Syntheses of substituted benzosiloles and siloles by diisobutylaluminium hydride-promoted cyclization of 1-silyl-2-(2-silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes

Article abstract of DOI:10.1016/j.tet.2018.02.011

An efficient method for preparing substituted benzosiloles and unsymmetrically substituted siloles by intramolecular C-Si bond formation has been developed. The reaction of 1-methoxysilyl-2-[2-(trimethylsilyl)ethynyl]benzenes with 1.5 equiv of diisobutylaluminium hydride (DIBAL-H) gave benzosiloles in good to high yields. Similarly 4-methoxysilyl-1-silylalk-3-en-1-ynes were cyclized to multisubstituted siloles. Mechanistic study of this transformation uncovered that the methoxysilyl group was initially converted into the corresponding hydrosilyl group by the action of DIBAL-H, and that the resultant hydrosilanes underwent the DIBAL-H-promoted cyclization to benzosiloles. When 1-hydrosilyl-2-[2-(trimethylsilyl)ethynyl]benzenes were used as substrates, a substoichiometric amount of DIBAL-H was enough for the cyclization. The DIBAL-H-promoted transformation could be applied to regio-defined synthesis of unsymmetrically substituted siloles from 4-hydrosilyl-1-silylalk-3-en-1-ynes. This pre-installation approach provides a straightforward access to multisubstituted siloles with complete regioselection.

Full text of DOI:10.1016/j.tet.2018.02.011

Tetrahedron xxx (2018) 1e14
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Syntheses of substituted benzosiloles and siloles by
diisobutylaluminium hydride-promoted cyclization of 1-silyl-2-(2-
silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes
Hidenori Kinoshita*, Hiroki Fukumoto, Akihiro Ueda, Katsukiyo Miura**
Department of Applied Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-ohkubo, Sakura-ku, Saitama 338-8570,
Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient method for preparing substituted benzosiloles and unsymmetrically substituted siloles by
intramolecular C-Si bond formation has been developed. The reaction of 1-methoxysilyl-2-[2-(trime-
thylsilyl)ethynyl]benzenes with 1.5 equiv of diisobutylaluminium hydride (DIBAL-H) gave benzosiloles in
good to high yields. Similarly 4-methoxysilyl-1-silylalk-3-en-1-ynes were cyclized to multisubstituted
siloles. Mechanistic study of this transformation uncovered that the methoxysilyl group was initially
converted into the corresponding hydrosilyl group by the action of DIBAL-H, and that the resultant
hydrosilanes underwent the DIBAL-H-promoted cyclization to benzosiloles. When 1-hydrosilyl-2-[2-
(trimethylsilyl)ethynyl]benzenes were used as substrates, a substoichiometric amount of DIBAL-H was
enough for the cyclization. The DIBAL-H-promoted transformation could be applied to regio-defined
synthesis of unsymmetrically substituted siloles from 4-hydrosilyl-1-silylalk-3-en-1-ynes. This pre-
installation approach provides a straightforward access to multisubstituted siloles with complete
regioselection.
Received 30 November 2017
Received in revised form
2 February 2018
Accepted 3 February 2018
Available online xxx
Keywords:
Cyclization
Alkynes
Benzosiloles
Siloles
Diisobutylaluminium hydride
© 2018 Elsevier Ltd. All rights reserved.
1. Introduction
conjugated compounds (eq. (1)) is a conventional method catego-
rized as type (a).6,7 A variety of silole rings are accessible by this
Siloles and benzosiloles are cyclic organosilicon compounds
having a silicon-bridged -electron system. Their physical and
method. As another example of type (a), the Ruecatalyzed double
trans-hydrosilylation of 1,3-dienynes with dihydrosilanes is useful
for the synthesis of 2,5-disubstituted siloles (eq. (2)).8 The approach
of type (b) is represented by catalytic cycloadditions between al-
kynes and organosilicon reagents. For instance, the Rh-9 and Pd-
catalyzed10 reactions of internal alkynes with o-functionalized
(trimethylsilyl)benzenes via sp3-C-Si bond activation provide a
convenient access to 2,3-disubstituted benzosiloles (eq. (3)). The
transition metal-catalyzed [2 þ 2þ1] cycloadditions of silylene
equivalents to alkynes also yield substituted siloles (eq. (4)).11 The
silole construction of type (c), which is frequently used for the
synthesis of benzosiloles and dibenzosiloles, includes intra-
molecular hydrosilylation,8 KH-promoted cyclization,12 and tin-
mediated cyclization13 of alkynylated hydrosilanes (eq. (5)) and
dehydrogenative coupling between Si-H and aryl C-H bonds14,15
(eq. (6)). For the silole ring construction of type (d), reductive
coupling of diynes (eq. (7))16 and intramolecular coupling of 2-
(arylsilyl)aryl triflates (eq. (8))17 can be effectively utilized. Addi-
tionally, benzosilole syntheses by ring-closing alkene metathesis18
and anti-hydroarylation via ortho-C-H activation19 are known as an
p
chemical properties are intriguingly different from their carbon
analogues, cyclopentadienes and indenes. Especially, they show
beneficial photo- and electro-physical properties due to their
unique electronic structures.1,2 Therefore much attention has been
paid for their use as electroluminescence and electron-transporting
materials.3 In this context, synthetic methods for siloles4 and
benzosiloles5 have also been investigated intensively so far. The
main approaches for silole ring construction can be classified into
four types (Scheme 1): (a) intermolecular double C-Si bond for-
mation, (b) intermolecular C-Si and C-C bond formation, (c) intra-
molecular C-Si bond formation, and (d) intramolecular C-C bond
formation. The reaction of dichlorosilanes with 1,4-dimetallated p-
* Corresponding author.
** Corresponding author.
E-mail addresses: hkino@mail.saitama-u.ac.jp (H. Kinoshita), kmiura@apc.
saitama-u.ac.jp (K. Miura).
https://doi.org/10.1016/j.tet.2018.02.011
0040-4020/© 2018 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Kinoshita H, et al., Syntheses of substituted benzosiloles and siloles by diisobutylaluminium hydride-
promoted cyclization of 1-silyl-2-(2-silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes, Tetrahedron (2018), https://doi.org/10.1016/
j.tet.2018.02.011

2
H. Kinoshita et al. / Tetrahedron xxx (2018) 1e14
Scheme 2. Our previous work and this work.
unsymmetrically substituted siloles VI21 were successfully ob-
tained with complete regioselection by the pre-installation
approach categorized as type (c). We herein report full investiga-
tion of the DIBAL-H-promoted cyclization of the silylethynylated
methoxysilanes (IIIa and Va) and hydrosilanes (IIIb and Vb).
2. Results and discussion
Methoxysilane 1a was used as a model substrate to optimize the
reaction conditions for the DIBAL-H-promoted cyclization. The re-
action conditions for the synthesis of indenes II [DIBAL-H (2.0
equiv), Et2AlCl (1 equiv),100 ꢀC,14 h]20 were initially adopted to the
cyclization of 1a. In the indene synthesis, Et2AlCl serves as Lewis
acid to promote nucleophilic substitution at the benzylic carbon by
C-O bond activation (Scheme 2, eq. (1)). The reaction of 1a using
both DIBAL-H and Et2AlCl gave the desired silole 2a in 14% yield
along with the reduced product 3a in 19% yield (Table 1, entry 1).
The cyclization to 2a proceeded without Et2AlCl and in an increased
yield (entry 2). When the amount of DIBAL-H was decreased to 1.5
Scheme 1. Syntheses of benzosiloles and siloles.
examples of type (d).
In the view of the known methods for silole ring construction,
there are many options for regio-controlled synthesis of substituted
benzosiloles including dibenzosiloles. Contrary to the matured
route to benzosiloles, the method for preparing substituted non-
fused siloles still has much room for improvement. Regio-defined
synthesis of unsymmetrically substituted siloles bearing different
substituents remains unsolved although the approaches of types (c)
and (d), which can be called pre-installation approaches, seem
fruitful in solving this subject. Therefore, a versatile method, which
enables to synthesize both multisubstituted benzosiloles and un-
symmetrically substituted siloles with complete regioselection, is
ideal for synthesizing silole derivatives.
We recently reported the DIBAL-H-promoted cyclization of o-(2-
silylethynyl)benzyl ethers I to indenes II (Scheme 2, eq. (1)).20 It
was also found that several benzosiloles IV were successfully ob-
tained from IIIa (eq. 2, X ¼ OMe), which is the silicon analogue of
I.20
In the course of our studies on mechanistic studies on the
DIBAL-H-promoted benzosilole construction, we revealed that a
methoxysilane IIIa was initially reduced to the corresponding
hydrosilane IIIb, which was converted into IV by the action of
DIBAL-H. With these findings, the DIBAL-H-promoted cyclization of
hydrosilanes IIIb and Vb was examined (eqs. 2 and 3, X ¼ H).
Consequently, various substituted benzosiloles IV and
Table 1
Optimization for benzosilole synthesis.a
entry
DIBAL-H (equiv)
temp. (ºC)
time (h)
isolated
yield (%)
2a
3a
1b
2
3
4
5
6
7
8
9
2.0
2.0
1.5
1.5
1.5
1.5
1.5
1.5
1.3
100
100
100
80
75
70
75
75
75
14
14
14
14
14
14
6
14
40
49
80
88
81
89
86
86
19
12
13
2
0
0
0
0
0
3
6
a
All reactions were carried out with 1a (0.25 mmol) in octane (0.75 mL).
Et2AlCl (0.25 mmol) was used.
b
Please cite this article in press as: Kinoshita H, et al., Syntheses of substituted benzosiloles and siloles by diisobutylaluminium hydride-
promoted cyclization of 1-silyl-2-(2-silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes, Tetrahedron (2018), https://doi.org/10.1016/
j.tet.2018.02.011

H. Kinoshita et al. / Tetrahedron xxx (2018) 1e14
3
equiv, 2a was obtained in 49% yield, and 3a was still formed (entry
3). Lowering the reaction temperature was quite effective in
improving the yield of 2a (entries 4e6). The reaction at 75 ꢀC
provided 2a in 88% yield as a sole product (entry 5). Variation of the
reaction time revealed that the reaction was completed in 6 h
(entry 7). Since further adjustment of the reaction conditions was
unsuccessful in achieving more favourable results (entries 8 and 9),
the conditions of entry 7 were determined as the optimized con-
ditions for the cyclization of 1a to 2a.
1n with 3.0 equiv of DIBAL-H gave the corresponding bissiloles 2m
and 2n in good yields.
We next attempted the synthesis of multi-substituted siloles by
the DIBAL-H-promoted cyclization of 1,4-disilylalk-3-en-1-ynes 4.
In contrast with the case of 1a, the reaction of 4a at 75 ꢀC for 14 h
resulted in a moderate yield (52%) of the desired silole 5a. Elon-
gating the reaction time to 24 h was effective, and 5a was obtained
in 80% isolated yield (Scheme 4). Further prolonged time merely led
to the decrease of 5a. When 1,3-enynes 4b and 4c were submitted
to the reaction conditions, multi-substituted siloles 5b and 5c were
With the optimized reaction conditions in hand, the scope of the
benzosilole synthesis was investigated (Table 2). Methoxysilanes
1b and 1c, bearing a phenyl group as R1, were cyclized to benzo-
siloles 2b and 2c in excellent yields. The reaction site of 1d
(R1 ¼ R2 ¼ iPr) is sterically more hindered by the isopropyl groups.
As anticipated, 1d hardly underwent the transformation into 2d
under the standard conditions. However, the yield of 2d was
dramatically improved by both elevating the reaction temperature
and elongating the reaction time (100 ꢀC,14 h). The cyclization of 1e
(Si ¼ SiMe2tBu) and 1f (Si ¼ SiMe2Ph), possessing a bulky silyl
group at the alkyne terminus, proceeded smoothly. In the case of 1g
(Si ¼ SiiPr3), where the silyl group is sterically more demanding,
only a trace amount of 2g was detected with nearly quantitative
recovery of 1g. Methoxysilanes 1hek, having a substituent on the
o-phenylene tether, successfully reacted with DIBAL-H to give the
corresponding benzosiloles 2hek. Naphthosilole 2l was also pre-
pared from methoxy(naphthyl)silane 1l in an excellent yield.
This transformation could be applied to the synthesis of bissi-
loles (Scheme 3). The reactions of bis(methoxysilyl)diynes 1m and
Scheme 3. Synthesis of bissiloles.
Table 2
Synthesis of benzosiloles 2.a
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promoted cyclization of 1-silyl-2-(2-silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes, Tetrahedron (2018), https://doi.org/10.1016/
j.tet.2018.02.011

