Nickel-Catalyzed Decarbonylative Silylation, Borylation, and Amination of Arylamides via a Deamidative Reaction Pathway

Article abstract of DOI:10.1055/s-0036-1591495

A nickel-catalyzed decarbonylative silylation, borylation, and amination of amides has been developed. This new methodology allows the direct interconversion of amides to arylsilanes, arylboronates, and arylamines and enables a facile route for carbon-heteroatom bond formations in a straightforward and mild fashion.

Full text of DOI:10.1055/s-0036-1591495

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© Georg Thieme Verlag Stuttgart · New York
2017, 28, A–E
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S.-C. Lee et al.
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Nickel-Catalyzed Decarbonylative Silylation, Borylation, and
Amination of Arylamides via a Deamidative Reaction Pathway
Shao-Chi Leea
Lin Guoa
Huifeng Yuea
Hsuan-Hung Liaoa
Magnus Rueping*a,b
R
SiEt3
Bpin
Et3Si-Bpin
O
O
R'
N
0
0
0
0
0-
0
0
3
4-
5
8
0
5-
2
2
7
Ni Ln
B2pin2
R'
R
R
N
R
Ni
Ln
R''
a Institute of Organic Chemistry, RWTH Aachen University,
Landoltweg 1, 52074 Aachen, Germany
Magnus.Rueping@rwth-aachen.de
b King Abdullah University of Science and Technology
(KAUST), KAUST Catalysis Center (KCC), Thuwal,
23955-6900, Saudi Arabia
R''
R = aryl, heteroaryl
NH
Ph
R
NH2
magnus.rueping@kaust.edu.sa
Ph
23 examples
up to 95% yield
Published as part of the Cluster C–O Activation
Received: 11.07.2017
Accepted after revision: 25.09.2017
Published online: 23.10.2017
tive of synthesis, amides would be ideal starting materials
for their conversion into further functional groups. Howev-
er, the C–N bonds are highly stable and difficult to insert
and cleave with transition metals. Therefore, direct meth-
ods for the transfer of amide moieties into other functional
groups would be very advantageous and are highly de-
manded.12
Given our recent developments in the field of Ni cataly-
sis13 and in particular decarbonylative cross-coupling reac-
tions with esters, we decided to expand our newly devel-
oped protocols to valuable amide substrates (Scheme 1).
DOI: 10.1055/s-0036-1591495; Art ID: st-2017-s0552-c
Abstract A nickel-catalyzed decarbonylative silylation, borylation, and
amination of amides has been developed. This new methodology allows
the direct interconversion of amides to arylsilanes, arylboronates, and
arylamines and enables a facile route for carbon–heteroatom bond for-
mations in a straightforward and mild fashion.
Key words nickel catalysis, decarbonylation, amination, silylation, bo-
rylation
O
Nickel-catalyzed cross-coupling reactions have become
promising alternatives to traditional noble-metal-mediated
reactions mainly due to the low-cost of nickel catalysts and
the environmental friendly nature of coupling partners.1
Over the last ten years, nickel has been widely used for
cross-coupling reactions1,2 as well as for C–H functionaliza-
tions.3 Initially, cross-coupling reactions were used to con-
struct biaryls from halides and organometallic reagents.
However, organohalides can be toxic compounds and waste
production is observed. Yet, due to the outstanding ability
of oxidative addition of nickel,1b a wide range of reactions
can be performed with halide-free substrates by activating
stable C–X bonds, including C–S,4 C–O,5 and C–N6 bonds.
Nevertheless, the types of reactions disclosed are still limited,
and hence new reactivities and reaction types are desirable.
