Synthesis of cyclic alkenylborates via silaboration of alkynes followed by hydrolysis for utilization in external-base-free cross coupling

Article abstract of DOI:10.1021/om400138u

Cyclic alkenylborates have been synthesized regioselectively via a palladium-catalyzed regioselective silaboration of terminal alkynes with ClMe₂Si-B(pin) followed by basic hydrolysis. The cyclic borates undergo cross coupling with 4-iodoanisole in the absence of an external base.

Full text of DOI:10.1021/om400138u

Note
pubs.acs.org/Organometallics
Synthesis of Cyclic Alkenylborates via Silaboration of Alkynes
Followed by Hydrolysis for Utilization in External-Base-Free Cross
Coupling
Toshimichi Ohmura,* Kazuyuki Oshima, and Michinori Suginome*
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura,
Nishikyo-ku, Kyoto 615-8510, Japan
S
* Supporting Information
ABSTRACT: Cyclic alkenylborates have been synthesized regiose-
lectively via a palladium-catalyzed regioselective silaboration of
terminal alkynes with ClMe2Si−B(pin) followed by basic hydrolysis.
The cyclic borates undergo cross coupling with 4-iodoanisole in the
absence of an external base.
n transition-metal-catalyzed bond-forming reactions using
group on the silicon atom (eq 1).8,9 Complementary
regiochemical control in the silaboration of terminal alkynes
I
organoboron compounds, such as Suzuki−Miyaura cou-
pling,1 use of isolable ate complexes of organoboron
compounds has received increasing attention in recent years.
For example, the organoborates 1−6 shown in Figure 1 have
was achieved by the choice of ligand on the palladium catalyst,
allowing selective synthesis of regioisomeric alkenylboronic
esters 8 and 9 bearing a chlorodimethylsilyl group on the β-
carbon.8a,c It was expected that hydrolysis of the Cl−Si bond
would lead to the formation of a five-membered cyclic borate
via intramolecular attack of the resulting silanol oxygen on the
tricoordinated boron atom. Herein, we describe the synthesis of
cyclic alkenylborates 11−13 (Figure 2) via silaboration of
alkynes followed by borate formation, which show air and water
stability with interesting reactivity in Suzuki−Miyaura cou-
pling.10
Figure 1. Isolable organoborates for Suzuki−Miyaura coupling.
been found to have advantages over tricoordinated organo-
boronic acids in preparation, handling, and reactivity.2−7 In
particular, the trihydroxy- and trialkoxyborates 3−6 show
remarkably high reactivity in Suzuki−Miyaura coupling,
allowing the reaction to take place even in the absence of an
external base, which is essential for the coupling using
organoboronic acids.4−7 Such high reactivities of 3−6 are
attributed to acceleration of the transmetalation step in the
catalytic cycle, in which the nucleophilicity of the organic
groups on the boron atoms is enhanced by formation of the
four-coordinated borate structure.1b Use of such a reactive
coupling reagent makes the cross-coupling reaction more
practical through improved functional group compatibility and
operational simplicity. Despite such attractive features, reactive
borates are limited to trihydroxy- and trialkoxyorganoborate
derivatives. For further exploration of the utility of organo-
borates in transition-metal-catalyzed reactions, the development
of functionalized organoborate reagents is highly desirable.
We have recently established a palladium-catalyzed silabora-
tion of alkynes using the silylboronic ester 7, bearing a chloro
2-Boryl-1-silyl-1-octene 8a was prepared by silaboration of 1-
octyne with the silylboronic ester 7 using Pd/P(t-
Figure 2. Cyclic alkenylborates 11−13 synthesized in this study.
