Nickel-Catalyzed Decarbonylative Alkynylation of Acyl Fluorides with Terminal Alkynes under Copper-Free Conditions

Article abstract of DOI:10.1055/s-0040-1705954

Nickel-catalyzed decarbonylative alkynylation of acyl fluorides with terminal silylethynes under copper-free conditions is described. This newly developed method has a wide substrate scope, affording internal silylethynes in moderate to high yields. The formation of 1,3-diynes as homocoupled products and conjugate enones as carbonyl-retentive products were effectively suppressed.

Full text of DOI:10.1055/s-0040-1705954

SYNLETT
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart
2020, 31, A–E
cluster
A
Modern Nickel-Catalyzed Reactions
Q. Chen et al.
Cluster
Synlett
Nickel-Catalyzed Decarbonylative Alkynylation of Acyl Fluorides
with Terminal Alkynes under Copper-Free Conditions
Qiang Chena
Liyan Fua
Jingwen Youa
Yasushi Nishihara*b
Ni(cod)2 (10 mol%)
O
SiR2
3
DPPP (15 mol%)
Bu3N (1.5 equiv)
H
SiR2
3
F
R1
R1
1,4-dioxane (0.2 M)
140 °C, 24 h
0
0
0
0-0
0
0
1
-5
4
0
9
-
4
2
0
7
25 examples
a Graduate School of Natural Science and Technology, Okayama
University, 3-1-1 Tsushimanaka, Kita-ku, Okayama 700-8530, Japan
b Research Institute for Interdisciplinary Science, Okayama University,
3-1-1 Tsushimanaka, Kita-ku, Okayama 700-8530, Japan
ynishiha@okayama-u.ac.jp
decarbonylative coupling
broad substrate scope
copper-free
25–90% yields
Published as part of the Cluster Modern Nickel-Catalyzed Reactions
YReMeasaeuiaCslrhoycirnhrNiesIisnhsphsihotiihant@uadrtionaekgfaoAyrauImtnhtaoe-rrud.aiscc.ijplinary Science, Okayama University, 3-1-1 Tsushimanaka, Kita-ku, Okayama 700-8530, Japan
Received: 09.09.2020
Accepted after revision: 21.09.2020
Published online: 28.10.2020
first example of a Pd/Cu-co-catalyzed alkynylation of aro-
matic esters in a decarbonylative manner.12 Meanwhile,
Rueping and co-workers developed an effective Ni/Cu co-
catalyst for the deamidative cross-coupling of silylated ter-
minal alkynes with amides under base-free conditions,
which permitted the direct conversion of amides into
alkynes.13 An example in which copper is not used as a co-
catalyst is the Pd-catalyzed decarbonylative alkynylation of
amides with terminal alkynes, a reaction that can be ap-
plied to various alkynes bearing aryl, alkyl, or silyl substitu-
ents.14
DOI: 10.1055/s-0040-1705954; Art ID: st-2020-k0490-c
Abstract Nickel-catalyzed decarbonylative alkynylation of acyl fluo-
rides with terminal silylethynes under copper-free conditions is de-
scribed. This newly developed method has a wide substrate scope, af-
fording internal silylethynes in moderate to high yields. The formation
of 1,3-diynes as homocoupled products and conjugate enones as car-
bonyl-retentive products were effectively suppressed.
Key words nickel catalysis, decarbonylation, silylalkynes, alkynylation,
acyl fluorides, sila-Sonogashira–Hagihara reaction
Acyl fluorides, which can be prepared from the corre-
sponding carboxylic acids, have been widely used in car-
bon−carbon and carbon−heteroatom bond-formation reac-
tions15 as ‘RCO’ (carbonyl-retentive)16 or ‘R’ (decarbonyla-
tive)17–21 sources, due to their unique stability and
reactivity. In the decarbonylation reaction, since the first
examples of decarbonylative transformations of acid fluo-
rides were disclosed,17 acyl fluorides have been used as
coupling partners in reduction,18 Suzuki–Miyaura-type ary-
lation,19 and direct C–H arylation reactions.20 As an exten-
sion of our research on various decarbonylative reactions of
acyl fluorides,21 we recently succeeded in developing a
Pd/Cu-co-catalyzed decarbonylative sila-S–H alkynylation
of acyl fluorides with silylated internal alkynes (Scheme
1b).22 The reaction proceeds through cleavage of the C–Si
bond, so that no silicon is present in the product. On the
other hand, because silylated terminal alkynes can be sub-
jected to further conversions, more-direct methods for re-
acting silylated terminal alkynes with acyl fluorides, espe-
cially by using cheaper catalyst systems, are still highly de-
sirable. Here, we report a nickel-catalyzed decarbonylative
alkynylation of acyl fluorides with silylated alkynes under
copper-free condition, which provides a direct method for
converting acyl fluorides into the corresponding internal si-
lylalkynes (Scheme 1c).
