molecules
Article
Fused 1,2,3-Dithiazoles: Convenient Synthesis,
Structural Characterization, and
Electrochemical Properties
Lidia S. Konstantinova 1,2 , Ilia V. Baranovsky 1 , Irina G. Irtegova 3 , Irina Y. Bagryanskaya 3,4 ,
Leonid A. Shundrin 3,4 , Andrey V. Zibarev 3,5 and Oleg A. Rakitin 1,2, *
1
2
3
4
5
*
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russia;
[email protected] (L.S.K.); [email protected] (I.V.B.)
Nanotechnology Education and Research Center, South Ural State University, 454080 Chelyabinsk, Russia
N. N. Vorozhtsov Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences,
630090 Novosibirsk, Russia; [email protected] (I.G.I.); [email protected] (I.Y.B.);
[email protected] (L.A.S.); [email protected] (A.V.Z.)
Department of Natural Sciences, National Research University–Novosibirsk State University,
630090 Novosibirsk, Russia
Department of Chemistry, National Research University–Tomsk State University, 634050 Tomsk, Russia
Correspondence: [email protected]; Tel.: +7-499-135-53-27; Fax: +7-499-135-53-28
Academic Editors: Panayiotis A. Koutentis and Andreas S. Kalogirou
Received: 28 March 2016; Accepted: 29 April 2016; Published: 6 May 2016
Abstract: A new general protocol for synthesis of fused 1,2,3-dithiazoles by the reaction of cyclic
oximes with S2 Cl2 and pyridine in acetonitrile has been developed. The target 1,2,3-dithiazoles fused
with various carbocycles, such as indene, naphthalenone, cyclohexadienone, cyclopentadiene, and
benzoannulene, were selectively obtained in low to high yields. In most cases, the hetero ring-closure
was accompanied by chlorination of the carbocyclic moieties. With naphthalenone derivatives,
a novel dithiazole rearrangement (15Ñ13) featuring unexpected movement of the dithiazole
ring from α- to β-position, with respect to keto group, was discovered. Molecular structure of
4-chloro-5H-naphtho[1,2-d][1,2,3]dithiazol-5-one 13 was confirmed by single-crystal X-ray diffraction.
Electrochemical properties of 13 were studied by cyclic voltammetry and a complex behavior was
observed, most likely including hydrodechlorination at a low potential.
Keywords:
fused 1,2,3-dithiazoles;
cyclic voltammetry
synthesis;
sulfur monochloride;
X-ray diffraction;
1. Introduction
1,2,3-Dithiazoles, the five membered sulfur-nitrogen heterocycles, are promising for science and
technology because of their biological activity, unusual chemical transformations and interesting
physical properties [1–3]. In particular it has been shown that the 1,2,3-dithiazole scaffold can be
effectively used in the design and synthesis of stable neutral and negatively charged radicals (i.e.,
radical anions)—actual or potential building blocks for molecule-based conductive and/or magnetic
functional materials [4–7]. One can imagine that continued exploration of the 1,2,3-dithiazole chemistry
is guaranteed to yield new compounds of fundamental and/or applied significance.
Normally, monocyclic 1,2,3-dithiazoles are prepared from 4,5-dichloro-1,2,3-dithiazolium chloride
(the Appel salt) as the key synthon [8,9]. Benzo-fused 1,2,3-dithiazolium chlorides (the Herz salts)
can be easily prepared by the Herz reaction from aromatic amines and sulfur monochloride S2 Cl2 .
Although this reaction has been known for about one hundred years, it is still used nowadays as
well [10,11].
Molecules 2016, 21, 596; doi:10.3390/molecules21050596
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Other
synthetic
precursors
of
1,2,3-dithiazoles
are
cyclic
oximes
used
reactions
Other
of fused
1,2,3-dithiazoles
are cyclic
in reactions
S2 Cl2
Other synthetic
syntheticprecursors
precursors
of fused
fused
1,2,3-dithiazoles
are oximes
cyclic used
oximes
used in
inwith
reactions
with
S
2Cl2 in the presence of organic bases such as N-ethyldiisopropylamine (Hünig’s base) and
in
the Spresence
of organic
bases
such as N-ethyldiisopropylamine
(Hünig’s base) and
triisobutylamine.
with
2Cl2 in the
presence
of organic
bases such as N-ethyldiisopropylamine
(Hünig’s
base) and
triisobutylamine.
disadvantage
of
procedure
and
The
disadvantageThe
of this
method is that
no method
general is
procedure
is established
andis
all cases arduous
triisobutylamine.
The
disadvantage
of this
this
method
is that
that no
no general
general
procedure
isinestablished
established
and in
in
all
cases
arduous
purification
of
products
by
column
chromatography
is
required
[12–15].
purification
of products
by column
chromatography
required [12–15].is required [12–15].
all cases arduous
purification
of products
by columnischromatography
During our
with
SS22Cl
found
that
reaction
conditions
and
of
During
ourongoing
ongoingwork
work
with
Cl2 have
we have
the reaction
conditions
and
our
ongoing
work
with
ClS222we
we
have
foundfound
that the
thethat
reaction
conditions
and nature
nature
of
the
organic
base
have
a
crucial
role
influencing
the
yields
of
the
target
sulfur-nitrogen
heterocycles
nature
of the
organic
haverole
a crucial
role influencing
the target sulfur-nitrogen
the organic
base
have base
a crucial
influencing
the yields ofthe
theyields
targetofsulfur-nitrogen
heterocycles
[16–19].
shown
that
many
organic
bases,
such
as
example
heterocycles
[16–19].
It was
that many
nitrogen
organic
such asamines,
tertiaryfor
amines,
for
[16–19]. It
It was
was
shown
that shown
many nitrogen
nitrogen
organic
bases,
suchbases,
as tertiary
tertiary
amines,
for
example
1,4-diazabicyclooctane
(DABCO),
interact
with
S
2Cl2 forming ionic complexes in some cases [17].
example
1,4-diazabicyclooctane
interact
S2 Cl2ionic
forming
ionic complexes
in some
1,4-diazabicyclooctane
(DABCO),(DABCO),
interact with
S2Cl2with
forming
complexes
in some cases
[17].
However,
the
of
our
knowledge,
possible
between
Cl
cases
[17]. to
However,
of our knowledge,
possible interaction/complexation
S2 Cla2a
However,
to
the best
bestto
ofthe
ourbest
knowledge,
possible interaction/complexation
interaction/complexation
between SS22between
Cl22 and
and such
such
strong
nitrogen
organic
base
such
pyridine
has
not
investigated.
and
such
a strong
nitrogen
organic
base
such as
pyridine
has
not been investigated.
strong
nitrogen
organic
base
such as
as
pyridine
has
not been
been
investigated.
