2-(3-Cyanopropyldimethylsilyl)ethyl as a Polar Sulfur Protecting Group

Article abstract of DOI:10.1055/s-0039-1690184

Organosulfur compounds are ubiquitous in synthetic chemistry, biology and materials chemistry. The reactivity of free sulfhydryls requires their masking in many synthetic strategies. To facilitate the isolation of protected thiols by chromatography, we propose 2-(3-cyanopropyldimethylsilyl)ethyl as a polar protecting group analogue of 2-(trimethylsilyl)ethyl. The masked thiophenol is obtained in two synthetically complementing ways. Either an existing thiophenol is protected, or the protected thiol group is introduced by a cross-coupling reaction. In both cases the required reagents are readily available from inexpensive starting materials. Thiol protection and thiol introduction both tolerate a large variety of functional groups and substitution patterns, and the protected thiophenols are stable toward a broad range of reaction conditions. The stability of the protected derivatives in cross-coupling reactions and the mild reaction conditions for the release of the protecting group further emphasizes the potential of the methodology.

Full text of DOI:10.1055/s-0039-1690184

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2019, 51, A–L
paper
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de
L. M. Bannwart et al.
Paper
Synthesis
2-(3-Cyanopropyldimethylsilyl)ethyl as a Polar Sulfur Protecting
Group
Linda M. Bannwarta
Pascal S. Riedera
Marcel Mayor*a,b,c
a Department of Chemistry, University of Basel, St. Johanns-
Ring 19, 4056 Basel, Switzerland
marcel.mayor@unibas.ch
b Institute for Nanotechnology (INT), Karlsruhe Institute of
Technology (KIT), P.O. Box 3640, 76021 Karlsruhe, Germany
c Lehn Institute of Functional Materials (LIFM), School of
Chemistry, Sun Yat-Sen University (SYSU), Guangzhou
510275, P. R. of China
Received: 19.06.2019
Accepted after revision: 02.08.2019
Published online: 03.09.2019
versity of reactivity of sulfur, this becomes challenging in
many reaction strategies in synthetic organic chemistry.
Examples are the tendency of free thiols to form disulfides
and other oxidation products under more oxidative condi-
tions.6,7 Another issue is the strong affinity of thiols to met-
als and metal ions, being responsible for the poisoning of
various catalytic systems.8
DOI: 10.1055/s-0039-1690184; Art ID: ss-2019-t0337-op
Abstract Organosulfur compounds are ubiquitous in synthetic chem-
istry, biology and materials chemistry. The reactivity of free sulfhydryls
requires their masking in many synthetic strategies. To facilitate the iso-
lation of protected thiols by chromatography, we propose 2-(3-cyano-
propyldimethylsilyl)ethyl as a polar protecting group analogue of
2-(trimethylsilyl)ethyl. The masked thiophenol is obtained in two syntheti-
cally complementing ways. Either an existing thiophenol is protected,
or the protected thiol group is introduced by a cross-coupling reaction.
In both cases the required reagents are readily available from inexpen-
sive starting materials. Thiol protection and thiol introduction both tol-
erate a large variety of functional groups and substitution patterns, and
the protected thiophenols are stable toward a broad range of reaction
conditions. The stability of the protected derivatives in cross-coupling
reactions and the mild reaction conditions for the release of the pro-
tecting group further emphasizes the potential of the methodology.
Our own interest in masking the thiol group is related to
its role as an anchor group immobilizing molecules on no-
ble-metal surfaces. We have also developed numerous sin-
gle-molecule devices integrated in physical experiments
with thiol–metal bonds. While the thiol–gold bond might
have intrinsic challenges due to the variety of atomistic re-
alizations on Au(111) surfaces, it remains the workhorse in
single-molecule electronics.9 In particular, the combination
of reliable electronic contact and mechanical stability with
enough mobility enabling, for example, the formation of
self-assembled monolayers makes the thiol anchor group
very appealing for this purpose. The examples of single-
molecule experiments range from terminally thiol-func-
tionalized rigid rods10–15 and shape-persistent macrocy-
cles16,17 over mechano-sensitive structures18,19 to three-di-
mensional objects, spatially oriented by three parallel im-
mobilizing thiol–gold bonds.20–25 In many cases, the
syntheses of these functional molecules require the protec-
tion of the sulfhydryl groups.
So far, known protected aryl thiols can be categorized
into five main groups: S-aryl thioates (e.g., acetyl),26–31 aryl-
alkylsulfides and arylheteroalkylsulfides,32–36 S-aryl car-
bonothioates and S-aryl carbamothioates,37–39 arylbenzyl-
sulfides,40–42 and silicon-comprising43–46 aryl sulfides. Par-
ticularly appealing is the ethyl silane sulfur protecting
group (PG)43,47–49 due to its wide range of tolerated reaction
conditions. On the other hand, trialkyl arylthiosilanes are
considerably less stable than their oxygen analogues and
are thus synthetically less useful.
Key words thiols, protecting groups, cross-coupling, easy to purify,
polarity
Thiol (sulfhydryl) groups are ubiquitous as important
functional groups, e.g., in biology, materials chemistry and
molecular devices. Due to their rich and unique chemistry,
they are often involved in highly functional areas of pro-
teins. An example is the formation of disulfides under rath-
er mild conditions. The formation of disulfide bonds be-
tween thiols exposed by the amino acid cysteine contrib-
utes crucially to the stability of the tertiary structure of
folded proteins.1 The importance of sulfur-containing scaf-
folds for biological activity is also reflected in their frequent
appearance in natural products,2 medicinal chemistry3 and
sulfur-comprising proteins.4
The importance of sulfhydryl groups arises from the
unique chemistry of sulfur (e.g., nucleophilicity, affinity to
metals, rich redox chemistry),5 reflected in a broad range of
reactivity. While nature profits extensively from the rich di-
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–L
Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B
L. M. Bannwart et al.
Paper
Synthesis
Ideal protecting groups are on the one hand stable un-
der a wide range of reaction conditions, but on the other
hand they remain removable under mild conditions, allow-
ing a large variety of functional groups to be present. In ad-
dition, the protected and deprotected compounds should
provide polarity features enabling their separation by chro-
matography.
Herein we report 2-(3-cyanopropyldimethylsilyl)ethyl
(Figure 1, c) as a promising polar protecting group of ar-
ylthiols. The objective of the study is an analogue of the
popular 2-(trimethylsilyl)ethyl protecting group (Figure 1,
b),43 but with optimized polarity features to facilitate sepa-
ration by chromatography. The concept to enhance the po-
larity of a silyl protecting group with an exposed nitrile
group is borrowed from Höger and Bonrad, who reported
the potential of 3-cyanopropyldimethylsilyl as a protecting
group for alkynes in 2000.50 The peripheral nitrile group fa-
cilitates separation of the protected derivatives by flash col-
umn chromatography, while the trialkyl-silyl core structure
provides similar stability features and deprotection condi-
tions as the classical analogues. As displayed in Figure 1, the
polarity of the 2-(3-cyanopropyldimethylsilyl)ethyl-pro-
tected thiophenol is increased considerably compared to
the 2-(trimethylsilyl)ethyl analogue.
HS
Si
Si
N
N
1
3
(a)
(b)
O
(c)
S
Cl
Si
Si
N
N
4
2
Scheme 1 Preparation of reagents 1 and 3. (a) Vinylmagnesium chlo-
ride, THF, 10 °C, 30 min, 78%; (b) thioacetic acid, AIBN, 60 °C, 2 h, 91%;
(c) K2CO3, MeOH, H2O, Et2O, room temperature, 2 h, then citric acid,
75%.
MS), the reaction was complete after the addition of vinyl-
magnesium chloride at 10 °C to a solution of chloro-(3-cy-
anopropyl)dimethylsilane (CPDMS-Cl) (4) in THF, and sub-
sequent heating was not required. Product 1 was obtained
as a colorless oil in 78% yield after vacuum distillation.
The thiol-ene addition between vinylsilanes and thio-
phenols with 2,2′-azobis(isobutyronitrile) (AIBN) as a radi-
cal initiator is well known,43 and the protected thiophenols
are usually obtained in excellent yields. Here, in our case,
di-tert-butyl peroxide (DTBP) was favored as a radical initi-
ator, because it is liquid at room temperature and thus it is
better suited for the selected neat reaction conditions.53–55
The radical reaction between 1 and the parent thiophenol 5
(Scheme 2) provided protected thiophenol 6 in a very good
93% yield on a half-gram scale, and in an even better 99%
isolated yield on a 5 g scale.
cyclohexane/EtOAc
SH
20:1
a)
S
Si
b)
S
Si
c)
N
SH
+
S
(a)
a
b
c
Si
Si
N
N
Figure 1 Thin-layer chromatography (TLC) of (a) benzenethiol
(Rf = 0.52), (b) 2-(trimethylsilyl)ethyl thiophenol (Rf = 0.61), and
(c) 2-(3-cyanopropyldimethylsilyl)ethyl thiophenol (Rf = 0.17), showing
the enhanced polarity of the protecting group reported herein, which
facilitates isolation of the protected compound by flash column chro-
matography
5
1
6
Scheme 2 Protection of benzenethiol (5) with protecting group pre-
cursor 1. (a) DTBP, neat, 100 °C, 1 h, 93% (0.5 g), 99% (5.0 g).
