Hydroboration and Diboration of Internal Alkynes Catalyzed by a Well-Defined Low-Valent Cobalt Catalyst

Article abstract of DOI:10.1055/s-0036-1588996

The use of a simple well-defined low-valent cobalt(I) catalyst [HCo(PMe ₃) ₄ ] capable of performing the regio- and stereoselective hydroboration of internal alkynes is reported. Extension to the diboration of internal alkynes is also related using the same reaction conditions.

Full text of DOI:10.1055/s-0036-1588996

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2017, 49, A–J
special topic
A
en
L. Ferrand et al.
Special Topic
Synthesis
Hydroboration and Diboration of Internal Alkynes Catalyzed by a
Well-Defined Low-Valent Cobalt Catalyst
Laura Ferrand
regio- and stereoselective
simple well-defined cobalt complex
no excess of borane reagents
Ye Lyu
Alejandro Rivera-Hernández
Brendan J. Fallon
Muriel Amatore
same conditions for mono- or diboration
HCo(PMe3)4 (5 mol%)
HCo(PMe3)4 (5 mol%)
H
Bpin
R2
PinB
R1
Bpin
R2
R1
R2
B2Pin2 (1.05 equiv)
toluene, 110–160 °C
6 h
HBPin (1.05 equiv)
toluene, 110–160 °C
0.5 h
R1
Corinne Aubert
Marc Petit*
15–78%
41–87%
= alkyl, silyl, (hetero)aryl, ester
R
5 examples
17 examples
Sorbonne Universités, UPMC Université Paris 06, Institut
Parisien de Chimie Moléculaire, UMR CNRS 8232, Case 229,
4 Place Jussieu, 75252 Paris Cedex 05, France
marc.petit@upmc.fr
Published as part of the Special Topic Cobalt in Organic Syn-
thesis
Received: 13.02.2017
Accepted after revision: 17.03.2017
Published online: 06.04.2017
Previous work :
a. Chirik
DOI: 10.1055/s-0036-1588996; Art ID: ss-2017-c0089-st
(
CyADPI)CoMe
N
R
Cy
N
Co
R
BPin
HBPin, 23 °C, 6 h
N
Abstract The use of a simple well-defined low-valent cobalt(I) catalyst
[HCo(PMe3)4] capable of performing the regio- and stereoselective hy-
droboration of internal alkynes is reported. Extension to the diboration
of internal alkynes is also related using the same reaction conditions.
Cy
Z-selective
CH3
(
CyADPI)CoMe
no internal alkynes, sophisticated ligands
b. Lin & Marder
Co(PMe3)4
CatB
Ar
BCat
Ar
Key words cobalt, hydroboration, diboration, regioselectivity, low-
valent
Ar
Ar
B2Cat2, 80 °C, 24 h
Ar = 4-CF3-C6H4
Transition-metal-catalyzed hydroboration and dibora-
tion of alkynes represent one of the most straightforward
methods to obtain valuable alkenyl organoboron com-
pounds.1 There have been several reports on group 10-cata-
lyzed hydroboration and diboration of alkynes using ex-
pensive metals such as Pd and Pt.2 Over the last decades re-
ports on copper-catalyzed borylation of alkynes had seen
an exponential increase. Significant levels of control in both
the stereo- and regioselectivity have been obtained, howev-
er, this often requires the use of expensive ligands such as
N-heterocycle carbenes.3 In comparison, catalysis using
other earth abundant metals such as Fe4 and Co remains
rare. Chirik has reported the stereo- and regioselective hyd-
roboration of terminal alkynes using a cobalt complex bear-
ing a functionalized, non-innocent, bis(imino)pyridine li-
gand (Scheme 1, a).5,6 In 2006, Lin and Marder studied the
reactivity of cobalt boryl complexes, and reported the only
example of cobalt-catalyzed diboration of alkynes, howev-
er, no yield was reported (Scheme 1, b).7
one example, no yield, no ratio for isomers
PinB
Bpin
This work :
HCo(PMe3)4
R1
R2
Bpin
R2
R1
R2
or
PinB–BPin or HBPin
H
toluene, 110–160 °C
0.5 h
R1
regio- and stereoselective, simple cobalt complex
Scheme 1 Cobalt-catalyzed hydroboration of alkynes
was an efficient catalyst for the highly regio- and stereose-
lective hydrosilylation of unsymmetrical alkynes through a
hydrocobaltation mechanism.10 Herein we report, the dibo-
ration and hydroboration of internal alkynes using a well-
defined cobalt catalyst. The present study is notable for a
number of features: (i) good to high regio- and stereoselec-
tivies have been obtained for unsymmetrical alkynes, (ii)
regioselectivities are opposite compare to our previously
reported hydrosilylation reaction, (iii) diboration is accessi-
ble using the same catalyst and reaction conditions, and (iv)
the catalyst is inexpensive and can be synthesized in one
step on gram scale.
Our group has been interested in the application of two
well-defined simple low-valent cobalt complexes,
HCo(PMe3)4 and Co(PMe3)4 toward cycloaddition8 and C–H
functionalization.9 Recently, we reported that HCo(PMe3)4
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–J

B
L. Ferrand et al.
Special Topic
Synthesis
To begin this study, the ability of complexes Co(PMe3)4
and HCo(PMe3)4 to perform the hydroboration of diphenyl-
acetylene (1a) in the presence of HBpin (pinacolborane)
was first examined. The results are shown in Table 1. Both
complexes are capable of catalyzing the reaction with a
loading of 5 mol% in the presence of a slight excess of HBpin
(1.05 equiv). The reaction can be performed either at 110 °C
in 18 hours (Table 1, entries 1 and 2) or at 160 °C in 30 min-
utes (entries 3 and 4) to give the desired alkenyl borane in
good yields. Blank reactions without catalyst in thermal
conditions (entry 5) or in the presence of 20 mol% of PMe3
(entry 6) were carried out in order to show the necessity of
the cobalt catalyst. Based on our previous studies the use of
microwave conditions was also explored, but no significant
increases in the yield were observed (entries 7 and 8). Due
to its easy synthesis and its usefulness in mechanism inter-
pretation HCo(PMe3)4 was chosen as catalyst for the follow-
ing study.
