Nickel(ii)-catalyzed addition of aryl-, alkenyl-, and alkylboronic acids to alkenylazaarenes

Article abstract of DOI:10.1021/acs.orglett.0c01425

A nickel(II)-catalyzed addition of aryl-, alkenyl-, and alkylboronic acids to alkenylazaarenes was presented. This reaction exhibited high efficiency (up to 93% yield), a broad substrate scope (seven types of heterocycles), and good functional group compatibility. The resulting products can be further transformed to many useful building blocks. Finally, the preliminary studies suggested that the adjacent N atom of the heterocycles was essential for the high reactivity.

Full text of DOI:10.1021/acs.orglett.0c01425

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Letter
Nickel(II)-Catalyzed Addition of Aryl‑, Alkenyl‑, and Alkylboronic
Acids to Alkenylazaarenes
Xing-Yu Liu, Yun-Xuan Tan, Xin Wang, Hao Xu, Yu-Hui Wang,* Ping Tian,* and Guo-Qiang Lin*
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ABSTRACT: A nickel(II)-catalyzed addition of aryl-, alkenyl-, and
alkylboronic acids to alkenylazaarenes was presented. This reaction
exhibited high efficiency (up to 93% yield), a broad substrate scope
(seven types of heterocycles), and good functional group
compatibility. The resulting products can be further transformed
to many useful building blocks. Finally, the preliminary studies
suggested that the adjacent N atom of the heterocycles was
essential for the high reactivity.
Scheme 1. Catalytic Nucleophilic Addition of Boronic Acids
to Alkenylazaarenes
itrogen-containing heteroarenes are privileged scaffolds
in pharmaceutical molecules, advanced materials, and
N
natural products.1 Therefore, significant efforts have been put
into developing methods for the functionalization of the
heteroarenes and their derivatives. The metal-catalyzed cross-
coupling reactions2 and the recently emerged C−H function-
alization reactions including biaryl coupling and insertions of
an unsaturated bond initiated by ortho-C−H activation have
been identified as powerful tools to afford these structures.3
Apart from these commonly used methods, the catalytic
nucleophilic addition to the alkenylheteroarenes, in which the
adjacent alkene groups were activated by the electron-
withdrawing heteroaromatic moiety, provided an alternative
approach to constructing the heteroarene-containing building
blocks.4−7
However, compared with the addition of common α,β-
unsaturated carbonyl derivatives, alkenylheteroarenes are less
reactive due to the weak activation from the heteroaromatic
environment.4c,6a,f In most cases, Grignard reagents,4,6a,b,g
which have to be carefully handled, were essential for the
success of the reaction. Boronic acids are widely used due to
their stability, low toxicity, and commercial availability. But as
for the addition of boronic acids to the alkenylheteroarenes, it
was not until 2001 that an effective Rh-catalyzed addition of
arylboronic acid to β-unsubstituted alkenyl N-heteroarenes was
disclosed by Lautens and coworkers (Scheme 1a).5a Then, in
2010, Lam and coworkers made a seminal contribution by
developing an enantioselective Rh-catalyzed addition of
arylboronic acids to β-substituted alkenyl N-heteroarenes.5d
Unfortunately, as for the alkenylboronic acids, no products
were observed in their report. As the alternatives to
alkenylboronic acids, the alkenyl N-methyliminodiacetic acid
(MIDA) boronates were essential to afford the alkenylation
product in modest yield with a modest ee value. At almost the
same time, Yorimitsu, Oshima, and coworkers realized a Co-
catalyzed alkenylation of the alkenylazaarenes (Scheme 1b);5g
however, arylboronic, alkylboronic, and cyclic alkenylboronic
acids were incompatible in the reaction system, and only one-
type products of the β-substituted alkenyl N-heteroarene have
been presented. Considering the paucity of the current
methodologies for the addition of alkenylheterocyclic aromatic
rings with boronic acids and the lack of reports on the Ni-
Received: April 24, 2020
https://dx.doi.org/10.1021/acs.orglett.0c01425
© XXXX American Chemical Society
Org. Lett. XXXX, XXX, XXX−XXX
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catalyzed 1,4-addition of the organoboron reagents,8 herein,
we present a highly efficient nickel(II)-catalyzed addition of
aryl-, alkenyl-, and alkylboronic acids to alkenylazaarenes.
