Selective synthesis of multisubstituted olefins utilizing gem - And vic -diborylated vinylsilanes prepared by silylborylation of an alkynylboronate and diborylation of alkynylsilanes

Article abstract of DOI:10.1021/jo4024057

The synthesis of a series of gem- and vic-diborylated vinylsilanes was accomplished via highly selective transition-metal-catalyzed syn-dimetalation to the alkynylmetal species. This protocol served as a general synthetic method toward regio- and stereode

Full text of DOI:10.1021/jo4024057

Article
pubs.acs.org/joc
Selective Synthesis of Multisubstituted Olefins Utilizing gem- and vic-
Diborylated Vinylsilanes Prepared by Silylborylation of an
Alkynylboronate and Diborylation of Alkynylsilanes
Jiao Jiao,† Keita Hyodo,† Hao Hu,† Kiyohiko Nakajima,§ and Yasushi Nishihara*,†,‡
†Division of Earth, Life, and Molecular Sciences, Graduate School of Natural Science and Technology, Okayama University, 3-1-1
Tsushimanaka, Kita-ku, Okayama 700-8530, Japan
‡ACT-C, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
§Department of Chemistry, Aichi University of Education, Igaya, Kariya 448-8542, Japan
S
* Supporting Information
ABSTRACT: The synthesis of a series of gem- and vic-diborylated vinylsilanes was accomplished via highly selective transition-
metal-catalyzed syn-dimetalation to the alkynylmetal species. This protocol served as a general synthetic method toward regio-
and stereodefined multisubstituted olefins. The key steps are the diastereoselective Suzuki−Miyaura cross-coupling reactions of
gem- and vic-diborylated vinylsilanes, in which the two boron groups showed discrete reactivities to afford diverse precursors of
multisubstituted olefins.
bearing reactive functional groups were found to be
incompatible with these protocols.
INTRODUCTION
■
Olefins are one of the major classes of chemical building blocks
for organic synthesis. Although numerous methods exist for the
preparation of olefins, the regio- and stereoselective synthesis of
multisubstituted olefins still presents a challenge and is of great
importance.1 Great efforts have been made to establish a series
of general methods for multisubstituted olefins such as
substitution of alkenes,2 addition across alkynes,3 carbonyl
olefination,4 olefin metathesis,5 etc.; in particular, the
exploration of methods for tetrasubstituted olefins6 has been
well-investigated but is still a continuing important issue in
organic synthesis. Because of the widespread applications of
tetrasubstituted olefins in natural products,7 pharmaceuti-
cals,6c,8 and functional materials,9 there is still a high demand
to explore facile, practical, and general synthetic strategies
toward regio- and stereodefined tetrasubstituted olefins, in
particular, those with four different substituents.
Moreover, in view of their potential use as pharmaceuticals
and functional materials, extended π-system-based multi-
substituted olefins such as triarylated10 and tetraarylated
olefins11 are valuable synthetic targets. A straightforward
strategy was envisaged by Itami and Yoshida12 in which
sequential installation of aryl groups (π-component) onto the
CC cores of heteroatom-substituted ethenes gave rise to
unsymmetrical tetraarylated olefins selectively. Nevertheless,
the participation of aryllithium and Grignard reagents limited
the diversity of the introduced aryl components, as those
On the other hand, our research group has established a
practical strategy that provides a series of general synthetic
approaches to tetrasubstituted olefins via carbozirconation of
alkynylmetal compounds bearing low-toxicity, mild, and readily
available boron and silicon functionalities.13 The sequential Pd-
catalyzed cross-couplings could transform these boron and
silicon groups on the CC core into other carbon linkages,
which were found to extend the diversity of multisubstituted
derivatives. For example, tamoxifen-type motifs13a as well as
tetraalkylated olefins13c were successfully synthesized.
Recently, considerable attention has been directed toward
the potential and straightforward synthesis of dimetalated
olefins in regio- and stereocontrolled manners;14 the transition-
metal-catalyzed dimetalations of alkynes using Si−Si,15 B−B,16
and Si−B17,18 bond-containing compounds significantly con-
tributed to the generation of various vic-dimetalated olefins. In
addition, Hiyama and Shimizu reported dimetalations of
lithium carbenoids with such M−M′ compounds (M, M′ = B
and/or Si), yielding versatile gem-dimetalated olefins.19 The
discrete reactivities of the resulting carbon−boron bonds allow
diastereo- and regioselective cross-couplings to serve as
precursors of multisubstituted olefins and render the strategy
more versatile.
Received: November 1, 2013
Published: December 9, 2013
© 2013 American Chemical Society
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In sharp contrast, the synthesis of trimetalated olefins with
several boron and silicon moieties to derive multisubstituted
olefins has remained unexplored. Compared with the synthesis
of dimetalated olefins, the development of trimetalated variants
faces challenges in searching for suitable combinations and
arrangements of metal components in the olefin framework to
serve as readily available, stable, and versatile precursors of
multisubstituted olefins. It is also challenging and highly
demanding to investigate the selective transformation of these
trimetalated olefins in diastereo- and regioselective manners by
using two different metals, leading to the selective synthesis of
multisubstituted olefins (Scheme 1).
take place regio- and stereoselectively with the two boryl
moieties situated in the geminal position. To the best of our
knowledge, this is the first example of the synthesis of a 2-
silylated 1,1-diboryl-1-alkene as a unique trimetalated olefin,
because it would be problematic to synthesize this compound
under basic conditions.21
Suzuki−Miyaura Cross-Couplings of 2-Silylated gem-
Diboryl-1-alkene 3 with Aryl Iodides 4. gem-Diborylated
vinylsilane 3 was designed as a potential candidate to synthesize
various tetrasubstituted olefins. To further test the utility of this
building block, compound 3 was subsequently subjected to
Suzuki−Miyaura coupling with an equimolar amount of
iodobenzene (4a) to ascertain whether the first coupling
would be diastereoselective. Screening of various palladium
catalysts and ligands in diastereoselective Suzuki−Miyaura
cross-couplings were conducted, and the results are listed in
Table 1. A combination of Pd(dba)2 with the [HPtBuMe2]BF4
salt, which had proved to be the best catalyst for the Suzuki−
Miyaura coupling reaction of alkenylboronates with alkyl
bromides,13d,22 was found to be suboptimal for the present
reaction because of desilylation of 3 (entry 1). The reaction did
not proceed smoothly with the Pd(OAc)2 catalyst in MeOH23
(entry 2). The participation of water in the reaction using
Pd(OAc)2/SPhos dramatically improved the yield of 5a, which
can be explained by the increased solubility of K3PO4 in toluene
(entry 3 vs 4). Thus, aqueous solutions of bases were employed
for further examinations instead of solid states. The better
performance of KOH to facilitate faster transmetalation of the
Bpin group is still empirical, and no general theory has been
established to provide a plausible explanation (entries 7 and 8).
Finally, THF was found to be the best solvent, considering its
solubility and polarity to supply a homogeneous reaction
system. PEPPSI-IPr24 and Pd2(dba)3·CHCl3/PtBu3 proved
more reactive and afforded relatively higher yields, albeit with
reduced diastereoselectivity (entries 6 and 7). Since the
palladium catalysts with monodentate ligands were not
particularly efficient, several bidentate ligands with different
bite angles were examined. As a result, the diastereoselectivity
was obviously increased (entries 9−12). Finally, the reaction
using 5 mol % PdCl2(dppf)25 at room temperature was
determined as the optimal condition, affording the desired
compound efficiently in satisfactory yield (85%) and diaster-
eoselectivity (88:12) (entry 12).
Scheme 1. Trimetalated Olefins as Precursors of
Tetrasubstituted Olefins
In this work, we envisaged transition-metal-catalyzed
silylborylation of an alkynylboronate and diborylation of
alkynylsilanes, followed by sequential diastereoselective Suzu-
ki−Miyaura cross-coupling reactions that provide straightfor-
ward synthetic entries to hardly available unsymmetrical
tetrasubstituted olefins, including an example substituted by
four different aryl groups. A series of novel trimetalated olefins
with boron and silicon functionalities were synthesized, and
their reactivities toward the highly selective synthesis of
multisubstituted olefins were investigated.20
RESULTS AND DISCUSSION
■
Synthesis of gem-Diborylated Vinylsilanes via Pd-
Catalyzed Silylborylation of an Alkynylboronate. Accord-
ing to a report in 1999,18c in the presence of an in situ-
generated palladium(0)−isonitrile complex, the reaction of
silylborane 1 with alkynylboronate 2 took place in refluxing
toluene. A catalytic amount of Pd(OAc)2 (2 mol %) and
1,1,3,3-tetramethylbutyl isonitrile (tOctNC) (30 mol %)
efficiently gave rise to the silylborylation product 3 in 60%
yield as a single regioisomer (Scheme 2; Bpin is pinacolato-
boryl).
The Z geometry of the major isomer of product 5a was
confirmed by X-ray crystallographic analysis (Figure 1).
Furthermore, the minor product (E)-5a was distinct from
(Z)-5a, as shown by comparison of its NMR data with those of
an authentic sample obtained by silylborylation of diphenyle-
thyne.18c
After the optimization of the reaction conditions for the
diastereoselective Suzuki−Miyaura coupling of 3, a series of aryl
iodides 4 were subjected to the reaction to survey its scope. As
shown in Table 2, aryl bromides such as 4a′ and 4f′ also gave
the desired products in moderate to good yields. A chloride
group in the substrate 4g remained intact, and an ester group in
4h was compatible with the reaction, with no trace of side
products observed.
