1,2,5-Thiadiazole 2-oxides: Selective synthesis, structural characterization, and electrochemical properties

Article abstract of DOI:10.1016/j.tet.2014.06.096

A new general procedure for the selective synthesis of 1,2,5-thiadiazole 2-oxides (including fused derivatives) 8a,b,c,g,h from the reaction of vic-glyoximes with S₂Cl₂ and pyridine in acetonitrile was elaborated together with general procedure for the synthesis of 1,2,5-thiadiazoles 7a-i, 10, 12, and 14 from the same starting materials and reagents. Molecular structures of 3,4-dimethyl-1,2,5-thiadiazole 2-oxide 8a and [1,2,5]thiadiazolo[3,4-b]quinoxaline 10 were confirmed by single-crystal X-ray diffraction. Electrochemical properties of 1,2,5-thiadiazole 2-oxides 8 were studied by cyclic voltammetry and different behavior was observed for monocyclic and benzo-fused derivatives. With compounds 8g and 17, previously unknown deoxygenation of 2,1,3-benzothiadiazole 1-oxides was discovered by electrochemical reduction, and resulted 2,1,3-benzothiadiazoles 7g and 19 were detected in the forms of their radical anions by EPR spectroscopy combined with DFT calculations.

Full text of DOI:10.1016/j.tet.2014.06.096

Accepted Manuscript
1,2,5-Thiadiazole 2-oxides: selective synthesis, structural characterization and
electrochemical properties
Lidia S. Konstantinova, Ekaterina A. Knyazeva, Natalia V. Obruchnikova, Nadezhda
V. Vasilieva, Irina G. Irtegova, Yulia V. Nelyubina, Irina Yu. Bagryanskaya, Leonid A.
Shundrin, Zhanna Yu. Sosnovskaya, Andrey V. Zibarev, Oleg A. Rakitin
PII:
S0040-4020(14)00970-3
10.1016/j.tet.2014.06.096
TET 25762
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 16 April 2014
Revised Date: 9 June 2014
Accepted Date: 23 June 2014
Please cite this article as: Konstantinova LS, Knyazeva EA, Obruchnikova NV, Vasilieva NV, Irtegova
IG, Nelyubina YV, Bagryanskaya IY, Shundrin LA, Sosnovskaya ZY, Zibarev AV, Rakitin OA, 1,2,5-
Thiadiazole 2-oxides: selective synthesis, structural characterization and electrochemical properties,
Tetrahedron (2014), doi: 10.1016/j.tet.2014.06.096.
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ACCEPTED MANUSCRIPT
Graphical Abstract
1,2,5-Thiadiazole 2-oxides: selective synthesis, structural
characterization and electrochemical properties
Lidia S. Konstantinova, Ekaterina A. Knyazeva, Natalia V.
Obruchnikova, Nadezhda V. Vasilieva, Irina G. Irtegova,
Yulia V. Nelyubina, Irina Yu. Bagryanskaya, Leonid A.
Shundrin, Zhanna Yu. Sosnovskaya, Andrey V. Zibarev,
Oleg A. Rakitin*

ACCEPTED MANUSCRIPT
2
1,2,5-Thiadiazole 2-oxides: selective synthesis, structural
characterization and electrochemical properties
Lidia S. Konstantinova,a Ekaterina A. Knyazeva,a Natalia V. Obruchnikova,a Nadezhda V.
Vasilieva,b Irina G. Irtegova,b Yulia V. Nelyubina,c Irina Yu. Bagryanskaya,b,d Leonid A.
Shundrin,b,d Zhanna Yu. Sosnovskaya,a Andrey V. Zibarev,b,e,f Oleg A. Rakitina*
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991
Moscow, Russia
bN. N. Vorozhtsov Institute of Organic Chemistry, Siberian Branch, Russian Academy of
Sciences, 630090 Novosibirsk, Russia
cA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
119991 Moscow, Russia
dDepartment of Natural Sciences, National Research University – Novosibirsk State
University, 630090 Novosibirsk, Russia
eDepartment of Physics, National Research University – Novosibirsk State University,
630090 Novosibirsk, Russia
fDepartment of Chemistry, National Research University – Tomsk State University, 634050
Tomsk, Russia
Abstract
A new general procedure for the selective synthesis of 1,2,5-thiadiazole 2-oxides (including
fused derivatives) 8a,b,c,g,h from the reaction of vic-glyoximes with S2Cl2 and pyridine in
acetonitrile was elaborated together with general procedure for the synthesis of 1,2,5-
thiadiazoles 7a-i, 10, 12 and 14 from the same starting materials and reagents. Molecular
structures of 3,4-dimethyl-1,2,5-thiadiazole 2-oxide 8a and [1,2,5]thiadiazolo[3,4-
b]quinoxaline 10 were confirmed by single-crystal X-ray diffraction. Electrochemical
properties of 1,2,5-thiadiazole 2-oxides 8 were studied by cyclic voltammetry and different
behavior was observed for monocyclic and benzo-fused derivatives. With compounds 8g and
17, previously unknown deoxygenation of 2,1,3-benzothiadiazole 1-oxides was discovered by
electrochemical reduction, and resulted 2,1,3-benzothiadiazoles 7g and 19 were detected in
the forms of their radical anions by EPR spectroscopy combined with DFT calculations.

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Keywords: 1,2,5-Thiadiazole 2-oxides, Sulfur monochloride, X-Ray diffraction, Cyclic
voltammetry, EPR spectroscopy, DFT calculations
Corresponding author. Tel.: +7-499-135-53-27; fax: +7-499-135-53-28; e-mail:
orakitin@ioc.ac.ru.
1.
Introduction
1,2,5-Thiadiazoles and their benzo-fused derivatives (i.e. 2,1,3-benzothiadiazoles)
have been known for many years, and their synthesis, chemical and physical properties were
extensively studied and reviewed.1-4 Apart their use in numerous branches of chemistry,
medicine1,2 and agriculture,5-8 they were found to be an efficient electron acceptors and were
employed as building blocks of many actual or potential molecule-based functional materials
for organic electronics9 and spintronics (in this case as ligands for coordination compounds of
paramagnetic metal cations).10 Recently, they were used in the synthesis of thermally-stable
radical-anion (RA) salts,11 revealing antiferromagnetic exchange interactions in their spin
systems,12 and conductive charge-transfer complexes also possessing photoconductivity.13
Based on DFT calculations of electron affinity, it was expected that N-oxides of the
aforementioned compounds, i.e. 1,2,5-thiadiazole 2-oxides and 2,1,3-benzothiadiazole 1-
oxides, can also be good precursors of stable RAs isolable in the form of salts.14
It should be emphasized that in contrast to well-studied chemistry of S-oxides and S,S-
dioxides of 1,2,5-thiadiazoles including electrochemistry and potential applications in
materials science (see ref. 15 and references therein), the chemistry of N-oxides of this ring
system is still in its infancy. 1,2,5-Thiadiazole 2-oxides and their derivatives are rare
compounds. According to search in the SciFinder and Reaxys databases, only 16 compounds
were described. Benzo- and heterocyclic fused derivatives have been obtained in the reaction
of sulfur monochloride with o-aminonitroso16-18 and o-aminonitro19 precursors (Scheme 1).