We commenced our studies by examining the arylation of
alkenylquinoxaline 1a with (3-methoxyphenyl)boronic acid
(2a) in the presence of Ni(acac)2, DPPE, and K2CO3. To our
delight, the desired product 3aa was observed with 45% yield
accompanied by a trace reduction product (Table 1, entry 1).5d
dichloroethane (DCE), 2,2,2-trifluoroethanol (TFE), 1,4-
dioxane, and 1,4-dioxane/H2O (9:1), were then screened,
but only dioxane afforded the desired product with a slight
increase in yield (Table 1, entries 10−13). The Lewis acid
additive (BF3·OEt2) was proved to promote the Cu-catalyzed
addition of alkenylazaarenes;6a however, it was detrimental in
our case (Table 1, entry 14). Increasing the reaction
temperature could significantly enhance the yield to 84%
(Table 1, entry 15), whereas reducing the loading of boronic
acid 2a or the catalyst caused a decrease in the yield (Table 1,
entries 16 and 17). Finally, this reaction showed lower
efficiency without the ligand (Table 1, entry 18).
a
Table 1. Selected Optimization Studies
With the optimized condition in hand, various substrates
were screened, and the results are summarized in Scheme 2. A
variety of meta-substituted and para-substituted arylboronic
acids, regardless of the electron-donating or electron-with-
drawing property of the substituent at the benzene ring, were
amenable in this reaction (Scheme 2, 3aa−ah), and a wide
array of functional groups, including ether (3aa), ester (3ab),
halides (3ac and 3ad), and trifluoromethyl (3ae) and silyl
groups (3ag), were comfortably tolerated under the condition.
It should be mentioned that the sterically hindered boronic
acid, that is, 2-methylphenyl boronic acid, could also afford the
addition product in excellent yield (3ai). As for the 1-
naphthyl-, 2-naphthyl-, and di- and trisubstituted aryl boronic
acids, the reaction proceeded equally well (Scheme 2, 3aj−
am). Other functionalized alkyl groups at the β-position of the
2-alkenylquinoxaline had no influence on the efficiency of the
reaction (Scheme 2, 3ba and 3ca). The 1-dibenzothiophenyl
group can also be present in our reaction (Scheme 2, 3an).
Additionally, other alkenylazaarenes, including 2-alkenylquino-
line and 2-alkenylbenzoxazole, afforded the desired product in
moderate yield by modifying the ligand from rac-BINAP to
DPPF (Scheme 2, 3da and 3ea). When the readily available
phenylboronic acids 2o and 2p derived from estrone and
clofibrate were subjected to this transformation, the addition
products were obtained in high to excellent yields (Scheme 2,
3ao and 3ap). As for the internal alkenes, alkenyl- and
alkylboronic acids failed to afford the desired addition
products, and only small amounts of homocoupling products
were observed.
b
entry
ligand
DPPE
DPPE
DPPE
DPPE
PPh3
DPPP
Xantphos
DPPF
rac-BINAP
rac-BINAP
rac-BINAP
rac-BINAP
rac-BINAP
rac-BINAP
rac-BINAP
rac-BINAP
rac-BINAP
-
base
solvent
toluene
yield (%)
c
1
2
3
4
5
6
7
8
K2CO3
Na2CO3
Cs2CO3
KOH
45(2)
10(0)
c
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
DCE
0
c
12(0)
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
0
c
40(4)
44(0)
62(9)
58(0)
c
c
c
9
10
11
12
13
0
0
TFE
c
dioxane
dioxane/H2O
dioxane
dioxane
dioxane
dioxane
dioxane
61(0)
h
0
0
d
14
e
c
15
16
84(0)
64(0)
52(0)
69(0)
f
c
g
c
17
c
18
a
Reactions were carried out with 1a (0.2 mmol), 2a (0.6 mmol),
Ni(acac)2 (10 mol %), ligand (12 mol %), base (0.4 mmol), and
b
1
solvent (2.0 mL) under an Ar atmosphere, 6 h. Determined by H
As for the 2-vinyl N-heteroarenes, a broader scope of
boronic acids was applied to this reaction. Not only the
arylboronic acids but also the alkenylboronic acids and even
the alkylboronic acids could afford the addition product in
moderate to high yields (Scheme 2, 3fa−nx). It is noteworthy
that 2-vinylpyridine 1h bearing a methyl group at the six
position still provided the product 3hr, albeit in relatively low
yield. Considering that the heteroarenes play an important role
in the pharmaceuticals and natural products, different
heteroarenes including quinoxaline (3iw and 3ir), triazine
(3jr), quinoline (3kr), pyrimidine (3lr and 3mr), and
benzothiazole (3nr and 3nx) were tested under the same
reaction condition, and all of them afforded the desired
addition products.