Over the past few decades, the Sonogashira–Hagihara
(S–H) reaction,1 the Pd/Cu-co-catalyzed coupling of termi-
nal alkynes with aryl (pseudo)halides, has resulted in sig-
nificant progress in the construction of C(sp2)–C(sp)
bonds.2 Further explorations of this reaction have involved
optimizing the reaction conditions to avoid the formation
of homocoupled byproducts through the use of copper-free
reactions3 or sila-S–H reactions,4,5 and the development of
more economical catalyst systems to replace expensive Pd
with Ni/Cu,6 Ni,7 or Cu.8 However, in most cases, palladium
is still used as the primary catalyst for the S–H reaction, and
only a few examples have been reported in which nickel or
other metals have been used as catalysts.
Finding a naturally abundant coupling partner is anoth-
er approach to optimizing the S–H reaction. Sodium sulfon-
ates,9 arylhydrazines,10 and arylsulfonyl hydrazides11 have
been employed as coupling partners instead of the com-
monly used aryl or vinyl (pseudo)halides, but there is still a
need to develop other coupling partners that can be ob-
tained from naturally abundant starting materials. Recent-
ly, esters and amides derived from carboxylic acids have
been applied as coupling partners in S-H reactions (Scheme
1a).12–14 The group of Itami and Yamaguchi developed the
© 2020. Thieme. All rights reserved. Synlett 2020, 31, A–E
Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

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Q. Chen et al.
Cluster
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Table 1 Optimization of the Reaction Conditionsa
SiR2
a) Previous work
O
3
H
SiR2
3
Ni(cod)2 (10 mol%)
Ar
Ar
R = OPh, Pd/Cu (Itami, Yamaguchi)
R = NR''2, Ni/Cu (Rueping)
O
ligand (20 mol%)
Et3N (1.5 equiv)
SiiPr3
R1
R2
Ar
F
+
H
SiiPr3
H
R2
R = NR32, Pd (Chen)
solvent (0.2 M)
140 °C, 24 h
1a
2a
3aa
b) Our previous work
O
Entry
Ligand (20 mol%) Solvent
Yieldb (%)
R2
Pd/Cu
R13Si
R2
1
DPPE
DPPP
DCYPE
DPPP
DPPP
DPPP
DPPP
DPPP
DPPP
DPPP
DPPP
DPPP
1,4-dioxane
32
64
5
+
F
Ar
Ar
2
1,4-dioxane
1,4-dioxane
toluene
3
c) This work
SiR3
O
4
51
18
68
65
73
58
13
33
0
Ni
H
SiR3
+
F
5
DMF
Ar
copper-free
Ar
6c
7c,d
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
Scheme 1 Decarbonylative alkynylation reactions of carboxylic acid
derivatives
8c,d,e
9c,f
10c,g
11c,h
12c,i
To optimize the reaction conditions, we initially con-
ducted the reaction by employing 2-naphthoyl fluoride (1a)
and ethynyl(triisopropyl)silane (2a) as coupling partners
and Ni(cod)2 as the catalyst in 1,4-dioxane (Table 1). The na-
ture of the phosphine ligands had a significant effect on the
outcome of the reaction (Table 1, entries 1–3). When 1,3-
bis(diphenylphosphino)propane (DPPP) was used as a li-
gand, the desired product was obtained in 64% GC yield,
twice that given by 1,2-bis(diphenylphosphino)ethane
(DPPE). Other bidentate or monodentate phosphine ligands
gave much lower yields [see Supporting Information (SI),
Table S2]. Subsequently, toluene, DMF, and DMI were tested
as solvents instead of 1,4-dioxane, but all of these gave poor
yields of 3aa (entries 4 and 5 and SI, Table S3). To our de-
light, reducing the amount of 2a to two equivalents afford-
ed 3aa in 68% yield (entry 6). However, when the amount of
2a was further reduced to one equivalent, only 42% of 3aa
was obtained (SI, Table S4). Furthermore, lowering the
amount of DPPP to 15 mol% gave 3aa in 65% yield (entry 7).