4
H. Kinoshita et al. / Tetrahedron xxx (2018) 1e14
Scheme 4. Synthesis of multi-substituted siloles.
formed in moderate yields (Scheme 4). However, the reaction of 4d,
bearing a methoxy(dimethyl)silyl group, gave 5d in a low yield
despite complete conversion of 4d. This is probably because 5d is
less stable under the reaction conditions than 5a-c. Unfortunately,
any side reactions consuming 5d could not be identified. Generally,
the synthesis of multisubstituted siloles 5 from 4 was not effective
under the reaction conditions.
To ascertain the role of the silyl group at the alkyne terminus,
methoxysilanes 1o and 1p, bearing a non-silylated alkyne part,
were treated with DIBAL-H (Scheme 5). The reaction of 1o gave
hydrosilanes 6o and 6o’ by hydride attack to the silicon center and
further reduction of the alkyne moiety. Alkyne 1p also underwent
the reduction to form similar products 6p and 6p’. The minor stil-
bene product 6p’ was assigned to be Z-configurated. Thus, no silole
products were obtained in both reactions. This fact clearly indicates
that the silyl group at the sp-carbon is pivotal to promoting the
present cyclization (vide infra).
To gain a mechanistic insight, the time course of the DIBAL-H-
promoted reaction was investigated by using 1a as a probe
(Scheme 6). The reaction of 1a was carried out while changing the
reaction time (0.25, 0.5, 1, 2, and 3 h). After quenching with 1 M aq.
HCl, the products were purified and identified. The reaction for
0.25 h provided hydrosilane 6a in preference to 2a and the doubly
reduced product 6a'. The methoxysilane product formed by simple
reduction of the alkyne part was not detected. These results suggest
that reduction of the methoxysilane part with DIBAL-H22 is rather
fast and occurs prior to that of the alkyne part. The perfect E-
configuration of 6a' can be rationalized by highly regioselective
Scheme 6. Variation of product yields with reaction time. All reactions were carried
out with 1a (0.25 mmol) and DIBAL-H (0.375 mmol) in octane (0.75 mL) at 75 ꢀC.
hydroalumination of 6a and subsequent rapid geometrical isom-
erization of the initially formed Z-alkenylalane to the E-isomer (E)-
7a (vide infra). The yields of 6a and 6a' decreased with reaction
time. In contrast, the yield of 2a increased with the decrease of 6a
and 6a'. On the basis of these observations, it is highly probable that
the formation of 2a proceeds via hydrosilane 6a and alkenylalane
(E)-7a.
To make sure that the present cyclization starts with the se-
lective formation of hydrosilane 6a, the reaction of 1a with an
equimolar amount of DIBAL-H was first conducted (Scheme 7).
Expectedly, 6a was obtained exclusively without the formation of
silole 2a. Next, the isolated hydrosilane 6a was treated with a
substoichiometric amount (0.5 equiv) of DIBAL-H. The cyclization
of 6a to 2a proceeded successfully in accordance with the mecha-
nistic consideration. A similar examination was conducted using 4e.
As a result, selective formation of hydrosilane 8e and its conversion
into silole 5e could be observed.
The efficient cyclization of hydrosilanes 6a and 8e with a sub-
stoichiometric amount of DIBAL-H (0.5 equiv) implies the regen-
eration of DIBAL-H in the C-Si bond-forming step. To prove the
unprecedented process, deuterium-labelling experiments were
performed with 6a-d and 8b-d (Scheme 8). When
a sub-
stoichiometric amount of DIBAL-H acted on these deuterium-
Scheme 5. Reactions of methoxysilanes bearing a non-silylated alkyne moiety.
Scheme 7. Stepwise cyclization of methoxysilanes 1a and 4e with DIBAL-H.
Please cite this article in press as: Kinoshita H, et al., Syntheses of substituted benzosiloles and siloles by diisobutylaluminium hydride-
promoted cyclization of 1-silyl-2-(2-silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes, Tetrahedron (2018), https://doi.org/10.1016/
j.tet.2018.02.011

H. Kinoshita et al. / Tetrahedron xxx (2018) 1e14
5
lower its rotation barrier.
Generally, hydrotriorganosilanes are more stable and easily
handled than the corresponding methoxytriorganosilanes. In
addition, the DIBAL-H-promoted cyclization of methoxysilanes 1 or
4 proceeds via the formation of hydrosilanes 6 or 8. We therefore
took on the cyclization of 6 and 8 for efficient syntheses of ben-
zosiloles 2 and siloles 5. The optimization of the reaction conditions
was initially conducted using hydrosilane 6a as a probe (Table 3). As
described above (Scheme 7), the cyclization of 6a with 0.5 equiv of
DIBAL-H gave benzosilole 2a in 85% isolated yield as a sole product
(entry 1). A less amount (0.3 equiv) of DIBAL-H was enough for the
cyclization, but with a slight decrease in yield (entry 2). Further
decrease of DIBAL-H (0.2 equiv) caused an incomplete conversion
of 6a (entry 3). The low catalytic turnover of DIBAL-H is likely due to
its thermal instability. Shortening the reaction time to 1 h allowed
an efficient cyclization even though small amounts of 6a' and 6a
were detected (entry 4). When the reaction temperature was
elevated to 80 ꢀC, the cyclization was completed in 1 h to afford 2a
in 86% yield (entry 5). Use of an equimolar or more amount of
DIBAL-H hardly affected the yield of 2a (entries 6 and 7). However,
when the reaction using 1.2 equiv of DIBAL-H was conducted for
0.5 h, the yield of 2a reached 87% (entry 9).
Based on the results shown in Table 3, two sets of reaction
conditions (methods A and B) were applied to the cyclization of
various hydrosilanes 6 (Table 4). In the reactions using 1.2 equiv of
DIBAL-H at 80 ꢀC for 0.5 h (method A), benzosiloles 2 except 2d and
2e were obtained in excellent yields. The reactions of 6d and 6e,
sterically hindered around the reaction centers, needed a pro-
longed time and an elevated temperature. It is noteworthy that
large-scale reactions of 6j (1.01 mmol) and 6l (1.14 mmol) under the
conditions of method A also gave the desired benzosiloles 2j and 2l
in 84% and 91% yields, respectively. When selected substrates 6
were treated with 0.5 equiv of DIBAL-H at 80 ꢀC for 1 h (method B),
the cyclization to benzosiloles 2 proceeded smoothly. The sub-
stoichiometric use of DIBAL-H was also effective although the
yields by method B were generally lower than those by method A.
Contrary to the benzosilole synthesis from methoxysilane 1, the
DIBAL-H-promoted cyclization of methoxysilanes 4 was not so
efficient for the synthesis of unsymmetrically substituted siloles 5
(Scheme 4). To overcome the difficulty, the cyclization of hydro-
silanes 8 was conducted by method A and B (Table 5). Upon the
treatment with DIBAL-H (1.2 equiv) for 0.5 h (method A), various
Scheme 8. Deuterium-labelling experiments.
labelled substrates, the cyclized products were obtained in good
yields. The characterization of each product by NMR analysis
revealed that it was partially deuterated at C(3), that is, a mixture of
2a and 2a-d or a mixture of 5b and 5b-d. In other words, deuterium
transfer from the Si center to the C(3) center occurred. This result
can be rationalized by the generation of DIBAL-D in the ring-closing
step. DIBAL-D as well as DIBAL-H should promote the cyclization of
6a-d and 8b-d via highly regioselective deuterioalumination of the
alkyne part, which should lead to the deuteration at C(3) (vide
infra).
Taking all the observations into consideration, we propose a
plausible mechanism for the DIBAL-H-promoted cyclization of a
methoxysilane 1 (Scheme 9). The first step is hydride substitution
of the methoxysilane part with DIBAL-H.22 The resultant hydro-
silane 6 undergoes highly regioselective hydroalumination of the
alkyne part with DIBAL-H.23 Then the initially formed alkenylalane
(Z)-7 is isomerized to (E)-7, the thermodynamically favored iso-
mer.23 Intramolecular nucleophilic substitution of (E)-7 between
the hydrosilane part24 and the sp2-C bound to Al forms the cyclized
product 2 to regenerate DIBAL-H. The in situ generated DIBAL-H
promotes the cyclization of hydrosilane 6 again. As mentioned
above, the silyl group at the alkyne terminus is essential to the
present cyclization. Its roles certainly consist of promoting the site
selective hydroalumination step and facilitating the subsequent
geometrical isomerization of (Z)-7.23 The former role can be
explained by
C-C triple bond and stabilizes the newly formed C-Al bond
silicon by hyperconjugation with * orbital of the C-Si bond. In
addition, the -effect and cooperative interaction with unoccupied
a
-effect of the silyl group, which lowers
p
* level of the
a
to
s
a
p orbital of the Al metal can polarize the C-C double bond of (Z)-7 to
Table 3
Optimization for benzosilole synthesis using hydrosilane 6.a
entry
DIBAL-H (equiv)
temp (ºC)
time (h)
yield (%)b
2a
6a'
6a
1
2
3
4
5
6
7
8
9
0.5
0.3
0.2
0.5
0.5
1.0
1.2
1.0
1.2
75
75
75
75
80
80
80
80
80
3
3
3
1
1
1
1
0.5
0.5
85
0
0
(84)
(76)
(82)
86
85
85
(0)
(0)
(2)
0
0
0
(1)
(10)
(1)
0
0
0
(82)
87
(11)
0
(2)
0
a
All reactions were carried out with 6a (0.25 mmol) in octane (0.75 mL).
b
Scheme 9. A plausible mechanism for the DIBAL-H-promoted cyclization of 1.
Isolated yield. 1H NMR yield is shown in parentheses.
Please cite this article in press as: Kinoshita H, et al., Syntheses of substituted benzosiloles and siloles by diisobutylaluminium hydride-
promoted cyclization of 1-silyl-2-(2-silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes, Tetrahedron (2018), https://doi.org/10.1016/
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H. Kinoshita et al. / Tetrahedron xxx (2018) 1e14
Table 4
Synthesis of benzosiloles 2 from hydrosilanes 6.a
unsymmetrically substituted siloles were obtained in good to
excellent yields, except for sterically hindered silole 5e. A pro-
longed reaction improved the yield of 5e to 63%. Compared with
1,1-diphenyl-substituted siloles, 1,1-dimethyl-substituted silole 5d
was inferior in isolated yield probably due to its instability under
these conditions. It is noteworthy that four or five different sub-
stituents could be introduced on the silole ring in 5k-o. The present
reaction was scalable, and a large-scale reaction of 8b (1 mmol)
gave 5b in 83% isolated yield. The reaction of several substrates 8
with a substoichiometric amount of DIBAL-H (0.5 equiv) for 1 h at
80 ꢀC (method B) was conducted and the results are shown in pa-
rentheses. The corresponding siloles were obtained in satisfied
yields although, in most cases, the yields were slightly lower than
those by method A.
To expand synthetic utility of the products of the present reac-
tion, halodesilylation of the cyclized products 2 and 5 were
attempted (Scheme 10). Bromodesilylation of 2l with bromine
proceeded successfully to form 2-bromonaphthosilole 9 in 72%
yield. The reaction of 2j with ICl afforded 2-iodobenzosilole 10 in
85% yield. Contrary to the case of silylated benzosiloles, hal-
odesilylation of silylated siloles is known to be cumbersome.25
Indeed, iododesilylation of silole 5b by the reported method26
resulted in a low yield of the desired 2-iodosilole 11 although 5b
was consumed completely. However, these halogenated siloles can
be potential building blocks for further transformations including
transition metal-catalyzed coupling reactions.
3. Conclusions
We developed the DIBAL-H-promoted cyclization of 1-
methoxysilyl-2-[2-(trimethylsilyl)ethynyl]benzenes
methoxysilyl-1-(trimethylsilyl)alk-3-en-1-ynes
1
and 4-
4
to substituted
benzosiloles 2 and siloles 5. The cyclization of 1 was quite valuable
for benzosilole synthesis. The reaction mechanism involves the
formation of hydrosilanes 6 and 8 by hydride substitution of the
methoxysilane part with DIBAL-H. When hydrosilanes 6 and 8 were
used as substrates, substituted benzosiloles 2 and siloles 5 were
obtained efficiently. Particularly, the cyclization of 8 enabled the
synthesis of unsymmetrically substituted siloles bearing four or five
different groups on the ring, which are inaccessible by the known
methods. In addition, a substoichiometric amount of DIBAL-H (0.5
equiv) allowed efficient cyclization to 2 and 5. As shown in eq. (5) of
Scheme 1, intramolecular reaction between Si-H bond and C-C
triple bond is known to be useful for silole construction. However,
unlike the known methods, the present method is practicable with
DIBAL-H, or a readily accessible and handling, common reagent.
Please cite this article in press as: Kinoshita H, et al., Syntheses of substituted benzosiloles and siloles by diisobutylaluminium hydride-
promoted cyclization of 1-silyl-2-(2-silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes, Tetrahedron (2018), https://doi.org/10.1016/
j.tet.2018.02.011

H. Kinoshita et al. / Tetrahedron xxx (2018) 1e14
7
Table 5
Synthesis of siloles 5 from hydrosilanes 8.a
products could be converted to halogenated benzosiloles and
siloles useful for further modifications. Consequently, we suc-
ceeded in providing not only an inclusive regio-defined, efficient
approach to both multi-substituted benzosiloles and siloles but also
synthetically valuable, novel information on the reactivity of
organoalanes.
4. Experimental section
4.1. General experimental
Unless otherwise noted, all reactions were carried out under
argon atmosphere. All reagents were purchased from common
suppliers and used as received. Analytical thin layer chromatog-
raphy was performed using 0.25 mm silica gel 60 F254 plates.
Chromatography was performed using silica gel 60 N (spherical,
neutral, 63e210 mm). NMR spectra were recorded on a 300, 400, or
500 MHz NMR spectrometer. The chemical shifts are reported with
reference at 7.26 ppm (CHCl3) for the proton and at 77.0 ppm
Scheme 10. Halodesilylation of 2-(trimethylsilyl)siloles.
Additionally, it enables efficient synthesis of unsymmetrically poly-
substituted siloles as well as substituted benzosiloles. The silylated
Please cite this article in press as: Kinoshita H, et al., Syntheses of substituted benzosiloles and siloles by diisobutylaluminium hydride-
promoted cyclization of 1-silyl-2-(2-silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes, Tetrahedron (2018), https://doi.org/10.1016/
j.tet.2018.02.011