In
this
paper
we
report
a
study
of
a
reaction
between
cyclic
oximes
and
2/pyridine covering
a study
of aof
reaction
between
cyclic cyclic
oximesoximes
and SS22Cl
Cl
2/pyridine
covering
In this
this paper
paperwe
wereport
report
a study
a reaction
between
and
S2 Cl2 /pyridine
selective
synthesis
of
fused
1,2,3-dithiazoles
together
with
their
structural
characterization
selective selective
synthesis
of fused
1,2,3-dithiazoles
together
withwith
their
structural
covering
synthesis
of fused
1,2,3-dithiazoles
together
their
structuralcharacterization
characterization by
by
single-crystal X-ray
X-ray diffraction
diffraction (XRD)
(XRD) and
and investigation
investigation of
of their
their electrochemical
electrochemical properties
properties by
by
cyclic
by cyclic
cyclic
single-crystal
voltammetry
(CV).
voltammetry (CV).
(CV).
voltammetry
2.
2.
Resultsand
andDiscussion
Discussion
2. Results
Results
and
Discussion
2.1.
2.1. Syntheses
Syntheses
an
effort
to
improve
the
synthesis
fused
1,2,3-dithiazoles,
re-investigated
reaction
In
wewe
re-investigated
thethe
reaction
of
In an
an effort
effortto
toimprove
improvethe
thesynthesis
synthesisofof
offused
fused1,2,3-dithiazoles,
1,2,3-dithiazoles,
we
re-investigated
the
reaction
of
oxime
11 with
of
SS22Cl
2 in dimethylformamide
i.e., a
1-indanone
oxime
1 with
S2 Cl2SS.22Cl
Treatment
of 1 with
dimethylformamide
(DMF),(DMF),
i.e., a solvent
2 Cl2 in
of 1-indanone
1-indanone
oxime
with
Cl22.. Treatment
Treatment
of 11 Swith
with
Cl
2 in dimethylformamide (DMF), i.e., a
˝to
2
Cl
2
reactions
[16,19],
in
the
temperature
range
from
−25
20
°C
solvent
which
is
frequently
used
in
S
which
is
frequently
used
in
S
Cl
reactions
[16,19],
in
the
temperature
range
from
´25
to
20
C
gave
2 2in S2Cl2 reactions [16,19], in the temperature range from −25 to 20
°C
solvent which is frequently used
gave
8-chloroindeno[1,2-d]-1,2,3-dithiazole
2
in
low
yields.
Note,
that
in
this
case
the
hetero
ring-closure
8-chloroindeno[1,2-d]-1,2,3-dithiazole
2
in
low
yields.
Note,
that
in
this
case
the
hetero
ring-closure
was
gave 8-chloroindeno[1,2-d]-1,2,3-dithiazole 2 in low yields. Note, that in this case the hetero ring-closure
was
by
The
of
was
for
the
of
accompanied
by chlorination.
The type
of base
usedused
was important
for the
of reactions
with
was accompanied
accompanied
by chlorination.
chlorination.
The type
type
of base
base
used
was important
important
forsuccess
the success
success
of reactions
reactions
S
2
Cl
2
in
other
solvents,
such
as
chloroform
or
acetonitrile
(MeCN).
Reaction
of
1
with
a
two-fold
Swith
Cl
in
other
solvents,
such
as
chloroform
or
acetonitrile
(MeCN).
Reaction
of
1
with
a
two-fold
excess
2 2 S2Cl2 in other solvents, such as chloroform or acetonitrile (MeCN). Reaction of 1 with a two-fold
with
excess
SS22Cl
2 and DABCO
in chloroform
to complex
mixtures
containing
2 inyield
the yield
of
of
S2 Clof
in chloroform
at ´5 ˝atC−5
led°Ctoled
complex
mixtures
containing
2 in the
of 35%.
2 and
excess
of
ClDABCO
2 and DABCO in chloroform at −5 °C led to complex mixtures containing 2 in the yield of
35%.
The
best
results
were
achieved
by
treating
1
with
a
three-fold
excess
of
S
2Cl
2a
or
a
four-fold
excess
The
best
results
were
achieved
by
treating
1
with
a
three-fold
excess
of
S
Cl
or
four-fold
excess
of
2
2
35%. The best results were achieved by treating 1 with a three-fold excess of S2Cl2 or a four-fold excess
of
MeCN
11 h
gave
target
selectively
81%
yield
(Scheme
1).
The
main
pyridine
in in
MeCN
at at
5 ˝55C°C
forfor
1h
which
gave
of pyridine
pyridine
in
MeCN
at
°C
for
h which
which
gavetarget
target2 22selectively
selectivelyinin
in81%
81%yield
yield(Scheme
(Scheme1).
1). The
The main
main
this
and
other
S
2Cl2
2/pyridine
reactions
is
that
the
reaction
mixtures
are
not
tarry,
feature
of
this
and
other
S
/pyridine
reactions
is
that
the
reaction
mixtures
are
not
tarry,
and
2
feature of this and other S2Cl2/pyridine reactions is that the reaction mixtures are not tarry, and the
the
product
isolations
do
not
require
chromatography
in
contrast
with
the
literature
procedures
[12–15].
product
product isolations
isolations do
do not
not require
require chromatography
chromatographyin
incontrast
contrastwith
withthe
theliterature
literatureprocedures
procedures[12–15].
[12–15].
Scheme1.1.Reaction
Reaction ofoxime
oxime 1 withSS22Cl
Cl2/pyridine to
Scheme
togive
givedithiazole
dithiazole 2.
2.
Scheme 1. Reactionof
of oxime11with
with S2Cl22/pyridine
/pyridine to
give
dithiazole
2.
Under the
the same
same
conditions,
3-phenylindanone
oxime 33 gave
gave
the
corresponding
1,2,3-dithiazole
same conditions,
conditions, 3-phenylindanone
3-phenylindanone oxime
gave the
the corresponding
corresponding 1,2,3-dithiazole
1,2,3-dithiazole
Under
4
even
in
a
higher
yield,
meanwhile
chlorination
was
not
observed
(Scheme
2).
even in
in aa higher
higher yield,
yield, meanwhile
meanwhile chlorination
chlorination was
was not
not observed
observed (Scheme
(Scheme2).
2).
4 even
Scheme 2. Reaction of oxime 3 with S2Cl2/pyridine to give dithiazole 4.
Scheme
to give
give dithiazole
dithiazole 4.
4.
Scheme2.2.Reaction
Reactionof
ofoxime
oxime33with
withSS22Cl
Cl22/pyridine
/pyridine to
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Treatment of the archetypal cyclopentanone oxime 5a with an excess of S2Cl2 (6 equiv) and
Treatment
of the
archetypal
cyclopentanone
oxime 5a with an excess of S2 Cl26a(6inequiv)
and
pyridine
(8 equiv)
in
boiling
MeCN
gave 4,5,6-trichlorocyclopenta-1,2,3-dithiazole
moderate
Treatment
of the
archetypal
cyclopentanone
oxime
excess
of Sof
2ClS
22Cl
(6 2equiv)
and and
Treatment
of the
archetypal
cyclopentanone
oxime5a5awith
withanan
excess
(6 equiv)
pyridine
(8
equiv)
in
boiling
MeCN
gave
4,5,6-trichlorocyclopenta-1,2,3-dithiazole
6a
in
moderate
Cl2 or/and
pyridine
in an attempt to obtain less chlorinated
product
yield.
