Anti-Markovnikov addition of 2-mercaptobenzoxazole and 2-mercaptobenzothiazole to trimethoxy(vinyl)silane under solvent- and catalyst-free conditions

Article abstract of DOI:10.1016/j.jorganchem.2020.121269

The addition of 2-mercaptobenzoxazole or 2-mercaptobenzothiazole to trimethoxy(vinyl)silane was studied. The thiol-ene reaction leads to previously unknown carbofunctional (trimethoxysilyl)ethyl derivatives of 2-mercaptobenzazoles C₆H₄N(Y)CS(CH₂)₂Si(OMe)₃ (Y = O, S) with anti-Markovnikov orientation. The proposed mechanism is confirmed by EPR spectroscopy and quantum chemical calculations.

Full text of DOI:10.1016/j.jorganchem.2020.121269

Journal Pre-proof
Anti-Markovnikov addition of 2-mercaptobenzoxazole and 2-mercaptobenzothiazole
to trimethoxy(vinyl)silane under solvent- and catalyst-free conditions
O.M. Trofimova, E.A. Grebneva, YuI. Bolgova, D.V. Pavlov, T.I. Vakul'skaya, A.I.
Emelyanov, A.S. Pozdnyakov
PII:
S0022-328X(20)30171-6
DOI:
https://doi.org/10.1016/j.jorganchem.2020.121269
JOM 121269
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 24 December 2019
Revised Date: 27 March 2020
Accepted Date: 29 March 2020
Please cite this article as: O.M. Trofimova, E.A. Grebneva, Y. Bolgova, D.V. Pavlov, T.I. Vakul'skaya,
A.I. Emelyanov, A.S. Pozdnyakov, Anti-Markovnikov addition of 2-mercaptobenzoxazole and 2-
mercaptobenzothiazole to trimethoxy(vinyl)silane under solvent- and catalyst-free conditions, Journal of
Organometallic Chemistry (2020), doi: https://doi.org/10.1016/j.jorganchem.2020.121269.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition
of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of
record. This version will undergo additional copyediting, typesetting and review before it is published
in its final form, but we are providing this version to give early visibility of the article. Please note that,
during the production process, errors may be discovered which could affect the content, and all legal
disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier B.V.

1
Anti-Markovnikov addition of 2-mercaptobenzoxazole and 2-
mercaptobenzothiazole to trimethoxy(vinyl)silane under solvent- and catalyst-free
conditions
O.M. Trofimova 1, E.A. Grebneva, Yu.I. Bolgova, D.V. Pavlov, T.I. Vakul’skaya, A.I. Emelyanov,
A.S. Pozdnyakov
A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy Sciences, 1 Favorsky Str., 664033
Irkutsk, Russia
Abstract
The addition of 2-mercaptobenzoxazole or 2-mercaptobenzothiazole to trimethoxy(vinyl)silane was
studied. The thiol-ene reaction leads to previously unknown carbofunctional (trimethoxysilyl)ethyl
derivatives of 2-mercaptobenzazoles C6H4N(Y)CS(CH2)2Si(OMe)3 (Y = O, S) with anti-Markovnikov
orientation. The proposed mechanism is confirmed by EPR spectroscopy and quantum chemical
calculations.
Keywords: 2-mercaptobenzoxazole; 2-mercaptobenzothiazole; trimethoxy(vinyl)silane; thiol-ene
reaction; EPR spectroscopy; DFT calculations
1. Introduction
The addition of thiols to alkenes has been known for a long time [1–4]. The thiol-ene reaction has
recently seen widespread use for the formation of various polymeric organic materials [4]. It is known
that the addition to 1-alkenes occurs with high selectivity with anti-Markovnikov orientation [1,2]. The
thiyl radical adds to the less substituted end of the C=C bond to form a carbon-centered radical. The
addition is initiated photochemically or thermally, with or without the initiators. A radical initiator
(peroxide, AIBN, UV irradiation) or an oxidizing agent was used to promote the formation of sulfur-
centered radicals and anti-Markovnikov adducts [5–7]. At the present time, the efforts of researchers
are focused on the search for alternative conditions for the synthesis of anti-Markovnikov adducts.
Solvent- and catalyst-free reactions have attracted increasing interest of synthetic chemists, due to the
highly facile, efficient and environmentally benign process. The high reactivity of the thiyl radicals
makes them unique for implementation of complex catalyst-free reactions. The active applications of
the thiyl radicals for the synthesis and modification of polymers with bulky or highly reactive
substituents are based upon their ability to add to carbon-carbon multiple bonds, which allows
functional systems with tailor-made properties to be obtained [2].
1 Corresponding author.
E-mail address: omtrof@irioch.irk.ru (O.M. Trofimova)