Received: February 18, 2013
Published: April 23, 2013
© 2013 American Chemical Society
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Organometallics
Note
a
Table 1. Synthesis of Cyclic Alkenylborates 11−13
b
entry
R1
R2
MOH
KOH
product
yield (%)
1
H
n-C6H13
n-C6H13
n-C6H13
8a
8a
8a
8b
8c
8d
8e
9a
9b
9c
9d
9e
10
11a-K
11a-Na
11a-Cs
11b-K
11c-K
11d-K
11e-K
12a-K
12b-Na
12c-Na
12d-Na
12e-Na
13-K
94
94
91
92
95
87
84
98
83
82
87
88
90
2
H
NaOH
CsOH•H2O
KOH
3
H
4
H
(CH2)3OSiMe2-t-Bu
5
H
(CH2)3Cl
KOH
6
H
(CH2)3CN
KOH
7
H
cyclo-C6H11
KOH
8
n-C6H13
H
KOH
9
(CH2)3OSiMe2-t-Bu
(CH2)3Cl
H
NaOH
NaOH
NaOH
NaOH
KOH
10
11
12
13
H
(CH2)3CN
cyclo-C6H11
n-C3H7
H
H
n-C3H7
a
b
Conditions: MOH (1.2 mmol) and 8, 9, or 10 (0.40 mmol) in toluene (0.2 mL) was stirred at 50 °C for 4 h. Isolated yield.
Bu)2(biphenyl-2-yl) catalyst8c and reacted with KOH (3 equiv)
in toluene at 50 °C (entry 1, Table 1). After 4 h, CH2Cl2 was
added to the resulting suspension and the insoluble precipitate
was removed by filtration. The filtrate was concentrated, and
the resulting solid was dried in vacuo to give a potassium salt of
cyclic alkenylborate, 11a-K, in 94% yield. Formation of 11a-K
may take place through nucleophilic substitution of the chlorine
group on the silicon atom by hydroxide ion, which is followed
by intramolecular attack of the silanol oxygen on the
tricoordinated boron atom to form a five-membered ring.
The 11B NMR chemical shift of 11a-K (δ 13 ppm in DMSO-
d6) indicates the formation of a four-coordinated boron
compound.11 Use of 3 equiv of KOH was crucial for high-
yield formation of 11a-K, whereas a lower yield of 11a-K was
observed in the reaction with 2 equiv of KOH. Borate
formation did not take place at room temperature. NaOH and
CsOH·H2O could also be used for borate formation, in which
cases the respective products 11a-Na and 11a-Cs were
obtained in high yields (entries 2 and 3).
KOH with alkene 10, which was prepared by silaboration of 4-
octyne (entry 13).
The potassium borates 11a-K and 12a-K were subjected to
Suzuki−Miyaura coupling with 4-iodoanisole in DMSO in the
presence of Pd[P(t-Bu)3]2 (5 mol %) and H2O (7 equiv)
(Scheme 1a,b). The coupling took place at 80 °C within 2 h to
Scheme 1. External-Base-Free Suzuki−Miyaura Coupling of
11a-K and 12a-K
A variety of cyclic alkenylborates were synthesized by the
reaction of (boryl)(silyl)alkenes with alkali-metal hydroxides in
toluene at 50 °C (entries 4−13, Table 1). 2-Boryl-1-silyl-1-
alkenes 8b−e reacted with KOH to give the corresponding
borates 11b−e in high yields (entries 4−7). Functional groups
such as silyloxy (entry 4), chloro (entry 5), and cyano groups
(entry 6) were compatible under the reaction conditions. The
protocol was applicable to the synthesis of borates 12a−e from
1-boryl-2-silyl-1-alkenes 9a−e (entries 8−12), which were
synthesized by silaboration of 1-alkynes through a regiocom-
plementary reaction in which a Pd/PPh3 catalyst was used.8a
While the potassium borate 12a-K was synthesized from 9a in
high yield according to the procedure described above, the
corresponding potassium borates 12b−e could not be obtained
in pure form because of their insolubility in CH2Cl2. We found
that 12b−e could be synthesized as sodium salts, which were
soluble in CH2Cl2, by the reaction of 9b−e with NaOH. The
potassium borate 13 was also synthesized via the reaction of
give alkenylsilanes 14 and 15 in good yields, respectively,
without adding an external base. A control reaction of
alkenylboronic ester 16, which bears an isopropoxydimethylsilyl
group β to the boron atom, with 4-iodoanisole under identical
conditions resulted in no coupling product (Scheme 1c),12
indicating that the carbon−boron bonds in 11a-K and 12a-K
are activated by the borate formation. In a previous study, we
demonstrated Hiyama coupling of the related alkenylsilanes
bearing an isopropoxysilyl group instead of a boryloxysilyl
group in 14 and 15.8a
In conclusion, we have established a synthetic route to cyclic
alkenylborates via catalytic silaboration of alkynes followed by
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Organometallics
Note
Potassium (2,3-Dimethyl-2,3-butanediolato-κO,κO′)[1,1-dimeth-
yl-1-(5-chloropent-1-en-1-yl-κC2)silanolato-κO]borate (11c-K). The
title compound 11c-K (98 mg, 95%) was obtained as a white solid
from 8c (98 mg, 0.30 mmol) with KOH (53 mg, 0.95 mmol). 11c-K:
1H NMR (400 MHz, DMSO-d6) δ 5.61 (s, 1H), 3.60 (t, J = 7.2 Hz,
treatment with metal hydroxides. This method allows efficient
access to the two possible regioisomers 11 and 12 on the basis
of catalyst-controlled regioselective silaboration of terminal
alkynes. The cyclic alkenylborates could be utilized in Suzuki−
Miyaura coupling, which proceeds in the absence of an external
base.