The configuration of the adduct 3 was unambiguously
confirmed by X-ray crystallographic analysis (Figure S1 in the
Supporting Information). Thus, silylborylation was found to
Scheme 2. Regio- and Stereoselective Silylborylation of 1
with 2
It is noteworthy that it is difficult to prepare compounds 5
via anti-silylborylation18d using unsymmetrical diarylated olefins
because the regioselectivity of the addition would not be
controllable. This protocol affords an approach to the synthesis
of trans-stilbene derivatives 5, although the diastereoselectivity
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Table 1. Screening of the Optimal Conditions for the Diastereoselective Suzuki−Miyaura Coupling of 3 with Iodobenzene
a
(4a)
b
entry
Pd/ligand (mol %)
Pd(dba)2 (5)/[HPtBuMe2]BF4 (20)
base (equiv)
solvent
temp
rt
% yield (Z:E)
1
2
3
4
5
KOH
THF
0
Pd(OAc)2 (5)
K2CO3
MeOH
toluene
toluene
dioxane
toluene
THF
rt
17 (>99:1)
trace
Pd(OAc)2 (10)/SPhos (20)
Pd(OAc)2 (10)/SPhos (20)
Pd(PPh3)4 (20)
K3PO4
100 °C
100 °C
70 °C
50 °C
rt
rt
rt
rt
rt
rt
K3PO4 aq.
KOH aq.
KOH aq.
KOH aq.
Cs2CO3 aq.
KOH aq.
KOH aq.
KOH aq.
KOH aq.
58 (86:14)
24 (96:4)
55 (92:8)
76 (75:25)
64 (92:8)
60 (86:14)
64 (85:15)
89 (87:13)
85 (88:12)
c
6
c
PEPPSI-IPr (10)
7
Pd2(dba)3·CHCl3 (5)/PtBu3 (20)
Pd2(dba)3·CHCl3 (5)/PtBu3 (20)
PdCl2(NCPh)2 (10)/dppe (20)
PdCl2(NCPh)2 (10)/1,8-dppn(20)
PdCl2(NCPh)2 (10)/dppp (20)
PdCl2(dppf) (5)
8
9
THF
THF
10
11
12
THF
THF
THF
a
b
Reaction conditions: 3 (0.1 mmol), 4a (0.1 mmol), Pd cat./ligand, base (0.3 mmol, 3 equiv) in the solvent (1 mL) for 12 h. Isolated yields of the
c
1
isomeric mixtures; the Z:E ratios were determined from the H NMR spectra. The reaction time was 3 h.
multisubstituted olefins, compound 8a was initially employed
to clarify the diastereoselectivity (Scheme 4).
The reaction of 8a with iodobenzene (4a) in the presence of
Pd2(dba)3·CHCl3 and PtBu3 gave rise to a mixture of two cross-
coupled products in an 86:14 ratio. The major product was
confirmed to be (Z)-5a after a comparison of its spectroscopic
data with that of the authentic sample. It is noteworthy that
diastereoselective Suzuki−Miyaura cross-couplings of the
structural isomers 8a and 3 yielded the same compound, (Z)-
5a. The authentic sample of the minor product 9a was also
readily available from I through the reported synthetic
procedure.21c The ratios of major and minor products under
different reaction conditions can be precisely calculated (for
more details, see the Supporting Information). The results are
listed in Table 3.
A 5 mol % loading of PdCl2(dppf) was sufficient to afford
(Z)-5a in 80% yield, and the ratio of (Z)-5a to 9a was
improved to 92:8 (entry 2). PdCl2(dppp) also performed well
to show a relatively higher diastereoselectivity, albeit in a lower
chemical yield of 72% (entry 3). It was a delight to find that
PEPPSI-IPr is the best catalyst for the synthesis of 8a in regard
to the diastereoselectivity among all of the catalysts examined.
When 8b was employed instead of 8a (entries 5−7),
PdCl2(dppp) was found to be superior to PEPPSI-IPr (entry
6 vs 7).
In view of the conformational energies (A values) of the Ph
group (2.8) and the SiMe2Ph group (2.5−2.8),27 the
diastereoselectivities of the Suzuki−Miyaura cross-couplings
of 3 and 8a cannot be explained simply by a steric effect.
However, the different reactivities of the two boryl groups may
possibly be attributed to the α-effect of the silicon moiety,
which may facilitate the diastereoselective transmetalation at
the position geminal to the silicon moiety because vic-
diborylated alkyl aryl alkenes underwent diastereoselective
Suzuki coupling at a position geminal to the aryl moiety.28
With the optimized reaction conditions (Table 3, entry 6) in
hand, we next screened the substrate scope of diastereoselective
cross-couplings of 8b and 8c bearing a trimethylsilyl group with
various aryl iodides 4, considering its relatively broader
Figure 1. ORTEP drawing of 5a.
of this Suzuki−Miyaura coupling of 3 is not perfect (up to
92%).
Highly Selective Synthesis of vic-Diborylated Vinyl-
silanes via Pt-Catalyzed Diborylation of Alkynylsilanes.
Although we demonstrated that a highly selective silylbor-
ylation of an alkynylboronate could provide trimetalated olefins
as precursors of diastereoselective transformations, for con-
tinuous research interests, we further explored an alternative
synthetic approach to trimetalated olefins based on another
combination of the boron and silicon functionalities, expecting
improved diastereoselectivity of the sequential Suzuki−Miyaura
coupling reaction.
The first diborylation of alkynes with bis(pinacolato)diboron
(7) (B2pin2) was discovered by Suzuki and Miyaura.26
Accordingly, diborylation of a series of alkynylsilanes 6a−c
with 7 were conducted in toluene at 80 °C for 12 h in the
presence of Pt(PPh3)4 (Scheme 3). A 5 mol % loading of the
platinum catalyst was sufficient to give the diborylated products
8a−c in high yields. It is noteworthy that compound 8a is a
structural isomer of 3.
Suzuki−Miyaura Cross-Couplings of vic-Diboryl-1-
alkenylsilanes 8 with Aryl Iodides 4. The obtained vic-
diborylated vinylsilanes 8 were expected to be good precursors
for diastereoselective Suzuki−Miyaura couplings as variants of
3. To further test the utility of the synthesized 8 to give
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a
Table 2. Diastereoselective Suzuki−Miyaura Coupling of 3 with Aryl Iodides 4 or Aryl Bromides 4′
a
Reaction conditions: 3 (0.5 mmol), 4 or 4′ (0.5 mmol), PdCl2(dppf) (2−10 mol %), 3 M KOH solution (1.5 mmol) in THF (5 mL). Isolated
1
yields after silica gel column chromatography are shown; the Z:E ratios shown in parentheses were determined from the H NMR spectra.
Scheme 3. Diborylation of Alkynylsilanes 6 with
Bis(pinacolato)diboron (7)
Table 3. Screening of the Optimal Conditions of the
Diastereoselective Suzuki−Miyaura Coupling of 8 with 4a
a
b
entry
Pd cat./ligand (mol %)
% yield ((Z)-5a:9)
c
1
Pd2(dba)3·CHCl3 (5)/PtBu3 (20)
PdCl2(dppf) (5)
68 (86:14)
80 (92:8)
72 (97:3)
76 (>99:1)
75 (97:3)
78 (>99:1)
36 (>99:1)
c
2
c
Scheme 4. Determination of the Configurations of the
Suzuki−Miyaura Coupling Products
3
PdCl2(dppp) (5)
c
4
PEPPSI-IPr (10)
d
5
PdCl2(dppf) (5)
d
6
PdCl2(dppp) (10)
PEPPSI-IPr (10)
d
7
a
Reaction conditions: 8 (0.1 mmol), 4a (0.1 mmol), and a base (0.3
b
mmol) in THF (1 mL). Isolated yields of the isomeric mixtures; Z:E
c
ratios were determined from the 1H NMR spectra. Compound 8a was
d
used. Compound 8b was used.
compatible, generating the (Z)-10 series in moderate to high
yields. The 4-CF3C6H4-substituted vinylsilane 8c also reacted
with aryl iodides 4a and 4b to furnish (Z)-10ca and (Z)-10cb,
respectively, in good yields.
Synthesis of Triarylated Vinylsilanes 11. With the
synthesized 1,2-diarylated vinylsilanes (Z)-5 and (Z)-10 in
hand, we successively introduced different aryl groups by
Suzuki−Miyaura coupling with 1.5 equiv of aryl iodides 4
utilizing the remaining boryl moiety. As a result, various
triarylated vinylsilanes 11 were successfully synthesized in the
presence of Pd2(dba)3·CHCl3/PtBu3 (Scheme 5). Compound
generality compared with the SiMe2Ph group (Table 4).4a,b,6b,29
In all cases, since the diastereoselectivity was perfect, Z-
configured products 10 were solely obtained. A variety of aryl
iodides 4 having electron-donating and -withdrawing groups
were applicable to the diastereoselective coupling. For example,
compounds (Z)-10bb and (Z)-10bc were formed in com-
parable yields. Reactive functional groups such as acetyl (10bg),
ester (10bh), cyano (10bi), and nitro (10bj) groups were
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a
Table 4. Diastereoselective Suzuki−Miyaura Coupling of 8 with Aryl Iodides 4
a
Reaction conditions: 8 (1.0 mmol), 4 (1.0 mmol), PdCl2(dppp) (10 mol %), and KOH (3 M, 1 mL) in THF (10 mL). Isolated yields after silica gel
column chromatography are shown.
11a was first synthesized from (Z)-5b and 4f in 85% yield. The
TMS variants were also synthesized from vinylsilanes 10 with a
series of aryl iodides 4 under the same conditions. It is
noteworthy that the different starting vinylsilanes 10 and
sequential introduction of appropriate aryl groups in an
opposite order of the first and second Suzuki−Miyaura
coupling reactions afforded the corresponding triarylated
vinylsilanes 11b, 11c, and 11d as mutual regio- and
stereoisomers. This protocol serves as a practical synthetic
method for the regio- and stereodefined synthesis of the desired
structural isomers of trisubstituted vinylsilanes.