seems to have an effect on the yield, but only a slight effect
on the regioselectivity, which was observed to be lower in
the presence of an electron-withdrawing group (entries 2
and 3). Next, the reactivity of TMS-protected alkynes 1e–k
was examined. Previous reports on the hydroboration of
similar alkynes indicated that both regioisomers 3 and 3′
could be selectively obtained. Under our reaction condi-
tions, the hydroboration of TMS-protected arylacetylenes
1e–i (entries 4–8) led in good yields and complete regiose-
lectivity toward the adduct of type 3, that is, with the boron
atom close to the larger group. The catalytic system also al-
lowed the use of heteroatoms with TMS-protected pyridyl-
alkynes 1j and 1k, providing only the products of type 3 in
moderate to good yields (entries 9 and 10). Surprisingly,
compound 3j and 3k have the opposite stereochemistry,
with the cis- or Z-isomer for the 3-pyridyl group and the
trans- or E-isomer for the 2-pyridyl group. The position of
the nitrogen in the newly-formed alkenyl boronate 3k
would be favorable for a chelation of the cobalt complex
that could catalyze a post-isomerization pathway. The reac-
tion of non-sterically differentiated unsymmetrical alkynes
but bearing electronically distinct substituents (1l and 1m)
gave, respectively, a 57:43 and 40:60 mixtures of vinylbo-
ranes of type 3 and 3′ (entries 11–12). These latter results
imply that the regio- and stereocontrol of the reaction are
predominantly governed by steric factors of the starting
substrates, while electronic factors have no significant ef-
fect on the outcome of the reaction. On the other hand,
adding two methyl groups in the ortho-position on a phenyl
ring generates a steric bulk on one side of the alkyne, which
counter intuitively directs the addition of the boron atom to
the sterically hindered carbon to give product 3n (entry
13). This result suggests that the mechanism is not going
through a hydrocobaltation pathway that should give obvi-
ously the other regioisomer. Finally, the use of ester-substi-
tuted substrates 1o, 1p, and 1q in the hydroboration with
HBpin yields solely the product of type 3, presumably due
to the chelating effect of the ester, which appears to over-
come the steric control (entries 14–16).11 Previous reports
have shown that phosphines can be used as organocatalysts
for the silaboration or diboration of alkynoates.12 In order to
establish if the phosphine presumably liberated from our
complex was the catalyst of the non-described hydrobora-
tion of alkynoates, the reactions were reproduced without
cobalt using 20 mol% of trimethylphosphine as potential or-
ganocatalyst. For 1o the yield, the regio- and stereoselectiv-
ities are identical suggesting that the cobalt catalyst is not
involved in this special case. However, for the two other
alkynoates 1p and 1q, HCo(PMe3)4 allows better reactivity
with an increase of the yields.
Table 1 Optimization of the Hydroboration Reaction
[Co] (5 mol%)a
PinB
H
+
Ph
HBpin
Ph
toluene, T °C, time
Ph
Ph
1a
2
(Z/E)-3a
Entry [Co]
Temp (°C)
Time (h) Yield (%)b Z/Ec
1
2
3
4
5
6
7
8
HCo(PMe3)4
Co(PMe3)4
HCo(PMe3)4
Co(PMe3)4
–
110
18
18
78
87
85
78
n.r.
n.r.
85
82
110
160
0.5
160
0.5
0.5
0.5
0.5
0.5
160
PMe3 (20 mol%)
HCo(PMe3)4
Co(PMe3)4
160
160 (MW)d
160 (MW)d
a Diphenylacetylene (0.5 mmol), HBPin (1.05 equiv, 0.52 mmol).
b Isolated yields; n.r. = no reaction.
c Z/E ratio determined by 1H NMR analysis was always around 85:15.
d MW = microwave.
Our attention was then turned to the more challenging
hydroboration of unsymmetrical internal alkynes (Table 2).
These alkynes were substituted by functional groups with
different degrees of steric hindrance, described as RS
(smaller group) and RL (larger group). Using less reactive
alkynes such as alkyne 1b the desired product was not ob-
tained at 110 °C. Thus, the optimal reaction conditions
were established at 160 °C for 0.5 hour in toluene to give
55% yield of the alkenyl borane 3b (Table 2, entry 1). Prod-
ucts from the hydroboration of 1-arylhex-1-ynes were iso-
lated in 46% and 73% yield, respectively, for the 4-MeO- and
4-F3C-substituted aryls (entries 2 and 3). The syn-adducts
3c and 3d (product of type 3 with the boron atom posi-
tioned close to the larger substituent) are the major iso-
mers. Variation of the electronics on the phenyl moiety
It is worth noting that the regioselectivity observed in
the hydroboration reaction is opposite to the one we previ-
ously reported for the hydrosilylation using the exact same
reaction conditions (catalyst, temperature, and solvent).
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–J

C
L. Ferrand et al.
Special Topic
Synthesis
This in combination with the result observed from entry 13
in Table 2 strongly suggests that the mechanism is different
and does not involve a hydrocobaltation pathway.13
pound without catalyst (entry 6). Finally, using trimethyl-
phosphine as organocatalyst, no conversion occurred (entry
7).
Table 2 Hydroboration of Unsymmetrical Alkynes
Table 3 Optimization of the Diboration Reaction
H
BPin
RL
PinB
RS
H
HCo(PMe3)4 (5 mol%)
PinB
Ph
BPin
Ph
[Co] (5 mol%)a
Rs
RL
+
Ph
Ph
+
B2pin2
HBpin (1.05 equiv)
toluene, 160 °C, 0.5 h
1
RS
RL
toluene, T °C, time
1a
4
(Z/E)-5a
(Z/E)-3
(Z/E)-3'
Yield (%)b,c
(Z/E)-3/
(Z/E)-3′b
Yield
(%)a
Entry
[Co] or catalyst
Temp (°C)
Time (h)
Entry
1
RS
RL
1
2
3
4
5
6
7
HCo(PMe3)4
Co(PMe3)4
HCo(PMe3)4
Co(PMe3)4
HCo(PMe3)4
–
110
110
160
160
160
160
160
18
18
0.5
0.5
6
50
37
30
31
52
n.r.
n.r.
1
2
1b
1c
1d
1e
1f
n-Pr
n-Pr
55
46
73
71
57
85
66
75
41
68
58
68
69
63
100 (Z):0
85 (Z):15 (Z)
65 (Z):35 (Z)
100 (Z):0d
100 (Z):0d
100 (Z):0
100 (Z):0
100 (Z):0
100 (Z):0
100 (E):0
57 (Z):43
40:60 (Z)
87 (Z):13
4-MeOC6H4
4-F3CC6H4
Ph
n-Bu
n-Bu
TMS
TMS
TMS
TMS
3
4c
5
4-MeOC6H4
4-F3CC6H4
3,5-(MeO)2C6H3
6
6
1g
1h
1i
PMe3
6
7
a Diphenylacetylene (0.5 mmol), B2Pin2 (1.05 equiv, 0.52 mmol).
b Isolated yields; n.r. = no reaction.
8
6-methoxynaphthyl TMS
c Z/E ratio was not determined in the optimization study.
9
1j
3-pyridyl
2-pyridyl
Ph
TMS
TMS
Next our attention turned to the diboration of various
alkynes and we studied the Z/E ratio of the alkenyl diborane
compounds 5 (Table 4). Symmetrical alkyne 1a and unsym-
metrical alkynes 1e and 1g gave the desired compounds 5a,
5e, and 5g in moderate to good yields with a stereoselectiv-
ity around 70:30 in favor of the syn addition of the diboron
moiety (Table 4, entries 1–3). For alkynes 1c and 1d bearing
an alkyl group, yields decreased to 29% and 15% and only Z-
isomers are isolated (entries 4 and 5). Alkyne 1b did not de-
liver the desired product under our reaction conditions,
rather complete degradation of the starting material was
observed. Generally, when alkynes are less reactive, due to
the high temperature and the longer reaction times neces-
10
11
12
13
14e
1k
1l
4-F3CC6H4
4-MeOC6H4
2,4,6-Me3C6H2
n-Bu
1m
1n
1o
Ph
Ph
CO2Me
100
(38/62):0
15f
1p
CO2Et
CO2Et
TMS
Ph
61
47
100 (E):0
100 (E)/0
16g 1q
a Isolated yields.
b Regio- and stereoselectivities were determined by 1H and NOESY NMR
analyses (see SI).
c Blank reaction without catalyst gives no conversion.
d Stereochemistry of 1e and 1f was confirmed after protodesilylation to
produce 6e and 6f.
e Reaction with 20% of PMe3 as catalyst gives the same yield and ratio.
f Reaction with 20% of PMe3 as catalyst gives only traces of the desired com-
pound.