The reaction conditions for introducing the protecting
group tolerate a variety of functional groups (Scheme 3).
There are however general trends. Liquid thiophenols (e.g.,
6, 20, and 21) react faster and the masked derivatives are
obtained in higher yields than for solid thiophenols (e.g.,
13, 14, 16, 17 and 18). Steric hindrance in the investigated
thiophenols requires extended reaction periods (e.g., 7 and
10 vs 6, 8 and 9). Strongly polarizing substituents tend to
slow the reaction down (e.g., 13, 14, 15, 16, 17 or 19). Ani-
line 13 required 150 °C as the reaction temperature, other-
wise the reaction was extremely slow. The protocol also
works in excellent yields with aliphatic thiols, as demon-
strated with 1-octanethiol giving masked product 21 as a
representative example.
An appealing aspect of this protecting group is that it
can be introduced with both 3-cyanopropyldimethyl vinyl-
silane (1) to mask an exposed aryl or alkyl thiol, and with
2-(3-cyanopropyldimethylsilyl)ethanethiol (3) in a masked-
thiol-introducing cross-coupling reaction, substituting a
suitable leaving group. As displayed in Scheme 1, the re-
quired reagent 3 is obtained via S-[2-(3-cyanopropyldi-
methylsilyl)ethyl] ethanethioate (2).
The protection of the thiols was investigated first. The
reagent 1 for introducing the protecting group was pre-
pared via a similar protocol to that reported for the synthe-
sis of vinyl trimethylsilane51,52 (Scheme 1). However, ac-
cording to gas chromatography–mass spectrometry (GC-
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–L

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L. M. Bannwart et al.
Paper
Synthesis
The reaction protocol of Itoh and Mase34 was adapted to
substitute aryl bromides with thiol 3. The reported proce-
dure uses Pd2(dba)3 (2.5 mol%) as a pre-catalyst and Xant-
phos (5 mol%) as the ligand. The similar polarities of dba
and compound 6 motivated the search for an alternative
palladium source. By using (Ph3P)4Pd or (Ph3P)2PdCl2 as cat-
alysts the same yields were obtained without purification
issues. For the cross-coupling protocol (Ph3P)2PdCl2 was
chosen as the pre-catalyst due to its lower price and larger
tolerance to oxygen impurities compared to (Ph3P)4Pd.
The protected thioaryls 6, 14, 15, and 19 were all ob-
tained in good to excellent yields with this protocol within
a reaction time of 12 hours (Scheme 4). The syntheses of 7
and 13 required repeated addition of (Ph3P)2PdCl2 and
Xantphos until complete disappearance of the starting ma-
terial was observed by GC-MS after 48 hours. The steric
hindrance of the neighboring methyl group in compound 7
and the electron-donating amine group in 13 were not only
reflected in reduced reaction rates, but also in lower isolat-
ed yields. While model compound 7 was obtained in a bet-
ter yield by the radical reaction between 2-methylbenzen-
ethiol and 1 (82% vs 65%), the cross-coupling reaction ap-
pears to be the better strategy for aniline 13 (72% vs 42%).
SH
S
(a)
Si
Si
N
N
R
R
1
SR′
SR′
SR′
6 (1 h)
93% (quant.)a
7 (12 h)
82%
8 (2 h)
84%
SR′
SR′
SR′
Br
9 (2 h)
84%
10 (24 h)
69%
11 (3 h)
71% (85%)a
SR′
SR′
SR′
H2N
O2N
12 (4 h)
78%
13 (20 h, 150 °C)b,c
14 (20 h)c
42%
82%
SR′
SR′
SR′
N
(HO)2B
F
15 (5 h)
16 (6 h)c
17 (6 h)c
93%
43%
60%
Br
HS
S
(a)
Si
Si
N
SR′
N
SR′
SR′
R
R
F
F
3
O
F
SR′
SR′
SR′
18 (12 h)c
19 (6 h)
20 (2 h)
84%
93%
81%
H2N
SR′
6 (12 h)
quant.
7 (48 h)
65%
13 (48 h)
72%
21 (1 h)
92%
SR′
SR′
SR′
R′ =
Si
O2N
F
O
N
14 (12 h)
96%
15 (12 h)
quant.
19 (12 h)
79%
Scheme 3 Reaction scope of the protection of thioaryl derivatives (in-
cluding a thioalkyl model compound) with the reagent 1. (a) 1
(1.2 equiv), DTBP, 100 °C, 1–20 h. a Reaction on 5 g scale. b Reaction
was extremely slow at 100 °C. c Reagent 1 (2.4 equiv) was used for reac-
tions of solid compounds.
R′ =
Si
N
Scheme 4 Reaction scope of the masked thiol introduction by a
cross-coupling protocol with reagent 3. (a) 3 (1.2 equiv), (Ph3P)2PdCl2
(2.5 mol%), Xantphos (5 mol%), iPr2NEt, dioxane, 110 °C.
As an alternative approach to protected thiophenol
derivatives, a cross-coupling protocol for the introduction
of the masked thiol was considered. For the synthesis of
2-(3-cyanopropyldimethylsilyl)ethanthiol (3), the route de-
veloped by Schwan et al.48 was used (Scheme 1). Freshly
distilled thioacetic acid was stirred with 1 and AIBN as a
radical initiator at 60 °C for 2 hours. Compound 2 was ob-
tained as a light yellow oil in 91% yield after vacuum distil-
lation. Thioacetate 2 was hydrolyzed with K2CO3 in a sol-
vent mixture of MeOH, H2O and Et2O. After addition of citric
acid to protonate the thiolate, 2-(3-cyanopropyldimethyl-
silyl)ethanethiol (3) was isolated by fractional vacuum dis-
tillation in 75% yield as a colorless oil.
To remove the PG four different procedures were inves-
tigated, using 6 as a model compound (Scheme 5). In the
first approach, benzenethiol (5) was obtained from 6 by
deprotection with TBAF in THF at room temperature. Unfor-
tunately, benzenethiol (5) is not suited as a model com-
pound due to its challenging isolation features. While the
deprotection reaction proceeded quantitatively according
to reaction monitoring by gas chromatography, purification
of 5 by column chromatography, acid–base extraction, and
distillation resulted only in fractions comprising impurities.
Finally, a pure fraction of 5 was isolated in a poor 42% yield
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–L

D
L. M. Bannwart et al.
Paper
Synthesis
by extraction in Et2O with NaHCO3. As a more representa-
tive example, derivative 11 was exposed to the same reac-
tion conditions and the corresponding less volatile thiophe-
nol derivative 24 was isolated in 90% yield. However, thiol
24 was also quickly oxidized to the corresponding disulfide
in the presence of oxygen. To facilitate isolation of the re-
leased thiophenols, their in situ transformation into the
corresponding disulfides or acetyl-protected derivatives
was investigated. Both derivatives are appealing due to
their potential as precursors of self-assembled monolayers.
To favor disulfide formation, iodine and pyridine were add-
ed to the TBAF deprotection reaction mixture and indeed,
1,1′-disulfanediyldibenzene (22) was isolated in an excel-
lent 95% yield. Also, the capture of the thiophenol as S-phe-
nyl ethanethioate (23) by addition of acetyl chloride to the
deprotection reaction mixture was successful (83%). In an
alternative protocol, 6 was treated with AgBF4 and AcCl in
CH2Cl2 at room temperature for 12 hours, providing ethane-
thioate 23 in 89% yield.
starting with compound 11 and, in a second approach, us-
ing boronic acid 16 as starting material. The reaction of
compound 11 with phenylboronic acid was investigated
with two catalytic systems, (Ph3P)2PdCl2 and SPhos Pd G2
(2 mol% respectively), with the second one giving a slightly
better yield (90% vs 92%). Consequently, the same catalyst
(SPhos Pd G2, 2 mol%) was used to couple boronic acid 16
with iodobenzene, yielding again 25 in a good 87% isolated
yield and demonstrating the suitability of iodoaryls as reac-
tion partners in the presence of PG. Compound 11 was also
engaged in a Sonogashira reaction with phenylacetylene,
using a mixture of THF and piperidine as solvent, and the
combination of CuI (6 mol%) and (Ph3P)2PdCl2 (5 mol%) as
catalytic system.56 Also, under these cross-coupling condi-
tions, the PG proved to be perfectly stable and the desired
tolane 26 was isolated in 91% yield.
S
Si
N
(c)
Br
S
Si
11
(a)
N
S
Si
N
or
(b)
R
R = H 6
R = Br 11
26
S
Si
(c) or (d)
N
(a)
(b)
25
SH
S
(d)
S
S
O
R
R = H 5
R = Br 24
S
Si
22
23
N
HO
B
Scheme 5 Release of the PG demonstrated with compound 6, provid-
ing benzenethiol (5), 1,1′-disulfanediyldibenzene (22), and S-phenyl
ethanethioate (23). Procedure (a) was further studied with 11 yielding
4-bromobenzenethiol (24). (a) TBAF, THF, room temperature, 4 h, 42%
(5), 90% (24); (b) TBAF, THF, room temperature, 4 h, then pyridine, I2,
30 min, 95%; (c) TBAF, THF, room temperature, 4 h, then AcCl, 8 h, 83%;
(d) AgBF4, AcCl, CH2Cl2, room temperature, 12 h, 89%.
