Nickel-Catalyzed Regioselective Arylboration of Conjugated Dienes

Article abstract of DOI:10.1002/ejoc.202001659

The nickel-catalyzed arylboration of conjugated dienes is reported. Good 1,4-regioselectivity and (E)-stereoselectivity were obtained using isoprene, together with very good 1,2-regioselectivity and (E)-stereoselectivity using 1-arylbutadienes. The high reactivity and selectivity of this process were dependent on the use of the appropriate nitrogen-based ligand. Moreover, wide functional group tolerance was observed under mild reaction conditions. This protocol provides a path to allyl or homoallyl boronic ester derivatives starting from 1,3-dienes, aryl bromides, and B₂pin₂. The downstream transformation of allyl boronic esters was also achieved, suggesting a strategy for the diastereoselective 1,2-difunctionalization of isoprene and demonstrating the potential for the synthesis of complex molecules.

Full text of DOI:10.1002/ejoc.202001659

Communications
doi.org/10.1002/ejoc.202001659
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Nickel-Catalyzed Regioselective Arylboration of Conjugated
Dienes
Haoyang Li,[a] Jiao Long,[a] Yuqiang Li,[a] Wang Wang,[a] Hailiang Pang,[a] and Guoyin Yin*[a]
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The nickel-catalyzed arylboration of conjugated dienes is
reported. Good 1,4-regioselectivity and (E)-stereoselectivity
were obtained using isoprene, together with very good 1,2-
regioselectivity and (E)-stereoselectivity using 1-arylbutadienes.
The high reactivity and selectivity of this process were depend-
ent on the use of the appropriate nitrogen-based ligand.
Moreover, wide functional group tolerance was observed under
mild reaction conditions. This protocol provides a path to allyl
or homoallyl boronic ester derivatives starting from 1,3-dienes,
aryl bromides, and B2pin2. The downstream transformation of
allyl boronic esters was also achieved, suggesting a strategy for
the diastereoselective 1,2-difunctionalization of isoprene and
demonstrating the potential for the synthesis of complex
molecules.
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The transformations of 1,3-dienes have attracted much atten-
tion in the field of organic synthesis, partly because these
substrates are readily available. As a consequence, significant
advances have been achieved based on both transition metal
and metal-free catalysis over the past several decades.[1] The
incorporation of boron-based moieties increases the trans-
latability of a molecule, and so the synthesis of boron-
containing compounds from 1,3-dienes is of particular
interest.[2] The carboboration of 1,3-dienes with the one-step
addition of carbon- and boron-based groups greatly increases
the complexity of the products that can be obtained as well as
the efficiency of the synthesis.[3] However, it is challenging to
perform such reactions with both regioselectivity and stereo-
selectivity at the double bonds (Figure 1a).[4] Currently, such
syntheses are primarily performed on the basis of copper
catalysis.[3a] As an example, the Oestreich group demonstrated
the use of ketone electrophiles to quench copper-based
intermediates,[5] while Cao and Liao demonstrated the reactions
of imine electrophiles to generate homoallylic amines.[6] Procter
et al.[7] and Meng et al.[8] independently reported the borylcya-
Figure 1. Arylboration of Conjugated Dienes.
nation of 2-substituted 1,3-dienes. Moreover, the Brown group
combined the use of copper intermediates with palladium-
catalyzed cross-coupling[9] to achieve the arylboration of
conjugated dienes.[10] However, significant progress, including
the regiodivergent arylboration of isoprene derivatives, is
possible through the use of palladium catalysts (Figure 1b).[11]
Regiodivergent products can also be obtained from 1-aryl-
substituted butadienes by employing alternate catalysts and
bases[12] (Figure 1c). Intriguingly, the (Z)-isomer is always
favored when the arylboration reactions proceed in a 1,4-
regioselective fashion.
