Nickel-catalyzed hydroalkylation of 1,3-dienes with malonates using a homoallyl carbonate as the 1,3-diene and hydride source

Article abstract of DOI:10.1016/j.tetlet.2021.152916

The use of a malonate nucleophile in the transition metal-catalyzed hydroalkylation of 1,3-dienes remains immature. Herein, we report the nickel-catalyzed hydroalkylation of 1,3-dienes with malonates using a homoallyl carbonate as the 1,3-diene and hydride source. A broad range of homoally carbonates and malonate derivatives were well tolerated under a Ni/DPEphos catalyst system, providing the corresponding 1,2-hydroalkylation products in 40–94% yields with excellent regioselectivity (32 examples). We also suggested the possible reaction mechanism for the nickel-catalyzed hydroalkylation of in situ generated 1,3-dienes with malonates.

Full text of DOI:10.1016/j.tetlet.2021.152916

Tetrahedron Letters 68 (2021) 152916
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Nickel-catalyzed hydroalkylation of 1,3-dienes with malonates using a
homoallyl carbonate as the 1,3-diene and hydride source
⇑
⇑
Hiroaki Tsuji , Yoshiyuki Takahashi, Motoi Kawatsura
Department of Chemistry, College of Humanities & Sciences, Nihon University, Sakurajosui, Setagaya-ku, Tokyo 156-8550, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The use of a malonate nucleophile in the transition metal-catalyzed hydroalkylation of 1,3-dienes
remains immature. Herein, we report the nickel-catalyzed hydroalkylation of 1,3-dienes with malonates
using a homoallyl carbonate as the 1,3-diene and hydride source. A broad range of homoally carbonates
and malonate derivatives were well tolerated under a Ni/DPEphos catalyst system, providing the corre-
sponding 1,2-hydroalkylation products in 40–94% yields with excellent regioselectivity (32 examples).
We also suggested the possible reaction mechanism for the nickel-catalyzed hydroalkylation of in situ
generated 1,3-dienes with malonates.
Received 18 December 2020
Revised 3 February 2021
Accepted 9 February 2021
Available online 12 February 2021
Keywords:
Nickel Catalysis
Hydroalkylation
Ó 2021 Elsevier Ltd. All rights reserved.
1
,3-Dienes
Malonates
Homoallyl carbonates
The catalytic hydroalkylation of unsaturated hydrocarbons by
means of a transition metal catalyst presents an attractive strategy
for the formation of carbon–carbon bond in an efficient and atom
economical manner [1]. Due to the presence of an alkene group
on the resulting alkylation products, the catalytic hydroalkylation
of 1,3-dienes offers a rationale route for the manipulation of com-
plex organic molecules [2]. Therefore, this type of reaction has
received continuous interests from the synthetic community and
a wide variety of C-pronucleophiles, such as active methylene
compounds [3], simple carbonyl compounds [4], oxazolones [5],
hydrazones [6], and others [7,1b], were attempted to employ in
the hydroalkylation of 1,3-dienes using nickel and palladium as
the representative catalysts. However, attentions have been spo-
radically paid to the use of a malonate nucleophile, which would
lead to a valuable synthetic intermediate in organic synthesis [8].
Hata and co-workers reported the palladium-catalyzed hydroalky-
lation of 1,3-butadiene with malonates, even though telomeriza-
tion and 1,2- and 1,4-additions occurred during the catalysis
alyzed hydroalkylation of a series 1,3-dienes with activated C-
pronucleophiles, providing the hydroalkylation products in up to
95% yield with high enantioselectivity (Scheme 1b) [11]. However,
only Meldrum’s acid derivatives can be utilized as a malonate ana-
logue in this palladium catalysis. Given these research precedents,
the transition metal-catalyzed hydroalkylation of 1,3-dienes with
malonates is still immature in terms of the generality of 1,3-dienes
as well as malonates.
