Copper-Free Double Silylation of 1,2-Dibromobenzenes Using a Mg/LiCl/DMI System

Article abstract of DOI:10.1055/s-0036-1588726

The reaction of 1,2-dibromobenzenes with chlorotrimethylsilane efficiently proceeded in the presence of Mg and LiCl in DMI under mild conditions, giving 1,2-bis(trimethylsilyl)benzenes in good to high yields. The reaction of 1,2-dibromobenzenes with chlorodimethylsilane under the same conditions afforded the corresponding 1,2-bis(dimethylsilyl)benzenes in high yields. Functional group transformations of 1,2-bis(trimethylsilyl)benzene were conducted to demonstrate the synthetic utility.

Full text of DOI:10.1055/s-0036-1588726

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2017, 49, A–F
paper
A
T. Kitamura et al.
Paper
Synthesis
Copper-Free Double Silylation of 1,2-Dibromobenzenes Using a
Mg/LiCl/DMI System
Tsugio Kitamura*
Rin Yamada
Copper-Free Double Silylation
Under Mild Conditions
Keisuke Gondo
Nobuo Eguchi
Juzo Oyamada
Br
SiHMe2
SiHMe2
SiMe3
SiMe3
Me3SiCl
Mg, LiCl, DMI
rt or 55 o
Me2HSiCl
R
R
R
Mg, LiCl, DMI
Br
rt
C
Department of Chemistry and Applied Chemistry,
Graduate School of Science and Engineering, Saga
University, Hojo-machi, Saga 840-8502, Japan
kitamura@cc.saga-u.ac.jp
Received: 26.12.2016
Accepted after revision: 01.02.2017
Published online: 22.02.2017
the drawbacks of the use of HMPA solvent and severe reac-
tion conditions, a disadvantage that remains is the use of a
complex reagent system composed of Mg, CuCl, LiCl, and
DMI.
DOI: 10.1055/s-0036-1588726; Art ID: ss-2016-f0885-op
Abstract The reaction of 1,2-dibromobenzenes with chlorotrimethyl-
silane efficiently proceeded in the presence of Mg and LiCl in DMI under
mild conditions, giving 1,2-bis(trimethylsilyl)benzenes in good to high
yields. The reaction of 1,2-dibromobenzenes with chlorodimethylsilane
under the same conditions afforded the corresponding 1,2-bis(dimeth-
ylsilyl)benzenes in high yields. Functional group transformations of 1,2-
bis(trimethylsilyl)benzene were conducted to demonstrate the synthet-
ic utility.
Previous studies
Cl
SiMe3
SiMe3
Mg, cat. I2
HMPA
(a)
Me3SiCl
+
Cl
Harmful HMPA and severe conditions
Cl
SiMe3
SiMe3
Mg, CuCl, LiCl
Key words copper-free reaction, double silylation, 1,2-bis(trimethyl-
silyl)benzenes, mild conditions, 1,2-dibromobenzenes, Mg/LiCl/DMI
system
Me3SiCl
+
(b)
(c)
(d)
DMI
Cl
A complex reagent system
Br
SiMe3
SiMe3
1,2-Bis(trimethylsilyl)benzenes are useful intermedi-
ates for constructing vicinal functionalized compounds be-
cause the trimethylsilyl group is not only a stable protect-
ing group, but also a replaceable functional group.1 In addi-
tion, 1,2-bis(trimethylsilyl)benzenes can be applied to the
synthesis of (i) hypervalent iodine benzyne precursors,2 (ii)
9,10-dihydro-9,10-diboraanthracene as the building block
of luminescent boron-containing polymers3 and functional
materials,4 and (iii) 9,10-dimethyl-9,10-dihydro-9,10-dibo-
raanthracene as a powerful Lewis acid catalyst.5
Synthesis of 1,2-bis(trimethylsilyl)benzene has been
conducted so far by the Grignard reaction of 1,2-dichloro-
benzene with chlorotrimethylsilane using Mg metal in