After screening a series of inorganic and organic bases, we
found that when Bu3N was employed instead of Et3N, the
yield of 3aa was improved to 73% (entry 8). Compound 1a
was converted to 3aa in 58% yield in the absence of the base
(entry 9). Interestingly, the addition of CuI, which is gener-
ally required for S–H reactions, dramatically reduced the
yield of the target product (entry 10). The activity of 2-
naphthoyl chloride was lower than that of 2-naphthoyl flu-
oride, yielding only 33% of 3aa (entry 11), implying that the
acyl fluoride has unique properties in the decarbonylative
alkynylation reaction. This reaction did not proceed at all in
the absence of the Ni catalyst (entry 12).
a Reaction conditions: 1a (0.2 mmol), 2a (0.6 mmol), Ni(cod)2 (0.02
mmol), ligand (0.04 mmol), Et3N (1.5 equiv), solvent (1 mL), 140 °C, 24 h.
b GC yields with dodecane as an internal standard.
c 2a (2.0 equiv).
d DPPP (15 mol%).
e Bu3N instead of Et3N.
f No base.
g With CuI (10 mol %).
h 2-Naphthoyl chloride instead of 1a.
i Without Ni(cod)2.
With the optimized reaction conditions in hand
[Ni(cod)2 (10 mol %), DPPP (15 mol %), Bu3N (1.5 equiv), 140
°C], we investigated the substrate scope of acyl fluorides
(Scheme 2). Naphthoyl fluorides 1a and 1b and benzoyl flu-
oride (1c) were smoothly converted into the corresponding
products 3aa–ca in good yields. Acyl fluorides with elec-
tron-donating methyl (1d), tert-butyl (1e), or phenyl (1f)
groups in the para-position were efficiently converted into
the corresponding alkynylsilanes 3da–fa in yields of 76–
90%. Although it is known that carbon–OMe bonds are
cleaved in the presence of nickel catalysts,23 substrate 1g
bearing a methoxy group nevertheless gave 3ga in 81%
yield. Substrate 1h bearing an acetal functional group was
also tolerated in this reaction, giving product 3ha in 90%
yield. Alkynylsilanes 3ia–ma bearing electron-withdrawing
groups in the para-position were also obtained in moderate
to good yields. Unlike the previously reported coupling of
aryl esters,12 this reaction tolerates both methyl and phenyl
esters. Moreover, acyl fluoride 1n functionalized with a flu-
oro group was also tolerated.24 Next, the steric effects of or-
tho-substituents on the acyl fluoride were evaluated. Acyl
fluoride 1o with an ortho-Me group reacted smoothly,
yielding 3oa in 81% yield. However, when the Me group was
replaced by a bulkier Ph group, the yield of 3pa decreased
© 2020. Thieme. All rights reserved. Synlett 2020, 31, A–E

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Q. Chen et al.
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to 58%, and only 53% of product 3qa was obtained from
2,4,6-trimethylbenzoyl fluoride (1q), which has a higher
steric hindrance. Heterocyclic acyl fluorides 1r–t were also
suitable substrates, giving products 3ra–ta in moderate
yields. The reaction of 1u, derived from commercially avail-
able probenecid, afforded 3ua in 78% yield. We also synthe-
sized the conjugated enyne 3va in 76% yield as a 1:1 mix-
ture of (E)- and (Z)-isomers.
yield of the desired product decreased, with 3ab, 3ac, and
3ad being obtained in yields of 25, 44, and 49%, respective-
ly. To our delight, however, when we increased the amount
of 2 to five equivalents, 3ac and 3ad were obtained in yields
of 66 and 62%, respectively. Attempts were also made to ex-
tend the range of substrate to include terminal alkynes with
aryl or alkyl groups. However, when ethynylbenzene or oct-
1-yne was used as a coupling partner, the desired product
was not obtained (see SI for details), probably due to tri-
merization or polymerization of the aromatic or aliphatic
terminal alkyne by the Ni catalyst.