We have recently succeeded in the development of the nickel-
catalyzed hydroarylation of in situ generated 1,3-dienes with aryl-
boronic acids using a secondary homoallyl carbonate as a surrogate
for the 1,3-diene and hydride source [12]. This method features the
use of homoallyl carbonates, which is readily prepared by the ally-
lation of aldehydes [13] followed by the formation of carbonate
esters, as both 1,3-dienes and hydride sources. To address the
above-mentioned issue in the transition metal-catalyzed
hydroalkylation of 1,3-dienes, we sought to investigate the
hydroalkylation of 1,3-dienes with malonates based on the
methodology we developed. Herein, we report the nickel-catalyzed
hydroalkylation of in situ generated 1,3-dienes with a malonate
using a secondary homoallyl carbonate as the 1,3-diene and
hydride source (Scheme 1c).
(Scheme 1a) [9]. After the pioneering work, Moberg, Jolly, and
Hartwig independently disclosed the nickel- and palladium-cat-
alyzed hydroalkylation of 1,3-dienes, such as 1,3-butadiene, 2,3-
dimethylbutadiene, 1,3-cyclohexadiene, and 1,3-cyclopentadiene,
with a limited number of malonates as a carbon nucleophile [10].
Recently, Malcolmson and co-workers reported the palladium-cat-
We initially examined the optimization of the reaction condi-
tions using secondary homoallyl carbonate 1a as the 1,3-diene
and hydride source (Table 1). At the outset of the optimization
study, dimethyl methylmalonate (2a) was subjected to a catalyst
⇑
Corresponding authors.
E-mail addresses: tsuji@chs.nihon-u.ac.jp (H. Tsuji), kawatsur@chs.nihon-u.ac.jp
2 6
system consisting of 10 mol% Ni(cod) and 20 mol% P(p-MeOC -
4 3
H ) ,
which was proved to be effective for the previous
(
M. Kawatsura).
https://doi.org/10.1016/j.tetlet.2021.152916
040-4039/Ó 2021 Elsevier Ltd. All rights reserved.
0

H. Tsuji, Y. Takahashi and M. Kawatsura
Tetrahedron Letters 68 (2021) 152916
hydroarylation reaction [12], in the presence of N,O-bis
(
trimethylsilyl)acetamide (BSA) as a base (Table 1, entry 1). The
use of P(p-tol) and PPh as the ligands afforded the comparable
3
3
yield and regioselectivity (Entries 2 and 3). Electron-deficient and
sterically congested monophosphine ligands were totally ineffec-
tive in this nickel catalysis (Entries 4 and 5). We next tested several
bidentate phosphine ligands (Entries 6–14). The reaction with
1
0 mol% DPPE and DPPP failed to give desired hydroalkylation pro-
duct 3aa (Entries 6 and 7). Nickel catalyst systems derived from
DPPB, DPPPent, DPPF exclusively produced 3aa in 13–46% yields
(
Entries 8–10). When 10 mol% DPEphos was used as the ligand,
hydroalkylation product 3aa was obtained in 82% yield with excel-
lent regioselectivity (Entry 11). Xantphos and NiXantphos also
facilitated the hydroalkylation reaction to give 3aa in 78% and
6
7% yield, respectively, even though the formation of small amount
of 1,4-hydroalkylation product 4aa was observed (Entries 12 and
3). BINAP was not beneficial as a bisphophine ligand in the pre-
1
sent catalyst system (Entry 14). Additionally, we also examined
the reaction in the presence of bidentate nitrogen ligands such as
0
4
,4 -di-tBu-bipyridine and 1,10-phenanthroline (Entries 15 and
1
6). However, the desired hydroalkylation reaction did not take
place under the reaction conditions. The screening revealed that
DPEphos is the suitable choice of the ligand in the present nickel
catalysis. To achieve the improvement of the yield of 3aa, we
investigated further optimization of the reaction conditions using
DPEphos as the optimal ligand. The reaction was conducted at
80 °C to give 3aa in maintained yield (Entry 17). Fortunately, the
Scheme 1. Transition metal-catalyzed hydroalkylation of 1,3-dienes with
malonate and its analogue.
a
Table 1
a
Optimization of reaction conditions.