Table 4 Diboration of Internal Alkynes
g Reaction with 20% of PMe3 as catalyst gives a lower yield of 30%.
PinB
BPin
R2
PinB
R2
HCo(PMe3)4 (5 mol%)
R1
R2
+
We next decided to study the diboration of alkynes as
initiated by Lin and Marder using Co(PMe3)4.7b Indeed, al-
though diboration is well described using expensive metal
(Pt or Pd),14 this process using more accessible metals such
as Cu,15 Fe16 and Co7b remains sparse with only one example
for each metal.
We first screened the reaction conditions using both
catalysts with different temperatures and reaction times
(Table 3). It appears that HCo(PMe3)4 was the most efficient
in the diboration process compared to Co(PMe3)4 (Table 3,
entries 1, 3 vs entries 2, 4). It is important to note that the
diboration process is slower than the hydroboration and a
time of 6 hours at 160 °C is necessary to reach decent yields
(entry 5). The reaction does not provide the desired com-
B2Pin2 (1.05 equiv),
toluene, 160 °C, 6 h
1
R1
R1
(E)-5
BPin
(Z)-5
Entry
Alkyne
Yield (%)a 5 (Z)/5 (E)b
R1
R2
1
2
3
4
5
6
1a
1e
1g
1c
1d
1b
Ph
Ph
52
70
58
29
15
n.r.
75:25
65:35
68:32
100:0
100:0
–
Ph
TMS
TMS
n-Bu
n-Bu
n-Pr
4-CF3C6H4
4-MeOC6H4
4-CF3C6H4
n-Pr
a Isolated yields; n.r. = no reaction.
b Z/E ratio determined by 1H NMR analysis.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–J

D
L. Ferrand et al.
Special Topic
Synthesis
sary for the diboration reaction, degradation of the alkynes
is observed and lower yields are obtained. The moderate se-
lectivity observed above is disappointing, due to the fact
that trans-diborylations are rare in the literature and often
reported as traces.17 In order to establish, if the trans-iso-
mers were obtained during the process or via post-isomeri-
zation, compound (Z)-5a was reintroduced in the reaction
conditions, in the presence and absence of HCo(PMe3)4 and
B2Pin2. In both cases, no traces of (E)-5a were observed sug-
gesting that the trans-isomer was obtained during the dibo-
ration pathway.
Hydroboration of Alkynes with Pinacolborane; General Procedure
A
In a glove box, a microwave reaction vial (0.5–2 mL) was charged with
HCo(PMe3)4 (18.2 mg, 0.05 mmol, 5 mol%) and then sealed. Next, a
degassed mixture of the corresponding alkyne (1.00 mmol, 1 equiv)
and pinacolborane (97%, 157 μL 1.05 mmol, 1.05 equiv) in toluene (1
mL) was added via syringe. The reaction mixture was heated in an oil
bath at 160 °C for 30 min. The mixture was diluted with petroleum
ether (2 mL), filtered through a plug of silica gel, and washed with
Et2O (3 × 10 mL). The crude product was purified by silica gel chroma-
tography (mixtures of pentane/Et2O as eluents) to afford the final
products.
In summary, we have demonstrated that a simple well-
defined low valent cobalt species HCo(PMe3)4 is an efficient
catalyst to access a wide variety of synthetically useful vinyl
boranes. We have reported the regio- and stereoselective
hydroboration of a variety of internal alkynes, and also suc-
cessfully managed to extend this methodology to the dibo-
ration of internal alkynes. The observed regioselectivity
seems to suggest the reaction does not proceed via a hydro-
cobaltation pathway as we previously reported for the hy-
drosilylation of alkynes using the same catalytic system.
This curiosity will be further explored in our future studies
with a full mechanistic investigation.
Diboration of Alkynes with Bis(pinacolato)diboron; General Pro-
cedure B
In a glove boxe, a microwave reaction vial (0.5–2 mL) was charged
with HCo(PMe3)4 (18.2 mg, 0.05 mmol, 5 mol%) and then sealed. Next,
a degassed mixture of the corresponding alkyne (1.00 mmol, 1 equiv)
and bis(pinacolato)diboron (97%, 266.6 mg, 1.05 mmol, 1.05 equiv) in
toluene (1 mL) was added via syringe. The reaction was heated in an
oil bath at 160 °C for 6 h. The reaction mixture was diluted with pe-
troleum ether (2 mL), filtered through a plug of silica gel and washed
with Et2O (3 × 10 ml). The crude product was purified by silica gel
chromatography (mixtures of pentane/Et2O as eluents) to afford the
final products.
(Z)-2-(1,2-Diphenylvinyl)-4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lane (3a)19
Unless otherwise mentioned, all reactions were carried out in oven-
dried glassware under argon atmosphere with magnetic stirring, and
all commercially available compounds were used as received. Toluene
was purified by mean of distillation under dry nitrogen atmosphere
on sodium benzophenone ketyl and degassed by sparging argon.
Chromatographic purification of products were accomplished using
force-flow chromatography on neutral Davisil 60 Å (40–63 μm; pH
7.3) silica gel according to the method of Still.18 TLC was performed
on Merck 60 F254 silica gel plates. TLC visualization was performed
by fluorescence quenching (λ = 254 nm), dipping in KMnO4, or p-ani-
saldehyde stains. Filtration through Celite were performed using Hyf-
lo Super Cel from Fluka. Organic solutions were concentrated under
reduced pressure on a Büchi rotary evaporator. 1H NMR spectra were
recorded on a Bruker 400 Avance or 300 Avance (400 and 300 MHz,
respectively) and are referenced relative to residual CDCl3 protons sig-
nals at δ 7.26 ppm. 13C NMR spectra were recorded on a Bruker 400
Avance or 300 Avance (100 and 75 MHz respectively) and are refer-
enced relative to CDCl3 at δ = 77.16. 11B and 19F NMR spectra were re-
corded on a Bruker 400 Avance (400 MHz) using pinacolborane (δ =
28.1) and trifluorotoluene (δ = –63.7), respectively, as external refer-
ence. Data are reported as follows: chemical shift (δ ppm), multiplici-
ty (standard abbreviations), coupling constant (J, Hz), and integration.
IR spectra were recorded on a Bruker Tensor 27 (ATR diamond) and
are reported in terms of frequency of absorption (cm–1). Melting
points were measured on a Kofler bench. High-resolution mass spec-
trometry (HRMS) analyses were performed at the IPCM on a Bruker
MicroTof mass spectrometer.
The general procedure A was applied to diphenylacetylene (1a; 180.0
mg, 1.00 mmol, 1 equiv) and the reaction mixture was heated in an
oil bath at 160 °C for 30 min. Purification by silica gel flash chroma-
tography (pentane/Et2O 99:1 to 98:2) afforded the title compound as
a white solid (261.0 mg, 85%) and as an 87:13 mixture of Z/E-isomers.
The major product, the Z-isomer 3a was isolated by flash chromatog-
raphy for characterization; mp 91–98 °C.
1H NMR (400 MHz, CDCl3): δ = 7.41 (s, 1 H), 7.32–7.27 (m, 2 H), 7.26–
7.20 (m, 3 H), 7.16–7.08 (m, 5 H), 1.35 (s, 12 H).