8
H. Kinoshita et al. / Tetrahedron xxx (2018) 1e14
(centered on the signal of CDCl3) for the carbon. Data for 1H NMR
are reported as follows: chemical shift, multiplicity (s ¼ singlet,
d ¼ doublet, t ¼ triplet, q ¼ quartet, quint ¼ quintet, sept. ¼ septet,
m ¼ multiplet), coupling constants (J, reported as values in hertz
(Hz)), and integration. Infrared spectra and high-resolution mass
spectra were obtained for all new compounds. The high-resolution
mass analysis was conducted by a double focusing magnetic sector
mass spectrometer. Melting points were measured for solid
compounds.
J ¼ 7.6 Hz, 6H), 1.09 (d, J ¼ 7.6 Hz, 6H), 1.56 (sept, J ¼ 7.6 Hz, 2H), 3.68
(s, 3H), 7.29e7.34 (m, 2H), 7.49e7.52 (m, 1H), 7.60e7.63 (m, 1H); 13
NMR (100 MHz, CDCl3, 77.0 ppm)
107.2, 127.4, 128.1, 128.8, 133.4, 135.6, 138.1; IR (neat) 3052, 2155,
1098 cmꢁ1; HRMS (EIþ) calcd for C18H30OSi2 [Mþ] 318.1835, found
318.1843.
C
d
ꢁ0.4, 13.1, 17.4, 18.0, 52.4, 95.6,
4.1.1.4. 1-Bromo-2-[2-[(1,1-dimethylethyl)dimethyl-silyl]ethynyl]
benzene (1e’). For the synthesis of 1e, the title compound 1e’ was
prepared as follows. A solution of LDA, prepared from iPr2NH
(0.93 mL, 6.5 mmol) and nBuLi (2.7 M in hexane, 2.4 mL, 6.5 mmol)
in THF (6 mL) at 0 ꢀC, was added to a solution of 1-bromo-2-
ethynylbenzene [766-46-1] (1.1 g, 5.9 mmol) in THF (6 mL)
at ꢁ78 ꢀC for 30 min tert-Butyldimetylsilyl chloride [18162-48-6]
(1.1 g, 7.1 mmol) was added to the mixture at that temperature.
The reaction mixture was warmed to room temperature and stirred
for 12 h. After adding aqueous NH4Cl, the aqueous mixture was
extracted with hexane three times. The combined organic phase
was dried over Na2SO4 and evaporated. Purification of the residue
by silica-gel column chromatography gave 1-bromo-2-[2-[(1,1-
dimethylethyl)dimethyl-silyl]ethynyl]benzene in (1.6 g, 5.4 mmol,
92%) as a pale yellow liquid. 1H NMR (400 MHz, CDCl3, 7.26 ppm)
4.1.1. Synthesis of methoxysilanes 1 (typical procedure)
Et2NH (20 mL), THF (20 mL), 1-bromo-2-iodobenzene (2.2 mL g,
18 mmol), and trimethylsilylacetylene (2.9 mL, 21 mmol) were
successively added to a flask containing PdCl2(PPh3)2 (0.25 g,
0.35 mmol) and CuI (0.067 g, 0.35 mmol). The mixture was stirred
at room temperature for 12 h and then evaporated. The residue was
diluted with hexane/AcOEt (5:1) and washed with 1 M aqueous
HCl. The organic layer was dried over Na2SO4 and evaporated. Pu-
rification of the residue by silica-gel column (hexane) gave 1-
bromo-2-[2-(trimethylsilyl)ethynyl]benzene [38274-16-7] (1a’) as
a pale yellow clear liquid (4.12 g, 16.3 mmol, 92% yield).
nBuLi (2.65 M in hexane, 701 mL, 1.86 mmol) was added to a
stirred solution of 1a’ (472 mg, 1.86 mmol) in THF (4 mL) at ꢁ78 ꢀC.
After 0.5 h, Me2SiCl2 (223 mL, 1.86 mmol) was added to the mixture
at that temperature. Then the mixture was warmed to room tem-
perature and stirred for 2 h. MeOH (0.5 mL) and Et3N (290 mL,
2.08 mmol) were successively added to the reaction mixture
at ꢁ78 ꢀC. After removing the cooling bath, the resultant mixture
was stirred at room temperature for 1 h. The mixture was quenched
with water and extracted with hexane/AcOEt (30:1) three times.
The combined organic layer was dried over Na2SO4 and evaporated.
The residue was purified by flash column chromatography (hexane/
AcOEt ¼ 40:1). The title compound,1-(methoxydimethylsilyl)-2-[2-
(trimethylsilyl)ethynyl]benzene (1a), was obtained as a pale yellow
liquid (0.721 g, 2.75 mmol, 71% yield). 1H NMR (500 MHz, CDCl3,
d
0.21 (s, 6H), 1.02 (s, 9H), 7.15 (ddd, J ¼ 7.6, 7.6, 1.6 Hz, 1H), 7.24
(ddd, J ¼ 7.6, 7.6, 1.2 Hz, 1H), 7.50 (dd, J ¼ 7.6, 1.6 Hz, 1H), 7.57 (dd,
J ¼ 8.0, 1.2 Hz, 1H).
4.1.1.5. 1-(Methoxydimethylsilyl)-2-[2-(tert-butyldimethylsilyl)ethy-
nyl]benzene (1e). Colorless liquid (1.1 g, 3.5 mmol, 54% yield from
1e’); 1H NMR (400 MHz, CDCl3, 7.26 ppm)
d 0.19 (s, 6H), 0.47 (s, 6H),
1.00 (s, 9H), 3.55 (s, 3H), 7.29e7.34 (m, 2H), 7.48e7.52 (m, 1H),
7.57e7.61 (m, 1H); 13C NMR (100 MHz, CDCl3, 77.0 ppm)
d
ꢁ4.7, ꢁ1.8, 16.8, 26.2, 50.8, 95.4, 107.0, 127.7, 127.9, 129.2, 133.3,
134.0, 140.5; IR (neat) 3052, 2930, 2153, 1250, 1092 cmꢁ1; HRMS
(EIþ) calcd for C17H28OSi2 [Mþ] 304.1679, found 304.1685.
7.26 ppm)
d
0.25 (s, 9H), 0.47 (s, 6H), 3.56 (s, 3H), 7.30e7.34 (m, 2H),
4.1.1.6. 1-(Methoxydimethylsilyl)-2-[2-(dimethylphenylsilyl)ethynyl]
benzene (1f). Pale yellow liquid (1.1 g, 3.2 mmol, 71% yield from 1-
bromo-2-[2-(dimethylphenylsilyl)ethynyl]benzene [935221-20-8]
7.48e7.50 (m, 1H), 7.59e7.61 (m, 1H); 13C NMR (125 MHz, CDCl3,
77.0 ppm)
d
ꢁ1.8, ꢁ0.3, 50.9, 96.9, 106.4, 127.7, 127.7, 129.2, 132.8,
134.0, 140.8; IR (neat) 3073, 3052, 2959, 2831, 2155, 1429 cmꢁ1
;
instead of 1a’); 1H NMR (300 MHz, CDCl3, 7.26 ppm)
d 0.44 (s,
HRMS (EIþ) calcd for C14H22OSi2 [Mþ] 262.1209, found 262.1209.
6H), 0.50 (s, 6H), 3.53 (s, 3H), 7.31e7.35 (m, 2H), 7.36e7.41 (m, 3H),
The substrates 1b-l, and 1p were synthesized by the same
manner as described for the preparation of 1a.
7.51e7.55 (m, 1H), 7.59e7.62 (m, 1H), 7.66e7.71 (m, 2H); 13C NMR
(100 MHz, CDCl3, 77.0 ppm)
d
ꢁ1.8, ꢁ1.1, 50.8, 94.9, 107.9, 127.5,
127.9, 127.9, 129.2, 129.5, 133.1, 133.8, 134.1, 136.7, 140.9; IR (neat)
3051, 2959, 2154, 1428, 1250 cmꢁ1; HRMS (EIþ) calcd for C19H24OSi2
[Mþ] 324.1366, found 324.1373.
4.1.1.1. 1-(Methoxydiphenylsilyl)-2-[2-(trimethylsilyl)ethynyl]ben-
zene (1b). Pale yellow powder (1.58 g, 4.09 mmol, 74% yield from
1a’); m.p. 89e90 ꢀC; 1H NMR (500 MHz, CDCl3, 7.26 ppm)
d
ꢁ0.10 (s,
9H), 3.63 (s, 3H), 7.32e7.44 (m, 8H), 7.54 (d, J ¼ 7.5 Hz, 1H),
7.65e7.69 (m, 5H); 13C NMR (125 MHz, CDCl3, 77.0 ppm)
4.1.1.7. 1-(Methoxydimethylsilyl)-2-[2-(triisopropylsilyl)ethynyl]ben-
zene (1g). Pale yellow liquid (932 mg, 2.66 mmol, 79% yield from 1-
bromo-2-[2-[tris(1-methylethyl)silyl]ethynyl]benzene [261713-83-
d
ꢁ0.7,
52.0, 98.3, 106.1, 127.6, 127.8, 129.1, 129.8, 133.3, 133.8, 135.5, 136.3,
136.7; IR (nujol) 3069, 2854, 2156, 1249, 1118 cmꢁ1; HRMS (EIþ)
calcd for C24H26OSi2 [Mþ] 386.1522, found 386.1511.
1] instead of 1a’); 1H NMR (400 MHz, CDCl3, 7.26 ppm)
d 0.49 (s,
6H), 1.13e1.15 (m, 21H), 3.54 (s, 3H), 7.29e7.35 (m, 2H), 7.51e7.55
(m 1H), 7.58e7.62 (m, 1H); 13C NMR (100 MHz, CDCl3, 77.0 ppm)
4.1.1.2. 1-[Methoxy(methyl)(phenyl)silyl]-2-[2-(trimethylsilyl)ethy-
d
ꢁ1.6, 11.5, 18.6, 50.8, 93.8, 108.1, 127.5, 128.2, 129.2, 134.0, 134.0,
nyl]benzene (1c). Pale yellow liquid (1.69 g, 5.21 mmol, 84% yield
139.9; IR (neat) 3052, 2943, 2866, 2148, 1250, 1129 cmꢁ1; HRMS
from 1a’); 1H NMR (400 MHz, CDCl3, 7.26 ppm)
d 0.08 (s, 9H), 0.76
(EIþ) calcd for C20H34OSi2 [Mþ] 346.2148, found 346.2151.
(s, 3H), 3.56 (s, 3H), 7.32e7.36 (m, 3H), 7.36e7.41 (m, 2H), 7.49e7.52
(m, 1H), 7.57e7.60 (m, 2H), 7.63e7.66 (m, 1H); 13C NMR (100 MHz,
4.1.1.8. 2-(Methoxydiphenylsilyl)-4-methyl-1-[2-(trimethylsilyl)ethy-
nyl]benzene (1h). White powder (1.01 g, 2.51 mmol, 52% yield form
2-bromo-4-methyl-1-[2-(trimethylsilyl)ethynyl]benzene [935223-
82-8] instead of 1a’); m.p. 91e92 ꢀC; 1H NMR (500 MHz, CDCl3,
CDCl3, 77.0 ppm)
d
ꢁ3.4, ꢁ0.5, 51.4, 97.6, 106.1, 127.7, 127.7, 128.4,
129.5, 129.6, 133.0, 134.4, 135.1, 135.6, 138.6; IR (neat) 3069, 3050,
3001, 2899, 2155, 1582, 1250 cmꢁ1; HRMS (EIþ) calcd for C19H24OSi2
[Mþ] 324.1366, found 324.1360.
7.26 ppm)
1H), 7.34e7.38 (m, 4H), 7.40e7.45 (m, 3H), 7.49e7.51 (m, 1H),
7.67e7.70 (m, 4H); 13C NMR (100 MHz, CDCl3, 77.0 ppm)
ꢁ0.6,
21.6, 51.9, 97.5, 106.4, 126.1, 127.6, 129.8, 130.6, 133.3, 133.9, 135.5,
136.5, 136.8, 137.7; IR (nujol) 3054, 2152, 1250, 1117, 1080 cmꢁ1
d
ꢁ0.12 (s, 9H), 2.34 (s, 3H), 3.61 (s, 3H), 7.18e7.21 (m,
4.1.1.3. 1-(Methoxydiisopropylsilyl)-2-[2-(trimethylsilyl)ethynyl]ben-
d
zene (1d). Pale yellow liquid (886.8 mg, 2.78 mmol, 47% yield from
1a’); 1H NMR (400 MHz, CDCl3, 7.26 ppm)
d
0.23 (s, 9H), 1.05 (d,
;
Please cite this article in press as: Kinoshita H, et al., Syntheses of substituted benzosiloles and siloles by diisobutylaluminium hydride-
promoted cyclization of 1-silyl-2-(2-silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes, Tetrahedron (2018), https://doi.org/10.1016/
j.tet.2018.02.011