[a] H. Li, J. Long, Y. Li, Dr. W. Wang, Dr. H. Pang, Prof. Dr. G. Yin
The Institute for Advanced Studies
Wuhan University
299 Bayi Road, Wuhan, Hubei province, China
E-mail: yinguoyin@whu.edu.cn
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejoc.202001659
Herein, we report the nickel-catalyzed arylboration of
conjugated dienes (Figure 1d) with high reactivity resulting
Part of the ”YourJOC Talents” Special Collection.
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from the use of nitrogen-based ligands. Both excellent
line or 2,2’-bipyridine frameworks (L2-L5) were ineffective in
this reaction (entry 2). The pyridine-oxazoline (PyrOx) ligand L6
was also not useful.[17] In contrast, the 6-methyl-substituted
PyrOx ligand L7 provided the 1,4-addition product (E)-4a in a
73% yield (as determined by gas chromatography) with
excellent stereoselectivity (E/Z>20:1). Incorporating ligand L8,
with slightly modified steric hindrance associated with the
pyridine moiety (entries 4 and 5), also afforded a better yield. A
subsequent survey of solvents in conjunction with L8 (en-
tries 7–12) showed that dimethoxyethane (DME) was optimal,
and gave an improved yield of 93% without reducing the
stereoselectivity (entry 9). Notably, no other regioisomers were
detected when applying these reaction conditions. Control
experiments demonstrated that no arylboration products were
observed in the case of ligand-free reactions (entries 13 and 14)
or in the absence of the nickel catalyst (entry 15). Additionally,
none of the desired product was obtained when the reaction
was performed under air, demonstrating that the process is
very sensitive to oxygen (entry 16).
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regioselectivity and stereoselectivity were obtained from this
system.[13] In particular, in contrast to dual metal catalytic
systems, (E)-1,4-addition products were obtained using isoprene
as the substrate in conjunction with nickel-based catalysis.
On the basis of our continued interest in the nickel-
catalyzed carboboration of alkenes[14] and asymmetric hydro-
amination of conjugated dienes,[15] we assessed the extension
of these concepts to conjugated dienes, especially with regard
to the regioselectivity and stereoselectivity of the reactions. In
addition, we examined a new single catalyst system so as to
provide an operationally simple option. On this basis, we
explored the arylboration of isoprene. Considering that the
reactivity of conjugated dienes might be similar to that of
styrenes, the standard reaction conditions employed during the
1,2-arylboration of styrenes in our prior work were selected for
the initial trial (Table 1, entry 1).[16] Surprisingly, only a trace
amount of products 4a incorporating all three reagents was
obtained. We speculated that modification of the ligand could
promote the reaction, so a series of ligands was evaluated.
Table 1 demonstrates that ligands based on 1,10-phenanthro-
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With the optimal reaction conditions in hand, we next
turned our attention to the scope of this process. As
Haoyang Li was born in Henan Province,
China. He received his B.Sc. degree from
Northwest A&F University in 2019. Subse-
quently, he pursued his master‘s degree under
the guidance of Prof. Guoyin Yin at the
Institute for Advanced Studies of Wuhan
University.
vision of Prof. Xin-Yuan Liu at South University
of Science and Technology of China.
Hailiang Pang is from Shandong Province,
China. He had completed his Master’s degree
in 2017 from Beijing University of Technology.
He joined the Institute For Advanced Studies,
Wuhan University in September 2017 for his
doctoral studies. He completed his Ph.D.
under the supervision of Prof. Guoyin Yin in
June 2020.
Yuqiang Li was born in Anhui Province, China.
He received his B.Sc. degree from Central
South University in 2016. Subsequently, he
pursued his Ph.D. degree under the guidance
of Prof. Guoyin Yin at the Institute for
Advanced Studies of Wuhan University.
Prof. Dr. Guoyin Yin received his Ph.D. from
the Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences in 2011, under
the supervision of Prof. Guosheng Liu. He
conducted postdoctoral research at the Tech-
nical University of Munich with Prof. Thorsten
Bach, at RWTH Aachen University with Prof.
