Nickel-Catalyzed Dimerization and Alkylarylation of 1,3-Dienes with Alkyl Fluorides and Aryl Grignard Reagents

Article abstract of DOI:10.1002/anie.201601126

In the presence of a nickel catalyst, 1,3-butadiene undergoes selective dimerization and alkylarylation with alkyl fluorides and aryl Grignard reagents to give 1,6-octadienes with alkyl and aryl groups at the 3- and 8-positions, respectively, by the consecutive formation of three carbon-carbon bonds. The formation of an anionic nickel complex plays an important role in forming C-C bonds with alkyl fluorides.

Full text of DOI:10.1002/anie.201601126

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International Edition: DOI: 10.1002/anie.201601126
German Edition: DOI: 10.1002/ange.201601126
Multicomponent Reactions
Nickel-Catalyzed Dimerization and Alkylarylation of 1,3-Dienes with
Alkyl Fluorides and Aryl Grignard Reagents
Takanori Iwasaki,* Xin Min, Asuka Fukuoka, Hitoshi Kuniyasu, and Nobuaki Kambe*
Abstract: In the presence of a nickel catalyst, 1,3-butadiene
undergoes selective dimerization and alkylarylation with alkyl
fluorides and aryl Grignard reagents to give 1,6-octadienes
with alkyl and aryl groups at the 3- and 8-positions, respec-
tively, by the consecutive formation of three carbon–carbon
bonds. The formation of an anionic nickel complex plays an
À
important role in forming C C bonds with alkyl fluorides.
M
ulticomponent reactions provide strategically challeng-
ing and synthetically useful methods for constructing unique
carbon frameworks from relatively simple molecules.[1] 1,3-
Butadiene is an important four-carbon feedstock in the
chemical industry and is widely used in huge amounts,
mainly for producing oligomerization and polymerization
products. In terms of synthetic applications of 1,3-butadiene
in fine chemistry based on its selective functionalization,
many efforts have been devoted to the transition-metal-
catalyzed telomerization reaction since its discovery in
1967.[2a,b] This transformation proceeds via bis(p-allyl)metal
intermediate A, which reacts with nucleophiles to give rise to
octadienes with the concomitant introduction of a functional
group (Scheme 1a).[2] When CO or CO2 were employed,
a carboxyl group was produced.[3]
Scheme 1. Dimerization and functionalization of 1,3-butadiene.
because of the rapid direct cross-coupling between alkyl
halides and organometallic reagents.[7–9] We herein report that
the use of a combination of alkyl fluorides[9–12] and appro-
priate aryl Grignard reagents solves this problem, thus
enabling the four-component coupling of alkyl fluorides,
aryl Grignard reagents, and two 1,3-butadiene molecules that
leads to the formation of 1,6-octadienes with alkyl and aryl
groups at the 3- and 8-positions (Scheme 1d).[13]
The reaction of nOctF (1a) and oTolMgBr (2a) with 1,3-
butadiene was examined using 10 mol% of Group 10 metal
salts in THF (Table 1). When NiBr2(dme) was used, dimeri-
zation and coupling took place regio- and stereoselectively to
give the E-configured four-component-coupling product 3aa
in 92% yield (Table 1, entry 1). As a side product, 2-
It has also been reported that the combined use of
ketones, aldehydes, or imines with organozinc or -aluminum
reagents enables the bifunctionalization of both terminal
carbon atoms of octadienes via metallacycle intermediates
(Scheme 1b).[4] This reaction provides a useful method for
introducing two different carbon moieties into the 2,6-
octadiene framework, although the three-component cou-
pling of these reagents in a 1:1:1 ratio competes or even occurs
preferentially in some cases.[4a,c]
We previously reported on the dimerization and arylsily-
lation[5] or disilylation[6] of 1,3-butadiene with chlorosilanes as
the electrophile in the presence of a Ni or Pd catalyst,
respectively (Scheme 1c). This reaction is promoted by
Grignard reagents, which enable the formation of an anionic
nickel complex B as the catalytically active species. However,
the use of a simple alkyl electrophile, such as an alkyl halide,
in this transformation has not yet been achieved, mainly
Table 1: Four-component coupling reaction of 1,3-butadiene, nOctF, and
oTolMgBr.
Entry
Cat. (mol%)
2a [equiv]
T [8C]
3aa [%][a]
1
2
3
4
5
6
7
8
NiBr2(dme) (10)
NiCl2(PPh3)2 (10)
NiCl2(dppf) (10)
PdCl2 (10)
2.0
2.0
2.0
2.0
2.0
1.5
1.5
1.5
30
30
30
30
30
30
30
40
92
43
8
4
n.d.
88
[*] Dr. T. Iwasaki, X. Min, A. Fukuoka, Prof. Dr. H. Kuniyasu,
Prof. Dr. N. Kambe
Department of Applied Chemistry
Graduate School of Engineering, Osaka University
Suita, Osaka 565-0871 (Japan)
E-mail: iwasaki@chem.eng.osaka-u.ac.jp
kambe@chem.eng.osaka-u.ac.jp
PtCl2 (10)
NiBr2(dme) (10)
NiBr2(dme) (5)
NiBr2(dme) (5)
79
87 (86)
Supporting information and ORCID(s) from the author(s) for this
article are available on the WWW under
http://dx.doi.org/10.1002/anie.201601126.