H. Kinoshita et al. / Tetrahedron xxx (2018) 1e14
9
HRMS (EIþ) calcd for C25H28OSi2 [Mþ] 400.1679, found 400.1674.
4.1.1.14. 1,4-Bis(methoxydiphenylsilyl)-2,5-bis[2-(trimethylsilyl)ethy-
nyl]benzene (1m). The title compound 1m was prepared from 1,4-
dibromo-2,5-bis[2-(trimethylsilyl)ethynyl]benzene (1m’) and
Ph2SiCl2 according to the method for the synthesis of 1a. Dibro-
mobenzene 1m’ was obtained by the method reported by Liu's
group.28 White powder (214 mg, 0.308 mmol, 31% yield); m.p.
4.1.1.9. 4-Chloro-2-(methoxydiphenylsilyl)-1-[2-(trimethylsilyl)ethy-
nyl]benzene (1i). Pale yellow liquid (1.13 g, 2.69 mmol, 55% yield
from
[935222-84-7] instead of 1a’); 1H NMR (300 MHz, CDCl3, 7.26 ppm)
ꢁ0.11 (s, 9H), 3.60 (s, 3H), 7.32e7.47 (m, 8H), 7.65e7.69 (m, 5H);
13C NMR (100 MHz, CDCl3, 77.0 ppm)
2-bromo-4-chloro-1-[2-(trimethylsilyl)ethynyl]benzene
156e158 ꢀC; 1H NMR (400 MHz, CDCl3, 7.26 ppm)
3.59 (s, 6H), 7.34e7.45 (m, 12H), 7.68e7.71 (m, 8H), 7.90 (s, 2H); 13
NMR (125 MHz, CDCl3, 77.0 ppm)
d
ꢁ0.12 (s, 18H),
d
C
d
ꢁ0.8, 51.9, 99.5, 105.0, 127.4,
d
ꢁ0.7, 51.9, 100.7, 106.2, 127.7,
127.8, 130.0, 130.1, 133.0, 134.5, 134.7, 135.5, 135.9, 139.5; IR (neat)
128.1, 130.0, 133.2, 135.6, 138.6, 140.6; IR (nujol) 3069, 2834, 2151,
1249, 1116 cmꢁ1; HRMS (EIþ) calcd for C42H46O2Si4 [Mþ] 694.2575,
found 694.2553.
3070, 3050, 2835, 2156, 1450, 1117 cmꢁ1; HRMS (EIþ) calcd for
C
24H25ClOSi2 [Mþ] 420.1132, found 420.1131.
4.1.1.10. 4-Fluoro-2-(methoxydiphenylsilyl)-1-[2-(trimethylsilyl)
ethynyl]benzene (1j). White powder (942 mg, 2.33 mmol, 48% yield
4.1.1.15. Bis[(2-(methoxydiphenylsilyl)phenyl)ethynyl]dimethylsilane
(1n). A solution of LDA, prepared from iPr2NH (0.29 mL, 2.0 mmol)
and nBuLi (2.6 M in hexane, 0.77 mL, 2.0 mmol) in THF (2 mL) at
0 ꢀC, was added to a solution of (2-ethynylphenyl)(methoxy)
diphenylsilane (1o) (0.58 g, 1.8 mmol) in THF (2 mL) at ꢁ78 ꢀC. After
30 min of stirring, Me2SiCl2 (0.11 mL, 0.9 mmol) was added to the
mixture. The reaction mixture was gradually warmed to room
temperature and stirred for 12 h. After adding MeOH (10 mL), the
resultant mixture was concentrated under reduced pressure. The
residue was purified by silica-gel column chromatography (hexane/
AcOEt ¼ 20:1). Pale yellow liquid (45 mg, 0.65 mmol, 74% yield); 1H
from
[1609556-12-8] instead of 1a’); m.p. 107e108 ꢀC; 1H NMR
(400 MHz, CDCl3, 7.26 ppm)
2-bromo-4-fluoro-1-[2-(trimethylsilyl)ethynyl]benzene
d
ꢁ0.11 (s, 9H), 3.61 (s, 3H), 7.05 (ddd,
J ¼ 8.4, 8.4, 2.8 Hz, 1H), 7.35e7.40 (m, 5H), 7.41e7.46 (m, 2H), 7.51
(dd, J ¼ 8.4, 8.4 Hz, 1H), 7.66e7.68 (m, 4H); 13C NMR (100 MHz,
2
CDCl3, 77.0 ppm)
d
ꢁ0.7, 52.0, 97.9, 105.1, 117.0 (d, JC-F ¼ 22.0 Hz),
122.9 (d, 2JC-F ¼ 22.0 Hz), 125.1 (d, 3JC-F ¼ 4.0 Hz), 127.8, 130.1, 133.0,
3
1
135.5, 135.5, 140.4 (d, JC-F ¼ 5.0 Hz), 162.2 (d, JC-F ¼ 251.5 Hz); IR
(nujol) 3068, 2156, 1250, 1117, 1081 cmꢁ1; HRMS (EIþ) calcd for
C
24H25FOSi2 [Mþ] 404.1428, found 404.1428.
NMR (400 MHz, CDCl3, 7.26 ppm)
7.31e7.41 (m, 16H), 7.51e7.54 (m, 2H), 7.64e7.67 (m, 10H); 13C NMR
(100 MHz, CDCl3, 77.0 ppm)
d
ꢁ0.31 (s, 6H), 3.61 (s, 6H),
d
ꢁ0.9, 52.0, 94.6, 106.5, 127.7, 128.0,
4.1.1.11. 4,5-Difluoro-1-(methoxydiphenylsilyl)-2-[2-(trimethylsilyl)
ethynyl]benzene (1k). Pale yellow liquid (1.5 g, 3.6 mmol, 50% yield
from 1-bromo-4,5-difluoro-2-[2-(trimethylsilyl)ethynyl]benzene
[2073117-80-1] instead of 1a’); 1H NMR (400 MHz, CDCl3,
128.8, 129.8, 129.8, 133.5, 133.7, 135.5, 136.3, 137.0; IR (neat) 3050,
3010, 2835, 2158,1117 cmꢁ1; HRMS (EIþ) calcd for C44H40O2Si3 [Mþ]
684.2336, found 684.2336.
7.26 ppm)
d
ꢁ0.10 (s, 9H), 3.61 (s, 3H), 7.31e7.51 (m, 8H), 7.64e7.67
ꢁ0.8, 52.0, 99.1,
103.9, 122.5 (d, JC-F ¼ 17.0 Hz), 125.1 (d, JC-F ¼ 16.0 Hz), 126.1 (m),
(m, 4H); 13C NMR (100 MHz, CDCl3, 77.0 ppm)
d
4.1.1.16. (2-Ethynylphenyl)(methoxy)diphenylsilane (1o). A solution
of methoxysilane 1b (2.6 g, 6.7 mmol) and K2CO3 (0.28 mg,
2.0 mmol) in MeOH (7 mL)/THF (7 mL) was stirred at room tem-
perature for 14 h under the atmosphere. After the solvent was
evaporated, the residue was purified by silica-gel column chro-
matography (hexane/AcOEt ¼ 20:1). Pale yellow liquid (1.28 g,
2
2
3
1
127.8, 130.2, 132.8, 135.1 (d, JC-F ¼ 4.0 Hz), 135.4, 150.3 (dd, JC-
2
1
2
¼ 252.0 Hz, JC-F ¼ 12.0 Hz), 150.8 (dd, JC-F ¼ 250.0 Hz, JC-
¼ 13.0 Hz); IR (neat) 3071, 2960, 2838, 2155, 1587, 1483, 1293,
F
F
1118, 845 cmꢁ1; HRMS (EIþ) calcd for C24H24F2OSi2 [Mþ] 422.1334,
found 422.1328.
4.08 mmol, 61% yield); 1H NMR (400 MHz, CDCl3, 7.26 ppm)
d 2.84
(s, 1H), 3.66 (s, 3H), 7.34e7.41 (m, 6H), 7.41e7.46 (m, 2H), 7.54e7.57
(m, 1H), 7.65e7.68 (m, 5H); 13C NMR (100 MHz, CDCl3, 77.0 ppm)
4.1.1.12. 2-Bromo-3-[2-(trimethylsilyl)ethynyl]naphthalene
(1l’).
d
52.1, 81.1, 84.5, 127.7, 127.9, 128.0, 128.1, 129.9, 133.5, 133.7, 135.5,
136.4, 137.2; IR (neat) 3283, 3049, 1116 cmꢁ1; HRMS (EIþ) calcd for
21H18OSi [Mþ] 314.1127, found 314.1126.
For the synthesis of 1l, the title compound 1l’ was prepared from 3-
bromonaphthalen-2-yl trifluoromethanesulfonate [1245602-31-6]
and trimethylsilylacetylene according to the method for the syn-
thesis of 1a’. The triflate was obtained from 3-bromonaphthalen-2-
ol [30478-88-7]27 by treatment with trifluoromethanesulfonic an-
hydride and pyridine in CH2Cl2. Yellow powder (1.30 g, 4.30 mmol,
65%
fluoromethanesulfonate); m.p. 64e65 ꢀC; 1H NMR (400 MHz,
CDCl3, 7.26 ppm) 0.31 (s, 9H), 7.46e7.52 (m, 2H), 7.70e7.77 (m,
2H), 8.03 (s, 1H), 8.07 (s, 1H); 13C NMR (100 MHz, CDCl3, 77.0 ppm)
C
4.1.1.17. Methoxydiphenyl[2-(phenylethynyl)phenyl]silane
(1p).
Pale yellow powder (1.08 g, 2.77 mmol, 79% yield from 1-bromo-2-
(2-phenylethynyl)benzene [21375-88-2] instead of 1a’); m.p.
yield
from
3-bromonaphthalen-2-yl
tri-
106e107 ꢀC; 1H NMR (500 MHz, CDCl3, 7.26 ppm)
d 3.65 (s, 3H),
6.85e6.87 (m, 2H), 7.14e7.18 (m, 2H), 7.2e7.24 (m, 1H), 7.33e7.36
(m, 5H), 7.38e7.45 (m, 3H), 7.59 (d, J ¼ 7.5 Hz, 1H), 7.68e7.72 (m,
d
5H); 13C NMR (100 MHz, CDCl3, 77.0 ppm)
d 52.0, 91.1, 93.3, 123.1,
d
ꢁ0.1, 99.3,103.3,121.9,122.5,126.8,127.6,127.6,130.9,131.6, 133.6,
127.6, 127.7, 127.9, 128.0, 129.3, 129.8, 130.0, 131.2, 132.6, 133.9,
135.5, 136.4, 136.6; IR (nujol) 3050, 2834, 1117, 1087 cmꢁ1; HRMS
(EIþ) calcd for C27H22OSi [Mþ] 390.1440, found 390.1438.
133.7; IR (nujol) 3056, 2898, 2156, 1425, 1250, 1132 cmꢁ1; HRMS
(EIþ) calcd for C15H15BrSi2 [Mþ] 302.0126, found 302.0122.
4.1.1.13. 2-(Methoxydiphenylsilyl)-3-[2-(trimethylsilyl)ethynyl]naph-
4.1.2. Synthesis of methoxysilanes 4 (typical procedure)
thalene (1l). Pale yellow liquid (1.12 g, 2.57 mmol, 65% yield from
CH3CN (15 mL), 4-octyne (1.6 mL, 6.3 mmol), and (2-
bromoethynyl)dimethyl(phenyl)silane (1.8 g, 7.6 mmol) were suc-
cessively added to a flask containing Pd(OAc)2 (72 mg, 0.32 mmol).
After 8 h stirring at 30 ꢀC, the solution was filtered though a silica
gel pad on a Na2SO4 column and evaporated. Purification of the
residue by silica gel column chromatography (hexane) gave (Z)-4-
bromo-7-[dimethyl(phenyl)silyl]-5-(propyl)hept-4-en-6-yne
(4a’)21,29 as a pale yellow liquid (2.0 g, 5.7 mmol, 91%). 1H NMR
1l’); 1H NMR (500 MHz, CDCl3, 7.26 ppm)
d
ꢁ0.08 (s, 9H), 3.68 (s,
3H), 7.35e7.40 (m, 4H), 7.41e7.45 (m, 2H), 7.46e7.54 (m, 2H), 7.72
(dd, J ¼ 6.4, 0.8 Hz, 4H), 7.79 (dd, J ¼ 7.6, 7.6 Hz, 2H), 8.07 (s,1H), 8.18
(s, 1H); 13C NMR (100 MHz, CDCl3, 77.0 ppm)
d
ꢁ0.6, 52.1, 97.9,
106.4, 124.8, 126.8, 127.4, 127.5, 127.7, 128.4, 129.8, 132.2, 133.0,
133.2, 133.7, 134.0, 135.6, 138.0; IR (neat) 3051, 2958, 2149, 1250,
1116 cmꢁ1; HRMS (EIþ) calcd for C28H28OSi2 [Mþ] 436.1679, found
436.1672.
(500 MHz, CDCl3)
d
0.45 (s, 6H), 0.93 (t, J ¼ 7.5 Hz, 3H), 0.94 (t,
Please cite this article in press as: Kinoshita H, et al., Syntheses of substituted benzosiloles and siloles by diisobutylaluminium hydride-
promoted cyclization of 1-silyl-2-(2-silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes, Tetrahedron (2018), https://doi.org/10.1016/
j.tet.2018.02.011