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Scheme 1. Synthesis of 1,2,5-thiadiazole 2-oxides (1) from o-aminonitroso (2) and o-
aminonitro (3) derivatives.
Unfortunately in both cases starting materials are limited especially in the case of non-
fused derivatives. Vicinal dioximes 4 are more available precursors for the synthesis of 1,2,5-
thiadiazole 2-oxides. Their reactions with sulfur monochloride (S2Cl2) or sulfur dichloride
(SCl2) led to mixtures of thiadiazole oxides 5 and non oxygenated 1,2,5-thiadiazoles 6 both in
low yield (Scheme 2).20,21
Scheme 2. Synthesis of 1,2,5-thiadiazole 2-oxides (5) from vic-dioximes (4).
Moreover, to date, conclusive proof of structure for non-fused 1,2,5-thiadiazole 2-
oxides has not been provided, nor have studies appeared on their physical and chemical
properties. In this paper we report a study of a reaction between vic-dioximes and sulfur
monochloride, a selective synthesis of 1,2,5-thiadiazole 2-oxides and corresponding 1,2,5-
thiadizoles covering monocyclic and fused derivatives, their structural characterization and
electrochemical properties.
2.
Results and Discussion

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2.1. Synthesis and structure elucidation
In an effort to improve the synthesis of 1,2,5-thiadiazole 2-oxides, we re-investigated
the reaction of commercial dimethylglyoxime with sulfur monochloride – a versatile reagent
in organic chemistry.22,23 Treatment of dimethylglyoxime with S2Cl2 in dimethylformamide
(DMF) – a solvent which is frequently used in S2Cl2 reactions22,23 – at low (–25 °C) to room
temperature gave 3,4-dimethyl-1,2,5-thiadiazole 7a in moderate yields. The type of base used
was important for the success of reactions with S2Cl2 in other solvents (chloroform or
acetonitrile). Reaction of dimethylglyoxime with a two-fold excess of S2Cl2 and 1,4-
diazabicyclooctane (DABCO) in chloroform at –5 °C led to the desired 3,4-dimethyl-1,2,5-
thiadiazole 2-oxide 8a although in low yield (35%) together with unreacted
dimethylglyoxime. Our attempts to increase the yield of N-oxide 8a by using an excess of
S2Cl2 and DABCO led to conversion of 8a to thiadiazole 7a even at low temperature (–25
°C). Our best results for the synthesis of N-oxide 8a were achieved by treating
dimethylglyoxime with two-fold excess of S2Cl2 and pyridine in acetonitrile at 5 °C for 1 h
which gave 3,4-dimethyl-1,2,5-thiadiazole 2-oxide 8a selectively in a moderate 53% yield
(Scheme 3).
R
R
R
R
R
R
rt
5 °C
+ S2Cl2/Py
in MeCN
N
N
20 h
N
N
1 h
HON
NOH
O
S
S
8, 48-76%
7, 54-76%
S2Cl2, Py, MeCN, rt
75-97%
R = a. Me, b. Ph, c. morphol-4-yl,
d. CN, e. Cl, f. NMe2,
R,R = g.-CH=CH-CH=CH-;
h. -CH2-CH2-CH2-CH2-
R = a. Me, b. Ph, c. morphol-4-yl,
R,R = g.-CH=CH-CH=CH-;
h. -CH2-CH2-CH2-CH2-
i.
Scheme 3. Synthesis of 1,2,5-thiadiazoles 7 and 1,2,5-thiadiazole 2-oxides 8 from vicinal
dioximes.

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Further on, we extended this reaction to other vicinal glyoximes. Monocyclic (methyl,
phenyl and morphol-4-yl substituted) and benzo- and cyclohexano-fused 1,2,5-thiadiazole 2-
oxides 8a-c,g,h were obtained in moderate yields. N-Oxides 8d,e containing electron-
withdrawing substituents (R = CN, Cl) were found to be unstable and readily deoxygenated
to the corresponding thiadiazoles 7d and 7e, respectively, whereas in the case of
bis(dimethylamino)glyoxime and (9E,10E)-phenanthrene-9,10-dione dioxime thiadiazole
oxides 8f,i were not isolated from the reaction mixtures. IR spectroscopy showed the
presence of characteristic stretching medieum frequencies of N-oxide group for all 1,2,5-
thiadiazole 2-oxides 8 at 1352-1364 cm-1; the mass spectra indicated major loss of an oxygen
with moderate intensity presumably for conversion to 1,2,5-thiadiazoles.
Synthesized 1,2,5-thiadiazole 2-oxides 8a-c,g,h were converted into the thiadiazoles 7
in high yields by treatment with S2Cl2 and pyridine in acetonitrile at room temperature.
Interesting and partly unexpected results were obtained when diaminoglyoximes were
involved in the reaction with sulfur monochloride. Treatment of (2Z,3Z)-1,4-
dihydroquinoxaline-2,3-dione dioxime 9 with S2Cl2 in the presence of pyridine in acetonitrile
under similar conditions led to the formation of [1,2,5]thiadiazolo[3,4-b]quinoxaline 10 in
moderate yield (Scheme 4). In that case two processes take place simultaneously – the
formation of thiadiazole ring from dioxime moiety and dehydration of dihydropiperazine into
aromatic pyrazine ring presumably by action of sulfur monochloride. The structure of
compound 10 (Fig. 1) was confirmed by single-crystal X-ray diffraction (XRD). As
compared with the 2,1,3-benzothiadiazole 7g,24 the structure of thiadiazoloquinoxaline 10
revealed very similar geometry within the thiadiazole ring. In the crystal, shortened
intermolecular contacts S2...N9 of 3.085 Å (normal contact S...N is 3.45 Å)25 lead to
formation of infinite chains of molecules along b axis. Additionally, weak π…π interaction of
neighboring chains is observed featuring interplane separation of 3.32–3.36 Å.
Scheme 4. Synthesis of [1,2,5]thiadiazolo[3,4-b]quinoxaline 10.