HMPA [Scheme 1,(a)].2,6 However, this procedure requires a
large amount of toxic HMPA as solvent together with the
severe conditions of high temperatures and a long reaction
time. Recently, we developed a practical and safe method
for the synthesis of 1,2-bis(trimethylsilyl)benzene from
1,2-dichlorobenzene in 1,3-dimethylimidazolidin-2-one
(DMI) using magnesium powder together with CuCl and
LiCl [Scheme 1,(b)].7 Although this method does not have
Mg, additives
Me3SiCl
+
or Rieke-Mg
Br
Conventional methods: moderate yields
Br
SiMe3
SiMe3
tBuLi (–70 °C)
–120 °C
Me3SIOTf (–70 °C)
Br
High yields, but inconvenient procedure
This study
Br
SiMe3
SiMe3
Mg, LiCl
DMI, rt
(e)
Me3SiCl
+
Br
Simple reagent system at room temperature
Scheme 1 Previous studies on double trimethylsilylation
1,2-Dibromobenzene and its derivatives are also good
candidates for double trimethylsilylation. However, the
hitherto reported methods using conventional procedures
generally provide moderate yields of the products [Scheme
1,(c)].8 Although a high-yield procedure using trimethylsilyl
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–F

B
T. Kitamura et al.
Paper
Synthesis
triflate has been reported [Scheme 1,(d)],9 it requires incon-
venient operations, such as lithiation of 1,2-dibromoben-
zene at –120 °C and the use of a highly cooled reagent at
–70 °C.
Thus, we started to study the double trimethylsilylation
of 1,2-dibromobenzene derivatives to find more conve-
nient, milder reaction conditions. In this paper, we want to
report our findings that double trimethylsilylation of 1,2-
dibromobenzenes proceed under copper-free and milder
conditions to give the corresponding double silylated prod-
ucts in good to high yields [Scheme 1,(e)].
First, we examined the reaction of 1,2-dibromobenzene
(1a) and chlorotrimethylsilane using DMI as solvent. The
results are given in Table 1. Since we observed promotion of
the reaction by the addition of LiCl in the previous study
using 1,2-dichlorobenzene,7 we examined the effect of LiCl.
Although the reaction of 1a and chlorotrimethylsilane in
the presence of Mg was carried out in DMI without LiCl at
room temperature for 2 hours, no products were formed
(entry 1). When LiCl (4 equiv) was added, the reaction gave
1,2-bis(trimethylsilyl)benzene (2a) in 60% yield (entry 2).
Increasing the amount of LiCl to 8 equiv, the yield of 2a in-
creased to 89% (entry 3). The reaction proceeded even at 0
°C to give 2a in 78% yield (entry 4). Finally, the best result
(91% yield) was obtained by reaction at room temperature
for 4 h (entry 5). Compared with the trimethylsilylation of
1,2-dichlorobenzene, it should be noted that the present re-
action using 1a proceeds without CuCl and it was complet-
ed under milder conditions (rt, 4 h vs. 55 °C, 17 h). To con-
firm the efficiency of the present reaction, the reaction of
1,2-dichlorobenzene was conducted under similar condi-
tions at 90 °C for 17 hours, but 2a was formed only in 4%
yield together with 1-chloro-2-(trimethylsilyl)benzene
(41%) (entry 6).
With the optimized conditions in hand, we next exam-
ined the scope of the substrate for the trimethylsilylation.