2H), 2.20 (t, J = 7.2 Hz, 2H), 1.90 (quintet, J = 7.2 Hz, 2H), 1.03 (s,
6H), 0.97 (s, 6H), −0.096 (s, 3H), −0.100 (s, 3H); 13C NMR (126
MHz, DMSO-d6) δ 128.9, 76.5, 46.3, 33.3, 31.3, 27.0, 26.7, 2.8, the
boron-bound carbon was not detected due to quadrupolar relaxation;
11B NMR (128 MHz, DMSO-d6) δ 12.6; HRMS (ESI) m/z calcd for
EXPERIMENTAL SECTION
■
General Comments. Alkenylboronic esters 8,8c 9,8a and 108a were
synthesized by the methods reported previously. KOH and NaOH
were crashed into a fine powder and dried under reducing pressure
with heating (300 °C/0.5 mmHg, 12 h). CsOH·H2O (nacalai) was
used as received from commercial sources.
C13H25BClO3Si− (M − K+) 303.1360, found 303.1369.
Potassium (2,3-Dimethyl-2,3-butanediolato-κO,κO′)[1,1-dimeth-
yl-1-(5-cyanopent-1-en-1-yl-κC2)silanolato-κO]borate (11d-K). The
title compound 11d-K (111 mg, 87%) was obtained as a white solid
from 8d (120 mg, 0.38 mmol) with KOH (65 mg, 1.2 mmol). 11d-K:
1H NMR (400 MHz, DMSO-d6) δ 5.62 (s, 1H), 2.39 (t, J = 7.2 Hz,
Synthesis of Cyclic Alkenylborates 11−13 (Table 1). General
Procedure. In a glovebox, KOH, NaOH, or CsOH·H2O (1.2 mmol)
was placed in a glass tube having a PTFE stopcock (J. Young) and
equipped with a magnetic stir bar. Toluene (0.8 mL) and alkenylboron
compound 8, 9, or 10 (0.40 mmol) were added to the tube. The tube
was then sealed by the stopcock and taken out from the glovebox.
After 4 h at 50 °C, CH2Cl2 (3.0 mL) was added to the reaction
mixture, and the insoluble precipitates were removed by filtration. The
filtrate was concentrated in vacuo. The borates were obtained with
high purity. Further purification of the products by bulb-to-bulb
distillation or silica gel column chromatography met with difficulty.
Potassium (2,3-Dimethyl-2,3-butanediolato-κO,κO′)[1,1-dimeth-
yl-1-(oct-1-en-1-yl-κC2)silanolato-κO]borate (11a-K). The title com-
pound 11a-K (128 mg, 94%) was obtained as a white solid from 8a
(128 mg, 0.39 mmol) with KOH (67 mg, 1.2 mmol). 11a-K: 1H NMR
(400 MHz, DMSO-d6) δ 5.60 (s, 1H), 2.08 (t, J = 7.2 Hz, 2H), 1.36−
1.45 (m, 2H), 1.24−1.34 (m, 6H), 1.03 (s, 6H), 0.97 (s, 6H), 0.89 (t, J
= 6.8 Hz, 3H), −0.09 (s, 6H); 13C NMR (126 MHz, DMSO-d6) δ
127.2, 76.5, 36.0, 31.7, 29.5, 27.9, 26.8, 26.7, 22.2, 14.0, 2.6, the boron-
bound carbon was not detected due to quadrupolar relaxation; 11B
NMR (128 MHz, DMSO-d6) δ 13.1; HRMS (ESI) m/z calcd for
C16H32BO3Si− (M − K+) 311.2219, found 311.2231.