The importance of the adjacent N atom in the heterocycles
was elaborated by several control experiments. Only trace
product was observed for the alkene substrate 1p, 1r, or 1s
without the nitrogen atom or with it at another position of the
heterocycles. This result clearly indicated that the coordination
between the metal catalyst and the N atom would activate the
β-carbon of heteroaryl alkenes and increase their reactivities
(Scheme 3).9
NMR analysis of unpurified mixtures using CH2Br2 as an internal
c
standard. Number in parentheses indicates the yield of reduction
d
e
f
product. BF3·OEt2 (40 mol %) was added. Under 120 °C. 2a (0.3
g
mmol) was used instead. Ni(acac)2 (5 mol %) and rac-BINAP (6
mol %) were used instead. Dioxane/H2O = 9/1 (v/v).
h
Other bases, including Na2CO3, Cs2CO3, and KOH, were then
tested, respectively, and led to a big erosion of the reaction
yield without exception (Table 1, entries 2−4). Next, several
representative phosphine ligands were carefully screened. The
monophosphine ligand PPh3 showed inefficiency for this
reaction (Table 1, entry 5). The usage of DPPP and Xantphos
ligands resulted in a slight decrease in the yields (Table 1,
entries 6 and 7). When the DPPF ligand was checked, the
reaction yield was dramatically improved; however, a certain
amount of reduction product as a side product was also
produced, which made purification difficult (Table 1, entry 8).
The commonly used rac-BINAP ligand gave a similar yield,
and to our pleasure, no reduction product was detected (Table
1, entry 9). Therefore, rac-BINAP was chosen as the privileged
ligand for further optimization. Other solvents, including 1,2-
B
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a
Scheme 2. Substrate Scope of Boronic Acids and Alkenylazaarenes
a
Reactions were performed using 1 (0.2 mmol, 1.0 equiv), 2 (0.6 mmol, 3.0 equiv), Ni(acac)2 (10 mol %), rac-BINAP or DPPF (12 mol %) and
b
c
1
dioxane (2.0 mL) under an Ar atmosphere, 120 °C, 6 h. Yield of isolated products 3. dr value was determined by H NMR analysis.
To demonstrate the practicality and robustness of this
method, gram-scale experiments of both internal and terminal
alkenes were conducted, respectively. Under standard con-
ditions, an acceptable yield was observed for the internal
alkene 1a (Scheme 4a). To our delight, as for the terminal
alkene 1f, we were able to lower the loading of both the
boronic acid and the catalyst with only a slight decrease in the
yield (Scheme 4b). Then, several transformations of the
products were elaborated. The addition product 3aa could be
oxidized to bis(N-oxide) compound 4aa by m-chloroperben-
zoic acid (Scheme 4c)10 or reduced to hydroquinoxaline 5aa
by BH3·THF in excellent yield (Scheme 4d).11 With the
assistance of the n-BuLi, we realized the aldol-type addition of
3fr with PhCHO in high yield with moderate diastereose-
lectivity (Scheme 4e).12 Next, the oxidative dibromination of
the olefin readily occurred to afford 5fr in the presence of HBr
and dimethyl sulfoxide (DMSO) (Scheme 4f).13 Additionally,
the Simmons−Smith reaction was carried out on the addition
C
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product to form the cyclopropane 6fr in a stereospecific
fashion (Scheme 4g).14 Lastly, the deprotection of phenyl-
methyl ether 3gp gave the phenol 4gp (Scheme 4h), which can
be used to prepare the dihydrodibenzoxepine 5gp through a
Pd-catalyzed C−O cross-coupling reaction.15
Scheme 3. Investigations of the Function of the N Atom in
the Heterocycles
In conclusion, we developed an efficient nickel(II)-catalyzed
addition of aryl-, alkenyl-, and alkylboronic acids to
alkenylazaarenes. This reaction exhibits high efficiency, a
broad substrate scope, and good functional group compatibility
and is an excellent complement to the previously reported Rh-
and Co-catalyzed system. Then, the products can be further
transformed to many useful building blocks. Finally, the
preliminary studies suggest that the adjacent N atom of the
heterocycles is essential for the high reactivity. Further studies
on the Ni(II)-catalyzed enantioselective addition of boronic
acids to alkenylazaarenes are ongoing in our laboratory.