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Figure 1. XRD molecular (left, displacement ellipsoids at 30%) and crystal (right) structure
of 10.25 The molecules are perfectly planar, the standard deviations from the mean plane are
0.020 Å. Selected bond distances and bond angles (o): C9a-N1 1.365(2), N1-S2 1.6105(16),
S2-N3 1.6110(16), N3-C3a 1.353(2), C3a-N4 1.346(2), C9a-N9 1.335(2); N1-S2-N3
102.55(8), S2-N1-C9a 105.4(1), S2-N3-C3a 105.7(1), N3-C3a-N4123.8(1), N3-C3a-C9a
113.3(1), N4-C3a-C9a 122.9(1), N1-C9a-N9 123.7(1), N1-C9a-C3a 113.0(1), N9-C9a-C3a
123.3(1). The distances and angles correspond to the statistical means.26
Under similar conditions, (5Z,6Z)-[1,2,5]oxadiazolo[3,4-b]pyrazine-5,6(4H,7H)-dione
dioxime 11 gave tricyclic bis([1,2,5]thiadiazolo)-[3,4-b;3',4'-e]pyrazine 1227 in moderate
yield (Scheme 5). In that case three reactions occurred: formation of thiadiazole ring from
dioxime, exchange of an oxygen atom in a 1,2,5-oxadiazole ring by a sulfur atom and
aromatization of piperazine ring. The yields of aromatic thiadiazoles 10 and 12 can be
improved substantially (73% and 66%, correspondingly) by treatment of fused glyoximes 9
and 11 with S2Cl2 in DMF presumably owing the better solubility of glyoximes in this
solvent.
Scheme 5. Synthesis of bis([1,2,5]thiadiazolo)-[3,4-b;3',4'-e]pyrazine 12.
Reaction of an easily available28 diaminoglyoxime 13 with S2Cl2 in the presence of
pyridine in acetonitrile gave [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole 14 in moderate yield
(Scheme 6). Thiadiazolothiadiazole 14 is one of the most useful precursor for the preparation
of persistent RA.3,11,14 The described method is the most simple and convenient for the

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synthesis of this compound and opens new possibilities for its use in the construction of new
materials.
Scheme 6. Synthesis of [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole 14.
The key steps of the reactions described in this work may be explained by the
sulfurization of the oxime with sulfur monochloride in the presence of a base to give an
intermediate chlorodithio derivative 15 followed by the intermolecular sulfuration of the
second oxime group to form 1,2,3,6-dithiadiazine 3,6-dioxide 16 which could easily extrude
sulfur monooxide (SO, which is thermodynamically unstable and decomposes very rapidly)29
via a cycloaddition/retrocycloaddition to afford 1,2,5-thiadiazole 2-oxides 8. Final formation
of the 1,2,5-thiadiazoles 7 from their 2-oxides 8 was confirmed by the reaction with sulfur
monochloride (see Scheme 3).
Scheme 7. A suggested reaction path for the formation of 1,2,5-thiadiazoles 7 and their 2-
oxides 8.
Synthesis of 1,2,5-thiadiazole 2-oxides 8 from vic-dioximes is isoelectronic to the
synthesis of fused 2,1,3-benzothiadiazole-1-oxides from vic-amino-nitro derivatives (see
Scheme 1).19 In both cases an extrusion of SO is required from the stoichiometric point of
view. No elemental sulfur was detected in the reaction mixtures.

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The structure of the compound 8a was confirmed by single-crystal XRD (Fig. 2).
Molecular geometry of the 1,2,5-thiadiazole 2-oxide moiety is not very different from those
reported
for 6-nitro-2,1,3-benzothiadiazole 1-oxide
(17,
Figure
3),19 and
[1,2,5]thiadiazolo[3,4-d]pyrimidine-5,7-dione-2-oxide dihydrate (18, Figure 3)30 both
containing such a moiety. Although the latter is more similar to 8a (average variation in bond
length is 0.015(1) vs. 0.024(1) Å), they both share the common feature: the largest difference
corresponds to the bond N-O, which is longer by 0.03(1) Å in 8a. In the case of 17,19
however, the reverse trend is observed for the bonds C-N, which become longer by the same
value and thus have a lower double-bond character. This may be associated with the different
behavior of 8a and 17 in release of oxygen atom to produce thiadiazoles.19
Note that in both compounds 18 and 8a, the sulfur atom is involved in shortened
S…O and S…N contacts with neighboring 1,2,5-thiadiazole 2-oxide molecules resulting in
infinite tapes in the crystal 8a; those are supplemented by N…O type of contacts. The
corresponding interatomic distances are 2.718(1), 2.958(1) and 3.049(1) Å for S…O, S…N
and N…O, respectively. For compound 18, the contacts S…O are longer (S…O 3.194 Å) but
the distance S…N coincide nicely (2.958 Å) with that in 8a. In bicycle 17, there is also a
shortened S…O contact with an interatomic distance 2.779 Å similar to that in 8a, although a
rather strong S…S interaction (3.432 Å) is present instead of S…N or N…O ones. The latter
apparently occurs as an overlap of sulfur atoms’ lone pairs; the largest SSN angle being
127.9(1)°. The angles OSN and NSN (178.3(1)–177.6(1)° in 8a and 162–167° in 18)19,30
corresponding to the aforementioned S…O and S…N interactions identify them as charge
transfer (CT) from lone-pair MOs of nitrogen or oxygen atoms (nX, X = N, O) to σ*-MOs of
the S-N bonds. Based on the ONC angle value of 173.6(1)°, the additional O…N contact in
8a can be attributed to the CT nO→σ*SN.

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Figure 2. A fragment of infinite tapes in the crystal of 3,4-dimethyl-1,2,5-thiadiazole 2-oxide
8a, which are formed through O…S, O…N and N…S short contacts, in representation of
atoms via thermal ellipsoids at 50% probability level. Atoms labeled with A and B are
obtained from the basic ones by symmetry operations -0.5+x, y, 1.5-z and 0.5+x, y, 1.5-z,
respectively.
Figure 3. Compounds 17-19.
2.2. Electrochemical properties
Electrochemical properties of 1,2,5-thiadiazoles were extensively studied,24,31-33 those
of their N-oxides were unknown. Meanwhile, both electrochemical reduction and oxidation
(ECR and ECO, respectively) of many other types of heterocyclic N-oxides were
investigated.34,35 The majority of the ECR are irreversible one- or two-electron processes,
although some of bicyclic N-oxides can undergo the one-electron reversible ECR and ECO in

