Divergent and Stereoselective Synthesis of Tetraarylethylenes from Vinylboronates

Article abstract of DOI:10.1002/anie.202008113

The synthesis of a new tetraborylethylene (TBE) is reported, and its application in the preparation of [4+0]-tetraarylethenes (TAEs) is elucidated. TAEs have widespread applications in material science and supramolecular chemistry due to their aggregation-induced emission (AIE) properties. The divergent and stereoselective synthesis of [3+1]-, [2+2]-, and [2+1+1]-TAEs via multiple couplings of vinylboronates with aryl bromides is demonstrated. These couplings feature a broad substrate scope and excellent functional group compatibility due to mild reaction conditions. Facile access to various tetraarylethenes is provided. This strategy represents an important complement to the conventional methods employed for the synthesis of TAEs, and would be a valuable tool for synthesizing TAE-based molecules useful in functional materials, biological imaging and chemical sensing.

Full text of DOI:10.1002/anie.202008113

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Accepted Article
Title: Divergent and Stereoselective Synthesis of Tetraarylethylenes
from Vinylboronates
Authors: Wanxiang Zhao, Minghao Zhang, Yisen Yao, and Peter J.
Stang
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10.1002/anie.202008113
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RESEARCH ARTICLE
Divergent and Stereoselective Synthesis of Tetraarylethylenes
from Vinylboronates
Minghao Zhang,[a] Yisen Yao,[a] Peter J. Stang*[b] and Wanxiang Zhao*[a]
Dedication to the 20th Anniversary of Aggregation-Induced Emission (AIE)
ABSTRACT: We here report the synthesis of
a
new
[2+1+1]-, and [1+1+1+1]-TAEs (Figure 1b). Among them,
although [4+0]- and [3+1]-TAEs have no stereoisomers, [2+2]-
and [2+1+1]-TAEs engross 3 stereoisomers, respectively. In
addition, [1+1+1+1]-TAEs are structurally diverse with up to six
stereoisomers. The diversity of TAEs undoubtedly provides a
powerful platform for the development of functional molecules
and materials, but their stereoselective synthesis challenges
synthetic chemists. For example, the synthesis of pure E-[2+2]-
and Z-[2+2]-TAEs so far still rely on HPLC separation or the
tetraborylethylene (TBE) and its application in the preparation of
[4+0]-tetraarylethenes (TAEs) that have widespread applications in
material science and supramolecular chemistry due to their
aggregation-induced emission (AIE) nature. The divergent and
stereoselective synthesis of [3+1]-, [2+2]-, [2+1+1]-TAEs via multi-
couplings of vinylboronates with aryl bromides were also
demonstrated. These couplings feature broad substrate scope and
excellent functional group compatibility due to mild reaction
conditions, providing facile access to various tetraarylethenes. This
strategy represents an important complement to the conventional
methods for the synthesis of TAEs, and would be a valuable tool for
synthesizing TAE-based molecules used in functional material,
biological imaging and chemical sensing.
Introduction
Tetraarylethylenes (TAEs) exhibit intriguing chemical and
physical properties due to their geometric and electronic
features, and have extensive applications in materials science,[1]
synthetic and biological chemistry,[2] and supramolecular
frameworks.[3] For instance, TAE-a and TAE-b are broadly
utilized in platinum-coordination driven self-assembly[4] and the
construction of metal−organic framework (MOF),[5] and TAE-c is
a versatile building block in the synthesis of covalent organic
frameworks (COF) via imine formation (Figure 1a).[6] In addition,
since the concept of aggregation-induced emission (AIE) was
originally proposed by Tang in 2001,[7] the TAEs and their
derivatives as AIE-active molecules have shown numerous
applications in biological probes and imaging, chemical sensing,
optoelectronic and stimuli-response materials.[8] For example,
Tang and Sun demonstrated that TAE-d can be used as a
biosensor for selective D-glucose detection from a saccharide
mixture in aqueous media.[8b] Liu and coworkers have developed
an elegant bioprobe with TAE-e as an imaging structural unit
and photosensitizer for photodynamic therapy of cancer cells
(Figure 1a).[8g]
Figure 1. The applications and classification of tetraarylethylene.