2
The addition of different thiols to the double С=С bond of vinylsilanes has been actively studied
since the beginning of the sixties of the last century [8,9]. Most sulfur-containing organosilicon
monomers were synthesized by photochemical thiylation of unsaturated organosilicon compounds. The
free radical addition of thiols to vinylsilanes and vinylsiloxanes occurs with classical anti-
Markovnikov regioselectivity. For instance, 2-, 3-, or 4-[(2-(triethoxysilyl)ethyl)thio]aniline is obtained
by adding 2-, 3-, or 4-mercaptoaniline to triethoxy(vinyl)silane upon heating in the presence of AIBN
[10]. Photoinitiated thiylation of triethoxy(vinyl)silane with hydrogen sulfide gas affords 2-
triethoxysilylethanethiol and bis(2-triethoxysilylethyl)sulfide [11]. However, photochemical reaction
of gaseous H2S to dimethyl(chloromethyl)vinylsilane gave 3,3-dimethyl-1-thia-3-silacyclopentane
[12]. The photochemical addition of 1,2-ethanedithiol to trichlorovinyl- and triorganylvinylsilanes
R3SiCH=CH2 (R = Cl, Et, EtO) leads to the formation of mono- and bisadducts. It is interesting to note
that vinylsilanes containing alkyl and alkoxy groups at the silicon atom react much more easily than
chlorosubstituted vinylsilanes [13]. The addition of ethanethiol, 1,2-ethanedithiol, or benzenethiol with
chlorovinylsilanes H2C=CHSiMe3-nCln (n = 1–3) gives the corresponding adducts in quantitative and
near quantitative yields [14]. It was found that a reaction with a benzenethiol required a significantly
longer reaction time. 2-Aminoethanethiol hydrochloride is also easily added under the action of UV
irradiation to R3SiCH=CH2 (R = Me, Et, MeO, EtO, AcO) [15]. The photochemical addition of
mercaptoacetic acid to vinyl(trialkoxy)silanes (R = OMe, OEt) gives a mixture of adducts due to intra-
and intermolecular condensation of S-trialkoxysilylethyl derivatives of thioglycolic acid [16]. 1-
Thioacetoxy-2-[methyl(didecyl)silyl]ethane
was
prepared
by
hydrothiolation
of
didecyl(methyl)vinylsilane with thioacetic acid under photochemical initiation in THF in the presence
of benzophenone [17].
The addition of thiols to carbon-carbon double bonds is well studied. However, organosilicon
derivatives containing a heterocyclic fragment with various heteroatoms (N, O, and S) in the cycle
bonded to the silicon atom by a thioethylene bridge still remains unknown.
Previously, we have synthesized organosilicon derivatives of 2-mercaptobenzoxazole and 2-
mercaptobenzothiazole, by nucleophilic substitution of (1-chloroalkyl)trimethoxysilanes with the
appropriate 2-mercaptoazoles. Their heterocyclic fragment is bonded to the silicon atom by a
thiomethylene or thiopropylene bridge [18–20] (Fig. 1).
Fig. 1. Organosilicon derivatives of 2-mercaptobenzoxazole and 2-mercaptobenzothiazole.

3
Organosilicon
carbofunctional
β-derivatives
of
2-mercaptobenzoxazole
and
2-
mercaptobenzothiazole have not yet been studied. In the present work, we report on the synthesis of the
anti-Markovnikov product by addition of 2-mercaptobenzoxazole and 2-mercaptobenzothiazole to
trimethoxy(vinyl)silane in solvent- and catalyst-free conditions.
2. Results and discussion
New 2-{[2-(trimethoxysilyl)ethyl]thio}-1,3-benzoxazole 1a and -1,3-benzothiazole 2a have been
prepared by addition of 2-mercaptobenzoxazole
1
or 2-mercaptobenzothiazole
2
to
trimethoxy(vinyl)silane upon heating to 145 °C of any solvent- and catalyst-free. Formally, the
reaction can proceed in two directions a and b (Scheme 1). The thiol-ene reactions with
trimethoxy(vinyl)silane can give either of two possible products corresponding to Markovnikov (α-
product) or anti-Markovnikov (β-product) addition (Scheme 1).
Scheme 1. The synthesis of compounds 1a and 2a.
Additions of 2-mercaptobenzazoles to vinylsilane occur with the classical anti-Markovnikov
regioselectivity (way b). The presence of electron-withdrawing substituents at the silicon atom in
vinylsilane (R = OMe) leads to additional polarization of the C=C multiple bond that enhances its
reactivity in H2C=CHSi(OMe)3. The reaction carried out in the presence of an excess of electron-rich
trimethoxy(vinyl)silane as a radical trap allowed the formation of the corresponding compounds 1a and
2a in good yield.
The reaction mixture was boiled upon stirring for 34 h in the absence of any solvent- and catalyst-
free. During the reaction, the temperature of the reaction mixture gradually increases to 145 °C, and the
thiol-ene reaction is completed. Compounds 1a and 2a are light yellow liquids, readily soluble in
organic solvents. Their yields are 70 (1a) and 80% (2a). It should be noted that the reaction of 2-
mercaptobenzoxazole with trimethoxy(vinyl)silane in a sealed ampoule without atmospheric oxygen
proceeds faster (1 h) to give the target product in 86% yield. The composition and structure of the
synthesized silanes 1a and 2a are confirmed by elemental analysis, IR and NMR spectroscopy, as well
as mass spectrometry.