Entry
L
Yieldb (%) of 3aa
Yieldb (%) of 4aa
3aa:4aac
1
2
3
4
5
6
7
8
9
P(p-MeOC
6
H
4
)
3
35
41
44
<1
<1
<1
<1
46
32
13
82
78
67
<1
<1
<1
83
1
1
1
98:2
98:2
98:2
–
–
–
P(p-tol)
PPh
P(p-CF
3
3
3
C
6
H
4
)
3
<1
<1
<1
<1
<1
<1
<1
1
6
5
<1
<1
<1
1
P(o-tol)
DPPE
3
DPPP
DPPB
DPPPent
DPPF
DPEphos
–
>99:1
>99:1
>99:1
99:1
93:7
93:7
–
–
–
99:1
99:1
10
11
12
13
14
15
16
17
18
Xantphos
NiXantphos
rac-BINAP
0
0
4,4 -di-t-Bu-2,2 -bpy
1,10-Phenanthroline
DPEphos
d
e
f
DPEphos
97 (88)
1
a
Reaction conditions: 1a (0.25 mmol), 2a (0.275 mmol), Ni(cod)
2
(0.025 mmol), L {0.05 mmol (20 mol%) for monophosphine ligands and 0.025 mmol (10 mol%) for
CN (0.25 M) at 60 °C for 18 h.
bidentate ligands}, N,O-bis(trimethylsilyl)acetamide (BSA) (0.275 mmol) in CH
3
b
c
d
e
f
1
The yields were determined by H NMR analyses of the crude reaction mixture using dibromomethane as an internal standard.
Determied by 1H NMR analyses of the crude reaction mixture.
The reaction was performed at 80 °C.
With 1.5 equiv of 2a and BSA.
Isolated yield.
2

H. Tsuji, Y. Takahashi and M. Kawatsura
Tetrahedron Letters 68 (2021) 152916
Table 2
a
Scope of secondary homoallyl carbonates.
Entry
1
R
3
Yieldb (%)
3:4c
1d
2
3
1a
1b
1c
1d
1e
1f
1g
1h
1i
1j
1k
1l
1m
1n
1o
1p
1q
1r
Ph
4-MeC
3aa
3ba
3ca
3da
3ea
3fa
3ga
3ha
3ia
3ja
3ka
3la
3ma
3na
3oa
3pa
3qa
3ra
94
87
87
83
92
70
81
87
87
86
85
51
89
55
80
49
77
76
>99:1
99:1
99:1
>99:1
>99:1
99:1
6
H
4
e
f
4-MeOC
4-CF
4-(CO
4-ClC
4-FC
3-MeC
piperonyl
3-CNC
2-MeOC
2-CF
6-MeO-2-naphthyl
3-pyridyl
3-thienyl
2-benzofuranyl
cyclohexyl
phenethyl
6
H
4
4
5
6
7
8
3
C
6
H
4
2
6 4
Me)C H
H
4
6
6
H
4
99:1
H
6 4
>99:1
>99:1
>99:1
>99:1
>99:1
99:1
>99:1
97:3
95:5
e
f
f
f
f
9
10
11
12
13
14
15
16
17
18
6
H
4
e
g
e
g
e
g
6
H
4
3
C
6
H
4
>99:1
95:5
a
b
c
d
e
f
Reaction conditions: 1 (0.25 mmol), 2a (0.375 mmol), Ni(cod)
Combined isolated yield of 3 and 4.
2 3
(0.025 mmol), DPEphos (0.025 mmol), BSA (0.375 mmol) in CH CN (0.25 M) at 60 °C for 18 h.
Determined by 1H NMR analyses of the crude reaction mixture.
3
4
mmol scale.
,1-Hydroalkylation product 5 was observed in the 1H NMR analyses of crude reaction mixture (5ca: 1% yield, 5ia: 2% yield, 5ka: 1% yield, 5ma: 6% yield, 5oa: 6% yield).
