Synthesis and properties of secondary thiocarbamoylsilanes

Article abstract of DOI:10.1246/bcsj.20090231

Secondary thioformamides were reacted with excess LDA and Me3SiCl at -78 °C. The silyl group was selectively introduced to the thiocarbonyl carbon atom to give secondary thiocarbamoylsilanes. The use of Me₂PhSiCl and t-BuMe₂SiCl gave similar products in reduced yields. While a variety of N-arylmethylthioformamides participated in the silylation reaction, the yields of the products were influenced by the substituents on the aromatic ring: electronwithdrawing groups decreased the yield. No reaction occurred with thioformamides having secondary alkyl groups on the nitrogen atom, whereas the reaction of those with primary alkyl groups proceeded smoothly to form the corresponding thiocarbamoylsilanes. Initially, deprotonation takes place at the nitrogen atom to generate lithium thioimidates, which are then silylated with chlorosilanes to form silyl thioimidates. Excess LDA deprotonates silyl thioimidates at the imidate carbon atom to generate lithium silyl thioimidates, which undergo reverse Brook rearrangement to form lithium thioimidates bearing a silyl group at the imide carbon atom. Hydrolysis of the intermediates may lead to the formation of secondary thiocarbamoylsilanes. In UVvisible spectra of thiocarbamoylsilanes, the absorptions ascribed to n -π* transitions were shifted to longer wavelengths by ca. 40-50nm compared to those of thioformates. Finally, the structures of thioformamide and silylated product and their oxygen counterparts were elucidated by DFT calculations. Elongation of the C=O and C=S bonds in carbamoyl- and thiocarbamoylsilanes is discussed in relation to secondary orbital interactions.

Full text of DOI:10.1246/bcsj.20090231

52
Bull. Chem. Soc. Jpn. Vol. 83, No. 1, 52–57 (2010)
© 2010 The Chemical Society of Japan
Synthesis and Properties of Secondary Thiocarbamoylsilanes
Toshiaki Murai* and Rumi Hori
Department of Chemistry, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-1193
Received September 1, 2009; E-mail: mtoshi@gifu-u.ac.jp
Secondary thioformamides were reacted with excess LDA and Me3SiCl at ¹78 °C. The silyl group was selectively
introduced to the thiocarbonyl carbon atom to give secondary thiocarbamoylsilanes. The use of Me2PhSiCl and t-
BuMe2SiCl gave similar products in reduced yields. While a variety of N-arylmethylthioformamides participated in the
silylation reaction, the yields of the products were influenced by the substituents on the aromatic ring: electron-
withdrawing groups decreased the yield. No reaction occurred with thioformamides having secondary alkyl groups on the
nitrogen atom, whereas the reaction of those with primary alkyl groups proceeded smoothly to form the corresponding
thiocarbamoylsilanes. Initially, deprotonation takes place at the nitrogen atom to generate lithium thioimidates, which are
then silylated with chlorosilanes to form silyl thioimidates. Excess LDA deprotonates silyl thioimidates at the imidate
carbon atom to generate lithium silyl thioimidates, which undergo reverse Brook rearrangement to form lithium
thioimidates bearing a silyl group at the imide carbon atom. Hydrolysis of the intermediates may lead to the formation of
secondary thiocarbamoylsilanes. In UV-visible spectra of thiocarbamoylsilanes, the absorptions ascribed to n-³*
transitions were shifted to longer wavelengths by ca. 40-50 nm compared to those of thioformates. Finally, the structures
of thioformamide and silylated product and their oxygen counterparts were elucidated by DFT calculations. Elongation of
the C=O and C=S bonds in carbamoyl- and thiocarbamoylsilanes is discussed in relation to secondary orbital
interactions.