CONCLUSION
■
We have successfully developed selective and practical gem- and
vic-diborylated vinylsilanes as the first examples of trimetalated
olefins via highly selective silylborylation of an alkynylboronate
and diborylation of alkynylsilanes. The obtained trimetalated
olefins served as useful precursors toward the synthesis of
multiarylated olefins, in particular an unsymmetrical tetraary-
lated olefin. Highly diastereoselective Suzuki−Miyaura cross-
couplings were well-investigated to discriminate the two boryl
moieties and to obtain high to perfect selectivities in
introducing various aryl groups. This protocol can be
compatible with a variety of functional groups on the aryl
moieties, including those not compatible with the organo-
lithium or Grignard reagents employed in previously reported
approaches. The development of a more straightforward way to
transform the silyl groups by C−Si bond activation/direct
Hiyama cross-coupling is currently in progress to expand this
protocol as a more general approach to complicated π-
conjugated molecules, and further studies to clarify the reasons
for the diastereoselectivity will be the subject of forthcoming
papers.
Synthesis of Unsymmetrical Tetraarylated Olefin 13.
Finally, the target unsymmetrical tetraarylated olefin 13 with
four different aryl groups was synthesized through sequential
cross-couplings of 11a by utilizing the remaining silyl moiety, as
shown in Scheme 6. With Br2 and NaOMe in MeOH,28 30 the
e,
silyl group in 11a was successfully transformed to the
corresponding bromide 12 along with an inversion of the
stereochemistry. A sequential Suzuki−Miyaura coupling of 12
with 4-cyanophenylboronic acid afforded the tetraarylated
olefin 13 in 89% yield as the sole product, and its structure
was unambiguously confirmed by X-ray diffraction (Figure S2
in the Supporting Information).
EXPERIMENTAL SECTION
Regio- and Stereoselective Silylborylation of 2: Synthesis of
1-Dimethylphenylsilyl-1-phenyl-2,2-bis(4,4,5,5-tetramethyl-
■
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Scheme 5. Selective Synthesis of Regio- and Stereoisomers of Triarylated Vinysilanes 11
(s, 12H), 1.06 (s, 12H), 6.97−7.00 (m, 2H), 7.08−7.19 (m, 3H),
7.24−7.27 (m, 3H), 7.52−7.56 (m, 2H). 13C{1H} NMR (75 MHz,
CDCl3, rt): δ −0.6, 24.3, 24.8, 83.1, 83.3, 125.4, 126.8, 127.31, 127.34,
128.4, 134.2, 139.5, 148.3, 172.3. The signal of the carbon attached to
B was not observed because of low intensity. 11B{1H} NMR (192
MHz, CDCl3, rt): δ 29.9 (brs, overlapped). MS (EI) m/z (relative
intensity): 490 (M+, 1), 475 (5), 363 (4), 307(11), 135(13), 129 (6),
84 (100), 83 (29), 69 (21). Anal. Calcd for C28H40SiB2O4: C, 68.59;
H, 8.22%. Found: C, 68.20; H, 8.40%.
Scheme 6. Synthesis of Tetraarylated Olefin 13
The authentic sample of (E)-5a was synthesized as a white solid
(612 mg, 1.39 mmol, 70%) according to the procedure above3 using
1
diphenylacetylene (356 mg, 2 mmol). H NMR (300 MHz, CDCl3,
rt): δ 0.39 (s, 6H), 1.09 (s, 12H), 1.06 (s, 12H), 6.75−6.78 (q, 2H),
6.78−7.07 (m, 8H), 7.37−7.39 (m, 3H) 7.68−7.71 (m, 2H).
Synthesis of (Z)-1-(Dimethylphenylsilyl)-2-(4,4,5,5-tetra-
methyl-1,3,2-dioxaborolan-2-yl)-1,2-diphenylethene (5a). To
a solution of PdCl2(dppf) (18 mg, 0.025 mmol, 5 mol %) in THF
(5 mL) as an orange suspension in a 20 mL Schlenk tube at room
temperature under an Ar atmosphere was added 3 (245 mg, 0.5
mmol) followed by aryl halide 4 (0.5 mmol, 1.0 equiv). After aqueous
3 M KOH solution (1.5 mmol, 0.5 mL) was added, the reaction
mixture turned deep brown immediately. The reaction mixture was
stirred for 12 h at room temperature. After the reaction was complete,
the reaction mixture was quenched with sat. NH4Cl solution and then
extracted with diethyl ether (20 mL × 2), and the combined ethereal
layers were washed with brine and dried over MgSO4. Filtration,
evaporation, and silica gel chromatography (hexane/ethyl acetate =
20:1) gave the pure (Z)-5a as a white solid (164 mg, 0.37 mmol, 75%
from 4a and 150 mg, 0.34 mmol, 68% from 4a′). Mp = 76−78 °C. Rf
= 0.28 (hexane/ethyl acetate = 20:1). FT-IR (KBr, cm−1): 3068 (m),
1,3,2-dioxaborolan-2-yl)ethene (3). To palladium(II) acetate (9.0
mg, 0.04 mmol) in a 20 mL Schlenk tube was added liquid l,1,3,3-
tetramethylbutyl isonitrile (105 μL, 0.6 mmol) with stirring at room
temperature under an argon atmosphere. The color of the mixture
immediately changed to a vivid red, indicating the formation of the
palladium(0)−isonitrile complex. Toluene (0.5 mL), silylborane 1
(787 mg, 3 mmol), and alkynylboronate 2 (456 mg, 2 mmol) were
added, and the reaction mixture was heated at reflux. The cooled
reaction mixture was subjected to a short column of silica gel (hexane/
ethyl acetate = 20:1) followed by recrystallization in hexane to afford
the title compound 3 (588 mg, 1.2 mmol, 60%) as a white solid. Mp =
104−105 °C. Rf = 0.26 (hexane/ethyl acetate = 20:1). FT-IR (neat,
cm−1): 2976 (m), 2929 (m), 1330 (m), 1294 (s), 1269 (s), 1141(s),
848 (s), 700 (s). 1H NMR (300 MHz, CDCl3, rt): δ 0.27 (s, 6H), 0.95
1
2974 (w), 1373 (s), 1336 (s), 1141 (s), 848 (s), 700 (s). H NMR
(300 MHz, CDCl3, rt): δ 0.03 (s, 6H), 0.97 (s, 12H), 7.21−7.34 (m,
13H), 7.40−7.43 (m, 2H). 13C{1H} NMR (75 MHz, CDCl3, rt): δ
−1.3, 24.2, 83.4, 125.7, 126.5, 127.3, 127.5, 127.7, 128.1, 128.4, 128.5,
133.9, 139.4, 142.0, 145.6, 153.8. The signal of the carbon attached to
B was not observed because of low intensity. 11B{1H} NMR (192
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MHz, CDCl3, rt): δ 29.4. MS (EI) m/z (relative intensity): 440 (M+,
22), 425 (35), 356 (28), 265 (21), 247 (18), 178 (39), 135 (100), 84
(58), 83 (27), 69 (14). Anal. Calcd for C28H33SiBO2: C, 76.35; H,
7.55%. Found: C, 76.52; H, 7.61%.
mmol) from p-bromo(trifluoromethyl)benzene (4f′). Mp = 104−105
°C. Rf = 0.12 (hexane/ethyl acetate = 20:1). FT-IR (KBr, cm−1): 2981
(w), 1348 (m), 1323 (s), 1159 (s), 1141 (s), 1116 (s), 1107 (s), 1064
(s), 702 (m). 1H NMR (300 MHz, CDCl3, rt): δ 0.01 (s, 6H), 0.89 (s,
12H), 7.15−7.30 (m, 12H), 7.37 (d, J = 8.1 Hz, 2H). 13C{1H} NMR
(150 MHz, CDCl3, rt): δ −1.2, 24.2, 83.6, 124.3 (q, JC−F = 272.2 Hz),
124.6 (q, JC−F = 3.3 Hz), 126.0, 127.5, 127.7, 128.2, 128.4, 128.5 (q,
JC−F = 32 Hz), 128.6, 133.7, 138.6, 145.3, 145.7, 155.8. The signal of
the carbon attached to B was not observed because of low intensity.
11B{1H} NMR (192 MHz, CDCl3, rt): δ 29.1. 19F{1H} NMR (282
(Z)-1-(Dimethylphenylsilyl)-1-phenyl-2-(4-methoxyphenyl)-2-
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)ethene (5b). White
solid (182 mg, 0.39 mmol, 77%). Mp = 122−123 °C. Rf = 0.13
(hexane/ethyl acetate = 20:1). FT-IR (KBr, cm−1): 3068 (m), 2980
(m), 1602 (m), 1508 (s), 1340 (s), 1298 (s), 1246 (s), 1143 (s), 852
(s). 1H NMR (300 MHz, CDCl3, rt): δ −0.03 (s, 6H), 0.90 (s, 12H),
3.79 (s, 3H), 6.73 (d, J = 8.7 Hz, 2H), 7.10 (d, J = 8.7 Hz, 2H), 7.14−
7.19 (m, 3H), 7.22−7.28 (m, 5H), 7.35−7.38 (m, 2H). 13C{1H} NMR
(75 MHz, CDCl3, rt): δ −1.1, 24.3, 55.1, 83.4, 113.2, 125.6, 127.3,
127.5, 128.4, 128.5, 129.2, 133.9, 134.5, 139.7, 145.7, 153.4, 158.4. The
signal of the carbon attached to B was not observed because of low
intensity. 11B{1H} NMR (192 MHz, CDCl3, rt): δ 29.4. MS (EI) m/z
(relative intensity): 470 (M+, 67), 455 (31), 386 (49), 295 (18), 227
(24), 208 (48), 135 (100), 84 (24), 83 (32). Anal. Calcd for
C29H35SiBO3: C, 74.03; H, 7.50%. Found: C, 74.43; H, 7.48%.