Using
lesser
amounts
ofMeCN
S2MeCN
pyridine
(8 equiv)
in boiling
gave 4,5,6-trichlorocyclopenta-1,2,3-dithiazole
4,5,6-trichlorocyclopenta-1,2,3-dithiazole
6a in6amoderate
pyridine
(8 equiv)
in boiling
gave
in moderate
yield.
Using
lesser
amounts
of
S
Cl
or/and
pyridine
in
an
attempt
to
obtain
less
chlorinated
product
2
2
2 or/and
pyridine
in
attempt
toto
obtain
less
chlorinated
product
Using
lesser
amounts
failed
since
only
6aamounts
was
isolated
in2Cl
yields.
With
similar
procedure,
4-carbethoxy
substituted
2lower
or/and
pyridine
inaan
an
attempt
obtain
less
chlorinated
product
yield.yield.
Using
lesser
ofof
S2SCl
failed
since
only
6a
was
isolated
in
lower
yields.
With
a
similar
procedure,
4-carbethoxy
substituted
failed
since
only
6a
was
isolated
in
lower
yields.
With
a
similar
procedure,
4-carbethoxy
substituted
derivative
5b
was
converted
into
dichlorocyclopentadithiazole
6b
in
a
good
yield
(Scheme
3).
In both
failed since only 6a was isolated in lower yields. With a similar procedure, 4-carbethoxy substituted
derivative
5b was
converted
into
dichlorocyclopentadithiazole
6binin
a good
yield
(Scheme
In both
derivative
5bofwas
converted
into
dichlorocyclopentadithiazole
6breported
a good
yield
(Scheme
3).[12,15].
In3).
both
cases,
the
yields
dithiazoles
6
were
slightly
higher
than
those
in
the
literature
derivative 5b was converted into dichlorocyclopentadithiazole 6b in a good yield (Scheme 3). In both
the yields
of dithiazoles6 6were
wereslightly
slightly higher
those
reported
in the
[12,15].[12,15].
cases,cases,
the yields
of dithiazoles
higherthan
than
those
reported
inliterature
the literature
cases, the yields of dithiazoles 6 were slightly higher than those reported in the literature [12,15].
Scheme 3. Reaction
of oximes55with
with S2Cl2/pyridine
to to
give
dithiazoles
6. 6.
Scheme
/pyridine
give
dithiazoles
Scheme3.3. Reaction
Reactionof
ofoximes
oximes 5 withSS22Cl
Cl22/pyridine
to give
dithiazoles
6.
Scheme
3. Reaction
of oximes 5oximes,
with S2Cl
2/pyridine to give
dithiazoles
6. a complex
In the previous
study
on six-membered
p-benzoquinone
monooxime
7 gave
In
the previous
study
on six-membered
oximes,
p-benzoquinone
monooxime
7 gave
the desired
fused dithiazole
was obtained
in aa complex
low
mixture
of products
on reaction
with S2Cl2 and
desired
fused
intoa low
mixture
of[13].
products
onfound
reaction
with
SS22Cl22 and
and
the
desired
fused dithiazole
dithiazole
was
obtained
In
the
previous
study
onthat
six-membered
oximes,
p-benzoquinone
7selectively
gave a complex
yield
We have
the treatment
of the
7 with
S2Cl2/pyridine
inmonooxime
MeCN was
leadsobtained
[13].
We
have
found
that
the
treatment
of
7
with
S
2
Cl
2
/pyridine
in
MeCN
leads
selectively
to
yield
We
have
found
that
the
treatment
of
7
with
S
Cl
/pyridine
in
MeCN
leads
selectively
dichloro
dithiazole
or to trichloro
depending
excesswas
of the
reagents.inIna low
desired
fused
dithiazole
obtained
mixture
of products
on8 reaction
with dithiazole
S2Cl2 and9the
2 on
2 the molar
dichloro
dithiazole
8
or
to
trichloro
dithiazole
9
depending
on
the
molar
excess
of
the
reagents.
In
boiling
MeCN,
athe
larger
excess
(Sof
2Cl7
2, 9
6with
equiv;
pyridine,
equiv)
gave
9, leads
whereas
with
a
to
dichloro
dithiazole
8 orwith
to trichloro
dithiazole
depending
on 8the
molar
excess
of selectively
the
reagents.
yield
[13]. We
havereaction
found
that
treatment
S2Cl
2/pyridine
in MeCN
to
smaller
excess
(S8
2Cl2, with
4 equiv)
both
cases,
however,
low
yields
4).with
boiling
MeCN,
reaction
a larger
excess
(S(S
2Cl
2depending
, in
62 ,equiv;
pyridine,
8 equiv)
gave
whereas
a
In
boiling
MeCN,
reaction
with
apyridine,
larger
excess
Cl
6 equiv;
pyridine,
8in
equiv)
gave
9,
whereas
with
dichloro
dithiazole
or 3toequiv;
trichloro
dithiazole
928,
on
the molar
excess
of9,(Scheme
the
reagents.
In
excess
(S
2
Cl
2
,
3
equiv;
pyridine,
4
equiv)
8,
in
both
cases,
however,
in
low
yields
(Scheme
4).
asmaller
smaller
excess
(S
Cl
,
3
equiv;
pyridine,
4
equiv)
8,
in
both
cases,
however,
in
low
yields
(Scheme
4).
boiling MeCN, reaction
2 2 with a larger excess (S2Cl2, 6 equiv; pyridine, 8 equiv) gave 9, whereas with a
smaller excess (S2Cl2, 3 equiv; pyridine, 4 equiv) 8, in both cases, however, in low yields (Scheme 4).
Scheme 4. Reaction of oxime 7 with S2Cl2/pyridine to give dithiazoles 8 and 9.
Treatment
of benzosuberone
with
gave
selectively 4,5,6-trichlorobenzo[6,7]
Scheme
Reactionof
ofoxime
oxime10
withSSS222Cl
Cl222/pyridine
/pyridine
Scheme
4.4. Reaction
oxime
77with
Cl
/pyridineto
togive
givedithiazoles
dithiazoles88and
and9.
9.
cyclohepta[1,2-d][1,2,3]dithiazole 11 independent of the quantities of reagents; the best yield of 11
Scheme 4. Reaction of oxime 7 with S2Cl2/pyridine to give dithiazoles 8 and 9.
of pyridine were employed (Scheme 5).
(61%) was obtained
when 6 equiv
of S2Cl
Treatment
of benzosuberone
oxime
102 and
with8 Sequiv
2Cl2/pyridine gave selectively 4,5,6-trichlorobenzo[6,7]
Treatment of benzosuberone oxime 10 with S2 Cl2 /pyridine gave selectively
cyclohepta[1,2-d][1,2,3]dithiazole
11 independent
of2/pyridine
the quantities
of reagents;
yield of 11
Treatment of benzosuberone oxime
10 with S2Cl
selectively
4,5,6-trichlorobenzo[6,7]
4,5,6-trichlorobenzo[6,7]cyclohepta[1,2-d][1,2,3]dithiazole
11gave
independent
ofthe
thebest
quantities
of
2Cl2 and 8 equiv
of
pyridine
were
employed
(Scheme
5).