10
H. Kinoshita et al. / Tetrahedron xxx (2018) 1e14
J ¼ 7.5 Hz, 3H), 1.56e1.65 (m, 4H), 2.19e2.23 (m, 2H), 2.54 (t,
J ¼ 7.0 Hz, 2H), 7.35e7.38 (m, 3H), 7.67e7.70 (m, 2H); 13C NMR
358.2148, found 358.2152.
(125 MHz, CDCl3)
d
ꢁ0.8, 13.3, 13.6, 21.9, 21.9, 35.1, 39.0, 96.3, 107.0,
4.1.2.4. (Z)-4-(Diisopropylmethoxysilyl)-7-[dimethyl(phenyl)silyl]-5-
(propyl)hept-4-en-6-yne (4e). Colorless clear oil (only pure fraction,
111 mg, 0.268 mmol, 20% yield from (Z)-4-bromo-7-[dimethyl(-
phenyl)silyl]-5-(propyl)hept-4-en-6-yne); 1H NMR (500 MHz,
124.3, 127.8, 129.3, 133.8, 134.0, 137.2; IR (neat) 3070, 3023, 2962,
2872, 2146, 2068 cmꢁ1; HRMS (EIþ) calcd for C18H25BrSi [Mþ]
348.0909, found 348.0914.
nBuLi (2.7 M in hexane, 0.69 mL, 1.8 mmol) was added to a
stirred solution of 4a’ (0.64 g, 1.8 mmol) in THF (2 mL) at ꢁ78 ꢀC.
After 0.5 h, Ph2SiCl2 (0.38 mL, 1.8 mmol) was added to the mixture.
The mixture was warmed to room temperature and stirred for 2 h.
MeOH (0.5 mL) and Et3N (0,29 mL, 2.1 mmol) were successively
added to the reaction mixture at ꢁ78 ꢀC. After removing the cooling
bath, the resultant mixture was stirred at room temperature for 1 h.
The mixture was quenched with water and extracted with hexane/
AcOEt (30:1) three times. The combined organic layer was dried
over Na2SO4 and evaporated. Purification of the residue by silica-gel
column chromatography (hexane/AcOEt ¼ 40:1) gave (Z)-4-
(methoxydiphenylsilyl)-7-[dimethyl(phenyl)silyl]-5-(propyl)hept-
4-en-6-yne (4a) as a pale yellow liquid (0.48 g, 1.0 mmol, 55%
CDCl3, 7.26 ppm)
d
0.39 (s, 6H), 0.89e0.95 (m, 6H), 1.02 (dd, J ¼ 7.5,
7.5 Hz, 12H), 1.26e1.34 (m, 2H), 1.35e1.45 (m, 2H), 1.55e1.63 (m,
2H), 2.13e2.16 (m, 2H), 2.21e2.24 (m, 2H), 3.59 (s, 3H), 7.35e7.38
(m, 3H), 7.58e7.61 (m, 2H); 13C NMR (125 MHz, CDCl3, 77.0 ppm)
d
ꢁ1.2, 13.5, 13.8, 14.7, 17.8, 18.4, 21.8, 23.2, 33.9, 34.9, 52.3, 93.6,
110.2, 127.8, 129.2, 132.8, 133.7, 137.2, 150.0; IR (neat) 3070, 2958,
2866, 2136, 2066, 1115 cmꢁ1; HRMS (EIþ) calcd for C25H42OSi2 [Mþ]
414.2774, found 414.2785.
4.1.3. Synthesis of hydrosilanes 6 (typical procedure)
A solution of methoxysilane 1a (0.38 g, 1.5 mmol) in Et2O (1 mL)
was added to a suspension of LiAlD4 (56 mg, 1.5 mmol) in Et2O
(2 mL) at 0 ꢀC. After 18 h stirring at room temperature, MeOH
(5 mL) and 1M aqueous HCl were successively added to the reaction
mixture at 0 ꢀC. The aqueous mixture was extracted with hexane
three times. The combined organic layer was dried over Na2SO4 and
evaporated. The residue was purified by silica-gel column chro-
matography (hexane). [(2-(Deuteriodimethylsilyl)phenyl)ethynyl]
trimethylsilane (6a-d) was obtained as a colorless liquid (0.29 g,
yield); 1H NMR (300 MHz, CDCl3, 7.26 ppm)
d 0.01 (s, 6H), 0.84 (t,
J ¼ 7.5 Hz, 3H), 0.96 (t, J ¼ 7.5 Hz, 3H), 1.30e1.39 (m, 2H), 1.57e1.70
(m, 2H), 2.26e2.35 (m, 4H), 3.45 (s, 3H), 7.24e7.40 (m, 11H),
7.66e7.69 (m, 4H); 13C NMR (125 MHz, CDCl3, 77.0 ppm)
d
ꢁ1.4,
13.9, 14.4, 21.8, 23.4, 33.5, 35.1, 51.8, 96.9, 109.0, 127.5, 127.6, 129.0,
129.5, 133.7, 134.6, 135.5, 136.4, 137.2, 146.0; IR (neat) 3068, 3049,
2959, 2871, 2138, 1115 cmꢁ1; HRMS (EIþ) calcd for C31H38OSi2 [Mþ]
482.2461, found 482.2477.
0.87 mmol, 84% yield). 1H NMR (500 MHz, CDCl3, 7.26 ppm)
(s, 9H), 0.41 (s, 6H), 7.27e7.33 (m, 2H), 7.46e7.49 (m, 1H), 7.50e7.52
(m, 1H); 13C NMR (100 MHz, CDCl3, 77.0 ppm)
d 0.25
The 1,4-bissilyl-1,3-enynes 4b-e were synthesized in the same
manner as described for the preparation of 4a.
d
ꢁ4.1, ꢁ0.2, 97.2,
105.7, 127.7, 128.6, 129.0, 132.2, 134.7, 140.4; IR (neat) 3052, 2959,
2155, 1548, 1127 cmꢁ1; HRMS (EIþ) calcd for C13H19DSi2 [Mþ]
233.1166, found 233.1173.
4.1.2.1. (Z)-4-(Methoxydiphenylsilyl)-7-(trimethylsilyl)-5-(propyl)
hept-4-en-6-yne (4b). Pale yellow liquid (664 mg, 1.58 mmol, 67%
yield from (Z)-4-bromo-7-(trimethylsilyl)-5-(propyl)hept-4-en-6-
yne [1231256-01-1]); 1H NMR (300 MHz, CDCl3, 7.26 ppm)
Hydrosilanes 6a and 6b are known compounds.12 Hydrosilanes
6c, 6h, 6j, 6k, and 6q were prepared by the method reported by this
group.21 Other hydrosilanes 6 were obtained from methoxysilanes
4 and LiAlH4 according to the same procedure used for the syn-
thesis of 6a-d.
d
ꢁ0.21 (s, 9H), 0.83 (t, J ¼ 7.2 Hz, 3H), 0.96 (t, J ¼ 7.5 Hz, 3H),
1.26e1.35 (m, 2H), 1.56e1.67 (m, 2H), 2.25e2.31 (m, 4H), 3.47 (m,
3H), 7.31e7.39 (m 6H), 7.66e7.72 (m, 4H); 13C NMR (125 MHz,
CDCl3, 77.0 ppm)
d
ꢁ0.7, 13.9, 14.4, 21.8, 23.4, 33.5, 35.0, 51.8, 99.1,
107.5, 127.4, 129.4, 134.8, 135.4, 136.6, 145.4; IR (neat) 3069, 3050,
2871, 2138, 1250, 1115 cmꢁ1; HRMS (EIþ) calcd for C26H36OSi2 [Mþ]
420.2305, found 420.2294.
4.1.3.1. 1-(Diisopropylsilyl)-2-[2-(trimethylsilyl)ethynyl]benzene
(6d). Colorless clear liquid (0.20 g, 0.70 mmol, 92% yield from 1d);
1H NMR (400 MHz, CDCl3, 7.26 ppm)
d 0.24 (s, 9H), 0.99 (d,
J ¼ 7.6 Hz, 6H), 1.10 (d, J ¼ 7.2 Hz, 6H), 1.40e1.49 (m, 2H), 4.02 (t,
4.1.2.2. (Z)-6-(Methoxydiphenylsilyl)-9-[dimethyl(phenyl)silyl]-7-
(pentyl)non-6-en-8-yne (4c). Colorless clear oil (only pure fraction,
142 mg, 0.263 mmol, 22% yield from (Z)-6-bromo-9-[dimethyl(-
phenyl)silyl)-7-(pentyl)non-6-en-8-yne); 1H NMR (300 MHz,
J ¼ 4.0 Hz, 1H), 7.24e7.32 (m, 2H), 7.47e7.48 (m, 1H), 7.49e7.50 (m,
1H); 13C NMR (100 MHz, CDCl3, 77.0 ppm)
96.1, 106.7, 127.4, 128.8, 128.9, 132.7, 136.6, 138.1; IR (neat) 3051,
2956, 2863, 2156, 1250 cmꢁ1; HRMS (EIþ) calcd for C17H28Si2 [Mþ]
288.1730, found 288.1720.
d
ꢁ0.2, 11.2, 19.1, 19.1,
CDCl3, 7.26 ppm)
d
0.03 (s, 6H), 0.84 (t, J ¼ 6.9 Hz, 3H), 0.92 (t,
J ¼ 7.2 Hz, 3H), 1.18e1.40 (m, 10H), 1.55e1.67 (m, 2H), 2.28e2.37 (m,
4H), 3.47 (s, 3H), 7.23e7.42 (m, 11H), 7.65e7.70 (m, 4H); 13C NMR
4.1.3.2. 1-(Dimethylsilyl)-2-[2-(tert-butyldimethylsilyl)ethynyl]ben-
(125 MHz, CDCl3, 77.0 ppm)
d
ꢁ1.4, 14.0, 14.0, 22.3, 22.5, 28.3, 29.6,
zene (6e). Pale yellow liquid (497 mg, 1.81 mmol, 83% yield from
31.4, 31.6, 32.1, 33.0, 51.8, 96.8, 109.1, 127.5, 127.6, 129.0, 129.5, 133.7,
134.6, 135.5, 136.5, 137.2, 145.9; IR (neat) 3069, 3051, 2960, 2830,
2136, 1116 cmꢁ1; HRMS (EIþ) calcd for C35H46OSi2 [Mþ] 538.3087,
found 538.3073.
1e); 1H NMR (500 MHz, CDCl3, 7.26 ppm)
d 0.19 (s, 6H), 0.41 (d,
J ¼ 4.0 Hz, 6H), 1.00 (s, 9H), 4.55 (sept, J ¼ 4.0 Hz, 1H), 7.27e7.33 (m,
2H), 7.48e7.52 (m, 2H); 13C NMR (125 MHz, CDCl3, 77.0 ppm)
d
ꢁ4.6, ꢁ4.0, 16.7, 26.2, 95.6, 106.3, 127.7, 128.8, 129.0, 132.6, 134.6,
140.1; IR (neat) 3053, 2929, 2857, 2153 cmꢁ1; HRMS (EIþ) calcd for
16H26Si2 [Mþ] 274.1573, found 274.1578.
4.1.2.3. (Z)-4-(Methoxydimethylsilyl)-7-[dimethyl(phenyl)silyl]-5-
(propyl)hept-4-en-6-yne (4d). Colorless clear oil (only pure fraction,
0.39 g, 1.1 mmol, 22% yield from (Z)-4-bromo-7-[dimethyl(phenyl)
silyl]-5-(propyl)hept-4-en-6-yne); 1H NMR (300 MHz, CDCl3,
C
4.1.3.3. 5-Chloro-1-(diphenylsilyl)-2-[2-(trimethylsilyl)ethynyl]ben-
7.26 ppm)
d
0.3 (s, 6H), 0.42 (s, 6H), 0.89e0.95 (m, 6H), 1.25e1.36
zene (6i). Colorless clear liquid (0.33 g, 0.85 mmol, 98% yield from
(m, 2H), 1.54e1.62 (m, 2H), 2.15e2.24 (m, 4H), 3.44 (s, 3H),
1i); 1H NMR (400 MHz, CDCl3, 7.26 ppm)
d
0.01 (s, 9H), 5.59 (s, 1H),
7.35e7.38 (m, 3H), 7.61e7.65 (m, 2H); 13C NMR (125 MHz, CDCl3,
7.30e7.47 (m, 9H), 7.54e7.58 (m, 4H); 13C NMR (100 MHz, CDCl3,
77.0 ppm)
d
ꢁ1.4, ꢁ1.0, 13.8, 14.4, 21.7, 23.4, 33.2, 34.6, 50.6, 94.5,
77.0 ppm)
d
ꢁ0.6, 99.8, 104.2, 128.0, 128.1, 129.9, 129.9, 132.2, 133.7,
109.4, 127.8, 129.3, 133.1, 133.7, 137.2, 150.4; IR (neat) 3069, 3051,
134.4, 135.9, 136.3, 139.1; IR (neat) 3069, 2959, 2156, 1251 cmꢁ1
HRMS (EIþ) calcd for C23H23ClSi2 [Mþ] 390.1027, found 390.1024.
;
2960, 2830, 2136, 1116 cmꢁ1; HRMS (EIþ) calcd for C21H34OSi2 [Mþ]
Please cite this article in press as: Kinoshita H, et al., Syntheses of substituted benzosiloles and siloles by diisobutylaluminium hydride-
promoted cyclization of 1-silyl-2-(2-silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes, Tetrahedron (2018), https://doi.org/10.1016/
j.tet.2018.02.011

