Aryltriolborates as air- and water-stable bases for wittig olefination

Article abstract of DOI:10.1055/s-0034-1378919

Tetrabutylammonium aryltriolborates have been synthesized in 37-66% yield by a one-pot procedure from arylboronic acids, 1,1,1-tris(hydroxymethyl)ethane, and aqueous tetrabutylammonium hydroxide. The aryltriolborates can be used as bases in Wittig reactions of aromatic aldehydes with all three types of phosphorus ylides: stabilized and semistabilized ylides can be generated at room temperature, and nonstabilized ylides at 120 °C (bath temperature).

Full text of DOI:10.1055/s-0034-1378919

SYNTHESIS
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
© Georg Thieme Verlag Stuttgart · New York
2015, 47, 359–366
paper
359
W. Huang et al.
Paper
Synthesis
Aryltriolborates as Air- and Water-Stable Bases for Wittig Olefination
O
HO
HO
HO
r.t.
a
–
Wenhua Huang*
Shuang-Hong Zhao
Ning Xu
ArB(OH)2
Ar
B
+
+
strong
base!
n-Bu4NOH
O
n-Bu4N+
one pot
O
O
O
even R1 = R2 = Me or R1–R2 = -(CH2)4-
OH
Ar
B
Department of Chemistry, Tianjin University, Tianjin 300072,
R3
R1
R2
R1
R2
P. R. of China
+
8
6
2
(
2
2
)
7
4
0
3
4
7
5
O
R3
R1
R2
+
huangwh@tju.edu.cn
Ph3P
Ph3P
X–
n-Bu4N+X–
Ph3P=O
Received: 02.07.2014
Accepted after revision: 10.10.2014
Published online: 12.11.2014
via a two-step procedure developed by Yamamoto and co-
workers:10h (1) the reaction of an arylboronic acid with triol
1 to form 2, and (2) the reaction of 2 with potassium hy-
droxide, as shown in the upper part of Scheme 1. Both steps
require the azeotropic removal of water with toluene.
Tetrabutylammonium aryltriolborates 4 can be obtained
from 3 by cation exchange with tetrabutylammonium hy-
droxide at room temperature.10h In the second step, potassi-
um hydroxide may be replaced by sodium hydride, leading
to the formation of sodium aryltriolborates.10e Alternative-
ly, lithium aryltriolborates can be prepared from the aryla-
tion of trimethyl or triisopropyl borate with aryllithium
compounds followed by the removal of methanol or isopro-
pyl alcohol through ester exchange with triol 1.10e The di-
rect transesterification of pinacol arylboronic esters with 1
in the presence of sodium hydroxide or potassium hydrox-
ide also affords aryltriolborates.11
We found that tetrabutylammonium aryltriolborates 4
could be prepared in one pot by simply mixing the appro-
priate arylboronic acid, triol 1, and tetrabutylammonium
hydroxide (25 wt% in water) at room temperature, as
shown in the lower part of Scheme 1. After being stirred
overnight, the reaction mixture was extracted with di-
chloromethane; aryltriolborates 4a, 4b, and 4d were ob-
tained in 61%, 66%, and 57% yield, respectively, after
concentration and crystallization. The removal of dichloro-
methane after extraction directly afforded almost pure 4c
in 37% yield, and further purification by crystallization was
unsuccessful. This one-pot protocol avoids the two-step
azeotropic removal of water, and provides a direct access to
aryltriolborates under mild conditions. However, attempts
to prepare tetrabutylammonium alkyltriolborates from alk-
ylboronic acids using this method failed.
DOI: 10.1055/s-0034-1378919; Art ID: ss-2014-h0414-op
Abstract Tetrabutylammonium aryltriolborates have been synthe-
sized in 37–66% yield by a one-pot procedure from arylboronic acids,
1,1,1-tris(hydroxymethyl)ethane, and aqueous tetrabutylammonium
hydroxide. The aryltriolborates can be used as bases in Wittig reactions
of aromatic aldehydes with all three types of phosphorus ylides: stabi-
lized and semistabilized ylides can be generated at room temperature,
and nonstabilized ylides at 120 °C (bath temperature).
Key words tetrabutylammonium aryltriolborates, Wittig olefination,
phosphorus ylides, organic bases, organoboron compounds
The Wittig reaction of a phosphorus ylide with an alde-
hyde or ketone is probably the most widely used method
for carbonyl olefination.1 The ylide is usually prepared by
treating a phosphonium salt with a base and, depending on
the nature of the phosphorus ylide, a variety of bases can be
used.2 While a stabilized ylide can be formed by using a
weak base such as ammonium hydroxide,3 triethylamine,4
or potassium hydroxide,5 a nonstabilized ylide, in particular
Ph3P=C(R1)R2 (where R1 and R2 = alkyl), often requires a
strong base. For example, a literature search of the reaction
of Ph3P+CHMe2(X–) with benzaldehydes revealed that the
most commonly used base has been butyllithium,6 with a
few cases using potassium tert-butoxide,7 sodium amide,8
and potassium hexamethyldisilazide,9 which are all air-
and/or water-sensitive compounds. Thus, for Wittig reac-
tions via nonstabilized ylides, employing an air- and water-
stable base remains a challenge. Herein, we report the use
of aryltriolborates as air- and water-stable, yet strong
enough, bases in the Wittig reaction.
Aryltriolborates have recently emerged as convenient
reagents for a variety of transition-metal-catalyzed C–C
coupling reactions due to their high reactivity, stability, and
solubility.10 Potassium aryltriolborates 3 can be prepared
In an attempt to prepare phosphonium salts with a
phenyltriolborate anion, we unexpectedly found that the
anion exchange of phenacyltriphenylphosphonium bro-
mide (6a) with potassium phenyltriolborate (3a) led to the
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 359–366

360
W. Huang et al.
Paper
Synthesis
R1
Yamamoto's method
CHO
Cl
HO
O
O
ArB(OH)2
R2
Ar
B
R1
R2
4a
+
toluene
azeotropic
HO
OH
OH
+
Ph3P
X–
CH2Cl2, r.t.