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aprotic media with the formation of long-lived RAs and radical cations, respectively, detected
by EPR.35 In this context, electrochemical behavior of 1,2,5-thiadiazoles N-oxides is of
interest from the standpoint of analysis of a reversibility and number of electrons in the first
stage of electrochemical process, because this analysis is a main indicator of stability of the
reduced or oxidized species, which are formed under electron transfer.
In this work, electrochemical properties of 8a,b,g and previously synthesized 6-nitro
derivative of 8g (i.e. 6-nitro-2,1,3-benzothiadiazole 1-oxide, 17)19 were studied with cyclic
voltammetry (CV) technique.
2.2.1. Electrochemical reduction.
Earlier, it was found that some 3,4-disubstituted 1,2,5-thiadiazoles undergo reversible
ECR into their RAs.32a In contrast, ECR of monocyclic N-oxides 8a-c is characterized by the
irreversible first reductive peaks 1C (Figure 3, Table 1). However, CV of 8b reveals peaks
2C-2A (Figure 4) corresponding to the reversible one-electron process. One can think that the
peak 2C in the CV of 8b corresponds to the reduction of intermediate ECR product, likely its
parent 3,4-diphenyl-1,2,5-thiadiazole (7b), into corresponding RA but attempts to detect it by
2C
EPR spectrometry at the potential Ep were unsuccessful. In the CV of 8a, peaks 2C-2A
were not observed. A reason may be they are out of the accessible potential sweep range and /
or overlap the background current range at high negative potentials. The oxidative peaks 1A
and 1A’ in the anodic branch of the CVs correspond obviously to the oxidation of the ECR
products formed at the first step of reduction of compounds 8a and 8b. For 8b these peaks
were observed in the range of potential sweep covering the first stage only (0 > E > −1.8 V)
and remained unchanged under expansion of potential sweep up to −2.4 V (Figure 4 b).
I, µA
I, µA
(a)
(b)
1C
-40
1C
-30
-30
-20
-10
0
-20
-10
0
2C
2A
10
20
1A
10
1A, 1A'
E, V
E, V
0.0 -0.5 -1.0 -1.5 -2.0
0.0 -0.5 -1.0 -1.5 -2.0

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12
Figure 4. CV of 8a within negative potential sweep range (a) and 8b within potential sweep
ranges 0 > E > −1.8 V (dotted line) and 0 > E > −2.4 V (solid line) (b) in MeCN (ν = 0.1 V s-
1). The beginning and direction of potential sweep are indicated by an arrow.
CV of the benzo-fused derivative 8g is characterized by two well-separated reductive
peaks 1C and 2C within the potential sweep range 0 > E > −1.80 V (Figure 5a and Table 1).
Peak 1C is irreversible, and the pair of peaks 2C-2A corresponds to the reversible one-
electron process. Peak potential Ep2C= −1.54 V is equal to the known potential of one-electron
reversible reduction of thiadiazole 7g (Figure 5a, curve 2), i.e. the parent compound of N-
oxide 8g.31,33
2C
ECR of 8g at the potential Ep using a combination of electrochemical and EPR
techniques gives the paramagnetic product whose spectrum is identical to the well-known
spectrum of the RA of 7g33 (Figure 6, Table 2), whereas reduction within the potential range
0 > E > −1.5 gives no paramagnetic species.
I, µA
I, µA
-150
I, µA
-150
-350
(a)
(b)
1C
-250
-150
-50
-100
-50
0
-100
-50
0
1
1
2
2C
2A
2
50
50
0.0
-0.5 -1.0 -1.5 -2.0
0.0
-0.5 -1.0 -1.5 -2.0
E, V
E, V
Figure 5. CV of 8g in MeCN (ν = 0.1 V s-1) within potential sweep range 0 > E > −1.8 V (1,
left axis) and that of 7g within potential sweep range 0 > E > −2.0 V (2, right axis) (a), and
corresponding digital simulation of the CV curves (b) using the assumed routes shown by
dashed line 2 and solid line 1 (for explanation, see text below). The beginning and direction
of potential sweep are indicated by an arrow.

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Table 1. Experimental ECR peak potentials (V) of 8a,b,g and 17.
1C
2C
2A
3C
4C
Compound Ep
Ep
Ep
Ep
Ep
8a
8b
8g
17
−1.67
−
−
−
−
−
−
−
−
−1.46 −2.07 −1.96
−1.11 −1.54 −1.44
−0.58 −0.82 −0.73 −1.39 −1.91
1
1
2
2
H, 10-4
T
H, 10-4
T
3493
3503
3513
3523
3533
3493
3503
3513
3523
3533
Figure 6. Experimental (1) and simulated (2) EPR spectra of RAs from electrochemical
reduction of compound 8g (left) and authentic 7g (right) at the potential –1.65 V.
Table 2. Experimental and UB3LYP/6-31+G(d)-calculated hfc constants (mT) for
RAsa of compounds 7g and 19 observed upon ECR of compounds 8g and 17.b
RA of
com-
hfc constants
experimental
calculated
pound
0.531 (N1,3), −0.261 (H4,7), −0.161 0.572 (N1,3), −0.308 (H4,7), −0.164
7g
(H5,6)
(H5,6)
0.338 (N1), 0.013 (N3), 0.450 (NNO2),
0.690 (H4), 0.007 (H6), 0.007 (H7)
0.394 (N1), −0.023 (N3), 0.467 (NNO2),
0.773 (H4), −0.018 (H6), 0.030 (H7)
19
a RAs of 2,1,3-benzothiadiazole (7g) and its 5-nitro derivative (19, see below) were observed
in the cases of 8g and 17, respectively.

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b In the calculations, PCM model was used to account for the MeCN solvent.
To describe ECR mechanism of 8g, its first step was assumed to be two-electron by
nature, because the large ratio of peak currents Ip1C / Ip2C = 16.5 (first cycle of potential sweep
at potential sweep rate ν = 0.1 V s-1) cannot be described adequately if two one-electron steps
of ECR (ECE process) are proposed.
Two possible routes of ECR can be considered: 1) Two-electron irreversible reduction
of 8g followed by proton addition to the oxygen atom of the formed short-lived dianion with
the following fast detachment of H2O and the subsequent one-electron reversible ECR of 7g
into its RA at Ep2C; and 2) previous process accompanied by parallel irreversible non-
electrochemical homogeneous reaction of the dianion with thiadiazole cycle opening33 or
proton addition to nitrogen atom (Scheme 8).
To describe adequately the form of CV, it does not matter from the kinetic point of
view if proton addition to the dianion or the dianion’s ring-opening will be taken into
consideration. Obviously, compounds A-D will not possess an electrochemical reductive
2C
activity at less negative potentials than Ep due to π-conjugation cleavage resulting in the
decrease of electron affinity.
Scheme 8. Proposed mechanism of the ECR of 8g used for simulation of CV curve.