H. Kinoshita et al. / Tetrahedron xxx (2018) 1e14
11
4.1.3.4. 2-(Diphenylsilyl)-3-[2-(trimethylsilyl)ethynyl]naphthalene
4.1.4.2. (Z)-14-Ethyl-16-(trimethylsilyl)-13-(diphenylsilyl)hexadec-
13-en-15-yne (8m). Colorless liquid (270 m g, 0.54 mmol, 43% yield
(6l). Colorless clear gum (0.83 g, 2.1 mmol, 99% yield from 1l); 1H
NMR (400 MHz, CDCl3, 7.26 ppm)
d
0.03 (s, 9H), 5.73 (s, 1H),
from 8m’); 1H NMR (500 MHz, CDCl3, 7.26 ppm)
d
ꢁ0.09 (s, 9H),
7.35e7.53 (m, 9H), 7.60e7.63 (m, 3H), 7.71 (d, J ¼ 8.0 Hz, 1H), 7.78
0.88 (t, J ¼ 7.5 Hz, 3H), 1.05e1.34 (m, 23 H), 2.14e2.18 (m, 2H), 2.33
(d, J ¼ 8.0 Hz, 1H), 7.87 (s, 1H), 8.06 (s, 1H); 13C NMR (100 MHz,
(q, J ¼ 7.5 Hz, 2H), 5.29 (s,1H), 7.31e7.39 (m, 6H), 7.57e7.60 (m, 4H);
CDCl3, 77.0 ppm)
d
ꢁ0.5, 98.2, 105.6, 125.4, 126.8, 127.4, 127.5, 127.9,
13C NMR (125 MHz, CDCl3, 77.0 ppm)
d
ꢁ0.5, 13.4, 14.1, 22.7, 25.8,
128.2, 129.6, 132.2, 132.8, 133.3, 133.6, 136.0, 138.3; IR (neat) 3068,
2148, 1250 cmꢁ1; HRMS (EIþ) calcd for C27H26Si2 [Mþ] 406.1573,
found 406.1571.
29.2, 29.4, 29.5, 29.6, 29.6, 29.7, 31.9, 32.3, 98.5, 106.8, 127.7, 129.3,
134.0, 135.9, 138.2, 143.7; IR (neat) 3068, 2958, 2138, 1112 cmꢁ1
HRMS (EIþ) calcd for C33H50Si2 [Mþ] 502.3451, found 502.3453.
;
4.1.4.3. (Z)-6-Ethyl-5-iodo-2-methyl-8-(trimethylsilyl)oct-5-en-7-
4.1.3.5. Bis[(2-(diphenylsilyl)phenyl)ethynyl]dimethylsilane
Colorless clear gum (0.21 g, 0.34 mmol, 86% yield from 1n); 1H NMR
(400 MHz, CDCl3, 7.26 ppm)
ꢁ0.04 (s, 6H), 5.64 (s, 2H), 7.27e7.40
(m, 18H), 7.53e7.59 (m, 10H); 13C NMR (100 MHz, CDCl3, 77.0 ppm)
(6n).
yne (8n’). 30 Colorless liquid (571 mg, 1.64 mmol, 55% yield from 5-
methylhex-1-yne); 1H NMR (500 MHz, CDCl3, 7.26 ppm)
d 0.22 (s,
d
9H), 0.91 (d, J ¼ 6.5 Hz, 6H), 1.12 (t, J ¼ 7.5 Hz, 3H), 1.38e1.43 (m,
2H), 1.58 (sept, J ¼ 6.5 Hz, 1H), 2.26 (q, J ¼ 7.5 Hz, 2H), 2.56e2.60 (m,
d
ꢁ0.5, 94.8, 105.9, 127.9, 128.1, 129.4, 129.6, 129.7, 132.6, 133.0,
2H); 13C NMR (125 MHz, CDCl3, 77.0 ppm)
27.3, 38.6, 38.9, 97.5, 109.0, 113.9, 132.2; IR (neat) 2958, 2143,
1044 cmꢁ1; HRMS (EIþ) calcd for C14H25ISi [Mþ] 348.0770, found
348.0773.
d
ꢁ0.2, 13.5, 22.5, 26.1,
136.0, 136.6, 136.8; IR (neat) 3063, 2855, 2197, 2154, 1455 cmꢁ1
;
HRMS (EIþ) calcd for C42H36Si3 [Mþ] 624.2125, found 624.2119.
4.1.3.6. 1-(Diphenylsilyl)-2-[2-(dimethylphenylsilyl)ethynyl]benzene
(6q). Colorless clear liquid (195 mg, 0.465 mmol, quant from 2-
bromo-1-[2-(dimethyl(phenyl)silyl)ethynyl]benzene [935221-20-
4.1.4.4. (Z)-6-Ethyl-2-methyl-8-(trimethylsilyl)-5-(diphenylsilyl)oct-
8]);21 1H NMR (500 MHz, CDCl3, 7.26 ppm)
d
0.26 (s, 6H), 5.66 (s,
1H), 7.26e7.42 (m, 13H), 7.46e7.48 (m, 2H), 7.54e7.60 (m, 4H); 13
NMR (125 MHz, CDCl3, 77.0 ppm)
5-en-7-yne (8n). Colorless liquid (146 mg, 0.361 mmol, 45% yield
from 8n’); 1H NMR (300 MHz, CDCl3, 7.26 ppm)
(d, J ¼ 6.6 Hz, 6H), 0.99e1.08 (m, 2H), 1.17 (t, J ¼ 7.5 Hz, 3H), 1.29
(sept, J ¼ 6.5 Hz, 1H), 2.11e2.17 (m, 2H), 2.32 (q, J ¼ 7.5 Hz, 2H), 5.30
(s, 1H), 7.30e7.41 (m, 6H), 7.55e7.62 (m, 4H); 13C NMR (125 MHz,
d
ꢁ0.09 (s, 9H), 0.66
C
d
ꢁ1.3, 96.3, 106.8, 127.8, 127.9,
128.0, 129.3, 129.6, 129.7, 132.7, 132.9, 133.7, 135.9, 136.5, 136.7; IR
(neat) 3068, 3049, 3000, 2958, 2155, 1429, 1117 cmꢁ1; HRMS (EIþ)
calcd for C28H26Si2 [Mþ] 418.1573, found 418.1576.
CDCl3, 77.0 ppm)
d
ꢁ0.5, 13.4, 22.1, 25.7, 28.3, 30.1, 38.6, 98.5, 106.7,
127.7, 129.3, 134.0, 135.9, 138.2, 143.7; IR (neat) 3068, 2957, 2139,
1112 cmꢁ1; HRMS (EIþ) calcd for C26H36Si2 [Mþ] 404.2356, found
404.2358.
4.1.4. Synthesis of hydrosilanes 8 (typical procedure)
nBuLi (2.7 M in hexane, 2.2 mL, 5.9 mmol) was added to a so-
lution of 4a’ (1.9 g, 5.6 mmol)29 in THF (15 mL) at ꢁ78 ꢀC. After 0.5 h
stirring, Ph2SiCl2 (1.2 mL, 5.6 mmol) was added to the mixture. The
resultant mixture was stirred for 1 h at ꢁ78 ꢀC and then warmed to
0 ꢀC. After adding LiAlH4 (0.21 g, 5.6 mmol), the mixture was
warmed to room temperature and stirred for 2 h. The reaction
mixture was quenched with water and extracted with hexane three
times. The combined organic layer was dried over Na2SO4 and
evaporated. Purification of the residue by silica-gel column chro-
matography (hexane) and then recycling preparative HPLC (CHCl3)
4.1.4.5. (Z)-6-Ethyl-2-methyl-8-(trimethylsilyl)-5-[methyl(phenyl)
silyl]oct-5-en-7-yne (8o). Colorless liquid (147 mg, 0.429 mmol,
39% yield from 8n’); 1H NMR (500 MHz, CDCl3, 7.26 ppm)
d 0.07 (s,
9H), 0.54 (d, J ¼ 3.5 Hz, 3H), 0.79 (d, J ¼ 7.0 Hz, 6H), 1.05e1.12 (m,
2H), 1.21 (t, J ¼ 7.5 Hz, 3H), 1.43 (sept, J ¼ 7.0 Hz, 1H), 2.16 (t,
J ¼ 8.0 Hz, 2H), 2.26 (q, J ¼ 7.5 Hz, 2H), 4.75 (q, J ¼ 3.5 Hz, 1H),
7.31e7.35 (m, 3H), 7.58e7.60 (m, 2H); 13C NMR (125 MHz, CDCl3,
77.0 ppm)
d
ꢁ5.1, ꢁ0.3, 13.3, 22.3, 25.6, 28.4, 30.3, 38.7, 97.3, 107.0,
127.6, 129.0, 134.8, 136.1, 136.4, 145.7; IR (neat) 3068, 2958, 2138,
1112 cmꢁ1; HRMS (EIþ) calcd for C21H34Si2 [Mþ] 342.2199, found
342.2191.
gave
(Z)-4-(diphenylsilyl)-7-[dimethyl(phenyl)silyl]-5-(propyl)
hept-4-en-6-yne (8a)21 was obtained as a colorless clear liquid
(only pure fraction, 0.99 g, 2.2 mmol, 39% yield); 1H NMR (300 MHz,
CDCl3)
d
0.14 (s, 6H), 0.73 (t, J ¼ 7.2 Hz, 3H), 0.98 (t, J ¼ 7.2 Hz, 3H),
1.15e1.28 (m, 2H), 1.61e1.72 (m, 2H), 2.14e2.20 (m, 2H), 2.30e2.35
4.1.5. Synthesis of benzosiloles 2 from Methyl silyl ethers 1 (general
procedure)
(m, 2H), 5.33 (s, 1H), 7.24e7.40 (m, 11H), 7.56e7.7.59 (m, 4H); 13C
NMR (125 MHz, CDCl3)
d
ꢁ1.3, 13.9, 14.2, 21.9, 23.1, 34.6, 96.1, 108.5,
DIBAL-H (1.0 M solution in hexane, 0.33 mL, 0.33 mmol) was
added to a flask containing substrate 1 (0.25 mmol). After removing
the hexane under reduced pressure, octane (0.75 mL) was added to
the residue. The resultant mixture was stirred at 75 ꢀC for 6 h. The
mixture was cooled to room temperature. Then 1 M aqueous HCl
(2.0 mL) was added to the mixture. The aqueous mixture was stir-
red vigorously and extracted with hexane three times. The com-
bined organic layer was dried over Na2SO4 and evaporated. The
residue was purified by silica-gel column chromatography
(hexane).
127.6, 127.7, 129.1, 129.3, 133.7, 133.8, 135.9, 136.8, 137.2, 144.9; IR
(neat) 3068, 3049, 2959, 2138 cmꢁ1; HRMS (EIþ) calcd for C30H36Si2
[Mþ] 452.2356, found 452.2358.
The substrates 8beh were prepared following our previous
report.21
The alkenyl iodides 8k’, 8l’, 8m’, and 8n’ were prepared by the
reported methods,30 and used for the synthesis of 8keo by the
method reported by this group.21
4.1.4.1. (Z)-14-Ethyl-13-iodo-16-(trimethylsilyl)hexadec-13-en-15-
yne (8m’). 21,30 Colorless liquid (558 mg, 1.25 mmol, 42% yield from
4.1.5.1. 1,1-Dimethyl-2-(trimethylsilyl)-1H-benzo[b]silole
[152554-94-4]. Colorless liquid (52 mg, 0.22 mmol, 89%); 1H NMR
(500 MHz, CDCl3, 7.26 ppm) 0.17 (s, 9H), 0.32 (s, 6H), 7.21 (ddd,
(2a)
hexadec-1-yne); 1H NMR (500 MHz, CDCl3, 7.26 ppm)
d 0.22 (s, 9H),
0.88 (t, J ¼ 7.5 Hz, 3H), 1.12 (t, J ¼ 7.5 Hz, 3H), 1.25e1.31 (m, 18H),
d
1.45e1.51 (m, 2H), 2.27 (q, J ¼ 7.5 Hz, 2H), 2.57 (t, J ¼ 7.5 Hz, 2H); 13
C
J ¼ 7.5, 7.0, 1.0 Hz, 1H), 7.27 (d, J ¼ 7.0 Hz, 1H), 7.32 (ddd, J ¼ 7.5, 7.0,
NMR (125 MHz, CDCl3, 77.0 ppm)
d
ꢁ0.1, 13.5, 14.1, 22.7, 26.3, 28.6,
1.0 Hz, 1H), 7.50 (s, 1H), 7.53 (d, J ¼ 7.0 Hz, 1H); 13C NMR (100 MHz,
29.4, 29.5, 29.5, 29.6, 31.9, 40.8, 97.5, 109.1, 113.9, 132.4; IR (neat)
2925, 2143, 1249 cmꢁ1; HRMS (EIþ) calcd for C21H39ISi [Mþ]
446.1866, found 446.1872.
CDCl3, 77.0 ppm)
d
ꢁ3.2, ꢁ0.6, 124.0, 126.9, 129.7, 131.5, 140.7, 146.8,
150.0, 155.3; IR (neat) 3055, 2952, 1519, 1249 cmꢁ1; HRMS (EIþ)
calcd for C13H20Si2 [Mþ] 232.1104, found 232.1093.
Please cite this article in press as: Kinoshita H, et al., Syntheses of substituted benzosiloles and siloles by diisobutylaluminium hydride-
promoted cyclization of 1-silyl-2-(2-silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes, Tetrahedron (2018), https://doi.org/10.1016/
j.tet.2018.02.011