13C NMR (75 MHz, CDCl3): δ = 143.3, 140.6, 137.1, 130.1 (2 C), 129.0 (2
C), 128.4 (2 C), 128.0 (2 C), 127.7, 126.4, 83.9 (2 C), 24.9 (4 C). The car-
bon directly attached to the boron atom was not detected due to
quadrupolar relaxation.
11B NMR (128 MHz, CDCl3): δ = 30.6.
(Z)-4,4,5,5-Tetramethyl-2-(oct-4-en-4-yl)-1,3,2-dioxaborolane
(3b)20
The general procedure A was applied to oct-4-yne (1b; 147 μL, 1.00
mmol, 1 equiv) and the reaction mixture was heated in an oil bath at
160 °C for 30 min. Purification by silica gel flash chromatography
(pentane/Et2O 100:0 to 98:2) afforded the title compound 3b as a col-
orless oil (130.2 mg, 55%).
1H NMR (400 MHz, CDCl3): δ = 6.29 (t, J = 7.1 Hz, 1 H), 2.13–2.08 (m, 4
H), 1.44–1.33 (m, 4 H), 1.25 (s, 12 H), 0.93–0.88 (m, 6 H)
13C NMR (100 MHz, CDCl3): δ = 146.1, 83.1 (2 C), 30.8, 30.7, 24.9 (4 C),
23.5, 22.6, 14.2, 14.2. The carbon directly attached to the boron atom
was not detected due to quadrupolar relaxation.
The preparation and full characterization of compounds 1c–q were
reported previously.10
11B NMR (128 MHz, CDCl3): δ = 30.4.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–J

E
L. Ferrand et al.
Special Topic
Synthesis
(Z)-2-[1-(4-Methoxyphenyl)hex-1-en-2-yl]-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane (3c) and (Z)-2-[1-(4-Methoxyphenyl)hex-1-
en-1-yl]-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3′c)
3′d
1H NMR (400 MHz, CDCl3): δ = 7.56 (d, J = 10.0 Hz, 2 H), 7.23 (d, J = 8.0
Hz, 2 H), 6.65 (t, J = 7.4 Hz, 1 H), 2.11 (q, J = 7.4 Hz, 2 H), 1.49–1.24 (m,
4 H), 1.27 (s, 12 H), 0.84 (t, J = 7.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 144.4, 141.7, 129.4 (2 C), 124.9 (q, J =
3.8 Hz, 2 C), 83.8 (2 C), 31.5, 29.8, 24.9 (4 C), 22.6, 14.0. The carbon
directly attached to the boron atom was not detected due to quadru-
polar relaxation.
The general procedure A was applied to 1-(hex-1-yn-1-yl)-4-meth-
oxybenzene (1c; 188.3 mg, 1.00 mmol, 1 equiv) and the reaction mix-
ture was heated in an oil bath at 160 °C for 30 min. Purification by
silica gel flash chromatography (pentane/Et2O 99:1 to 97:3) afforded
an 85:15 mixture of the title compounds 3c/3′c as a colorless oil
(147.0 mg, 46%). The two products were isolated by an additional
flash chromatography for characterization.
11B NMR (128 MHz, CDCl3): δ = 32.1.
19F NMR (376 MHz, CDCl3): δ = –63.2.
3c
(Z)-Trimethyl[2-phenyl-1-(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)vinyl]silane (3e)
IR (ATR): 2976, 2930, 1607, 1508, 1347, 1246, 829 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.32–7.29 (m, 2 H), 7.15 (s, 1 H), 6.89–
6.85 (m, 2 H), 3.81 (s, 3 H), 2.40 (m, 2 H), 1.52–1.44 (m, 2 H), 1.41–
1.30 (m, 2 H), 1.30 (s, 12 H), 0.91 (t, J = 7.2 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 158.8, 141.3, 130.8, 130.6 (2 C), 113.6
(2 C), 83.4 (2 C), 55.3, 32.3, 29.3, 24.9 (4 C), 23.0, 14.2. The carbon di-
rectly attached to the boron atom was not detected due to quadrupo-
lar relaxation.
The general procedure A was applied to 1-phenyl-2-(trimethylsi-
lyl)acetylene (1e; 199 μL, 1.00 mmol, 1 equiv) and the reaction mix-
ture was heated in an oil bath at 160 °C for 30 min. Purification by
silica gel flash chromatography (pentane/Et2O 98:2) afforded the title
compound 3e as a yellowish oil (213.6 mg, 71%).
IR (ATR): 2981, 1569, 1446, 1319, 1246, 1142, 845 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 8.02 (s, 1 H), 7.31–7.21 (m, 5 H), 1.30
(s, 12 H), 0.00 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 157.2, 141.6, 128.4 (2 C), 127.8 (2 C),
127.6, 83.4 (2 C), 25.0 (4 C), 1.1 (3 C). The carbon directly attached to
the boron atom was not detected due to quadrupolar relaxation.
11B NMR (128 MHz, CDCl3): δ = 32.4.
HRMS (ESI): m/z calcd for C17H27BO2SiLi [M + Li]+: 309.2032; found:
11B NMR (128 MHz, CDCl3): δ = 30.8.
HRMS (ESI): m/z calcd for C19H29BO3Na [M + Na]+: 339.2105; found:
329.2106.
3′c
IR (ATR): 2923, 1604, 1511, 1244, 830 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.09–7.07 (m, 2 H), 6.87–6.84 (m, 2 H),
6.53 (t, J = 7.3 Hz, 1 H), 3.80 (s, 3 H), 2.16 (q, J = 7.3 Hz, 2 H), 1.43–1.27
(m, 4 H), 1.27 (s, 12 H), 0.84 (t, J = 7.2 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 157.9, 148.1, 132.7, 130.2 (2 C), 113.3
(2 C), 83.5 (2 C), 55.3, 31.7, 29.8, 24.9 (4 C), 22.7, 14.1. The carbon di-
rectly attached to the boron atom was not detected due to quadrupo-
lar relaxation.
309.2021.
(Z)-[2-(4-Methoxyphenyl)-1-(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)vinyl]trimethylsilane (3f)
The general procedure
A
was applied to [(4-methoxyphe-
nyl)ethynyl]trimethylsilane (1f; 204.3 mg, 1.00 mmol, 1 equiv) and
the reaction mixture was heated in an oil bath at 160 °C for 30 min.
Purification by silica gel flash chromatography (pentane/Et2O 98:2)
afforded the title compound 3f as a white solid (189.4 mg, 57%); mp
85 °C.
11B NMR (128 MHz, CDCl3): δ = 30.2.
HRMS (ESI): m/z calcd for C19H29BO3Na [M + Na]+: 339.2105; found:
329.2114.
IR (ATR): 2985, 1606, 1557, 1504, 1466, 1308, 1241, 1139, 837, 760
cm–1
.
(Z)-4,4,5,5-Tetramethyl-2-{1-[4-(trifluoromethyl)phenyl]hex-1-
en-2-yl}-1,3,2-dioxaborolane (3d) and (Z)-4,4,5,5-Tetramethyl-2-
{1-[4-(trifluoromethyl)phenyl]hex-1-en-1-yl}-1,3,2-dioxaboro-
lane (3′d)
1H NMR (400 MHz, CDCl3): δ = 7.95 (s, 1 H), 7.22–7.20 (m, 2 H), 6.84–
6.82 (m, 2 H), 3.81 (s, 3 H), 1.29 (s, 12 H), 0.04 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 159.4, 156.9, 134.0, 130.0 (2 C), 113.2
(2 C), 83.3 (2 C), 55.4, 25.0 (4 C), 1.2 (3 C). The carbon directly at-
tached to the boron atom was not detected due to quadrupolar relax-
ation.