4
The FTIR spectra of compounds 1a and 2a contains the characteristic frequencies of the absorption
bands of the Si(OMe)3 group, as well as the absorption bands of the corresponding heterocyclic
fragments, shifted to the high-frequency region in the range of 1000-1400 cm-1. The chemical shifts in
the 29Si NMR spectra of compounds 1a and 2a are shifted upfield (-46.1 ppm and -46.0 ppm,
respectively). This indicates the presence of a tetracoordinated silicon atom in them. The mass spectra
of compounds 1a and 2a are characterized by a low intensity of the molecular ion peaks with m/z 299
(6%) and 315 (9%), respectively. The peak of the ion [Si(OMe)3]+ with m/z 121 has the highest
intensity (100%) in the mass spectra of compounds 1a and 2a.
The interaction of 2-mercaptobenzoxazole
1
or 2-mercaptobenzothiazole
2
with
trimethoxy(vinyl)silane without a photoinitiator, catalyst and solvent most likely occurs under thermal
initiation with the formation of the β-isomer, 2-{[2-(trimethoxysilyl)ethyl]thio}-1, 3-benzoxazole 1a or
-1,3-benzothiazole 2a.
The thermal initiation of the S–H bond facilitates the generation of thiyl radicals. After thermal
initiation, the thiyl radical C6H4N(Y)CS• (Y = O, S) adds to the less substituted end of the C=C bond to
form a carbon-centered thioethyl radical via a reversible process. The resulting radical can then abstract
a hydrogen atom from another molecule of thiol to give the thioethyl product and thiyl radical, which
propagates the chain (Scheme 2).
The reaction carried out in the presence of an excess of electron-rich vinylsilane as a radical trap
allowed the formation of the corresponding adducts in good yields.
N
S
Si(OMe)3
Y
1a (Y = O), 2a (Y = S)
N
SH
Si(OMe)3
Si(OMe)3
Si(OMe)3
A
Y
ET
+
H
N
Y
N
Y
N
N
S
S
SH
SH
Si(OMe)3
Y
Y
1 (Y = O), 2 (Y = S)
Si(OMe)3
Scheme 2. The proposed mechanism for the synthesis of compounds 1a and 2a (ET – one electron
transfer).

5
However, direct confirmation of the radical mechanism by EPR detection of radicals involved in
the reaction has not yet been obtained. Both thiyl and vinyl radicals of the compounds are unstable and
their detection in some cases is possible only in the presence of spin traps [21–23]. An experiment,
carried out in resonator EPR spectrometer, with a mixture of 2-mercaptobenzoxazole and
trimethoxy(vinyl)silane under the above conditions has shown that silane, thiol and their mixture are
EPR-silent. This evidences that the radicals under these conditions either are not formed or are
unstable.
C-phenyl-N-tert-butyl nitrone (PBN) spin-trap has been used to detect the possible radicals. This
was allowed recording a signal of adduct I (Fig. 2), the characteristics of which are given in Table.
Fig. 2. The EPR spectrum of spin adduct I recorded in the reaction mixture at 202 °C (experimental
above, simulated below).
Table
Experimental and calculated characteristics of the EPR of spin adduct I.
Value
aN, G
14.62
14.23
aH, G
2.84
2.24
g-factor
2.0065
2.0078
experimental
calculated
The analysis of EPR data and results of quantum-chemical calculations of the hyperfine structure
(HFS) constants of radicals reveals that the spin adduct corresponds to structure I (Scheme 3), which is
formed upon trapping the radical •CH2CH2Si(OMe)3 (A) by PBN trap (Scheme 3).
Scheme 3. Formation of adduct I.