(61%)
was
obtained
when
6
equiv
of
S
cyclohepta[1,2-d][1,2,3]dithiazole
11
independent
of
the
quantities
of
reagents;
the
best
yield
of
11
reagents; the best yield of 11 (61%) was obtained when 6 equiv of S2 Cl2 and 8 equiv of pyridine were
(61%) was (Scheme
obtained 5).
when 6 equiv of S2Cl2 and 8 equiv of pyridine were employed (Scheme 5).
employed
Scheme 5. Reaction of oxime 10 with S2Cl2/pyridine to give dithiazole 11.
1,4-Naphthoquinone oxime 12 treated with 3 equiv of S2Cl2 and 4 equiv of pyridine gave
4-chloro-5H-naphtho[1,2-d][1,2,3]dithiazol-5-one 13 in 74% yield (Scheme 6). The structure of 13 was
5. Reaction
of oxime
confirmed by Scheme
single-crystal
XRD (Figure
1).10 with S2Cl2/pyridine to give dithiazole 11.
Scheme5.5.Reaction
Reactionof
ofoxime
oxime10
10with
withSS22Cl
Cl22/pyridine
/pyridine to
Scheme
to give
give dithiazole
dithiazole 11.
11.
1,4-Naphthoquinone oxime 12 treated with 3 equiv of S2Cl2 and 4 equiv of pyridine gave
4-chloro-5H-naphtho[1,2-d][1,2,3]dithiazol-5-one
74% yield
The structure
of 13gave
was
1,4-Naphthoquinone oxime
treated with
with1333inequiv
equiv
of SS2(Scheme
Cl2 and 6).
4 equiv
of pyridine
1,4-Naphthoquinone
oxime 12
12 treated
of
2 Cl2 and 4 equiv of pyridine gave
confirmed
by
single-crystal
XRD
(Figure
1).
4-chloro-5H-naphtho[1,2-d][1,2,3]dithiazol-5-one 13
13 in
in 74%
74% yield
yield (Scheme
(Scheme 6).
6). The
The structure
structure of
of 13
13 was
was
4-chloro-5H-naphtho[1,2-d][1,2,3]dithiazol-5-one
confirmed
by
single-crystal
XRD
(Figure
1).
confirmed by single-crystal XRD (Figure 1).
Molecules 2016, 21, 596
Molecules 2016, 21, 596
4 of 10
4 of 10
Molecules 2016, 21, 596
4 of 10
Molecules 2016, 21, 596
4 of 10
Scheme 6. Reaction of oxime 12 with S2Cl2/pyridine to give dithiazole 13.
Scheme
/pyridineto
togive
givedithiazole
dithiazole13.
13.
Scheme 6.
6. Reaction
Reaction of
of oxime
oxime 12
12 with
with SS22Cl
Cl22/pyridine
Scheme 6. Reaction of oxime 12 with S2Cl2/pyridine to give dithiazole 13.
Figure 1. XRD molecular structure of dithiazole 13 (displacement ellipsoids at 50%, atoms H are
shown as cycles). Selected bond distances (Å) and angles (o) (crystallographic numbering): C3-S1
1.7264(5), S1-S2 2.0774(5), S2-N1 1.6297(13), N1-C4 1.3054(19), C4-C3 1.456(2), C1-O1 1.2301(19),
C2-Cl1 1.7259(16); C3-S1-S2 92.18(5), S1-S2-N1 98.13(5), S2-N1-C4 117.09(11), N1-C4-C3 118.65(13),
C4-C3-S1 113.94(10).
Figure 1. XRD molecular structure of dithiazole 13 (displacement ellipsoids at 50%, atoms H are
Figure 1. XRD molecular structure of dithiazole 13 (displacement ellipsoids at 50%, atoms H are shown
o) (crystallographic
molecule is perfectly
and the
distances (and
angles correspond to
the statisticalC3-S1
numbering):
shown
as The
cycles).
bond planar
distances
(Å)bond
and
as cycles).
SelectedSelected
bond distances
(Å) and angles
(o )angles
(crystallographic
numbering):
C3-S1 1.7264(5),
means
[20]. 2.0774(5),
The crystalS2-N1
packing
reveals shortened
contacts S···O
together
with π-π
and Cl-π
1.7264(5),
S1-S2
1.6297(13),
N1-C4
1.3054(19),
C4-C3
1.456(2),
C1-O1
1. XRD
molecular
structure
of1.3054(19),
dithiazole C4-C3
13 (displacement
ellipsoids
at 50%, C2-Cl1
atoms 1.2301(19),
H
are
S1-S2Figure
2.0774(5),
S2-N1
1.6297(13),
N1-C4
1.456(2),
C1-O1
1.2301(19),
1.7259(16);
interactions [21].
C2-Cl1
1.7259(16);
C3-S1-S2
92.18(5),
S1-S2-N1
98.13(5),
S2-N1-C4
117.09(11),
N1-C4-C3
118.65(13),
o) (crystallographic
numbering):
C3-S1
shown
as
cycles).
Selected
bond
distances
(Å)
and
angles
(
C3-S1-S2 92.18(5),
S1-S2-N1
S2-N1-C4
117.09(11), N1-C4-C3
C4-C3-S1
113.94(10).
An unexpected
result98.13(5),
was obtained
with naphthoquinone
oxime 14, an118.65(13),
isomer of oxime
12. Treatment
C4-C3-S1
1.7264(5),
2.0774(5),
S2-N1 gave
1.6297(13),
N1-C4
C4-C3 1.456(2), C1-O1 1.2301(19),
of 14113.94(10).
withS1-S2
S2Cl2/pyridine
in MeCN
a mixture
of two1.3054(19),
isomeric chloronaphthodithiazolones
13 and 15
C2-Cl1 1.7259(16); C3-S1-S2 92.18(5), S1-S2-N1 98.13(5), S2-N1-C4 117.09(11), N1-C4-C3 118.65(13),
in comparable
yields (Scheme
7). First
of all,
was shown
that 14 was
individual
compound with
no statistical
The molecule
is perfectly
planar
and
theit bond
distances
andanangles
correspond
to the
C4-C3-S1
The molecule
perfectly
planar
and the on
bond
distances
anglesthat
correspond
the
traces of 113.94(10).
itsisisomer
12. Special
experiments
individual
13 andand
15 showed
15 convertsto
into
13 statistical
means [20].
The
crystal
packing
reveals shortened contacts S¨ ¨ ¨ O together with π-π and Cl-π
when
treated
with
S
2Cl2/pyridine, whereas 13 remains unchanged. Effectively, the dithiazole ring
means [20]. The crystal packing reveals shortened contacts S···O together with π-π and Cl-π
interactions
[21].
moved
from αβ-position,
withand
respect
to the distances
keto group,
and
the reaction
undertodiscussion
The
molecule
is to
perfectly
planar
the bond
and
angles
correspond
the statistical
interactions
[21].
represents
rearrangement.