introduction of polar or unique functional groups,[9] such as
triazole[9a, 9b] and oxetane,[9d] to enlarge the difference between Z
and E isomers in the shape and polarity. The divergent and
stereoselective synthesis of TAEs is still challenging and
remains to be deciphered, but it is highly desirable as it is the
The tetraarylethylenes used in chemistry and materials
science in the last two decades can be divided into 5 groups
based on the categories of aryl groups, i.e., [4+0]-, [3+1]-, [2+2]-,
precondition
for
the
elucidation
of
their
structure−property−function
relationships.
Moreover,
[a]
[b]
M. Zhang, Y. Yao, Prof. Dr. W. Zhao
State Key Laboratory of Chemo/Biosensing and Chemometrics,
College of Chemistry and Chemical Engineering, Hunan University,
Changsha, Hunan 410082, P. R. China
E-mail: zhaowanxiang@hnu.edu.cn
Prof. Dr. P. J. Stang
Department of Chemistry, University of Utah, 315 South 1400 East,
Room 2020, Salt Lake City, Utah 84112, United States
E-mail: stang@chem.utah.edu
stereoisomers probably present marked difference in molecular
properties and functions due to their different configurations.[8d,
8h]
Conventionally, tetraarylethylenes are usually synthesized
from diarylketones via the McMurry reaction in the presence of
titanium and zinc (eq 1, Figure 2a).[10] However, the McMurry
reaction suffers from restricted substrate scope and poor
functional-group compatibility due to the use of strong Lewis
Supporting information for this article is given via a link at the end of
the document.
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tetrasubstituted olefins based on Suzuki-Miyaura cross coupling
has garnered considerable attention, and significant progress
has been described in the formation of di- and tri-arylated
alkenes.[15] However, the preparation of tetraarylethylenes using
Suzuki-Miyaura reaction has been little explored. The existing
protocol focuses on the coupling of gem-dibromides with
arylboronic acids.[12] Taking into account the rapid development
of vinylboronate synthesis,[16] and the fact that there are more
aryl electrophiles (i.e. aryl halides) listed as commercially
available than aryl nucleophiles (i.e. arylboronic acids), we
envision that the coupling of vinylboronates with aryl halides
would be a promising strategy for the synthesis of TAEs.
Vinylboronates have found widespread applications in the
introduction of C−C double bonds into various functional
molecules via Suzuki-Miyaura cross coupling.[17] The
vinylboronates employed so far are mainly limited to
monoborylalkenes that undergo single coupling with aryl halide.
The examples of double couplings for diborylalkenes are rare
and triple and quadruple couplings, to the best of our knowledge,
are yet to be reported, although diborylalkenes and
triborylalkenes can be readily synthesized by Pt-catalyzed
diboration reaction.[18]
Figure 2. Synthesis of tetraarylethylene.
acid (TiCl4).[10] Furthermore, stereoselectivity control is still an
unsolved issue in the McMurry reaction. Specifically, as for self-
coupling, the use of unsymmetrical diarylketone would generate
an E/Z mixture of TAEs, which is mostly inseparable by column
chromatography.[10d] With regard to cross-coupling, poor
stereoselectivity is also obtained when either symmetrical or
asymmetrical diarylketones are utilized. Additionally, the self-
coupling is a quite competitive reaction in cross-coupling,
resulting in low-yield formation of the desired TAEs and
separation issues.[10d] To avoid these problems, other strategies
have been developed for the preparation of unsymmetrical TAEs.