6
We have assumed that the radical A is the result of outer-sphere one-electron transfer (ET) from
thiol [24] to silane to form thiol radical cation and a silane radical anion, respectively. This process is
accompanied by a fast deprotonation of the thiol radical cation followed by equally fast protonation of
the silane radical anion to deliver a pair of benzazolylthiyl and trimethoxy(ethyl)silyl radicals, which
further give the reaction products 1a or 2a (Scheme 2).
To confirm the proposed mechanism, quantum-chemical calculations [25], evaluating energy
profile of the reaction, have been performed. It turns out that energy of the pair of benzazolylthiyl and
trimethoxysilylethyl radicals is by 39 (Y = S) and 49 (Y = O) kcal mol-1 higher than that of the initial
singlet state, while energy of the reaction products is lower by 24 (compound 2a) and 19 kcal mol-1
(compound 1a) (Scheme 4).
Scheme 4. Energy profile of the reaction.
The easier addition of 2-mercaptobenzothiazole 1 to trimethoxy(vinyl)silane as compared to 2-
mercaptobenzoxazole 2 can be explained by a larger change in total energy (by 5 kcal mol-1) and a
lower total energy of trimethoxysilylethyl and benzazolylthiyl radical pair (by 10 kcal mol-1).
The synthesized compounds 1a and 2a are promising biologically active substances. According to
the PASS program [26], 2-{[2-(trimethoxysilyl)ethyl]thio}-1,3-benzoxazole 1a and -1,3-benzothiazole
2a can be used as medicines that protect the body or improve its functions. Silanes 1a and 2a are the
starting compounds in the synthesis of new trifluorosilylethyl- and silatranylethyl derivatives of 2-
mercaptobenzoxazole and 2-mercaptobenzothiazole.
3. Conclusions
In summary, we have developed an efficient protocol for the anti-Markovnikov addition of 2-
mercapto-1,3-benzoxazole and 2-mercapto-1,3-benzothiazole to trimethoxy(vinyl)silane in solvent-

7
and catalyst-free reactions. The thiol-ene addition reaction is effective method for the introduction of
the 2-mercaptobenzazoles into unsaturated compounds
4. Experimental
4.1. General information
2-Mercaptobenzoxazole, 2-mercaptobenzothiazole and trichloro(vinyl)silane were purchased from
commercial sources and used as received, without further purification. The trimethoxy(vinyl)silane
was synthesized by the alkoxylation of trichloro(vinyl)silane. A mixture of trichloro(vinyl)silane
(161.49 g, 1.0 mol) and hexane (171.50 g, 1.99 mol) (volume ratio 1: 1) was added dropwise over 1 h
to urea (180.18 g, 3.0 mol) in abs. methanol (96.12 g, 3.0 mol). The reaction mixture was stirred for 2
h. Then the upper layer was separated and distilled at atmospheric pressure. Yield 128.96 g (87%),
colorless liquid, bp 123 °С, nD25 1.3920 and consistent with literature data [27].
All reactions were carried out under argon atmosphere using а typical borosilicate glassware.
FTIR spectra were recorded on a Varian 3100 FTIR spectrometer in the spectral range between
4000–400 cm–1, using sample as a thin film. The 1H, 13C, 15N and 29Si NMR spectra were recorded on a
Bruker DRX-400 spectrometer (1H, 400.13 MHz; 13C, 100.62 MHz; 15N 40.55 MHz; 29Si 79.50 MHz).
The NMR spectra were performed at 297 K in CDCl3. For 1H NMR spectra, HMDSO (0.05 ppm) was
13
used as internal standard; in C NMR spectra, chemical shifts were assigned relative to the residual
15
signal of the solvent CDCl3 (77.0 ppm), for 15N NMR spectra, internal standard was MeNO2. The N
1
chemical shifts were obtained using the H–15N HMBC-gp method of heteronuclear inverse two-
dimensional spectroscopy with a gradient pulse. Standard 5 mm glass NMR tubes were used. 29Si
chemical shifts were measured with respect to internal standard Me4Si.
EPR spectra were recorded on a FT ELEXSYS E580 Bruker radio spectrometer (9.7 GHz) in
sealed quartz capillaries. The accuracy of g-factor measurement is ± 0.0002. Spectrum recording
conditions: modulation amplitude 1 G, modulation frequency 100 kHz, time constant 0.04 s,
conversion time 0.08 s, microwave power 0.6325 mW, gain 60 dB. EPR spectra were simulated using
the WINEPR SimFonia 1.25 program (Bruker Inc. 1996). Quantum chemical calculations were
performed using the GAUSSIAN 09 program. Geometry optimization and g-factors values were
calculated using B3LYP functional in DFT method at the 6-311++G(d,p) basis set. The hyperfine
structure constants were calculated using M062X/6-311++G(d,p), due to the calculations in B3LYP
functional turned out to be basis-dependent. Thus, addition of diffuse functions to basis set or change
of basis set double-zeta to triple-zeta, leads to increase the calculated HFSC values as much as twice
that is unsatisfactory [28]. The use of special basis sets such as EPR-II, EPR-III is impossible, since