Earlier,
similar
by us
for an
fused
An
unexpected
result
was obtained
with processes
naphthoquinone
oxime
14,
means
[20]. Thea novel
crystal
packing
reveals
shortened
contacts were
S···O discovered
together
with
π-π
andisomer
Cl-π of
An unexpected
result was[22–24].
obtained
with naphthoquinone
oxime
14, an isomer
of oxime
12. Treatment
1,2,3,4,5-pentathiepines
Apparently,
the
mechanism
of
this
rearrangement
includes
dithiazole
interactions
[21].
oxime
12. Treatment
of 14 with S2 Cl2 /pyridine in MeCN gave a mixture of two isomeric
of 14 withAn
Sring-opening
2Cl2/pyridine
inby
MeCN
gave
mixture
of two
isomeric
15
the action
of a
the
chlorinating
agent
(i.e., S2Clchloronaphthodithiazolones
2) followed by the ring-closure to 13 and 15
unexpectedinresult
was
obtained
naphthoquinone
oxime
14, an7).
isomer
Treatment
chloronaphthodithiazolones
13 scope
and
15
inwith
comparable
yields
(Scheme
Firstofofoxime
all, it12.
was
shown that
afford
13 (Scheme
7). The
ofofthis
rearrangement
is under
consideration.
in comparable
yields
(Scheme
7).
First
all,
it
was
shown
that
14
was
an individual compound with no
of
14
with
S
2Cl2/pyridine in MeCN gave a mixture of two isomeric chloronaphthodithiazolones 13 and 15
14 was an individual compound with no traces of its isomer 12. Special experiments on individual
tracesinof
its isomeryields
12. Special
onwas
individual
15 converts
into 13
comparable
(Schemeexperiments
7). First of all, it
shown that1314and
was15
an showed
individualthat
compound
with no
13 and 15 showed that 15 converts into 13 when treated with S2 Cl2 /pyridine, whereas 13 remains
whentraces
treated
S2Cl
2/pyridine,
whereas on
13 individual
remains unchanged.
Effectively,
the dithiazole
of itswith
isomer
12.
Special experiments
13 and 15 showed
that 15 converts
into 13 ring
unchanged. Effectively, the dithiazole ring moved from α- to β-position, with respect to the keto
when
treated
S2Cl2/pyridine,
13 the
remains
Effectively,
the dithiazole
ring
moved
from
α- towith
β-position,
with whereas
respect to
ketounchanged.
group, and
the reaction
under discussion
group,
and the
reaction
under discussion
represents
a novel
rearrangement.
Earlier,
similar
processes
moved
from
αto
β-position,
with
respect
to
the
keto
group,
and
the
reaction
under
discussion
represents a novel rearrangement. Earlier, similar processes were discovered by us for fused
were represents
discovereda by
us for
fused 1,2,3,4,5-pentathiepines
[22–24].
Apparently,
mechanism
of this
novel
rearrangement.
Earlier,
processes
were
discoveredthe
byincludes
us for fused
1,2,3,4,5-pentathiepines
[22–24].
Apparently,
thesimilar
mechanism
of this
rearrangement
dithiazole
rearrangement
includes dithiazole
ring-opening
in 15 by of
the
action
of the chlorinating
agent (i.e.,
1,2,3,4,5-pentathiepines
[22–24]. Apparently,
the mechanism
this
rearrangement
includes dithiazole
ring-opening
in 15 by the action
of the chlorinating
agent (i.e.,
S2Cl
2) followed by the ring-closure to
S2 Cl2ring-opening
) followed by
the
to chlorinating
afford 13 (Scheme
7).S2Cl
The
scope of
rearrangement
is
in 15
byring-closure
the action of the
agent (i.e.,
2) followed
by this
the ring-closure
to
afford 13 (Scheme 7). The scope of this rearrangement is under consideration.
13 (SchemeScheme
7). The7.scope
ofofthis
rearrangement
is under
consideration.
underafford
consideration.
Reaction
oxime
14 with S2Cl2/pyridine
to give
dithiazoles 15 and 13.
Scheme 7. Reaction of oxime 14 with S2Cl2/pyridine to give dithiazoles 15 and 13.
Scheme
/pyridineto
togive
givedithiazoles
dithiazoles15
15and
and13.
13.
Scheme 7.
7. Reaction
Reaction of
of oxime
oxime 14
14 with
with SS22Cl2/pyridine
Molecules 2016, 21, 596
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Molecules 2016, 21, 596
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2.2.Molecules
Electrochemical
Reduction and Oxidation of Dithiazole 13
2016, 21, 596
5 of 10
2.2. Electrochemical Reduction and Oxidation of Dithiazole 13
Recently, it was shown that benzo-fused 1,2,3-dithiazoles are able to form persistent radical-anions
2.2. Electrochemical
Reduction
andthat
Oxidation
of Dithiazole
13
it was
shown
benzo-fused
1,2,3-dithiazoles
are one
ableoftotheform
(RAs) Recently,
under conditions
of
electrochemical
and chemical
reduction and
RAs persistent
was isolated
radical-anions
(RAs)
under
conditions
of
electrochemical
and
chemical
reduction
and
one persistent
of the RAs
Recently,
it
was
shown
that
benzo-fused
1,2,3-dithiazoles
are
able
to
form
in the form of thermally-stable paramagnetic salts [6,7]. Amongst compounds synthesized in this
was
isolated in
the under
form conditions
of thermally-stable
paramagnetic
salts reduction
[6,7]. Amongst
radical-anions
(RAs)
and chemical
and
onecompounds
ofof
theRAs
RAssince
work
napthoquinone-fused
derivatives of
13electrochemical
and 15 are especially
interesting
in the
context
synthesized
in
this
work
napthoquinone-fused
derivatives
13
and
15
are
especially
interesting
in
the
in theconcentration
form of thermally-stable
Amongst
compounds
onewas
mayisolated
expect some
of a negativeparamagnetic
charge on thesalts
C=O [6,7].
moieties
(ultimately
leading to
context
of
RAs
since
one
may
expect
some
concentration
of
a
negative
charge
on
the
C=O
moieties
in thissituation)
work napthoquinone-fused
derivatives
13 and 15metal
are especially
interesting
thesynthesized
C–O´ bonding
enlarging
their ability
to coordinate
cations. This
mightinbethe
a new
− bonding situation) enlarging their ability to coordinate metal cations.
(ultimately
leading
to one
the C–O
context of RAs
since
may expect
some concentration of a negative charge on the C=O moieties
approach
to
the
design
and
synthesis
of
sulfur-nitrogen
π-heterocyclic
RA
salts
as
potential
building
This
might be
a newto
approach
the design
and synthesis
oftheir
sulfur-nitrogen
π-heterocyclic
RA salts
(ultimately
leading
the C–O−tobonding
situation)
enlarging
ability to coordinate
metal cations.
blocks
of
magnetic
functional
materials
[25–29].
asThis
potential
of magnetic
functional
materials
[25–29].
might building
be a new blocks
approach
to the design
and synthesis
of sulfur-nitrogen
π-heterocyclic RA salts
The
behavior
ofof1313
was
studied
andand
found
to be
very
complex
multistep
process.
Theelectrochemical
electrochemical
behavior
was
studied
found
to abe
a very
complex
multistep
as potential
building blocks
of magnetic
functional
materials
[25–29].
Thus,
the
CV
of
13
in
MeCN
(0
>
E
>
´2.0
V)
contains
six
irreversible
peaks
in
the
cathodic
branch
process.
the CV of 13
in MeCN
E > −2.0
V) contains
six to
irreversible
in the
cathodic of
TheThus,
electrochemical
behavior
of (0
13>was
studied
and found
be a verypeaks
complex
multistep
the
voltammogram.