16
OH
Scheme 6 Stability of the PG in cross-coupling reactions. Assembly of
biphenyl 25 in a Suzuki reaction with either bromine 11 or boronic acid
16, and the synthesis of tolane 26 in a Sonogashira reaction. (a) Phenyl-
boronic acid, K2CO3, (Ph3P)2PdCl2 (2 mol%), toluene, H2O, 80 °C, 3 h,
90%; (b) phenylboronic acid, K2CO3, SPhos Pd G2 (2 mol%), toluene,
H2O, 80 °C, 3 h, 92%; (c) phenylacetylene, CuI (6 mol%), (Ph3P)2PdCl2
(5 mol%), THF, piperidine, 80 °C, 3 h, 91%; (d) iodobenzene, K2CO3,
SPhos Pd G2 (2 mol%), toluene, H2O, 80 °C, 12 h, 87%.
With our research topic geared toward rigid structures
exposing thiophenols as anchor groups, the stability of the
protected thiophenols in cross-coupling reactions was of
particular interest. In particular, Suzuki cross-coupling con-
ditions are known to be troublesome for a variety of thio-
phenol PGs.29 As displayed in Scheme 6, 2-(3-cyanopro-
pyldimethylsilyl)ethyl-protected thiophenol derivatives
have been engaged successfully in both Suzuki and Sono-
gashira reactions. To explore the limit of the PG stability,
bromine-substituted thiophenol 11 was selected as the
starting material, requiring considerably higher reaction
temperatures than the corresponding iodine analogues. In
the case of the Suzuki reaction the stability of the PG was
studied as a subunit of both reaction partners, the halide
and the boronic acid. Biphenyl 25 was assembled first,
Of particular interest, with respect to a new protecting
group, is its behavior under typical reaction conditions.
Without claiming to be comprehensive, a variety of 29 dif-
ferent reaction conditions were investigated and are sum-
marized in Table 1. In particular, the stability of the PG in
aqueous conditions, and in the presence of bases, nucleop-
hiles, electrophiles and redox agents was investigated. In
each test reaction compound 6 (50 mg) was dissolved in the
solvent (5 mL) (water/EtOH, 4:1, THF, EtOH or CH2Cl2) and
the mixture was stirred at –78 °C, room temperature or
100 °C. With respect to the color code used in Table 1, a
dark green background signals stability for a period of
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–L

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L. M. Bannwart et al.
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Synthesis
Table 1 Stability of the 2-(3-Cyanopropyldimethylsilyl)ethyl Thiophenol Protecting Groupa
Aqueous:
pH = 1, 100 °Cb,c
pH = 1, r.t.d,e
pH = 4, r.t.d,e
pH = 9, r.t.d,e
pH = 12, r.t.d,e
–
pH = 12, 100 °Cb,c
Bases:
LDAf,g
nBuLif,i
AcCle,k
pyridinee,h
iPrMgCle,f
AcHe,h
tBuOKg,h
Me2CuLif,i
MeIe,h
–
–
NaOEte,j
AcOHe,k
NH3
–
e,h
Nucleophiles:
Electrophiles:
Reduction:
Oxidation:
Ac2Oe,k
–
Raney Ni, H2
Pd/C, H2
Fe, HCle,j,m
mCPBAi,k
LiAlH4
NaBH4
NaBH3CNe,j
–
e,j
e,j,l
e,h
e,j
g,h
e,k
g,k
OsO4
MnO2
Br2
–
a Conditions for the stability measurements were as follows: the masked thiophenol 6 (50 mg) and the reagent (1.0 equiv) in solvent (5.0 mL) were stirred at
room temperature under argon; GC-MS measurements were made after 1 h, 10 h, 24 h, 3 d and 7 d.
b Water (4 mL) + EtOH (1 mL), 100 °C.
c Stable for less than 1 h.
d Water (4 mL) + EtOH (1 mL).
e Stable for at least 7 d.
f THF, –78 °C.
g Stable for at least 3 d.
h THF.
i Partially stable (nBuLi: ~35% dec. within the first hour increasing to ~50% dec. after 7 d; Me2CuLi: ~15% dec. within the first hour then stable in that range;
mCPBA: ~50% of the protected thiophenol is oxidized to the corresponding sulfone within the first hour then stable in that range).
j EtOH.
k CH2Cl2.
l Pd/C (0.1 equiv).
m Fe (10 equiv) + conc. HCl (0.5 mL).
seven days, a light green background indicates no signs of
degradation within 3 days, while a dark red background ex-
presses that the masked thiophenol did not survive the first
hour. The pale red background indicates challenging stabili-
ty features and individual details are given as footnotes in
Table 1. In 20 cases, compound 6 was stable for at least
7 days under the conditions employed (dark green back-
ground), and in four cases (LDA, tBuOK, OsO4 and Br2) for at
least 3 days (light green background). Under conditions us-
ing electrophiles and reducing agents the 2-(3-cyanopro-
pyldimethylsilyl)ethane thiol protecting group seems to be
especially stable, as under none of the tested conditions
were decomposition or side reactions observed. Under
strongly acidic or basic aqueous conditions at 100 °C, com-
pound 6 was not stable at all. nBuLi and Me2CuLi reacted
partially with compound 6, but full decomposition was not
observed. mCPBA oxidized ~50% of the protected thiophe-
nol to the corresponding sulfone. If 2.5 equivalents of
mCPBA were used, full conversion into the sulfone was ob-
served.
In summary, 2-(3-cyanopropyldimethylsilyl)ethyl has
been investigated as a polar protecting group for thiophe-
nols, whilst maintaining the reactivity features of the par-
ent TMS-ethyl protecting group. The new PG can be intro-
duced by simple protocols, either from the corresponding
vinylsilane 1 masking a free thiophenol, or sulfur-introduc-
ing reagent 3 substituting a halide atom in a cross-coupling
protocol. In both cases, the required reagent is available
from inexpensive, commercially available starting materials
in good yields. A variety of substituents and substitution
patterns are tolerated and the protected thiophenols are
stable toward a wide range of reaction conditions. Further-
more, the PG is suited for cross-coupling reactions, as typi-
cal Pd-catalyzed Suzuki and Sonogashira reactions were
performed in good yields. The 2-(3-cyanopropyldimethylsi-
lyl)ethyl protecting group is released by mild reaction con-
ditions, comparable to those used for the deprotection of
the parent TMS-ethyl. The increased polarity of the pre-
sented PG considerably facilitates isolation of protected
thiophenol derivatives by chromatographic methods.
All chemicals were directly used for synthesis without further purifi-
cation unless stated otherwise. Dry solvents were used with crown
caps as purchased from Sigma-Aldrich. Column chromatography was
performed using SILICYCLE SilicaFlash® P60 (particle size: 40–63 m,
230–400 mesh). The NMR solvent (CD2Cl2) was obtained from CIL
Cambridge Isotope Laboratories, Inc. (Andover, MA, USA). All NMR ex-
periments were performed on Bruker Avance III or III HD, two or four-
channel NMR spectrometers operating at 500.13 MHz proton fre-
quency. The instrument was equipped with direct observe BBFO
5 mm probes, with self-shielded z-gradient. C13{1H} spectra were re-
corded using the zgpg30 pulse sequence with power gated decou-
pling, DEPT-135 spectra with the sequence deptsp135, using a Crp60-
comp4 shaped pulse for inversion. In both experiments, relaxation
delay d1 was set to 1.0 s, acquisition times were 1.5 s and a waltz16
proton decoupling was applied. The experiments were performed at
298 K. All chemical shifts () are reported in ppm relative to the used
solvent and coupling constants (J) are given in Hertz (Hz). Multiplici-
ties are written as: s = singlet, d = doublet, t = triplet, q = quartet,
quin = quintet, dd = doublet of doublets, m = multiplet. A Shimadzu
GC–MS-QP2010 SE gas chromatograph system, with a ZB-5HT infer-
no column (30 m × 0.25 mm × 0.25 mm), at 1 mL/min He-flow rate
(split = 20:1) with a Shimadzu mass detector (EI 70 eV) was used.
High-resolution mass spectra (HRMS) were measured with a Bruker
Maxis 4G ESI-TOF instrument or on a Waters Micromass AutoSpec
Ultima (EI-Sector).
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L. M. Bannwart et al.
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Synthesis
3-Cyanopropyldimethyl Vinylsilane (1)57
GC-MS, the reaction mixture was carefully quenched with citric acid
(38.2 g, 197 mmol, 1.1 equiv) in small portions. TBME (250 mL) was
added and the reaction mixture was transferred into a separating fun-
nel. The separated organic layer was washed with aq citric acid solu-
tion (1%, 2 × 150 mL), dried over Na2SO4 and concentrated to give a
yellow oil. Compound 3 (25.1 g, 134 mmol, 75%) was obtained as a
colorless liquid after two consecutive fractional distillations (88–
93 °C, 8.8 × 10–3 mbar).
[CAS Reg. No. 954114-30-8]
A 2 L three-neck round-bottom flask was equipped with a dropping
funnel, a reflux condenser and a thermometer, heated out and then
flushed with argon. Chloro-(3-cyanopropyl)dimethylsilane (CPDMS-Cl)
(4) (100 mL, 611 mmol, 1.0 equiv) was added to the flask and dis-
solved in dry THF (300 mL). A solution of vinylmagnesium chloride in
THF (420 mL, 1.6 M, 672 mmol, 1.1 equiv) was added dropwise over
30 min at 5–10 °C. The reaction was finished after the addition ac-
cording to GC-MS, and the cold mixture was diluted with TBME
(450 mL). The mixture was poured into ice-cold water (250 mL)
(slightly exothermic) and acidified with aq HCl (1 M, ~125 mL). The
organic layer was separated and washed with H2O (450 mL) and brine
(450 mL), dried over Na2SO4 and concentrated under reduced pressure
to afford a yellow oil. The crude mixture was purified by vacuum dis-
tillation (82–94 °C at 5 × 10–1 mbar). Compound 1 (72.9 g, 475 mmol,
78%) was obtained as a colorless liquid.