In recent years, various decarbonylative cross-coupling
reactions via transition-metal catalysis have been de-
scribed.7 As conventional electrophilic substrates, acyl chlo-
rides,8 acid anhydrides,9 and esters10 are normally selected
and used in decarbonylative reactions. In contrast, the am-
ide C–N bond cleavage is more challenging and requires
particular attention.11 Amides exist abundantly in nature,
e.g., in proteins and peptides and are widely used in artifi-
cial compounds like drugs and polymers. From the perspec-
Ni
X
NRR'
Ar
Ar
X = SiEt3, Bpin, NH2
Scheme 1 New Ni-catalyzed decarbonylative cross-coupling reactions
with amides
Over the past few decades, organosilicon and organobo-
ron compounds proved to provide a good platform for fur-
ther functional-group interconversion to access complex
molecular scaffolds.14,15 Furthermore, their application in
the synthesis of natural products and drug molecules is
widely acknowledged.16,17 In addition to organosilicon and
organoboron derivatives, amines are further valuable inter-
mediates in organic synthesis.18 Conventionally, organosili-
con and organoboron compounds are synthesized from
sensitive Grignard reagents or organolithium reagents.19
Recently, transition-metal-catalyzed silyl/boryl substitu-
tion of aryl halides20 and arene C–H silylation/borylation21
have been achieved. However, poor functional-group toler-
ance, the utilization of expensive substrates, or site selectiv-
ity might cause limitations of the above methods. Herein,
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

B
S.-C. Lee et al.
Cluster
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Table 1 (continued)
we report a practical method to achieve the silylation, bory-
lation, and amination of amides in an easy manner via C–N
bond cleavage.
Entry 1a–6a Ni(COD)2 (mol%) Base
Solvent (concn,
M)
Yield (%)b
Recently, we and the Shi group have described the nick-
el/copper-catalyzed decarbonylative silylation reaction of
esters by applying silylboranes as coupling partners.10o,p In
addition, the Martin group described the nickel/copper-cat-
alyzed silylation of pivalates with silylboranes as coupling
partners.22 Building up on these results, we started our in-
vestigation for the decarbonylative silylation of amides by
examining various amides 1a–6a in reaction with silylbo-
rane 7 (Table 1). Firstly, we evaluated N-Boc, N-benzyl and
N-Boc, N-phenyl imides 1a and 2a, however, only low yields
of the desired arylsilane product 8a were observed (Table 1,
entries 1 and 2). Replacing the Boc protecting group with
methyl and trifluoroacetyl groups (3a, 4a) resulted in con-
siderably lower yields (Table 1, entries 3 and 4). Next, we
turned our attention to sterically distorted amides 5a and
6a11 and were pleased to see that derivative 6a provided the
desired product in good yield (Table 1, entry 6). To further
enhance the yield, we examined different reaction condi-
tions. Use of 30 mol% of LiCl as additive under the standard
conditions did not improve the yield (Table 1, entry 7). A
1:2 ratio of Ni/monodentate ligand was less effective, and
the product was obtained in 45% yield only (Table 1, entry 8).
The effect of concentration was also evaluated, however,
no positive effect was observed upon increasing or decreas-
ing the concentration (Table 1, entries 9 and 10 vs 6). The
yield slightly decreased when changing the solvent to 1,4-
dioxane, which has a similar solubility and boiling point as
toluene (Table 1, entry 11). Next, we turned our attention to
the loading of Ni(COD)2. When the catalyst amount was re-
duced from 10 mol% to 5 mol%, a lower yield was obtained
(Table 1, entry 12). Finally, different bases were tested (Ta-
ble 1, entries 13–15), however, better yields were not
achieved. Furthermore, no product was observed in the ab-
sence of CuF2 (Table 1, entry 16).
6
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
6a
10
10
10
10
10
10
5
KF
KF
KF
KF
KF
KF
KF
CsF
toluene (0.2)
toluene (0.2)
toluene (0.2)
toluene (0.4)
toluene (0.13)
dioxane (0.2)
toluene (0.2)
toluene (0.2)
83 (79)c
62
7d
8e
9
45
68
10
34
11
12
13
14
15
16f
61
50
10
10
10
10
30
Cs2CO3 toluene (0.2)
36
K3PO4
KF
toluene (0.2)
toluene (0.2)
41
0
O
N
O
Ph
Ph
Ph
N
N
N
Ph
N
N
Me
Boc
Boc
2a
O
CF3
O
O
1a
3a
4a
5a
6a
a Reaction conditions: 1a–6a (0.20 mmol), 7 (96.6 mg, 0.40 mmol),
Ni(COD)2 (5.5 mg, 10 mol%), PnBu3 (20 μL, 40 mol%), CuF2 (6.1 mg, 30
mol%), base (3.0 equiv) in solvent (1 mL, 0.2 M) at 160 °C for 36 h; Boc =
tert-butoxycarbonyl, COD = 1,5-cyclooctadiene.