8
they do not have functions for silicon atoms. We used the M062X functional of the M06 family, as this
functional shows an essentially lower dependence on the basis sets [29].
Mass spectra were recorded on a Shimadzu GCMS-QP5050A mass spectrometer, injector
temperature 200–250°С, helium carrier gas, detector temperature 290°С, quadrupole mass analyzer, EI
ionization (70 eV). Chromatographic separation of the studied compound samples was done on a SPB-
5 (60 m × 0.25 mm × 0.25 μm) capillary column, helium carrier gas, 0.7 ml/min flow, evaporator
temperature 230°С, 280 kPa pressure, gradient from 60 to 250°С at 10°С/min. Elemental analysis was
performed with a Thermo Scientific Flash 2000 CHNS-Analyzer. Gravimetric determination of silicon
content was carried out by the literature method [30]. Melting points were determined on a Boetius
heating bench.
4.2. Synthesis and characterization
4.2.1. Synthesis of 2-{[2-(trimethoxysilyl)ethyl]thio}-1,3-benzoxazole (1a).
Method 1. Trimethoxy(vinyl)silane (11.86 g, 0.08 mol) was added to 2-mercaptobenzoxazole 1
(10.58 g, 0.07 mol) under argon atmosphere. The reaction mixture was heated under reflux for 34 h. A
homogeneous reaction mass formed, and its temperature increased from 122 to 145 °С by the end of
the experiment. Fractional distillation under reduced pressure afforded the 14.67 g (70%) of compound
1a. The product obtained was a light yellow liquid, bp 164-167 °C (3 mmHg), nD20 1.4795.
Method 2. In an ampoule previously purged with dry argon, 2-mercaptobenzoxazole 1 (1.06 g,
0.007 mol) and trimethoxy(vinyl)silane (1.19 g, 0.008 mol) are placed. The cooled ampoule with the
reaction mixture was sealed in vacuo and placed in an oven (ES-4610). The reaction mixture was kept
at 200 °C for 1 h. Fractional distillation under reduced pressure afforded the 1.8 g (86%) of compound
20
1a, a light yellow liquid, bp 164–167 °C (3 mmHg), nD 1.4795. FTIR (ν, cm–1): 805, 1088, 1189
1
(Si(OMe)3), 748, 1011, 1126, 1281, 1499, 1597 (benzoxazole), 2841 (Si(OMe)3). Н NMR (CDCl3,
3
ppm): δ 1.25 (m, 2Н, CH2Si); 3.38 (m, 2Н, SCH2); 3.58 (s, 9H, OCH3); 7.15 (dd, 1H, H-5, J5-6 = 7.5
Hz, 3J5-4 = 7.6 Hz); 7.20 (dd, 1H, H-6, 3J6-5 = 7.4 Hz, 3J6-7= 7.8 Hz); 7.36 (d, 1Н, Н-7, 3J6-7 = 7.8 Hz);
3
7.54 (d, 1Н, Н-4, J4-5 = 7.6 Hz). 13C NMR (СDCl3, ppm): δ 10.38 (CH2Si); 26.95 (SCH2); 50.94
(OCH3); 109.40 (С-7); 117.97 (С-4); 123.36 (С-6); 123.81 (С-5); 141.73 (С-3а); 151.43 (С-7а);
29
15
164.57 (С-2). Si NMR (СDCl3, ppm): δ -46.1. N NMR (CDCl3, ppm): δ -146.0. MS m/z (Irel, %):
299 [M]+ (6), 271 [M–CH2CH2]+ (5), 266 [M−S–H]+ (6), 240 [M–SCH2CH2+H]+ (4), 239 [M–
SCH2CH2]+ (11), 238 [M–SCH2CH2–H]+ (18), 208 [M–SCH2CH2–OMe]+ (4), 151 [M–
CH2CH2Si(OMe)3+H]+ (51), 133 [M–SCH2Si(OMe)3+H]+ (6), 122 [M–C6H4NOCSCH2CH2+H]+ (18),
121 [Si(OMe)3]+ (100), 118 [M–SCH2CH2Si(OMe)3]+ (8), 107 [Si(OMe)3–Me+H]+ (6), 91 [Si(OMe)3–
OMe+H]+ (62), 90 [Si(OMe)3–OMe]+ (8), 75 [Si(OMe)3–OMe–Me]+ (6), 61 [Si(OMe)3–OMe–