Density (24 °C):0.932 g/mL
1H NMR (500 MHz, CD2Cl2):  = 2.64–2.55 (m, 2 H), 2.35 (t, J = 7.0 Hz,
2 H), 1.68–1.60 (m, 2 H), 1.55 (t, J = 6.9 Hz, 1 H), 1.00–0.94 (m, 2 H),
0.71–0.65 (m, 2 H), 0.03 (s, 6 H).
13C NMR (126 MHz, CD2Cl2):  = 120.3, 22.0, 21.3, 21.1, 21.0, 15.3,
–3.5.
DEPT-135 (126 MHz, CD2Cl2):  = 22.0, 21.3, 21.1, 21.0, 15.3, –3.5.
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C8H17NNaSSi: 210.0743;
found: 210.0743.
Density (24 °C): 0.839 g/mL.
1H NMR (500 MHz, CD2Cl2):  = 6.14 (dd, J = 20.3 Hz, 14.7 Hz, 1 H),
5.98 (dd, J = 14.7 Hz, 3.8 Hz, 1 H), 5.71 (dd, J = 20.3 Hz, 3.8 Hz, 1 H),
2.34 (t, J = 7.0 Hz, 2 H), 1.70–1.61 (m, 2 H), 0.75–0.68 (m, 2 H), 0.09 (s,
6 H).
13C NMR (126 MHz, CD2Cl2):  = 138.7, 132.6, 120.4, 21.20, 21.15,
15.5, –3.4.
Protection of Free Thiols via a Radical Reaction; General Protocol
1
A microwave tube was charged with the thiol (500 mg, 1.0 equiv),
compound 1 (1.2 equiv for liquid starting materials or 2.4 equiv for
solid starting materials) and di-tert-butyl peroxide (0.15 equiv). The
mixture was purged with argon, the tube was sealed and the contents
stirred at 100 °C. After full conversion according to GC-MS, the reac-
tion mixture was cooled to room temperature, diluted with EtOAc
(50 mL) and washed with aqueous NaOH solution (1 M, 50 mL). The
aqueous layer was extracted with EtOAc (50 mL) and the combined
organic layers washed with brine (50 mL) and dried over Na2SO4. The
mixture was concentrated under reduced pressure and the residue
subjected to column chromatography.
DEPT-135 (126 MHz, CD2Cl2):  = 138.7, 132.6, 21.20, 21.15, 15.5,
–3.4.
HRMS (EI, 70 eV): m/z [M – CH3]+ calcd for C7H12NSi: 138.07335;
found: 138.07332.
The spectroscopic data for this compound are identical to those re-
ported in the literature.
S-[2-(3-Cyanopropyldimethylsilyl)ethyl] Ethanethioate (2)
Palladium-Catalyzed Carbon–Sulfur Bond Formation; General
Protocol 2
Compound 1 (30.0 g, 196 mmol, 1.0 equiv) was added to an argon-
flushed and dried one-neck round-bottom flask equipped with a re-
flux condenser. Freshly distilled thioacetic acid (17 mL, 235 mmol,
1.2 equiv) and AIBN (328 mg, 1.96 mmol, 0.01 equiv) were added and
the mixture was heated at 60 °C for 2 h using a preheated oil bath. Af-
ter full conversion according to GC-MS, the reaction mixture was
cooled to room temperature and the reflux condenser was replaced
with a short distillation bridge. Compound 2 (41.1 g, 179 mmol, 91%)
was obtained after distillation (137–157 °C, 4–7 × 10–1 mbar) as a
light yellow liquid.
To a dry and argon-flushed Schlenk tube (25 mL) were added the cor-
responding bromide (500 mg, 1.0 equiv), iPr2NEt (2.0 equiv) and diox-
ane (6.0 mL), and the resulting solution was degassed by bubbling ar-
gon through the reaction mixture for 10 min. Compound 3 (1.2 equiv)
was added and the mixture degassed for another 5 min. (Ph3P)2PdCl2
(2.5 mol%) and Xantphos (5.0 mol%) were added together and the re-
action mixture was stirred at 110 °C. After full conversion according
to GC-MS, the reaction was cooled to room temperature, diluted with
EtOAc (50 mL) and washed with H2O (50 mL) and brine (50 mL). The
organic layer was dried over Na2SO4 and concentrated under reduced
pressure before subjecting the residue to column chromatography.
1H NMR (500 MHz, CD2Cl2):  = 2.90–2.85 (m, 2 H), 2.36 (t, J = 7.0 Hz,
2 H), 2.28 (s, 3 H), 1.69–1.62 (m, 2 H), 0.92–0.86 (m, 2 H), 0.73–0.67
(m, 2 H), 0.05 (s, 6 H).
13C NMR (126 MHz, CD2Cl2):  = 196.3, 120.3, 31.0, 25.6, 21.3, 21.0,
16.5, 15.2, –3.5.
4-{Dimethyl[2-(phenylthio)ethyl]silyl}butanenitrile (6)
Protocol 1: 500 mg scale. Compound 6 (1.10 g, 4.18 mmol, 93%) was
isolated as a light yellow liquid after purification by column chroma-
tography [100 g SiO2, cyclohexane/ethyl acetate (Cy/EtOAc) 99:1 →
90:10].
DEPT-135 (126 MHz, CD2Cl2):  = 31.0, 25.6, 21.3, 21.0, 16.5, 15.2,
–3.5.
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C10H19NNaOSSi: 252.0849;
found: 252.0850.
Protocol 1: 5.00 g scale. Compound 6 (11.9 g, 45.2 mmol, quant.) was
isolated as a light yellow liquid after purification by column chroma-
tography (340 g SiO2, Cy/EtOAc, 99:1 → 91:9).
2-(3-Cyanopropyldimethylsilyl)ethanethiol (3)
In an argon-flushed and dried one-neck round-bottom flask, a sus-
pension of K2CO3 (27.2 g, 197 mmol, 1.1 equiv) in MeOH (170 mL) and
H2O (80 mL) was degassed with argon for 30 min. Compound 2
(41.0 g, 179 mmol, 1.0 equiv) in Et2O (80 mL) was added and the reac-
tion mixture was stirred for 2 h. After full conversion according to
Protocol 2: Compound 6 (829 mg, 3.15 mmol, quant.) was isolated as
a light yellow liquid after purification by column chromatography
(100 g SiO2, Cy/EtOAc, 98:2 → 82:18).
Rf = 0.17 (Cy/EtOAc, 20:1).
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L. M. Bannwart et al.
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Synthesis
1H NMR (500 MHz, CD2Cl2):  = 7.32–7.27 (m, 4 H), 7.20–7.15 (m,
1 H), 3.00–2.94 (m, 2 H), 2.34 (t, J = 7.0 Hz, 2 H), 1.67–1.60 (m, 2 H),
1.00–0.93 (m, 2 H), 0.73–0.67 (m, 2 H), 0.06 (s, 6 H).
DEPT-135 (126 MHz, CD2Cl2):  = 130.2, 130.1, 30.4, 21.30, 21.25,
21.1, 15.9, 15.3, –3.5.
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C15H23NNaSSi: 300.1213;
found: 300.1209.
13C NMR (126 MHz, CD2Cl2):  = 137.7, 129.4, 129.3, 126.2, 120.3,
29.7, 21.3, 21.1, 15.7, 15.2, –3.5.
4-({2-[(2,6-Dimethylphenyl)thio]ethyl}dimethylsilyl)butane-
nitrile (10)
DEPT-135 (126 MHz, CD2Cl2):  = 129.4, 129.3, 126.2, 29.7, 21.3, 21.1,
15.7, 15.2, –3.5.
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C14H21NNaSSi: 286.1056;
found: 286.1060.
Protocol 1: Compound 10 (701 mg, 2.40 mmol, 69%) was isolated as a
light yellow liquid after purification by column chromatography
(340 g SiO2, Cy/EtOAc, 98:2 → 88:12).
Rf = 0.23 (Cy/EtOAc, 10:1).
4-{Dimethyl[2-(o-tolylthio)ethyl]silyl}butanenitrile (7)
Protocol 1: Compound 7 (891 mg, 3.21 mmol, 82%) was isolated as a
light yellow liquid after purification by column chromatography
(340 g SiO2, Cy/EtOAc 99:1, → 92:8).
1H NMR (500 MHz, CD2Cl2):  = 7.10 (s, 3 H), 2.71–2.65 (m, 2 H), 2.53
(s, 6 H), 2.32 (t, J = 7.0 Hz, 2 H), 1.64–1.55 (m, 2 H), 0.89–0.83 (m, 2 H),
0.68–0.61 (m, 2 H), 0.00 (s, 6 H).