For instance, Rathore and co-workers disclosed an elegant
method for the coupling of benzophenone with diarylmethane in
the presence of organolithium and acid (eq 2, Figure 2a), which
is suitable for the synthesis of [4+0]-, [3+1]-, and gem-[2+2]-
TAEs.[11] However, the stereoselectivity control is a formidable
challenging for this protocol in the synthesis of E/Z-[2+2] and
[2+1+1] TAEs. Furthermore, a range of functional groups such
as aldehyde, ester, and nitrile are incompatible due to the use of
organolithium compounds and acid. Pd-catalyzd Suzuki-Miyaura
coupling of 1,1-dibromoalkene with arylboronic acid is also an
attractive alternative for the TAE synthesis (eq 3, Figure 2a).[12]
Although this method is an efficient strategy for preparing
geminal-substituted TAEs, it is inapplicable to the synthesis of
other kinds of TAEs. Moreover, Pd-catalyzed alkyne-diarylation
with an organometallic reagent allowed facile access to the
unsymmetrical TAEs (eq 4, Figure 2a).[13] Notably, the ability to
simultaneously introduce two aryl groups makes this protocol
appealing, but the regioselectivity control is still problematic (e.g.
when Ar2 ≠ Ar3). In common, these approaches suffer from poor
stereoselectivity and limited substrate scope, and require either
multi-step synthesis of starting materials or the use of
organometallic reagents. Consequently, the development of a
general, especially stereospecific method to streamline the
preparation of TAEs is in great demand.
Herein, we describe the preparation of tetraarylethylenes from
di-, tri-, and tetra-borylalkenes via the corresponding double,
triple, and quadruple Suzuki-Miyaura couplings with good
efficiency and stereoselectivity (Figure 2b), which provides a
facile and efficient protocol for synthesizing various functional
TAE molecules.
Figure 3. Synthesis of tetraborylethylene.
Results and Discussion
In principle, tetraborylethylene (TBE) coupled with aryl halides
would be the most straightforward method for the synthesis of
tetraarylethylenes. However, this process has never been
achieved as there is no protocol available for the synthesis of
TBE that is suitable to the Suzuki-Miyaura coupling. The lone
example to make TBE was reported by Siebert in 1996[19]
.
Unfortunately, the TBE made by Siebert is inapplicable to
Suzuki-Miyaura coupling due to its base sensitivity. Since
pinacol boronates are significantly more stable than catechol
boronates,[20] we envision that tetraborylethylene 1 derived from
pinacol would be applicable to TAE synthesis using the Suzuki-
Miyaura reaction. To this end, we started our investigation by
preparing TBE 1. We found that the TBE 1 could be readily
prepared from commercially available and inexpensive
trichloroethylene in high efficiency. The lithiation of
trichloroethylene by n-BuLi generated dilithium acetylide
intermediate, which was then trapped by iPrOBpin
(isopropoxyboronic acid pinacol ester) to give diborylacetylene A.
The Suzuki-Miyaura cross coupling is among the most
extensively used method for forging C−C bonds in chemical
synthesis, pharmaceutical industry, and materials science due to
its mild reaction conditions and well-precedented functional
group compatibility.[14] Not surprisingly, the synthesis of
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Table 1. Synthesis of [4+0]-tetraarylethylenes.[a]
[a] Reaction conditions: TBE (0.2 mmol), aryl bromide (0.96 mmol), Pd(dppf)Cl2 (0.01 mmol), Cs2CO3 (1.2 mmol), H2O (40 µL), dioxane (3 mL) at 70 °C for 48 h.
Isolated yields. [b] KOH was used as base and DME as solvent.
The subsequently Pt-catalyzed diboration afforded the
desired TBE 1 (Figure 3). No chromatographic purification is
required, and the reaction can be performed on a multigram
scale, allowing easy access to TBE 1. It is worth mentioning
that TBE 1 is air-stable and can be stored under an ambient
atmosphere for months without decomposition.
to excellent yields. Notably, the products 5ah-k can be used
as (precursors) building blocks for the synthesis of MOF,
COF, and/or self-assembled metallacages. Furthermore, the
vinyl group was compatible to provide TAE 5an amenable for
further downstream diversification via alkene functionalization.