2H), 2.20 (t, J = 7.2 Hz, 2H), 1.75 (quintet, J = 7.2 Hz, 2H), 1.03 (s,
6H), 0.97 (s, 6H), −0.09 (s, 6H); 13C NMR (126 MHz, DMSO-d6) δ
129.7, 121.2, 76.5, 35.2, 27.0, 26.7, 23.8, 16.1, 2.8, the boron-bound
carbon was not detected due to quadrupolar relaxation; 11B NMR
(128 MHz, DMSO-d6) δ 12.6; HRMS (ESI) m/z calcd for
C14H25BNO3Si− (M − K+) 294.1702, found 294.1708.
Potassium (2,3-Dimethyl-2,3-butanediolato-κO,κO′)[1,1-dimeth-
yl-1-(2-cyclohexylethen-1-yl-κC2)silanolato-κO]borate (11e-K). The
title compound 11e-K (97 mg, 84%) was obtained as a white solid
from 8e (109 mg, 0.33 mmol) with KOH (59 mg, 1.1 mmol). 11e-K:
1H NMR (400 MHz, DMSO-d6) δ 5.59 (s, 1H), 2.10−2.19 (m, 1H),
1.60−1.78 (m, 4H), 1.10−1.34 (m, 6H), 1.04 (s, 6H), 0.98 (s, 6H),
−0.11 (s, 6H); 13C NMR (126 MHz, DMSO-d6) δ 124.2, 76.4, 41.9,
33.0, 27.0, 26.9, 26.8, 26.6, 2.9, the boron-bound carbon was not
detected due to quadrupolar relaxation; 11B NMR (128 MHz, DMSO-
d6) δ 13.1; HRMS (ESI) m/z calcd for C16H30BO3Si− (M − K+)
309.2063, found 309.2074.
Potassium (2,3-Dimethyl-2,3-butanediolato-κO,κO′)[1,1-dimeth-
yl-1-(oct-1-en-2-yl-κC1)silanolato-κO]borate (12a-K). The title com-
pound 12a-K (132 mg, 98%) was obtained as a white solid from 9a
(126 mg, 0.38 mmol) with KOH (66 mg, 1.2 mmol). 12a-K: 1H NMR
(400 MHz, DMSO-d6) δ 6.32 (s, 1H), 2.07 (t, J = 6.8 Hz, 2H), 1.21−
1.39 (m, 8H), 0.99 (s, 6H), 0.96 (s, 6H), 0.89 (t, J = 6.8 Hz, 3H),
−0.05 (s, 6H); 13C NMR (126 MHz, DMSO-d6) δ 148.5, 76.2, 35.3,
31.4, 29.6, 29.0, 26.1, 25.9, 22.1, 14.0, 2.1, the boron-bound carbon
was not detected due to quadrupolar relaxation; 11B NMR (128 MHz,
DMSO-d6) δ 12.5; HRMS (ESI) m/z calcd for C16H32BO3Si− (M −
K+) 311.2219, found 311.2230.
Potassium (2,3-Dimethyl-2,3-butanediolato-κO,κO′)[1,1-dimeth-
yl-1-(oct-4-en-4-yl-κC5)silanolato-κO]borate (13-K). The title com-
pound 13-K (93 mg, 90%) was obtained as a white solid from 10 (98
mg, 0.30 mmol) with KOH (50 mg, 0.89 mmol). 13-K: 1H NMR (400
MHz, DMSO-d6) δ 1.96−2.05 (m, 4H), 1.40 (sextet, J = 7.2 Hz, 2H),
1.32 (sextet, J = 7.2 Hz, 2H), 1.03 (s, 6H), 0.96 (s, 6H), 0.87 (t, J = 7.2
Hz, 3H), 0.82 (t, J = 7.2 Hz, 3H), −0.10 (s, 6H); 13C NMR (126
MHz, DMSO-d6) δ 140.5, 76.3, 32.2, 31.1, 27.0, 26.9, 23.6, 22.6, 15.1,
14.7, 2.9, the boron-bound carbon was not detected due to
quadrupolar relaxation; 11B NMR (128 MHz, DMSO-d6) δ 12.6;
HRMS (ESI) m/z calcd for C16H32BO3Si− (M − K+) 311.2219, found
311.2231.