9
Me2+H]+ (14), 59 [Si(OMe)3–(OMe)2]+ (12). Elemental analysis (%): Calculated for С12Н17NO4SiS: С
48.14; Н 5.72; N 4.68; Si 9.38; S 10.71. Found: С 47.88; Н 5.85; N 4.61; Si 9.60; S 11.07.
4.2.2. Synthesis of 2-{[2-(trimethoxysilyl)ethyl]thio}-benzothiazole (2a).
The title compound was prepared following procedure 1, stating from 2-mercaptobenzothiazole (1.0
g, 0.006 mol) and trimethoxy(vinyl)silane (1.19 g, 0.008 mol). The product 2a was obtained as an a
light yellow liquid (1.51 g, 80%), bp 186-190 °С (3 mmHg). FTIR (ν, cm–1): 806, 1085, 1189
(Si(OMe)3), 672, 761, 999, 1277, 1315, 1427, 1459 (benzoxazole), 2841 (Si(OMe)3). 1Н NMR (CDCl3,
3
ppm): δ 1.24 (m, 2Н, CH2Si); 3.41 (m, 2Н, SCH2); 3.57 (s, 9H, OCH3); 7.20 (t, 1H, H-6, 3J6-5 J6-7
=
3
8.0 Hz); 7.32 (t, 1Н, Н-5, 3J5-6 J5-4 = 8.0 Hz); 7.66 (d, 1Н, Н-7, 3J7-6 = 8.0 Hz); 7.80 (d, 1Н, Н-4, 3J4-
13
= 8.0 Hz). C NMR (СDCl3, ppm): δ 10.33 (CH2Si); 28.18 (SCH2); 50.31 (OCH3); 120.61 (С-7);
5
121.05 (С-4); 123.80 (С-5); 125.65 (С-6); 134.81 (С-7а); 152.92 (С-3а); 166.66 (С-2). 29Si NMR
(CDCl3, ppm): δ -46.0. 15N NMR (CDCl3, ppm): δ -85.5. MS m/z (Irel, %): 315 [M]+ (16), 284
[M−S+H]+ (4), 283 [M−S]+ (11), 282 [M−S–H]+ (11), 256 [M–SCH2CH2+H]+ (13), 255 [M–
SCH2CH2]+ (14), 254 [M–SCH2CH2–H]+ (52), 223 [M–SCH2CH2–OMe–H]+ (9), 193 [M–Si(OMe)3–
H]+ (6), 194 [M–Si(OMe)3]+ (4), 168 [M–CH2CH2Si(OMe)3]+ (7), 167 [M–CH2CH2Si(OMe)3+H]+
(44), 165 [M–CH2CH2Si(OMe)3–H]+ (25), 135 [M–SCH2CH2Si(OMe)3+H]+ (3), 122 [M–
C6H4NSCSCH2CH2+H]+ (20), 121 [Si(OMe)3]+ (100), 91 [Si(OMe)3–OMe+H]+ (56), 90 [Si(OMe)3–
OMe]+ (9), 77 [Si(OMe)3–Me3+H]+ (4), 61 [Si(OMe)3–OMe–Me2+H]+ (18), 60 [Si(OMe)3–
(OMe)2+H]+ (5), 59 [Si(OMe)3–(OMe)2]+ (16). Elemental analysis (%): Calculated for С12Н17NO3SiS2:
С 45.68; Н 5.43; N 4.44; Si 8.90; S 20.33. Found: С 45.31; Н 5.10; N 4.72; Si 8.57; S 19.96.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
Acknowledgement
The results were obtained using the equipment of Baikal analytical centre of collective using SB
RAS. All calculations of the molecular geometry and HFS constants were performed on the
«Akademik V.M. Matrosov» computation cluster (Irkutsk Supercomputer Center of the Siberian
Branch of the Russian Academy of Sciences).2
2 The website: Irkutsk: IDSTU SO RAN. URL: http://hpc.icc.ru (2019).