The replacement of formyl protons with silyl groups in
of secondary thiocarbamoylsilanes from secondary thioform-
amides with a base and chlorosilanes. UV-spectra of the
products and DFT calculations of the starting thioformamide
and the product are also reported.
carbonyl compounds provides compounds that exhibit unique
properties and reactivities. One of the most characteristic
features is the decrease in the energy gap between HOMO and
LUMO of the carbonyl groups, to give a higher reactivity silyl-
substituted carbonyl compounds. In this context, a wide variety
of acylsilanes are synthesized and used as synthetic tools.1 The
synthesis2 and reactions3 of sulfur isologues of acylsilanes, i.e.,
thioacylsilanes, have also been well documented. However, the
lability of the thiocarbonyl groups has hampered the isolation
of aliphatic thioacylsilanes, which are in equilibrium with
enethiols.4 Alternatively, thioacylsilanes undergo cycloaddition
reactions with 1,3-dipoles, ¡,¢-unsaturated ketones, alkenes,
and dienes.5 The introduction of heteroatom-containing func-
tional groups such as alkoxy, amino, and alkylthio groups to
the carbon atom of thiocarbonyl groups enhances the stability
of the compounds, but they still possess characteristics of
thiocarbonyl groups. While tertiary thiocarbamoylsilane6 and
dithiocarboxylsilanes7 have been isolated, they have been much
less explored.
Initially, to confirm the generation of thioformamide
dianion, thioformamide 1a was treated with excess BuLi
(Scheme 2). Me3SiCl was then used as an electrophile.
However, the reaction with BuLi gave a complex mixture
containing a butyl group. Therefore, lithium diisopropylamide
(LDA) was used as a base to avoid the nucleophilic
introduction of a base. The reaction of 1a with LDA (2 equiv)
at 0 °C for 5 min, followed by the reaction with Me3SiCl at 0 °C
for 15 min resulted in the recovery of 1a. After several surveys
of the reaction conditions, the reaction at ¹78 °C for 10 min,
followed by the reaction with Me3SiCl at that temperature for
24 h, gave thiocarbamoylsilane 2a as a yellow oil in 62% yield.
To the best of our knowledge, 2a is the first example of a
S
S
E
LiS
Li
E+
BuLi
In contrast, while sulfur isologues of amides, i.e., thioamides
have been studied in great depth,8 their unique properties have
not yet been fully disclosed. Along these lines, we have
developed new synthetic reactions using thioamides.9 For
example, we found that the deprotonation of aromatic N-
arylmethylthioamides with excess BuLi selectively gives
thioamide dianions (Scheme 1).10 The initial deprotonation
takes place at the nitrogen atom, and the protons at the benzylic
carbon atoms are then eliminated. We applied this protocol to
N-arylmethylthioformamides, but the generation of similar
dianions was not observed. We report herein the first synthesis
Ar
N
Ar
(2 equiv)
Ar
N
Ar
Ar
N
Ar
H
H
Scheme 1. Generation and reaction of thioamide dianions.
1) LDA or BuLi
THF
S
S
H
N
Ph
Me3Si
N
Ph
2) Me3SiCl
H
H
1a
2a
Scheme 2. Reaction of thioformamide 1a with LDA and
Me3SiCl.
Published on the web December 18, 2009; doi:10.1246/bcsj.20090231

T. Murai et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 1 (2010)
53
S
A plausible reaction pathway is outlined in Scheme 4.
Initially, the deprotonation of 1a with LDA takes place at the
nitrogen atom to generate lithium thioimidate 5. Further
deprotonation of 5 may lead to dianions 10 and 11, similar to
the reaction of N-benzylthioamides shown in Scheme 1.
However, the deprotonation of 1a¤ with LDA followed by
silylation resulted in the formation of 2a¤ (Scheme 5). No
protonation at the benzylic carbon atom of 1a¤ was observed.
Similarly, the deprotonation of 1a with LDA and deuteration
with D2O leads to the partly deuterated 1a, where 60%
deuterium was incorporated to the nitrogen atom of 1a.
Additionally, the use of aldehydes as an electrophile instead
of chlorosilanes resulted in recovery of the starting formamide
1a. These results appear to exclude the formation of dianions
10 and 11. The generated anion 5 may then be silylated with
Me3SiCl to give S-silyl thioimidate 6.16 At this stage, the
deprotonation of 6 with excess LDA, which is present in the
reaction mixture, proceeds at the imide carbon atom to form
anion 7.17 Subsequent silylation at this carbon atom occurs
to give disilylated product 8 (path a). Alternatively, 7 under-
goes reverse Brook rearrangement to form lithium thioimidate
9 (path b) possibly because a negative charge may be
preferably located on a more electronegative atom. To confirm
whether path a or path b is more plausible, thioformamide
1a was reacted with various amounts of LDA and Me3SiCl
(Scheme 6). The use of one equiv of Me3SiCl led to the
product 2a, whereas the reaction with one equiv of LDA
resulted in the recovery of the starting 1a. In the latter case,
silylated product 7 may be formed, but it readily undergoes
hydrolysis during the aqueous workup. Nevertheless, these
results are consistent with path b in Scheme 4. Reverse Brook
rearrangement similar to that in Scheme 4 is observed for
the siloxyvinyllithium 13 derived by the lithium-tin exchange
reaction of 12 (Scheme 7).18 The silylation of 13 does not
proceed, and instead 13 undergoes reverse Brook rearrange-
ment to form lithium enolate 14. Finally, silylation of 14 takes
place at the oxygen atom to form enol silyl ether.