Franziska Schoenebeck, and at the University
of Delaware with Prof. Donald A. Watson. In
2016, he began his independent career at the
Institute for Advanced Studies at Wuhan
University. His research interest focuses on
transformations involving metal migration.
Jiao Long was born in Hunan Province, China.
She received her B. Sc. Degree from Nanchang
University in 2015. In the same year, she
joined The College of Chemistry and Molec-
ular Sciences of Wuhan University for her
master‘s degree, supervised by Prof. Xumu
Zhang. From 2018, she pursued her Ph.D.
under the guidance of Prof. Guoyin Yin at the
Institute for Advanced Studies of Wuhan
University.
Wang Wang was born in Anhui Province,
China. He received his Bachelor’s degree from
Huainan Normal University in 2014 and a
Master’s degree from Zhejiang University of
Technology in 2017. Subsequently, he pur-
sued his Ph.D. degree under the supervision
of Prof. Guoyin Yin at Wuhan University.
Currently, he is a postdoc under the super-
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Table 1. Optimization of Arylboration of Isoprene.
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Entry
Ligand
Solvent
E/Z[a]
Yield of (E)-4a [%][b]
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12
13
14
15
16
17
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20
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29
30
31
32
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35
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40
41
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49
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1
2
3
4
5
6
7
8
L1
L2–L5
L6
L7
L8
L9
L8
L8
L8
L8
L8
L8
no
no
L8
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
NMP
DMA
DME
THF
toluene
nd
nd
nd
<5
<5
<5
73
82
72
33
35
93(73)[c]
53
53
8
23:1
19:1
24:1
14:1
15:1
27:1
24:1
18:1
6:1
–
9
10
11
12
13
14
15[d]
16[e]
CH3CN
DME, DMA, NMP
CH3CN, DMSO
DME
0
0
0
0
–
–
–
L8
DME
[a] The ratio of E/Z was determined by GC-MS analysis. [b] Yield was
determined by gas chromatography analysis with naphthalene as internal
standard. [c] The number in parenthesis is isolated yield of the
corresponding alcohol after oxidation on 0.5 mmol scale. [d] The reaction
was conducted without nickel catalyst. [e] The reaction was performed
under air.
summarized in Figure 2, various aryl bromides bearing different
functional groups were initially examined. To simplify the
isolation step, the boron-containing products were converted
to their corresponding alcohols by in situ oxidation. Overall,
both electron-deficient and electron-rich aryl bromides, as well
as bromonaphthalene (5p) and 2-bromoindene (5q), gave the
regioselective 1,4-addition products in good yields with suitable
(E)-selectivity. The use of aryl bromides bearing ortho-substitu-
ents, such as methyl (5e) and methoxyl (5n) groups, also did
not affect the efficiency or selectivity. A variety of functional
groups, including ether (5b, 5j, 5m, and 5n), ester (5c),
chloride (5f and 5g), fluoride (5i and 5o), amine (5h), ketone
(5k) and unprotected aniline (5o) moieties, were all highly
compatible with these mild reaction conditions. However, some
heteroaryl bromides, such as bromopyridine and bromoquino-
line, did not react efficiently, likely as a result of their strong
coordinating characteristics (see Supporting Information for
details). Isoprene analogs also provided the desired arylboration
products under the same reaction conditions (5r and 5s), albeit
with poor stereoselectivity. Finally, 1-alkyl-1,3-dienes primarily
generated 1,4-addition products but 1,2- products were also
obtained (5t and 5t’).
Figure 2. Scope of the Arylboration of Isoprene and Its Analogues.
and regioselectivity under the same reaction conditions
(Table 2, entry 1). Optimization of this system led to the
identification of the pyridylcarboamide ligand L10 as the most
successful promoter,[19] with a 75% isolated yield (Table 2,
entry 2). It should be noted that there was no 1,4-addition
product (E)-8a was detected in these reaction conditions.