The general procedure A was applied to 1-(hex-1-yn-1-yl)-4-(trifluo-
romethyl)benzene (1d; 226.2 mg, 1.00 mmol, 1 equiv) and the reac-
tion mixture was heated in an oil bath at 160 °C for 30 min. Purifica-
tion by silica gel flash chromatography (pentane/Et2O 99:1 to 98:2)
afforded an inseparable 65:35 mixture of the title compounds 3d/3′d
as a colorless oil (259.7 mg, 73%).
11B NMR (128 MHz, CDCl3): δ = 31.5.
HRMS (ESI): m/z calcd for C18H29BO3SiLi [M + Li]+: 339.2137; found:
339.2131.
3d
1H NMR (400 MHz, CDCl3): δ = 7.58 (d, J = 8.3 Hz, 2 H), 7.39 (d, J = 8.3
Hz, 2 H), 7.20 (s, 1 H), 2.34 (m, 2 H), 1.49–1.24 (m, 4 H), 1.31 (s, 12 H),
0.88 (t, J = 7.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 150.0, 140.1, 129.2 (2 C), 125.2 (q, J =
3.8 Hz, 2 C), 83.7 (2 C), 32.2, 29.4, 24.9 (4 C), 22.9, 14.1. The carbon
directly attached to the boron atom was not detected due to quadru-
polar relaxation.
(Z)-Trimethyl{1-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2-
[(4-(trifluoromethyl)phenyl]vinyl}silane (3g)
The general procedure A was applied to trimethyl{[4-(trifluorometh-
yl)phenyl]ethynyl}silane (1g; 242.3 mg, 1.00 mmol, 1 equiv) and the
reaction mixture was heated in an oil bath at 160 °C for 30 min. Puri-
fication by silica gel flash chromatography (pentane/EtOAc 98:2) af-
forded the title compound 3g as a white solid (314.0 mg, 85%); mp
81 °C.
11B NMR (128 MHz, CDCl3): δ = 32.1.
19F NMR (376 MHz, CDCl3): δ = –63.4.
IR (ATR): 2982, 1577, 1312, 1156, 1109, 1057, 833, 759 cm–1
.
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L. Ferrand et al.
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Synthesis
1H NMR (400 MHz, CDCl3): δ = 7.97 (s, 1 H), 7.55 (d, J = 8.1 Hz, 2 H),
7.34 (d, J = 8.5 Hz, 2 H), 1.31 (s, 12 H), –0.01 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 155.1, 145.1, 129.6 (q, J = 32.4 Hz),
128.6 (2 C), 124.8 (q, J = 3.7 Hz, 2 C), 124.4 (q, J = 270 MHz), 83.6 (2 C),
25.0 (4 C), 1.0 (3 C). The carbon directly attached to the boron atom
was not detected due to quadrupolar relaxation.
11B NMR (128 MHz, CDCl3): δ = 32.6.
19F NMR (376 MHz, CDCl3): δ = –63.4.
HRMS (ESI): m/z calcd for C18H26BF3O2SiNa [M + Na]+: 393.1643;
IR (ATR): 2980, 1590, 1470, 1325, 1311, 1247, 1141, 836 cm–1
1H NMR (400 MHz, CDCl3): δ = 8.51 (m, 2 H), 7.91 (s, 1 H), 7.55–7.52
(m, 1 H), 7.22 (dd, J = 7.7, 4.8 Hz, 1 H), 1.30 (s, 12 H), 0.00 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 152.7, 149.3, 148.7, 137.0, 135.4,
122.8, 83.6 (2 C), 25.0 (4 C), 1.0 (3 C). The carbon directly attached to
the boron atom was not detected due to quadrupolar relaxation.
.
11B NMR (128 MHz, CDCl3): δ = 32.2.
HRMS (ESI): m/z calcd for C16H27BNO2Si [M + H]+: 304.1902; found:
304.1900.
found: 393.1641.
(E)-2-[1-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-2-(tri-
(Z)-[2-(3,5-Dimethoxyphenyl)-1-(4,4,5,5-tetramethyl-1,3,2-dioxa-
methylsilyl)vinyl]pyridine (3k)
borolan-2-yl)vinyl]trimethylsilane (3h)
The general procedure
A
was applied to 2-[(trimethylsi-
The general procedure
A
was applied to [(3,5-dimethoxyphe-
lyl)ethynyl]pyridine (1k; 175.3 mg, 1.00 mmol, 1 equiv) and the reac-
tion mixture was heated in an oil bath at 160 °C for 30 min. Purifica-
tion by silica gel flash chromatography (pentane/Et2O 80:20 to 70:30)
afforded the title compound 3k as a brown oil (205.8 mg, 68%).
nyl)ethynyl]trimethylsilane (1h; 234.4 mg, 1.00 mmol, 1 equiv) and
the reaction mixture was heated in an oil bath at 160 °C for 30 min.
Purification by silica gel flash chromatography (pentane/Et2O 97:3)
afforded the title compound 3h as a colorless oil (240.0 mg, 66%).
IR (ATR): 2982, 1598, 1459, 1317, 1302, 1243, 1147, 840 cm–1
1H NMR (400 MHz, CDCl3): δ = 7.93 (s, 1 H), 6.42 (m, 2 H), 6.37 (t, J =
IR (ATR): 2974, 1582, 1473, 1289, 1244, 1140, 833 cm–1
.
.
1H NMR (400 MHz, CDCl3): δ = 8.49 (d, J = 4.9 Hz, 1 H), 7.66 (td, J = 7.6,
1.7 Hz, 1 H), 7.16–7.11 (m, 2 H), 7.03 (s, 1 H), 1.39 (s, 12 H), 0.22 (s, 9
H).
2.3 Hz, 1 H), 3.77 (s, 6 H), 1.30 (s, 12 H), 0.04 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 160.3 (2 C), 156.9, 143.6, 106.3 (2 C),
100.2, 83.4 (2 C), 55.5 (2 C), 25.0 (4 C), 1.0 (3 C). The carbon directly
attached to the boron atom was not detected due to quadrupolar re-
laxation.
11B NMR (128 MHz, CDCl3): δ = 31.4.
HRMS (ESI): m/z calcd for C19H31BO4SiNa [M + Na]+: 385.1981; found:
13C NMR (100 MHz, CDCl3): δ = 155.4, 146.6, 143.7, 138.3, 122.2,
122.1, 82.5 (2 C), 26.2 (4 C), –0.8 (3 C). The carbon directly attached to
the boron atom was not detected due to quadrupolar relaxation.
11B NMR (128 MHz, CDCl3): δ = 27.0.
HRMS (ESI): m/z calcd for C16H27BNO2Si [M + H]+: 304.1902; found:
304.1911.
385.1983.
(Z)-4,4,5,5-Tetramethyl-2-{2-phenyl-1-[4-(trifluoromethyl)phe-
nyl]vinyl}-1,3,2-dioxaborolane (3l) and 4,4,5,5-Tetramethyl-2-{1-
phenyl-2-[4-(trifluoromethyl)phenyl]vinyl}-1,3,2-dioxaborolane
(3′l)
(Z)-[2-(6-Methoxynaphthalen-2-yl)-1-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)vinyl]trimethylsilane (3i)
The general procedure A was applied to [(6-methoxynaphthalen-2-
yl)ethynyl]trimethylsilane (1i; 254.4 mg, 1.00 mmol, 1 equiv) and the
reaction mixture was heated in an oil bath at 160 °C for 30 min. Puri-
fication by silica gel flash chromatography (pentane/Et2O 98:2 to
95:5) afforded the title compound 3i as a white solid (285.5 mg, 75%);
mp 102–103 °C.