The results are given in Table 2. In analogy with 1a (entry
1), other 1,2-dibromobenzenes 1 bearing Me, MeO, and F
groups underwent double trimethylsilylation efficiently to
give the corresponding 1,2-bis(trimethylsilyl)benzenes 2 in
78–89% yields (entries 2–5). For 1,2,4-tribromobenzene
(1f) and 1,2,4,5-tetrabromobenzene (1g), the trimethylsi-
lylation reaction also proceeded to provide 1,2,4-
tris(trimethylsilyl)benzene (2f) and 1,2,4,5-tetrakis(tri-
methylsilyl)benzene (2g) in 83% and 89% yields, respective-
ly. Although the reaction of 1a was conducted again with a
decreased amount of Mg and Me3SiCl in consideration of
Table 2 Synthesis of 1,2-Bis(trimethylsilyl)benzenes 2a
Br
Br
SiMe3
SiMe3
Mg, LiCl
DMI
Me3SiCl
+
R
R
1
2
Entry
1
Temp (°C) Time (h)
Product
Yield (%)
89
SiMe3
rt
rt
rt
rt
rt
4
4
4
4
4
SiMe3
2a
Me
SiMe3
2
3
4
5
80
81
81
78
SiMe3
2b
F
SiMe3
SiMe3
2c
Table 1 Optimization of the Reaction of 1a with Chlorotrimethylsilanea
F
F
SiMe3
SiMe3
SiMe3
SiMe3
Br
Br
Mg, LiCl
DMI
Me3SiCl
+
2d
MeO
SiMe3
1a
2a
SiMe3
Entry
LiCl (mmol)
Temp (°C)
Time (h)
Yield (%)b
2e
1
2
3
4
5
6c
0
4
8
8
8
8
rt
rt
rt
0
2
2
0
60
89
78
91
4
Me3Si
SiMe3
SiMe3
6b
55
55
4
83
2
2
2f
rt
90
4
Me3Si
Me3Si
SiMe3
SiMe3
17
7c
17
89
a Reaction conditions: 1a (1 mmol), Me3SiCl (16 mmol), Mg powder (8
mmol), LiCl, DMI (10 mL).
2g
b The yield was determined by 1H NMR using 1,4-dimethoxybenzene as an
internal standard.
a Reaction conditions: 1 (1 mmol), Me3SiCl (16 mmol), Mg powder (8
mmol), LiCl (8 mmol), DMI (10 mL).
c 1,2-Dichlorobenzene was used instead of 1a. In addition, 1-chloro-2-
(trimethylsilyl)benzene was formed in 41% yield.
b 1,2,4-Tribromobenzene (1f, 1 mmol) was used.
c 1,2,4,5-Tetrabromobenzene (1g, 1 mmol) was used.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–F

C
T. Kitamura et al.
Paper
Synthesis
the reaction of 1g, it was found that the purification proce-
dure became complicated due to contamination with a by-
product, (trimethylsilyl)benzene.
To explore the 1,2-bis-silylation, we examined dimeth-
ylsilylation reaction of 1,2-dibromobenzenes 1. Under the
optimized conditions, the reaction of 1 was conducted. The
results are given in Table 3. In most cases 1,2-bis(dimethyl-
silyl)benzenes 3 were obtained in high yields. It is indicated
that the present reaction can be applied to bis-dimethylsi-
lylation as well as bis-trimethylsilylation.
provides an alternative method for synthesis of 1-halo-2-
(trimethylsilyl)benzene derivatives.11 According to this pro-
cedure, one-pot synthesis of 1-bromo-2-iodobenzene (6)
was conducted by reaction of 2a with NIS, followed by bro-
mination with NBS, giving 6 in 87% yield. Furthermore,
acetylation of 2a using AcCl and AlCl3 also gave 1-acetyl-2-
(trimethylsilyl)benzene (7) in 71% yield. Nitration of 2a
with HNO3 and Ac2O proceeded to give 1-nitro-2-(trimeth-
ylsilyl)benzene (8) in 63% yield under milder conditions (rt,
21 h) than that of the previous work (160 °C).10
SiMe3
SiMe3
I
Table 3 Synthesis of 1,2-Bis(dimethylsilyl)benzenes 3
Br
Br
SiHMe2
SiHMe2
Mg, LiCl
DMI
NIS, AcOH
SiMe3
O
Me2HSiCl
+
R
R
7
71%
4
94%
AcCl, AlCl3
CH2Cl2
Br
I
NIS
NBS
1
3
AcOH
SiMe3
Entry
1
Temp (°C) Time (h) Product
Yield (%)
95
HNO3, Ac2O
SiMe3
2a
6
87%
SiHMe2
SiHMe2
NBS, AcOH
SiMe3
rt
4
4
NO2
63%
Br
3a
8
5
95%
Me
SiHMe2
SiHMe2
Scheme 2 Functional group transformation of 2a
2
rt
90
88
84
50
In summary, we have developed a convenient and mild
method for the synthesis of 1,2-bis(trimethylsilyl)benzene
derivatives from 1,2-dibromobenzene derivatives using
chlorotrimethylsilane and a Mg/LiCl reagent in DMI. This
method proceeds without copper salts and under milder
conditions to give the products in good to high yields. This
procedure has been applied to the synthesis of 1,2-bis(di-
methylsilyl)benzene derivatives. Furthermore, the synthet-
ic utility of 1,2-bis(trimethylsilyl)benzenes for 1,2-substi-
tuted benzene derivatives has been demonstrated.