The generality of these reaction conditions was investigated
next, with the results presented in Figure 3. Varying the
substituents on the aryl group, and even replacing this moiety
with a furyl group, did not greatly affect the reactivity. Both 1,1-
and 1,2-disubstituted alkenes were found to generate the
corresponding arylboration products under the same reaction
conditions (9f and 9g), although the latter afforded a lower
yield. More importantly, a quaternary carbon center could also
be constructed using this arylboration reaction (9h).[20] Notably,
when 1-alkyl-1,3-diene was used, the 1,2-addition product (5t’)
was still favored under these reaction conditions. The reverse
regioselectivities were obtained by employing two different
sets of reaction parameters, indicating that the choice of ligands
could modify the regioselectivity of the arylboration. Addition-
Encouraged by the results described above, we subse-
quently examined the reactions of 1-aryl-1,3-dienes, which
represent another type of conjugated diene widely used in
organic synthesis.[18] The thermodynamically favored 1,2-addi-
tion product (E)-7a was isolated in 13% yield with good stereo-
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Table 2. Optimization of the Arylboration of 1-Phenyl-1,3-diene.
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Entry
Ligand
Solvent
(E)-7a/(E)-8a[a]
Yield of (E)-7a [%][b]
10
11
12
13
14
15
16
17
18
19
20
21
22
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1
2
3
4
5
6
7
8
L8
DME
THF
THF
THF
THF
THF
THF
THF
>99:1
>99:1
nd
>99:1
>99:1
>99:1
>99:1
>99:1
13
L10
L11
L12
L13
L14
L15
L16
81(75)[c]
<5
27
73
47
67
19
[a] The ratio of (E)-7a/(E)-8a was determined by GC-MS analysis. [b] Yield
was determined by gas chromatography analysis with naphthalene as
internal standard. [c] The number in parenthesis is isolated yield of the
corresponding alcohol after oxidation on 0.4 mmol scale.
Figure 4. Attempted Development of an Asymmetric Variant and Trans-
formations of Arylboration Products.
likely not a good choice with regard to controlling the
enantioselectivity.
Transformations of the arylboration products were also
assessed. The allylboronic ester 5b was found to react with
benzoquinone to formally produce the 1,4-addition product 10
in 51% yield (Figure 4b).[21] In addition, the allylboronic ester
obtained from the arylboration of isoprene could be converted
to the homoallylic alcohol 11 bearing a quaternary carbon
center with a 75% isolated yield and good diastereoselectivity
(dr=10:1). This reaction, therefore, represents a strategy for the
1,2-difunctionalization of isoprene (Figure 4c).[22] This efficient
one-pot procedure has potential applications to the synthesis
of complex molecules.
In summary, this work demonstrated the nickel-catalyzed
arylboration of conjugated dienes, thus providing a route to the
formation of allyl and homoallyl boronic ester derivatives from
1,3-dienes, aryl bromides, and B2pin2. The reactivity and
selectivity of this synthetic procedure were found to be
governed by the nitrogen-based ligand. Further research
regarding the synthetic applications and reaction mechanism of
this technique is ongoing in our laboratory.
Acknowledgements
We thank Profs. Aiwen Lei, Qianghui Zhou, Wen-Bo Liu, and Xiao
Shen at Wuhan University for sharing of basic instruments and
chemicals. We are grateful for the financial support from National
Natural Science Foundation of China (21702151, 21871211) and
the Fundamental Research Funds for Central Universities
(2042019kf0208). Michael D. Judge, MSc, from Liwen Bianji, Edanz
Editing China (www.liwenbianji.cn/ac), for editing the English text
of this manuscript.
Figure 3. Scope of the Arylboration of 1-Aryl-1,3-dienes.
ally, only a very small degree of enantioisomeric excess (4% ee)
was observed (Figure 4a) when the chiral ligand (S)-10 was
used. This result suggests that pyridylcarboamide ligands are
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Conflict of Interest
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The authors declare no conflict of interest.
4
Keywords: nickel catalysis · arylboration · allylboronic esters ·
1,3-dienes · regioselectivity
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