[a] Determined by GC (yields of isolated products given in parentheses).
dme=1,2-dimethoxyethane, dppf=1,1’-bis(diphenylphosphino)ferro-
cene, oTol =ortho-tolyl.
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Table 2: Scope and limitations.[a]
octyltoluene was formed in only
4% yield by the direct coupling of
nOctF with oTolMgBr, but three-
component-coupling products com-
prising one molecule each of 1,3-
butadiene, 1a, and 2a were not
detected at all.[4,14] The use of PPh3
and dppf affected the reaction,
resulting in lower yields (entries 2
and 3), and Pd and Pt catalysts were
found to be ineffective (entries 4
and 5). The amount of oTolMgBr
could be reduced to 1.5 equiv with-
out a substantial loss of efficiency
(entry 6). The desired product was
obtained in good yield (87%) when
5 mol% of the Ni catalyst were
used at 408C (entry 8). When an
alkyl chloride, bromide, iodide, or
mesylate was used instead of the
alkyl fluoride, the desired product
was obtained in 4, 64, 45, and 16%
yield, respectively.[15] Under the
same conditions, isoprene afforded
a mixture of four regioisomers
having two methyl groups at the
different positions of the 1,6-octa-
diene skeleton, and the reaction of
1,3-pentadiene was sluggish. When
alkyl Grignard reagents were
employed instead of aryl Grignard
reagents, the direct cross-coupling
of the alkyl fluoride with the alkyl
Grignard reagent predominated.[9a]
Under the optimized reaction
Entry
1
ArMgBr
Yield [%]
89
Entry
7
ArMgBr
Yield [%]
66
2b
2h
2
3
4
85
90
8
9
96
67
2c
2d
2i
2j
n.d.
10[c]
81
27
2e
2k
2l
5[b]
48
77
11
2 f
6
2g
[a] For the reaction conditions, see Table 1, entry 8. [b] With 10 mol% of the Ni catalyst at 308C for 24 h.
37% of nOctAr was obtained. [c] At a 0.1m concentration of 1a in THF for 20 h.
conditions (Table 1, entry 8), we
investigated the scope and limita-
tions of Grignard reagents (Table 2). When 2-substituted and
even more sterically congested 2,6-disubstituted aryl
Grignard reagents were employed, the coupling reaction
proceeded smoothly to give the corresponding products 3 in
excellent yields (entries 1–3). However, an ortho-methoxy
group significantly affected the reaction (entry 4). The use of
p-FC6H4MgBr (2 f) resulted in the desired product in
moderate yield (48%), accompanied by the corresponding
direct cross-coupling product, nOctAr, in 37% yield. On the
other hand, the introduction of an ortho-methyl group (2g)
increased the yield to 77% (entries 5 and 6). These results
suggest that ortho substituents sterically suppress the nucle-
ophilic attack of the Ni center towards the alkyl fluoride[8,9a]
(see below). An electron-donating methyl group at the para
position led to an increased yield, whereas electron-with-
drawing substituents somewhat reduced the yields (entries 6–
9). The 2-methyl-1-naphthyl Grignard reagent 2k gave 3ak in
81% yield (entry 10), whereas thienyl Grignard reagent 2l
resulted in a lower yield (entry 11).
Fluoro-1-undecene (1b) participated in the reaction to give
3bd in 91% yield without isomerization of the terminal
double bond. Acid-sensitive tetrahydropyranyl and tert-
butyldimethylsilyl (TBS) ethers as well as thiophene and
N-tosyl and N-Boc piperidine were all tolerated. Further-
2
2
3
À
À
À
more, C(sp ) F and C(sp ) Cl bonds as well as C(sp ) Cl
bonds in the alkyl fluorides remained intact. In all cases, the
desired product was formed exclusively, and no side products
were formed except for small amounts of the direct cross-
coupling products.
When 6-fluoro-1,1-diphenyl-1-hexene (1l) was employed
in an attempt to examine the possibility of radical intermedi-
ates in the reaction, the corresponding product 3ld was
obtained in 93% yield without any evidence for a 5-exo
radical cyclization,[16] suggesting that the alkylation process
proceeds through an ionic pathway [Eq. (1)].
To gain insight into the mechanism of the present
reaction, we conducted control experiments with NiBr2(dme),
1.1 equiv of nOctF (1a), and 2 to 4 equiv of the Grignard
reagent 2a in the presence of an excess amount of 1,3-
butadiene (Table 3). When 2 equiv of the Grignard reagent
2a were used, the NiII species should be reduced to Ni0 and
As shown in Scheme 2, alkyl fluorides with various
functional groups afforded the corresponding four-compo-
nent-coupling products 3 in good to excellent yields. 11-
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react with 1,3-butadiene to form p-complexes 5, which results
in the oxidative dimerization of 1,3-butadiene to give bis(p-
allyl)nickel intermediate A [Eq. (2)]. When the mixture was
stirred at 408C for 3 h, only 14% of 1a were consumed, and
3aa was formed in 10% yield, suggesting that p-complexes
5[17] and bis(p-allyl)nickel intermediate A are inert towards
alkyl fluorides (entry 1). When 3 equiv of 2a were used, 3aa
was formed in 75% yield, and a nearly quantitative yield of
3aa was obtained by using 4 equiv of 2a (entries 2 and 3).