The general procedure A was applied to 1-(phenylethynyl)-4-(trifluo-
romethyl)benzene (1l; 246.2 mg, 1.00 mmol, 1 equiv) and the reac-
tion mixture was heated in an oil bath at 160 °C for 30 min. Purifica-
tion by silica gel flash chromatography (pentane/Et2O 97:3) afforded
a 57:43 mixture of the title compounds 3l/3′l as a pale yellow solid
(216.7 mg, 58%). The major product was isolated by flash chromatog-
raphy for characterization.
IR (ATR): 2972, 1571, 1313, 1262, 1138, 838 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 8.14 (s, 1 H), 7.72–7.67 (m, 3 H), 7.39
(dd, J = 8.5, 1.5 Hz, 1 H), 7.16–7.12 (m, 2 H), 3.92 (s, 3 H), 1.33 (s, 12
H), 0.05 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 158.0, 157.3, 136.8, 134.1, 129.8,
128.5, 127.5, 127.3, 126.2, 119.1, 105.9, 83.4 (2 C), 55.4, 25.0 (4 C), 1.2
(3 C). The carbon directly attached to the boron atom was not detect-
ed due to quadrupolar relaxation.
3l
Mp 112 °C.
IR (ATR): 2985, 1610, 1322, 1168, 1117, 1062, 850, 751, 694 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.51 (d, J = 8.0 Hz, 2 H), 7.45 (s, 1 H),
7.28 (d, J = 8.0 Hz, 2 H), 7.15–7.11 (m, 3 H), 7.04–7.02 (m, 2 H), 1.32 (s,
12 H).
11B NMR (128 MHz, CDCl3): δ = 31.5.
13C NMR (100 MHz, CDCl3): δ = 144.5, 136.5, 136.4, 129.9 (2 C), 129.3
(2 C), 128.0 (2 C), 128.0, 125.2 (q, J = 3.9 Hz, 2 C), 84.0 (2 C), 24.8 (4 C).
The carbon directly attached to the boron atom was not detected due
to quadrupolar relaxation.
HRMS (ESI): m/z calcd for C22H31BO3SiNa [M + Na]+: 405.2032; found:
405.2043.
(Z)-3-[2-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-2-(trimeth-
ylsilyl)vinyl]pyridine (3j)
11B NMR (128 MHz, CDCl3): δ = 31.8.
The general procedure
A
was applied to 3-[(trimethylsi-
HRMS (ESI): m/z calcd for C21H22BF3O2Na [M + Na]+: 397.1561; found:
lyl)ethynyl]pyridine (1j; 175.3 mg, 1.00 mmol, 1 equiv) and the reac-
tion mixture was heated in an oil bath at 160 °C for 30 min. Purifica-
tion by silica gel flash chromatography (pentane/Et2O 80:20 to 70:30)
afforded the title compound 3j as a colorless oil (125.4 mg, 41%).
397.1566.
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L. Ferrand et al.
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Synthesis
2-[1-(4-Methoxyphenyl)-2-phenylvinyl]-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane (3m) and (Z)-2-[2-(4-Methoxyphenyl)-1-phenylvi-
nyl]-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3′m)
Methyl 3-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)oct-2-
enoate (3o)
The general procedure A was applied to methyl oct-2-ynoate (1o; 168
μL, 1.00 mmol, 1 equiv) and the reaction mixture was heated in an oil
bath at 160 °C for 30 min. Purification by silica gel flash chromatogra-
phy (pentane/Et2O 95:5) afforded the title compound 3o as a colorless
oil (178.1 mg, 63%) and as a 38:62 mixture of Z/E-isomers. The two
isomers were separated by flash chromatography for characteriza-
tion.
The general procedure A was applied to 1-methoxy-4-(phenyl-
ethynyl)benzene (1m; 208.3 mg, 1.00 mmol, 1 equiv) and the reac-
tion mixture was heated in an oil bath at 160 °C for 30 min. Purifica-
tion by silica gel flash chromatography (pentane/Et2O 93:7) afforded
an inseparable 40:60 mixture of the title compounds 3m/3′m as a
white solid (228.2 mg, 68%).
3m
(Z)-3o
1H NMR (400 MHz, CDCl3): δ = 7.33 (s, 1 H), 7.30–7.29 (m, 2 H), 7.23–
7.21 (m, 2 H), 6.83–6.80 (m, 2 H), 3.80 (s, 3 H), 1.32 (s, 12 H); other
signals are overlapped with the major product.
IR (ATR): 2987, 2925, 1724, 1330, 1264, 1133 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 6.39 (s, 1 H), 3.70 (s, 3 H), 2.66 (m, 2 H),
1.45–1.38 (m, 2 H), 1.32–1.28 (m, 4 H), 1.26 (s, 12 H), 0.88 (m, 3 H).
13C NMR (100 MHz, CDCl3): δ = 158.1, 140.9, 137.2, 132.5, 130.1,
129.6, 127.8, 126.1, 113.7, 83.7; other signals are overlapped with the
major product. The stereoselectivity could not be assigned by NMR
analysis.
13C NMR (100 MHz, CDCl3): δ = 166.6, 129.3, 84.2 (2 C), 51.1, 32.0,
30.2, 29.4, 24.8 (4 C), 22.7, 14.1. The carbon directly attached to the
boron atom was not detected due to quadrupolar relaxation.
11B NMR (128 MHz, CDCl3): δ = 30.0.
HRMS (ESI): m/z calcd for C15H27BO4Na [M + Na]+: 305.1897; found:
305.1888.
3′m
1H NMR (400 MHz, CDCl3): δ = 7.31 (s, 1 H), 7.20–7.17 (m, 2 H), 7.14–
7.08 (m, 3 H), 7.02–6.99 (m, 2 H), 6.67–6.63 (m, 2 H), 3.74 (s, 3 H),
1.30 (s, 12 H).
13C NMR (100 MHz, CDCl3): δ = 159.0, 142.7, 142.7, 131.5, 129.9,
128.8, 128.3, 127.4, 113.3, 83.6, 55.1, 24.8. The carbon directly at-
tached to the boron atom was not detected due to quadrupolar relax-
ation.
(E)-3o
IR (ATR): 2986, 2926, 1715, 1305, 1137 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 6.00 (s, 1 H), 3.71 (s, 3 H), 2.27 (m, 2 H),
1.51–1.45 (m, 2 H), 1.35 (s, 12 H), 1.31–1.25 (m, 4 H), 0.88 (m, 3 H).
13C NMR (100 MHz, CDCl3): δ = 168.3, 125.6, 84.1 (2 C), 51.7, 35.9,
31.6, 27.8, 25.0 (4 C), 22.5, 14.1. The carbon directly attached to the
boron atom was not detected due to quadrupolar relaxation.
11B NMR (128 MHz, CDCl3): δ = 31.8.
(Z)-2-(1-Mesityl-2-phenylvinyl)-4,4,5,5-tetramethyl-1,3,2-dioxa-
borolane (3n) and 2-(2-Mesityl-1-phenylvinyl)-4,4,5,5-tetrameth-
yl-1,3,2-dioxaborolane (3′n)
11B NMR (128 MHz, CDCl3): δ = 30.3.