10
References
[1] U. Biermann, J.O. Metzger, Regioselectivity of radical addition of thiols to 1‐alkenes, Eur. J. Org.
Chem. (2018) 730–734. https://doi.org/10.1002/ejoc.201701692.
[2] F. Dénès, M. Pichowicz, G. Povie, Ph. Renaud, Thiyl radicals in organic synthesis, Chem. Rev. 114
(2014) 2587–2693. https://doi.org/10.1021/cr400441m.
[3] Ch. E. Hoyle, Ch. N. Bowman, Thiol–ene click chemistry, Angew. Chem. Int. Ed. 49 (2010) 1540–
1573. https://doi.org/10.1002/anie.200903924.
[4] Ch. E. Hoyle, T. Y. Lee, T. Roper, Thiol–enes: chemistry of the past with promise for the future, J.
Polym. Sci. Part A: Polym. Chem. 42 (2004) 5301–5338. https://doi.org/10.1002/pola.20366.
[5] F.-W. Lou, J.-M. Xu, B.-K. Liu, Q. Wu, Q. Pan, X.-F. Lin, Highly selective anti-Markovnikov
addition of thiols to vinyl ethers under solvent- and catalyst-free conditions, Tetrahedron Lett. 48
(2007) 8815–8818. https://doi.org/10.1016/j.tetlet.2007.10.072.
[6] C. Rissing, D.Y. Son, Thiol−ene reaction for the synthesis of multifunctional branched
organosilanes, Organometallics 27 (2008) 5394–5397. https://doi.org/10.1021/om8003527.
[7] A.B. Lowe, Thiol-ene “click” reactions and recent applications in polymer and materials synthesis,
Polym. Chem. 1 (2010) 17–36. https://doi.org/10.1039/B9PY00216B.
[8] C. Rissing, D.Y. Son, Thiol-ene chemistry of vinylsilanes, Main Group Chem. 8 (2009) 251–262.
http://doi.org/10.1080/10241220903134411.
[9] K. Wetterlin, The addition of some mercapto compounds to alpha,beta-unsaturated silanes, Acta
Chem. Scand. 18 (1964) 899–903. https://doi.org/10.3891/acta.chem.scand.18-0899.
[10] T. Seshadri, H.J. Haupt, Silica-immobilized 2-[(2-(triethoxysily)ethyl)thio]aniline as a selective
sorbent for the separation and preconcentration of palladium, Anal. Chem. 60 (1988) 47–52.
https://doi.org/10.1021/ac00152a013.
[11] M.G. Voronkov, N.N. Vlasova, M.Y. Adamovich, Y.N. Pozhidaev, A.I. Kirillov,
Bis(triorganylsilylalkyl) sulfide and polymer complexing sorbents at their base, Zh. Obsh. Khim.
54 (1984) 865–868.
[12] M.G. Voronkov, S.V. Kirpichenko, E.N. Suslova, V.V. Keiko, A.I. Albanov, 1,3-
Thiasilacyclopentane and 1,3- and 1,4-thiasilacyclohexane derivatives, J. Organomet. Chem. 243
(1983) 271–279. https://doi.org/10.1016/S0022-328X(00)98548-6.
[13] N.N. Vlasova, G.Y. Zhila, A.I. Albanov, V.Y. Vitkovskii, M.G. Voronkov, Photochemical
addition of 1,2-ethanedithiol to alkenyltrichlorosilanes and triorganylalkenylsilanes, Zh. Obsh.
Khim. 53 (1983) 378–382.
[14] A.R. Jennings, Z.S. Bassampour, A.G. Patel, D.Y. Son, Orthogonal reactivity of thiols toward
chlorovinylsilanes: selective thiol-ene chemistry, Tetrahedron Lett. 55 (2014) 6773–6775.