Theofadditional
1c’´1a’
and 2c’´2a’
were
observed
in the
branch
ofThus,
the voltammogram.
Thequasi-reversible
additional
peaks
1c’−1a’
and
were
process.
the CV
13 in MeCN
(0 > E > −2.0quasi-reversible
V)peaks
contains
six irreversible
peaks
in 2c’−2a’
the
cathodic
1C (Figure 2). 1C
second
cycle
at
lower
potentials
than
E
observed
in
the
second
cycle
at
lower
potentials
than
E
(Figure
2).
p
p
branch of
voltammogram. The additional
quasi-reversible
peaks 1c’−1a’ and 2c’−2a’ were
1C
observed in the second cycle at lower potentials than Ep (Figure 2).
I / μA
I / μA
6C
-20
4C
1C
-20
1C
-10
3C4C
2C
6C
5C
5C
3C
2C
-10
1c'
0
1c'
0
2c'
2c'
1a'
2a'
0.0 1a'
2a'
-0.5
0.0
-0.5
-1.0
E/V
-1.0
E/V
-1.5
-2.0
-1.5
-2.0
Figure2.2.CV
CVofof13
13in
inMeCN
MeCN (black
(black curve:
curve: first
cycle).
The
potential
sweep
Figure
first cycle;
cycle;red
redcurve:
curve:second
second
cycle).
The
potential
sweep
ij
ij 1C,
–1
Figure
2. 0CV
of
in MeCN
curve: first
cycle;
red
second
cycle).
The (−E
potential
sweep
. Peak
potentials
V):
range
was
0>> E
E >>13´2.0
−2.0
VVand
the
sweep
rate
100curve:
mV·s
p [30],
range
was
and(black
thepotential
potential
sweep
rate
100
mV¨
s–1 . Peak
potentials
(´E
[30],
V):
p
–1. Peak potentials (−Eij [30], V): 1C,
range
was
0 >3C,
E >1.37;
−2.04C,
V and
the
potential
sweep
rate0.24;
100 1a’,
mV·s
p
0.80;
2C,
0.93;
1.47;
5C,
1.68,
6C,
1.76;
1c’,
0.19;
2c’,
0.62;
2a’,
0.56.
1C, 0.80; 2C, 0.93; 3C, 1.37; 4C, 1.47; 5C, 1.68, 6C, 1.76; 1c’, 0.24; 1a’, 0.19; 2c’, 0.62; 2a’, 0.56.
0.80; 2C, 0.93; 3C, 1.37; 4C, 1.47; 5C, 1.68, 6C, 1.76; 1c’, 0.24; 1a’, 0.19; 2c’, 0.62; 2a’, 0.56.
With a limited potential sweep covering only reduction peaks 1C and 2C (0 > E > −1.2 V), peaks
With a limited
sweep
covering
only
reductionpeaks
peaks 1Cand
and2C2C
E−1.2
> ´1.2
V), peaks
limitedpotential
potential
sweep(Figure
covering
only
reduction
(0 (0
> E>>potential
V), peaks
1c’–1a’With
anda2c’–2a’
did
not vanish
3a).
Moreover,
further 1C
decrease
in
the
sweep
1c’–1a’
andand
2c’–2a’ diddid
not vanish
(Figure
3a).3a).
Moreover,
further decrease
in the potential
sweep
down
1c’–1a’
vanish
(Figure
Moreover,
decrease
sweep
down
to the 2c’–2a’
range 0 > Enot
> −0.88
V embracing
only
the firstfurther
irreversible
stepinofthe
thepotential
reduction
of 13
to the
range
0
>
E
>
´0.88
V
embracing
only
the
first
irreversible
step
of
the
reduction
of
13
(Figure
down to
range
> E >any
−0.88qualitative
V embracing
onlyin
thethe
first
irreversibleCV.
stepWe
of the
reduction
13 3b)
(Figure
3b)thedid
not 0cause
change
compound’s
conclude
thatofboth
did
not cause
any
change
in the
compound’s
CV.
We conclude
electrode
processes
(Figure
3b)
did qualitative
not1c’–1a’
cause any
qualitative
change
in product(s)
the
compound’s
CV.that
Weboth
conclude
that
both
electrode
processes
and
2c’–2a’
belong
to the
of transformation
of
13 at
the
first
electrode
processes
1c’–1a’
and
2c’–2a’
belong
to
the
product(s)
of
transformation
13
at
the
1c’–1a’
and
2c’–2a’
belong
to
the
product(s)
of
transformation
of
13
at
the
first
step
of
its
reduction,
step of its reduction, and their currents are kinetically controlled by the reactions at the peak 1C.first and
step
of its reduction,
and their
currents by
arethe
kinetically
controlled
by the
their
currents
are kinetically
controlled
reactions
at the peak
1C.reactions at the peak 1C.
I / μA
-40I / μA
-40
-30
-30
-20
-20
-10
-10
0
0
2C
1C 2C
1C
2c'
2c'
30
30
0.0
0.0
1C
1C
-30
-30
-20
-20
1c'
1c'
-10
-10
2c'
2c'
1c'
1c'
0
0
10
10
20
20
I / μA
I / μA
-40
-40
1a'
1a'
2a'
2a'
-0.5
-0.5E / V
E/V
(a)
(a)
10
10
-1.0
-1.0
0.0
0.0
1a'
1a'
2a'
2a'
-0.5
-0.5
E/V
E/V
-1.0
-1.0
(b)
(b)
Figure
3. CVs of 13 in MeCN with potential sweep ranges 0 > E > −1.2 (a) and 0 > E > −0.88; (b) V.
Figure 3. CVs of 13 in MeCN with potential sweep ranges 0 > E > −1.2 (a) and 0 > E > −0.88; (b) V.
Figure
3. sweep
CVs of 13 in
MeCN(first
with potential
sweep250,
ranges
0 > 850,
E > 1050,
´1.2 and
(a) and
0(2–7
> Ecycles,
> ´0.88;
Potential
450, 650.
650.
1250(2–7
Potential sweeprates
rates were
were 50
50 (first cycle,
cycle, red
red curve),
curve), 250,
450,
850, 1050,
and 1250
cycles,
(b)
V. Potential mV·s
sweep
–1 rates were 50 (first cycle, red curve), 250, 450, 650. 850, 1050, and 1250 (2–7 cycles,
black
blackcurves)
curves) mV·s–1. .
black curves) mV¨ s–1 .
Molecules 2016, 21, 596
Molecules 2016, 21, 596
6 of 10
6 of 10
The
Theelectrochemical
electrochemicalreduction
reductionofof1313could
couldbe
beaccompanied
accompaniedby
byits
itsrapid
rapidirreversible
irreversibledechlorination
dechlorination
initiated
initiatedby
byelectron
electrontransfer
transfer(cf.
(cf.[31]).