b Yields given were determined by 1H NMR analysis of the crude reaction
mixture with 1,3,5-trimethoxybenzene.
c Yield of isolated product.
d 30 mol% LiCl was used as additive.
e PnBu3 (10 μL, 20 mol%).
f Without CuF2.
To evaluate the applicability and utility of the optimized
protocol, different amide substrates were employed to de-
termine the scope of the Ni-catalyzed deamidative silyla-
tion reaction. As illustrated in Scheme 2, different amide
substrates could be converted into the corresponding aryl-
triethylsilanes 8 in moderate to high yields. For example,
naphthyl (6a) and a wide range of phenyl (6b–j) and het-
erocyclic (6k–m) derived amides could be efficiently con-
verted into the corresponding arylsilanes 8a–m by employ-
ing silylborane compound 7. The protocol shows a good
functional-group tolerance and groups such as tert-butyl
(8c), methyl ester (8d), methoxy (8e),22b,23 methyl (8h), flu-
oride (8i), benzofuran (8k), benzothiophene (8l), and quin-
oline (8m) are tolerated. The para and ortho substitutions
are also tolerated, as shown by the formation of aryl silanes
8b and 8g, respectively. Notably, a high yield (95%) was ob-
tained for the dioxole and m-methoxy derivatives 8f and 8j.
With a slightly modified protocol conversion of the am-
ides into the corresponding arylboronate products 10 was
also accomplished. Glutarimide substrates 6 can be easily
prepared in a one-step procedure from the appropriate acyl
chlorides and are therefore useful starting materials for the
synthesis of arylsilanes as well as arylboronates. For the C–B
bond-forming protocol,24 representative substrates 6a–f
were selected to undergo reaction using bispinacolato
Table 1 Optimization of Arylsilane Synthesis through Decarbonylation
of Amidesa
Ni(COD)2 (10 mol%)
O
PnBu3 (40 mol%)
CuF2 (30 mol%)
SiEt3
R'
N
+
Et3Si-Bpin
R''
base (3.0 equiv)
toluene, 160 °C, 36 h
1a–6a
7
8a
Entry 1a–6a Ni(COD)2 (mol%) Base
Solvent (concn,
M)
Yield (%)b
1
2
3
4
5
1a
2a
3a
4a
5a
10
10
10
10
10
KF
KF
KF
KF
KF
toluene (0.2)
toluene (0.2)
toluene (0.2)
toluene (0.2)
toluene (0.2)
9
34
<5
<5
40
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

C
S.-C. Lee et al.
Cluster
Synlett
Based on the results in Schemes 2 and 3, we subse-
quently turned our interest to the use of imine nucleophiles
to examine the decarbonylative amination of amides
(Scheme 4). Based on our previous protocol,10r we selected
benzophenone imine 11 as amine source with dppf as sup-
porting ligand, K3PO4 as base, LiCl as additive, Ni(COD)2 as
catalyst in 0.2 M toluene at 170 °C for 24 hours under Ar. As
shown in Scheme 4, naphthyl (12a), para-substituted bi-
phenyl (12b), quinoline (12c), and dioxole (12d) derived
amines were obtained in moderate yields.