Combined isolated yield of 3, 4, and 4,1-hydroalkylation products 5.
g
2
2
0 mol% Ni(cod) and 20 mol% DPEphos were used.
desired product 3aa was obtained in 97% NMR yield (88% isolated
yield) with excellent regioselectivity, when 1.5 equivalents of 2a
and BSA were employed in the reaction system (Entry 18).
products 3na–pa in 49–80% yields, even though increasing the
loading amount of the catalyst was required for the reaction of
1n and 1p (Entries 14–16). In contrast to the previous hydroaryla-
We investigated the scope of secondary homoallyl carbonates 1
with dimethyl methylmalonate (2a) as the model nucleophile
under the optimized reaction conditions (Table 2). The reaction
of homoallyl carbonate 1a with 2a could be conducted on 3 mmol
scale without loss of the catalytic performance, providing 3aa in
2 6 4 3
tion reaction using a combination of Ni(cod) and P(p-MeOC H )
as the catalyst [12], the present nickel catalyst system enabled
the use of aliphatic substrates 1q and 1r, providing the hydroalky-
lation products 3qa and 3ra in 77% and 76% yield, respectively
(Entries 17 and 18). During the scope of a series of homoallyl car-
bonates, we confirmed that the reactions of homoallyl carbonates
bearing electron-rich aromatic rings, such as 1c, 1i, 1k, 1m, and
1o, are prone to give the corresponding 4,1-hydroalkylation prod-
ucts 5ca, 5ia, 5ka, 5ma, and 5oa in 1%, 2%, 1%, 6%, 6% NMR yields,
respectively.
We next turned our attention to reveal the scalability of malo-
nate derivatives 2 in the nickel-catalyzed hydroalkylation of in situ
generated 1,3-dienes (Table 3). Diethyl methylmalonate (2b) and
diisopropyl methylmalonate (2c) also engaged in the reaction to
give the desired hydroalkylation products 3ab and 3ac in 82%
and 83% yield, respectively (Table 3, Entries 1 and 2). The effect
of substituents on the active methylene carbon of malonates was
also surveyed (Entries 3–10). Diethyl malonate derivatives 2d–h
bearing a series of linear alkyl chains participated in the hydroalky-
lation reaction, providing the corresponding hydroalkylation prod-
ucts 3ad–ah in 76–88% yields (Entries 3–7). It is worth mentioning
that the functionalized linear alkyl chains such as cyanoethyl (2f),
chloropropyl (2g), and 3-oxobutyl (2h) groups were well tolerated
under the reaction conditions. When diethyl isobutylmalonate (2i)
9
4% yield with >99:1 regioselectivity (Table 2, entry 1).
The introduction of electron-donating and -withdrawing sub-
stituents and halogen atoms at the para position on their aromatic
rings was well tolerated to deliver the corresponding 1,2-
hydroalkylation products 3ba–ga in 70–92% yields with excellent
regioselectivity (Entries 2–7). Desired hydroalkylation products
3
ha–ja having 3-methylphenyl, piperonyl, and 3-cyanophenyl
groups could be obtained without significant influence to the yield
and regioselectivity (Entries 8–10). Homoallyl carbonate 1k con-
taining a methoxy group at the ortho position on the aromatic ring
reacted with 2a to give desired product 3ka in 85% yield (Entry 11).
However, the introduction of a trifluoromethyl substituent at the
ortho position (1l) affected the reaction efficiency, resulting in
moderate yield of 3la (Entry 12). When homoallyl carbonate 1m
bearing 6-MeO-2-naphthalene ring was subjected to the reaction
system, desired product 3ma was obtained in 89% yield with
9
9:1 regioselectivity (Entry 13). Homoallyl carbonates 1n–p hav-
ing heterocyclic rings, such as pyridine, thiophene, and benzofuran,
underwent the reaction to give the corresponding hydroalkylation
3

H. Tsuji, Y. Takahashi and M. Kawatsura
Tetrahedron Letters 68 (2021) 152916
Table 3
Scope of malonates.a
Entry
1
R1
R2
3
Yieldb (%)
3:4c
1
2
3
4
5
6
7
8
9
1
1
1
1
1
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
2n
2o
Me
Me
Et
nBu
–CH
-CH
-CH
iBu
F
Ph
H
Et
iPr
Et
Et
Et
Et
Et
Et
Et
Et
Me
Et
Bn
tBu
3ab
3ac
3ad
3ae
3af
3ag
3ah
3ai
3aj
3ak
3al
3am
3an
3ao
82
83
78
78
83
88
76
69
59
40
77
78
50
76
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
98:2
>99:1
>99:1
>99:1
>99:1
>99:1
2
CH
2
CN
CH
COMe
2
CH
CH
2
2
2
Cl
2
0
1
2
3
4
H
H
H
a
b
c
Reaction conditions: 1a (0.25 mmol), 2 (0.375 mmol), Ni(cod)
Combined isolated yield of 3 and 4.