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15
Digital simulation of the CV of 8g using both possible routes of ECR reveals the most
exact description of experimental CV curve if to propose that the ECR mechanism includes
both reactions controlled by kf1 and kf2 (k’f2) (Figure 5b, curve 1). Otherwise, the adequate
description of Ip1C / Ip2C is not achieved (Figure 5b, curve 2; details of the CV simulation and
optimized peak potentials and kinetic parameters for the ECR mechanism of 8g are listed in
Table 3).
Table 3. Optimized peak potentials and kinetic constants for homogeneous reactions
(Scheme 8, route 2) used for CV curves simulation.
Compound
Ep1C, V
−1.115
−0.585
Ep2C, V
−1.538
−0.815
kf1, mM−1 s−1
466
kf2, s−1
220
8g
17
324
1081
CV of N-oxide 17 contains four reduction peaks within the potential sweep range 0 >
E > − 2.3 V. (Figure 7a). Corresponding peak potentials are listed in Table 1. The presence of
nitro group in the carbocycle leads to the shift of the first peak potential towards less negative
values from –1.11 V (8g) to –0.58 V (17).
I
-75
, µA
I
-75
, µA
I
, µA
I
, µA
(a)
(b)
(c)
-100
-50
0
1C
-300
1C
-50
-200
-50
-25
0
1
1
4C
2
2C
2A
-25
3C
2C
1
-100
2
2
0
0
*
25
0.0
25
-0.5
-1.0
-1.5
E, V
0.0 -0.5 -1.0 -1.5 -2.0 -2.5
E, V
0.0
-0.5
-1.0
-1.5
E, V
Figure 7. CV of 17 in MeCN (ν = 0.1 V s-1) within potential sweep ranges 0 > E > −2.3 V (1
− first cycle, 2 − second cycle) (a) and 0 > E > −1.1 V (сurve 1, left axis) together with CV of
19 within potential sweep range 0 > E > −1.3 V (curve 2, right axis) (b), and corresponding
digital simulation of the CV curves of 17 (c) using the ECR mechanism assumed for 8g

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16
(route 1, dashed line; route 2, solid line). Arrows indicate the direction of potential sweep and
an asterisk (b) the oxidative peak of products resulting from ECR of 17.
First two steps of ECR of 17 (Figure 7b) and 8g (Figure 5a) are identical in fact.
Potentials of the reversible peaks 2A-2C are equal to the corresponding peak potentials of the
first CV wave under ECR of 19 (Figure 7b, curve 2). Digital simulation of CV curve of 17
within the range of potentials covering first two steps of ECR (0 > E > 1.1 V) and using the
scheme of the proposed ECR mechanism for 8g (Scheme 8) leads to the similar results
(Figure 6c). The nature of other peaks (3C, 4C) was not studied.
Note, that optimized value of kf2 for ECR of 8g is 4.9 times less than the
corresponding value for ECR of 17 (Table 3). This fact can be explained by the decrease in
electron density within benzothiadiazole cycle because of its redistribution between the cycle
and conjugated nitro group.
2C
According to EPR measurements, ECR of 17 at the peak potential Ep gives
paramagnetic product whose EPR spectrum is shown in Figure 7a, whereas ECR in the
potential range from 0 to –0.8 gives no paramagnetic species. Starting from the mechanisms
of ECR proposed for 17 and 8g we suggest, that the observed spectrum is related to the RA of
5-nitro-2,1,3-benzothiadiazole (19, Figure 3). Experiment with authentic compound 1919 has
proven the suggestion unambiguously (Figure 8b, Table 2).
1
1
2
2
H, 10-4
T
H, 10-4
T
3497
3507
3517
3527
3497
3507
3517
3527
Figure 8. Experimental (1) and simulated (2) EPR spectra of RAs resulting from ECR of
compound 17 (left) and authentic 19 (right) at the potential –0.85 V.

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17
The DFT-calculated spin density distribution in the RA of 19 demonstrates its
noticeable transfer from bicyclic moiety onto nitro group which leads to the sufficient
1
magnetic nonequivalence of the 14N nuclei of the heterocycle and decrease of the H hfc
constants in positions 6 and 7 (Figure 9). Based on these results together with experimental
data we can conclude that the earlier reported assignment of hfc constants for RA of 19 was
incorrect.36
Figure 9. The UB3LYP/6-31+G(d) distribution of the spin density in RA of 19. Signs plus
and minus indicate positive and negative spin density, respectively.37 Polarizable continuum
model (PCM)38 was used to account for the MeCN solvent.
2.2.2. Electrochemical oxidation (ECO).
Compounds 8a,b,g and 17 display an ECO activity. Within potential range 0 < E < 2.5
1Ox
V, ECO of 8a and 8b is characterized by the first oxidation peaks Ep = 2.07 and 2.02 V,
2Ox
respectively. CV of 8a reveals the second oxidative peak Ep
= 2.44 V. Peaks 1Ox are
diffusion-controlled for all compounds and their irreversibility at potential sweep rates up to
2 V s–1 indicates that the corresponding products of ECO are unstable (Figure 10).

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18
I, µA
I, µA
100
(a)
(b)
1Ox
2Ox
75
1Ox
2
75
50
25
0
1
50
25
0
E, V
E, V
0.0 0.5 1.0 1.5 2.0 2.5
0.0 0.5 1.0 1.5 2.0 2.5
Figure 10. CVs of compounds 8a in potential sweep ranges 0 < E < 2.3 V (1) and 0 < E < 2.6
V) (2) (a), and that of 8b in potential sweep range 0 < E < 2.6 V (b) in MeCN. Arrows
indicate the direction of potential sweep.
Within potential range 0 < E < 2.5 V, ECO of 8g is characterized by two oxidation
1Ox
2Ox
peaks with the potentials Ep = 1.77 V and Ep = 2.36 V, whereas CV of 17 has the only
oxidative peak at Ep1Ox = 2.00 V. Peaks 1Ox are diffusion-controlled for both compounds and
their irreversibility at potential sweep rates up to 2 V s–1 indicates the unstability of the ECO
products (Figure 11). The nature of oxidation peaks for the compounds 8a,b,g and 17 was not
investigated. We would like to only note that oxidative peaks of compounds studied are at
least two or more electron by nature that arises from a comparison of peak currents of
oxidative and two electron-reductive peaks.39
I, µA
I, µA
(b)
150
100
50
(a)
100
50
0
1Ox
2Ox
1Ox
0
-50
-50
0.0 0.5 1.0 1.5 2.0 2.5
0.0 0.5 1.0 1.5 2.0 2.5
E, V
E, V
Figure 11. CV of 8g (a) and 17 (b) in MeCN in the oxidative potential range. Dashed line (a)
shows a CV measured in the range of potential sweep 0 > E > 2.5 V.