It is worth noting that TAE 5ao-ap with a pyridyl that exhibit
wide applications in metal-coordination driven self-assembly,
previously required multiple-step synthesis and now can be
With the tetraborylethylene 1 in hand, we next investigated
the Suzuki-Miyaura coupling of TBE 1 with aryl bromides for
the preparation of symmetric [4+0]-tetraarylethenes using 4-
bromotoluene as the model substrate. After exploring a series
of reaction parameters, the use of TBE, aryl bromide (4.8
equiv), Pd(dppf)Cl2 (5 mol%), and Cs2CO3 (6.0 equiv) in
dioxane with H2O at 70 °C for 48 h afforded the desired TAE
5aa in good yield. Noticeably, all the TAE products can be
purified by routine silica gel chromatography (see more
details on purification methods in SI). We then examined the
generality of the aromatic bromide substrate for this
quadruple Suzuki-Miyaura coupling, and the results are
summarized in Table 1. As shown, a wide range of aryl
bromides with various substituents at different positions all
successfully participated in this reaction to afford the desired
tetraarylethylenes in moderate to excellent yields. A series of
functional groups, such as methoxyl (5ac), methylthio (5ad),
protected alcohol (5ag), nitrile (5aj), trifluoromethyl (5al), and
chloride (5am), were all tolerated under the mild reaction
conditions. Of particular note, the functional groups
incompatible with the McMurry reaction conditions, including
amide (5ae), formyl (5ah), acetyl (5ai), and ester (5ak),
remain intact to produce the corresponding TAEs in moderate
synthesized by
a single-step procedure with moderate
efficiency. In addition, multi-substituted aryl bromides also
reacted smoothly with TBE 1 to deliver TAE 5ar-at, which are
challenging for the existing methods. Likewise, naphthalenes
(5au-aw) were tolerated for these quadruple couplings.
AIEgens bearing heterocycles have drawn attention due to
their unique distinctive electronic structures, and the lack of
efficient approaches for their synthesis encourage our
attempt to prepare them using this four-fold coupling reaction.
A range of heteroaromatic rings, such as indole (5ax),
benzofuran (5ay), benzothiophene (5az), benzothiadiazole
(5ba), and carbozole (5bb) were competent substrates,
providing the desired products in moderate to good yields.
These results highlight the excellent substrate diversity and
high efficiency of this coupling reaction for the synthesis of
symmetrical [4+0]-tetraarylethylenes, especially those bearing
reactive functional groups.
The conventional methods for synthesizing [3+1]-TAE such
as McMurry reaction typically result in low efficiency due to
the inevitably competing homo-coupling reactions.[21]
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Table 2. Synthesis of [3+1]-tetraarylethylenes.[a]
[a] Reaction conditions: 2 (0.2 mmol), aryl bromides (0.72 mmol), Pd(dppf)Cl2 (0.01 mmol), Cs2CO3 (0.9 mmol), H2O (40 µL), dioxane (3 mL) at 70 °C for 36 h.
Isolated yields.
Table 3. Synthesis of [2+2]- and [2+1+1]-tetraarylethylenes.[a]
[a] Reaction conditions: 2 (0.5 mmol), aryl iodide (0.5 mmol), Pd(PPh3)4 (0.05 mmol), K3PO4 (1.5 mmol), H2O (1 mL), THF ( 4 mL) at 70 °C for 24 h (the first step);
E-3 (0.2 mmol), aryl bromides (0.48 mmol), Pd(dppf)Cl2 (0.01 mmol), Cs2CO3 (0.6 mmol), H2O (40 µL), dioxane (3 mL) at 70 °C for 24 h (the second step). Yields
given were isolated yields for the second step.
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Table 4. Synthesis of [2+2]- and [2+1+1]-tetraarylethylenes.[a]
[a] Reaction conditions: Z-3 (0.2 mmol), aryl bromide (0.48 mmol), Pd(dppf)Cl2 (0.01 mmol), Cs2CO3 (0.6 mmol), H2O (40 µL), dioxane (3 mL) at 70 °C for 24 h.