Scheme 4. Gram-Scale Experiments and Several
Transformations of the Products
a
ASSOCIATED CONTENT
* Supporting Information
■
sı
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.0c01425.
Experimental procedures and spectra for all new
compounds (PDF)
AUTHOR INFORMATION
■
Corresponding Authors
Yu-Hui Wang − The Research Center of Chiral Drugs,
Innovation Research Institute of Traditional Chinese Medicine,
Shanghai University of Traditional Chinese Medicine, Shanghai
201203, China; Email: yuhuiwang@shutcm.edu.cn
Ping Tian − CAS Key Laboratory of Synthetic Chemistry of
Natural Substances, Shanghai Institute of Organic Chemistry,
University of Chinese Academy of Sciences, Shanghai 200032,
China; The Research Center of Chiral Drugs, Innovation
Research Institute of Traditional Chinese Medicine, Shanghai
University of Traditional Chinese Medicine, Shanghai 201203,
China; orcid.org/0000-0002-5612-0664;
Email: tianping@sioc.ac.cn, tianping@shutcm.edu.cn
Guo-Qiang Lin − CAS Key Laboratory of Synthetic Chemistry
of Natural Substances, Shanghai Institute of Organic Chemistry,
University of Chinese Academy of Sciences, Shanghai 200032,
China; The Research Center of Chiral Drugs, Innovation
Research Institute of Traditional Chinese Medicine, Shanghai
University of Traditional Chinese Medicine, Shanghai 201203,
China; School of Physical Science and Technology,
a
ShanghaiTech University, Shanghai 201210, China;
Email: lingq@sioc.ac.cn
(a) 1a (1.04 g, 4 mmol, 1.0 equiv), 2a (1.83 g, 12 mmol, 3.0 equiv),
Ni(acac)2 (10 mol %), rac-BINAP (12 mol %), and dioxane (40.0
mL), 120 °C, 6 h. (b) 1f (1.05 g, 10 mmol, 1.0 equiv), 2r (2.96 g, 20
mmol, 3.0 equiv), Ni(acac)2 (5 mol %), rac-BINAP (6 mol %), and
dioxane (40.0 mL), 120 °C, 6 h. (c) 3aa (0.2 mmol, 1 equiv), m-
CPBA (0.6 mmol, 3 equiv), CHCl3, rt, 12 h. (d) 3aa (0.1 mmol, 1
equiv), BH3·THF (0.25 mmol, 2.5 equiv), rt. (e) 3fr (0.2 mmol, 1
equiv), n-BuLi (0.25 mmol, 1.25 equiv), PhCHO (0.24 mmol, 1.2
equiv), THF (2 mL), −40 °C, 2 h. (f) 3fr (0.2 mmol, 1 equiv),
DMSO (0.24 mmol, 1.2 equiv), aqueous HBr (48%, 0.72 mmol, 3.6
equiv), ethyl acetate (1 mL), 60 °C, 0.5 h. (g) 3fr (0.2 mmol, 1
equiv), Et2Zn (0.8 mmol, 4 equiv), TFA (0.4 mmol, 2 equiv), CH2I2
(0.4 mmol, 2 equiv), CH2Cl2 (2 mL), 0 °C, 3 h. (h) 3gq (0.1 mmol, 1
equiv), aqueous HBr (48%, 2 mL), 120 °C, 2 h. m-CPBA = m-
chloroperbenzoic acid, DMSO = dimethyl sulfoxide, TFA =
trifluoracetic acid.