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19
Overall, different ECR behavior was observed for monocyclic 1,2,5-thiadiazole 2-
oxides and their benzo-fused derivatives, and previously unknown deoxygenation of 2,1,3-
benzothiadiazole 1-oxides into the parent 2,1,3-benzothiadiazoles under ECR conditions was
observed. Earlier, deoxygenation of N-oxides in aprotic media was detected for two-electron
ECR of acyclic α-aryl-N-alkyl(aryl)nitrons and cyclic nitrons, viz. pyrroline derivatives.40 On
the contrary, the ECR of heteroaromatic N-oxides and N,N'-dioxides in aprotic media is one-
electron reversible process giving rise to corresponding RAs.41
3.
Conclusions
In this work, new general procedures for the selective synthesis of various 1,2,5-
thiadiazole 2-oxides (both monocyclic and fused), rather rare compounds, and their parent
and related 1,2,5-thiadiazoles based on the reaction of vic-glyoximes with S2Cl2 and pyridine
in acetonitrile were established.
2,1,3-Benzothiadiazole 1-oxides were found to undergo under conditions of ECR
unusual deoxygenation into parent 2,1,3-benzothiadiazoles observed by EPR in the form of
corresponding RAs. For monocyclic 1,2,5-thiadiazole 2-oxides, paramagnetic products were
not detected under conditions of ECR. Tentative mechanism of ECR of the 1,2,5-thiadiazole
N-oxides studied was suggested featuring their irreversible two-electron reduction at the first
stage.
One can think that it might be possible to avoid two-electron character of the N-oxides
reduction observed under the ECR conditions dealing with one-electron chemical reducing
agents such as, for example, metal sandwich compounds MCp2 and MAr2 (M = d-metal) (cf.
refs. 12, 54). In this case one might hope for preparation of RAs of the N-oxides followed by
their isolation in the form of thermally stable salts. Chemical reduction of 1,2,5-thiadiazole 2-
oxides and their benzo-fused derivatives may therefore be a direction of further research in
the field.
4.
Experimental Section
4.1. General

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All synthetic operations were performed under a dry argon atmosphere. Solvents,
including MeCN for CV / EPR experiments, were purified by distillation from the
appropriate drying agents and degassed before use. The residual water content in MeCN for
CV / EPR was 5 mM.
Elemental analyses were performed on Perkin Elmer 2400 Elemental Analyser.
Melting points were determined on a Kofler hot-stage apparatus and are uncorrected.
1H and 13C NMR spectra were taken with a Bruker AM-300 machine (at frequencies
of 300.1 and 75.5 MHz, respectively) in CDCl3 solutions, with TMS as the standard. J
values are given in Hz. MS spectra (EI, 70 eV) were obtained with a Finnigan MAT
INCOS 50 instrument. High-resolution MS spectra were measured on a Bruker micrOTOF II
instrument using electrospray ionization (ESI). The measurement was operated in a positive
ion mode (interface capillary voltage –4500 V) or in a negative ion mode (3200 V); mass
range was from m/z 50 to m/z 3000 Da; external or internal calibration was done with
Electrospray Calibrant Solution (Fluka). A syringe injection was used for solutions in
acetonitrile, methanol, or water (flow rate 3 µL.min–1). Nitrogen was applied as a dry gas;
interface temperature was set at 180 °C. IR spectra were measured with a Specord M-80
instrument in KBr pellets.
Vicinal glyoximes were prepared according to the published methods. Other reagents
were purchased from commercial sources and used as received.
For previously known compounds 7a,b,d,e,g,h,i, 8b,g, 10, 12 and 14, NMR, IR and
MS spectra were similar to the literature data.19,20,27,42-46
4.2. Syntheses
4.2.1. General procedure for the synthesis of 1,2,5-thiadiazole 2-oxides 8 from the
reaction of vic-glyoximes with sulfur monochloride and pyridine in acetonitrile
Sulfur monochloride (0.32 mL, 4.00 mmol) was added dropwise to a stirred solution of
the vic-glyoxime (2.0 mmol) and pyridine (0.40 mL, 5.0 mmol) in dry acetonitrile (10 mL)
under argon at –25 °C. The mixture was stirred for 1 h at –5 °C, filtered and the solvent was
evaporated under reduced pressure. The residue was separated by column chromatography
(silica gel Merck 60, hexane / CH2Cl2 mixtures).

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4.2.1.1. 3,4-Dimethyl-1,2,5-thiadiazole 2-oxide (8a). Yield 53%. Colorless solid, mp 78-79
ºС, Rf = 0.35 (CH2Cl2/acetone = 5:1). Anal. calcd for С4Н6N2ОS (130.17): C 36.41, H 4.65,
N 21.52, S 24.63. Found: C 36.29, H 4.57, N 21.39, S 24.81. NMR (δ), 1H: 2.32 (3H, s, СН3),
2.47 (3H, s, CН3); 13C: 10.8 (CН3), 18.6 (CН3), 141.3, 156.8. MS, m/z (%): 130 (M+, 100),
114 (M - O, 25), 89 (25), 73 (75). ESI-MS: found m/z 131.0274; calc. for С4Н6N2ОS [M+H]+
131.0278. IR, ν, cm–1: 2925 and 2855 (С-Н), 1463, 1358 (N→O), 1275, 1121.
4.2.1.2. 3,4-Diphenyl-1,2,5-thiadiazole 2-oxide (8b). Yield 76%. Colorless solid, mp 122-123
ºС (124 ºС),20 Rf = 0.75 (CH2Cl2/acetone = 5:1). IR and mass spectra are similar to the
literature data.20
4.2.1.3. 4,4'-(2-Oxido-1,2,5-thiadiazole-3,4-diyl)dimorpholine (8c). Yield 56%. Yellow solid,
mp 88-89 ºС, Rf = 0.40 (CH2Cl2/acetone = 5:1). Anal. calcd for C10H18N6OS (272.33): С
1
44.43, Н 6.71, N 31.09, S 11.86. Found: С 44.82, Н 6.53, N 31.23, S 11.12. NMR (δ), H:
3.82 (8H, t, 4СН2, J = 3.0), 3.39 (8H, t, 4СН2, J = 3.0). 13C: 48.4 (CH2), 66.1 (CH2), 127.4,
153.5. MS, m/z (%): 272 (М+, 10); 256 (M – O, 53); 160 (45); 113 (62); 86 (100). ESI-MS:
found m/z 273.1018; calc. for C10H16N4O3S [M+H]+ 273.1021. IR, ν, cm–1: 2953 and 2860
(С-Н), 1655, 1448, 1346 (N→O), 1253, 1115.
4.2.1.4. 2,1,3-Benzothiadiazole 1-oxide (8g). Yield 76%. Yellow solid, mp 78-79 ºС (78-80
ºС),20 Rf = 0.35 (CH2Cl2). IR and mass spectra are similar to the literature data.20
4.2.1.5. 4,5,6,7-Tetrahydro-2,1,3-benzothiadiazole 1-oxide (8h). Yield 48%. Yellow solid,
mp 109-110 ºС, Rf = 0.55 (CH2Cl2/acetone = 5:1). Anal. calcd for С6Н8N2ОS (156.21): С
1
46.13, Н 5.16, N 17.93, S 20.53. Found: С 46.26, Н 5.01, N 17.83, S 21.02. NMR (δ), H:
2.97-2.94 (4H, m, 2СН2), 1.96-1.93 (4H, m, 2СН2); 13C: 21.21 (CH2), 22.16 (CH2), 23.57
(CH2), 29.7 (CH2), 141.8, 158.7. MS, m/z (%): 156 (M+, 100), 140 (M –O, 8), 55 (35). ESI-
MS: found m/z 157.0427; calc. for С6Н8N2ОS [M+H]+ 157.0430. IR, ν, cm–1: 2924 and 2854
(С-Н), 1449, 1364 (N→O), 1104.
4.2.2. General procedure for the synthesis of 1,2,5-thiadiazoles 7, 10, 12 and 14 from
the reaction of vic-glyoximes with sulfur monochloride and pyridine in acetonitrile