Protocol 2: (Ph3P)2PdCl2 (2.5 mol%) and Xantphos (5.0 mol%) were
added 4 times over a reaction time of 48 h. Compound 7 (525 mg,
1.89 mmol, 65%) was isolated as a light yellow liquid after purification
by column chromatography (100 g SiO2, Cy/EtOAc, 99:1 → 90:10).
13C NMR (126 MHz, CD2Cl2):  = 143.6, 134.3, 128.6, 128.5, 120.3,
31.2, 22.4, 21.3, 21.1, 16.5, 15.2, –3.5.
DEPT-135 (126 MHz, CD2Cl2):  = 128.6, 128.5, 31.2, 22.4, 21.3, 21.1,
16.5, 15.2, –3.5.
Rf = 0.18 (Cy/EtOAc, 20:1).
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C16H25NNaSSi: 314.1369;
found: 314.1369.
1H NMR (500 MHz, CD2Cl2):  = 7.26–7.22 (m, 1 H), 7.16 (m, 2 H),
7.10–7.05 (m, 1 H), 3.03–2.87 (m, 2 H), 2.40–2.30 (m, 5 H), 1.70–1.59
(m, 2 H), 1.03–0.94 (m, 2 H), 0.76–0.66 (m, 2 H), 0.07 (s, 6 H).
4-({2-[(4-Bromophenyl)thio]ethyl}dimethylsilyl)butanenitrile
(11)
13C NMR (126 MHz, CD2Cl2):  = 137.7, 137.0, 130.5, 128.0, 126.9,
125.9, 120.3, 28.9, 21.3, 21.1, 20.6, 15.5, 15.3, –3.4.
Protocol 1: 500 mg scale. Compound 11 (610 mg, 1.78 mmol, 71%)
was isolated as a light yellow liquid after purification by column chro-
matography (100 g SiO2, Cy/EtOAc, 98:2 → 81:19).
DEPT-135 (126 MHz, CD2Cl2):  = 130.5, 127.9, 126.9, 125.9, 28.9,
21.3, 21.1, 20.6, 15.5, 15.3, –3.4.
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C15H23NNaSSi: 300.1213;
found: 300.1209.
Protocol 1: 3.00 g scale. Compound 11 (4.39 g, 12.8 mmol, 85%) was
isolated as a light yellow liquid after purification by column chroma-
tography (680 g SiO2, Cy/EtOAc, 98:2 → 82:18).
Rf = 0.29 (Cy/EtOAc, 10:1).
4-{Dimethyl{2-(m-tolylthio)ethyl]silyl}butanenitrile (8)
Protocol 1: Compound 8 (938 mg, 3.38 mmol, 84%) was isolated as a
light yellow liquid after purification by column chromatography
(340 g SiO2, Cy/EtOAc, 100:0 → 92:8).
1H NMR (500 MHz, CD2Cl2):  = 7.45–7.37 (m, 2 H), 7.20–7.16 (m,
2 H), 3.00–2.90 (m, 2 H), 2.35 (t, J = 6.9 Hz, 2 H), 1.68–1.59 (m, 2 H),
0.98–0.90 (m, 2 H), 0.73–0.66 (m, 2 H), 0.06 (s, 6 H).
Rf = 0.17 (Cy/EtOAc, 20:1).
13C NMR (126 MHz, CD2Cl2):  = 137.1, 132.4, 130.9, 120.3, 119.8,
29.9, 21.3, 21.1, 15.7, 15.2, –3.5.
1H NMR (500 MHz, CD2Cl2):  = 7.18 (t, J = 7.6 Hz, 1 H), 7.13 (m, 1 H),
7.10 (m, 1 H), 6.99 (m, 1 H), 3.00–2.94 (m, 2 H), 2.37–2.31 (m, 5 H),
1.70–1.59 (m, 2 H), 0.99–0.92 (m, 2 H), 0.74–0.66 (m, 2 H), 0.07 (s,
6 H).
DEPT-135 (126 MHz, CD2Cl2):  = 132.4, 130.9, 29.9, 21.3, 21.1, 15.7,
15.2, –3.5.
HRMS (ESI, MeOH): m/z [M
364.0161; found: 364.0158.
+
Na]+ calcd for C14H20BrNNaSSi:
13C NMR (126 MHz, CD2Cl2):  = 139.3, 137.4, 129.9, 129.2, 127.1,
126.2, 120.3, 29.6, 21.6, 21.3, 21.1, 15.8, 15.3, –3.4.
4-({2-[(4-(tert-Butyl)phenyl]thio}ethyl)dimethylsilyl)butane-
DEPT-135 (126 MHz, CD2Cl2):  = 129.9, 129.2, 127.1, 126.2, 29.6,
nitrile (12)
21.6, 21.3, 21.1, 15.8, 15.3, –3.4.
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C15H23NNaSSi: 300.1213;
found: 300.1209.
Protocol 1: Compound 12 (723 mg, 2.26 mmol, 78%) was isolated as a
colorless liquid after purification by column chromatography (50 g
SiO2, Cy/EtOAc, 98:2 → 82:18).
Rf = 0.29 (Cy/EtOAc, 10:1).
4-{Dimethyl[2-(p-tolylthio)ethyl]silyl}butanenitrile (9)
Protocol 1: Compound 9 (947 mg, 3.41 mmol, 84%) was isolated as a
light yellow liquid after purification by column chromatography
(340 g SiO2, Cy/EtOAc, 99:1 → 90:10).
1H NMR (500 MHz, CD2Cl2):  = 7.36–7.29 (m, 2 H), 7.28–7.21 (m,
2H), 2.97–2.92 (m, 2 H), 2.34 (t, J = 7.0 Hz, 2 H), 1.67–1.60 (m, 2 H),
1.30 (s, 9 H), 0.98–0.93 (m, 2 H), 0.72–0.67 (m, 2 H), 0.06 (s, 6 H).
Rf = 0.18 (Cy/EtOAc, 20:1).
13C NMR (126 MHz, CD2Cl2):  = 149.7, 134.0, 129.5, 126.5, 120.3,
34.9, 31.6, 30.1, 21.3, 21.1, 15.9, 15.3, –3.4.
1H NMR (500 MHz, CD2Cl2):  = 7.24–7.19 (m, 2 H), 7.14–7.09 (m,
2 H), 2.97–2.88 (m, 2 H), 2.38–2.29 (m, 5 H), 1.68–1.58 (m, 2 H), 0.98–
0.89 (m, 2 H), 0.73–0.64 (m, 2 H), 0.05 (s, 6 H).
DEPT-135 (126 MHz, CD2Cl2):  = 129.5, 126.5, 31.6, 30.1, 21.3, 21.1,
15.9, 15.3, –3.4.
13C NMR (126 MHz, CD2Cl2):  = 136.5, 133.8, 130.2, 130.1, 120.3,
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C18H29NNaSSi: 342.1682;
30.4, 21.30, 21.25, 21.1, 15.9, 15.3, –3.5.
found: 342.1680.
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–L

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L. M. Bannwart et al.
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Synthesis
4-({2-[(4-Aminophenyl)thio]ethyl}dimethylsilyl)butanenitrile
(13)
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C14H20FNNaSSi: 304.0962;
found: 304.0960.
Protocol 1: Reaction temperature was 150 °C. Compound 13 (419 mg,
1.51 mmol, 42%) was isolated as a yellow liquid after purification by
column chromatography (340 g SiO2, Cy/EtOAc, 90:10 → 0:100).
[4-({2-[(3-Cyanopropyl)dimethylsilyl]ethyl}thio)phenyl]boronic
Acid (16)
Protocol 1: Compound 16 (388 mg, 1.26 mmol, 43%) was isolated as a
white solid after purification by column chromatography (100 g SiO2,
Cy/EtOAc, 90:10 → 0:100).
Protocol 2: (Ph3P)2PdCl2 (2.5 mol%) and Xantphos (5.0 mol%) were
added 4 times over a reaction time of 48 h. Compound 13 (586 mg,
2.10 mmol, 72%) was isolated as a yellow liquid after purification by
column chromatography (100 g SiO2, Cy/EtOAc, 90:10 → 0:100).
Rf = 0.22 (Cy/EtOAc, 1:1).
1H NMR (500 MHz, CD2Cl2):  = 8.14–8.10 (m, 2 H), 7.40–7.35 (m,
2 H), 3.11–3.05 (m, 2 H), 2.37 (t, J = 7.0 Hz, 2 H), 1.71–1.62 (m, 2 H),
1.07–1.01 (m, 2 H), 0.78–0.71 (m, 2 H), 0.11 (s, 6 H).
13C NMR (126 MHz, CD2Cl2):  = 144.3, 136.4, 126.8, 120.3, 28.3, 21.3,
21.1, 15.5, 15.2, –3.4. The resonance of the aryl carbon atom with the
boron substituent was not detectable in the 13C NMR spectrum, prob-
ably because of line broadening due to the short relaxation time and
the quadrupole moment of 11B.58
Rf = 0.21 (Cy/EtOAc, 1:1).
1H NMR (500 MHz, CD2Cl2):  = 7.22–7.17 (m, 2 H), 6.64–6.60 (m,
2 H), 3.77 (s, 2 H), 2.84–2.77 (m, 2 H), 2.32 (t, J = 7.0 Hz, 2 H), 1.65–
1.54 (m, 2 H), 0.93–0.84 (m, 2 H), 0.69–0.61 (m, 2 H), 0.01 (s, 6 H).