HRMS (ESI): m/z calcd for C15H27BO4Li [M + Li]+: 289.2160; found:
289.2150.
The general procedure A was applied to 1,3,5-trimethyl-2-(phenyl-
ethynyl)benzene (1n; 220.3 mg, 1.00 mmol, 1 equiv) and the reaction
mixture was heated in an oil bath at 160 °C for 30 min. Purification by
silica gel flash chromatography (pentane/Et2O 93:7) afforded an in-
separable 87:13 mixture of the title compounds 3n/3′n as a white
solid (240.8 mg, 69%).
Ethyl (E)-3-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-3-
(trimethylsilyl)acrylate (3p)
The general procedure A was applied to ethyl 3-(trimethylsilyl)propi-
olate (1p; 170.3 mg, 1.00 mmol, 1 equiv) and the reaction mixture
was heated in an oil bath at 160 °C for 30 min. Purification by silica
gel flash chromatography (pentane/Et2O 94:6) afforded the title com-
pound 3p as a pale yellow oil (181.9 mg, 61%).
3n
1H NMR (400 MHz, CDCl3): δ = 7.43 (s, 1 H), 7.16–7.11 (m, 3 H), 7.04–
6.99 (m, 2 H), 6.90 (s, 2 H), 2.34 (s, 3 H), 2.08 (s, 6 H), 1.31 (s, 12 H).
13C NMR (100 MHz, CDCl3): δ = 143.0, 137.5, 136.7, 135.3, 134.3,
129.1, 128.4, 128.1, 127.9, 83.5, 24.6, 21.2, 20.1. The carbon directly
attached to the boron atom was not detected due to quadrupolar re-
laxation.
IR (ATR): 2983, 1716, 1598, 1345, 1299, 1251, 1190, 1139, 842, 757
cm–1
.
1H NMR (400 MHz, CDCl3): δ = 6.39 (s, 1 H), 4.19 (q, J = 7.1 Hz, 2 H),
1.36 (s, 12 H), 1.27 (t, J = 7.1 Hz, 3 H), 0.16 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 166.5, 137.0, 84.0 (2 C), 60.8, 25.3 (4
C), 14.4, –1.4 (3 C). The carbon directly attached to the boron atom
was not detected due to quadrupolar relaxation.
11B NMR (128 MHz, CDCl3): δ = 31.4.
11B NMR (128 MHz, CDCl3): δ = 31.7.
HRMS (ESI): m/z calcd for C14H27BO4SiNa [M + Na]+: 321.1667; found:
3′n
1H NMR (400 MHz, CDCl3): δ = 6.75 (s, 2 H), 2.25 (s, 3 H), 2.03 (s, 6 H),
1.38 (s, 12 H); other signals are overlapped with the major product.
321.1672.
13C NMR (100 MHz, CDCl3): δ = 143.4, 140.2, 136.1, 135.2, 134.2,
128.7, 127.9, 127.5, 126.1, 83.7, 24.8, 21.0, 20.2. The carbon directly
attached to the boron atom was not detected due to quadrupolar re-
laxation. The stereoselectivity could not be assigned by NMR analysis.
Ethyl (E)-3-Phenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)acrylate (3q)21
The general procedure A was applied to ethyl 3-phenylpropiolate 1q
(168 μL, 1.00 mmol, 1 equiv) and the reaction mixture was heated in
an oil bath at 160 °C for 30 min. Purification by silica gel flash chro-
matography (pentane/Et2O 90:10) afforded the title compound 3q as
a yellowish oil (140.7 mg, 47%).
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–J

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L. Ferrand et al.
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Synthesis
1H NMR (400 MHz, CDCl3): δ = 7.51–7.48 (m, 2 H), 7.38–7.32 (m, 3 H),
HRMS (ESI): m/z calcd for C25H40B2O5Na [M + Na]+: 465.2962; found:
6.43 (s, 1 H), 4.26 (q, J = 7.1 Hz, 2 H), 1.42 (s, 12 H), 1.31 (t, J = 7.2 Hz, 3
465.2977.
H).
13C NMR (100 MHz, CDCl3): δ = 168.2, 138.8, 129.2, 128.8 (2 C), 127.3
(2 C), 126.2, 84.5 (2 C), 60.9, 25.2 (4 C), 14.4. The carbon directly at-
tached to the boron atom was not detected due to quadrupolar relax-
ation.
(Z)-2,2′-{1-[4-(Trifluoromethyl)phenyl]hex-1-ene-1,2-di-
yl}bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) (5d)
The general procedure B was applied to 1-(hex-1-yn-1-yl)-4-(trifluo-
romethyl)benzene (1d; 226.2 mg, 1.00 mmol, 1 equiv) and the reac-
tion mixture was heated in an oil bath at 160 °C for 6 h. Purification
by silica gel flash chromatography (pentane/Et2O 100:0 to 90:10) af-
forded the title compound 5d as a white solid (72.8 mg, 15%); mp 97–
98 °C.
11B NMR (128 MHz, CDCl3): δ = 30.1.
(Z)-1,2-Diphenyl-1,2-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
2-yl)ethane and (E)-1,2-Diphenyl-1,2-bis(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)ethane [(Z/E)-5a]
IR (ATR): 2986, 2927, 1602, 1466, 1321, 1267, 1119, 847 cm–1
.
The general procedure B was applied to diphenylacetylene (1a; 180.0
mg, 1.00 mmol, 1 equiv) and the reaction mixture was heated in an
oil bath at 160 °C for 6 h. Purification by recrystallization from hexane
afforded the title compound (Z/E)-5a as a white solid (224.0 mg, 52%)
and as a 75:25 mixture of Z/E-isomers. The two isomers were sepa-
rated by flash chromatography (pentane/Et2O 90:10) for characteriza-
tion.
1H NMR (400 MHz, CDCl3): δ = 7.53 (d, J = 8.0 Hz, 2 H), 7.19 (d, J = 7.9
Hz, 2 H), 2.04 (m, 2 H), 1.35 (s, 12 H), 1.33–1.30 (m, 2 H), 1.24 (s, 12
H), 1.20–1.13 (m, 2 H), 0.75 (t, J = 7.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 146.1, 128.7 (2 C), 128.0 (q, J = 32.2
Hz), 124.9 (q, J = 3.7 Hz, 2 C), 124.7 (q, J = 270 MHz), 84.0 (4 C), 32.5,
31.9, 25.2 (4 C), 24.9 (4 C), 22.9, 14.0. The carbons directly attached to
the boron atoms were not detected due to quadrupolar relaxation.
11B NMR (128 MHz, CDCl3): δ = 29.9.
19F NMR (376 MHz, CDCl3): δ = –63.2.
HRMS (ESI): m/z calcd for C25H37B2F3O4Na [M + Na]+: 503.2731;
(Z)-5a22
1H NMR (400 MHz, CDCl3): δ = 7.09–7.00 (m, 6 H), 6.96–6.93 (m, 4 H),
1.32 (s, 24 H).
13C NMR (100 MHz, CDCl3): 141.4 (2 C), 129.5 (4 C), 127.6 (4 C), 125.9
(2 C), 84.2 (4 C), 25.0 (8 C). The carbons directly attached to the boron
atoms were not detected due to quadrupolar relaxation.
found: 503.2736.
