and the mixture was stirred for 10 min at room temperature. The obtained solution
of 8-quinolinesulfenyl bromide was added dropwise to a solution of 2,3-dihydrofuran
(63 mg, 0.9 mmol) in methylene chloride (10 mL), and the reaction mixture was stirred for
20 h at room temperature. The solvent was removed by rotary evaporator. The residue
was washed with hexane and dried in vacuum, giving product 10b (265 mg, 97% yield) as
1
a light yellow oil. H-NMR (400 MHz, D2O):
δ
1.93–2.04 (m, 1H, CH2), 2.65–2.74 (m, 1H,
CH2), 4.14–4.19 (m, 1H, SCH), 4.29–4.35 (m, 1H, CH2O), 6.50 (d, 1H, OCHN+, 3J = 4.6 Hz),
7.84–7.88 (m, 1H, Cquino), 8.09–8.18 (m, 3H, Cquino), 9.15–9.17 (m, 1H, Cquino), 9.54–9.57 m
(1H, N+Cquino). 13C-NMR (101 MHz, D2O):
δ 27.83 (CH2), 37.29 (SCH), 69.05 (CH2O), 91.35
(OCHN+), 121.60 (Cquino), 127.34 (Cquino), 128.88 (Cquino), 130.35 (Cquino), 133.50 (Cquino),
145.80 (Cquino), 149.18 (CN+, Cquino). Anal. Calcd for C13H12BrNOS: C 50.33, H 3.90, N 4.52,
Br 25.76, S 10.34. Found: C 50.61, H 4.07, N 4.35, Br 26.03, S 10.53.
4. Conclusions
An efficient synthetic approach to 2H,3H-[1,4]thiazino[2,3,4-ij]quinolin-4-ium deriva-
tives has been developed by regioselective annulation reactions of 8-quinolinesulfenyl
halides with vinyl chalcogenides (vinyl ethers, divinyl sulfide, divinyl selenide and phenyl
vinyl sulfide) and tetravinyl silane. 8-Quinolinesulfenyl bromide was used for the first
time. The obtained compounds 3–5, 7a, b–10a, b are water-soluble, and this property is
favorable with respect to possible biological activeity.
The annulation reactions with vinyl chalcogenides proceeded with the attachment
of the sulfur atom of 8-quinolinesulfenyl halides exclusively at the
β-position of the
vinylchacogenyl group, whereas the opposite regiochemistry was observed in the case of
tetravinyl silane. The reactivity of vinyl chalcogenides in the annulation reactions was
found to decrease in the following order: vinyl ethers > vinyl sulfides > vinyl selenide.
This corresponds to the reactivity order of vinyl chalcogenides in electrophilic addition
reactions [52].

Molecules 2021, 26, 1116
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Supplementary Materials: The following are available online: examples of 1H- and 13C-NMR
spectra of the obtained compounds.
Author Contributions: Conceptualization and paper preparation, V.A.P.; methodology and research
experiments, R.S.I.; data curation and supervision, S.V.A. All authors have read and agreed to the
published version of the manuscript.
Funding: This research received no external funding.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Acknowledgments: The authors thank Baikal Analytical Center SB RAS for providing the instru-
mental equipment for structural investigations.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.
Sample Availability: Samples of the compounds are not available from the authors.
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