3b
F
SiHMe2
3
rt
4
SiHMe2
3c
F
F
SiHMe2
SiHMe2
4
rt
4
3d
Me2HSi
Me2HSi
SiHMe2
SiHMe2
5b
0 to rt
24
All solvents and starting materials were used as received without fur-
ther purification unless otherwise indicated. 1H NMR (400 MHz) and
13C NMR (100 MHz) were recorded on a Agilent NMR System 400
spectrometer in CDCl3 solution. Column chromatographic separations
were carried out using silica gel as the stationary phase. Pre-coated
plates (silica gel 60 F254, Merck) were used for TLC examination.
3e
a Reaction conditions: 1 (3 mmol), Me2SiHCl (48 mmol), Mg powder (24
mmol), LiCl (24 mmol), and DMI (20 mL).
b 1,2,4,5-Tetrabromobenzene (1g, 2 mmol) was used.
To demonstrate the synthetic utility of 1,2-bis(si-
lyl)arenes, we explored the reaction of 1,2-bis(trimethylsi-
lyl)benzene (2a) with some electrophiles. This method is
valuable as a regiospecific synthesis of 1,2-disubstituted
benzene derivatives.10 Thus, we explored transformation of
the trimethylsilyl group into several useful functional
groups. The results are outlined in Scheme 2. Reaction of
1,2-bis(trimethylsilyl)benzene (2a) with NIS in AcOH at
room temperature gave 1-iodo-2-(trimethylsilyl)benzene
(4) in 94% yield. Similar treatment of 2a with NBS afforded
1-bromo-2-(trimethylsilyl)benzene (5). This procedure
1,2-Bis(trimethylsilyl)benzenes 2; General Procedure
Into a dried two-necked flask (50 mL) equipped with a condenser
were placed a stirrer bar, Mg powder (99.9%, 8 mmol), LiCl (8 mmol),
DMI (10 mL), and chlorotrimethylsilane (16 mmol). After stirring the
mixture at rt for 15 min, 1,2-dibromoarene (1 mmol) was added and
the mixture was stirred for 4 h. The mixture was quenched with sat.
NaHCO3 and the resulting precipitates were filtered off. The filtrate
was extracted with hexane (3 ×) and the combined organic extracts
were washed with brine, dried (anhyd Na2SO4), and concentrated by a
rotary evaporator. The crude product was purified by column chro-
matography (silica gel, hexane or hexane/CH2Cl2).
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D
T. Kitamura et al.
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Synthesis
1,2-Bis(trimethylsilyl)benzene (2a)2b
1,2-Bis(dimethylsilyl)benzenes 3; General Procedure
Colorless oil; isolated yield: 0.198 g (89%).
1H NMR (400 MHz, CDCl3): δ = 0.37 (s, 18 H, Me), 7.34–7.36 (m, 2 H,
ArH), 7.68–7.71 (m, 2 H, ArH).
13C NMR (100 MHz, CDCl3): δ = 1.91, 127.74, 135.16, 146.03.