Isolated yields. Py = 4-pyridyl.
Table 5. Synthesis of [2+2]- and [2+1+1]-tetraarylethylenes.[a]
[a] Reaction conditions: 4 (0.2 mmol), aryl bromide (0.48 mmol), Pd(dppf)Cl2 (0.01 mmol), Cs2CO3 (0.6 mmol), H2O (40 µL), dioxane (3 mL) at 70 °C for 24 h.
Isolated yields. Py = 4-pyridyl.
Encouraged by the success of synthesizing [4+0]-TAEs, we
turned our attention to the synthesis of [3+1]-TAEs using
Suzuki-Miyaura reaction. We conjectured that the Pd-
coupling reaction, regardless of the position as well as
electronic nature of the substituents. Specifically, substrates
bearing functional groups, such as acetyl, ester, chloride,
amide, trifluoromethyl, formyl, pyridyl, and sulfonyl were well-
tolerated and provided the desired tri-coupled products in
good to excellent yields. With respect to the triborylalkene,
para- and meta-monosubstituted ones were found to be
suitable substrates in this transformation (5bl-br). Moreover,
the reaction was amenable to the triborylalkenes with
electron-withdrawing and electron-donating groups, including
methoxyl, fluoride, chloride, and protected alcohol.
catalyzed quadruple couplings of TBE
1
involve
a
triborylalkene intermediate generated from TBE 1 via single
coupling with ayrl bromide. Accordingly, triborylalkenes
generated from alkynyl boronates via Pt-catalyzed diboration
were used under the standard reaction conditions for the
formation of [4+0]-TAEs, and the tri-coupled products were
afforded in moderate to excellent yields. As shown in Table 2,
a variety of aryl bromides can be employed for this triple
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Figure 4. (a) 5ax (20 μM) in THF–water mixtures with different volume fractions of water, photographs taken upon excitation at 365 nm using an UV lamp at 298k.
(b) Normalized absorption spectra (dotted lines) and fluorescence emission spectra (solid lines) in DCM (1 × 10 −5 M). (c) Synthesis of TPE-core crown ether.
The greatest challenge in the synthesis of tetraarylethylenes is
the control of stereoselectivity that is of importance for the
systematic dissection of the relationships between structure and
function. Although stereoselectivity control is not an issue for the
preparation of [4+0]- and [3+1]-TAEs, it is a great challenge for
synthesizing [2+2]-, [2+1+1]-, and [1+1+1+1]-TAEs. Recently,
Ozerov disclosed the lone example of a Pd-catalyzed Suzuki–
Miyaura coupling of triborylalkene with 4-iodoanisole when they
studied the synthesis of triborylalkenes from terminal alkynes
that showed excellent stereoselectivity to give the trans-
diborylalkene product.[22] Inspired by this precedent, we
hypothesized that the stereoselectivity issue for the synthesis of
[2+2]- and [2+1+1]-TAEs may be addressed by a stereoselective
Suzuki–Miyaura coupling. Hence, we reacted the triborylalkenes
and aryl iodides under the reaction conditions reported by
and carbazole (5cj) were all viable in this coupling, and the
reaction was also viable for functionalized diborylalkenes,
furnishing TAEs 5ck-cm. Furthermore, tetraarylethylenes other
than [2+2]-TEAs, such as [2+1+1]-TAEs (5cn-cp), were also
obtained from Z-diborylalkenes 3.
Finally, we aimed to synthesize gem-[2+2]-TEAs from gem-
diborylalkenes 4. As depicted in Table 5, the coupling was found
to be tolerant to functional groups, including chloride, formyl,
ester, sulfonyl, and pyridyl, and provides a platform for the
construction of structurally complex molecules. The [2+1+1]-
TAEs 5da-db were also obtained from unsymmetrical gem-
diborylalkenes 4 in good yields and excellent stereoselectivity.