O
N
O
O
Ni(COD)2 (10 mol%)
PnBu3 (40 mol%)
R
R
SiEt3
Et3Si-Bpin
+
CuF2 (30 mol%)
KF (3.0 equiv)
toluene, 160 °C, 36 h
6
7
8
SiEt3
SiEt3
SiEt3
8a, 79%
8b, 75%
8e, 68%
8c, 52%
8f, 95%
SiEt3
1) Ni(COD)2 (10 mol%)
dppf (10 mol%)
SiEt3
SiEt3
O
O
O
O
O
K3PO4 (3 equiv)
LiCl (2 equiv)
toluene, 170 °C, 24 h
O
N
O
NH
R
O
NH2
R
+
Ph
Ph
8d, 66%
SiEt3
2) acidic hydrolysis
6
11
12
O
SiEt3
SiEt3
NH2
R
R = Me: 8h, 61%
NH2
NH2
O
NH2
8g, 75%
8j, 95%
R = F:
8i, 44%
O
SiEt3
N
O
S
12a, 56%
12b, 50%
12c, 53%
12d, 55%
SiEt3
SiEt3
N
Scheme 4 Substrate scope for the amination reaction. Reagents and
conditions: 6 (0.20 mmol), 11 (72.5 mg, 0.40 mmol), Ni(COD)2 (5.5 mg,
10 mol%), dppf (11.0 mg, 10 mol%), K3PO4 (127.0 mg, 3.0 equiv), LiCl
(17.0 mg, 2.0 equiv), toluene (1 mL, 0.2 M), 170 °C, 24 h. Yields for iso-
lated products.
8k, 61%
8l, 57%
8m, 69%
Scheme 2 Substrate scope for the silylation of aryl amides. Reagents
and conditions: 6 (0.20 mmol), 7 (96.9 mg, 0.40 mmol), Ni(COD)2 (5.5
mg, 10 mol%), PnBu3 (20 μL, 40 mol%), CuF2 (6.1 mg, 30 mol%), KF (34.9
mg, 3.0 equiv), toluene (1 mL, 0.2 M), 160 °C, 36 h. Yields for isolated
products.
In summary, we have developed Ni-catalyzed decarbon-
ylative silylation, borylation, and amination reactions of
amides.25 Under the optimized conditions, various arylsila-
nes, arylboronates, and arylamines, which are important
building blocks in synthetic chemistry, were prepared with
good yields and high stereospecificity. The here described
cross-coupling stands out due to the ready accessibility of
substrates, mild reaction conditions, and simple reaction
handling allowing a stereoselective product formation. Fur-
ther mechanistic studies and other related transformations
are currently under way in our laboratories.
diboron as coupling nucleophile and the products 10a–f
were obtained in acceptable yields (Scheme 3).
O
O
Ni(COD)2 (10 mol%)
N
O
R
PnBu3 (40 mol%)
R
Bpin
Bpin
B2pin2
+
LiCO3 (1.5 equiv)
dioxane, 160 °C, 36 h
6
9
10
Bpin
Bpin
Bpin
Acknowledgment
L. Guo and H. Yue acknowledge the China Scholarship Council and
H.-H. Liao the DAAD for a fellowship.
10c, 50%
10b, 61%
Bpin
10a, 63%
Bpin
O
O
O
O
Supporting Information
O
10e, 54%
10f, 56%
10d, 52%
Supporting information for this article is available online at
https://doi.org/10.1055/s-0036-1591495.
S
u
p
p
o
nrtogI
f
rmoaitn
S
u
p
p
ortiInfogrmoaitn
Scheme 3 Substrate scope for the borylation of aryl amides. Reagents
and conditions: 6 (0.20 mmol), 9 (76.2 mg, 0.30 mmol), Ni(COD)2 (5.5
mg, 10 mol%), PnBu3 (20 μL, 40 mol%), Li2CO3 (22.2 mg, 1.5 equiv), 1,4-
dioxane (1 mL, 0.2 M), 160 °C, 36 h. Yields for isolated products; B2pin2
= bis(pinacolato)diboron.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

D
S.-C. Lee et al.
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© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

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cyclic carbene ligand, the N-Boc,N-Me-derived amides were
converted into the corresponding borylation products in mod-
erate to high yields. Interestingly, distorted cyclic imides were
completely unsuccessful.