13C NMR (126 MHz, CD2Cl2):  = 146.8, 134.3, 123.9, 120.3, 115.8,
32.5, 21.3, 21.1, 16.1, 15.2, –3.5.
DEPT-135 (126 MHz, CD2Cl2):  = 134.3, 115.8, 32.5, 21.3, 21.1, 16.1,
15.2, –3.5.
DEPT-135 (126 MHz, CD2Cl2):  = 136.4, 126.8, 28.3, 21.3, 21.1, 15.5,
15.24, –3.4.
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C14H22BNNaO2SSi:
HRMS (ESI, MeOH): m/z [M + H]+ calcd for C14H23N2SSi: 279.1346;
found: 279.1343.
330.1126; found: 330.1127.
4-(Dimethyl{2-[(4-nitrophenyl)thio]ethyl}silyl)butanenitrile (14)
Protocol 1: Compound 14 (784 mg, 2.54 mmol, 82%) was isolated as a
yellow liquid after purification by column chromatography (340 g
SiO2, Cy/EtOAc, 98:2 → 82:18).
4-{Dimethyl[2-(pyridin-4-ylthio)ethyl]silyl}butanenitrile (17)
Protocol 1: Compound 17 (321 mg, 1.21 mmol, 60%) was isolated as a
yellow liquid after purification by column chromatography (340 g
SiO2, Cy 100%).
Protocol 2: Compound 14 (731 mg, 2.37 mmol, 96%) was isolated as a
yellow liquid after purification by column chromatography (100 g
SiO2, Cy/EtOAc, 98:2 → 82:18).
Rf = 0.07 (Cy 100%).
1H NMR (500 MHz, CD2Cl2):  = 8.38–8.33 (m, 2 H), 7.11–7.07 (m,
2 H), 3.06–2.99 (m, 2 H), 2.37 (t, J = 6.9 Hz, 2 H), 1.70–1.61 (m, 2 H),
1.04–0.98 (m, 2 H), 0.77–0.71 (m, 2 H), 0.10 (s, 6 H).
Rf = 0.17 (Cy/EtOAc, 10:1).
1H NMR (500 MHz, CD2Cl2):  = 8.13–8.09 (m, 2 H), 7.34–7.30 (m,
2 H), 3.11–3.04 (m, 2 H), 2.37 (t, J = 6.9 Hz, 2 H), 1.71–1.62 (m, 2 H),
1.06–0.99 (m, 2 H), 0.78–0.71 (m, 2 H), 0.10 (s, 6 H).
13C NMR (126 MHz, CD2Cl2):  = 150.0, 149.7, 121.1, 120.2, 27.0, 21.3,
21.1, 15.2, 15.0, –3.5.
13C NMR (126 MHz, CD2Cl2):  = 148.9, 145.4, 126.6, 124.4, 120.2,
DEPT-135 (126 MHz, CD2Cl2):  = 149.7, 121.1, 27.0, 21.3, 21.1, 15.2,
28.3, 21.3, 21.0, 15.1, 15.0, –3.5.
15.0, –3.5.
DEPT-135 (126 MHz, CD2Cl2):  = 126.6, 124.4, 28.3, 21.3, 21.0, 15.1,
HRMS (ESI, MeOH): m/z [M + H]+ calcd for C13H21N2SSi: 265.1189;
15.0, –3.5.
found: 265.1189.
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C14H20N2NaO2SSi:
331.0907; found: 331.0907.
4-{Dimethyl[2-(naphthalen-2-ylthio)ethyl]silyl}butanenitrile (18)
Protocol 1: Compound 18 (780 mg, 2.49 mmol, 81%) was isolated as a
light yellow liquid after purification by column chromatography
(340 g SiO2, Cy/EtOAc, 99:1 → 90:10).
4-({2-[(4-Fluorophenyl)thio]ethyl}dimethylsilyl)butanenitrile
(15)
Protocol 1: Compound 15 (999 mg, 3.55 mmol, 93%) was isolated as a
light yellow liquid after purification by column chromatography
(340 g SiO2, Cy/EtOAc, 98:2 → 83:17).
Rf = 0.15 (Cy/EtOAc, 20:1).
1H NMR (500 MHz, CD2Cl2):  = 7.81 (dq, J = 7.7 Hz, 0.8 Hz, 1 H), 7.77
(dd, J = 8.2 Hz, 0.8 Hz, 2 H), 7.72 (dd, J = 1.9 Hz, 0.8 Hz, 1 H), 7.48 (ddd,
J = 8.1 Hz, 6.7 Hz, 1.4 Hz, 1 H), 7.46–7.43 (m, 1 H), 7.43–7.39 (m, 1 H),
3.13–3.06 (m, 2 H), 2.34 (t, J = 7.0 Hz, 2 H), 1.68–1.60 (m, 2 H), 1.05–
0.99 (m, 2 H), 0.77–0.69 (m, 2 H), 0.09 (s, 6 H).
13C NMR (126 MHz, CD2Cl2):  = 135.4, 134.4, 132.1, 128.8, 128.2,
127.6, 127.4, 127.1, 126.6, 126.0, 120.3, 29.5, 21.3, 21.1, 15.7, 15.2,
–3.4.
Protocol 2: Compound 15 (796 mg, 2.83 mmol, quant.) was isolated as
a light yellow liquid after purification by column chromatography
(100 g SiO2, Cy/EtOAc, 98:2 → 81:19).
Rf = 0.18 (Cy/EtOAc, 10:1).
1H NMR (500 MHz, CD2Cl2):  = 7.35–7.30 (m, 2 H), 7.04–6.99 (m,
2 H), 2.95–2.88 (m, 2 H), 2.34 (t, J = 6.9 Hz, 2 H), 1.66–1.58 (m, 2 H),
0.95–0.89 (m, 2 H), 0.71–0.65 (m, 2 H), 0.04 (s, 6 H).
DEPT-135 (126 MHz, CD2Cl2):  = 128.8, 128.2, 127.6, 127.4, 127.1,
126.6, 126.0, 29.5, 21.3, 21.1, 15.7, 15.2, –3.4.
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C18H23NNaSSi: 336.1213;
13C NMR (126 MHz, CD2Cl2):  = 162.2 (d, JC–F = 245.0 Hz), 132.5 (d,
JC–F = 7.9 Hz), 120.4, 116.4 (d, JC–F = 21.8 Hz), 31.2, 21.4, 21.2, 16.0,
15.3, –3.4.
found: 336.1210.
DEPT-135 (126 MHz, CD2Cl2):  = 132.5 (d, JC–F = 7.9 Hz), 116.4 (d,
JC–F = 21.8 Hz), 31.2, 21.4, 21.2, 16.0, 15.3, –3.4.
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–L

I
L. M. Bannwart et al.
Paper
Synthesis
4-({2-[(4-Methoxyphenyl)thio]ethyl}dimethylsilyl)butanenitrile
(19)
cording to GC-MS, the reaction was quenched with TFA (292 L,
3.80 mmol, 2.0 equiv). The reaction mixture was diluted with Et2O
(100 mL) and washed with aq citric acid solution (1%, 100 mL) and
water (2 × 100 mL). The organic layer was then washed with aq sat.
Na2CO3 solution (3 × 100 mL). The combined sat. Na2CO3 solutions
were acidified with conc. HCl and extracted with Et2O (3 × 100 mL)
and the three combined organic layers (not the first) were dried over
Na2SO4 and concentrated. Remaining Et2O was removed from the
product by distillation. Product 5 (88.1 mg, 800 mol, 42%) was isolat-
ed as a light yellow liquid.
Protocol 1: Compound 19 (878 mg, 2.99 mmol, 84%) was isolated as a
light yellow liquid after purification by column chromatography
(340 g SiO2, Cy/EtOAc, 98:2 → 84:16).
Protocol 2: Compound 19 (622 mg, 2.12 mmol, 79%) was isolated as a
light yellow liquid (100 g SiO2, Cy/EtOAc, 98:2 → 82:18).
Rf = 0.19 (Cy/EtOAc, 10:1).
1H NMR (500 MHz, CD2Cl2):  = 7.34–7.29 (m, 2 H), 6.87–6.83 (m,
2 H), 3.78 (s, 3 H), 2.90–2.83 (m, 2 H), 2.33 (t, J = 7.0 Hz, 2 H), 1.65–
1.56 (m, 2 H), 0.94–0.85 (m, 2 H), 0.71–0.63 (m, 2 H), 0.03 (s, 6 H).
13C NMR (126 MHz, CD2Cl2):  = 159.4, 133.4, 127.5, 120.3, 115.0,
55.8, 31.9, 21.3, 21.1, 16.1, 15.2, –3.5.
Rf = 0.52 (Cy/EtOAc, 20:1).
1H NMR (500 MHz, CD2Cl2):  = 7.30–7.27 (m, 2 H), 7.26–7.22 (m,
2 H), 7.18–7.14 (m, 1 H), 3.54 (s, 1 H).
The spectroscopic data of this compound are identical to those re-
ported in the literature.59
DEPT-135 (126 MHz, CD2Cl2):  = 133.4, 115.0, 55.8, 31.9, 21.3, 21.1,
16.1, 15.2, –3.5.
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C15H23NNaOSSi: 316.1162;
1,2-Diphenyldisulfane (22)
found: 316.1163.
[CAS Reg. No. 882-33-7]
To a round-bottom flask equipped with a magnetic stir bar were add-
ed compound 6 (500 mg, 1.90 mmol, 1.0 equiv) and THF (25 mL).