Into a dried two-necked flask (50 mL) equipped with a condenser
were placed a stirrer bar, Mg powder (99.9%, 24 mmol), LiCl (24
mmol), DMI (20 mL), and chlorodimethylsilane (48 mmol). After stir-
ring the mixture at rt for 15 min, 1,2-dibromoarene (3 mmol) was
added and the mixture was stirred for 4 h. The mixture was quenched
with sat. NaHCO3 and the resulting precipitates were filtered off. The
filtrate was extracted with hexane (3 ×) and the combined organic ex-
tract was washed with brine, dried (anhyd Na2SO4), and concentrated
by a rotary evaporator. The crude product was purified by column
chromatography (silica gel, hexane or hexane/CH2Cl2).
4-Methyl-1,2-bis(trimethylsilyl)benzene (2b)2b
Colorless oil; isolated yield: 0.189 g (80%).
1H NMR (400 MHz, CDCl3): δ = 0.37 (s, 9 H, Me), 0.38 (s, 9 H, Me), 2.36
(s, 3 H, Me), 7.17 (d, J = 7.8 Hz, 1 H, ArH), 7.50 (s, 1 H, ArH), 7.59 (d, J =
7.8 Hz, 1 H, ArH).
13C NMR (100 MHz, CDCl3): δ = 1.91, 1.98, 21.43, 128.55, 135.41,
136.18, 137.22, 142.27, 145.99.
1,2-Bis(dimethylsilyl)benzene (3a)12
Colorless oil; isolated yield: 0.554 g (95%).
1H NMR (400 MHz, CDCl3): δ = 0.37 (d, J = 3.8 Hz, 12 H, Me), 4.68
(sept, J = 3.8 Hz, 2 H, SiH), 7.35–7.37 (m, 2 H, ArH), 7.56–7.59 (m, 2 H,
ArH).
4-Fluoro-1,2-bis(trimethylsilyl)benzene (2c)7
Colorless oil; isolated yield: 0.195 g (81%).
13C NMR (100 MHz, CDCl3): δ = –2.62, 128.39, 134.28, 144.31.
1H NMR (400 MHz, CDCl3): δ = 0.35 (s, 9 H, Me), 0.37 (s, 9 H, Me),
6.96–7.01 (m, 1 H, ArH), 7.33–7.36 (m, 1 H, ArH), 7.62–7.65 (m, 1 H,
ArH).
1,2-Bis(dimethylsilyl)-4-methylbenzene (3b)
13C NMR (100 MHz, CDCl3): δ = 1.73, 2.03, 114.35 (d, J = 18.5 Hz),
122.01 (d, J = 17.1 Hz), 137.32 (d, J = 6.2 Hz), 141.31 (d, J = 4.7 Hz),
149.75 (d, J = 3.1 Hz), 162.72 (d, J = 249 Hz).
Colorless oil; isolated yield: 0.563 g (90%).
1H NMR (400 MHz, CDCl3): δ = 0.33 (d, J = 3.6 Hz, 6 H, Me), 0.35 (d, J =
3.6 Hz, 6 H, Me), 2.35 (s, 3 H, Me), 4.649 (sept, J = 3.6 Hz, 1 H, SiH),
4.651 (sept, J = 3.6 Hz, 1 H, SiH), 7.17 (d, J = 7.6 Hz, 1 H, ArH), 7.39 (s, 1
H, ArH), 7.47 (d, J =7.6 Hz, 1 H, ArH).
4,5-Difluoro-1,2-bis(trimethylsilyl)benzene (2d)
Colorless oil; isolated yield: 0.209 g (81%).
13C NMR (100 MHz, CDCl3): δ = –2.59, –2.51, 21.48, 129.24, 134.48,
135.22, 137.98, 140.58, 144.24.
HRMS (EI): m/z [M]+ calcd for C11H20Si2: 208.1104; found: 208.1102.
1H NMR (400 MHz, CDCl3): δ = 0.15 (s, 18 H, Me), 7.22 (t, J = 10.4 Hz, 2
H, ArH).
13C NMR (100 MHz, CDCl3): δ = 1.78, 124.43 (dd, J = 4.7, 9.3 Hz),
143.88 (t, J = 3.1 Hz), 149.67 (dd, J = 13.1, 252 Hz).