External-Base-Free Suzuki−Miyaura Coupling of 11a-K and
12a-K (Scheme 1). General Procedure. In a glovebox, Pd[P(t-Bu)3]2
(5.1 mg, 10 μmol), 4-iodoanisole (70 mg, 0.30 mmol), and 11a-K or
12a-K (66 mg, 0.20 mmol) were placed in a glass tube having a PTFE
stopcock (J. Young) with a magnetic stir bar. After addition of DMSO
(0.4 mL), the tube was sealed by the stopcock and taken out from the
glovebox. H2O (25 mg, 1.4 mmol) was added to the mixture under an
atmosphere of nitrogen. The tube was sealed by the stopcock again
and heated at 80 °C for 2 h with stirring. After it was cooled to room
temperature, the mixture was filtered through a pad of Celite and the
resulting solution was dried over anhydrous MgSO4. The coupling
product was isolated by bulb-to-bulb distillation (140 °C/0.6 mmHg).
1-Dimethyl(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yloxy)silyl-
2-(4-methoxyphenyl)-1-octene (14). The title compound 14 (65 mg,
Sodium (2,3-Dimethyl-2,3-butanediolato-κO,κO′)[1,1-dimethyl-
1-(oct-1-en-1-yl-κC2)silanolato-κO]borate (11a-Na). The title com-
pound 11a-Na (99 mg, 94%) was obtained as a white solid from 8a
1
(105 mg, 0.32 mmol) with NaOH (43 mg, 1.1 mmol). 11a-Na: H
NMR (400 MHz, DMSO-d6) δ 5.62 (s, 1H), 2.08 (t, J = 7.2 Hz, 2H),
1.36−1.45 (m, 2H), 1.24−1.34 (m, 6H), 1.04 (s, 6H), 0.99 (s, 6H),
0.89 (t, J = 6.8 Hz, 3H), −0.08 (s, 6H); 13C NMR (126 MHz, DMSO-
d6) δ 127.2, 76.5, 36.0, 31.7, 29.5, 27.9, 26.8, 26.7, 22.2, 14.0, 2.7, the
boron-bound carbon was not detected due to quadrupolar relaxation;
11B NMR (128 MHz, DMSO-d6) δ 12.3; HRMS (ESI) m/z calcd for
C16H32BO3Si− (M − Na+) 311.2219, found 311.2231.
Cesium (2,3-Dimethyl-2,3-butanediolato-κO,κO′)[1,1-dimethyl-1-
(oct-1-en-1-yl-κC2)silanolato-κO]borate (11a-Cs). The title com-
pound 11a-Cs (165 mg, 91%) was obtained as a white solid from 8a
(135 mg, 0.41 mmol) with CsOH·H2O (186 mg, 1.1 mmol). 11a-Cs:
1H NMR (400 MHz, DMSO-d6) δ 5.59 (s, 1H), 2.07 (t, J = 7.2 Hz,
2H), 1.36−1.44 (m, 2H), 1.25−1.34 (m, 6H), 1.03 (s, 6H), 0.97 (s,
6H), 0.89 (t, J = 6.8 Hz, 3H), −0.10 (s, 6H); 13C NMR (126 MHz,
DMSO-d6) δ 127.1, 76.4, 36.1, 31.7, 29.5, 27.9, 26.9, 26.7, 22.2, 14.0,
2.9, the boron-bound carbon was not detected due to quadrupolar
relaxation; 11B NMR (128 MHz, DMSO-d6) δ 12.7; HRMS (ESI) m/z
calcd for C16H32BO3Si− (M − Cs+) 311.2219, found 311.2232.