UV-visible spectra of thioformamides 1 and thiocarbamoyl-
silanes 2 are of interest, since 1 are colorless and 2 are yellow.
Some are listed in Table 2. Notably, the absorptions at the
longest wavelengths, which can be ascribed to n-³* transitions
of the thiocarbonyl group of 2, were red-shifted by ca. 39-55 nm
compared to those of 1. This difference is smaller than those
between ketones and acylsilanes, which are ca. 80 nm.19 No
previous studies have compared the UV spectra of secondary
formamides and secondary carbamoylsilanes, probably because
both compounds show absorptions only in the UV regions.
Geometry optimizations of the starting thioformamide 1a
and thiocarbamoylsilane 2a were performed using B3LYP
density functional theory (DFT)20 with the 6-31+G(d) basis
set. Representative bond distances of 1a and 2a are shown in
Figure 1. For comparison, those of formamide 15 and
carbamoylsilane 16 are also listed. Elongation of C=S bond
distances by 0.019 ¡ was observed when a hydrogen atom in
1a was replaced with a silyl group, whereas distances of C-N
bonds remained nearly the same. A similar tendency was
observed for 15 and 16. The C=O bond distance was elongated
by 0.015 ¡ upon moving from 15 to 16. The elongation of the
C=O bond between acetaldehyde and acetylsilane was con-
S
1) LDA (2.1 equiv), THF
-78 °C, 10 min
R3Si
N
Ph
H
N
Ph
H
H
1a
2) R3SiCl (2.1 equiv)
-78 °C, 24 h
3
4
R3 = PhMe2
R3 = t-BuMe2
26%
9%
Scheme 3. Reaction of thioformamide 1a with LDA and
PhMe2SiCl and t-BuMe2SiCl.
secondary thiocarbamoylsilane, although the synthesis11 and
synthetic applications12 of several tertiary carbamoylsilanes
and studies on tertiary thiocarbamoylsilanes6,13 have been
reported. Secondary carbamoylsilanes are prepared by the
addition reaction of silyl groups to isocyanates as colorless
compounds, and have been reported to be labile at room
temperature.14 Silyl groups in secondary carbamoyl groups are
prone to shift to nitrogen or oxygen atoms to form N-
silylformamides or silyl imidates. In contrast, the thiocarba-
moylsilane 2a is stable at room temperature and can be stored
in the refrigerator for at least 3 months. As chlorosilanes,
Me2PhSiCl and t-BuMe2SiCl were also used, but they gave the
corresponding thiocarbamoylsilanes 2a¤ and 2a¤¤ in reduced
yields (Scheme 3).
Second, a range of thioformamides were used as a starting
material (Table 1). The reaction of N-arylmethylthioform-
amides 1b-1h proceeded in a similar manner, but the yields
of the products 2 were highly dependent on the substituents
in the aromatic groups (Entries 1-8). The introduction of a
methoxy group did not influence the efficiency (Entry 1),
whereas the introduction of electron-withdrawing groups such
as a chlorine and trifluoromethyl reduced the yield of 2 and
led to recovery of the starting thioformamides (Entries 2 and 3).
The methoxy group at the ortho position also retarded the
silylation (Entry 4). The reaction of N-2-arylethylthioform-
amides 1i and 1j proceeded in a similar manner, but an
electron-withdrawing group such as a chlorine atom still
influenced the yield of 2j (Entries 8 and 9). N-Cinnamylthio-
formamide (1k) and N-n-hexylthioformamide (1l) participated
in the silylation reaction. In the former case, the product 2k was
obtained in only 8% yield (Entry 10). For the latter case, the
use of a large excess of Me3SiCl improved the efficiency to
give the product 2l in 82% yield (Entry 11). In other cases, a
large excess of Me3SiCl was not effective at improving the
yields of the products 2. In addition, thioformamides 1m-1p
did not give the corresponding silylated products at all. In most
cases, the starting thioformamides were recovered. Therefore,
the methylene group in thioformamides appears to be a
prerequisite to lead to thiocarbamoylsilanes 2.