(Z)-1-(Dimethylphenylsilyl)-1-phenyl-2-(2-methoxyphenyl)-2-
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)ethene (5c). White
solid (123 mg, 0.26 mmol, 52%). Mp = 95−96 °C. Rf = 0.19
(hexane/ethyl acetate = 20:1). FT-IR (KBr, cm−1): 2980 (m), 2980
(m), 1456 (m), 1338 (s), 1303 (s), 1242 (m), 1141 (s), 1111 (s), 813
(m), 700 (s). 1H NMR (300 MHz, CDCl3, rt): δ 0.00 (s, 6H), 0.89 (s,
12H), 3.75 (s, 3H), 6.69 (dd, J = 8.4, 0.6 Hz, 1H), 6.77 (td, J = 7.5, 1.5
Hz, 1H), 7.05 (dd, J = 7.5, 1.5 Hz, 1H), 7.12−7.31 (m, 11H). 13C{1H}
NMR (75 MHz, CDCl3, rt): δ −1.3, 24.2, 55.0, 83.0, 109.5, 120.0,
125.5, 127.2 (overlapped), 128.2, 128.3, 129.0, 130.9, 132.0, 133.8,
139.7, 145.7, 155.7, 156.7. The signal of the carbon attached to B was
not observed because of low intensity. 11B{1H} NMR (192 MHz,
CDCl3, rt): δ 29.6. MS (EI) m/z (relative intensity): 470 (M+, 35),
455 (43), 356 (31), 355 (88), 354 (23), 277 (23), 251 (18), 208 (19),
135 (100), 84 (15), 83 (21). Anal. Calcd for C29H35SiBO3: C, 74.03;
H, 7.50%. Found: C, 73.73; H, 7.40%.
MHz, CDCl3, rt): δ −62.8. MS (EI) m/z (relative intensity): 508 (M+,
19), 493 (35), 431 (14), 354 (32), 227 (17), 135 (100), 84 (71), 83
(31). Anal. Calcd for C29H32SiBO2F3: C, 68.50; H, 6.34%. Found: C,
68.49; H, 6.05%.
(Z)-1-(Dimethylphenylsilyl)-1-phenyl-2-(4-chlorophenyl)-2-
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)ethene (5g). White
solid (192 mg, 0.40 mmol, 81%). Mp = 105−106 °C. Rf = 0.16
(hexane/ethyl acetate = 20:1). FT-IR (KBr, cm−1): 2983 (m), 1489
(m), 1338 (s), 1303 (s), 1141 (s), 1111 (m), 840 (s), 773 (m), 702
1
(s). H NMR (300 MHz, CDCl3, rt): δ 0.00 (s, 6H), 0.90 (s, 12H),
7.03−7.08 (m, 2H), 7.10−7.18 (m, 5H), 7.19−7.32 (m, 7H). 13C{1H}
NMR (75 MHz, CDCl3, rt): δ −1.2, 24.2, 83.5, 125.8, 127.4, 127.6,
127.8, 128.3, 128.5, 129.5, 132.4, 133.8, 139.0, 140.5, 145.4, 155.0. The
signal of the carbon attached to B was not observed because of low
intensity. 11B{1H} NMR (192 MHz, CDCl3, rt): δ 29.2. MS (EI) m/z
(relative intensity): 474 (M+, 14), 459 (18), 390 (13), 211 (16), 135
(100), 84 (47), 83 (23). Anal. Calcd for C28H32SiBO2Cl: C, 70.82; H,
6.79%. Found: C, 70.99; H, 6.70%.
(Z)-1-(Dimethylphenylsilyl)-1-phenyl-2-(4-ethoxycarbonylphen-
yl)-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)ethene (5h).
White solid (154 mg, 0.30 mmol, 60%). Mp = 91−92 °C. Rf = 0.27
(hexane/ethyl acetate = 20:1). FT-IR (KBr, cm−1): 2983 (m), 1489
(m), 1338 (s), 1303 (s), 1141 (s), 1111 (m), 840 (s), 773 (m), 702
(s). 1H NMR (300 MHz, CDCl3, rt): δ −0.03 (s, 6H), 0.88 (s, 12H),
1.40 (t, J = 7.2 Hz, 3H), 4.37 (q, J = 7.2 Hz, 2H), 7.13−7.33 (m, 12H),
7.87 (d, J = 8.7 Hz, 2H). 13C{1H} NMR (75 MHz, CDCl3, rt): δ −1.2,
14.3, 24.2, 60.8, 83.6, 125.9, 127.4, 127.6, 128.1, 128.2, 128.51, 128.58,
129.1, 133.8, 138.8, 145.3, 147.0, 155.1, 166.6. The signal of the
carbon attached to B was not observed because of low intensity.
11B{1H} NMR (192 MHz, CDCl3, rt): δ 28.6. MS (EI) m/z (relative
(Z)-1-(Dimethylphenylsilyl)-1-phenyl-2-(3-methoxyphenyl)-2-
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)ethene (5d). White
solid (173 mg, 0.37 mmol, 74%). Mp = 90−91 °C. Rf = 0.14
(hexane/ethyl acetate = 20:1). FT-IR (KBr, cm−1): 2974 (m), 2929
(w), 1456 (m), 1338 (s), 1305 (s), 1263 (s), 1141 (s), 845 (s), 816
1
(m), 702 (s). H NMR (300 MHz, CDCl3, rt): δ −0.02 (s, 6H), 0.91
intensity): 512 (M+, 21), 468 (17), 397 (21), 355 (40), 337 (32), 250
(37), 206 (33), 205 (59), 204 (20), 135 (100), 107 (16), 105 (24).
Anal. Calcd for C31H37SiBO4: C, 72.65; H, 7.28%. Found: C, 72.55; H,
7.10%.
(s, 12H), 3.58 (s, 3H), 6.70−6.74 (m, 2H), 6.80−6.83 (m, 1H), 7.12
(t, J = 7.8 Hz, 1H), 7.17−7.19 (m, 3H), 7.23−7.26 (m, 5H), 7.37−
7.40 (m, 2H). 13C{1H} NMR (75 MHz, CDCl3, rt): δ −1.2, 24.2, 54.9,
83.4 112.6, 113.3, 120.6, 125.7, 127.4, 127.5, 128.4, 128.5, 128.8, 133.9,
139.7, 143.3, 145.6, 153.6, 159.0. The signal of the carbon attached to
B was not observed because of low intensity. 11B{1H} NMR (192
MHz, CDCl3, rt): δ 29.5. MS (EI) m/z (relative intensity): 470 (M+,
20), 455 (40), 386 (29), 295 (18), 277 (23), 277 (23), 208 (42), 135
(100), 84 (39), 83 (38). Anal. Calcd for C29H35SiBO3: C, 74.03; H,
7.50%. Found: C, 73.63; H, 7.59%.
General Procedure for the Synthesis of (Z)-1,2-Diboryl-1-
silylated Stilbenes 8 by Highly Selective Diborylation of 6. A
100-mL flask equipped with a magnetic stirring bar and reflux
condenser was charged with Pt(PPh3)4 (311 mg, 0.25 mmol, 5 mol %)
and bis(pinacolato)diboron (7) (1.27 g, 5 mmol, 1.0 equiv) under an
Ar atmosphere. Toluene (50 mL) and 1-alkynylsilane 6 (5 mmol)
were added, affording a yellow solution. After the reaction reached
completion overnight at 80 °C, the reaction mixture was cooled to
room temperature. Toluene was removed via a rotary evaporator to
yield a yellow residue, which was subjected to a short column
chromatography on neutral silica gel with hexanes/EtOAc = 20:1 as
the eluent to afford an off-white solid. Further recrystallization with
CH2Cl2/hexane gave analytically pure white crystals of 8.
(Z)-1-(Dimethylphenylsilyl)-1-phenyl-2-(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)-2-(4-methylphenyl)ethene (5e). White
solid (192 mg, 0.42 mmol, 81%). Mp = 83−84 °C. Rf = 0.27
(hexane/ethyl acetate = 20:1). FT-IR (KBr, cm−1): 2980 (m), 1342
1
(s), 1305 (m), 1141 (s), 1111 (m), 850 (m), 700 (s). H NMR (300
MHz, CDCl3, rt): δ −0.05 (s, 6H), 0.89 (s, 12H), 2.31 (s, 3H), 6.97−
7.00 (m, 2H), 7.05−7.07 (m, 2H), 7.12−7.17 (m, 3H), 7.20−7.26 (m,
5H), 7.32−7.35 (m, 2H). 13C{1H} NMR (75 MHz, CDCl3, rt): δ
−1.2, 21.1, 24.2, 83.3, 125.6, 127.3, 127.4, 128.0, 128.3, 128.4, 128.5,
133.9, 136.0, 139.1, 139.5, 145.7, 153.5. The signal of the carbon
attached to B was not observed because of low intensity. 11B{1H}
NMR (192 MHz, CDCl3, rt): δ 29.4. MS (EI) m/z (relative intensity):
454 (M+, 37), 439 (31), 370 (33), 279 (21), 261 (24), 192 (59), 135
(100), 84 (47), 83 (39). Anal. Calcd for C29H35SiBO2: C, 76.64; H,
7.76%. Found: C, 76.56; H, 7.60%.