Ni(cod)2 (10 mol%)
O
SiiPr3
DPPP (15 mol%)
Bu3N (1.5 equiv)
+
H
SiiPr3
F
R
R
1,4-dioxane (0.2 M)
140 °C, 24 h
Ni(cod)2 (10 mol%)
O
SiR3
1
2a
3
DPPP (15 mol%)
Bu3N (1.5 equiv)
H
SiR3
+
F
1,4-dioxane (0.2 M)
140 °C, 24 h
SiiPr3
SiiPr3
SiiPr3
SiiPr3
1a
2
3
SiMe3
SiEt3
SiMe2tBu
Me
3aa, 87%
3ea, 90%
3ba, 75%
3fa, 81%
3ca, 75%
3ga, 81%
3da, 76%
3ha, 90%
SiiPr3
Ph
SiiPr3
SiiPr3
O
SiiPr3
3ab, 25%
3ac, 44%, 66%a
3ad, 49%, 62%a
Scheme 3 Scope of silylated alkynes. Reagents and conditions: 1a (0.2
mmol), 2 (0.4 mmol), Ni(cod)2 (0.02 mmol), DPPP (0.03 mmol), Bu3N
(0.3 mmol), 1,4-dioxane (1 mL), 140 °C, 24 h. Yields of the pure isolated
products 3 are reported. a 2 (5 equiv).
tBu
MeO
O
SiiPr3
O
SiiPr3
SiiPr3
NC
SiiPr3
O
By combining the reaction mechanism proposed in pre-
vious reports2,25 with our experimental results described
above, we developed a plausible catalytic cycle for this reac-
tion, shown in Scheme 4. First, oxidative addition of the
acyl fluoride to Ni(0) proceeds through C–F bond cleavage
to give complex A. This reacts with silyl alkyne 2 under ba-
sic conditions to give complex B, as proposed for a reported
copper-free palladium-catalyzed S–H reaction.26 Subse-
quent decarbonylation gives intermediate C, and further CO
extrusion gives intermediate D, from which reductive elim-
ination yields the cross-coupled product 3 with regenera-
tion of the initial Ni(0) catalyst. Because few aryl alkynyl
ketones were generally produced, CO extrusion might occur
before reductive elimination and might constitute a rate-
limiting step. Considering the formation of enyne 4 as a by-
product, oxidative addition of silylated alkynes 2 to Ni(0)
results in the formation of complex E, which further reacts
with a second molecule of 2 to give 4 through homohy-
droalkynylation.27 Another possibility for the formation of
intermediate B without copper salt assistance is as follows.
As shown in Table 1, entry 9, the fact that the coupled prod-
ucts 3 can be obtained in the absence of a base suggests
that this reaction may proceed by ligand exchange between
complex A and complex E, resulting in the formation of
complex B along with the hydrido(fluoro)nickel complex.
Thus, the yield of the desired product 3 might be affected by
a competing oxidative addition of acyl fluoride 1 or silylated
alkyne 2 to the Ni(0) catalyst.
F3C
Ph
OMe
3ia, 79%
3ja, 66%
3ka, 90%
3la, 76%
SiiPr3
SiiPr3
Me
SiiPr3
Ph
SiiPr3
O
F
OPh
3pa, 58%a
3ma, 62%
3na, 77%
3oa, 81%
SiiPr3
SiiPr3
Me
SiiPr3
O
S
Me
Me
3qa, 53%a
3ra, 52%
3sa, 44%
SiiPr3
SiiPr3
SiiPr3
O
Me
S
O
N
N
3va, 76% (E:Z = 1:1)a
3ta, 64%
3ua, 78%
Me
Scheme 2 Scope of acyl fluorides: Reagents and conditions: 1 (0.2
mmol), 2a (0.4 mmol), Ni(cod)2 (0.02 mmol), DPPP (0.03 mmol), Bu3N
(0.3 mmol), 1,4-dioxane (1 mL), 140 °C, 24 h. Yields of the pure isolated
products 3 are reported. a 1 (0.3 mmol), 2a (0.2 mmol), 48 h.