Thiocarbamoylsilanes 2 were characterized by IR, NMR,
and mass spectra. In 13C NMR spectra, the signals due to
thiocarbonyl carbon atoms of the starting thioamides were
observed at around ¤ 190. They were shifted to lower fields by
more than 30 ppm by the introduction of silyl groups. A similar
downfield shift was observed for N,N-dimethylformamide and
N,N-dimethylcarbamoyl(trimethyl)silane, and the difference in
the chemical shift was 22.9 ppm.11g Theoretical calculations for
silylketones and -thioketones have also supported these types
of large downfield shifts for the carbonyl and thiocarbonyl
groups.15

54
Bull. Chem. Soc. Jpn. Vol. 83, No. 1 (2010)
Secondary Thiocarbamoylsilanes
Table 1. Reaction of Various Thioformamides 1 with Me3SiCla)
Me3SiCl
S
LDA
S
(2.1 equiv)
(2.1 equiv)
R
R
N
H
N
Me3Si
-78 °C, 24 h
H
H
THF, -78 °C, 10 min
1
2
Entry
1
1 R
Productb)
Entry
1 R
Productb)
S
S
O
O
O
7
Me3Si
N
H
Me3Si
N
H
OMe
Cl
O
OMe
1b
1c
2b 65% (19%)
1h
1i
2h 18% (54%)
S
OMe
OMe
S
2
3
8
Me3Si
N
H
Me3Si
Me3Si
N
H
Cl
2c 18%
2i 67% (8%)
S
Cl
Cl
S
Me3Si
N
H
9
10
11
N
H
CF3
CF3
1d
2d 10% (53%)
1j
2j 28% (38%)
OMe
S
OMe
S
4
5
Me3Si
N
H
Ph
Me3Si
N
H
Ph
1e
1f
2e 36% (30%)
1k
1l
2k 8% (63%)
S
S
Me3Si
N
H
Me3Si
N
H
Ph
Ph
2f 37%
2l 82%c) (5%)
S
Me3Si
N
H
6
1g
2g 46% (40%)
a) The reaction was carried out as follows unless otherwise noted: To a THF solution (5 mL) of LDA (2.1 mmol) was added
thioformamide 1 (1.0 mmol), and the mixture was stirred at ¹78 °C for 10 min, and then, Me3SiCl (2.1 mmol) was added,
and the stirring was continued at ¹78 °C for 24 h. b) Yields of the recovered thioformamides 1 are shown in parentheses.
c) Me3SiCl (10 mmol) was used.
S
S
S
S
H
N
H
N
H
N
H
H
1o
N
H
N
H
H
1m
1n
1p
firmed by molecular orbital calculations at the MP2/6-31G
level.21 To further elucidate the elongation of C=O and C=S
bonds, NBO analyses of 1a, 2a, 15, and 16 were performed,
and some of the orbital interaction energies around the
thiocarbamoyl and carbamoyl groups determined by NBO
second-order perturbation analysis are listed in Table 3. Oxy-
gen and sulfur atoms have two lone-pair electrons and the
energy values are indicated as the sum of the two possible nE
(E = O and S) orbital interactions. The replacement of a
hydrogen atom with a silicon atom almost has little affect
on the orbital interaction energies of nE ¼ ·*C-N and
nN ¼ ·*C=E. In contrast, the energies of nE ¼ ·*C-H in 1a
and 15 are greater than those of nE ¼ ·*C-Si in 2a and 16 by
¹1
more than 4.5 kcal mol
(1 kcal mol¹1 = 4.184 kJ mol¹1).