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S2Cl2 (0.64 mL, 8.00 mmol) was added dropwise to a stirred solution of the vic-glyoxime (2.0
mmol) and pyridine (0.80 mL, 10.0 mmol) in dry acetonitrile (10 mL) under argon at –25 °C.
The mixture was stirred for 1 h at ambient temperature, refluxed for 4 h, filtered and the
solvent evaporated under reduced pressure. The residue was separated by column
chromatography (silica gel Merck 60, hexane / CH2Cl2 mixtures).
4.2.2.1. 3,4-Dimethyl-1,2,5-thiadiazole (7a). Yield 58%. Colorless oil,42 Rf = 0.65 (CH2Cl2).
IR and mass spectra are similar to the literature data.42
4.2.2.2. 3,4-Diphenyl-1,2,5-thiadiazole (7b). Yield 66%. Colorless solid, mp 85-87 ºС (83-84
ºС),20 Rf = 0.70 (CH2Cl2). IR and mass spectra are similar to the literature data.20
4.2.2.3. 4,4'-(1,2,5-Thiadiazole-3,4-diyl)dimorpholine (7c). Yield 65%. Colorless solid, mp
94-95 ºС, Rf = 0.85 (CH2Cl2/acetone = 5:1). Anal. calcd for С10Н16N4О2S (256.33): С 46.86,
Н 6.29, N 21.86, S 12.51. Found: C 46.98, H 5.96, N 21.72, S 12.72. NMR (δ), 1H: 2.82 (8H,
t, 4СН2, J = 3.0), 2.94 (8H, t, 4СН2, J = 3.0); 13C: 48.4 (CH2), 66.5 (CH2), 153.5. MS, m/z
(%): 256 (M+, 100), 140 (35), 97 (66), 85 (78), 69 (81), 55 (84). ESI-MS: found m/z
256.0984; calc. for С10Н16N4О2S [M+H]+ 256.0988. IR, ν, cm–1: 2925 and 2858 (C-H), 1508,
1448, 1254, 1116.
4.2.2.4. 1,2,5-Thiadiazole-3,4-dicarbonitrile (7d). Yield 64%. Colorless solid, mp 48-50 ºС
(50-51 ºС),43 Rf = 0.40 (CH2Cl2/hexane = 1:1). IR and mass spectra are similar to the
literature data.43
4.2.2.5. 3,4-Dichloro-1,2,5-thiadiazole (7e). Yield 78%. Colorless oil,44 Rf = 0.55 (hexane).
IR and mass spectra are similar to the literature data.44
4.2.2.6. N,N,N',N'-Tetramethyl-1,2,5-thiadiazole-3,4-diamine (7f). Yield 64%. Colourless oil,
Rf = 0.60 (CH2Cl2). Anal. calcd for С6Н12N4S (172.25): С 41.84, Н 7.02, N 32.53, S 18.62.
1
Found: C 41.92, H 6.89, N 32.47, S 19.08. NMR (δ), H: 2.95 (12H, s, 4СН3); 13C: 40.2
(CH3), 154.9. MS, m/z (%): 172 (M+, 100), 102 (36); 46 (23). ESI-MS: found m/z 172.0784;
calc. for С6Н12N4S [M+H]+ 172.0777. IR, ν, cm–1: 2954 and 2856 (C-H), 1509, 1448, 1448,
1254, 1182.

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4.2.2.7. 2,1,3-Benzothiadiazole (7g). Yield 66%. Colorless solid, mp 41-42 ºС (43-44 ºС),20
Rf = 0.75 (CH2Cl2). IR and mass spectra are similar to the literature data.20
4.2.2.8. 4,5,6,7-Tetrahydro-2,1,3-benzothiadiazole (7h). Yield 54%. Colorless oil,44 Rf = 0.35
(CH2Cl2). NMR (δ), 1H: 1.86 (4H, m, 2СН2), 2.85 (4H, m, 2СН2); 13C: 20.2, 21.9, 151.6. MS,
m/z (%): 140 (M+, 100), 94 (55); 71 (82).
4.2.2.9. Acenaphtho[1,2-c][1,2,5]thiadiazole (7i). Yield 71%. Yellow solid, mp 130-131 ºС
1
(132-133 ºС),20,46 Rf = 0.70 (CH2Cl2). NMR (δ), H: 7.75 (2H, t, 2СН, J=9.0), 8.02 (2H, d,
2СН, J = 9.0), 8.15 (2H, d, 2СН, J = 9.0); 13C: 122.4, 127.0, 128.2, 129.2, 131.0, 141.4,
165.8. MS, m/z (%): 210 (M+, 95), 178 (100); 152 (20); 126 (8). IR, ν, cm–1: 2923 and 2853
(C-H), 1571, 1360, 1014, 829, 762.
4.2.2.10. [1,2,5]Thiadiazolo[3,4-b]quinoxaline (10). Yield 73%. Yellow solid, mp 195-197
ºС (199.5-200.5 ºС),43 Rf = 0.55 (CH2Cl2/acetone = 5:1). IR and mass spectra are similar to
the literature data.43
4.2.2.11. Bis([1,2,5]thiadiazolo)-[3,4-b;3',4'-e]pyrazine (12). Yield 60%. Yellow solid, mp
320-322 ºС (323-329 ºС),27 Rf = 0.15 (CH2Cl2/acetone = 3:1). MS, m/z (%): 196 (M+, 80),
104 (8); 46 (100). IR, ν, cm–1: 1331, 940, 930, 519.
4.2.2.12. [1,2,5]Thiadiazolo[3,4-c][1,2,5]thiadiazole (14). Yield 59%. Colorless solid, mp
113-116 ºС (116-118 ºС),19 Rf = 0.55 (CH2Cl2/hexane = 2:1). IR and mass spectra are similar
to the literature data.19
4.3. Crystallographic data
Crystal data for 8a: C4H4N2OS, M = 128.15 g mol–1, orthorhombic, space group Pnma,
a = 7.7454(5), b = 6.4865(4), c = 11.2728(7) Å, V = 566.35(6) Å3, Z = 4 (Z’ = 1/2), ρcalc
=
1.503 g m–3, ꢀ = 4.61 mm–1, F(000) = 264. Intensities of 4379 reflections were measured with
a Bruker Apex II DUO CCD diffractometer [λ(MoKα) = 0.71072 Å, ω-scans, θ < 58°], and
818 independent reflections [Rint = 0.0170] were used in further refinement. The structure
was solved by direct method and refined by the full-matrix least-squares technique against F2