1
2
toluene
azeotropic
6
KOH
O
5a
Cl 7a
COPh
n-Bu4N+
K+
O
O
+
O
O
n-Bu4NOH
–
B
–
B
Ph3P
Ar
Ar
Br–
O
COPh
7aa, 65% (0:100)a
6a
+
Cl
4
COOEt
Ph3P
3
Cl–
this work
COOEt
Ph
7ab, 93% (8:92)b
r.t.
one-pot
n-Bu4N+
6b
+
Cl
Cl
Cl
Cl
ArB(OH)2
+
+
n-Bu4NOH
1
4
Ph
Ph3P
n-Bu4N+
Cl–
O
O
7ac, 94%c (61:39)b
–
–
B
6c
+
B
MeO
O
O
O
Ph
O
O
Ph3P
Cl–
4a, 61%
4b, 66%
n-Bu4N+
7ad, 99% (66:34)a
F
n-Bu4N+
6d
Ph
O
O
–
B
COOEt
–
B
+
MeO
F
Ph3P
O
O
O
Br–
COOEt
OMe
F
4c, 37%
Scheme 1 Synthesis of aryltriolborates
4d, 57%
7ae, 88% (0:100)a
6e
+
Ph3P Me
I–
7af, trace
6f
Cl
formation of the phosphorus ylide (Ph3P=CHCOPh), indicat-
ing that 3a could act as a base to generate a phosphorus
ylide. This prompted us to evaluate 4a, which has better sol-
ubility in organic solvents than 3a, as a base in the Wittig
olefination, and the results are summarized in Scheme 2.
When a mixture of 4a, p-chlorobenzaldehyde (5a), and
phosphonium salt 6a was stirred at room temperature for
24 hours, the olefination product 7aa was obtained in 65%
yield. A number of phosphonium salts that can form stabi-
lized or semistabilized ylides were further examined under
the same conditions, and all afforded the corresponding
olefins in good to excellent yields. The Z/E selectivity is fa-
vorable toward the E-isomer for stabilized ylides, and
slightly favorable toward the Z-isomer for semistabilized
ylides, following the rules of the Wittig olefination.1 In the
case of 6c, when 4a was replaced by potassium phenyltriol-
borate (3a), the olefin 7ac was obtained in the same yield
although 3a is insoluble in dichloromethane. For methyl-
triphenylphosphonium iodide (6f), however, only a trace of
7af was detected by TLC, indicating that the basicity of 4a is
not strong enough to generate the nonstabilized ylide at
room temperature.
Scheme 2 Wittig olefination using phenyltriolborate 4a as a base at
room temperature. a The Z/E ratio was determined by 1H NMR spectros-
copy. b The isolation Z/E ratio. c When 4a was replaced by 3a, the yield
was also 94%, with a Z/E ratio of 58:42 (determined by 1H NMR spec-
troscopy).
yield, respectively (entries 1–3). Notably, toluene at 120 °C
(bath temperature) led to a 60% yield of 7bf (Table 1, entry
4). For phosphonium salt 6g under the same conditions,
however, the yield of 7bg was only 46%, and further in-
creasing the reaction temperature by refluxing in xylene
led to a decreased 30% yield (Table 1, entries 5 and 6). The
lower yield of 7bg compared with 7bf is probably due to the
electronic and steric effects of the additional two methyl
groups of 6g, suggesting that a stronger base is needed. To
increase the basicity of 4a, we pinned our hope on the
modification of its structure by introducing a methoxy
group into the para position of the phenyl ring. The yield of
7bg increased to 53% when 4a was replaced with 4b, but
further introduction of a methoxy group (namely, 4c) re-
sulted in a reduced 28% yield of 7bg (Table 1, entries 7 and
8). A slightly lower yield (47%) of 7bg was obtained when
4d containing three fluoro groups at the 3,4,5-positions
was used (Table 1, entry 9). Fortunately, returning to 4b and
simply increasing the reaction time to 10 hours led to a 73%
yield of 7bg, a significant improvement over the 53% yield
achieved upon refluxing for six hours (Table 1, entries 7 and
10).
Therefore, we sought to increase the reaction tempera-
ture by refluxing the reaction mixture in different solvents
for alkyltriphenylphosphonium salts. As shown in Table 1,
refluxing a mixture of 4a, 1-naphthaldehyde (5b), and 6f in
tetrahydrofuran, acetonitrile, and 1,2-dichloroethane af-
forded the olefination product 7bf in 24%, 14%, and 10%
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 359–366

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W. Huang et al.
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Synthesis
Table 1 Screening for Optimal Conditions for the Wittig Reaction via
Table 2 The Wittig Reaction of Alkyltriphenylphosphonium Salts Us-
ing 4b as a Basea
Nonstabilized Ylidesa
R1
R1
R1
R1
R2
4b
+
O
R3
R3
+
+
Ph3P
X–
4
O
R2
Ph3P
R2
R2
7
+
X–
5
6
6
6f, R1 = R2 = H; X = I
6g, R1 = R2 = Me; X = I
5b
7b
Entry
5
6
7
1
2
5b
6g
6f
7bg, 73%
7bf, 86%
Entry
4
6
Solvent
Tempb (°C) 7b
Yield (%)
5b
1
2
4a
4a
4a
4a
4a
4a
4b
4c
4d
4b
6f
THF
70
7bf
24
14
10
60
46
30
53
28
47
73c
+
6f
MeCN
DCE
90
7bf
Ph3P
3
4
5b
Br–
3
6f
90
7bf
6h
7bh, 88% (65:35)b
n-Pr
4
6f
toluene
toluene
xylene
toluene
toluene
toluene
toluene
120
120
150
120
120
120
120
7bf
5
6g
6g
6g
6g
6g
6g
7bg
7bg
7bg
7bg
7bg
7bg
+
6
Ph3P n-Bu
5b
Br–
7
6i
8
7bi, 91% (73:27)b
9
+
Ph3P
10
5
6
5a
5a
Br–
Cl
7aj, 91%
a Reaction conditions: 6 (0.5 mmol), 4 (0.5 mmol), 5b (0.4 mmol), refluxed
6j
for 6 h.
b Bath temperature.
c Refluxed for 10 h.
+
Ph3P
Br–
O
O
Cl
7ak, 84%c (62:38)d
O
O
With the success of 6g, we continued to examine a
number of alkyltriphenylphosphonium salts using 4b as a
base. As shown in Table 2, phosphonium salts 6f and 6h–j
gave the corresponding olefins in 86–91% yield (entries 2–
5). In the case of 6h and 6i, the Z-isomer is predominant,
which is in agreement with the general pattern of the
Wittig reaction via nonstabilized ylides.1 For phosphonium
salt 6k, refluxing in dichloromethane is enough to afford
7ak in good yield (Table 2, entry 6) and with the same Z/E
selectivity (62:38) as that reported12 when using potassium
carbonate as a base under phase-transfer conditions.
It was of interest next to explore the reactions of a vari-
ety of aldehydes with 6j and 4b, and the results are summa-
rized in Scheme 3. Aromatic aldehydes with an electron-
withdrawing group at the phenyl ring gave the correspond-
ing olefination products (7aj and 7cj–ej) in good to excel-
lent yields (86–93%). For 4-nitrobenzaldehyde (5f), the
reaction at 120 °C led to a complicated mixture, probably
due to the high activity of its carbonyl group caused by the
strongly electron-withdrawing nitro group at the para posi-
tion; however, reducing the bath temperature to 80 °C gave
7fj in 67% yield, indicating that the reaction temperature
can be adjusted based on the aldehyde reactivity. For
phthalaldehyde, the monoolefination product 7gj was ob-
tained in 50% yield. The yields of the olefination products
(7ij–kj) were generally lower for electron-rich aldehydes
than for electron-deficient ones. Two heteroaromatic alde-
hydes also underwent olefination to give 7lj and 7mj in 96%
6k
a Reaction conditions: 4b (0.5 mmol), 6 (0.5 mmol), 5 (0.4 mmol), toluene,
120 °C (bath temperature), 10 h.
b The Z/E ratio was determined by 1H NMR spectroscopy.
c Using CH2Cl2 as solvent, 40 °C.
d The isolation Z/E ratio.
and 71% yield, respectively. However, the reaction of alde-
hyde 5n led to a complicated mixture, and no olefination
product 7nj was detected.
When the reaction of aldehyde 5n was carried out in di-
chloromethane at room temperature, 5n was completely
consumed (as followed by TLC) but the only isolatable prod-
uct was a yellow oil, which was identified by H and 13C
1
NMR spectroscopy and HRMS as 2b, in 61% yield (Scheme
4). The formation of 2b is probably from the α-deprotona-
tion of 5n by 4b to form the enolate which might polymer-
ize to a complicated mixture. In fact, in the absence of 6j,
the reaction of 5n with 4b also afforded 2b in 65% yield.
However, for the reactions of aromatic aldehydes 5a and
5c–m with 4b and 6j, attempts to isolate the pure 2b were
unsuccessful due to the contamination of byproduct tri-
phenylphosphine oxide. In addition, attempts to regenerate
4b from 2b by using a catalytic amount of 4b and a stoichio-
metric amount of tetrabutylammonium hydroxide in the
reaction of 6j with 5a were also unsuccessful, probably due
to the easy decomposition of tetrabutylammonium hydrox-
ide at 120 °C. Based on these results and the initial observa-
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 359–366

362
W. Huang et al.
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Synthesis
O
O
O–
n-Bu4N+
4b
R3
R3
+
6j
4
O
Ar
B
toluene
120 °C, 10 h
5
7
8
R3CHO
2
Cl
F
Br
R1
R2
R1
R3
R1
R2
8
+
+
Ph3P
–
Ph3P
X–
R2
n-Bu4NX
Ph3PO
6
9
7
O2N
Scheme 5 Proposed reaction mechanism
In summary, tetrabutylammonium aryltriolborates are
readily prepared in one pot at room temperature from aryl-
boronic acids, 1,1,1-tris(hydroxymethyl)ethane, and aque-
ous tetrabutylammonium hydroxide. Furthermore, we have
demonstrated that aryltriolborates are strong enough bases
for Wittig reactions with all three types of ylides: nonstabi-
lized, semistabilized, and stabilized. It is notable that even
isopropyltriphenylphosphonium iodide can be deprotonat-
ed by aryltriolborates to form the corresponding nonstabi-
lized ylide, suggesting that other base-promoted reactions
are worth trying with aryltriolborates, a new class of organ-
ic bases.
7aj, 91%
O2N
7cj, 86%
7dj, 92%
7ej, 93%
OMe
CHO
7fj, 67%a 7gj, 50%
7hj, 73% 7ij, 72% 7jj, 64%
MeO
MeO
OMe
O
N
O
O
N
All solvents were freshly distilled before use. All aldehydes were puri-
fied by preparative TLC before use. The olefination reactions were
performed under nitrogen by connecting the flask to a nitrogen bal-
loon; the reaction temperatures referred to are oil bath temperatures.
NMR spectra were recorded on a Bruker Avance III 400 or 600 NMR
spectrometer. IR spectra were obtained on a Thermo Nicolet Avatar
360 IR spectrometer. Electrospray ionization mass spectra were ob-
tained on a Finnigan LCQ Advantage MAX instrument. Melting points
were measured on a melting point apparatus equipped with micro-
scope and hot stage, and are uncorrected. PE = petroleum ether (bp
60–90 °C).
7kj, 73%
7lj, 96%
7mj, 71%
7nj, 0%
Scheme 3 Wittig reactions of aldehydes 5 with 6j using 4b as a base. a
The reaction was run at 80 °C (bath temperature).
tion of ylide Ph3P=CHCOPh from the reaction of 6a with 4a,
we reasoned that the tetrabutylammonium aryltriolborate
4 in solution is in equilibrium with 8 (Scheme 5). The
alkoxy anion arm of 8 can act as a base to capture an α-pro-
ton of the phosphonium salt 6 to form the arylboronic ester
2 and the ylide 9 which reacts with an aldehyde to give the
olefin 7.
Tetrabutylammonium Aryltriolborates 4; General Procedure
To a round-bottom flask (25 mL), an arylboronic acid (2 mmol), 1,1,1-
tris(hydroxymethyl)ethane (1; 0.240 g, 2 mmol), and n-Bu4NOH (25
wt% in H2O; 6.228 g, 6 mmol) were added. After being stirred at r.t.
overnight, the reaction mixture was extracted with CH2Cl2 (3 × 10
mL). The combined extract was dried over anhyd MgSO4, concentrat-
ed, and dried in vacuo to give the almost pure product 4, which was
further purified by crystallization if appropriate.
6j
+
+
4b
5n
7nj
O
O
OH
MeO
B
2b
Tetrabutylammonium 4-Methyl-1-phenyl-2,6,7-trioxa-1-borabi-
cyclo[2.2.2]octan-1-uide (4a)10e
O
O–
Yield: 0.542 g (61%) (after crystallization from CH2Cl2–EtOAc, 1:5);
colorless needles; mp 205–206 °C.
complex
mixture
N
1H NMR (600 MHz, DMSO-d6): δ = 0.48 (s, 3 H), 0.93 (t, J = 7.5 Hz, 12
H), 1.26–1.33 (m, 8 H), 1.50–1.56 (m, 8 H), 3.12 (t, J = 8.1 Hz, 8 H), 3.57
(s, 6 H), 6.90 (t, J = 7.2 Hz, 1 H), 6.97 (dd, J = 6.9, 7.2 Hz, 2 H), 7.31 (d,
J = 6.9 Hz, 2 H).
O
Scheme 4 Reaction of aldehyde 5n with 6j using 4b as a base
13C NMR (151 MHz, DMSO-d6): δ = 13.5, 16.3, 19.2, 23.0, 34.4, 57.3,
73.7, 123.8, 125.4, 132.1 (C–B not observed).
11B NMR (128 MHz, CD3CN): δ = 1.54.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 359–366

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W. Huang et al.
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Synthesis
HRMS-ESI: m/z (+) calcd for C16H36N+: 242.2842; found: 242.2842;
m/z (–) calcd for C11H14BO3–: 205.1042; found: 205.1043.
was stirred at r.t., and the reaction progress was monitored by TLC.
After reaction completion, the reaction mixture was concentrated and
separated by preparative TLC (silica gel) to afford the olefination
product.
Tetrabutylammonium 1-(4-Methoxyphenyl)-4-methyl-2,6,7-tri-
oxa-1-borabicyclo[2.2.2]octan-1-uide (4b)
Wittig Olefination of Nonstabilized Ylides Using 4 as a Base; Gen-
eral Procedure
Yield: 0.627 g (66%) (after crystallization from CH2Cl2–EtOAc, 1:5);
short, colorless needles; mp 202–203 °C.
To a round-bottom flask (25 mL), a phosphonium salt 6 (0.5 mmol),
an aryltriolborate 4 (0.5 mmol), an aldehyde 5 (0.4 mmol), and sol-
vent (5 mL) were added. The mixture was refluxed in an oil bath (bath
temperature as indicated in Table 1), and the reaction progress was
monitored by TLC. After the completion of the reaction, the reaction
mixture was passed through a short silica gel column, which was
eluted with EtOAc. The eluate was concentrated and separated by pre-
parative TLC (silica gel) to afford the olefination product.
1H NMR (600 MHz, DMSO-d6): δ = 0.47 (s, 3 H), 0.93 (t, J = 7.5 Hz, 12
H), 1.26–1.33 (m, 8 H), 1.49–1.54 (m, 8 H), 3.10 (t, J = 8.4 Hz, 8 H), 3.57
(s, 6 H), 3.65 (s, 3 H), 6.56 (d, J = 7.8 Hz, 2 H), 7.22 (d, J = 7.8 Hz, 2 H).
13C NMR (151 MHz, DMSO-d6): δ = 13.5, 16.3, 19.1, 23.0, 34.4, 54.3,
57.3, 73.8, 111.0, 133.0, 156.5 (C–B not observed).
11B NMR (128 MHz, CD3CN): δ = 1.59.
MS (EI, 70 eV): m/z (%) = 142.6 (100), 237.0 (13) [M – C16H34N]+.
HRMS-ESI: m/z (+) calcd for C16H36N+: 242.2842; found: 242.2841;
m/z (–) calcd for C12H16BO4–: 235.1147; found: 235.1148.
3-(4-Chlorophenyl)-1-phenylprop-2-en-1-one (7aa)
Only the E-isomer was observed.
Tetrabutylammonium 1-(2,4-Dimethoxyphenyl)-4-methyl-2,6,7-
trioxa-1-borabicyclo[2.2.2]octan-1-uide (4c)
Yield: 62.7 mg (65%); yellow solid; mp 113–115 °C (Lit.13 113–
115 °C); Rf = 0.20 (PE–EtOAc, 50:1).
IR (KBr): 1659 (C=O) cm–1
.
Yield: 0.378 g (37%); white solid; mp 151–154 °C.
1H NMR (400 MHz, CD3CN): δ = 0.54 (s, 3 H), 0.98 (t, J = 7.2 Hz, 12 H),
1.29–1.40 (m, 8 H), 1.51–1.60 (m, 8 H), 3.04 (t, J = 8.6 Hz, 8 H), 3.65 (s,
3 H), 3.69 (s, 6 H), 3.72 (s, 3 H), 6.25 (d, J = 1.8 Hz, 1 H), 6.29 (dd, J =
1.8, 8.0 Hz, 1 H), 7.40 (d, J = 8.0 Hz, 1 H).
1H NMR (400 MHz, CDCl3): δ = 7.40 (d, J = 8.4 Hz, 2 H), 7.50–7.55 (m, 2
H), 7.52 (d, J = 15.6 Hz, 1 H), 7.58 (d, J = 8.0 Hz, 2 H), 7.59–7.63 (m, 1
H), 7.77 (d, J = 15.6 Hz, 1 H), 8.03 (d, J = 7.2 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 122.5, 128.5, 128.7, 129.3, 129.6,
132.9, 133.4, 136.4, 138.0, 143.3, 190.2.
13C NMR (100 MHz, CD3CN): δ = 12.9, 15.7, 19.3, 23.4, 34.4, 54.4, 54.7,
58.1, 73.9, 97.6, 103.2, 135.6, 158.8, 164.1 (C–B not observed).
11B NMR (128 MHz, CD3CN): δ = 1.93.
Ethyl 3-(4-Chlorophenyl)acrylate (7ab)14
MS (EI, 70 eV): m/z (%) = 142.6 (100), 243.1 (33), 267.1 (9) [M –
C
16H34N]+.
(Z)-7ab
HRMS-ESI: m/z (+) calcd for C16H36N+: 242.2842; found: 242.2835;
m/z (–) calcd for C13H18BO5–: 265.1253; found: 265.1246.
Yield: 5.98 mg (7%); yellow oil; Rf = 0.24 (PE–EtOAc, 50:1).
IR (KBr): 1721 (C=O) cm–1
.
1H NMR (600 MHz, CDCl3): δ = 1.28 (t, J = 7.2 Hz, 3 H), 4.20 (q, J = 7.2
Hz, 2 H), 5.98 (d, J = 12.8 Hz, 1 H), 6.90 (d, J = 12.8 Hz, 1 H), 7.34 (d, J =
8.4 Hz, 2 H), 7.57 (d, J = 8.4 Hz, 2 H).
Tetrabutylammonium 4-Methyl-1-(3,4,5-trifluorophenyl)-2,6,7-
trioxa-1-borabicyclo[2.2.2]octan-1-uide (4d)
Yield: 0.572 g (57%) (after crystallization from EtOAc); colorless
flakes; mp 177–179 °C.
1H NMR (600 MHz, DMSO-d6): δ = 0.48 (s, 3 H), 0.93 (t, J = 7.5 Hz, 12
H), 1.26–1.33 (m, 8 H), 1.51–1.57 (m, 8 H), 3.14 (t, J = 8.4 Hz, 8 H), 3.58
(s, 6 H), 6.96 (dd, JH–F = 8.6, 9.0 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 14.1, 60.4, 120.4, 128.2, 131.2, 133.3,
134.9, 141.8, 165.9.
(E)-7ab
Yield: 72.67 mg (86%); yellow oil; Rf = 0.19 (PE–EtOAc, 50:1).
13C NMR (151 MHz, DMSO-d6): δ = 13.4, 15.9, 19.1, 23.0, 34.5, 57.4,
IR (KBr): 1714 (C=O) cm–1
.
73.6, 114.4 (d, JC–F = 11.8 Hz), 136.0 (d, JC–F = 241.4 Hz), 149.0 (dd, JC–F
=
1H NMR (600 MHz, CDCl3): δ = 1.34 (t, J = 7.2 Hz, 3 H), 4.27 (q, J = 7.2
Hz, 2 H), 6.41 (d, J = 16.0 Hz, 1 H), 7.36 (d, J = 8.4 Hz, 2 H), 7.45 (d, J =
8.4 Hz, 2 H), 7.63 (d, J = 16.0 Hz, 1 H).
13C NMR (100 MHz, CDCl3): δ = 14.3, 60.6, 118.9, 129.15, 129.19,
133.0, 136.1, 143.1, 166.7.
8.10, 245.5 Hz).
11B NMR (128 MHz, CDCl3): δ = 1.39.
19F NMR (376 MHz, CDCl3): δ = –168.9 (t, J = 20.0 Hz), –140.2 (d, J =
20.0 Hz).
MS (EI, 70 eV): m/z (%) = 142.7 (100), 159.6 (26), 227.9 (23), 261.1
(10) [M – C16H34N]+.
HRMS-ESI: m/z (+) calcd for C16H36N+: 242.2842; found: 242.2838;
m/z (–) calcd for C11H11BF3O3–: 259.0759; found: 259.0758.
1-Chloro-4-styrylbenzene (7ac)15
(Z)-7ac
Yield: 48.81 mg (57%); pale yellow oil; Rf = 0.50 (PE).
1H NMR (600 MHz, CDCl3): δ = 6.51 (d, J = 12.0 Hz, 1 H), 6.61 (d, J =
12.0 Hz, 1 H), 7.14–7.24 (m, 9 H).
13C NMR (151 MHz, CDCl3): δ = 127.4, 128.4, 128.5, 128.8, 129.0,
Wittig Olefination of Stabilized and Semistabilized Ylides Using 4a
as a Base; General Procedure
To a round-bottom flask (25 mL), a phosphonium salt 6 (0.5 mmol),
phenyltriolborate 4a (223.8 mg, 0.5 mmol), p-chlorobenzaldehyde
(5a; 56.2 mg, 0.4 mmol), and CH2Cl2 (5 mL) were added. The mixture
130.2, 131.0, 132.8, 135.7, 136.9.
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(E)-7ac
Total yield: 59.46 mg (88%); yellow oil; Rf = 0.50 (PE).
(Z)-7bh
Yield: 31.97 mg (37%); white solid; mp 131–132 °C (Lit.15 128–
129 °C); Rf = 0.35 (PE).
1H NMR (400 MHz, CDCl3): δ = 1.84 (dd, J = 1.6, 7.2 Hz, 3 H), 6.09–6.18
(m, 1 H), 7.00 (d, J = 11.2 Hz, 1 H), 7.45 (d, J = 7.2 Hz, 1 H), 7.48–7.60
(m, 3 H), 7.80–7.86 (m, 1 H), 7.90–7.95 (m, 1 H), 8.07–8.11 (m, 1 H).
1H NMR (600 MHz, CDCl3): δ = 7.03 (d, J = 16.2 Hz, 1 H), 7.06 (d, J =
16.2 Hz, 1 H), 7.26 (t, J = 7.2 Hz, 1 H), 7.31 (d, J = 8.4 Hz, 2 H), 7.35 (dd,
J = 7.2, 7.8 Hz, 2 H), 7.42 (d, J = 8.4 Hz, 2 H), 7.49 (d, J = 7.8 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 14.7, 125.1, 125.3, 125.7, 125.8, 126.6,
13C NMR (151 MHz, CDCl3): δ = 126.6, 127.4, 127.7, 127.9, 128.8,
127.2, 128.0, 128.4, 128.6, 132.0, 133.7, 134.6.
128.9, 129.4, 133.2, 135.9, 137.0.
1-Chloro-4-(4-phenylbuta-1,3-dien-1-yl)benzene (7ad)16
(E)-7bh
1H NMR (400 MHz, CDCl3): δ = 2.08 (dd, J = 1.6, 6.4 Hz, 3 H), 6.28–6.38
(m, 1 H), 7.22 (d, J = 15.6 Hz, 1 H), 7.48–7.60 (m, 3 H), 7.62 (d, J = 7.2
Hz, 1 H), 7.80–7.86 (m, 1 H), 7.90–7.95 (m, 1 H), 8.22 (d, J = 7.6 Hz, 1
H).
Mixture of the (1Z,3E)- and (1E,3E)-isomers (Z/E = 66:34, determined
by 1H NMR spectroscopy).
Total yield: 95.76 mg (99%); white solid; Rf = 0.33 (PE).
13C NMR (100 MHz, CDCl3): δ = 19.0, 123.6, 124.0, 125.6, 125.7, 125.8,
127.3, 128.3, 128.5, 129.0, 131.2, 133.7, 135.8.
(1Z,3E)-7ad
1H NMR (600 MHz, CDCl3): δ = 6.41 (m, 2 H), 6.70 (d, J = 15.6 Hz, 1 H),
7.20–7.24 (m, 2 H), 7.27–7.34 (m, 6 H), 7.37 (d, J = 7.8 Hz, 2 H).
13C NMR (151 MHz, CDCl3): δ = 124.7, 126.7, 128.0, 128.6, 128.74,
1-(Pent-1-en-1-yl)naphthalene (7bi)18
Mixture of the Z- and E-isomers (Z/E = 73:27, determined by 1H NMR
128.75, 130.4, 131.0, 132.8, 135.5, 136.2, 137.2.
spectroscopy).
Total yield: 71.55 mg (91%); yellow oil; Rf = 0.68 (PE).
(1E,3E)-7ad
1H NMR (600 MHz, CDCl3): δ = 6.55–6.60 (m, 1 H), 6.63–6.68 (m, 1 H),
6.85–6.93 (m, 2 H), 7.20–7.24 (m, 1 H), 7.24–7.30 (m, 6 H), 7.41 (d, J =
7.2 Hz, 2 H).
13C NMR (151 MHz, CDCl3): δ = 126.5, 127.6, 127.8, 128.9, 128.96,
129.0, 129.9, 131.4, 133.1, 133.4, 135.9, 137.3.
(Z)-7bi
1H NMR (600 MHz, CDCl3): δ = 0.85 (t, J = 7.5 Hz, 3 H), 1.37–1.45 (m, 2
H), 2.10–2.15 (m, 2 H), 5.92 (dt, J = 7.5, 11.4 Hz, 1 H), 6.87 (d, J = 11.4
Hz, 1 H), 7.33 (d, J = 7.2 Hz, 1 H), 7.39–7.50 (m, 3 H), 7.74 (d, J = 7.8 Hz,
1 H), 7.80–7.84 (m, 1 H), 7.98–8.01 (m, 1 H).
13C NMR (151 MHz, CDCl3): δ = 13.9, 23.1, 30.8, 125.2, 125.3, 125.78,
125.83, 126.5, 127.0, 127.2, 128.4, 132.0, 133.6, 134.6, 135.0.
Ethyl 3-(4-Chlorophenyl)-2-methylacrylate (7ae)14
Only the E-isomer was observed.
Yield: 79.23 mg (88%); yellow oil; Rf = 0.33 (PE–EtOAc, 10:1).
(E)-7bi
IR (KBr): 1708 cm–1
.
1H NMR (600 MHz, CDCl3): δ = 1.00 (t, J = 7.5 Hz, 3 H), 1.52–1.59 (m, 2
H), 2.27–2.32 (m, 2 H), 6.22 (dt, J = 6.9, 15.6 Hz, 1 H), 7.11 (d, J = 15.6
Hz, 1 H), 7.39–7.50 (m, 3 H), 7.54 (d, J = 7.2 Hz, 1 H), 7.72 (d, J = 8.4 Hz,
1 H), 7.80–7.84 (m, 1 H), 8.12 (d, J = 8.4 Hz, 1 H).
1H NMR (600 MHz, CDCl3): δ = 1.35 (t, J = 7.2 Hz, 3 H), 2.09 (s, 3 H),
4.27 (q, J = 7.2 Hz, 2 H), 7.32 (d, J = 8.4 Hz, 2 H), 7.35 (d, J = 8.4 Hz, 2 H),
7.62 (s, 1 H).
13C NMR (151 MHz, CDCl3): δ = 14.1, 14.3, 61.0, 128.6, 129.2, 130.9,
13C NMR (151 MHz, CDCl3): δ = 13.9, 22.7, 35.6, 123.6, 124.1, 125.7,
134.1, 134.3, 137.3, 168.4.
125.8, 125.9, 127.2, 127.3, 128.5, 131.2, 133.7, 134.4, 135.9.
1-Vinylnaphthalene (7bf)17
1-Chloro-4-(cyclopentylidenemethyl)benzene (7aj)19
Yield: 52.88 mg (86%); pale yellow oil; Rf = 0.45 (PE).
Yield: 69.94 mg (91%); yellow oil; Rf = 0.69 (PE).
1H NMR (600 MHz, CDCl3): δ = 5.45 (dd, J = 0.9, 10.8 Hz, 1 H), 5.77 (dd,
J = 0.9, 17.4 Hz, 1 H), 7.40–7.51 (m, 4 H), 7.60 (d, J = 7.2 Hz, 1 H), 7.76
(d, J = 7.8 Hz, 1 H), 7.82 (d, J = 7.8 Hz, 1 H), 8.09 (d, J = 7.8 Hz, 1 H).
1H NMR (400 MHz, CDCl3): δ = 1.68–1.76 (m, 2 H), 1.79–1.88 (m, 2 H),
2.50–2.58 (m, 4 H), 6.35 (s, 1 H), 7.26 (d, J = 8.6 Hz, 2 H), 7.32 (d, J = 8.6
Hz, 2 H).
13C NMR (151 MHz, CDCl3): δ = 117.1, 123.6, 123.8, 125.6, 125.8,
13C NMR (100 MHz, CDCl3): δ = 25.7, 27.2, 31.2, 36.1, 119.8, 128.3,
126.1, 128.1, 128.5, 131.1, 133.6, 134.4, 135.6.
129.2, 131.1, 137.4, 148.0.
1-(2-Methylprop-1-en-1-yl)naphthalene (7bg)6b
2-(4-Chlorostyryl)-1,3-dioxolane (7ak)12
Yield: 53.51 mg (73%); yellow oil; Rf = 0.70 (PE).
(Z)-7ak
1H NMR (400 MHz, CDCl3): δ = 1.78 (s, 3 H), 2.10 (s, 3 H), 6.74 (s, 1 H),
7.37 (d, J = 6.8 Hz, 1 H), 7.49–7.56 (m, 3 H), 7.80 (d, J = 7.6 Hz, 1 H),
7.89–7.93 (m, 1 H), 8.05–8.10 (m, 1 H).
13C NMR (100 MHz, CDCl3): δ = 19.6, 26.2, 123.0, 125.3, 125.4, 125.6
(overlapped, 2 C), 126.68, 126.75, 128.3, 132.3, 133.6, 136.1, 136.9.
Yield: 43.57 mg (52%); yellow oil; Rf = 0.36 (PE–EtOAc, 10:1).
1H NMR (600 MHz, CDCl3): δ = 3.90–3.96 (m, 2 H), 4.04–4.10 (m, 2 H),
5.45 (d, J = 7.5 Hz, 1 H), 5.74 (dd, J = 7.5, 12.2 Hz, 1 H), 6.76 (d, J = 12.2
Hz, 1 H), 7.29–7.35 (m, 4 H).
13C NMR (151 MHz, CDCl3): δ = 65.2, 99.5, 128.3, 128.5, 130.3, 133.8,
134.1, 134.5.
1-(Prop-1-en-1-yl)naphthalene (7bh)18
Mixture of the Z- and E-isomers (Z/E = 65:35, determined by 1H NMR
spectroscopy).
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(E)-7ak
1H NMR (600 MHz, CDCl3): δ = 1.63–1.69 (m, 2 H), 1.75–1.80 (m, 2 H),
2.46–2.51 (m, 2 H), 2.52–2.57 (m, 2 H), 6.34–6.37 (m, 1 H), 7.12–7.17
(m, 1 H), 7.28–7.31 (m, 4 H).
13C NMR (151 MHz, CDCl3): δ = 25.7, 27.2, 31.2, 36.0, 120.8, 125.6,
128.0, 128.2, 138.9, 147.2.
Yield: 27.02 mg (32%); white solid; mp 82–84 °C; Rf = 0.21 (PE–EtOAc,
10:1).
1H NMR (600 MHz, CDCl3): δ = 3.93–4.00 (m, 2 H), 4.03–4.10 (m, 2 H),
5.42 (d, J = 6.0 Hz, 1 H), 6.14 (dd, J = 6.0, 16.2 Hz, 1 H), 6.73 (d, J = 16.2
Hz, 1 H), 7.30 (d, J = 8.4 Hz, 2 H), 7.34 (d, J = 8.4 Hz, 2 H).
1-(Cyclopentylidenemethyl)-4-methylbenzene (7ij)20
13C NMR (151 MHz, CDCl3): δ = 65.2, 103.7, 125.7, 128.2, 128.8, 133.6,
Yield: 49.47 mg (72%); yellow oil; Rf = 0.45 (PE).
134.1, 134.3.
1H NMR (600 MHz, CDCl3): δ = 1.63–1.67 (m, 2 H), 1.73–1.79 (m, 2 H),
2.32 (s, 3 H), 2.46 (t, J = 6.9 Hz, 2 H), 2.52 (t, J = 7.2 Hz, 2 H), 6.32 (s, 1
H), 7.11 (d, J = 7.8 Hz, 2 H), 7.19 (d, J = 7.8 Hz, 2 H).
13C NMR (151 MHz, CDCl3): δ = 21.1, 25.7, 27.3, 31.2, 35.9, 120.6,
127.9, 128.9, 135.2, 136.1, 146.1.
1-(Cyclopentylidenemethyl)-4-fluorobenzene (7cj)20
Yield: 60.96 mg (86%); yellow oil; Rf = 0.49 (PE).
1H NMR (600 MHz, CDCl3): δ = 1.62–1.68 (m, 2 H), 1.74–1.79 (m, 2 H),
2.44–2.50 (m, 4 H), 6.30 (s, 1 H), 6.96–7.00 (m, 2 H), 7.21–7.25 (m, 2
H).
13C NMR (151 MHz, CDCl3): δ = 25.7, 27.2, 31.0, 35.9, 115.0 (d, JC–F
1-(Cyclopentylidenemethyl)-4-methoxybenzene (7jj)25
=
Yield: 48.26 mg (64%); yellow oil; Rf = 0.68 (PE–EtOAc, 10:1).
21.6 Hz), 119.7, 129.4 (d, JC–F = 7.7 Hz), 135.1 (d, JC–F = 3.0 Hz), 146.7
(d, JC–F = 1.7 Hz), 160.9 (d, JC–F = 245.0 Hz).
1H NMR (600 MHz, CDCl3): δ = 1.61–1.67 (m, 2 H), 1.73–1.80 (m, 2 H),
2.43–2.47 (m, 2 H), 2.48–2.53 (m, 2 H), 3.78 (s, 3 H), 6.29 (s, 1 H), 6.85
(d, J = 8.4 Hz, 2 H), 7.23 (d, J = 8.4 Hz, 2 H).
1-Bromo-4-(cyclopentylidenemethyl)benzene (7dj)21
13C NMR (151 MHz, CDCl3): δ = 25.7, 27.3, 31.0, 35.9, 55.3, 113.7,
Yield: 87.04 mg (92%); waxy oil; Rf = 0.59 (PE).
1H NMR (600 MHz, CDCl3): δ = 1.62–1.68 (m, 2 H), 1.74–1.80 (m, 2 H),
2.43–2.50 (m, 4 H), 6.27 (s, 1 H), 7.14 (d, J = 8.4 Hz, 2 H), 7.40 (d, J = 8.4
Hz, 2 H).
120.1, 129.1, 131.8, 144.8, 157.6.
5-(Cyclopentylidenemethyl)-1,2,3-trimethoxybenzene (7kj)25
13C NMR (151 MHz, CDCl3): δ = 25.6, 27.2, 31.3, 36.1, 119.3, 119.8,
Yield: 72.97 mg (73%); yellow oil; Rf = 0.68 (PE–EtOAc, 5:1).
1H NMR (600 MHz, CDCl3): δ = 1.64–1.69 (m, 2 H), 1.76–1.82 (m, 2 H),
2.48 (t, J = 7.2 Hz, 2 H), 2.56 (t, J = 7.2 Hz, 2 H), 3.84 (s, 3 H), 3.86 (s, 6
H), 6.29 (s, 1 H), 6.54 (s, 2 H).
129.5, 131.3, 137.8, 148.2.
1-(Cyclopentylidenemethyl)-2-nitrobenzene (7ej)22
13C NMR (151 MHz, CDCl3): δ = 25.6, 27.2, 31.1, 35.9, 56.0, 60.9, 105.3,
Yield: 75.87 mg (93%); yellow oil; Rf = 0.47 (PE–EtOAc, 10:1).
1H NMR (600 MHz, CDCl3): δ = 1.65–1.75 (m, 4 H), 2.34–2.39 (m, 2 H),
2.48–2.53 (m, 2 H), 6.60–6.63 (m, 1 H), 7.28–7.31 (m, 1 H), 7.46–7.53
(m, 2 H), 7.85 (dd, J = 1.0, 14.1 Hz, 1 H).
120.8, 134.7, 136.3, 146.6, 153.0.
2-(Cyclopentylidenemethyl)pyridine (7lj)26
13C NMR (151 MHz, CDCl3): δ = 25.5, 26.7, 31.0, 35.0, 115.7, 124.2,
Yield: 61.45 mg (96%); yellow oil; Rf = 0.75 (PE–EtOAc, 5:1).
1H NMR (600 MHz, DMSO-d6): δ = 1.60–1.65 (m, 2 H), 1.70–1.76 (m, 2
H), 2.47–2.51 (m, 2 H), 2.71 (t, J = 6.9 Hz, 2 H), 6.44 (s, 1 H), 7.12 (dd,
J = 4.8, 7.2 Hz, 1 H), 7.28 (d, J = 7.8 Hz, 1 H), 7.68–7.72 (m, 1 H), 8.52
(d, J = 3.6 Hz, 1 H).
13C NMR (151 MHz, DMSO-d6): δ = 25.2, 26.6, 31.8, 35.7, 120.3, 120.6,
122.8, 136.1, 149.0, 151.9, 156.7.
126.6, 130.7, 132.2, 133.7, 148.3, 151.1.
1-(Cyclopentylidenemethyl)-4-nitrobenzene (7fj)23
The reaction was carried out at 80 °C.
Yield: 54.29 mg (67%); yellow oil; Rf = 0.80 (PE–EtOAc, 10:1).
1H NMR (600 MHz, CDCl3): δ = 1.59–1.65 (m, 2 H), 1.71–1.78 (m, 2 H),
2.43–2.51 (m, 4 H), 6.34 (s, 1 H), 7.31 (d, J = 8.7 Hz, 2 H), 8.07 (d, J = 8.7
Hz, 2 H).
2-(Cyclopentylidenemethyl)furan (7mj)27
Yield: 42.05 mg (71%); yellow oil; Rf = 0.63 (PE).
13C NMR (151 MHz, DMSO-d6): δ = 25.0, 26.7, 31.2, 36.2, 119.3, 123.5,
128.4, 144.7, 145.0, 153.2.
1H NMR (600 MHz, CDCl3): δ = 1.55–1.62 (m, 2 H), 1.65–1.73 (m, 2 H),
2.36 (t, J = 6.3 Hz, 2 H), 2.42 (t, J = 5.4 Hz, 2 H), 6.03 (s, 1 H), 6.17 (s, 1
H), 6.29 (s, 1 H), 7.24 (s, 1 H).
13C NMR (151 MHz, CDCl3): δ = 26.3, 27.0, 31.6, 35.3, 106.2, 109.9,
111.1, 140.4, 146.3, 154.3.
2-(Cyclopentylidenemethyl)benzaldehyde (7gj)24
Yield: 37.61 mg (50%); yellow oil; Rf = 0.10 (PE–EtOAc, 50:1).
IR (KBr): 1697 cm–1
.
1H NMR (600 MHz, CDCl3): δ = 1.67–1.75 (m, 4 H), 2.27–2.31 (m, 2 H),
2.53 (t, J = 6.0 Hz, 2 H), 6.85 (s, 1 H), 7.31–7.37 (m, 2 H), 7.50–7.54 (m,
1 H), 7.85 (d, J = 7.2 Hz, 1 H).
13C NMR (151 MHz, CDCl3): δ = 25.6, 26.6, 30.9, 34.8, 116.5, 126.5,
129.0, 129.7, 133.2, 133.4, 142.3, 151.5, 192.7.
(2-(4-Methoxyphenyl)-5-methyl-1,3,2-dioxaborinan-5-yl)meth-
anol (2b)
The reaction of 5n with 6j and 4b in toluene at 120 °C afforded no ole-
fination product 7nj, leading to a complicated mixture. When the re-
action was performed in CH2Cl2 at r.t., 7nj was also not detected, and
2b was isolated as a yellow oil in 61% yield (72.18 mg). In the absence
of 6j, the reaction of 5n with 4b in CH2Cl2 at r.t. gave 2b in 65% yield
(27.69 mg, 0.18-mmol scale).
(Cyclopentylidenemethyl)benzene (7hj)25
Yield: 46.50 mg (73%); yellow oil; Rf = 0.43 (PE).
Rf = 0.67 (CH2Cl2–MeOH, 80:1).
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1H NMR (400 MHz, DMSO-d6): δ = 0.93 (s, 3 H), 3.40 (d, J = 4.8 Hz, 2
H), 3.80 (d, J = 10.8 Hz, 2 H), 3.82 (s, 3 H), 3.99 (d, J = 10.8 Hz, 2 H),
4.90 (t, J = 4.8 Hz, 1 H), 6.95 (d, J = 8.4 Hz, 2 H), 7.69 (d, J = 8.4 Hz, 2 H).
13C NMR (100 MHz, DMSO-d6): δ = 22.4, 41.8, 60.1, 68.1, 72.7, 118.4,
140.5, 166.6 (C–B not observed).
11B NMR (128 MHz, DMSO-d6): δ = 30.8 (br s).
MS (EI, 70 eV): m/z (%) = 135.5 (86), 178.7 (7), 237.0 (100) [M + H]+.
HRMS (QFT-ESI): m/z (+) [M + Na]+ calcd for C12H17BNaO4+: 259.1112;
found: 259.1115.
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Acknowledgment
We thank the National Natural Science Foundation of China for their
financial support of our program (Grant No. 21272170).
Supporting Information
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0034-1378919.
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