These results indicate that the present reaction is catalyzed by
an anionic nickel complex B that is generated by the reaction
of bis(p-allyl)nickel intermediate A with Grignard reagents
[Eq. (2)].
To confirm the formation of nickelate intermediate B,
Ni(cod)2 was treated with 5 equiv of 1,3-butadiene in
[D8]THFat room temperature, and the mixture was examined
by NMR spectroscopy. The NMR spectrum showed signals
corresponding to Ni(cod)2 and free COD, accompanied by
new broad signals at 4.7–6.5 ppm, along with the disappear-
ance of the signals for free 1,3-butadiene.[15] The broad
resonances were assigned to p-complexes 5, which are in
rapid equilibrium with free 1,3-butadiene.[15] The addition of
2 equiv of Grignard reagent 2d to the reaction mixture led to
the generation of a new species with an aryl group and
a dimerized 1,3-butadiene moiety in a 1:1 ratio. This could be
nickelate B, which is formed via bis(p-allyl)nickel A, which in
turn is generated transiently or exists at a low concentration in
equilibrium with 5 and/or B [Eq. (2)].[15,17c,18]
Scheme 2. Nickel-catalyzed four-component couplings with various
alkyl fluorides. [a] At a 0.1m concentration of 1 for 20 h. Boc=tert-
butoxycarbonyl, TBS=tert-butyldimethylsilyl, Ts =para-toluenesulfonyl.
Nickelate 6 was isolated as an orange semisolid in 94%
yield using 2,6-dimethylphenyllithium 2d’ [Eq. (3)], and
shows resonances corresponding to 2,6-dimethylphenyl, s-
allyl, and p-allyl groups in its NMR spectra.[15] When isolated
nickelate 6 was employed as the catalyst in the reaction of
nOctF with Grignard reagent 2d, the corresponding product
3ad was obtained in 88% yield [Eq. (4)], strongly supporting
the intermediacy of B.
Table 3: Stoichiometric reactions of the NiII catalyst with 1a and 2a.
Based on these results, a plausible reaction pathway is
proposed in Scheme 3. Reduction of the NiII salt by the aryl
Grignard reagent gives a Ni0 species, which then participates
Entry
o-TolMgBr
Conv. 1a [%]
3aa [%]
1
2
3
2 equiv
3 equiv
4 equiv
14
80
99
10
75
95
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German Graduate Externship from the JSPS, and a Grant-
in-Aid for Scientific Research on Innovative Area “Molec-
ular Activation Directed toward Straightforward Synthesis”
(2204) from MEXT. T.I. thanks the UBE Foundation and the
Sumitomo Foundation.
Keywords: alkylation · dimerization ·
multicomponent reactions · nickel · regioselectivity
How to cite: Angew. Chem. Int. Ed. 2016, 55, 5550–5554
Angew. Chem. 2016, 128, 5640–5644
Scheme 3. Plausible reaction mechanism.
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insertion of 1,3-dienes but possesses enhanced nucleophilicity.
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group in B to give intermediate C by an SN2 mechanism in
a process that is probably assisted by the coordination of MgX
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p-coordination of the Ni species upon going from B to C.
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Telomerization and related transformations (Scheme 1a
and b) are useful for constructing functionalized C8 frame-
works, but often suffer from side reactions, including 1) the
direct functionalization of the 1,3-diene without dimeriza-
tion[3c,4,14] and 2) oligomerization of the 1,3-dienes,[2d,e] and
from poor product selectivities with respect to 3) the regio-
À
selectivity of C C bond formation with nucleophiles and/or
electrophiles[2a–c] and 4) the stereochemistry of the newly
[4a,c,5,6]
À
formed internal C C double bonds.
In contrast, the
present reaction resulted in perfect selectivities and appears
to proceed through a unique mechanism that involves an
anionic complex B as the active catalytic species.
In conclusion, we have disclosed herein that a nickel
complex catalyzes the dimerization and alkylarylation of 1,3-
butadiene with alkyl fluorides and aryl Grignard reagents to
give 3-alkyl-8-aryl-1,6-octadienes. The present catalytic reac-
tion tolerates a wide variety of functional groups, and
3
[11]
À
C(sp ) F bonds were cleaved efficiently and selectively.
As a catalytically active species towards alkyl fluorides,
anionic nickel complexes play an important role in the
À
À
formation of C C bonds by C F bond cleavage.
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Acknowledgements
This work was partially supported by a Grant-in-Aid for
Scientific Research (A) (25248025),
a JSPS Japanese–
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À
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Received: January 31, 2016
Published online: March 3, 2016
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