Trimethyl[2-phenyl-1,2-bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)vinyl]silane (5e)
11B NMR (128 MHz, CDCl3): δ = 30.2.
The general procedure B was applied to 1-phenyl-2-(trimethylsi-
lyl)acetylene (1e; 199 μL, 1.00 mmol, 1 equiv) and the reaction mix-
ture was heated in an oil bath at 160 °C for 6 h. Purification by flash
chromatography (pentane/Et2O 95:5) afforded the title compound 5e
as a white solid (300.1 mg, 70%) as a 65:35 mixture of Z/E-isomers.
The two isomers were separated by an additional flash chromatogra-
phy for characterization.
(E)-5a
Mp 172–173 °C.
IR (ATR): 2923, 1317, 1263, 1134, 845 cm–1
1H NMR (400 MHz, CDCl3): δ = 7.37–7.34 (m, 4 H), 7.30–7.26 (m, 4 H),
7.24–7.20 (m, 2 H), 1.08 (s, 24 H).
.
13C NMR (100 MHz, CDCl3): δ = 143.3 (2 C), 128.2 (4 C), 128.1 (4 C),
126.8 (2 C), 83.7 (4 C), 24.7 (8 C). The carbons directly attached to the
boron atoms were not detected due to quadrupolar relaxation.
11B NMR (128 MHz, CDCl3): δ = 30.1.
HRMS (ESI): m/z calcd for C26H34B2O4Na [M + Na]+: 455.2544; found:
(Z)-Trimethyl[2-phenyl-1,2-bis(4,4,5,5-tetramethyl-1,3,2-dioxa-
borolan-2-yl)vinyl]silane23
1H NMR (400 MHz, CDCl3): δ = 7.27–7.17 (m, 3 H), 7.14–7.11 (m, 2 H),
1.38 (s, 12 H), 1.24 (s, 12 H), –0.17 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 146.0, 127.9 (2 C), 127.6 (2 C), 126.3,
84.0 (2 C), 83.8 (2 C), 25.7 (4 C), 24.9 (4 C), 1.0 (3 C). The carbons di-
rectly attached to the boron atoms were not detected due to quadru-
polar relaxation.
455.2557.
(Z)-2,2′-[1-(4-Methoxyphenyl)hex-1-ene-1,2-diyl]bis(4,4,5,5-tet-
ramethyl-1,3,2-dioxaborolane) (5c)
11B NMR (128 MHz, CDCl3): δ = 30.3.
The general procedure B was applied to 1-(hex-1-yn-1-yl)-4-meth-
oxybenzene (1c; 188.3 mg, 1.00 mmol, 1 equiv) and the reaction mix-
ture was heated in an oil bath at 160 °C for 6 h. Purification by silica
gel flash chromatography (pentane/Et2O 100:0 to 90:10) afforded the
title compound 5c as a colorless oil (129.0 mg, 29%).
(E)-Trimethyl[2-phenyl-1,2-bis(4,4,5,5-tetramethyl-1,3,2-dioxa-
borolan-2-yl)vinyl]silane
Mp 171–174 °C.
IR (ATR): 2982, 1305, 1255, 1138, 843 cm–1
.
IR (ATR): 2983, 2924, 1604, 1508, 1337, 1242, 1145, 1129, 845 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.22–7.20 (m, 4 H), 7.19–7.14 (m, 1 H),
1.23 (s, 12 H), 0.99 (s, 12 H), 0.25 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 147.1, 127.9 (2 C), 127.5 (2 C), 126.1,
83.7 (2 C), 83.2 (2 C), 25.2 (4 C), 24.9 (4 C), 0.9 (3 C). The carbons di-
rectly attached to the boron atoms were not detected due to quadru-
polar relaxation.
1H NMR (400 MHz, CDCl3): δ = 7.04–7.01 (m, 2 H), 6.84–6.81 (m, 2 H),
3.79 (s, 3 H), 2.12–2.08 (m, 2 H), 1.33 (s, 12 H), 1.29–1.15 (m, 4 H),
1.24 (s, 12 H), 0.77 (t, J = 7.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 157.8, 134.2, 129.4 (2 C), 129.2, 128.4,
113.3 (2 C), 83.7 (2 C), 83.7 (2 C), 55.2, 32.2, 32.1, 25.1 (4 C), 24.9 (4 C),
23.0, 14.1.
11B NMR (128 MHz, CDCl3): δ = 30.
HRMS (ESI): m/z calcd for C23H38B2O4SiNa [M + Na]+: 451.2626; found:
11B NMR (128 MHz, CDCl3): δ = 31.1.
451.2627.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–J

I
L. Ferrand et al.
Special Topic
Synthesis
{1,2-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2-[4-(tri-
fluoromethyl)phenyl]vinyl}trimethylsilane (5g)
13C NMR (100 MHz, CDCl3): δ = 160.4, 149.2, 130.6, 128.6 (2 C), 114.1
(2 C), 83.4 (2 C), 55.4, 25.0 (4 C). The carbon directly attached to the
boron atom was not detected due to quadrupolar relaxation.
The general procedure B was applied to trimethyl{[4-(trifluorometh-
yl)phenyl]ethynyl}silane (1g; 242.3 mg, 1.00 mmol, 1 equiv) and the
reaction mixture was heated in an oil bath at 160 °C for 6 h. Purifica-
tion by flash chromatography (pentane/Et2O 97:3 to 95:5) afforded
the title compound 5g as a white solid (290.4 mg, 58%) and as an in-
separable 68:32 mixture of Z/E-isomers.
11B NMR (128 MHz, CDCl3): δ = 30.0.
Acknowledgment
This work was supported by CNRS, MRES, UPMC, CSC, and ANR (ANR-
12-BS07-0031-01COCACOLIGHT), which we gratefully acknowledge.
We also thank CONACYT for the postdoctoral fellowship granted to
A.R.-H. (Registry No. 252113).
(Z)-{1,2-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2-[4-
(trifluoromethyl)phenyl]vinyl}trimethylsilane23
1H NMR (400 MHz, CDCl3): δ = 7.51–7.48 (m, 2 H), 7.22 (d, J = 8.0 Hz, 2
H), 1.38 (s, 12 H), 1.22 (s, 12 H), –0.18 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 149.8, 128.5 (q, J = 32 MHz), 128.3 (2
C), 124.7 (q, J = 238 Hz), 124.6 (q, J = 3.8 Hz, 2 C), 84.3 (2 C), 84.0 (2 C),
25.7 (4 C), 24.9 (4 C), 0.99 (3 C). The carbons directly attached to the
boron atoms were not detected due to quadrupolar relaxation.
Supporting Information
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0036-1588996.
S
u
p
p
ortiInfogrmoaitn
S
u
p
p
o
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rmoaitn
11B NMR (128 MHz, CDCl3): δ = 28.8.
19F NMR (376 MHz, CDCl3): δ = –63.1.
References
(E)-{1,2-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2-[4-
(trifluoromethyl)phenyl]vinyl}trimethylsilane
1H NMR (400 MHz, CDCl3): δ = 7.51–7.48 (m, 2 H), 7.31 (d, J = 8.0 Hz, 2
H), 1.22 (s, 12 H), 0.97 (s, 12 H), 0.26 (s, 9 H).
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11B NMR (128 MHz, CDCl3): δ = 28.8.
19F NMR (376 MHz, CDCl3): δ = –63.2.
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Special Topic
Synthesis
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–J