1,2-Bis(dimethylsilyl)-4-fluorobenzene (3c)
HRMS (EI): m/z [M]+ calcd for C12H20F2Si2: 258.1072; found: 258.1072.
Colorless oil; isolated yield: 0.561 g (88%).
1H NMR (400 MHz, CDCl3): δ = 0.35 (d, J = 3.6 Hz, 6 H, Me), 0.36 (d, J =
3.6 Hz, 6 H, Me), 4.64–4.67 (m, 2 H, SiH), 7.01–7.06 (m, 1 H, ArH),
7.24–7.27 (m, 1 H, ArH), 7.52–7.56 (m, 1 H, ArH).
13C NMR (100 MHz, CDCl3): δ = –2.86, –2.55, 115.27 (d, J = 19.3 Hz),
121.00 (d, J = 17.0 Hz), 136.44 (d, J = 6.2 Hz), 139.58, 147.77 (d, J = 3.1
Hz), 163.32 (d, J = 249 Hz).
4-Methoxy-1,2-bis(trimethylsilyl)benzene (2e)7
Colorless oil; isolated yield: 0.197 g (78%).
1H NMR (400 MHz, CDCl3): δ = 0.39 (s, 9 H, Me), 0.41 (s, 9 H, Me), 3.85
(s, 3 H, OMe), 6.90 (d, J = 8.4 Hz, 1 H, ArH), 7.29 (s, 1 H, ArH), 7.66 (d,
J = 8.4 Hz, 1 H, ArH).
HRMS (EI): m/z [M]+ calcd for C10H17FSi2: 212.0853; found: 212.0853.
13C NMR (100 MHz, CDCl3): δ = 1.79, 2.09, 54.76, 111.83, 122.34,
136.54, 136.95, 148.06, 158.89.
1,2-Bis(dimethylsilyl)-4,5-difluorobenzene (3d)
1,2,4-Tris(trimethylsilyl)benzene (2f)7
Colorless oil; isolated yield: 0.581 g (84%).
From 1,2,4-tribromobenzene (1f, 0.315 g, 1 mmol); colorless oil; iso-
lated yield: 0.245 g (83%).
1H NMR (400 MHz, CDCl3): δ = 0.35 (d, J = 3.6 Hz, 12 H, Me), 4.63
(sept, J = 3.6 Hz, 2 H, SiH), 7.33 (t, J = 9.6 Hz, 2 H, ArH).
1H NMR (400 MHz, CDCl3): δ = 0.31 (s, 9 H, Me), 0.40 (s, 9 H, Me), 0.41
(s, 9 H, Me), 7.54 (d, J = 7.4 Hz, 1 H, ArH), 7.70 (d, J = 7.4 Hz, 1 H, ArH),
7.88 (s, 1 H, ArH).
13C NMR (100 MHz, CDCl3): δ = –2.76, 123.39 (dd, J = 4.6, 8.5 Hz),
141.91, 150.52 (dd, J = 3.2, 253 Hz).
HRMS (EI): m/z [M]+ calcd for C10H16F2Si2: 230.0759; found: 230.0764.
13C NMR (100 MHz, CDCl3): δ = –1.22, 1.87, 1.96, 132.78, 134.34,
1,2,4,5-Tetrakis(dimethylsilyl)benzene (3e)13
139.32, 139.95, 144.80, 146.55.
From 1,2,4,5-tetrabromobenzene (1g, 0.787 g, 2 mmol); colorless
crystals; isolated yield: 0.311 g (50%); mp 66–68 °C.
1,2,4,5-Tetrakis(trimethylsilyl)benzene (2g)7
From 1,2,3,4-tetrabromobenzene (1g, 0.394 g, 1 mmol); colorless oil;
isolated yield: 0.326 g (89%).
1H NMR (400 MHz, CDCl3): δ = 0.37 (s, 36 H, Me), 7.97 (s, 2 H, ArH).
13C NMR (100 MHz, CDCl3): δ = 1.77, 141.46, 144.77.