(Z)-1-(Dimethylphenylsilyl)-2-phenyl-1,2-bis(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)ethene (8a). White crystals (2.08 g, 4.25
mmol, 85%). Mp = 127−128 °C. FT-IR (neat, cm−1): 2974 (m), 1369
(m), 1339 (m), 1321 (s), 1300 (s), 1202 (m), 1146 (s), 1111 (w), 843
1
(m), 772 (w), 704 (m). H NMR (600 MHz, CDCl3, rt): δ 0.09 (s,
6H), 1.34 (s, 12H), 1.35 (s, 12H), 7.10−7.12 (m, 2H), 7.25−7.26 (m,
3H), 7.38−7.39 (m, 3H), 7.58−7.59 (m, 2H). 13C{1H} NMR (150
MHz, CDCl3, rt): δ −0.7, 24.7, 25.3, 83.6, 83.9, 126.3, 127.3, 127.4,
127.8, 128.2, 134.2, 140.9, 145.4. The signals of the two carbons
attached to B were not observed because of low intensity. 11B{1H}
NMR (192 MHz, CDCl3, rt): δ 29.2 (brs, overlapped). MS (EI) m/z
(relative intensity): 490 (M+, 2), 475 (3), 363 (6), 307 (14), 271 (7),
(Z)-1-(Dimethylphenylsilyl)-1-phenyl-2-(4-trifluoromethylphen-
yl)-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)ethene (5f).
White solid isolated in 50% yield (126 mg, 0.25 mmol) from p-
iodo(trifluoromethyl)benzene (4f) and 50% yield (127 mg, 0.26
291
dx.doi.org/10.1021/jo4024057 | J. Org. Chem. 2014, 79, 285−295

The Journal of Organic Chemistry
Article
221 (7), 135 (13), 119 (21), 84 (100), 83 (27), 69 (24). Anal. Calcd
for C28H40B2O4Si: C, 68.59; H, 8.22%. Found: C, 68.61; H, 8.06%.
(Z)-1-(Trimethylsilyl)-2-phenyl-1,2-bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)ethene (8b). White crystals (1.82 g, 4.25 mmol,
85%). Mp = 169−170 °C. FT-IR (neat, cm−1): 2980 (m), 1371 (w),
(28), 101 (22), 84 (100), 73 (64), 69 (22). Anal. Calcd for
C23H31BO2Si: C, 73.01; H, 8.26%. Found: C, 73.05; H, 8.25%.
(Z)-1-(Trimethylsilyl)-1-(4-methoxyphenyl)-2-phenyl-2-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)ethene (10bb). White solid
(148 mg, 0.36 mmol, 73%). Mp = 106−107 °C. Rf = 0.21 (hexane/
ethyl acetate = 20:1). FT-IR (KBr, cm−1): 2980 (m), 1506 (m), 1342
(m), 1302 (m), 1246 (s), 1142 (m), 849 (s), 708 (m). 1H NMR (600
MHz, CDCl3, rt): δ −0.25 (s, 9H), 0.93 (s, 12H), 3.80 (s, 3H), 6.83
(d, J = 9 Hz, 2H), 7.08 (d, J = 9 Hz, 2H), 7.23−7.24 (m, 1H), 7.28−
7.30 (m, 4H). 13C{1H} NMR (150 MHz, CDCl3, rt): δ 0.2, 24.3, 55.3,
83.3, 113.0, 126.4, 127.8, 128.1, 129.1, 138.4, 142.6, 155.5, 157.9. The
signal of the carbon attached to B was not observed because of low
intensity. 11B{1H} NMR (192 MHz, CDCl3, rt): δ 29.5. MS (EI) m/z
(relative intensity): 408 (M+, 100), 393 (65), 293 (30), 251 (47), 208
(81), 165 (29), 135 (16), 84 (26), 83 (41), 73 (45). Anal. Calcd for
C24H33BO3Si: C, 70.58; H, 8.14%. Found: C, 70.43; H, 8.14%.
(Z)-1-(Trimethylsilyl)-1-(4-trifluoromethylphenyl)-2-phenyl-2-
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)ethene (10bc). White
solid (163 mg, 0.37 mmol, 73%). Mp = 107−108 °C. Rf = 0.37
(hexane/ethyl acetate = 20:1). FT-IR (KBr, cm−1): 2990 (w), 2978
(w), 1341 (s), 1329 (s), 1315 (m), 1248 (w), 1155 (m), 1121 (m),
1069 (m), 851 (s). 1H NMR (600 MHz, CDCl3, rt): δ −0.24 (s, 9H),
0.89 (s, 12H), 7.27−7.29 (m, 5H), 7.31−7.34 (m, 2H), 7.54 (d, J = 8
Hz, 2H). 13C{1H} NMR (150 MHz, CDCl3, rt): δ 0.1, 24.2, 83.6,
124.47 (q, JC−F = 270.2 Hz), 124.50 (q, JC−F = 3.5 Hz), 126.8, 127.98,
127.99 (q, JC−F = 21.6 Hz), 128.0, 128.4, 142.2, 150.1, 155.3. The
signal of the carbon attached to B was not observed because of low
intensity. 11B{1H} NMR (192 MHz, CDCl3, rt): δ 29.4. 19F{1H} NMR
(564 MHz, CDCl3, rt): δ −62.6. MS (EI) m/z (relative intensity): 446
(M+, 37), 431 (46), 354 (19), 289 (13), 227 (16), 135 (11), 101 (53),
84 (100), 73 (53). Anal. Calcd for C24H30BO2SiF3: C, 64.58; H,
6.77%. Found: C, 64.60; H, 6.42%.
(Z)-1-(Trimethylsilyl)-1-(4-methylphenyl)-2-phenyl-2-(4,4,5,5-tet-
ramethyl-1,3,2-dioxaborolan-2-yl)ethene (10bd). White solid (137
mg, 0.35 mmol, 70%). Mp = 102−103 °C. Rf = 0.37 (hexane/ethyl
acetate = 20:1). FT-IR (KBr, cm−1): 2980 (m), 2953 (w), 1506 (w),
1340 (s), 1304 (s), 1246 (m), 1142 (s), 984 (m), 845 (s), 706 (m). 1H
NMR (600 MHz, CDCl3, rt): δ −0.25 (s, 9H), 0.91 (s, 12H), 2.32 (s,
3H), 7.04 (d, J = 8 Hz, 2H), 7.08 (d, J = 8 Hz, 2H), 7.23−7.25 (m,
1H), 7.28−7.32 (m, 4H). 13C{1H} NMR (150 MHz, CDCl3, rt): δ 0.2,
21.0, 24.3, 83.3, 126.4, 127.8, 127.9, 128.1, 128.2, 135.0, 142.7, 142.9,
156.0. The signal of the carbon attached to B was not observed
because of low intensity. 11B{1H} NMR (192 MHz, CDCl3, rt): δ 29.3.
MS (EI) m/z (relative intensity): 392 (M+, 82), 377 (52), 295 (15),
277 (48), 235 (41), 193 (20), 192 (100), 84 (53), 83 (37), 73 (47).
Anal. Calcd for C24H33BO2Si: C, 73.46; H, 8.48%. Found: C, 73.26; H,
8.47%.
1
1317 (s), 1296 (s), 1269 (m), 1146 (s), 845 (s), 704 (w). H NMR
(600 MHz, CDCl3, rt): δ −0.19 (s, 9H), 1.22 (s, 12H), 1.37 (s, 12H),
7.10−7.12 (m, 2H), 7.19−7.20 (m, 1H), 7.22−7.25 (m, 2H). 13C{1H}
NMR (150 MHz, CDCl3, rt): δ 0.8, 24.7, 25.5, 83.6, 83.9, 126.2, 127.4,
127.8, 145.8. The signals of the two carbons attached to B were not
observed because of low intensity. 11B{1H} NMR (192 MHz, CDCl3,
rt): δ 29.2, 30.9. MS (EI) m/z (relative intensity): 429 (M+, 0.01), 413
(7), 287 (13), 286 (6), 231 (5), 129 (4), 84 (100), 69 (30). Anal.
Calcd for C23H38B2O4Si: C, 64.51; H, 8.94%. Found: C, 64.49; H,
8.97%.
(Z)-1-(Trimethylsilyl)-2-(4-trifluoromethylphenyl)-1,2-bis(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)ethene (8c). White needlelike
crystals (2.06 g, 4.15 mmol, 83%). Mp = 170 °C. FT-IR (neat, cm−1):
2984 (w), 1310 (s), 1204 (w), 1119 (m), 1064 (m), 1018 (w), 851
1
(s), 604 (w). H NMR (600 MHz, CDCl3, rt): δ −0.19 (s, 9H), 1.23
(s, 12H), 1.38 (s, 12H), 7.21 (d, J = 9 Hz, 2H), 7.50 (d, J = 9 Hz, 2H).
13C{1H} NMR (150 MHz, CDCl3, rt): δ 0.8, 24.7, 25.6, 83.8, 84.2,
124.4 (q, JC−F = 270.5 Hz), 124.4 (q, JC−F = 3.5 Hz), 128.1, 128.3 (q,
JC−F = 32 Hz), 149.6. The signals of the two carbons attached to B
were not observed because of low intensity. 11B{1H} NMR (192 MHz,
CDCl3, rt): δ 28.8 (brs, overlapped). 19F{1H} NMR (564 MHz,
CDCl3, rt): δ −62.5. MS (EI) m/z (relative intensity): 496 (M+, 0),
481 (3), 438 (4), 355 (16), 84 (100), 83 (29), 69 (25). Anal. Calcd for
C24H37B2F3O4Si: C, 58.09; H, 7.51%. Found: C, 58.23; H, 7.11%.
Diastereoselective Suzuki−Miyaura Cross-Coupling of 8
with Aryl Iodide 4a and Determination of the Ratio of the
Two Regioisomers. To a THF solution of the palladium catalyst and
the ligand in a 20 mL Schlenk tube under an Ar atmosphere was added
8a (49 mg, 0.1 mmol). To the reaction mixture were then added
iodobenzene 4a (11.2 μL, 20.4 mg, 0.1 mmol) and the base (3.0
equiv). After being stirred at room temperature for 3 h, the reaction
mixture was quenched with sat. NH4Cl solution and then extracted
with diethyl ether (10 mL × 2). The combined ethereal layers were
washed with brine and dried over MgSO4. Filtration, evaporation, and
preparative TLC gave a mixture of regioisomers of the target products
(Z)-5a and 9a in 68% combined yield. The (Z)-5a:9a ratio (86:14)
1
was determined from the H NMR spectrum using different protons
assigned to the methyl groups of −SiMe2Ph as the references (see the
1H NMR spectrum shown in Figure S3 in the Supporting
Information).