11
http://dx.doi.org/10.1016/j.tetlet.2014.09.113.
[15] G.Y. Zhila, O.G. Yarosh, N.N. Vlasova, A.I. Albanov, M.G. Voronkov, Photochemical addition
of 2-aminoethanethiol hydrochloride and 2-(diethylamino)ethanethiol to triorganyl(vinyl)silanes
and triorganyl(ethynyl)silanes, Zh. Obsh. Khim. 58 (1988) 536–539.
[16] Y.N. Pozhidaev, O.Y. Raspopina, N.N. Vlasova, M.G. Voronkov, Sorption of noble metal ions by
organosilicon polymer based on S-triethoxysilylethyl derivatives of thioglycolic acid, Russ. J.
Appl. Chem. 72 (1999) 610–612.
[17] А.N. Tarasenkov, E.V. Getmanova, E.A. Tatarinova, М.I. Buzin, N.V. Demchenko, G.V.
Cherkaev, А.М. Muzafarov, Synthesis of thioether-containing carbosilane dendrimers with
sterically shielded sulfur atoms, Russ. Chem. Bull., Int. Ed. 66 (2017) 1675– 1685.
https://doi.org/10.1007/s11172-017-1940-3.
[18] E.А. Grebneva, Y.I. Bolgova, O.M. Trofimova, A.I. Albanov, T.N. Borodina, Synthesis and
structure of novel Si-substituted silylpropyl derivatives of 2-mercaptobenzoxazole and 2-
mercaptobenzothiazole, Chem. Heterocycl. Compd. 2019, 55, 762–767.
https://doi.org/10.1007/s10593-019-02532-3.
[19] M.G. Voronkov, O.M. Trofimova, Yu.I. Bolgova, N.F. Chernov, Hypervalent silicon-containing
organosilicon derivatives of nitrogen heterocycles, Russ. Chem. Rev. 76 (2007) 825–845.
https://doi.org/10.1070/RC2007v076n09ABEH003706.
[20] M.G. Voronkov, N.F. Chernov, O.M. Trofimova, T.N. Aksamentova, Organosilicon derivatives of
2-mercapto-substituted benzoxazoles, benzothiazoles and benzimidazoles, Russ. Chem. Bull., Int.
Ed. 42 (1993) 1883–1886. https://doi.org/10.1007/BF00699009.
[21] D.N. Polovyanenko, V.F. Plyusnin, V.A. Reznikov, V.V. Khramtsov, E.G. Bagryanskaya,
Mechanistic studies of the reactions of nitrone spin trap PBN with glutathiyl radical, J. Phys.
Chem. B 112 (2008) 4841–4847. https://doi.org/10.1021/jp711548x.
[22] M.E. Mullins, J.S. Stamler, J.A. Osborne, J. Loscalzo, D.J. Singel, EPR spectroscopic
characterization of biological thiyl radicals as PBN spin-trap adducts, Appl. Magnetic Resonance
3(1992) 1021–1032. https://doi.org/10.1007/BF03166170.
[23] P.D. Josephy, D. Rehorek, E.G. Janzen, Electron spin resonance spin trapping of thiyl, radicals
from the decomposition of thionitrites, Tetrahedron Lett. 25 (1984) 1685–1688.
https://doi.org/10.1016/S0040-4039(01)81144-8.
[24] R. Hermann, G.R. Dey, S. Naumov, O. Brede, Thiol radical cations and thiyl radicals as direct
products of the free electron transfer from aromatic thiols to n-butyl chloride radical cations, Phys.
Chem. Chem. Phys. 2 (2000) 1213–1220. https://doi.org/10.1039/A909608F.
[25] Gaussian 09, Revision C.01, M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb,
J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M.

12
Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada,
M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H.
Nakai, T. Vreven, J.A. Montgomery, Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E.
Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell,
J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin,
R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth,
P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, Ö. Farkas, J.B. Foresman, J.V. Ortiz, J.
Cioslowski, D.J. Fox, Gaussian, Inc., Wallingford CT, 2009.
[26] Prediction of Activity Spectra for Substances. http://www.pharmaexpert.ru/PASSOnline/
[27] R. Nagel, Ch. Tamborski, H.W. Post, Studies in silico-organic compounds. XVIII. The
preparation and properties of vinyltrialkoxysilanes, J. Org. Chem. 16 (1951) 1768–1771.
https://doi.org/10.1021/jo50005a017.
[28] E.F. Belogolova, T.I. Vakul'skaya, V.F. Sidorkin, Radical anions of hypervalent silicon
compounds: 1-substituted silatranes, Phys. Chem. Chem. Phys. 17 (2015) 12735–12746.
https://doi.org/10.1039/c4cp06046f.
[29] Y. Zhao, D.G. Truhlar, The M06 suite of density functionals for main group thermochemistry,
thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two
new functionals and systematic testing of four M06-class functionals and 12 other functionals,
Theor. Chem. Acc. 120 (2008) 215–241. https://doi.org/10.1007/s00214-007-0310-x.
[30] N.E. Gel’man, E.А. Terent'eva, T.М. Shanina, L.М. Kiparenko, V. Rezl, Methods of Quantitative
Organic Elemental Microanalysis [In Russian], Khimiya, Moscow, 1987.

The addition of 2-mercaptobenzazole to trimethoxy(vinyl)silane was studied
New (trimethoxysilyl)ethyl derivatives of 2-mercaptobenzazoles were obtained
The thiol-ene reaction leads to unknown silanes with anti-Markovnikov orientation
The mechanism of reaction is confirmed by EPR and quantum chemical calculations

Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests: