Synthesis of Pinacolylboronate-Substituted Stilbenes and their application to the synthesis of boron capped polyenes

Article abstract of DOI:10.1016/j.jorganchem.2015.08.007

A series of novel 4,4,5,5-tetramethyl-2-(4-substitutedstyrylphenyl)-1,3,2 dioxaborolane derivatives has been synthesized. 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-methyl triphenylphosphonium bromide (4) was treated with 3 equiv of tBuONa, various a

Full text of DOI:10.1016/j.jorganchem.2015.08.007

Journal of Organometallic Chemistry xxx (2015) 1e9
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis of Pinacolylboronate-Substituted Stilbenes and their
application to the synthesis of boron capped polyenes
,
b
,
c
,
, b
Bhaskar C. Das a
*, Sakkarapalayam M. Mahalingam a, Sasmita Das a
,
Narayan S. Hosmane d, Todd Evans c
a Division of Hematology and Oncology, Department of Internal Medicine, The University of Kansas School of Medicine, Kansas City, KS 66103, USA
b Molecular Bio-nanotechnology, Imaging and Therapeutic Research Unit, Veteran Affairs Medical Center, Kansas City, MO 64128, USA
c Department of Surgery, Weill Cornell Medical College of Cornell University, New York, NY 10065, USA
d Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115-2862, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel 4,4,5,5-tetramethyl-2-(4-substitutedstyrylphenyl)-1,3,2 dioxaborolane derivatives has
been synthesized. 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-methyl triphenylphosphonium bro-
mide (4) was treated with 3 equiv of tBuONa, various aldehydes in the presence of DMF, and stirred at
room temperature 4e6 h to yield the corresponding boron containing stilbene derivatives 1a-n in 71
e94% yields. A one-pot protocol transformation has also been developed and used this methodology to
synthesize boron containing resveratrol analogues. Simple and clean reactions, high yield of the products
are the salient features of this methodology. We used this reaction to synthesize the boron capped
polyenes. These boron containing polyene systems are potential intermediate to synthesize conjugated
polyene as new material for LCD (Liquid Crystal Display) technology. The biological testing of these
compounds is currently underway to identify potential therapeutic for Neurodegenerative diseases.
© 2015 Elsevier B.V. All rights reserved.
Received 7 April 2015
Received in revised form
5 August 2015
Accepted 12 August 2015
Available online xxx
Keywords:
Pinacolylboron
Stilbenes
Resveratrol
Alzheimer's diseases (AD)
Wittig reactions
Conjugated alkenes
Liquid Crystal Display
1. Introduction
Our hypothesis to develop boron-containing resveratrol ana-
logues is based on two expectations. First, it is expected that the
The idea of using zebrafish to screen small molecules for possible
drug activity is recent but now well validated by a number of studies.
There are two common approaches. 1) Screening a very large
random library, or 2) screening smaller “drug” libraries, e.g. FDA-
approved or drugs of known action. An alternative approach,
which is newer and less common, is to generate small but novel
libraries based on derivatives that are predicted by design to interact
with key path-ways. We call this LRD (Limited Rational Design)
because it is still a screen for unknown activities, but based on a
strong biological prediction. Using our LRD approach, in the context
of an ongoing chemical biology project focused on the Retinoic acid,
Oxidative, and TGF-beta (Transforming Growth Factor-beta)
pathway in developing zebrafish embryos [1e3], we envisioned
developing a pinacolylboronate-substituted resveratrol analogues.
boron atoms introduced into biologically active molecular frame-
works might interact with a target protein not only through
hydrogen bonds but also through covalent bonds, and this inter-
action would pro-duce potent biological activity [4,5]. The use of
boron atoms in pharmaceutical drug design possesses a high po-
tential for discovery of new biological activity [6]. Among various
boron compounds synthesized, much attention has been paid to
boronic acid containing pep-tides such as Velcade and DPP-IV in-
hibitors [7,8]. In these boropeptides, a carboxylic acid has been
replaced by a boronic acid group. Second, from a literature search
we found that reseveratrol (trans-3,4/, 5-trihydroxystilbene) (Fig.1)
is a polyphenolic compound that modulates TGF-beta signaling
pathway and potential therapeutic agent for the treatment of Alz-
heimer's disease [9,17]. In this context we under-took a project to
synthesize boron containing resveratrol analogues. In the process
of synthesizing boron-containing reseveratol analogues, we
developed
a
synthetic methodology to synthesize boron-
* Corresponding author. Division of Hematology and Oncology, Department of
Internal Medicine, The University of Kansas School of Medicine, Kansas City, KS
66103, USA.
containing stilbene derivatives and used this methodology to
synthesize our target compound 1o (Fig. 1).
E-mail address: bdas@kumc.edu (B.C. Das).
http://dx.doi.org/10.1016/j.jorganchem.2015.08.007
0022-328X/© 2015 Elsevier B.V. All rights reserved.
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B.C. Das et al. / Journal of Organometallic Chemistry xxx (2015) 1e9
Fig. 1. Resveratrol and boron-containing resveratrol.
Fig. 2. Retrosynthetic approach for pinacolylboronate-substituted stilbene derivatives 1.
2. Results and discussion
boronato phosphonium ylide 4 in the literature, the route appeared
highly attractive. Compound 4 is stable in air, so different phenyl and
alkyl aldehydes are easily available or can be derivatized to syn-
thesize a library of boron-containing stilbene derivatives. Herein, we
report the success of this new route based on disconnection B
(Fig. 1), the preparation of pinacol ester of boronato phosphonium
ylide 4, followed by the novel synthesis of pinacolylboronate-
substituted stilbene derivatives via the direct Wittig bromide (4)
from the corresponding 2-[4/-(bromomethyl)phenyl]-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane 6 in the presence of 1.01 equiv of
tri-phenylphosphine in acetonitrile at reflux condition (Scheme 1).
The most familiar and general strategy for synthesis of boron-
containing stilbenes 1 is based on disconnection A (Fig. 2) and in-
volves the Wittig reaction of the various substituted benzyl phos-
phonium ylide 2 with the pinacol ester of boronate aldehyde 3 [10].
To our surprise, literature search failed to uncover any examples of
pinacol ester of boronato phosphonium ylide. We report herein the
employment of this strategy to prepare novel pinacolylboronate-
substituted stilbene derivatives. Although Wittig and Hor-
nereWadswortheEmmons reactions have been carried out on
aldehyde derivatives of boronate esters [11e13], the problem with
this approach A (Fig. 2) to synthesize boron-containing stilbene
derivatives requires various substituted benzyl phosphonium
ylides and boron containing aldehydes. Boron-containing alde-
hydes are very prone to self-dimerization and oxidation and
decomposed for longer storage, so this method is limited in scope.
To overcome this problem, we undertook the disconnection B
approach (Fig. 2), envisaging the use of the pinacol ester of bor-
onato phosphonium ylide 4, which has not previously been
explored.
Compound
6 [14] was prepared starting from 4,4,5,5-
tetramethyl-2-p-tolyl-1,3,2-dioxaborolane 7, NBS and AIBN in car-
bon tetrachloride were refluxed for 12 h. In our initial attempt 4-
(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-methyl triphenyl-
phosphonium bromide 4 was isolated as a white solid in 92% yield.
The minor excess of PPh3 was removed from the product by trit-
uration with ether 2e3 times and the product was found to be
stable under normal atmospheric conditions. Subsequently, we
optimized the Wittig reaction of the ylide derived from this salt
using benzaldehyde (Scheme 2).
Our methodology is complementary to their finding, but more
practical applicable as it contains boronic esters and acids which are
biological active. Because there is no dearth of pinacol esters of
It is noteworthy that the three equivalents of sodium tert-
butoxide in DMF at room temperature led to the highest yield of
1a (Table 1, entry 1). With this optimized condition in hand, we
Scheme 1. Synthesis of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-methyl triphenylphosphonium bromide 4.
Scheme 2. Proposed synthesis of stibene 1.
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B.C. Das et al. / Journal of Organometallic Chemistry xxx (2015) 1e9
3
Table 1
Wittig reaction of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-methyl triphenylphosphonium bromide (4) with various aldehydes.a
Entry
1
Aldehyde
Product
Reaction time (h)
2
Yield (%)b
92
O
O
O
B
H
O2N
H
O2N
1b E:Z = 20: 80
2
4
94
O
O
B
H
O
F
H
F
1c E:Z = 37: 63
3
4
5
12
10
6
74
90
72
O
O
O
B
H
HOOC
H
H
CO C
1d E:Z = 76 : 24
O
O
O
H
B
O
B
O
B
O
H
O
1e E:Z = 14 : 86
O
O
HO
B
HO
B
H
O
HO
H
B
0 HO
1f E:Z = 64 : 36
6
7
12
12
81
71
O
Cl
O
Cl
B
H
O
H
OH
Cl
OH
1g E:Z = 42 : 58
Cl
O
O
B
O
H
H
OH
OH
1h E:Z = 75 : 25
8
10
4
76
78
87
O
O2N
O
O2N
B
H
O
H
OH
OH
1i E:Z = 55 : 45
9
O
O
B
O
H
N
N
1j E:Z = 100 : 0
10
2
O
O
B
H
O
S
S
1k E:Z = 0 : 100
11
12
4
5
80
88
O
O
B
H
O
O
O
H
1l E:Z = 40 : 60
O
O
B
O
Ph
H
Ph
H
1m E:Z = 70 : 30
13
11
85
O
O
B
H
O
H
1n E:Z = 67: 33
a
t
All reactions were performed using 1 equivalent of aldehyde and 3 equivalents of BuONa in DMF for 2e12 h.
b
Isolated yield (mixture of E and Z) refers to aldehyde and the E/Z ratios were determined by 1H NMR.
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B.C. Das et al. / Journal of Organometallic Chemistry xxx (2015) 1e9
examined the scope of the Wittig reaction for the synthesis of
pinacolylboronate-substituted stilbenes using various aryl alde-
hydes. The results are summarized in Table 1. Detail experimental
procedures and analytical data's are presented in Ref. [16].
refluxing conditions and use this salt to developed a novel direct
route to synthesize boron-containing stilbene derivatives via the
Wittig reaction with various aldehydes, to yield 71e94%. Addi-
tionally, one-pot protocol was also developed. In addition we used
this methodology to synthesize boron containing resveratrol ana-
logues and boron containing polyene chains. Experiments are
currently underway to test the biological activity of these de-
rivatives and to determine their utility as modulators of TGF-beta
signaling and therapeutic potential in Alzheimer's disease.
The reaction proved tolerant of both electron-withdrawing (p-
NO2, p-CO2Me; Table 1, entry 1 and 3) and electron-donating
groups (p-F, Table 1, entry 2) on the phenyl ring of the aldehyde.
Interestingly, methyl-4-formylbenzoate as a substrate was directly
converted to the corresponding boron containing stilbene carbox-
ylic acid 1d in good yield (Table 1, entry 3). Also we synthesized the
symmetrically substituted boron containing stilbene 1e in good
yield (Table 1, entry 4). Most surprisingly, 4-formylphenyl boronic
acid (Table 1, entry 5) gives corresponding product 1f (one side
pinacolylboronate and other side free boronic acid). The function-
alized salicyldehydes also react well with the 8 and yielded the
corresponding highly pinacolylboronate-substituted stilbenes with
good yields (Table 1, entries 6, 7 and 8). Though the stereo selec-
tivity (E:Z) is good to moderate, but changing substrates, base and
solvent may increase the selectivity. To get good stereo-selectivity,
we tried with different aryl aldehydes containing a heteroatom
such as oxygen, sulfur, or nitro-gen (Table 1, entries 9, 10 and 11),
the desired products were obtained in good yield, but to our sur-
prise isonicotinaldehyde entry 9 gives exclusively E isomer and
thiophene-2-carbaldehyde entry 1k gives exclusively Z isomer. The
reactivity of 2-thiophenecarboxaldehyde was higher compared to
other heterocyclic aldehydes (Table 1, entry 10). It clearly indicates
that, based on substrates high E:Z stereo selectivity could be
4. Experimental
4.1. General
All reagents were purchased from commercial sources and used
without treatment, unless otherwise indicated. The products were
purified by column chromatography over silica gel. 1H NMR and 13
C
NMR spectra were recorded at 25 ꢀC at 300 MHz and 75 MHz,
respectively, with TMS as internal standard. Abbreviations for
signal coupling are as follows: s, singlet; d, doublet; t, triplet; q,
quartet; m, multiplet; br, broad. Column chromatography was
performed using SiO2 (0.040e0.063 mm, 230e400 mesh ASTM)
from Merck. All reagents were obtained from commercial sources.
Mass spectra were recorded on Varian MS mass spectrometer.
4.1.1. Preparation of the 4-(4,4,5,5-tetramethyl-1,3,2-
dioxaboratophenyl)-methyl triphenylphosphonium bromide (4)
achievable. In addition to the aromatic aldehydes, a,b-unsaturated
aldehydes (Table 1, entries 12 and 13) also reacted successfully and
the corresponding conjugated diene functionalized boronic esters
1m and 1n were isolated in good yield. This method is versatile and
tolerant to all substrates and reaction conditions. However, E:Z
ratios obtained were good to moderate, but could be improved by
changing substrates, base and solvent system.
O
B
O
PPh3.Br
Having established the preferred reaction conditions, we applied
this methodology to synthesize a boron-containing resveratrol de-
rivative 1o (Scheme 3). Boronate phosphonium ylide 4 readily
reacted with 4-hydroxybenzaldehyde in the presence of tBuONa in
DMF to yield 58% of compound 1o, E:Z isomer ratio 70:30.
Also we developed a one-pot Wittig reaction. In this case, 4-
(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-methyl triphenyl-
phosphonium bromide (4), the intermediate generated by reaction
of 6 with triphenylphosphine, was reacted directly with methyl-4-
formylbenzoate in the presence of a base, and the desired boron-
containing stilbene carboxylic acid 1d product was isolated in
75% overall yield as a one-pot Wittig reaction followed by acid
hydrolysis (Scheme 4).
4
A mixture of 2-[4/-(bromomethyl)phenyl]-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane (6) (4 g, 1.0 mmol) and triphenylphosphine
(3.568 g,1.01 mmol) in acetonitrile (40 mL) was heated in an oil bath
at 90 ꢀC. After 12 h, the reaction mixture was cooled to rt and then
the solvent was evaporated and dried under high vacuum to obtain
the crude compound 8, then triturated with diethyl ether (3 ꢁ 5 mL)
to obtain the desired pure compound 4 as a white solid (6.92 g, 92%
yield). 1H NMR (300 MHz, CDCl3):
J ¼ 18 Hz, 2H), 7.03e7.10 (m, 2H), 7.53e7.57 (d, J ¼ 2 Hz), 7.57e7.66
(m, 6H), 7.66e7.82 (m, 9H). 13C NMR (75 MHz, CDCl3):
25.3, 84.4,
d 1.32 (s, 12H), 5.36e5.42 (d,
d
After generalizing the reaction conditions, we decided to
117.5, 118.8, 130.5, 130.6, 131.2, 131.3, 134.7, 134.8, 135.4. HRMS (ESI):
m/z calcd. for C31H33BO2P [M]þ 479.2311, found 479.2323.
examine the Wittig reaction of ylide
4 with benzene-1,4-
dicarbaldehyde 8 to synthesize the boron capped polyene system.
The boronate ylide 4 underwent Wittig reaction with benzene-1,4-
dicarbaldehyde 8 to provide diboronate of 1,4-distyryl-benzene 9
with good yield (85%) as our results are depicted in (Scheme 4).
These boron capped polyene spacers could be used as potential
intermediate to synthesize conjugated polyene as new material for
Liquid Crystal Display-LCD technology [15]. These boron based
stilbene derived could be used as potential therapeutic for treat-
ment of Alzheimer's disease [17].
4.1.2. Wittig reaction of 4-(4,4,5,5-tetramethyl-1,3,2-
dioxaboratophenyl)-methyl triphenylphosphonium bromide (4)
with various aldehydes (Table 1)
O
B
O
H
1a E:Z = 74: 26
3. Conclusions
In conclusion, we successfully prepared 4-(4,4,5,5-tetramethyl-
1,3,2-dioxaboratophenyl)-methyl tri-phenylphosphonium bromide
using PPh3 and the corresponding 2-[4/-(bromomethyl)phenyl]-
4,4,5,5- tetramethyl-1,3,2-dioxaborolane in acetonitrile under
4.1.3. 4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)stilbene (1a)
Benzaldehyde (0.05 g, 0.47 mmol) was added to a solution of 4-
(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-methyl
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B.C. Das et al. / Journal of Organometallic Chemistry xxx (2015) 1e9
5
Scheme 3. Synthesis of boron-containing resveratrol 1o.
Scheme 4. One-pot synthesis of stilbene 1d.
triphenylphosphonium bromide (4) (0.262 g, 0.47 mmol) in anhy-
drous DMF (7 mL) under nitrogen atmosphere. Sodium tert-buta-
nolate (0.135 g, 1.41 mmol) was added to the clear solution at room
temperature, and the mixture was stirred for 4 h. The reaction
mixture was poured into water (20 mL) and neutralized with 1 M
HCl. Then the resulting mixture was extracted by EtOAc
(3 ꢁ 10 mL), washed with H2O and brine, dried over anhydrous
Na2SO4 and filtered. Evaporation of the solvent followed by column
chromatography on silica gel to obtain the pure product 1a as a
mixture of E/Z. Yield: 0.124 g (86%). 1H NMR (300 MHz, CDCl3):
mixture was poured into water (20 mL) and neutralized with 1 M
HCl. Then the resulting mixture was extracted by EtOAc
(3 ꢁ 10 mL), washed with H2O and brine, dried over anhydrous
Na2SO4 and filtered. Evaporation of the solvent followed by column
chromatography on silica gel to obtain the pure product 1b as a
mixture of E/Z. Yield: 0.106 g (92%). 1H NMR (300 MHz, CDCl3):
d
1.36 (s), 1.38 (s), 6.60e6.90 (m), 7.14e7.46 (m), 7.54e7.59 (d,
J ¼ 15 Hz), 7.65e7.69 (d, J ¼ 12 Hz), 7.70e7.74 (d, J ¼ 12 Hz),
7.55e7.58 (d, J ¼ 9 Hz), 8.06e8.10 (d, J ¼ 12 Hz), 8.23e8.26 (d,
J ¼ 9 Hz). 13C NMR (75 MHz, CDCl3):
d 25.3, 84.4, 124.0, 124.6, 126.7,
d
1.36 (s), 1.38 (s), 6.59e6.68 (m), 7.10e7.30 (m), 7.33e7.40 (m),
127.4,127.6,128.0,129.3,130.1,131.7,132.8,134.0,134.5,135.0,135.2,
135.7, 139.1, 144.2, 147.3. HRMS (ESI): m/z calcd. for C20H22BNNaO4
[MþNa]þ 374.1540, found 374.1541.
7.50e7.58 (m), 7.67e7.70 (d, J ¼ 9 Hz), 7.81e7.84 (d, J ¼ 9 Hz). 13
C
NMR (75 MHz, CDCl3):
d 25.3, 84.2, 126.2, 127.0, 127.6, 128.6, 129.1,
129.3, 130.6, 131.3, 135.1, 135.6, 137.5, 137.6, 139.5, 140.0. HRMS
(ESI): m/z calcd. for C20H23BO2 [MþNa]þ 329.1689, found 329.1684.
O
B
O
F
O
B
O
H
O2N
1c E:Z = 37: 63
H
1b E:Z = 20: 80
4.1.5. 4-Fluoro-4/-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)
stilbene (1c)
4.1.4. 4-Nitro-4/-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)
stilbene (1b)
4-Fluorobenzaldehyde (0.05 g, 0.4 mmol) was added to a solu-
tion of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-methyl
triphenylphosphonium bromide (4) (0.225 g, 0.4 mmol) in anhy-
drous DMF (7 mL) under nitrogen atmosphere. Sodium tert-buta-
nolate (0.115 g, 1.2 mmol) was added to the clear solution at room
temperature, and the mixture was stirred for 2 h. The reaction
mixture was poured into water (20 mL) and neutralized with 1 M
HCl. Then the resulting mixture was extracted by EtOAc
4-Nitrobenzaldehyde (0.05 g, 0.33 mmol) was added to a solu-
tion of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-methyl
triphenylphosphonium bromide (4) (0.185 g, 0.33 mmol) in anhy-
drous DMF (7 mL) under nitrogen atmosphere. Sodium tert-buta-
nolate (0.095 g, 0.99 mmol) was added to the clear solution at room
temperature, and the mixture was stirred for 2 h. The reaction
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B.C. Das et al. / Journal of Organometallic Chemistry xxx (2015) 1e9
(3 ꢁ 10 mL), washed with H2O and brine, dried over anhydrous
Na2SO4 and filtered. Evaporation of the solvent followed by column
chromatography on silica gel to obtain the pure product 1c as a
mixture of E/Z. Yield: 0.122 g (94%). 1H NMR (300 MHz, CDCl3):
O
HO
B
O
B
H
HO
d
1.36 (s), 1.38 (s), 6.54e6.66 (m), 6.87e6.95 (m), 7.00e7.15 (m),
1f E:Z = 64 : 36
7.15e7.28 (m), 7.47e7.50 (m), 7.51e7.53 (d, J ¼ 6 Hz), 7.69e7.73 (d,
J ¼ 12 Hz), 7.82e7.85 (d, J ¼ 9 Hz). 13C NMR (75 MHz, CDCl3):
d 25.3,
84.2, 115.2, 115.5, 115.9, 116.1, 126.1, 128.4, 128.5, 128.6, 129.0, 130.2,
130.5, 131.0, 131.2, 133.5, 133.8, 134.0, 135.1, 135.6, 140.2, 140.4.
HRMS (ESI): m/z calcd. for C20H22BFNaO2 [MþNa]þ 347.1595, found
347.1621.
4.1.8. 4-(Boronic acid)-4/-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-
2-yl)stilbene (1f)
4-formylphenylboronic acid (0.05 g, 0.33 mmol) was added to a
solution
of
4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-
methyl triphenylphosphonium bromide (4) (0.184 g, 0.33 mmol) in
anhydrous DMF (7 mL) under nitrogen atmosphere. Sodium tert-
butanolate (0.062 g, 0.99 mmol) was added to the clear solution at
room temperature, and the mixture was stirred for 4 h. The reaction
mixture was poured into water (20 mL) and neutralized with 1 M
HCl. Then the resulting mixture was extracted by EtOAc
(3 ꢁ 10 mL), washed with H2O and brine, dried over anhydrous
Na2SO4 and filtered. Evaporation of the solvent followed by column
chromatography on silica gel to obtain the pure product 1f as a
mixture of E/Z. Yield: 0.084 g (72%). 1H NMR (300 MHz, CDCl3):
O
B
O
HOOC
H
1d E:Z = 76 : 24
4.1.6. 4-Carboxyl-4/-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)
stilbene (1d)
Methyl-4-formylbenzoate (0.05 g, 0.30 mmol) was added to a
solution
of
4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-
d
1.36 (s), 1.39 (s), 7.20 (s), 2.90e2.97 (d, J ¼ 21 Hz), 6.61e6.80 (m),
7.18e7.34 (m), 7.34e7.45 (m), 7.50e7.80 (m), 7.80e7.90 (m),
8.05e8.18 (m), 8.18e8.25 (m). 13C NMR (75 MHz, CDCl3):
25.3,
methyl triphenylphosphonium bromide (4) (0.170 g, 0.30 mmol) in
anhydrous DMF (7 mL) under nitrogen atmosphere. Sodium tert-
butanolate (0.086 g, 0.90 mmol) was added to the clear solution at
room temperature, and the mixture was stirred for 12 h. The re-
action mixture was poured into water (20 mL) and neutralized with
1 M HCl. Then the resulting mixture was extracted by EtOAc
(3 ꢁ 10 mL), washed with H2O and brine, dried over anhydrous
Na2SO4 and filtered. Evaporation of the solvent followed by column
chromatography on silica gel to obtain the pure product 1d as a
mixture of E/Z. Yield: 0.078 g (74%). 1H NMR (300 MHz, CDCl3):
d
84.2, 126.4, 125.5, 128.6, 128.9, 129.1, 129.2, 130.5, 130.6, 131.0, 135.0,
135.1, 1235.6, 135.9, 140.0, 141.8, 163.2. HRMS (ESI): m/z calcd. for
C
20H24B2O4 [MþNa]þ 373.1758, found 373.1757.
Cl
Cl
O
B
O
H
OH
1g E:Z = 42 : 58
d
1.36 (s), 1.38 (s), 6.62e6.81 (m), 7.23e7.26 (d, J ¼ 9 Hz), 7.33e7.36
(d, J ¼ 9 Hz), 7.51e7.68 (m), 7.69e7.72 (d, J ¼ 9 Hz), 7.82e7.87 (m),
7.94e7.98 (d, J ¼ 12 Hz), 8.08e8.20 (m). 13C NMR (75 MHz, CDCl3):
4.1.9. 2-Hydroxy-3,5-dichloro-4/-(4,4,5,5-Tetramethyl-1,3,2-
dioxaborolan-2-yl)stilbene (1g)
d
25.3, 84.4, 1267, 127.0, 128.1, 128.6, 129.5, 130.3, 130.8, 131.2, 132.0,
133.1, 135.2, 135.8, 140.0, 143.3. HRMS (ESI): m/z calcd. for
C
21H23BO4 [MꢂH]þ 349.1611, found 349.1630.
3,5-Dichloro-2-hydroxy-benzaldehyde (0.05 g, 0.26 mmol) was
added to
a solution of 4-(4,4,5,5-tetramethyl-1,3,2-dioxabora
O
tophenyl)-methyl triphenylphosphonium bromide (4) (0.146 g,
0.26 mmol) in anhydrous DMF (7 mL) under nitrogen atmosphere.
Sodium tert-butanolate (0.075 g, 0.78 mmol) was added to the clear
solution at room temperature, and the mixture was stirred for 12 h.
The reaction mixture was poured into water (20 mL) and neutral-
ized with 1 M HCl. Then the resulting mixture was extracted by
EtOAc (3 ꢁ 10 mL), washed with H2O and brine, dried over anhy-
drous Na2SO4 and filtered. Evaporation of the solvent followed by
column chromatography on silica gel to obtain the pure product 1g
as a mixture of E/Z. Yield: 0.083 g (81%). 1H NMR (300 MHz, CDCl3):
B
O
O
B
O
H
1e E:Z = 14 : 86
4.1.7. 4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan)-4/-(4,4,5,5-
Tetramethyl-1,3,2-dioxaborolan-2-yl)stilbene (1e)
4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)benzaldehyde
(0.05 g, 0.21 mmol) was added to a solution of 4-(4,4,5,5-
tetramethyl-1,3,2-dioxaboratophenyl)-methyl triphenylphospho-
nium bromide (4) (0.120 g, 0.21 mmol) in anhydrous DMF (7 mL)
under nitrogen atmosphere. Sodium tert-butanolate (0.062 g,
0.64 mmol) was added to the clear solution at room temperature,
and the mixture was stirred for 4 h. The reaction mixture was
poured into water (20 mL) and neutralized with 1 M HCl. Then the
resulting mixture was extracted by EtOAc (3 ꢁ 10 mL), washed with
H2O and brine, dried over anhydrous Na2SO4 and filtered. Evapo-
ration of the solvent followed by column chromatography on silica
gel to obtain the pure product 1e as a mixture of E/Z. Yield: 0.084 g
d
1.36 (s), 1.38 (s), 5.65 (s), 5.86 (s), 6.55e6.65 (m), 6.75e6.81 (d,
J ¼ 18 Hz), 7.06e7.08 (d, J ¼ 6 Hz), 7.17 (s), 7.18e7.26 (m), 7.32e7.38
(m), 7.43 (s), 7.50e7.52 (d, J ¼ 6 Hz), 7.53e7.57 (d, J ¼ 12 Hz),
7.61e7.73 (m), 7.82e7.85 (d, J ¼ 6 Hz). 13C NMR (75 MHz, CDCl3):
d
25.3, 84.3,121.0,122.7,124.1,125.2,125.5,125.7,125.9,126.2,126.5,
127.5, 127.7, 128.4, 129.0, 129.2, 132.0, 134.1, 135.2, 135.6, 139.0,
139.8, 148.8, 148.9. HRMS (ESI): m/z calcd. for C20H21BCl2O3
[MþNa]þ 413.0858, found 413.0860.
O
B
(90%). 1H NMR (300 MHz, CDCl3):
d 1.36 (s), 1.37 (s), 7.20 (s),
O
7.21e7.7.29 (m), 7.53e7.56 (d, J ¼ 9 Hz), 7.64e7.68 (m), 7.81e7.84 (d,
H
J ¼ 9 Hz). 13C NMR (75 MHz, CDCl3):
d 25.3, 84.5, 125.8, 128.3, 129.8,
OH
135.2, 140.0. HRMS (ESI): m/z calcd. for C26H34B2O4 [MþNa]þ
1h E:Z = 75 : 25
455.2541, found 455.2555.
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B.C. Das et al. / Journal of Organometallic Chemistry xxx (2015) 1e9
7
4.2.0. 3,5-Di-tert-butyl-2-hydroxy-4/-(4,4,5,5-Tetramethyl-1,3,2-
dioxaborolan-2-yl)stilbene (1h)
methyl triphenylphosphonium bromide (4) (0.263 g, 0.47 mmol) in
anhydrous DMF (7 mL) under nitrogen atmosphere. Sodium tert-
butanolate (0.135 g, 1.41 mmol) was added to the clear solution at
room temperature, and the mixture was stirred for 4 h. The reaction
mixture was poured into water (20 mL) and neutralized with 1 M
HCl. Then the resulting mixture was extracted by EtOAc
(3 ꢁ 10 mL), washed with H2O and brine, dried over anhydrous
Na2SO4 and filtered. Evaporation of the solvent followed by column
chromatography on silica gel to obtain the pure product 1j as a
mixture of E/Z. Yield: 0.112 g (78%). 1H NMR (300 MHz, CDCl3):
3,5-Di-tert-butyl-2-hydroxy-benzaldehyde (0.05 g, 0.21 mmol)
was added to
a
solution of 4-(4,4,5,5-tetramethyl-1,3,2-
dioxaboratophenyl)-methyl triphenylphosphonium bromide (4)
(0.119 g, 0.21 mmol) in anhydrous DMF (7 mL) under nitrogen at-
mosphere. Sodium tert-butanolate (0.061 g, 0.63 mmol) was added
to the clear solution at room temperature, and the mixture was
stirred for 12 h. The reaction mixture was poured into water
(20 mL) and neutralized with 1 M HCl. Then the resulting mixture
was extracted by EtOAc (3 ꢁ 10 mL), washed with H2O and brine,
dried over anhydrous Na2SO4 and filtered. Evaporation of the sol-
vent followed by column chromatography on silica gel to obtain the
pure product 1h as a mixture of E/Z. Yield: 0.065 g (71%). 1H NMR
d
1.36 (s), 6.52e6.57 (d, J ¼ 15 Hz), 6.80e6.85 (d, J ¼ 15 Hz),
7.10e7.12 (d, J ¼ 6 Hz), 7.22e7.25 (d, J ¼ 9 Hz), 7.69e7.72 (d,
J ¼ 9 Hz), 8.45e8.47 (d, J ¼ 6 Hz). 13C NMR (75 MHz, CDCl3):
d 25.3,
84.3,124.0,128.8,129.0,134.5,135.3,139.7,145.6,150.4. HRMS (ESI):
(300 MHz, CDCl3):
d
1.28 (s), 1.33 (s), 1.35 (s), 1.36 (s), 1.38 (s), 1.47
m/z calcd. for C19H22BNO2 [MþH]þ 308.1822, found 308.1816.
(s), 5.18 (s), 5.19 (s), 6.60e6.80 (m), 7.00e7.10 (m), 7.20e7.25 (m),
7.25e7.38 (m), 7.40 (s), 7.54e7.58 (d, J ¼ 12 Hz), 7.63e7.68 (m),
7.71e7.74 (d, J ¼ 9 Hz), 7.82e7.85 9d, J ¼ 9 Hz). 13C NMR (75 MHz,
CDCl3):
d 25.3, 30.3, 32.0, 35.0, 35.3, 84.3, 122.8, 124.1, 125.5, 126.1,
128.6, 128.8, 129.0, 132.4, 134.0, 135.0, 135.2, 135.6, 136.0, 140.5,
143.7, 150.2. HRMS (ESI): m/z calcd. for C28H39BO3 [MþNa]þ
457.2890, found 457.2955.
O2N
O
O
4.2.3. 4,4,5,5-Tetramethyl-2-[4-(2-thiophen-2-yl-vinyl)-phenyl]-
[1,3,2]dioxaborolane (1k)
B
H
Thiophene-2-carbaldehyde (0.05 g, 0.45 mmol) was added to a
OH
solution
of
4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-
1i E:Z = 55 : 45
methyl triphenylphosphonium bromide (4) (0.252 g, 0.45 mmol) in
anhydrous DMF (7 mL) under nitrogen atmosphere. Sodium tert-
butanolate (0.128 g, 1.34 mmol) was added to the clear solution at
room temperature, and the mixture was stirred for 2 h. The reaction
mixture was poured into water (20 mL) and neutralized with 1 M
HCl. Then the resulting mixture was extracted by EtOAc
(3 ꢁ 10 mL), washed with H2O and brine, dried over anhydrous
Na2SO4 and filtered. Evaporation of the solvent followed by column
chromatography on silica gel to obtain the pure product 1k as a
mixture of E/Z. Yield: 0.121 g (78%). 1H NMR (300 MHz, CDCl3):
4.2.1. 2-Hydroxy-5-nitro-4/-(4,4,5,5-Tetramethyl-1,3,2-
dioxaborolan-2-yl)stilbene (1i)
2-hydroxy-5-nitrobenzaldehyde (0.05 g, 0.30 mmol) was added
to a solution of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-
methyl triphenylphosphonium bromide (4) (0.167 g, 0.30 mmol) in
anhydrous DMF (7 mL) under nitrogen atmosphere. Sodium tert-
butanolate (0.086 g, 0.90 mmol) was added to the clear solution at
room temperature, and the mixture was stirred for 12 h. The reac-
tion mixture was poured into water (20 mL) and neutralized with
1 M HCl. Then the resulting mixture was extracted by EtOAc
(3 ꢁ 10 mL), washed with H2O and brine, dried over anhydrous
Na2SO4 and filtered. Evaporation of the solvent followed by column
chromatography on silica gel to obtain the pure product 1i as a
mixture of E/Z. Yield: 0.083 g (76%). 1H NMR (300 MHz, CDCl3):
d
1.38 (s), 6.57e6.61 (d, J ¼ 12 Hz), 6.70e6.75 (d, J ¼ 15 Hz),
6.86e6.92 (m), 6.96e7.05 (m), 7.08e7.11 (m), 7.22e7.24 (d,
J ¼ 6 Hz), 7.28e7.30 (d, J ¼ 6 Hz), 7.34 (s), 7.39e7.42 (d, J ¼ 9 Hz),
7.48e7.51 (d, J ¼ 9 Hz), 7.80e7.83 (d, J ¼ 9 Hz). 13C NMR (75 MHz,
CDCl3):
d 25.3, 84.2, 123.1, 125.1, 125.9, 126.8, 128.1, 128.6, 135.3,
135.6, 140.1, 143.2. HRMS (ESI): m/z calcd. for C18H21BO2S [MþNa]þ
335.1253, found 335.1261.
d
1.34 (s), 1.38 (s), 5.65 (s), 6.57e6.62 (d, J ¼ 15 Hz), 6.88e7.00 (m),
7.15e7.19 (d, J ¼ 12 Hz), 7.25e7.30 (m), 7.38e7.44 (d, J ¼ 18 Hz),
7.56e7.59 (d, J ¼ 9 Hz), 7.67e7.70 (d, J ¼ 9 Hz), 7.83e7.86 (d,
J ¼ 9 Hz), 8.04e8.06 (d, J ¼ 6 Hz), 8.06e8.10 (m), 8.10e8.17 (m),
O
B
O
8.47e8.49 (d, J ¼ 6 Hz). 13C NMR (75 MHz, CDCl3):
d
25.3, 84.4, 116.1,
O
H
116.3, 121.8, 132.1, 123.5, 124.6, 125.5, 126.0, 126.7, 126.9, 128.1, 133.2,
135.4, 135.5, 135.9, 138.2, 139.5, 142.2, 142.5, 158.6, 158.8. HRMS
(ESI): m/z calcd. for C20H22BNO5 [MþNa]þ 390.1489, found 390.1502.
1l E:Z = 40 : 60
4.2.4. 2-[4-(2-Furan-2-yl-vinyl)-phenyl]-4,4,5,5-tetramethyl-[1,3,2]
dioxaborolane (1l)
Furan-2-carbaldehyde (0.05 g, 0.52 mmol) was added to a so-
lution of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-methyl
triphenylphosphonium bromide (4) (0.290 g, 0.52 mmol) in anhy-
drous DMF (7 mL) under nitrogen atmosphere. Sodium tert-buta-
nolate (0.149 g, 1.56 mmol) was added to the clear solution at room
temperature, and the mixture was stirred for 4 h. The reaction
mixture was poured into water (20 mL) and neutralized with 1 M
HCl. Then the resulting mixture was extracted by EtOAc
(3 ꢁ 10 mL), washed with H2O and brine, dried over anhydrous
Na2SO4 and filtered. Evaporation of the solvent followed by column
4.2.2. 4-{2-[4-(4,4,5,5-Tetramethyl-[1,3,2]dioxaborolan-2-yl)-
phenyl]-vinyl}-pyridine (1j)
Pyridine-4-carbaldehyde (0.05 g, 0.47 mmol) was added to a
solution
of
4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-
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j.jorganchem.2015.08.007

8
B.C. Das et al. / Journal of Organometallic Chemistry xxx (2015) 1e9
chromatography on silica gel to obtain the pure product 1l as a
mixture of E/Z. Yield: 0.123 g (80%). 1H NMR (300 MHz, CDCl3):
O
O
B
d
1.37 (s), 1.38 (s), 6.27e6.30 (m), 6.30e6.34 (m), 6.37e6.40 (m),
HO
6.14e6.52 (m), 6.6.95e7.10 (dd, J ¼ 18 Hz & 12 Hz), 7.30e7.33 (m),
H
7.42e7.50 (m), 7.79e7.82 (d, J ¼ 9 Hz). 13C NMR (75 MHz, CDCl3):
1o
E:Z = 70: 30
d
25.3, 84.2, 109.0, 110.1, 111.2, 111.8, 118.1, 119.0, 125.2, 127.3, 128.0,
128.1, 134.5, 135.2, 140.0, 140.4, 141.1, 142.3151.5, 154.2. HRMS (ESI):
m/z calcd. for C18H21BO3 [MþNa]þ 297.1662, found 297.1670.
4.2.7. 4-{2-[4-(4,4,5,5-Tetramethyl-[1,3,2]dioxaborolan-2-yl)-
phenyl]-vinyl}-phenol (1o)
O
B
O
4-hydroxybenzaldehyde (0.1 g, 0.818 mmol) was added to a
solution
of
4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-
Ph
H
methyl triphenylphosphonium bromide (4) (0.457 g, 0.818 mmol)
in anhydrous DMF (10 mL) under nitrogen atmosphere. Sodium
tert-butanolate (0.235 g, 2.45 mmol) was added to the clear solu-
tion at room temperature, and the mixture was stirred for 12 h. The
reaction mixture was poured into water (20 mL) and neutralized
with 1 M HCl. Then the resulting mixture was extracted by EtOAc
(3 ꢁ 10 mL), washed with H2O and brine, dried over anhydrous
Na2SO4 and filtered. Evaporation of the solvent followed by column
chromatography on silica gel to obtain the pure product 1o as a
mixture of E/Z. Yield: 0.152 g (58%). 1H NMR (300 MHz, CDCl3):
1m E:Z = 70 : 30
4.2.5. 4,4,5,5-Tetramethyl-2-[4-(4-phenyl-buta-1,3-dienyl)-
phenyl]-[1,3,2]dioxaborolane (1m)
3-Phenyl-propenal (0.05 g, 0.38 mmol) was added to a solution
of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-methyl triphe-
nylphosphonium bromide (4) (0.212 g, 0.38 mmol) in anhydrous
DMF (7 mL) under nitrogen atmosphere. Sodium tert-butanolate
(0.109 g, 1.14 mmol) was added to the clear solution at room tem-
perature, and the mixture was stirred for 2 h. The reaction mixture
was poured into water (20 mL) and neutralized with 1 M HCl. Then
the resulting mixture was extracted by EtOAc (3 ꢁ 10 mL), washed
with H2O and brine, dried over anhydrous Na2SO4 and filtered.
Evaporation of the solvent followed by column chromatography on
silica gel to obtain the pure product 1m as a mixture of E/Z. Yield:
d
1.37 (s), 5.02 (bs), 6.72e6.75 (d, J ¼ 9 Hz), 6.82e6.86 (d, J ¼ 12 Hz),
6.94e6.98 (d, J ¼ 12 Hz), 7.10e7.29 (m), 4.41e7.45 (d, J ¼ 12 Hz),
7.48e7.56 (m), 7.75e7.83 (m), 7.96e7.80 (d, J ¼ 12 Hz). 13C NMR
(75 MHz, CDCl3):
d 25.3, 84.2, 112.6, 116.1, 125.9, 126.3, 126.9, 127.8,
128.5, 129.5, 129.9, 130.6, 132.1, 135.6, 140.3, 140.7, 155.8. HRMS
(ESI): m/z calcd. for C20H23BO3 [MꢂH]þ 321.1662, found 321.1683.
0.110 g (88%). 1H NMR (300 MHz, CDCl3):
d 1.38 (s), 1.39 (s),
O
B
O
B
6.41e6.58 (m), 6.65e6.80 (m), 6.94e7.10 (m), 7.20e7.31 (m),
7.31e7.45 9m), 7.46e7.48 (d, J ¼ 6 Hz), 7.79e7.82 (d, J ¼ 9 Hz),
O
O
7.85e7.88 (d, J ¼ 9 Hz). 13C NMR (75 MHz, CDCl3):
d 25.3, 84.2, 126.1,
126.8, 127.0, 128.1, 128.7, 129.1, 129.6, 130.7, 133.2, 133.8, 135.2,
135.5, 137.7, 140.5140.8. HRMS (ESI): m/z calcd. for C22H25BO2
[MþNa]þ 355.1845, found 355.1845.
9
Benzene-1,4-dicarbaldehyde 8 (0.05 g, 0.37 mmol) was added to
solution of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-
O
a
B
methyl triphenylphosphonium bromide (4) (0.417 g, 0.74 mmol) in
anhydrous DMF (10 mL) under nitrogen atmosphere. Sodium tert-
butanolate (0.214 g, 2.23 mmol) was added to the clear solution at
room temperature, and the mixture was stirred for 2 h. The reaction
mixture was poured into water (30 mL) and neutralized with 1 M
HCl. Then the resulting mixture was extracted by EtOAc
(3 ꢁ 10 mL), washed with H2O and brine, dried over anhydrous
Na2SO4 and filtered. Evaporation of the solvent followed by column
chromatography on silica gel to obtain the pure product 9. Yield:
O
H
1n E:Z = 67: 33
4.2.6. 4,4,5,5-Tetramethyl-2-[4-(5-methyl-hexa-1,3-dienyl)-
phenyl]-[1,3,2]dioxaborolane (1n)
4-Methyl-pent-2-enal (0.05 g, 0.51 mmol) was added to a so-
lution of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-methyl
triphenylphosphonium bromide (4) (0.285 g, 0.51 mmol) in anhy-
drous DMF (7 mL) under nitrogen atmosphere. Sodium tert-buta-
nolate (0.147 g, 1.53 mmol) was added to the clear solution at room
temperature, and the mixture was stirred for 2 h. The reaction
mixture was poured into water (20 mL) and neutralized with 1 M
HCl. Then the resulting mixture was extracted by EtOAc
(3 ꢁ 10 mL), washed with H2O and brine, dried over anhydrous
Na2SO4 and filtered. Evaporation of the solvent followed by column
chromatography on silica gel to obtain the pure product 1n as a
mixture of E/Z. Yield: 0.128 g (85%). 1H NMR (300 MHz, CDCl3):
0.169 g (85%). 1H NMR (300 MHz, CDCl3):
d 1.35 (s), 1.36 (s), 1.37 (s),
1.38 (s), 6.57e6.59 (d, J ¼ 6 Hz), 6.62 (s), 7.10e7.13 (m), 7.16e7.20
(m), 7.21e7.30 (m), 7.36e7.39 (d, J ¼ 9 Hz), 7.44e7.60 (m), 7.65e7.75
(m), 7.80e7.88 (m). 13C NMR (75 MHz, CDCl3):
d 25.3, 84.4, 126.2,
127.0, 127.8, 128.3, 128.9, 129.0, 129.3, 129.8, 131.0, 132.5, 132.6,
133.4, 135.1, 136.0, 140.2, 140.8. HRMS (ESI): m/z calcd. for
C
34H40B2O4 [MþNa]þ 557.3010, found 557.2982.
Acknowledgments
The author B.C.D. is thankful to KUMC for startup funding and
Dr. Peter Van Veldhuizhen for his support.
d
1.02e1.08 (m), 1.36 (s), 1.37 (s), 2.32e2.50 (m), 5.78e5.90 (m),
6.13e6.38 (m), 6.40e6.63 (m), 6.78e6.88 (m), 7.18e7.23 (m),
7.30e7.40 (m), 7.70e7.82 (m). 13C NMR (75 MHz, CDCl3):
22.7,
d
Appendix A. Supplementary data
25.3, 84.4, 124.5, 126.0, 128.1, 128.3, 128.9, 130.0, 131.1, 132.5, 141.5,
141.8, 144.2, 146.0. HRMS (ESI): m/z calcd. for C19H27BO2 [MþNa]þ
321.2002, found 321.1999.
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2015.08.007.
Please cite this article in press as: B.C. Das, et al., Journal of Organometallic Chemistry (2015), http://dx.doi.org/10.1016/
j.jorganchem.2015.08.007

B.C. Das et al. / Journal of Organometallic Chemistry xxx (2015) 1e9
9
c) Z.-Q. Tian, B.B. Brown, D.P. Mack, C.A. Hutton, P.A. Bartlett, J. Org. Chem. 62
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Please cite this article in press as: B.C. Das, et al., Journal of Organometallic Chemistry (2015), http://dx.doi.org/10.1016/
j.jorganchem.2015.08.007