TBAF (3.8 mL, 3.80 mmol, 2.0 equiv) was added and the reaction mix-
ture was stirred at room temperature for 4 h. After full conversion ac-
cording to GC-MS, pyridine (170 L, 2.09 mmol, 1.1 equiv) was added
followed by a solution of I2 (290 mg, 1.14 mmol, 0.60 equiv) in THF
(5.0 mL). The reaction mixture was stirred for 30 min and then dilut-
ed with EtOAc (100 mL). The mixture was washed with aq citric acid
solution (1%, 100 mL), sat. Na2S2O3 (100 mL) and brine (100 mL) and
then dried over Na2SO4. The organic layer was concentrated under re-
duced pressure and the residue subjected to column chromatography
(50 g SiO2, Cy/EtOAc, 98:2 → 86:14) to afford product 22 (196 mg,
898 mol, 95%) as a light yellow solid.
4-[Dimethyl(2-{[4-(trifluoromethyl)phenyl]thio}ethyl)silyl]bu-
tanenitrile (20)
Protocol 1: Compound 20 (836 mg, 2.52 mmol, 93%) was isolated as a
light yellow liquid after purification by column chromatography
(100 g SiO2, Cy/EtOAc, 98:2 → 82:18).
Rf = 0.21 (Cy/EtOAc, 10:1).
1H NMR (500 MHz, CD2Cl2):  = 7.54–7.51 (m, 2 H), 7.37–7.34 (m,
2 H), 3.07–3.00 (m, 2 H), 2.36 (t, J = 6.9 Hz, 2 H), 1.70–1.61 (m, 2 H),
1.03–0.96 (m, 2 H), 0.76–0.70 (m, 2 H), 0.09 (s, 6 H).
13C NMR (126 MHz, CD2Cl2):  = 143.7 (q, JC–F = 1,5 Hz), 127.7, 127.4
(q, JC–F = 32 Hz), 126.1 (q, JC–F = 3.8 Hz), 125.0 (q, JC–F = 271 Hz), 120.3,
28.7, 21.3, 21.1, 15.4, 15.2, –3.5.
Rf = 0.57 (Cy/EtOAc, 10:1).
1H NMR (500 MHz, CD2Cl2):  = 7.55–7.50 (m, 4 H), 7.35–7.30 (m,
4 H), 7.27–7.23 (m, 2 H).
DEPT-135 (126 MHz, CD2Cl2):  = 127.7, 126.1 (q, JC–F = 3.8 Hz), 28.7,
21.3, 21.1, 15.4, 15.2, –3.5.
HRMS (ESI, MeOH): m/z [M
+
Na]+ calcd for C15H20F3NNaSSi:
The spectroscopic data of this compound are identical to those re-
ported in the literature.60
354.0930; found: 354.0934.
4-{Dimethyl[2-(octylthio)ethyl]silyl}butanenitrile (21)
S-Phenyl Ethanethioate (23)
Protocol 1: Compound 21 (932 mg, 3.11 mmol, 92%) was isolated as a
light yellow liquid after purification by column chromatography
(400 g SiO2, Cy/EtOAc, 20:1).
[CAS Reg. No. 934-87-2]
Method 1: To a round-bottom flask equipped with a magnetic stir bar
were added compound 6 (500 mg, 1.90 mmol, 1.0 equiv) and THF
(25 mL). TBAF (3.8 mL, 3.80 mmol, 2.0 equiv) was added and the reac-
tion mixture was stirred at room temperature for 4 h. After full con-
version according to GC-MS, acetyl chloride (542 L, 7.60 mmol,
4.0 equiv) was added and the mixture was stirred for 8 h. The reaction
mixture was diluted with EtOAc (100 mL), washed with water
(100 mL) and brine (100 mL), and then dried over Na2SO4. The organic
layer was concentrated under reduced pressure and the residue sub-
jected to column chromatography (50 g SiO2, Cy/EtOAc, 98:2 → 90:10).
Compound 23 (240 mg, 1.58 mmol, 83%) was isolated as a light yellow
liquid.
Rf = 0.18 (Cy/EtOAc, 20:1), KMnO4 dip.
1H NMR (500 MHz, CD2Cl2):  = 2.56–2.52 (m, 2 H), 2.52–2.48 (m,
2 H), 2.37–2.33 (m, 2 H), 1.69–1.61 (m, 2 H), 1.60–1.52 (m, 2 H), 1.41–
1.24 (m, 10 H), 0.91–0.85 (m, 5 H), 0.71–0.66 (m, 2 H), 0.04 (s, 6 H).
13C NMR (126 MHz, CD2Cl2):  = 120.3, 32.41, 32.38, 30.2, 29.79,
29.79, 29.5, 27.8, 23.2, 21.3, 21.2, 16.3, 15.3, 14.4, –3.4.
DEPT-135 (126 MHz, CD2Cl2):  = 32.41, 32.38, 30.2, 29.79, 29.79,
29.5, 27.8, 23.2, 21.3, 21.2, 16.3, 15.3, 14.4, –3.4.
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C16H33NNaSSi: 322.1995;
found: 322.1990.
Method 2: To a round-bottom flask equipped with a magnetic stir bar
were added compound 6 (500 mg, 1.90 mmol, 1.0 equiv) and acetyl
chloride (542 L, 7.6 mmol, 4.0 equiv) in CH2Cl2 (25 mL). Then AgBF4
(740 mg, 3.80 mmol, 2.0 equiv) was added and the resulting mixture
was stirred at room temperature for 12 h. The reaction mixture was
diluted with EtOAc (100 mL), washed with water (100 mL) and brine
(100 mL), and then dried over Na2SO4. The organic layer was concen-
Benzenethiol (5)
[CAS Reg. No. 108-98-5]
To a round-bottom flask equipped with a magnetic stir bar were add-
ed compound 6 (500 mg, 1.90 mmol, 1.0 equiv) and THF (25 mL).
TBAF (3.8 mL, 3.80 mmol, 2.0 equiv) was added and the reaction mix-
ture was stirred at room temperature for 4 h. After full conversion ac-
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–L

J
L. M. Bannwart et al.
Paper
Synthesis
trated under reduced pressure and the residue subjected to column
chromatography (50 g SiO2, Cy/EtOAc, 98:2 → 90:10). Product 23
(256 mg, 1.68 mmol, 89%) was isolated as a light yellow liquid.
H NMR (500 MHz, CD2Cl2):  = 7.62–7.58 (m, 2 H), 7.57–7.53 (m, 2 H),
7.46–7.42 (m, 2 H), 7.40–7.37 (m, 2 H), 7.35 (ddt, J = 8.6 Hz, 7.0 Hz,
1.0 Hz, 1 H), 3.06–2.99 (m, 2 H), 2.35 (t, J = 6.9 Hz, 2 H), 1.70–1.60 (m,
2 H), 1.05–0.98 (m, 2 H), 0.77–0.68 (m, 2 H), 0.08 (s, 6 H).
13C NMR (126 MHz, CD2Cl2):  = 140.3, 138.4, 136.4, 129.0, 128.8,
127.4, 127.3, 126.7, 119.7, 29.2, 20.8, 20.5, 15.2, 14.7, –4.0.
Rf = 0.41 (Cy/EtOAc, 10:1).
1H NMR (500 MHz, CD2Cl2):  = 7.43 (s, 5 H), 2.41 (s, 3 H).
The spectroscopic data of this compound are identical to those re-
ported in the literature.61
DEPT-135 (126 MHz, CD2Cl2):  = 129.0, 128.8, 127.4, 127.3, 126.7,
29.2, 20.8, 20.5, 15.2, 14.7, –4.0.
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C20H25NNaSSi: 362.1369;
found: 362.1366.
4-Bromobenzenethiol (24)
[CAS Reg. No. 106-53-6]
To a round-bottom flask equipped with a magnetic stir bar were add-
ed compound 11 (500 mg, 1.46 mmol, 1.0 equiv) and THF (25 mL).
TBAF (7.3 mL, 7.30 mmol, 5.0 equiv) was added and the reaction mix-
ture was stirred at room temperature for 1 h. After full conversion ac-
cording to GC-MS, the reaction was quenched with TFA (225 L,
2.92 mmol, 2.0 equiv). The reaction mixture was diluted with EtOAc
(100 mL), washed with aq citric acid solution (1%, 100 mL), water
(100 mL) and brine (100 mL), and then dried over Na2SO4. The organic
layer was concentrated under reduced pressure and the residue sub-
jected to column chromatography (340 g SiO2, Cy/EtOAc, 95:5 →
66:34). Product 24 (249 mg, 1.32 mmol, 90%) was isolated as a light
yellow solid.
4-[Dimethyl(2-{[4-(phenylethynyl)phenyl]thio}ethyl)silyl]butane-
nitrile (26)
An oven-dried and argon-flushed Schlenk tube was charged with
compound 11 (500 mg, 1.46 mmol, 1.0 equiv), dry THF (3 mL) and
piperidine (1 mL) and the resulting yellow mixture was degassed with
argon for 10 min. Then phenylacetylene (245 L, 2.19 mmol,
1.5 equiv) was added and the reaction mixture was again bubbled
with argon for 5 min. (Ph3P)2PdCl2 (51.2 mg, 73.0 mol, 0.05 equiv)
and CuI (17.0 mg, 87.6 mol, 0.06 equiv) were added and the result-
ing exothermic mixture degassed with argon for an additional 5 min.