General Procedure for the Synthesis of (Z)-1-(Trimethylsil-
yl)-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1,2-diaryle-
thenes. To a solution of PdCl2(dppp) (29 mg, 0.025 mmol, 10 mol
%) in THF (5 mL) as an off-white suspension in a 20 mL Schlenk tube
at room temperature under an Ar atmosphere were added 8 (0.5
mmol) and aryl halide 4 (0.5 mmol, 1.0 equiv). When aqueous 3 M
KOH solution (1.5 mmol, 0.5 mL) was added, the reaction mixture
immediately turned deep brown. The reaction mixture was stirred for
an additional 3 h at room temperature. After the reaction was
complete, the reaction mixture was quenched with sat. NH4Cl solution
and then extracted with diethyl ether (20 mL × 2). The combined
ethereal layers were washed with brine and dried over MgSO4.
Filtration, evaporation, and column chromatography on silica gel gave
the analytically pure (Z)-10.
(Z)-1-(Trimethylsilyl)-1-(3-methoxyphenyl)-2-phenyl-2-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)ethene (10be). White solid
(147 mg, 0.36 mmol, 72%). Mp = 90 °C. Rf = 0.25 (hexane/ethyl
acetate = 20:1). FT-IR (KBr, cm−1): 2978 (m), 1585 (m), 1508 (s),
1489 (m), 1341 (s), 1304 (s), 1167 (m), 839 (s), 708 (m), 852 (s). 1H
NMR (600 MHz, CDCl3, rt): δ −0.23 (s, 9H), 0.93 (s, 12H), 3.82 (s,
3H), 6.72−6.77 (m, 3H), 7.17 (t, J = 8 Hz, 1H), 7.22−7.26 (m, 1H),
7.29−7.32 (m, 4H). 13C{1H} NMR (150 MHz, CDCl3, rt): δ 0.3, 24.3,
55.2, 83.4, 111.7, 113.1, 120.6, 126.5, 127.9, 128.1, 128.6, 142.5, 147.4,
155.8, 159.0. The signal of the carbon attached to B was not observed
because of low intensity. 11B{1H} NMR (192 MHz, CDCl3, rt): δ 29.4.
MS (EI) m/z (relative intensity): 408 (M+, 85), 393 (82), 294 (25),
293 (100), 292 (32), 251 (43), 208 (90), 135 (20), 84 (50), 83 (50),
73 (65). Anal. Calcd for C24H33BO3Si: C, 70.58; H, 8.14%. Found: C,
70.78; H, 8.34%.
(Z)-1-(Trimethylsilyl)-1,2-diphenyl-2-(4,4,5,5-tetramethyl-1,3,2-di-
oxaborolan-2-yl)ethene (10ba). White solid (147 mg, 0.39 mmol,
78%). Mp = 72−73 °C. Rf = 0.38 (hexane/ethyl acetate = 20:1). FT-
IR (KBr, cm−1): 2978 (m), 1344 (s), 1310 (s), 1246 (m), 1144 (s),
852 (s), 837 (s), 700 (s). 1H NMR (600 MHz, CDCl3, rt): δ −0.25 (s,
9H), 0.90 (s, 12H), 7.15−7.18 (m, 3H), 7.23−7.27 (m, 3H), 7.30−
7.31 (m, 4H). 13C{1H} NMR (150 MHz, CDCl3, rt): δ 0.2, 24.3, 83.4,
125.6, 126.5, 127.6, 127.9, 128.0, 128.1, 142.6, 146.0, 156.0. The signal
of the carbon attached to B was not observed because of low intensity.
11B{1H} NMR (192 MHz, CDCl3, rt): δ 29.3. MS (EI) m/z (relative
(Z)-1-(Trimethylsilyl)-1-(4-chlorophenyl)-2-phenyl-2-(4,4,5,5-tet-
ramethyl-1,3,2-dioxaborolan-2-yl)ethene (10bf). White solid (161
mg, 0.39 mmol, 78%). Mp = 141−142 °C. Rf = 0.20 (hexane/ethyl
acetate = 20:1). FT-IR (KBr, cm−1): 2976 (w), 1489 (m), 1371 (m),
1
1337 (s), 1302 (s), 1140 (s), 1011 (w), 849 (s), 702 (m). H NMR
(600 MHz, CDCl3, rt): δ −0.26 (s, 9H), 0.93 (s, 12H), 7.09 (d, J = 8
Hz, 2H), 7.24−7.32 (m, 7H). 13C{1H} NMR (150 MHz, CDCl3, rt): δ
0.1, 24.3, 83.5, 126.7, 127.6, 127.9, 128.0, 129.4, 131.5, 142.3, 144.5,
intensity): 378 (M+, 71), 363 (58), 263 (52), 221 (41), 178 (85), 135
292
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155.0. The signal of the carbon attached to B was not observed
because of low intensity. 11B{1H} NMR (192 MHz, CDCl3, rt): δ 29.4.
MS (EI) m/z (relative intensity): 412 (M+, 47), 397 (37), 255 (17),
212 (43), 101 (45), 84 (100), 83 (40), 73 (68), 69 (19). Anal. Calcd
for C23H30BClO2Si: C, 66.92; H, 7.32%. Found: C, 66.52; H, 7.03%.
(Z)-1-(Trimethylsilyl)-1-(4-acetylphenyl)-2-phenyl-2-(4,4,5,5-tetra-
methyl-1,3,2-dioxaborolan-2-yl)ethene (10bg). White solid (168 mg,
0.40 mmol, 80%). Mp = 132−133 °C. Rf = 0.18 (hexane/ethyl acetate
= 10:1). FT-IR (KBr, cm−1): 2980 (w), 2959 (w), 1678 (s), 1601 (m),
124.8 (q, JC−F = 3.7 Hz), 125.8, 127.7, 127.8, 128.4, 128.9 (q, JC−F =
31.8 Hz), 145.5, 146.5, 157.7. The signal of the carbon attached to B
was not observed because of low intensity. 11B{1H} NMR (192 MHz,
CDCl3, rt): δ 29.3. 19F{1H} NMR (564 MHz, CDCl3, rt): δ −62.6. MS
(EI) m/z (relative intensity): 446 (M+, 27), 431 (34), 354 (15), 289
(14), 227 (14), 101 (21), 84 (100), 73 (47), 69 (16). Anal. Calcd for
C24H30BF3O2Si: C, 64.58; H, 6.77%. Found: C, 64.49; H, 6.42%.
(Z)-1-(Trimethylsilyl)-1-(4-methoxyphenyl)-2-(4-trifluoromethyl-
phenyl)-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)ethene
(10cb). White solid (160 mg, 0.34 mmol, 67%). Mp = 148 °C. Rf =
0.19 (hexane/ethyl acetate = 20:1). FT-IR (KBr, cm−1): 2981 (w),
1612 (w), 1506 (m), 1373 (w), 1325 (s), 1284 (w), 1244 (m), 1064
(m), 848 (s). 1H NMR (600 MHz, CDCl3, rt): δ −0.25 (s, 9H), 0.93
(s, 12H), 3.80 (s, 3H), 6.83 (d, J = 8 Hz, 2H), 7.06 (d, J = 8 Hz, 2H),
7.40 (d, J = 8 Hz, 2H), 7.57 (d, J = 8 Hz, 2H). 13C{1H} NMR (150
MHz, CDCl3, rt): δ 0.2, 24.3, 55.3, 83.6, 113.1, 124.4 (q, JC−F = 270.5
Hz), 124.8 (q, JC−F = 3.7 Hz), 128.4, 128.7 (q, JC−F = 32.1 Hz), 128.9,
138.0, 146.5, 157.3, 158.1. The signal of the carbon attached to B was
not observed because of low intensity. 11B{1H} NMR (192 MHz,
CDCl3, rt): δ 29.4. 19F{1H} NMR (564 MHz, CDCl3, rt): δ −62.6. MS
(EI) m/z (relative intensity): 476 (M+, 81), 475 (18), 462 (30), 461
(100), 460 (22), 361 (20), 319 (43), 276 (68), 165 (22), 84 (59), 83
(65), 73 (63). Anal. Calcd for C25H32BF3O3Si: C, 63.03; H, 6.77%.
Found: C, 63.00; H, 6.40%.
Suzuki−Miyaura Cross-Coupling of 5b or 10 with 4:
Synthesis of 11. To a deep-purple solution of Pd2(dba)3·CHCl3
(26 mg, 0.025 mmol, 5 mol %) and PtBu3 (20 mg, 0.1 mmol, 20 mol
%) in THF (5 mL) in a 20 mL Schlenk tube were added 5b or 10 (0.5
mmol) and 4 (0.75 mmol, 1.5 equiv) at room temperature under an Ar
atmosphere. After aqueous 3 M KOH solution (1.5 mmol, 0.5 mL)
was added, the reaction mixture turned deep brown immediately. The
reaction mixture was heated to reflux and stirred for 12 h. After the
reaction was complete, the reaction mixture was quenched with sat.
NH4Cl solution and then extracted with diethyl ether (20 mL × 2),
and the combined ethereal layers were washed with brine and dried
over MgSO4. Filtration, evaporation, and silica gel chromatography
(hexane/ethyl acetate = 20:1) gave the title compound 11.