Next, the effect of the silyl group on the alkyne 2 was
investigated (Scheme 3). Regardless of whether steric hin-
drance by the silyl group was increased or reduced, the
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2003, 5, 4191. (c) Ljungdahl, T.; Pettersson, K.; Albinsson, B.;
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O
Ar
SiR3
LnNi0
3
Ar
F
1
reductive
elimination
oxidative
addtion
2
2
Ar
(4) (a) Nishihara, Y.; Ikegashira, K.; Mori, A.; Hiyama, T. Chem. Lett.
1997, 1233. (b) Nishihara, Y.; Ikegashira, K.; Hirabayashi, K.;
Ando, J.-i. J. Org. Chem. 2000, 65, 1780. (c) Nishihara, Y.; Inoue,
E.; Okada, Y.; Takagi, K. Synlett 2008, 3041. (d) Nishihara, Y.;
Inoue, E.; Ogawa, D.; Okada, Y.; Noyori, S.; Takagi, K. Tetrahedron
Lett. 2009, 50, 4643. (e) Nishihara, Y.; Noyori, S.; Okamoto, T.;
Suetsugu, M.; Iwasaki, M. Chem. Lett. 2011, 40, 972.
(f) Nishihara, Y.; Inoue, E.; Noyori, S.; Ogawa, D.; Okada, Y.;
Iwasaki, M.; Takagi, K. Tetrahedron 2012, 68, 4869. (g) Nishihara,
Y.; Ogawa, D.; Noyori, S.; Iwasaki, M. Chem. Lett. 2012, 41, 1053.
(5) (a) Koseki, Y.; Omino, K.; Anzai, S.; Nagasaka, T. Tetrahedron Lett.
2000, 41, 2377. (b) Halbes, U.; Pale, P. Tetrahedron Lett. 2002, 43,
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Henze, D. Synth. Commun. 2012, 42, 1622. (e) Capani, J. S. Jr.;
Cochran, J. E.; Liang, J. J. Org. Chem. 2019, 84, 9378.
NiLn
O
R3Si
CO
LnNi
SiR3
Ar
D
NiLn
E
4
H
F
A
CO extrusion
R3Si
ligand
exchange
H
SiR3
2
SiR3
CO
Ar
+
base
NiLn
O
R3Si
C
Ar
HF·base
NiLn
decarbonylation
R3Si
B
Scheme 4 Proposed mechanism
(6) For selected examples, see: (a) Beletskaya, I. P.; Latyshev, G. V.;
Tsvetkov, A. V.; Lukashev, N. V. Tetrahedron Lett. 2003, 44, 5011.
(b) Wang, L.; Li, P.; Zhang, Y. Chem. Commun. 2004, 514.
(c) Vechorkin, O.; Barmaz, D.; Proust, V.; Hu, X. J. Am. Chem. Soc.
2009, 131, 12078. (d) Pérez García, P. M.; Ren, P.; Scopelliti, R.;
Hu, X. L. ACS Catal. 2015, 5, 1164.
(7) For selected examples, see: (a) Biradar, D. B.; Gau, H.-M. Chem.
Commun. 2011, 47, 10467. (b) Xu, G.; Li, X.; Sun, H. J. Organomet.
Chem. 2011, 696, 3011. (c) Moghaddam, F. M.; Tavakoli, G.;
Rezvani, H. R. Catal. Commun. 2015, 60, 82. (d) Nowrouzi, N.;
Zarei, M. Tetrahedron 2015, 71, 7847.
(8) For selected examples, see: (a) Okuro, K.; Furuune, M.; Enna, M.;
Miura, M.; Nomura, M. J. Org. Chem. 1993, 58, 4716.
(b) Gujadhur, R. K.; Bates, C. G.; Venkataraman, D. Org. Lett.