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in the anisotropic-isotropic approximation. Hydrogen atom positions were calculated, and
they were refined in the isotropic approximation within the riding model. The refinement
converged to wR2 = 0.0921 and GOF = 1.006 for all independent reflections (R1= 0.0290
was calculated against F for 779 observed reflections with I > 2σ(I)).
Crystal data for 10: C8H4N4S, M = 188.22 g mol–1, monoclinic, space group P21/c, a =
3.7973(6), b = 9.3167(13), c = 21.578(4) Å, β = 93.703(8)o, V = 761.8(2) Å3, Z = 4, ρcalc
=
1.641 g m–3, ꢀ = 0.370 mm–1, F(000) = 384. Intensities of 1734 reflections were measured
with a Bruker Kappa APEX II CCD diffractometer [λ(MoKα) = 0.71072 Å, φ, ω scans of
narrow (0.5°) frames]. The structure was solved by direct method and refined by the full-
matrix least-squares technique against F2 in the anisotropic-isotropic approximation.
Hydrogen atom positions were calculated, and they were refined in the isotropic
approximation within the riding model. The refinement converged to wR2 = 0.0948 and GOF
= 1.150 for all independent reflections (R1= 0.0356 was calculated against F for 1585
observed reflections with I > 2σ(I)).
All calculations were performed using SHELXTL PLUS 5.0.47 For 10, absorption
corrections were applied empirically using SADABS programs48 (transmission: 0.84-0.97).
Structure of 10 was analyzed for shortened contacts between non-bonded atoms using the
PLATON program.49
CCDC 988698 contains the supplementary crystallographic data for 8a and CCDC
995869 for 10. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the CCDC, 12 Union Road,
Cambridge, CB21EZ, UK; fax: (+44) 1223-336033; or deposit@ccdc.cam.ac.uk.
4.4. Cyclic voltammetry and EPR measurements
The CV measurements on compounds 8a,b,g and 17 (~ 1–2 mM solutions in MeCN)
were performed with a PG 310 USB potentiostat (HEKA Elektronik) at 293 K in an argon
atmosphere at a stationary Pt spherical electrode (S = 0.08 cm2) with 0.1 M Et4NClO4 as a
supporting electrolyte. The potential sweep rate was 0.1 V.s–1. A standard electrochemical
cell (solution volume was 5mL) connected to the potentiostat with three-electrode scheme
was used. Peak potentials were quoted with reference to a saturated calomel electrode (s.c.e).
Fist both reduction and oxidation peaks for the compounds were diffusion-controlled, i.e.
Ip1C
Ip1C
is the peak current.
v–0.5 = const, where

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Digital simulation of the CV of 8g and 17 in reductive potentials area has been done
using the ESP program.50 Simplex algorithm was used for multiparameter optimization
implemented in the ESP. Fixed parameters were as follows: initial concentrations of
depolarizers were 1.9 mM for 8g and 0.8 mM for 17; the values of diffusion coefficients were
applied as 1.3 10-5 cm2 s–1, ke = 0.1 cm s–1, α = 0.5 (ke − heterogeneous rate constant, α −
transfer coefficient) for all electrochemical reactions. Scan rate was 0.1 V s−1, step time 20
ms; initial and final potentials were 0.000 V, vertex potentials −1.000 V for 17 and −1.797 V
for 8g. Since oximes and dioximes are very weak acids, the corresponding pK1(2) were fixed
as −11.0.51 The optimized peak potentials and rate constants for irreversible homogeneous
reactions (Scheme 8) are presented in Table 3.
The EPR spectra were measured with a Bruker ELEXSYS E-540 X-band
spectrometer (MW frequency ~9.87 GHz, MW power of 20 mW, modulation frequency of
100 KHz and modulation amplitude of 0.005 mT) equipped with a high-Q cylindrical
resonator ER4119HS. Paramagnetic products from 8g and 17 and RAs of 7g and 19 were
obtained under argon by ECR in MeCN at 298 K with the standard electrochemical cell for
EPR measurements. Simulations of the experimental EPR spectra were performed with the
WinSim 2002 program52 (the accuracy in calculating hfc constants is ±0.0001 mT).
4.5. Quantum chemical calculations
For the RAs of 7g and 19, UB3LYP/6-31+G(d) calculations were performed with full
geometry optimization using the GAMESS suite of programs.53 PCM model38 was used to
account for MeCN solvent.
Acknowledgments
We gratefully acknowledge financial support from the Russian Foundation for Basic
Research (Projects 13-03-00072 and 14-03-31051), the Presidium of the Russian Academy of
Sciences (Programme No. 8, Project 8.14) and the Leverhulme Trust (Project IN-2012-094). I.
Yu. B., L. A. S. and A. V. Z. are grateful to the Ministry of Education and Science of the
Russian Federation for the support within Project of Joint Laboratories of Siberian Branch of
the Russian Academy of Sciences and National Research Universities.

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Supplementary data
Supplementary data associated with this article can be found, in the online version, at …
References and notes
1. Koutentis, P. A. in Comprehensive Heterocyclic Chemistry III; Katritzky, A. R., Ramsden,
C. A., Scriven, E. F. V., Taylor, R. J. K., Eds.; Elsevier: Oxford, 2008; Vol. 5, Ch. 5.09, pp.
516-564.
2. Koutentis, P. A. in Science of Synthesis, Storr, R. C., Gilchrist, T. L., Eds.; Georg Thieme
Verlag KG: Stuttgart, 2003; Vol. 13, Ch. 13.11, pp. 297-348.
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