(Z)-1-(Dimethylphenylsilyl)-1-phenyl-2-(4-trifluoromethylphen-
yl)-2-(4-methoxyphenyl)ethene (11a). Colorless viscous oil (207 mg,
0.42 mmol, 85%). Rf = 0.41 (hexane/ethyl acetate = 20:1). FT-IR
(KBr, cm−1): 3068 (w), 1608 (m), 1506 (s), 1325 (s), 1247 (s), 1165
(s), 1122 (m), 1111 (s), 854 (s), 702 (s). 1H NMR (300 MHz,
CDCl3, rt): δ 0.09 (s, 6H), 3.84 (s, 3H), 6.78 (d, J = 8.1 Hz, 2H), 6.96
(d, J = 8.1 Hz, 2H), 7.05−7.10 (m, 5H), 7.13−7.18 (m, 2H), 7.29−
7.39 (m, 7H). 13C{1H} NMR (150 MHz, CDCl3, rt): δ −0.8, 55.2,
113.3, 124.1 (q, JC−F = 272.1 Hz), 124.2 (q, JC−F = 3.5 Hz), 125.3,
127.5, 127.6, 128.8 (q, JC−F = 32.6 Hz), 128.6, 129.5, 129.7, 130.8,
133.8, 135.6, 139.8, 143.3, 144.2, 147.1, 153.2, 159.0. 19F{1H} NMR
(282 MHz, CDCl3, rt): δ −62.8. MS (EI) m/z (relative intensity): 488
(M+, 77), 473 (21), 334 (20), 265 (20), 227 (66), 135 (100). Anal.
Calcd for C30H27SiOF3: C, 73.74; H, 5.57%. Found: C, 73.78; H,
5.74%.
1
1341 (m), 1317 (m), 1267 (m), 1142 (m), 851 (s). H NMR (600
MHz, CDCl3, rt): δ −0.28 (s, 9H), 0.85 (s, 12H), 2.57 (s, 3H), 7.22−
7.30 (m, 7H), 7.86 (d, J = 8 Hz, 2H). 13C{1H} NMR (150 MHz,
CDCl3, rt): δ 0.2, 24.2, 26.6, 83.5, 126.7, 127.8, 127.9, 128.0, 128.2,
134.7, 142.2, 151.7, 155.6, 198.0. The signal of the carbon attached to
B was not observed because of low intensity. 11B{1H} NMR (192
MHz, CDCl3, rt): δ 29.1. MS (EI) m/z (relative intensity): 420 (M+,
68), 405 (22), 305 (24), 205 (29), 204 (100), 84 (51), 73 (65). Anal.
Calcd for C25H33BO3Si: C, 71.42; H, 7.91%. Found: C, 71.53; H,
7.59%.
4-[(1Z)-1-(Trimethylsilyl)-2-phenyl-2-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)ethenyl]benzoic Acid Ethyl Ester (10bh). White
solid (159 mg, 0.35 mmol, 71%). Mp = 97−98 °C. Rf = 0.11 (hexane/
ethyl acetate = 20:1). FT-IR (KBr, cm−1): 2980 (m), 1717 (s), 1605
(m), 1341 (m), 1271 (s), 1142 (m), 851 (m), 700 (w). 1H NMR (600
MHz, CDCl3, rt): δ −0.26 (s, 9H), 0.90 (s, 12H), 1.41 (t, J = 7 Hz,
3H), 4.38 (q, J = 7 Hz, 2H), 7.23 (d, J = 8 Hz, 2H), 7.25−7.26 (m,
1H), 7.29−7.32 (m, 4H), 7.97 (d, J = 8 Hz, 2H). 13C{1H} NMR (150
MHz, CDCl3, rt): δ 0.2, 14.3, 24.2, 60.8, 83.5, 126.7, 127.7, 127.9,
127.99, 128.01, 129.0, 142.2, 151.3, 155.6, 166.8. The signal of the
carbon attached to B was not observed because of low intensity.
11B{1H} NMR (192 MHz, CDCl3, rt): δ 29.2. MS (EI) m/z (relative
intensity): 450 (M+, 48), 435 (17), 289 (19), 205 (100), 84 (29), 73
(32). Anal. Calcd for C26H35BO4Si: C, 69.33; H, 7.83%. Found: C,
68.93; H, 7.76%.
(Z)-1-(Trimethylsilyl)-1-(4-cyanophenyl)-2-phenyl-2-(4,4,5,5-tet-
ramethyl-1,3,2-dioxaborolan-2-yl)ethene (10bi). Off-white solid
(113 mg, 0.28 mmol, 56%). Mp = 214 °C. Rf = 0.11 (hexane/ethyl
acetate = 20:1). FT-IR (KBr, cm−1): 2978 (m), 2956 (m), 2224 (m),
1601 (w), 1327 (s), 1302 (s), 1140 (s), 982 (w), 849 (s), 708 (m). 1H
NMR (600 MHz, CDCl3, rt): δ −0.25 (s, 9H), 0.91 (s, 12H), 7.26−
7.28 (m, 5H), 7.31−7.34 (m, 2H), 7.59 (d, J = 8 Hz, 2H). 13C{1H}
NMR (150 MHz, CDCl3, rt): δ 0.1, 24.2, 83.6, 109.3, 119.3, 126.9,
127.9, 128.0, 128.8, 131.4, 141.9, 151.6, 155.1. The signal of the
carbon attached to B was not observed because of low intensity.
11B{1H} NMR (192 MHz, CDCl3, rt): δ 29.2. MS (EI) m/z (relative
intensity): 403 (M+, 589), 402 (28), 388 (40), 263 (52), 175 (20), 101
(49), 84 (96), 83 (27), 73 (100). Anal. Calcd for C24H30BNO2Si: C,
71.46; H, 7.50; N, 3.47%. Found: C, 71.49; H, 7.43; N, 3.43%.
(Z)-1-(Trimethylsilyl)-1-(4-nitrophenyl)-2-phenyl-2-(4,4,5,5-tetra-
methyl-1,3,2-dioxaborolan-2-yl)ethene (10bj). White solid (142 mg,
0.34 mmol, 67%). Mp = 204 °C. Rf = 0.13 (hexane/ethyl acetate =
20:1). FT-IR (KBr, cm−1): 2976 (w), 1589 (w), 1512 (m), 1344 (s),
1
1140 (m), 986 (w), 849 (m), 712 (w). H NMR (600 MHz, CDCl3,
(E)-1-(Trimethylsilyl)-1-(4-trifluoromethylphenyl)-2-phenyl-2-(4-
methoxyphenyl)ethene (11b). White solid (185 mg, 0.43 mmol,
87%). Mp = 74−75 °C. Rf = 0.42 (hexane/ethyl acetate = 20:1). FT-
IR (KBr, cm−1): 2955 (w), 1609 (m), 1506 (m), 1321 (s), 1113 (s),
rt): δ −0.24 (s, 9H), 0.91 (s, 12H), 7.27−7.29 (m, 3H), 7.32−7.34 (m,
4H), 8.17 (d, J = 9 Hz, 2H). 13C{1H} NMR (150 MHz, CDCl3, rt): δ
0.1, 24.2, 83.7, 122.9, 127.0, 127.9, 128.0, 128.8, 141.9, 146.1, 153.9,
155.0. The signal of the carbon attached to B was not observed
because of low intensity. 11B{1H} NMR (192 MHz, CDCl3, rt): δ 29.4.
MS (EI) m/z (relative intensity): 423 (M+, 37), 408 (45), 280 (68),
101 (52), 84 (100), 83 (38), 73 (86). Anal. Calcd for C23H30BNO4Si:
C, 65.25; H, 7.14; N, 3.31%. Found: C, 65.10; H, 6.75; N, 3.23%.
(Z)-1-(Trimethylsilyl)-1-phenyl-2-(4-trifluoromethylphenyl)-2-
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)ethene (10ca). White
solid (156 mg, 0.35 mmol, 70%). Mp = 103−104 °C. Rf = 0.32
(hexane/ethyl acetate = 20:1). FT-IR (KBr, cm−1): 2978 (m), 1612
(w), 1312 (s), 1269 (w), 1151 (s), 1124 (s), 1066 (m), 986 (w), 845
(s), 708 (m). 1H NMR (600 MHz, CDCl3, rt): δ −0.26 (s, 9H), 0.89
(s, 12H), 7.13 (d, J = 7 Hz, 2H), 7.17−7.19 (m, 1H), 7.24−7.27 (m,
2H), 7.41 (d, J = 7 Hz, 2H), 7.57 (d, J = 7 Hz, 2H). 13C{1H} NMR
(150 MHz, CDCl3, rt): δ 0.2, 24.2, 83.6, 124.4 (q, JC−F = 270.4 Hz),
1
1065 (m), 868 (m), 829 (m), 704 (m). H NMR (600 MHz, CDCl3,
rt): δ −0.19 (s, 9H), 3.66 (s, 3H), 6.56 (d, J = 8 Hz, 2H), 6.85 (d, J = 8
Hz, 2H), 7.13 (d, J = 8 Hz, 2H), 7.31−7.33 (m, 3H), 7.34−7.38 (m,
2H), 7.44 (d, J = 8 Hz, 2H). 13C{1H} NMR (150 MHz, CDCl3, rt): δ
0.4, 54.9, 112.8, 124.5 (q, JC−F = 270.5 Hz), 124.5 (q, JC−F = 3.5 Hz),
127.1 (q, JC−F = 32 Hz), 127.3, 128.0, 129.4, 129.6, 130.7, 135.1, 142.3,
144.2, 148.5, 154.0, 157.9. 19F{1H} NMR (564 MHz, CDCl3, rt): δ
−62.4. MS (EI) m/z (relative intensity): 426 (M+, 100), 411 (28), 257
(54), 227 (62), 165 (52), 135 (51), 73 (81). HRMS (FAB) Calcd for
C25H25F3OSi: 426.1627. Found: 426.1611.