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2014, 25, 443. (f) Zhang, H.; Sun, N.; Hu, B.; Shen, Z.; Hu, X.; Jin,
L. Org. Chem. Front. 2019, 6, 1983.
In summary, we have developed a nickel-catalyzed, cop-
per-free S–H reaction that proceeds by a decarbonylative
pathway with acyl fluorides as coupling partners and
shows a broad substrate scope.28 Detailed density function-
al theory calculations are currently being performed to elu-
cidate the sequence of transmetalation and decarbonylation
in the catalytic cycle.
Acknowledgment
We thank Ms. Megumi Kosaka and Mr. Motonari Kobayashi (Depart-
ment of Instrumental Analysis, Advanced Science Research Center,
Okayama University) for performing elemental analyses and the SC-
NMR Laboratory (Okayama University) for the NMR spectral mea-
surements.
(9) Xu, Y.; Zhao, J.; Tang, X.; Wu, W.; Jiang, H. Adv. Synth. Catal.
2014, 356, 2029.
Supporting Information
(10) Zhao, Y.; Song, Q. Chem. Commun. 2015, 51, 13272.
(11) (a) Qian, L.-W.; Sun, M.; Dong, J.; Xu, Q.; Zhou, Y.; Yin, S.-F.
J. Org. Chem. 2017, 82, 6764. (b) Tian, Z.-Y.; Wang, S.-M.; Jia, S.-J.;
Song, H.-X.; Zhang, C.-P. Org. Lett. 2017, 19, 5454.
Supporting information for this article is available online at
https://doi.org/10.1055/s-0040-1705954. Su
p
p
ortingInformationS
u
p
p
ortingI
n
formatio
n
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(13) Srimontree, W.; Chatupheeraphat, A.; Liao, H.-H.; Rueping, M.
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2741.
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tions of acyl fluorides, see: (a) Blanchard, N.; Bizet, V. Angew.
Chem. Int. Ed. 2019, 58, 6814. (b) Zhao, Q.; Szostak, M. ChemSus-
Chem 2019, 12, 2983. (c) Ogiwara, Y.; Sakai, N. Angew. Chem. Int.
Ed. 2020, 59, 574. (d) Wang, Z.; Wang, X.; Nishihara, Y. Chem.
Asian J. 2020, 15, 1234.
(16) (a) Zhang, Y.; Rovis, T. J. Am. Chem. Soc. 2004, 126, 15964.
(b) Ogiwara, Y.; Maegawa, Y.; Sakino, D.; Sakai, N. Chem. Lett.
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An oven-dried 20 mL Schlenk tube containing a magnetic stir-
ring bar was charged with Ni(cod)2 (5.5 mg, 0.02 mmol, 10
mol%), DPPP (12.4 mg, 0.03 mmol, 15 mol%), 1,4-dioxane (1 mL)
under dry N2, and the mixture was stirred for 30 s at r.t. The
appropriate acyl fluoride 1 (0.2 mmol), silyl alkyne 2 (0.4
mmol), and Bu3N (0.3 mmol) were added, and the mixture was
heated at 140 °C in a heating block with stirring for 24 h, then
cooled to r.t. The reaction was quenched with sat. aq NH4Cl, and
the mixture was extracted with Et2O. The combined organic
phase was dried (MgSO4) and concentrated under vacuum, and
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(24) 4-Chlorobenzoyl fluoride gave the desired product in only 34%
yield.
Triisopropyl(2-naphthylethynyl)silane (3aa)13
Yellow oil; yield: 53.6 mg (87%); Rf = 0.54 (hexane). 1H NMR
(400 MHz, CDCl3):  = 1.19 (s, 21 H), 7.48–7.50 (m, 2 H), 7.54
(dd, J = 8.4, 2.0 Hz, 1 H), 7.76–7.82 (m, 3 H), 8.02 (s, 1 H). 13C{1H}
NMR (101 MHz, CDCl3):  = 11.5, 18.9, 91.1, 107.6, 121.0, 126.6,
126.8, 127.85, 127.87, 128.0, 129.0, 132.0, 133.0, 133.1.
© 2020. Thieme. All rights reserved. Synlett 2020, 31, A–E