The yellow suspension was stirred at 80 °C for 3 h. After full conver-
sion according to GC-MS, the reaction mixture was diluted with
EtOAc (50 mL), washed with H2O (50 mL) and brine (50 mL), and then
dried over Na2SO4. The organic layer was concentrated under reduced
pressure and the residue subjected to column chromatography (340 g
SiO2, Cy/EtOAc, 98:2 → 83:17). Product 26 (481 mg, 1.32 mmol, 91%)
was isolated as a yellow liquid.
Rf = 0.13 (Cy/EtOAc, 4:1).
1H NMR (500 MHz, CD2Cl2):  = 7.39–7.34 (m, 2 H), 7.19–7.14 (m,
2 H), 3.56 (s, 1 H).
The spectroscopic data of this compound are identical to those re-
ported in the literature.62
Rf = 0.21 (Cy/EtOAc, 10:1).
1H NMR (500 MHz, CD2Cl2):  = 7.54–7.51 (m, 2 H), 7.47–7.44 (m,
2 H), 7.38–7.34 (m, 3 H), 7.28–7.25 (m, 2 H), 3.05–2.97 (m, 2 H), 2.36
(t, J = 7.0 Hz, 2 H), 1.70–1.60 (m, 2 H), 1.02–0.96 (m, 2 H), 0.77–0.68
(m, 2 H), 0.08 (s, 6 H).
13C NMR (126 MHz, CD2Cl2):  = 139.0, 132.4, 132.0, 129.0, 128.9,
128.3, 123.8, 120.5, 120.3, 90.0, 89.6, 29.2, 21.3, 21.1, 15.6, 15.2, –3.5.
4-{[2-([1,1′-Biphenyl]-4-ylthio)ethyl]dimethylsilyl}butanenitrile
(25)
Method 1: To a dry and argon-flushed Schlenk tube were added com-
pound 11 (500 mg, 1.46 mmol, 1.0 equiv), phenylboronic acid
(275 mg, 2.10 mmol, 1.5 equiv) and K2CO3 (611 mg, 4.38 mmol,
3.0 equiv) and the contents were placed under vacuum for 5 min.
Then dry toluene (10 mL) and H2O (2.5 mL) were added and the mix-
ture degassed by passing argon through for 5 min. SPhos Pd G2
(21.0 mg, 29.2 mol, 0.02 equiv) was added and the mixture was
heated at 80 °C for 3 h. After full conversion according to GC-MS, the
reaction mixture was diluted with CH2Cl2 (100 mL), washed with H2O
(100 mL) and brine (100 mL), and then dried over Na2SO4. The organic
layer was concentrated under reduced pressure and the residue sub-
jected to column chromatography (100 g SiO2, Cy/EtOAc, 98:2 → 82:18).
Product 25 (455 mg, 1.34 mmol, 92%) was isolated as a yellow liquid.
DEPT-135 (126 MHz, CD2Cl2):  = 132.4, 132.0, 129.0, 128.9, 128.3,
29.2, 21.3, 21.1, 15.5, 15.2, –3.5.
HRMS (ESI, MeOH): m/z [M + Na]+ calcd for C22H25NNaSSi: 386.1369;
found: 386.1369.
Trimethyl[2-(phenylthio)ethyl]silane (b)
[CAS Reg. No. 17988-59-9]
A microwave tube was charged with thiophenol (0.46 mL, 4.49 mmol,
1.00 equiv), vinyl trimethylsilane (0.81 mL, 5.39 mmol, 1.2 equiv) and
di-tert-butyl peroxide (0.12 mL, 0.673 mmol, 0.15 equiv). The mix-
ture was purged with argon and the tube was sealed and the contents
stirred for 1 h at 100 °C. After full conversion according to GC-MS, the
reaction mixture was cooled to room temperature, diluted with EtOAc
(50 mL) and washed with aqueous NaOH solution (1 M, 50 mL). The
aqueous layer was extracted with EtOAc (50 mL) and the combined
organic layers washed with brine (50 mL) and dried over Na2SO4. The
organic layer was concentrated under reduced pressure and the resi-
due subjected to column chromatography (100 g SiO2, Cy/EtOAc,
100:0 → 85:15). Trimethyl[2-(phenylthio)ethyl]silane (b) (888 mg,
4.22 mmol, 94%) was isolated as a colorless liquid.
Method 2: An oven-dried and argon-flushed Schlenk tube was
charged with compound 16 (240 mg, 781 mol, 1.2 equiv), iodoben-
zene (136 mg, 651 mol, 1.0 equiv) and K2CO3 (273 mg, 1.95 mmol,
3.0 equiv) and the contents were placed under vacuum for 5 min.
Then dry toluene (5 mL) and H2O (1.25 mL) were added and the mix-
ture degassed by passing argon through for 5 min. SPhos Pd G2
(9.38 mg, 13.0 mol, 0.02 equiv) was added and the mixture was
heated at 80 °C for 12 h. The solution was diluted with CH2Cl2
(100 mL), washed with H2O (100 mL) and brine (100 mL), and then
dried over Na2SO4. The organic layer was concentrated under reduced
pressure and the residue subjected to column chromatography (50 g
SiO2, Cy/EtOAc, 98:2 → 82:18). Product 25 (193 mg, 568 mol, 87%)
was isolated as a yellow liquid.
Rf = 0.61 (Cy/EtOAc, 20:1).
1H NMR (500 MHz, CD2Cl2):  = 7.33–7.26 (m, 4 H), 7.19–7.14 (m,
Rf = 0.24 (Cy/EtOAc, 10:1).
1 H), 3.02–2.94 (m, 2 H), 0.97–0.91 (m, 2 H), 0.06 (s, 9 H).
© 2019. Thieme. All rights reserved. — Synthesis 2019, 51, A–L

K
L. M. Bannwart et al.
Paper
Synthesis
The spectroscopic data of this compound are identical to those re-
ported in the literature.43
(17) Weibel, N.; Mishchenko, A.; Wandlowski, T.; Neuburger, M.;
Leroux, Y.; Mayor, M. Eur. J. Org. Chem. 2009, 6140.
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(19) Stefani, D.; Weiland, K. J.; Skripnik, M.; Hsu, C.; Perrin, M. L.;
Mayor, M.; Pauly, F.; van der Zant, H. S. J. Nano Lett. 2018, 18,
5981.
(20) Valášek, M.; Edelmann, K.; Gerhard, L.; Fuhr, O.; Lukas, M.;
Mayor, M. J. Org. Chem. 2014, 79, 7342.
(21) Gerhard, L.; Edelmann, K.; Homberg, J.; Valášek, M.; Bahoosh, S.
G.; Lukas, M.; Pauly, F.; Mayor, M.; Wulfhekel, W. Nat. Commun.
2017, 8, 14672.
Funding Information
The authors thank Schweizerischer Nationalfonds zur Förderung der
Wissenschaftlichen Forschung (Swiss National Science Foundation)
(SNF) (Grant No. 200020-178808) for continuous and generous finan-
cial support. M.M. acknowledges support from the 111 project (Grant
No. 90002-18011002).
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(22) Kolivoška, V.; Šebera, J.; Sebechlebská, T.; Lindner, M.; Gasior, J.;
Mészáros, G.; Mayor, M.; Valášek, M.; Hromadová, M. Chem.
Commun. 2019, 55, 3351.
(23) Lindner, M.; Valášek, M.; Homberg, J.; Edelmann, K.; Gerhard, L.;
Wulfhekel, W.; Fuhr, O.; Wächter, T.; Zharnikov, M.; Kolivoška,
V.; Pospíšil, L.; Mészáros, G.; Hromadová, M.; Mayor, M. Chem.
Eur. J. 2016, 22, 13218.
(24) Šebera, J.; Kolivoška, V.; Valášek, M.; Gasior, J.; Sokolová, R.;
Mészáros, G.; Hong, W.; Mayor, M.; Hromadová, M. J. Phys.
Chem. C 2017, 121, 12885.
(25) Homberg, J.; Lindner, M.; Gerhard, L.; Edelmann, K.;
Frauhammer, T.; Nahas, Y.; Valášek, M.; Mayor, M.; Wulfhekel,
W. Nanoscale 2019, 11, 9015.
(26) Stuhr-Hansen, N. Synth. Commun. 2003, 33, 641.
(27) Pearson, D. L.; Tour, J. M. J. Org. Chem. 1997, 62, 1376.
(28) Sawada, N.; Itoh, T.; Yasuda, N. Tetrahedron Lett. 2006, 47, 6595.
(29) Zeysing, B.; Gosch, C.; Terfort, A. Org. Lett. 2000, 2, 1843.
(30) Błaszczyk, A.; Elbing, M.; Mayor, M. Org. Biomol. Chem. 2004, 2,
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(31) Aliev, I. A.; Kalabin, G. A.; Trofimov, B. A. Sulfur Lett. 1991, 12,
123.
(32) Grunder, S.; Huber, R.; Horhoiu, V.; González, M. T.;
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8337.
Acknowledgment
We thank Loïc Le Pleux and Lukas Jundt for proofreading the manu-
script.
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0039-1690184.
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Primary Data
for this article are available online at https://doi.org/10.1055/s-0039-
1690184 and can be cited using the following DOI: 10.4125/pd0107th. Pri
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