Potassium (2,3-Dimethyl-2,3-butanediolato-κO,κO′)[1,1-dimeth-
yl-1-{5-(tert-butyldimethylsilyloxy)pent-1-en-1-yl-κC2}silanolato-
κO]borate (11b-K). The title compound 11b-K (111 mg, 92%) was
obtained as a white solid from 8b (115 mg, 0.27 mmol) with KOH (46
1
mg, 0.82 mmol). 11b-K: H NMR (400 MHz, DMSO-d6) δ 5.60 (s,
1H), 3.59 (t, J = 7.2 Hz, 2H), 2.10 (t, J = 7.2 Hz, 2H), 1.61 (quintet, J
= 7.2 Hz, 2H), 1.03 (s, 6H), 0.97 (s, 6H), 0.90 (s, 9H), 0.05 (s, 6H),
−0.09 (s, 6H); 13C NMR (126 MHz, DMSO-d6) δ 127.1, 76.4, 63.6,
32.0, 31.3, 27.0, 26.7, 25.9, 18.0, 2.8, −5.2, the boron-bound carbon
was not detected due to quadrupolar relaxation; 11B NMR (128 MHz,
−
DMSO-d6) δ 13.1; HRMS (ESI) m/z calcd for C19H40BO4Si2 (M −
K+) 399.2564, found 399.2570.
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Organometallics
Note
77%) was obtained from 11a-K (71 mg, 0.22 mmol) with 4-
iodoanisole (68 mg, 0.29 mmol). 14: H NMR (400 MHz, C6D6) δ
Chem., Int. Ed. 2008, 47, 4695. (f) Haag, B.; Samann, C.; Jana, A.;
Knochel, P. Angew. Chem., Int. Ed. 2011, 50, 7290. (g) Oberli, M. A.;
Buchward, S. L. Org. Lett. 2012, 14, 4606.
̈
1
7.14−7.19 (m, 2H), 6.85−6.90 (m, 2H), 5.51 (s, 1H), 3.75 (s, 3H),
2.38 (t, J = 6.8 Hz, 2H), 1.18−1.33 (m, 8H), 1.17 (s, 12H), 0.82 (t, J =
6.8 Hz, 3H), −0.25 (s, 6H); 13C NMR (126 MHz, DMSO-d6) δ 158.8,
158.6, 135.5, 128.9, 126.9, 113.2, 73.8, 55.1, 41.8, 31.2, 27.6, 25.0, 24.6,
22.2, 14.0, 1.9. 11B NMR (128 MHz, C6D6) δ 22.4; HRMS (ESI) m/z
calcd for C23H40BO4Si+ (M + H+) 419.2783, found 419.2801.
(6) For potassium, lithium, and sodium organotriolborates in
external-base-free Suzuki−Miyaura coupling, see: (a) Yamamoto, Y.;
Takizawa, M.; Yu, X.-Q.; Miyaura, N. Angew. Chem., Int. Ed. 2008, 47,
928. (b) Yamamoto, Y.; Takizawa, M.; Yu, X.-Q.; Miyaura, N.
Heterocycles 2010, 80, 359. (c) Li, G.-Q.; Yamamoto, Y.; Miyaura, N.
Synlett 2011, 1769. (d) Li, G.-Q.; Kiyomura, S.; Yamamoto, Y.;
Miyaura, N. Chem. Lett. 2011, 40, 702. (e) Li, G.-Q.; Yamamoto, Y.;
Miyaura, N. Tetrahedron 2011, 67, 6804. (f) Yamamoto, Y.; Ikizakura,
K.; Ito, H.; Miyaura, N. Molecules 2013, 18, 430. For application of
organotriolborates to other transition-metal-catalyzed reactions, see:
(g) Yu, X.-Q.; Yamamoto, Y.; Miyaura, N. Chem. Asian J. 2008, 3,
1517. (h) Yu, X.-Q.; Yamamoto, Y.; Miyaura, N. Synlett 2009, 994.
(i) Yu, X.-Q.; Yamamoto, Y.; Miyaura, N. Chem. Asian J. 2011, 6, 932.
For a review, see: (j) Yamamoto, Y. Heterocycles 2012, 85, 799.
(7) For a lithium (dialkoxy)(hydroxy)(1-methylpyrazol-4-yl)borate
in external-base-free Suzuki−Miyaura coupling, see: Mullens, P. R.