2
(0.025 mmol), DPEphos (0.025 mmol), BSA (0.375 mmol) in CH
3
CN (0.25 M) at 60 °C for 18 h.
Determined by 1H NMR analyses of the crude reaction mixture.
di-tert-butyl malonate (2o), producing the hydroalkylation prod-
ucts 3an and 3ao in 50% and 76% yield, respectively (Entries 13
and 14).
We show the putative reaction mechanism of the nickel-cat-
alyzed hydroalkylation of in situ generated 1,3-dienes with malo-
nates in Scheme 2. Given the Sigman’s study [14] and our
previous work [12], the alkene-directed oxidative addition of Ni
(
0) species to the CAO bond on homoallyl carbonates 1 would take
place to generate the secondary alkyl nickel species I. Subsequent
b-hydrogen elimination from the resultant alkyl nickel species I
would produce the diene-coordinated Ni-H species II [15,16]. The
Ni-H species II would undergo migratory insertion to generate p-
allylnickel intermediate III [4a,b,6a,b,17]. As shown in Table 2,
small amount of 4,1-hydroalkylation products were formed in
some cases. We assume that the migratory insertion of the
internal alkene moiety of the 1,3-dienes to the Ni-H species
might be a cause of the formation of the side products. Finally,
nucleophilic addition of the malonate anion would occur at the
less hindered terminus of the unsymmetrical
p-allylnickel
species III to provide the desired hydroalkylation products 3 [18].
We observed the formation of 1,4-hydroalkylation products during
the scope of homoallyl carbonates and malonate derivatives. These
results would be attributed to the formation of the unsymmetrical
Scheme 2. Putative reaction mechanism.
p
-allylnickel intermediate III and subsequent nucleophilic addition
was used as a nucleophile, hydroalkylation product 3ai was
obtained in 69% yield (Entry 8). Diethylmalonate analogues that
bear not only alkyl substituents but also a fluorine atom (2j) and
a phenyl group (2k) on the active methylene carbon were also
compatible with the reaction to afford the hydroalkylation product
with a malonate nucleophile.
In conclusion, we have developed the nickel-catalyzed
hydroalkylation of 1,3-dienes with malonate nucleophiles using
readily accessible homoallyl carbonates as the 1,3-diene and
2
hydride source. The Ni(cod) /DPEphos catalyst system found to
3
aj and 3ak in 59% and 40 yield, respectively (Entries 9 and 10).
be effective for the hydroalkylation of in situ generated 1,3-dienes
with malonates in terms of the reaction yields and regioselectivity,
providing a broad range of 1,2-hydroalkylation products. The
nickel catalysis would proceed via regioselective addition of the
The simple dialkyl malonates such as dimethyl malonate (2l) and
diethyl malonate (2m) also underwent the reaction to give the
desired hydroalkylation products 3al and 3am in satisfactory
yields (Entries 11 and 12). Furthermore, the catalyst system also
accommodated sterically congested dibenzyl malonate (2n) and
malonate nucleophile to the unsymmetrical
p-allylnickel interme-
diate generated from the diene-coordinated Ni-H species.
4

H. Tsuji, Y. Takahashi and M. Kawatsura
Tetrahedron Letters 68 (2021) 152916
[
6] (a) L. Lv, D. Zhu, Z. Qiu, J. Li, C.-J. Li, ACS Catal. 9 (2019) 9199–9205;
Declaration of Competing Interest
(
(
b) L. Cheng, M.-M. Li, B. Wang, L.-J. Xiao, J.-H. Xie, Q.-L. Zhou, Chem. Sci. 10
2019) 10417–10421;
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
(c) L. Lv, L. Yu, Z. Qiu, C.-J. Li, Angew. Chem. Int. Ed. 59 (2020) 6466–6472.
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b) Q. Zhang, H. Yu, L. Shen, T. Tang, D. Dong, W. Chai, W. Zi, J. Am. Chem. Soc.
41 (2019) 14554–14559;
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(
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