12
H. Kinoshita et al. / Tetrahedron xxx (2018) 1e14
4.1.5.2. 1,1-Dimethyl-2-(trimethylsilyl)-1H-benzo[b]silole
Colorless liquid (29.8 mg, 0.128 mmol, 51% from 6a-d). 1H NMR
(400 MHz, CDCl3, 7.26 ppm) 0.17 (s, 9H), 0.32 (s, 6H), 7.20 (ddd,
(2a-d).
4.1.5.9. 6-Methyl-1,1-diphenyl-2-(trimethylsilyl)-1H-benzo[b]silole
(2h). White powder (89.9 mg, 0.243 mmol, 97%); m.p.
d
53.0e54.0 ꢀC; 1H NMR (500 MHz, CDCl3)
d 0.04 (s, 9H), 2.32 (s, 3H),
J ¼ 7.5, 7.0, 1.0 Hz, 1H), 7.27e7.28 (m, 1H), 7.32 (ddd, J ¼ 7.5, 7.0,
7.16 (dd, J ¼ 7.8, 1.0 Hz, 1H), 7.24 (d. J ¼ 7.5 Hz, 1H), 7.32e7.43 (m,
1.0 Hz, 1H), 7.53 (d, J ¼ 7.0 Hz, 1H); 13C NMR (100 MHz, CDCl3,
7H), 7.60e7.62 (m, 4H), 7.71 (s, 1H); 13C NMR (125 MHz, CDCl3)
77.0 ppm)
d
ꢁ3.2, ꢁ0.5, 124.0, 126.9, 129.7, 131.5, 140.7, 146.6, 149.9,
d
ꢁ0.1, 21.4, 124.2,127.9,129.9,130.7, 132.9,133.8,135.6, 137.3, 138.4,
155.0 (t, J ¼ 23.8 Hz); IR (neat) 3055, 2953, 2209, 1249 cmꢁ1; HRMS
142.2, 148.4, 158.6; IR (nujol) 3067, 2953, 1510, 1248, 1114 cmꢁ1
;
(EIþ) calcd for C13H19DSi2 [Mþ] 233.1166, found 233.1174.
HRMS (EIþ) calcd for C24H26Si2 [Mþ] 370.1573, found 370.1574.
4.1.5.3. 1,1-Dimethyl-2-(trimethylsilyl)-2,3-dihydro-1H-benzo[b]
4.1.5.10. 6-Chloro-1,1-diphenyl-2-(trimethylsilyl)-1H-benzo[b]silole
31
silole (3a) [66535-02-2].
CDCl3, 7.26 ppm)
Colorless liquid. 1H NMR (400 MHz,
(2i). White powder (85.1 mg, 0.218 mmol, 87%); m.p. 96e97 ꢀC; 1H
d
0.08 (s, 9H), 0.25 (s, 3H), 0.34 (s, 3H), 0.44 (dd,
NMR (500 MHz, CDCl3, 7.26 ppm) d 0.05 (s, 9H), 7.25e7.27 (m, 1H),
J ¼ 10.0, 8.8 Hz,1H), 2.98 (dd, J ¼ 16.8,10.0 Hz,1H), 3.21 (dd, J ¼ 16.8,
7.31e7.38 (m, 5H), 7.41e7.45 (m, 2H), 7.50 (d, J ¼ 2.0 Hz, 1H),
Hz, 8.8 Hz, 1H), 7.17e7.32 (m, 3H), 7.50 (d, J ¼ 6.8 Hz, 1H); 13C NMR
7.58e7.60 (m, 4H), 7.68 (s, 1H); 13C NMR (125 MHz, CDCl3,
(100 MHz, CDCl3, 77.0 ppm)
d
ꢁ1.0, ꢁ0.9, ꢁ0.3, 14.1, 34.3, 125.2,
77.0 ppm)
d
ꢁ0.2, 125.4, 128.1, 130.1, 130.2, 131.8, 132.7, 133.9, 135.5,
125.6, 129.0, 131.6, 140.5, 153.5; IR (neat) 3055, 2952, 2120,
1250 cmꢁ1; HRMS (EIþ) calcd for C13H22Si2 [Mþ] 234.1260, found
234.1254.
141.0, 144.8, 149.0, 157.4; IR (nujol) 3068, 3045, 1509, 1428,
1115 cmꢁ1; HRMS (EIþ) calcd for C23H23ClSi2 [Mþ] 390.1027, found
390.1030.
4.1.5.4. 1,1-Diphenyl-2-(trimethylsilyl)-1H-benzo[b]silole
Colorless liquid (82 mg, 0.23 mmol, 92%); 1H NMR (500 MHz, CDCl3,
7.26 ppm)
0.06 (s, 9H), 7.22 (ddd, J ¼ 7.0, 6.5, 2.0 Hz,1H), 7.32e7.37
(m, 6H), 7.38e7.43 (m, 2H), 7.58 (d, J ¼ 6.5 Hz, 1H), 7.60e7.62 (m,
4H), 7.74 (s, 1H); 13C NMR (125 MHz, CDCl3, 77.0 ppm)
127.6, 128.0, 129.9, 130.2, 132.7, 132.9, 135.6, 138.2, 144.0, 150.9,
158.7; IR (neat) 3052, 3023, 2953, 1515, 1113 cmꢁ1; HRMS (EIþ)
calcd for C23H24Si2 [Mþ] 356.1417, found 356.1425.
(2b).
4.1.5.11. 6-Fluoro-1,1-diphenyl-2-(trimethylsilyl)-1H-benzo[b]silole
(2j). White powder (90 mg, 0.24 mmol, 96%); m.p. 78.0e79.0 ꢀC;
d
1H NMR (500 MHz, CDCl3)
d
0.05 (s, 9H), 7.03 (ddd, J ¼ 8.5, 8.5,
2.5 Hz, 1H), 7.25 (dd, J ¼ 7.5, 2.5 Hz, 1H), 7.30 (dd, J ¼ 8.3, 5.0 Hz, 1H),
d
ꢁ0.1, 124.5,
7.34e7.39 (m, 4H), 7.7.41e7.45 (m, 2H), 7.60 (dd, J ¼ 8.0, 1.5 Hz, 4H),
7.69 (s, 1H); 13C NMR (125 MHz, CDCl3)
d
ꢁ0.1, 116.6 (d, JC-
2
¼ 22.5 Hz), 119.8 (d, 2JC-F ¼ 21.3 Hz), 125.6 (d, 3JC-F ¼ 7.5 Hz), 128.1,
F
130.2, 132.0, 135.5, 141.6, (d, 3JC-F ¼ 6.3 Hz), 143.5, 146.7, 157.6, 162.8
1
(d, JC-F ¼ 248.8 Hz); IR (nujol) 3068, 3024, 2954, 2895, 2155,
4.1.5.5. 1-Methyl-1-phenyl-2-(trimethylsilyl)-1H-benzo[b]silole (2c).
1116 cmꢁ1; HRMS (EIþ) calcd for C23H23FSi2 [Mþ] 374.1322, found
374.1318.
Pale yellow liquid (70.0 mg, 0.238 mmol, 95%); 1H NMR (500 MHz,
CDCl3, 7.26 ppm)
7.29e7.39 (m, 5H), 7.47e7.50 (m, 2H), 7.50e7.52 (m, 1H), 7.62 (s,
1H); 13C NMR (125 MHz, CDCl3, 77.0 ppm)
d 0.06 (s, 9H), 0.66 (s, 3H), 7.19e7.23 (m, 1H),
4.1.5.12. 6-Chloro-1,1-diphenyl-2-(trimethylsilyl)-1H-benzo[b]silole
d
ꢁ5.6, ꢁ0.5, 124.2, 127.3,
(2k). Pale yellow liquid (88.3 mg, 0.225 mmol, 90%); 1H NMR
127.9, 129.6, 130.0, 132.2, 134.3, 134.5, 139.3, 145.7, 150.7, 156.7; IR
(400 MHz, CDCl3)
d
0.05 (s, 9H), 7.15 (dd, J ¼ 10.6, 7.2 Hz, 1H),
(neat) 3053, 3000, 2953, 1519, 1123 cmꢁ1; HRMS (EIþ) calcd for
7.29e7.47 (m, 7H), 7.56e7.60 (m, 5H); 13C NMR (100 MHz, CDCl3)
C
18H22Si2 [Mþ] 294.1260, found 294.1253.
d
ꢁ0.2, 113.4 (d, JC-F ¼ 17.1 Hz), 121.4 (d, JC-F ¼ 17.1 Hz), 128.2, 130.3,
131.6, 134.8 (dd, JC-F ¼ 4.0, 4.0 Hz), 135.4, 146.3 (d, JC-F ¼ 4.0 Hz),
147.5 (dd, JC-F ¼ 5.0, 4.0 Hz), 150.3 (dd, JC-F ¼ 251.0, 12.6 Hz), 152.0
(dd, JC-F ¼ 250.0, 13.6 Hz), 156.3; IR (neat) 3069, 2955, 1597, 1520,
1322, 1116 cmꢁ1; HRMS (EIþ) calcd for C23H22F2Si2 [Mþ] 392.1228,
found 392.1227.
4.1.5.6. 1,1-Diisopropyl-2-(trimethylsilyl)-1H-benzo[b]silole
Colorless liquid (65.7 mg, 0.228 mmol, 91%); 1H NMR (300 MHz,
CDCl3, 7.26 ppm)
(2d).
d
0.19 (s, 9H), 0.92 (d, J ¼ 7.5 Hz, 6H), 1.06 (d,
J ¼ 7.5 Hz, 6H), 1.30 (sept, J ¼ 7.5 Hz, 2H), 7.18 (ddd, J ¼ 6.9, 6.9,
1.5 Hz, 1H), 7.24e7.27 (m, 1H), 7.31 (ddd, J ¼ 7.2, 7.2, 1.2 Hz, 1H),
7.49e7.52 (m,1H), 7.59 (s,1H); 13C NMR (125 MHz, CDCl3, 77.0 ppm)
4.1.5.13. 1,1-Diphenyl-2-(trimethylsilyl)-1H-naphtho[2,3-b]silole (2l).
White powder (94.6 mg, 0.233 mmol, 93%); m.p. 176e177 ꢀC; 1H
d
ꢁ0.2, 11.2, 18.0, 123.9, 126.7, 129.5, 132.6, 137.4, 143.1, 151.2, 158.2;
IR (neat) 3055, 2952, 1514, 1248, 966 cmꢁ1; HRMS (EIþ) calcd for
17H28Si2 [Mþ] 288.1730, found 288.1724.
NMR (500 MHz, CDCl3, 7.26 ppm)
d 0.08 (s, 9H), 7.34e7.37 (m, 4H),
C
7.40e7.43 (m, 3H), 7.44e7.48 (m, 1H), 7.65e7.67 (m, 4H), 7.74 (s,
1H), 7.75 (d, J ¼ 8.0 Hz, 1H), 7.82 (d, J ¼ 8.0 Hz, 1H), 7.89 (s, 1H), 8.03
4.1.5.7. 2-(tert-Butyldimethylsilyl)-1,1-dimethyl-1H-benzo[b]silole
(s, 1H); 13C NMR (100 MHz, CDCl3, 77.0 ppm)
d
ꢁ0.1, 122.9, 126.0,
(2e). Colorless liquid (59.0 mg, 0.215 mmol, 86%); 1H NMR
126.7, 128.0, 128.4, 128.4, 130.0, 133.0, 133.4, 133.9, 134.9, 135.6,
135.9, 145.8, 147.6, 158.8; IR (nujol) 3055, 1516, 1427, 1245,
1117 cmꢁ1; HRMS (EIþ) calcd for C27H26Si2 [Mþ] 406.1573, found
406.1569.
(400 MHz, CDCl3, 7.26 ppm)
7.19e7.24 (m, 1H), 7.27e7.35 (m, 2H), 7.51e7.54 (m, 1H), 7.58 (s,1H);
13C NMR (100 MHz, CDCl3, 77.0 ppm)
d 0.14 (s, 6H), 0.33 (s, 6H), 0.92 (s, 9H),
d
ꢁ4.7, ꢁ2.7, 17.3, 26.8, 124.0,
127.0, 129.7, 131.4, 140.7, 143.9, 149.8, 157.7; IR (neat) 3055, 2953,
2855, 1514, 1252 cmꢁ1; HRMS (EIþ) calcd for C16H26Si2 [Mþ]
274.1573, found 274.1578.
4.1.5.14. 1,5-Dihydro-1,1,5,5-tetraphenyl-2,6-bis(trimethylsilyl)-1,5-
disila-s-indacene (2m). White powder (110 mg, 0.173 mmol, 69%);
m.p. 285e286 ꢀC; 1H NMR (500 MHz, CDCl3, 7.26 ppm)
d
0.03 (s,
18H), 7.33e7.36 (m, 8H), 7.39e7.43 (m, 4H), 7.57 (s, 2H), 7.61e7.64
(m, 8H), 7.72 (s, 2H); 13C NMR (100 MHz, CDCl3, 77.0 ppm)
4.1.5.8. 2-[Dimethyl(phenyl)silyl]-1,1-dimethyl-1H-benzo[b]silole
(2f). Colorless liquid (62 mg, 0.21 mmol, 84%); 1H NMR (500 MHz,
d
ꢁ0.1,
CDCl3, 7.26 ppm)
d
0.19 (s, 6H), 0.45 (s, 6H), 7.21 (ddd, J ¼ 7.0, 7.0,
128.0, 128.8, 130.0, 132.6, 135.6, 141.2, 144.0, 150.2, 159.0; IR (nujol)
1.0 Hz, 1H), 7.26e7.28 (m, 1H), 7.32 (ddd, J ¼ 7.5, 7.5, 1.0 Hz, 1H),
3068, 3051, 1522, 1429, 1248, 1116 cmꢁ1; HRMS (EIþ) calcd for
7.34e7.36 (m, 3H), 7.51e7.7.55 (m, 4H); 13C NMR (125 MHz, CDCl3,
C
40H42Si4 [Mþ] 634.2364, found 634.2353.
77.0 ppm)
d
ꢁ3.3, ꢁ2.0, 124.2, 127.1, 127.7, 128.9, 129.7, 131.5, 133.9,
139.0, 140.8, 144.5, 149.7, 157.0; IR (neat) 3052, 2954, 1518,
1110 cmꢁ1; HRMS (EIþ) calcd for C18H22Si2 [Mþ] 294.1260, found
294.1253.
4.1.5.15. Bis(1,1-diphenyl-1H-benzo[b]silol-2-yl)dimethylsilane (2n).
White powder (125 mg, 0.200 mmol, 80%); m.p. 169e170 ꢀC; 1H
NMR (400 MHz, CDCl3, 7.26 ppm)
d
0.08 (s, 6H), 7.15 (d, J ¼ 7.6 Hz,
Please cite this article in press as: Kinoshita H, et al., Syntheses of substituted benzosiloles and siloles by diisobutylaluminium hydride-
promoted cyclization of 1-silyl-2-(2-silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes, Tetrahedron (2018), https://doi.org/10.1016/
j.tet.2018.02.011