With numerous tetraarylethylenes in hand, the photophysical
properties were investigated by using representative AIEgens.
As shown in Figure 4a, AIE was observed by dissolving 5ax in
THF and water mixture with different fractions of water. Non- or
weak emission was observed when the fraction of water was
less than 60%, but the fluorescence intensity increased greatly
when the water content reached 90 vol %. The absorption and
emission spectra of representative tetraarylethylenes were also
measured. As seen in Figure 4b, 5ad and 5al displayed broad
absorption bands at 351 and 308 nm, respectively. In addition,
AIEgens 5bx and 5cj showed similar absorption bands centered
at 325 nm, and two absorption bands centered at 270 and 348
nm were observed for 5cl. With regard to the emission spectra,
these luminogens showed emission maxima at approximately
480−530 nm. These multi-coupled products exhibit large Stokes
shifts, making them potentially promising for biological imaging
and detections.[1f] It is also worth noting that electron-donating
groups could induce red-shifts in the emission spectra (5ad vs
5al), which enable this multi-coupling protocol to prepare near-
infrared TAEs with large Stokes shift.
Ozerov. E-diborylalkene
3
were obtained in excellent
stereoselectivity and moderate to good yields (Table 3), and E-3
was subjected to the quadruple coupling conditions. Pleasantly,
the mild reaction conditions delivered the corresponding bi-
coupled products in excellent stereoselectivity and in yields
ranging from 55% to 80% (Table 3). The stereochemistry was
unambiguously assigned by X-ray crystallographic analysis of
5bv. The functional groups are well tolerated including chloride,
ester, ketone, and sulfonyl. Furthermore, the efficiency of the
reaction was not affected when polycyclic and heterocyclic
substrates such as naphthalene, pyridine, and carbazole were
employed. Moreover, [2+1+1]-TAEs can also be obtained via
this stereospecific tandem Suzuki–Miyaura couplings. For
instance, TAEs 5ca-cd with two pyridyls were isolated in good
yields.
We next tested the viability of such Suzuki–Miyaura coupling
for the synthesis of Z-[2+2]-TEAs from Z-diborylalkenes 3, which
could be readily prepared via Pt-catalyzed diboration of alkynes.
Various aryl bromide with diverse substituents proved to be
suitable coupling partners, affording Z-[2+2]-TEAs with excellent
stereoselectivity (Table 4). Heteroarenes such as pyridine (5ci)
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21.80 ppm (1JPt-P =2376.5 Hz)
15.48 ppm (1JPt-P = 2303.6 Hz)
15.62 ppm (1JPt-P = 2319.8 Hz)
15.53 ppm (1JPt-P =2321.5 Hz)
Figure 5. (a) Synthesis of 7a-c via self-assembly of 5ch, 5ck, and 5cl with 6. (b-e) Partial 1H NMR spectra (400 M, CDCl3, 293 K) of ligand 5ch, and 7a-c. (f-i)
Partial 31P{1H} NMR spectra (162 M, CDCl3, 293 K) of diplatinum acceptor 6, and 7a-c. (j-k) Absorption and fluorescence emission spectra of 7a-c in DCM (λex =
365 nm, 10 μM).