1H NMR (400 MHz, CDCl3): δ = 0.38 (d, J = 3.6 Hz, 24 H, Me), 4.66
(sept, J = 3.6 Hz, 4 H, SiH), 7.75 (s, 2 H).
13C NMR (100 MHz, CDCl3): δ = –2.67, 139.53, 144.03.
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E
T. Kitamura et al.
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Synthesis
1-Iodo-2-(trimethylsilyl)benzene (4);11 Typical Procedure
1-Nitro-2-(trimethylsilyl)benzene (8)15
A solution of 2a (2.225 g, 10 mmol) and NIS (2.700 g, 12 mmol) in
AcOH (100 mL) was stirred at rt for 2 h. The mixture was poured into
water and extract with hexane (3 × 10 mL). The combined organic ex-
tract was washed with brine, dried (anhyd Na2SO4), and concentrated
in vacuo. The residue was purified by column chromatography (silica
gel, hexane). The product was obtained as a colorless oil; yield: 2.589
g (94%).
To a solution of 2a (1.112 g, 5 mmol) in Ac2O (30 mL) was added cond
HNO3 (60%, 1.575 g, 15 mmol). The mixture was stirred at rt for 21 h.
The mixture was poured into water and extract with hexane (3 × 10
mL). The combined organic extracts were washed with brine, dried
(anhyd Na2SO4), and concentrated in vacuo. The residue was purified
by Kugel Rohr distillation (120 °C/7 mbar). The product was obtained
as a colorless oil; yield: 0.615 g (63%).
1H NMR (400 MHz, CDCl3): δ = 0.45 (s, 9 H, Me), 7.01–7.05 (m, 1 H,
ArH), 7.31–7.35 (m, 1 H, ArH), 7.41–7.43 (m, 1 H, ArH), 7.88 (d, J = 8.0
Hz, 1 H, ArH).
1H NMR (400 MHz, CDCl3): δ = 0.36 (s, 9 H, Me), 7.52–7.56 (m, 1 H,
ArH), 7.61–7.65 (m, 1 H, ArH), 7.73 (d, J = 7.2 Hz, 1 H, ArH), 8.18 (d, J =
8.0 Hz, 1 H, ArH).
13C NMR (100 MHz, CDCl3): δ = –0.46, 104.03, 126.94, 130.60, 136.20,
13C NMR (100 MHz, CDCl3): δ = –0.46, 123.94, 130.00, 133.13, 136.18,
139.83, 145.37.
136.41, 153.53.
1-Bromo-2-(trimethylsilyl)benzene (5)11
Acknowledgment
A solution of 2a (1.112 g, 5 mmol) and NBS (1.068 g, 6 mmol) in AcOH
(50 mL) was stirred at rt for 2 h followed by the workup procedure
used for 4; the product was obtained as a colorless oil; yield: 1.083 g
(95%).
This work was partly supported by JSPS KAKENHI Grant Number
16K05703.
1H NMR (400 MHz, CDCl3): δ = 0.30 (s, 9 H), 7.07–7.11 (m, 1 H, ArH),
7.15–7.19 (m, 1 H, ArH), 7.32–7.34 (m, 1 H, ArH), 7.43 (d, J = 8.0 Hz, 1
H, ArH).
Supporting Information
13C NMR (100 MHz, CDCl3): δ = –0.58, 126.36, 130.56, 130.68, 132.71,
136.04, 141.08.
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0036-1588726.
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1-Bromo-2-iodobenzene (6)14
References
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the workup procedure used for 4 to give the product as a colorless oil;
yield: 1.235 g (87%).
1H NMR (400 MHz, CDCl3): δ = 6.98–7.02 (m, 1 H, ArH), 7.19–7.23 (m,
1 H, ArH), 7.63 (d, J = 8.0 Hz, 1 H, ArH), 7.87 (d, J = 7.6 Hz, 1 H, ArH).
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2-(Trimethylsilyl)acetophenone (7)
A solution of 2a (0.445 g, 2 mmol) in dry CH2Cl2 (5 mL) was cooled to
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–F