H. Kinoshita et al. / Tetrahedron xxx (2018) 1e14
13
2H), 7.19e7.28 (m, 10H), 7.31e7.38 (m, 6H), 7.51e7.56 (m, 12H); 13
NMR (100 MHz, CDCl3, 77.0 ppm) 0.1, 124.7, 127.6, 127.9, 129.9,
130.0, 132.6, 132.7, 135.6, 138.3, 141.8, 150.7, 160.6; IR (nujol) 3067,
3052, 1736, 1514, 1113 cmꢁ1; HRMS (EIþ) calcd for C42H36Si3 [Mþ]
624.2125, found 624.2119.
C
combined organic layer was dried over Na2SO4 and evaporated. The
residue was purified by silica-gel column chromatography
(hexane).
d
4.1.8.1. 5-[Dimethyl(phenyl)silyl]-1,1-diisopropyl-2,3-dipropyl-1H-
silole (5e). Colorless liquid (60.0 mg, 0.158 mmol, 21%); 1H NMR
4.1.5.16. (E)-1-(Dimethylsilyl)-2-[2-(trimethylsilyl)ethenyl]benzene
(300 MHz, CDCl3, 7.26 ppm) d 0.38 (s, 6H), 0.83e0.94 (m, 18H),
(6a’). Colorless liquid; 1H NMR (300 MHz, CDCl3, 7.26 ppm)
d
0.16
1.03e1.14 (m, 2H),1.34e1.47 (m, 4H), 2.15e2.29 (m, 4H), 7.12 (s, 1H),
(s, 9H), 0.37 (d, J ¼ 3.9 Hz, 6H), 4.60 (sept, J ¼ 3.9 Hz, 1H), 6.40 (d,
J ¼ 18.9 Hz, 1H), 7.21e7.27 (m, 2H), 7.37 (ddd, J ¼ 7.2, 7.2, 1.2 Hz, 1H),
7.51 (dd, J ¼ 7.2, 1.2 Hz, 1H), 7.60 (d, J ¼ 7.8 Hz, 1H); 13C NMR
7.30e7.35 (m, 3H), 7.46e7.55 (m, 2H); 13C NMR (125 MHz, CDCl3,
77.0 ppm)
d
ꢁ1.5, 11.0, 13.9, 14.8, 17.5, 17.7, 22.2, 23.3, 31.9, 32.5,
127.5, 128.6, 134.0, 135.2, 139.7, 140.4, 153.6, 162.3; IR (neat) 3068,
2956, 1246, 1112 cmꢁ1; HRMS (EIþ) calcd for C24H40Si2 [Mþ]
384.2669, found 384.2674.
(100 MHz, CDCl3, 77.0 ppm)
d
ꢁ3.2, ꢁ1.3, 124.7, 127.0, 129.7, 131.3,
134.8, 135.9, 144.3, 144.6; IR (neat) 3054, 2955, 2898, 2120,
1120 cmꢁ1; HRMS (EIþ) calcd for C13H22Si2 [Mþ] 234.1260, found
234.1255.
4.1.8.2. 2-Dodecyl-3-ethyl-1,1-diphenyl-5-(trimethylsilyl)-1H-silole
(5m). Colorless liquid (0.11 g, 0.23 mmol, 91%); 1H NMR (500 MHz,
4.1.6. Synthesis of siloles 5 from Methyl silyl ethers 4 (general
procedure)
CDCl3, 7.26 ppm)
d
ꢁ0.08 (s, 9H), 0.88 (t, J ¼ 7.0 Hz, 3H), 0.94e1.32
(m, 20H), 1.11 (t, J ¼ 7.5 Hz, 3H), 2.31 (t, J ¼ 7.5 Hz, 2H), 2.35 (q,
DIBAL-H (1.0 M solution in hexane, 0.33 mL, 0.33 mmol) was
added to a flask containing the substrate 4 (0.25 mmol). After
removing the hexane under reduced pressure, octane (0.75 mL)
was added to the residue. The resultant mixture was stirred at 75 ꢀC
for 24 h. The mixture was cooled to room temperature. Then 1 M
aqueous HCl (2.0 mL) was added to the mixture. The aqueous
mixture was stirred vigorously and extracted with hexane three
times. The combined organic layer was dried over Na2SO4 and
evaporated. The residue was purified by silica-gel column chro-
matography (hexane).
J ¼ 7.5 Hz, 2H), 7.25 (s,1H), 7.31e7.41 (m, 6H), 7.57e7.59 (m, 4H); 13
C
NMR (125 MHz, CDCl3, 77.0 ppm)
d
ꢁ0.2, 13.5, 14.1, 22.7, 23.4, 29.1,
29.3, 29.3, 29.5, 29.6, 29.6, 29.7, 30.2, 31.9, 127.8, 129.5, 133.4, 135.5,
140.4, 140.6, 155.8, 160.1; IR (neat) 3068, 3050, 2925, 1112 cmꢁ1
HRMS (EIþ) calcd for C33H50Si2 [Mþ] 502.3451, found 502.3449.
;
4.1.8.3. 3-Ethyl-2-isopentyl-1,1-diphenyl-5-(trimethylsilyl)-1H-silole
(5n). Colorless liquid (96 mg, 0.24 mmol, 95%); 1H NMR (500 MHz,
CDCl3, 7.26 ppm)
d
ꢁ0.08 (s, 9H), 0.65 (d, J ¼ 6.5 Hz, 6H), 0.99e1.04
(m, 2H), 1.11 (t, J ¼ 7.5 Hz, 3H), 1.29 (sept, J ¼ 6.5 Hz, 1H), 2.29e2.38
(m, 4H), 7.25 (s, 1H), 7.32e7.35 (4H), 7.38e7.40 (m, 2H), 7.57e7.59
4.1.7. Synthesis of benzosiloles 2 from hydrosilanes 6 (general
procedure)
(m, 4H); 13C NMR (125 MHz, CDCl3, 77.0 ppm)
d
ꢁ0.2, 13.6, 22.2,
23.4, 26.7, 27.8, 39.3, 127.8, 129.5, 133.4, 135.5, 140.4, 140.6, 155.6,
Method A: DIBAL-H (1.0 M solution in hexane, 0.30 mL,
0.30 mmol) was added to a flask containing the substrate 6
(0.25 mmol). Method B: DIBAL-H (1.0 M solution in hexane,
0.125 mL, 0.125 mmol) was added to a flask containing the sub-
strate 6 (0.25 mmol). After removing the hexane under reduced
pressure, octane (0.75 mL) was added to the residue. The resultant
mixture was stirred at 80 ꢀC for 0.5 h (method A) or 1 h (method B).
The mixture was cooled to room temperature. Then 1 M aqueous
HCl (2.0 mL) was added to the mixture. The aqueous mixture was
stirred vigorously and extracted with hexane three times. The
combined organic layer was dried over Na2SO4 and evaporated. The
residue was purified by silica-gel column chromatography
(hexane).
160.1; IR (neat) 3068, 2955, 1112 cmꢁ1; HRMS (EIþ) calcd for
C
26H36Si2 [Mþ] 404.2356, found 404.2362.
4.1.8.4. 3-Ethyl-2-isopentyl-1-methyl-1-phenyl-5-(trimethylsilyl)-
1H-silole (5o). Colorless liquid (76 mg, 0.22 mmol, 89%); 1H NMR
(500 MHz, CDCl3, 7.26 ppm)
d
ꢁ0.05 (s, 9H), 0.53 (s, 3H), 0.73 (d,
J ¼ 7.0 Hz, 3H), 0.81 (d, J ¼ 6.5 Hz, 3H), 1.09 (t, J ¼ 7.5 Hz, 3H),
1.09e1.17 (m, 2H), 1.40 (sept, J ¼ 6.5 Hz, 1H), 2.13e2.19 (m, 1H),
2.26e2.36 (m, 3H), 7.13 (s, 1H), 7.26e7.35 (m, 3H), 7.42e7.45 (m,
2H); 13C NMR (125 MHz, CDCl3, 77.0 ppm)
d
ꢁ5.9, ꢁ0.5, 13.6, 22.3,
22.4, 23.2, 26.5, 27.8, 39.4, 127.7, 129.1, 134.1, 135.2, 141.4, 141.5,
154.4, 158.3; IR (neat) 3068, 2954, 1500, 1247, 1109 cmꢁ1; HRMS
(EIþ) calcd for C21H34Si2 [Mþ] 342.2199, found 342.2187.
4.1.7.1. 2-[Dimethyl(phenyl)silyl]-1,1-diphenyl-1H-benzo[b]silole
4.2. Derivatization of silylated products
(2q). Colorless liquid (95.2 mg, 0.228 mmol, 91%); 1H NMR
(500 MHz, CDCl3, 7.26 ppm)
d
0.32 (s, 6H), 7.21e7.42 (m, 14H),
Bromine (0.50 M solution in CH2Cl2 (0.25 mL), 20 mg,
0.12 mmol) was added to a solution of 2l (51 mg, 0.12 mmol) in
CH2Cl2 (1 mL) at room temperature. After 0.5 h stirring, the resul-
tant mixture was quenched with saturated aqueous Na2S2O3. The
aqueous mixture was extracted with CH2Cl2 (20 mL) three times.
The combined organic layer was dried over Na2SO4 and evaporated.
Purification by silica-gel column chromatography (hexane/
AcOEt ¼ 20:1) gave 2-bromo-1,1-diphenyl-1H-naphtho[2,3-b]silole
(9) as a colorless needle crystal (37 mg, 0.089 mmol, 72%). m.p.
7.48e7.50 (m, 4H), 7.59 (d, J ¼ 7.0 Hz, 1H), 7.72 (s, 1H); 13C NMR
(125 MHz, CDCl3, 77.0 ppm)
d
ꢁ1.4, 124.7, 127.6, 127.8, 127.9, 128.8,
129.9, 130.2, 132.4, 132.9, 134.0, 135.5, 138.3, 138.7, 141.8, 150.7,
160.3; IR (neat) 3067, 3050, 2955, 1514, 1428, 1113 cmꢁ1; HRMS
(EIþ) calcd for C28H26Si2 [Mþ] 418.1573, found 418.1580.
4.1.8. Synthesis of siloles 5 from hydrosilanes 8 (general procedure)
Method A: DIBAL-H (1.0 M solution in hexane, 0.30 mL,
0.30 mmol) was added to a flask containing the substrate 8
(0.25 mmol). Method B: DIBAL-H (1.0 M solution in hexane,
0.125 mL, 0.125 mmol) was added to a flask containing the sub-
strate 8 (0.25 mmol). After removing the hexane under reduced
pressure, octane (0.75 mL) was added to the residue. The resultant
mixture was stirred at 80 ꢀC for 0.5 h (method A) or 1 h (method B).
The mixture was cooled to room temperature. Then 1 M aqueous
HCl (2.0 mL) was added to the mixture. The aqueous mixture was
stirred vigorously and then extracted with hexane three times. The
179e180 ꢀC; 1H NMR (500 MHz, CDCl3, 7.26 ppm)
8H), 7.65 (s, 1H), 7.72e7.74 (m, 4H), 7.78e7.82 (m, 3H), 8.09 (s, 1H);
13C NMR (100 MHz, CDCl3, 77.0 ppm)
122.5, 126.2, 127.3, 127.8,
d 7.38e7.51 (m,
d
128.3, 128.3, 128.4, 130.2, 130.7, 132.1, 132.9, 134.8, 134.9, 135.6,
145.1, 150.5; IR (nujol) 3051, 1269, 1118 cmꢁ1; HRMS (EIþ) calcd for
C
24H17BrSi [Mþ] 412.0283, found 412.0280.
4.2.1. 6-Fluoro-2-iodo-1,1-diphenyl-1H-benzo[b]silole (10)
ICl (0.10 M in CH2Cl2, 1.5 mL, 0.15 mmol) was added to a solution
Please cite this article in press as: Kinoshita H, et al., Syntheses of substituted benzosiloles and siloles by diisobutylaluminium hydride-
promoted cyclization of 1-silyl-2-(2-silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes, Tetrahedron (2018), https://doi.org/10.1016/
j.tet.2018.02.011

14
H. Kinoshita et al. / Tetrahedron xxx (2018) 1e14
2007;9:93e96;
of 2j (57 mg, 0.15 mmol) in CH2Cl2 (1.0 mL) at 0 ꢀC. The mixture was
stirred at 0 ꢀC for 1 h and then room temperature for 11 h. The
resultant mixture was quenched with saturated aqueous Na2S2O3.
The aqueous mixture was extracted with CH2Cl2 (20 mL) three
times. The combined organic layer was dried over Na2SO4 and
evaporated. Purification by silica-gel column chromatography
(hexane/AcOEt ¼ 20:1) gave the title compound 10 as a white solid
(56 mg, 0.13 mmol, 85%). m.p. 163e164 ꢀC; 1H NMR (300 MHz,
(c) Li L, Xiang J, Xu C. Org Lett. 2007;9:4877e4879;
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7. (a) Curtis MD. J Am Chem Soc. 1969;91:6011e6018;
CDCl3, 7.26 ppm) d 6.80e7.05 (m, 1H), 7.20e7.25 (m, 1H), 7.32e7.36
(b) Chen J, Law CCW, Lam JWY, et al. Chem Mater. 2003;15:1535e1546;
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19477e19488.
(m, 1H), 7.37e7.43 (m, 4H), 7.46e7.52 (m, 2H), 7.64e7.67 (m, 4H),
7.93 (s, 1H); 13C NMR (100 MHz, CDCl3, 77.0 ppm)
d 95.4, 116.9 (d,
2JC-F ¼ 22.1 Hz), 120.6 (d, JC-F ¼ 21.1 Hz), 125.0 (d, JC-F ¼ 7.0 Hz),
2
3
128.4, 129.4, 130.9, 135.6, 138.1 (d, 3JC-F ¼ 5.0 Hz), 146.7, 156.4, 162.5
10. (a) Liang Y, Geng W, Wei J, Xi Z. Angew Chem Int Ed. 2012;51:1934e1937;
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11. (a) Okinoshima H, Yamamoto K, Kumada M.
(d, 1JC-F ¼ 250.5 Hz); IR (nujol) 3070, 3050, 2854, 1195, 1117 cmꢁ1
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J Am Chem Soc. 1972;94:
HRMS (EIþ) calcd for C20H14FISi [Mþ] 427.9894, found 427.9891.
9263e9264;
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4.2.2. 5-Iodo-1,1-diphenyl-2,3-dipropyl-1H-silole (11)
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12. Ilies L, Tsuji H, Nakamura E. Org Lett. 2009;11:3966e3968.
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14324e14326;
2-Iodosilole 11 was derived from 5b (86 mg, 0.22 mmol) by the
reported method.26 Pale orange liquid (32 mg, 0.072 mmol, 33%);
1H NMR (300 MHz, CDCl3, 7.26 ppm)
d
0.73 (t, J ¼ 7.5 Hz, 3H), 0.95 (t,
J ¼ 7.5 Hz, 3H), 1.20e1.32 (m, 2H), 1.46e1.60 (m, 2H), 2.28e2.36 (m,
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4H), 7.35e7.50 (m, 7H), 7.58e7.65 (m, 4H); 13C NMR (100 MHz,
15. (a) Furukawa S, Kobayashi J, Kawashima T.
J Am Chem Soc. 2009;131:
14192e14193;
CDCl3, 77.0 ppm) d 13.9, 14.3, 21.7, 23.9, 32.0, 32.3, 92.6, 128.2, 130.3,
(b) Curless LD, Ingleson MJ. Organometallics. 2014;33:7241e7246;
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130.7, 135.6, 138.5, 155.3, 158.4; IR (neat) 3068, 2957, 2869, 1582,
1115 cmꢁ1; HRMS (EIþ) calcd for C22H25ISi [Mþ] 444.0770, found
444.0756.
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17. (a) Shimizu M, Mochida K, Hiyama T. Angew Chem Int Ed. 2008;47:9760e9764;
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Please cite this article in press as: Kinoshita H, et al., Syntheses of substituted benzosiloles and siloles by diisobutylaluminium hydride-
promoted cyclization of 1-silyl-2-(2-silylethynyl)benzenes and 1,4-disilylalk-3-en-1-ynes, Tetrahedron (2018), https://doi.org/10.1016/
j.tet.2018.02.011