(20) For a review on the silylation of organic halides, see: (a) Murata,
M.; Masuda, Y. J. Synth. Org Chem. 2010, 68, 845. For recent
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silylation and borylation of organic halides, see: (d) Murata, M.
(25) General Procedure for the Nickel-Catalyzed Decarbonylative
Silylation of Arylamides via a Deamidative Reaction Pathway
In a nitrogen-filled glovebox, a 10 mL oven-dried sealed tube
containing a stirring bar was charged with the corresponding
amide (0.20 mmol, 1.0 equiv), yellow Ni(COD)2 (5.5 mg, 10
mol%), copper fluoride(II) (6.1 mg, 30 mol%), and potassium flu-
oride (34.9 mg, 0.60 mmol, 3.0 equiv). Subsequently, freshly
distilled toluene (1.0 mL) was added, and then triethylsilylbo-
rane (96.9 mg, 0.40 mmol, 2.0 equiv) and tri-n-butylphosphine
ligand (20 μL, 40 mol%) were added, respectively, via microsy-
ringe. The tube with the mixture was sealed and removed from
the glovebox. After stirring at 160 °C for 36 h, the mixture was
allowed to cool to room temperature, diluted with EtOAc (5 mL),
and filtered through a Celite plug, eluting with additional EtOAc
(10 mL). The filtrate was concentrated and purified by column
chromatography on silica gel to yield the product.
In Science of Synthesis;
2
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Molander, G. A.; Wolfe, J. P.; Larhed, M.,
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Hartwig, J. F. Chem. Rev. 2015, 115, 8946. (b) Yang, Y.; Wang, C.
Sci. China Chem. 2015, 58, 1266. (c) Sharma, R.; Kumar, R.;
Kumar, I.; Singh, B.; Sharma, U. Synthesis 2015, 47, 2347. (d) Xu,
Z.; Huang, W.-S.; Zhang, J.; Xu, L.-W. Synthesis 2015, 47, 3645.
(e) Xu, Z.; Xu, L.-W. ChemSusChem 2015, 8, 2176. For recent
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Barnard, J. H.; Marder, T. B.; Murphy, J. M.; Hartwig, J. F. Chem.
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(22) (a) Zarate, C.; Martin, R. J. Am. Chem. Soc. 2014, 136, 2236. For
the Ni-catalyzed silylation of aryl, methyl ethers, see: (b) Zarate,
C.; Nakajima, M.; Martin, R. J. Am. Chem. Soc. 2017, 139, 1191.
For the Ni-catalyzed silylation of silyloxyarenes, see:
(c) Wiensch, E. M.; Todd, D. P.; Montgomery, J. ACS Catal. 2017,
7, 5568.
Synthesis of 8i
Following the general procedure, starting from 1-(4-fluoroben-
zoyl)piperidine-2,6-dione (47.0 mg, 0.20 mmol), the title
product was isolated as colorless oil after flash chromatography
on silica gel, 18.5 mg (44%). 1H NMR (600 MHz, CDCl3): δ = 7.48–
7.43 (m, 2 H), 7.08–7.01 (m, 2 H), 0.95 (t, J = 7.8 Hz, 9 H), 0.8–
0.76 (m, 6 H). 13C NMR (150 MHz, CDCl3): δ = 164.3, 162.7,
136.0, 135.9, 132.7, 132.7, 114.9, 114.7, 7.3, 3.4. 19F NMR (564
MHz, CDCl3): δ = –112.69; IR (ATR): ν = 3031, 2951, 2882, 2327,
2102, 1898, 1586, 1498, 1459, 1231, 1161, 1100, 1007, 818, 721
cm–1. ESI-MS: m/z (%) = 210.0 (38) [M+], 182.1 (28), 181.0 (47),
153.0 (20).
(23) We did not observe any disilylated product, which indicates
that C–OMe cleavage was not achieved under our reaction con-
ditions.
(24) Recently,
a protocol for the decarbonylative borylation of
amides was established by Shi and co-workers, see ref. 12c.
With a catalytic system consisting of nickel and an N-hetero-
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E