These orbital interactions can finely attenuate the bond
distances of C=O and C=S, and the weaker interaction of
nE ¼ ·*C-Si leads to the elongation of C=O and C=S in 16
and 2a compared to those in 15 and 1a.22
Finally, the energy levels of HOMO and LUMO or
LUMO+1 of 1a, 2a, 15, and 16 are shown in Figure 2 along
with their orbital shapes. The introduction of a silyl group at
the carbonyl carbon atom of 15 enhances the energy level of

T. Murai et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 1 (2010)
55
LiS
S
LiS
Li
HOMO by 0.76, whereas the energy level of LUMO+1 is
nearly equal in both cases. A similar trend in the change of
orbital energies was also observed for 1a and 2a. The HOMO
of 2a is higher than that of 1a by 0.30, and both LUMO have
nearly the same energies. As a result, the energy gap between
HOMO and LUMO of 2a becomes smaller than that of 1a,
which is consistent with the red shifts of the UV-visible spectra
of 2. This is also in good agreement with the elongation
of C=S bonds, which causes the less-efficient overlap of p
orbitals of the carbon and sulfur atoms leading to a C-S ³
bond.
Li
N
Ph
N
H
N
H
Ph
H
N
Ph
1a
10
11
LDA
LDA
LiS
Me3SiCl
Me3SiS
Me3Si
H
N
Ph
Ph
Ph
5
path a
8
Me3SiCl
H2O
Me3SiS
S
Me3SiS
LDA
Me3SiO
R3SiCl
Me3SiO
Me3SiO
R3Si
H
N
Ph
Me3Si
N
H
Li
N
Ph
BuLi
6
2a
7
Bu3Sn
Li
THF
-78 °C
10 min
12
13
H2O
R3 = Ph2Me, Et3
R3SiO
Me3Si
path b
reverse
Brook
LiS
LiO
rearrangement
R3SiCl
Me3Si
N
Ph
9
Me3Si
14
Scheme 4. Plausible reaction pathway.
Scheme 7. Reverse Brook rearrangement of siloxyvinyl-
lithium 13.
1) LDA (2.1 equiv), THF
-78 °C, 10 min
S
D
S
D
D
D
H
N
H
1a'
Ph
Me3Si
N
Ph
2) Me3SiCl (2.1 equiv)
-78 °C, 24 h
S
S
H
1.925 Å
Me3Si
1.676 Å
Ph
2a
1.094 Å
H
1.657 Å
Ph
2a' 47%
N
N
Scheme 5. Reaction of deuterated thioformamide 1a¤.
H
H
1.346 Å
1a
1.343 Å
S
S
O
O
1) LDA (X equiv), THF
-78 °C, 10 min
1.938 Å
Me3Si
1.366 Å
1.107 Å
1.239 Å
Ph
1.224 Å
N Ph
Me3Si
N
Ph
H
N
Ph
H
H
1a
N
2) Me3SiCl (Y equiv)
H
56%
0%
H
X = 2, Y = 1
X = 1, Y = 2
H
-78 °C, 24 h
1.358 Å
15
16
Scheme 6. Reaction of 1a with different amounts of LDA
and Me3SiCl.
Figure 1. Bond distances of optimal structures of com-
pounds 1a, 2a, 15, and 6 at the B3LYP/6-31+G(d) level.
Table 2. UV-Visible Spectra of Thioamides 1 and 2
S
S
-
/nm
-
max
/nm
max
log ¾
log ¾
R
R
H
N
H
Me3Si
N
H
1a (R = CH2C6H5)
226.0
265.0
353.0
3.44
4.22
1.75
2a (R = CH2C6H5)
216.0
241.0
279.0
392.0
234.0
278.0
398.0
213.0
262.0
400.0
223.0
261.0
402.0 (sh)
214.0
261.0
394.0
3.75
3.87
3.93
1.64
4.07
4.07
1.65
3.79
3.70
1.84
1.44
4.24
1.98
1.55
4.00
1.96
1b (R = CH2C6H4OMe-4)
1d (R = CH2C6H4CF3-4)
1k (R = CH2CH=CHPh)
1l (R = n-Hexyl)
229.0
266.0
356.0
265.0
350.0
3.95
4.15
1.67
4.19
1.75
2b (R = CH2C6H4OMe-4)
2d (R = CH2C6H4CF3-4)
2k (R = CH2CH=CHPh)
2l (R = n-Hexyl)
226.0
261.0
348.0
229.0
261.0
350.0
1.41
4.51
1.86
1.17
4.09
1.64

56
Bull. Chem. Soc. Jpn. Vol. 83, No. 1 (2010)
Secondary Thiocarbamoylsilanes
Table 3. Selected Orbital Interaction Energies Determined
by NBO Second-Order Perturbation Analysis
a silyl group at the imide carbon atom. In UV-visible spectra,
red shifts of the absorptions ascribed to n-³* transitions of
thiocarbonyl groups were observed. This is in good agreement
with DFT calculations, in which the energy gaps of HOMO and
LUMO of thiocarbamoylsilanes are smaller than those of
thioformamides. The elongation of C=O and C=S bond
lengths by the attachment of silyl groups can be understood in
terms of the efficiency of the secondary orbital interaction
between the lone-pair electrons of oxygen and sulfur atoms and
C-H or C-Si ·* bonds. Further studies on new synthetic
transformations using thiocarbonyl compounds and the appli-
cations of the resulting products are in progress.