To demonstrate the robustness and synthetic utility of this
protocol, TPE-core crown ether 5dc was synthesized in a single
step and convergent procedure with 61% yield via the quadruple
Suzuki-Miyaura couplings of TBE (Figure 4c). Of note, the TPE-
core crown ether could form cross-linked supramolecular
polymeric network with ammonium salt via host-guest
interaction,[4f] and might find applications in construction of
functional materials. In light of the facile preparation of
heteroaromatic TAEs via the couplings of vinylboronates and
their extensive applications in coordination-driven self-assembly,
the usefulness of this strategy was further demonstrated by the
construction of organoplatinum(II) metallacycles (Figure 5). The
rhomboid platinum (II) metallacycles 7a-c were prepared from
60° TAE-based dipyridyl ligand (5ch, 5ck, 5cl) and 120°
diplatinum acceptor 6. The formation of TAE-decorated
metallacycles 7a-c was confirmed by multinuclear NMR (1H and
Pt−pyridyl coordination bond. As illustrated in Figure 5g-i, the
31P{1H} NMR spectra of 7a-c and sharp singlets at δ = 15.48,
15.62, 15.53 ppm with concomitant 195Pt satellites, respectively,
suggesting a single phosphorus environment. These peaks are
shifted upfield in comparison with the signal of the di-Pt(II)
acceptors 6 (Figure 5f) by about 6.28, 6.14 and 6.23 ppm,
respectively. Electrospray ionization time-of-flight mass
spectrometry (ESI-TOF-MS) also provides evidences for the
stoichiometry of metallacycles 7a-c by possessing isotopically
well-resolved peaks that are in good agreement with the
calculated theoretical distributions (see SI for details). Figure 5j-
k depict the UV−vis absorption and emission profiles of 7a-c.
These three rhomboids displayed a broad absorption band
centered at 365 nm. The emission maximum of the
metallacycles 7a-c are at 540 nm, 540 nm, 590 nm, respectively
(Figure 5k). Interestingly, the emission spectra of 7c shows a
red shift to the near-infrared (NIR) region (650–900 nm)
probably due to its donor−π−acceptor structure. Based on these
results, we envision that the metallacycles with NIR emission
1
31P) analysis as well as ESI-TOF-MS. In the H NMR spectrum
(Figure 5c-e), the downfield shifts of the Ha-c protons of the
pyridine were observed, indicating the formation of the
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Conclusion
In conclusion, we have prepared a tetraborylethylene (TBE)
and demonstrated its application in the synthesis of [4+0]-
tetraarylethylenes via quadruple Suzuki-Miyaura couplings. The
stereoselective synthesis of [3+1]-, [2+2]-, and [2+1+1]-
tetraarylethylenes from the corresponding vinylboronates and
aryl halides were also established, which provides
a
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synthetically useful tool for the preparation of novel TAE-based
functional molecules. This protocol enabled the efficient
preparation of pure E- and Z-[2+2]-TAEs, which represents an
important complement to the existing methods that require multi-
step synthesis or have separation issues. The synthetic utilities
were illustrated by the construction of TPE-core crown ether and
the application of heteroaromatic TAEs in coordination-driven
self-assembly. Further applications based on this new
tetraborylethylene and the synthesis of new functional molecules
and materials via this unprecedented multi-coupling are now
under investigation in our lab.
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Acknowledgements
We thank Prof. Xiaopeng Li (University of South Florida), Dr.
Shuai Lu and Zhixuan Zhou for the ESI-TOF-MS measurements
and analysis. Prof. Shengyi Dong and Zebing Zeng are thanked
for helpful discussion. Financial support from the National
Natural Science Foundtion of China (Grant No. 21702056,
21971059), the National Program for Thousand Young Talents
of China and the Fundamental Research Funds for the Central
Universities are greatly appreciated.
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This article is protected by copyright. All rights reserved.

10.1002/anie.202008113
Angewandte Chemie International Edition
RESEARCH ARTICLE
M. Zhang, Y. Yao, P. J. Stang* and
W. Zhao*
Page No. – Page No.
Divergent and Stereoselective
Synthesis of Tetraarylethylenes
from Vinylboronates
We here report the synthesis of a new tetraborylethylene (TBE) and its application in the
preparation of [4+0]-tetraarylethenes (TAEs). The divergent and stereoselective
synthesis of [3+1]-, [2+2]-, [2+1+1]-TAEs via multi-couplings of vinylboronates with aryl
bromides were also demonstrated. This strategy represents an important complement to
the conventional methods for the synthesis of TAEs, and would be a valuable tool for
synthesizing TAE-based molecules used in functional material, biological imaging and
chemical sensing.
This article is protected by copyright. All rights reserved.