(E)-1-(Trimethylsilyl)-1-(4-methoxyphenyl)-2-phenyl-2-(4-
trifluoromethylphenyl)ethene (11c). White solid (182 mg, 0.43
mmol, 85%). Mp = 88−89 °C. Rf = 0.44 (hexane/ethyl acetate =
20:1). FT-IR (KBr, cm−1): 2958 (w), 1506 (m), 1321 (s), 1286 (w),
293
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Article
1242 (s), 1122 (s), 1109 (m), 837 (s), 700 (m). 1H NMR (600 MHz,
CDCl3, rt): δ −0.19 (s, 9H), 3.74 (s, 3H), 6.70 (d, J = 8 Hz, 2H), 6.86
(d, J = 8 Hz, 2H), 7.06 (d, J = 8 Hz, 2H), 7.26 (d, J = 8 Hz, 2H),
7.29−7.32 (m, 3H), 7.34−7.36 (m, 2H). 13C{1H} NMR (150 MHz,
CDCl3, rt): δ 0.3, 55.0, 113.1, 124.2 (q, JC−F = 270.5 Hz), 124.3 (q,
JC−F = 3.7 Hz), 127.4, 127.7 (q, JC−F = 32.1 Hz), 128.1, 129.5, 129.6,
130.1, 135.5, 143.6, 145.7, 147.0, 152.4, 157.3. 19F{1H} NMR (564
MHz, CDCl3, rt): δ −62.7. MS (EI) m/z (relative intensity): 426 (M+,
100), 412 (25), 411 (78), 257 (26), 227 (22), 203 (16), 165 (29), 135
(28), 73 (93). HRMS (FAB) Calcd for C25H25F3OSi: 426.1627.
Found: 426.1628.
(Z)-1-(Trimethylsilyl)-1-(4-methoxyphenyl)-2-phenyl-2-(4-
trifluoromethylphenyl)ethene (11d). White solid (188 mg, 0.44
mmol, 88%). Mp = 117−118 °C. Rf = 0.42 (hexane/ethyl acetate =
20:1). FT-IR (KBr, cm−1): 2955 (w), 1504 (m), 1325 (s), 1244 (m),
1122 (m), 1064 (m), 867 (m), 840 (m). 1H NMR (600 MHz, CDCl3,
rt): δ −0.20 (s, 9H), 3.73 (s, 3H), 6.69 (d, J = 8 Hz, 2H), 6.86 (d, J = 8
Hz, 2H), 6.91−6.92 (m, 2H), 6.97−6.98 (m, 1H), 7.02 (t, J = 8 Hz,
2H), 7.44 (d, J = 8 Hz, 2H), 7.60 (d, J = 8 Hz, 2H). 13C{1H} NMR
(150 MHz, CDCl3, rt): δ 0.4, 54.9, 113.0, 124.2 (q, JC−F = 270.4 Hz),
124.9 (q, JC−F = 3.5 Hz), 126.2, 127.5, 129.29 (q, JC−F = 32.1 Hz),
129.3, 129.8, 130.1, 135.6, 142.6, 145.1, 148.1, 152.4, 157.2. 19F{1H}
NMR (564 MHz, CDCl3, rt): δ −62.6. MS (EI) m/z (relative
intensity): 426 (M+, 100), 412 (25), 411 (77), 257 (24), 227 (20), 203
(18), 165 (27), 135 (24), 73 (51). HRMS (FAB) Calcd for
C25H25F3OSi: 426.1627. Found: 426.1607.
110.2, 113.3, 118.8, 124.0 (q, JC−F = 272.1 Hz), 124.9 (q, JC−F = 3.5
Hz), 127.1, 128.1, 129.0 (q, JC−F = 32 Hz), 131.1, 131.5, 131.6, 131.9,
132.4, 134.4, 139.6, 141.3, 142.4, 146.8, 148.3, 158.7. 19F{1H} NMR
(282 MHz, CDCl3, rt): δ −62.9. MS (EI) m/z (relative intensity): 456
(M+, 33), 455 (100), 436 (2), 353 (2), 278 (3), 277 (3), 266 (3), 264
(3), 239 (3), 218 (2). Anal. Calcd for C29H20NF3O: C, 76.47; H, 4.43;
N, 3.08%. Found: C, 76.53; H, 4.35, N, 3.02%.
X-ray Structural Analysis of 3, (Z)-5a, and 13. CCDC-931441
(3), CCDC-931442 [(Z)-5a], and CCDC-931443 (13) contain the
supplementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif, by e-mailing data_
request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ, U.K.; fax:
(+44) 1223-336-033.
ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental procedures; characterization data for all of the
compounds; and X-ray data for 3, (Z)-5a, and 13, including
CIFs. This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*ynishiha@okayama-u.ac.jp
■
Desilylbromination of 11a: Synthesis of (E)-1-Bromo-1-
phenyl-2-(4-trifluoromethylphenyl)-2-(4-methoxyphenyl)-
ethene (12). To a solution of 11a (212 mg, 0.43 mmol) in a 20 mL
Schlenk tube was added Br2 (0.64 mL, 0.64 mmol, 1.5 equiv, 1.0 M
CH2Cl2 solution) at −78 °C, followed by NaOMe (1.1 mL, 1.1 mmol,
1.0 M MeOH solution). After being stirred for 5 min at −78 °C, the
reaction mixture was allowed to warm slowly to room temperature,
stirred for another 2 h, quenched with H2O, and extracted with Et2O
(10 mL × 2). Evaporation and column chromatography (hexane/ethyl
acetate = 20:1) yielded a viscous oil. Recrystallization from Et2O/
hexane afforded the title compound 12 (112 mg, 0.26 mmol, 60%) as a
white solid. Mp = 97−98 °C. Rf = 0.30 (hexane/ethyl acetate = 20:1).
FT-IR (KBr, cm−1): 833 (m), 1066 (m), 1122 (s), 1165 (m), 1250 (s),
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was partially supported by the MEXT program for
promoting the enhancement of research universities. The
authors gratefully thank Dr. Masayuki Iwasaki (Okayama
University) for the HRMS measurements, Ms. Megumi Kosaka
and Mr. Motonari Kobayashi (Department of Instrumental
Analysis, Advanced Science Research Center, Okayama
University) for the elemental analyses, and the SC-NMR
Laboratory of Okayama University for the NMR measure-
ments. Y.N. is grateful to JNC Petrochemical Corporation for a
generous donation of trimethylsilylacetylene and also acknowl-
edges The Sumitomo Foundation.
1
1327 (s), 1510 (m), 1605 (m). H NMR (300 MHz, CDCl3, rt): δ
3.71 (s, 3H), 6.62 (d, J = 9 Hz, 2H), 6.84 (d, J = 9 Hz, 2H), 7.20−7.25
(m, 3H), 7.33−7.36 (m, 2H), 7.50 (d, J = 8.1 Hz, 2H), 7.65 (d, J = 8.1
Hz, 2H). 13C{1H} NMR (150 MHz, CDCl3, rt): δ 55.1, 113.4, 122.1,
124.1 (q, JC−F = 272.1 Hz), 125.2 (q, JC−F = 3.3 Hz), 128.09, 128.12,
129.4 (q, JC−F = 32.6 Hz), 130.0, 130.2, 131.6, 132.6, 140.8, 141.8,
147.5, 158.7. 19F{1H} NMR (282 MHz, CDCl3, rt): δ −62.9. MS (EI)
m/z (relative intensity): 434 (M+, 60), 432 (59), 354 (25), 353 (100),
252 (18), 239 (21). Anal. Calcd for C22H16BrF3O: C, 60.99; H, 3.72%.
Found: C, 60.87; H, 3.48%.
REFERENCES
■
(1) (a) Negishi, E.; Abramovitch, A. Tetrahedron Lett. 1977, 18, 411.
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Suzuki−Miyaura Cross-Coupling Reaction of 12 with 4-
Cyanophenylboronic Acid: Synthesis of (E)-1-(4-Cyanophenyl)-
1-phenyl-2-(4-trifluoromethylphenyl)-2-(4-methoxyphenyl)-
ethene (13). To a yellow solution of Pd(PPh3)4 (5 mg, 0.004 mmol, 2
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mg, 0.2 mmol), 4-cyanophenylboronic acid (44 mg, 0.3 mmol, 1.5
equiv), tetrabutylammonium bromide (TBAB) (6 mg, 0.02 mmol, 10
mol %), and 2 M K2CO3 aqueous solution (0.3 mL, 0.6 mmol, 3
equiv) at room temperature under an Ar atmosphere. The reaction
mixture was heated to 90 °C and stirred for 12 h. After the reaction
was complete, the reaction mixture was quenched with sat. NH4Cl
solution and then extracted with diethyl ether (20 mL × 2). The
combined ethereal layers were washed with brine and dried over
MgSO4. Filtration, evaporation, and silica gel chromatography
(hexane/ethyl acetate = 20:1) gave 13 (81 mg, 0.18 mmol, 89%) as
a pale-yellow fluffy solid. Mp = 135−136 °C. Rf = 0.18 (hexane/ethyl
acetate = 20:1). FT-IR (KBr, cm−1): 833 (m), 1066 (m), 1126 (s),
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1
1165 (m), 1247 (s), 1323 (s), 1506 (m), 1602 (m), 2227 (w). H
NMR (300 MHz, CDCl3, rt): δ 3.75 (s, 3H), 6.67 (d, J = 9 Hz, 2H),
6.90 (d, J = 9 Hz, 2H), 6.99−7.03 (m, 2H), 7.09−7.19 (m, 7H), 7.40
(d, J = 8.1 Hz, 4H). 13C{1H} NMR (150 MHz, CDCl3, rt): δ 55.1,
294
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The Journal of Organic Chemistry
Article
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