Authors
Xing-Yu Liu − CAS Key Laboratory of Synthetic Chemistry of
Natural Substances, Shanghai Institute of Organic Chemistry,
University of Chinese Academy of Sciences, Shanghai 200032,
China; The Research Center of Chiral Drugs, Innovation
Research Institute of Traditional Chinese Medicine, Shanghai
University of Traditional Chinese Medicine, Shanghai 201203,
China; School of Physical Science and Technology,
ShanghaiTech University, Shanghai 201210, China
Yun-Xuan Tan − CAS Key Laboratory of Synthetic Chemistry of
Natural Substances, Shanghai Institute of Organic Chemistry,
University of Chinese Academy of Sciences, Shanghai 200032,
China; orcid.org/0000-0002-5114-0359
D
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Letter
(6) For the Cu-catalyzed addition of Grignard reagents, see:
(a) Jumde, R. P.; Lanza, F.; Veenstra, M. J.; Harutyunyan, S. R. Science
2016, 352, 433−437. (b) Jumde, R. P.; Lanza, F.; Pellegrini, T.;
Harutyunyan, S. R. Nat. Commun. 2017, 8, 2058. For the Cu-
catalyzed hydride addition, boron addition, and silicon addition, see:
(c) Rupnicki, L.; Saxena, A.; Lam, H. W. J. Am. Chem. Soc. 2009, 131,
10386−10387. (d) Saxena, A.; Choi, B.; Lam, H. W. J. Am. Chem. Soc.
2012, 134, 8428−8431. (e) Choi, B.; Saxena, A.; Smith, J. J.;
Churchill, G. H.; Lam, H. W. Synlett 2015, 26, 350−354. (f) Wen, L.;
Yue, Z.; Zhang, H.; Chong, Q.; Meng, F. Org. Lett. 2017, 19, 6610−
6613. (g) Mao, W.; Xue, W.; Irran, E.; Oestreich, M. Angew. Chem.,
Int. Ed. 2019, 58, 10723−10726.
Xin Wang − CAS Key Laboratory of Synthetic Chemistry of
Natural Substances, Shanghai Institute of Organic Chemistry,
University of Chinese Academy of Sciences, Shanghai 200032,
China
Hao Xu − The Research Center of Chiral Drugs, Innovation
Research Institute of Traditional Chinese Medicine, Shanghai
University of Traditional Chinese Medicine, Shanghai 201203,
China
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.0c01425
(7) For reviews on the functionalization of N-heteroaryl alkenes, see:
(a) Klumpp, D. A. Synlett 2012, 23, 1590−1604. (b) Best, D.; Lam,
H. W. J. Org. Chem. 2014, 79, 831−845.
Notes
The authors declare no competing financial interest.
(8) For nickel-catalyzed 1,4-additions of arylboronic reagents to α,β-
unsaturated carbonyl compounds, see: (a) Shirakawa, E.; Yasuhara,
Y.; Hayashi, T. Chem. Lett. 2006, 35, 768−769. (b) Hirano, K.;
Yorimitsu, H.; Oshima, K. Org. Lett. 2007, 9, 1541−1544. (c) Lin, P.-
S.; Jeganmohan, M.; Cheng, C.-H. Chem. - Asian J. 2007, 2, 1409−
1416. (d) Meng, J.-J.; Gao, M.; Dong, M.; Wei, Y.-P.; Zhang, W.-Q.
Tetrahedron Lett. 2014, 55, 2107−2109. (e) Chen, W.; Sun, L.;
Huang, X.; Wang, J.; Peng, Y.; Song, G. Adv. Synth. Catal. 2015, 357,
1474−1482.
ACKNOWLEDGMENTS
■
Financial support was generously provided by the National
Natural Science Foundation of China (nos. 21871184 and
21871284), the Shanghai Municipal Education Commission
(2019-01-07-00-10-E00072), the Science and Technology
Commission of Shanghai Municipality (18401933500), the
Strategic Priority Research Program of the Chinese Academy
of Sciences (XDB 20020100), and the Key Research Program
of Frontier Science (QYZDY-SSW-SLH026).
(9) For more details of the proposed reaction mechanism, see the
Supporting Information.
(10) Uca̧ r, S.; Esş iz, S.; Dasţ an, A. Tetrahedron 2017, 73, 1618−
1632.
(11) McKinney, A. M.; Jackson, K. R.; Salvatore, R. N.; Savrides, E.-
M.; Edattel, M. J.; Gavin, T. J. Heterocycl. Chem. 2005, 42, 1031−
1034.
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E
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