nE ¼ ·*C-N
/kcal mol
nE ¼ ·*C-X nN ¼ ·*C=E
E
X
¹1
¹1
¹1
/kcal mol
/kcal mol
15
16
1a
2a
O
O
S
H
Si
H
Si
25.59
24.87
15.12
14.67
22.59
14.09
11.12
6.54
67.93
65.96
81.82
81.73
S
Experimental
Typical Procedure for the Synthesis of Secondary Thiocar-
bamoylsilanes.
To a solution of diisopropylamine (0.30 mL,
2.1 mmol) in THF (5 mL) was added n-butyllithium (1.6 M
solution in hexane, 1.3 mL, 2.1 mmol) at ¹78 °C under an Ar
atmosphere, and the mixture was stirred for 30 min. To the reaction
mixture was added a solution of N-phenylmethylthioformamide
(1a) (0.15 g, 1.0 mmol) in THF (1 mL) at ¹78 °C, and the mixture
was stirred for 10 min. To the reaction mixture was added
chlorotrimethylsilane (0.27 mL, 2.1 mmol) at ¹78 °C, and the
mixture was stirred for 24 h. The reaction mixture was poured into
water and extracted with Et2O. The organic layer was dried over
MgSO4, filtered and concentrated in vacuo. The residue was
subjected to column chromatography on silica gel (hexane:
EtOAc = 8:1) to give trimethyl(N-phenylmethylthiocarbamoyl)-
silane (2a) (0.14 g, 0.62 mmol, 62%, Rf = 0.40) as a yellow oil; IR
(neat): 3302, 2956, 1498, 1454, 1368, 1317, 1247, 958, 849, 751,
¹1
697 cm
;
1H NMR (CDCl3): ¤ 0.28 (s, 9H, SiCH3), 4.92 (d,
J = 5.4 Hz, 2H, CH2), 7.30-7.39 (m, 5H, Ar), 7.74 (br, 1H, NH);
13C NMR (CDCl3): ¤ ¹1.79 (SiCH3), 49.1 (CH2), 128.0, 128.3,
128.9, 129.0 (Ar), 224.4 (C=S); MS (EI): m/z: 223 [M+]; Anal.
Calcd for C11H17NSSi: C, 59.14; H, 7.67; N, 6.27%. Found: C,
59.10; H, 7.52; N, 6.34%.
This work was supported by a Grant-in-Aid for Scientific
Research on Priority Area (No. 20036020, “Synergy of
Elements”) from the Ministry of Education, Culture, Sports,
Science and Technology, Japan.
Supporting Information
Detailed experimental procedures and spectroscopic data for
new compounds, and Cartesian coordinates for the optimized
geometries of all the calculated compounds; these materials are
available free of charge on the web at http://www.csj.jp/journals/
bcsj/.
Figure 2. Energy levels of HOMO and LUMO or
LUMO+1 of compounds 1a, 2a, 15, and 16 at the
B3LYP/6-31+G(d) level.
Conclusion
References
In summary, we have demonstrated the first synthesis of
secondary thiocarbamoylsilanes by reacting thioformamides
with LDA and chlorosilanes. The yellow products were stable
at room temperature and could be stored in the refrigerator for
at least 3 months. The reaction could be applied to thioform-
amides with a methylene group on the nitrogen atom. In the
reaction, deprotonation at the nitrogen atom is followed by
silylation at the sulfur atom to form silyl thioimidates, which
undergo deprotonation at the imide carbon atom, followed by
reverse Brook rearrangement to give lithium thioimidates with
1
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