[31]).Additionally,
Additionally,the
thebond
bondC=N
C=Nofofthe
the1,2,3-dithiazole
1,2,3-dithiazolering
ringcan
can
undergo
undergoirreversible
irreversiblereduction
reductionininthe
theRA
RAstate
stateofofaamolecule,
molecule,ororthe
thering
ringcan
canbebeopened
openedby
bythe
thecleavage
cleavage
ofofS-S
S-N
bonds
(cf.(cf.
[32]).
However,
S-Sor/and
or/and
S-N
bonds
[32]).
However,it itis isimpossible
impossibletotoassign,
assign,unambiguously,
unambiguously,these
theseprocesses
processes
totothe
thepeaks
peaks1C
1Cor
or2C.
2C. No
No long-lived
long-livedparamagnetic
paramagneticproducts
productswere
wereobserved
observedby
byconventional
conventionalEPR
EPR
spectroscopy
−1.8
V. V.
spectroscopyunder
understationary
stationaryelectrolysis
electrolysisofof13
13ininthe
therange
rangeofofpotentials
potentials−0.8
´0.8> >E E> >
´1.8
CV
area
of of
potentials
is characterized
by the
onlyonly
irreversible
peakpeak
1A (Ox)
at theat
CVofof1313ininoxidative
oxidative
area
potentials
is characterized
by the
irreversible
1A (Ox)
1A(Ox)
2A(Ox)
1A(Ox)
2A(Ox)
potential
E
=
1.53
V
(Figure
4).
An
additional
irreversible
peak
2C
(Ox)
(E
=
0.85
V)
corresponding
the potential
Ep
= 1.53 V (Figure 4). An additional irreversible peak
= 0.85 V)
p
p 2C (Ox) (Ep
tocorresponding
the reduction to
of the
oxidation
products
of 13 isproducts
observedofin13
the
the CV.
reduction
of oxidation
is cathode
observedbranch
in the of
cathode
branch of the CV.
I / μA
30
1A(Ox)
20
10
0
2C(Ox)
-10
0.0
0.5
1.0
E/V
1.5
2.0
Figure
range of
ofpotential
potentialsweep
sweep0 0< <EE< <2.0
2.0V.V.
The
potential
sweep
Figure4.4.CV
CVofof13
13in
in MeCN
MeCN in the range
The
potential
sweep
raterate
was
was
100100
mV¨mV·s
s´1 .–1.
Overall, the electrochemical behavior of 13 is characterized by a large number of multistage
Overall, the electrochemical behavior of 13 is characterized by a large number of multistage
irreversible processes and their interpretation is a real challenge. Due to this complexity, at the
irreversible processes and their interpretation is a real challenge. Due to this complexity, at the
current state of research only a qualitative description of the electrochemical behavior of 13 is
current state of research only a qualitative description of the electrochemical behavior of 13 is possible.
possible. For further work preparative electrochemical reduction of 13 at controlled potentials is
For further work preparative electrochemical reduction of 13 at controlled potentials is planned
planned to obtain samples of reduction products enable their conventional characterization, together
to obtain samples of reduction products enable their conventional characterization, together with
with generation of RAs from chlorine-less 1,2,3-dithiazoles such as 4 and related derivatives.
generation of RAs from chlorine-less 1,2,3-dithiazoles such as 4 and related derivatives.
3.3.Experimental
Section
Experimental
Section
3.1.
3.1.General
GeneralInformation
Information
Elemental
Elementalanalyses
analysesfor
forC,C,H,
H,and
andNNwere
wereperformed
performedwith
withPerkin
PerkinElmer
Elmer2400
2400Elemental
ElementalAnalyser
Analyser
(Perkin
Waltham,MA,
MA,
USA).
Melting
points
determined
on a hot-stage
Boetius hot-stage
(Perkin Elmer,
Elmer, Waltham,
USA).
Melting
points
were were
determined
on a Boetius
apparatus
apparatus
and are uncorrected.
and are uncorrected.
1H
1H
(300.1
CC(75.5
33
solutions
(300.1MHz)
MHz)and
and1313
(75.5MHz)
MHz)NMR
NMRspectra
spectrawere
weretaken
takenfor
forCDCl
CDCl
solutionswith
witha aBruker
Bruker
AM-300
AM-300(Bruker
(BrukerAXS
AXSHandheld
HandheldInc.,
Inc.,Kennewick,
Kennewick,WA,
WA,USA).
USA).
MS
MSspectra
spectra(EI,
(EI,7070eV)
eV)were
wereobtained
obtainedwith
witha aFinnigan
FinniganMAT
MATINCOS
INCOS5050(Hazlet,
(Hazlet,NJ,
NJ,USA),
USA),and
and
high-resolution
high-resolutionMS
MSspectra
spectrawith
witha aBruker
BrukermicrOTOF
micrOTOFIIII(Bruker
(BrukerDaltonik
DaltonikGmbh,
Gmbh,Bremen,
Bremen,Germany)
Germany)
instruments
instrumentsusing
usingelectrospray
electrosprayionization.
ionization.The
Themeasurements
measurementswere
wereoperated
operatedinina apositive
positiveion
ionmode
mode
(interface
(interfacecapillary
capillaryvoltage
voltage−4500
´4500V)V)ororinina anegative
negativeion
ionmode
mode(3200
(3200V);
V);mass
massrange
rangewas
wasfrom
fromm/z
m/z5050toto
m/z
3000
Da;
external
or or
internal
calibration
was
done
with
Electrospray
Calibrant
Solution
(Fluka).
A
m/z
3000
Da;
external
internal
calibration
was
done
with
Electrospray
Calibrant
Solution
(Fluka).
´
−1). Nitrogen
syringe
injection
was
used
for
solutions
in
MeCN,
methanol,
or
water
(flow
rate
3
µL·min
A syringe injection was used for solutions in MeCN, methanol, or water (flow rate 3 µL¨ min 1 ).
was
applied
as applied
a dryingasgas;
interface
was 180 °C.was 180 ˝ C.
Nitrogen
was
a drying
gas;temperature
interface temperature
IRIRspectra
spectrawere
weremeasured
measuredwith
withaaSpecord
SpecordM-80
M-80instrument
instrument(Carl
(CarlZeiss,
Zeiss,Jena,
Jena,Germany)
Germany)inin
KBr
KBrpellets.
pellets.
Oximes
Oximes33[33],
[33],77[34],
[34],12
12[35]
[35]and
and14
14[36]
[36]were
wereprepared
preparedaccording
accordingto
tothe
thepublished
publishedprocedures.
procedures.
Molecules 2016, 21, 596
7 of 10
3.2. General Procedure for the Reaction of Cyclic Oximes with S2 Cl2 and Pyridine in Acetonitrile
At ´25 ˝ C and under argon, S2 Cl2 (0.24 mL, 3.0 mmol; or 0.48 mL, 6.0 mmol) was added dropwise
to a stirred solution of oxime (1.0 mmol) and pyridine (0.32 mL, 4.0 mmol; or 0.64 mL, 8.0 mmol) in dry
MeCN (10 mL). The mixture was stirred for 0.5 h at ´5–0 ˝ C, for 24 h at ambient temperature, refluxed
for 1 h, filtered and the solvent was distilled off under reduced pressure. The residue was dissolved in
EtOH (20 mL), diluted by H2 O (20 mL) and extracted with ether (3 ˆ 20 mL). Combined extracts were
washed with H2 O (20 mL), dried, and solvent was evaporated.