Tetrahedron Lett. 2009, 50, 6783.
(8) (a) Ohmura, T.; Oshima, K.; Suginome, M. Chem. Commun.
2008, 1416. (b) Ohmura, T.; Masuda, K.; Suginome, M. J. Am. Chem.
Soc. 2008, 130, 1526. (c) Ohmura, T.; Oshima, K.; Taniguchi, H.;
Suginome, M. J. Am. Chem. Soc. 2010, 132, 12194. For recent reviews
on silaboration, see: (d) Ohmura, T.; Suginome, M. Bull. Chem. Soc.
Jpn. 2009, 82, 29. (e) Suginome, M.; Ohmura, T. In Boronic Acids, 2nd
ed.; Hall, D. G., Ed.; Wiley-VCH: Weinheim, Germany, 2011; Vol. 1, p
171. (f) Oestreich, M.; Hartmann, E.; Mewald, M. Chem. Rev. 2013,
113, 402.
2-Dimethyl(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yloxy)silyl-
1-(4-methoxyphenyl)-1-octene (15). The title compound 15 (103
mg, 72%) was obtained from 12a-K (120 mg, 0.34 mmol) with 4-
1
iodoanisole (111 mg, 0.47 mmol). 15: H NMR (400 MHz, C6D6) δ
7.27 (d, J = 8.4 Hz, 2H), 7.00 (s, 1H), 6.87 (d, J = 8.4 Hz, 2H), 3.76
(s, 3H), 2.26 (t, J = 7.2 Hz, 2H), 1.40−1.49 (m, 2H), 1.25−1.36 (m,
6H), 1.18 (s, 12H), 0.90 (t, J = 7.2 Hz, 1H), −0.04 (s, 6H); 13C NMR
(126 MHz, DMSO-d6) δ 158.3, 143.2, 141.2, 132.1, 129.8, 113.2, 73.7,
55.1, 38.8, 31.3, 28.7, 25.0, 24.6, 22.2, 14.1, 2.1. 11B NMR (128 MHz,
C6D6) δ 22.0; HRMS (ESI) m/z calcd for C23H40BO4Si+ (M + H+)
419.2783, found 419.2803.
ASSOCIATED CONTENT
* Supporting Information
Text and figures giving additional general comments, character-
■
S
1
ization data of 12b-Na, 12c-Na, 12d-Na, and 12e-Na, and H
and 13C NMR spectra of new compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: ohmura@sbchem.kyoto-u.ac.jp (T.O.); suginome@
sbchem.kyoto-u.ac.jp (M.S.).
■
(9) For the preparation of 7, see: Ohmura, T.; Masuda, K.; Furukawa,
H.; Suginome, M. Organometallics 2007, 26, 1291.
(10) Cyclic alkenylborates derived from 1-(diethylboryl)-2-(triorga-
nosilyl)ethenes have been reported: Koster, R.; Seidel, G.;
̈
Notes
Wrackmeyer, B.; Horchler, K. Chem. Ber. 1990, 123, 1253.
(11) Biedrzycki, M.; Scouten, W. H.; Biedrzycka, Z. J. Organomet.
Chem. 1992, 431, 255.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(12) Double bond migration took place instead of Suzuki−Miyaura
coupling to give 2-boryl-1-silyl-2-octene in 63% yield. For the double-
bond migration in the presence of Pd[P(t-Bu)3]2 and aryl halides, see:
Ohmura, T.; Oshima, K.; Suginome, M. Angew. Chem., Int. Ed. 2011,
50, 12501.
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This work was supported in part by a Grant-in-Aid for Mizuho
Foundation for the Promotion of Science. K.O. acknowledges
the JSPS for fellowship support.
REFERENCES
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(1) For recent reviews on transition-metal-catalyzed bond-forming
reactions using organoboron compounds, see: (a) Miyaura, N.;
Yamamoto, Y. In Comprehensive Organometallic Chemistry III;
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(c) Hall, D. G. Boronic Acids; Wiley-VCH: Weinheim, Germany, 2010.
(d) Suzuki, A.; Yamamoto, Y. Chem. Lett. 2011, 40, 894.
(2) For reviews on potassium organotrifluoroborates in Suzuki−
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