8-Chloroindeno[1,2-d]-1,2,3-dithiazole 2. Red solid, mp 108–110 ˝ C (107–109 ˝ C [12]). IR and MS spectra
are similar to the literature data [12].
8-Phenylindeno[1,2-d]-1,2,3-dithiazole 4. Yellow solid, mp 111–112 ˝ C (111–113 ˝ C [12]). IR and MS
spectra are similar to the literature data [12].
4,5,6-Trichlorocyclopenta[d][1,2,3]dithiazole 6a. Deep purple solid, mp 122–124 ˝ C (125–127 ˝ C [12]).
IR and MS spectra are similar to the literature data [12].
Ethyl 5,6-dichlorocyclopenta[d][1,2,3]dithiazole-4-carboxylate 6b. Yellow solid, mp 80–82 ˝ C (83–84 ˝ C [15]).
IR and MS spectra are similar to the literature data [15].
5,7-Dichloro-6H-1,2,3-benzodithiazol-6-one 8. Red solid, mp 259–261 ˝ C (257–258 ˝ C [13]). IR and MS
spectra are similar to the literature data [13].
4,5,7-Trichloro-6H-1,2,3-benzodithiazol-6-one 9. Red solid, mp 214–215 ˝ C (216–217 ˝ C [13]). IR and MS
spectra are similar to the literature data [13].
4,5,6-Trichlorobenzo[6,7]cyclohepta[1,2-d][1,2,3]dithiazole 11. Red solid, mp 119–121 ˝ C (121–122 ˝ C [12]).
IR and MS spectra are similar to the literature data [12].
4-Chloro-5H-naphtho[1,2-d][1,2,3]dithiazol-5-one 13. Red solid, mp 230–233 ˝ C (234–235 ˝ C [13]). IR and
MS spectra are similar to the literature data [13].
9-Chloro-4H-naphtho[2,3-d][1,2,3]dithiazol-4-one 15. Blue solid, mp 192–195 ˝ C (195–196 ˝ C [13]). IR and
MS spectra are similar to the literature data [13].
All compounds synthesized had correct elemental analyses and NMR spectra.
3.3. Behavior of 1,2,3-Dithiazoles 13 and 15 in the S2 Cl2 /Pyridine System
At ´25 ˝ C and under argon, S2 Cl2 (0.048 mL, 0.6 mmol) was added dropwise to a stirred solution
of 15 (25 mg, 0.1 mmol) and pyridine (0.064 mL, 8.0 mmol) in dry MeCN (3 mL). The mixture was
refluxed for 2 h, filtered and the solvent was distilled off under reduced pressure. The residue was
dissolved in CH2 Cl2 (7 mL), washed with H2 O (3 ˆ 2 mL), dried over MgSO4 , and the residue was
separated by flash chromatography (silica gel Merck 60, hexane to hexane/CH2 Cl2 mixtures) to give
13 (10 mg, 39%) and 15 (11 mg, 43%).
In the experiment with 13 under the same reaction conditions it was quantitatively recovered.
3.4. X-ray Diffraction
XRD data of 13 were obtained with a Bruker Kappa Apex II CCD diffractometer (Bruker
AXS Gmbh, Karlsruhe, Germany) using ϕ, ω scans of narrow (0.5˝ ) frames with Mo Kα radiation
(λ = 0.71073 Å) and a graphite monochromator. The structure of 13 was solved by direct methods
and refined by full-matrix least-squares method against all F2 in anisotropic approximation using
the SHELX-97 (Bruker AXS, Madison, WI, USA) programs set [37]. The H atoms positions were
calculated with the riding model. Absorption corrections were applied empirically using SADABS
programs [38]. Shortened intermolecular contacts were analyzed using the PLATON [39] and
MERCURY [40] programs.
Molecules 2016, 21, 596
8 of 10
Compound 13 is orthorhombic, space group Pca21 , a = 16.6153(6), b = 3.8775(1), c = 15.4168(6) Å,
V = 993.24(6) Å3 , Z = 4, C10 H4 ClNOS2 , Dcalc = 1.697 g¨ cm–3 , µ = 0.770 mm–1 , F(000) = 512, crystal
size 0.80 ˆ 0.20 ˆ 0.07 mm3 , independent reflections 2254 (Rint. = 0.0404), wR2 = 0.0512, S = 1.09
for all reflections (R = 0.0196 for 2202 F > 4σ). Tables listing detailed crystallographic data, atomic
positional parameters, and bond lengths and angles are available as CCDC 1468963 from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
3.5. Cyclic Voltammetry
The CV measurements on compound 13 (~1.2 mM solutions in MeCN) were performed with a
PG 310 USB potentiostat (HEKA Elektronik, Germany) at 293 K in an argon atmosphere at a stationary
Pt spherical electrode (S = 0.08 cm2 ) with 0.1 M Et4 NClO4 as a supporting electrolyte. A standard
electrochemical cell (solution volume was 5 mL) connected to the potentiostat with three-electrode
scheme was used. Peak potentials were quoted with reference to a saturated calomel electrode (sce).
4. Conclusions
In this work, a new general procedure for the selective synthesis of carbocycle-fused
1,2,3-dithiazoles based on the reaction of cyclic oximes with S2 Cl2 and pyridine in MeCN was
established. With naphthalenone derivatives, a novel dithiazole rearrangement was discovered, i.e.,
isomerization of 15 into 13. The structure of 1,2,3-dithiazole 13 was confirmed by single-crystal XRD.
In most cases the hetero ring-closure was accompanied by chlorination. The presence of chlorine
atoms in the 1,2,3-dithiazoles synthesized most likely causes instability of their reduced forms.
Particularly, under the CV conditions and with compound 13, we speculate that hydrodechlorination
occurs at a low potential. In any case, no long-lived paramagnetic products were observed
by conventional EPR spectroscopy under stationary electrolysis of 13 in the potential range
´0.8 > E > ´1.8 V. In further syntheses of carbocycle-fused 1,2,3-dithiazoles as potential precursors
of persistent RAs (cf. [6,7]) using the established procedure the chlorination must be prevented by
appropriate substitution in starting oximes.
The effectiveness of the S2 Cl2 /pyridine system in the chemistry described in this work motivates
a special investigation of possible interaction/complexation between its components.
Acknowledgments: The authors are grateful to the Russian Science Foundation (grant no. 15-13-10022), the
Leverhulme Trust (project IN-2012-094), and the Ministry of Education and Science of the Russian Federation
(project of joint laboratories of Siberian Branch of the Russian Academy of Sciences and National Research
Universities) for financial support of various aspects of this work.
Author Contributions: OAR and AVZ suggested research upon fused 1,2,3-dithiazoles towards their use in
materials science; LSK and IVB performed synthetic work; LSK and OAR analyzed synthetic data; IYB obtained
and analized XRD data; IGI and LAS obtained and analyse CV data; and OAR and AVZ wrote the paper.
All authors read and approved the final manuscript.
Conflicts of Interest: The authors declare no conflict of interest.
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© 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC-BY) license (http://creativecommons.org/licenses/by/4.0/).