Efficient synthesis of 2-arylamino substituted pyridinyl nitriles by Buchwald-Hartwig amination

Article abstract of DOI:10.1016/j.tetlet.2013.03.085

Both nitrile and arylamino groups containing pyridine derivatives are synthesized from commercially available nitrile substituted pyridyl chlorides via a palladium-BINAP catalyst (the second generation catalyst for the amination) in moderate to good yields. The mild conditions permit the presence of base sensitive functional groups. Noteably, the halogen atoms linked to the aromatic ring were maintained in the structures of the products under the amination reaction conditions.

Full text of DOI:10.1016/j.tetlet.2013.03.085

Tetrahedron Letters 54 (2013) 3233–3237
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Tetrahedron Letters
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Efficient synthesis of 2-arylamino substituted pyridinyl nitriles by
Buchwald–Hartwig amination
Shuo Guo a,b, Yaping Wang a,b, Chunxia Sun a,b, Jingya Li b, Dapeng Zou a,b, Yangjie Wu a, , Yusheng Wu b,c,
⇑
⇑
a The College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou, Henan 450052, PR China
b Tetranov Biopharm, LLC 75 Daxue Road, Zhengzhou, Henan 450052, PR China
c Tetranov International Inc., 100 Jersey Avenue, Suite A340, New Brunswick, NJ 08901, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Both nitrile and arylamino groups containing pyridine derivatives are synthesized from commercially
available nitrile substituted pyridyl chlorides via a palladium–BINAP catalyst (the second generation cat-
alyst for the amination) in moderate to good yields. The mild conditions permit the presence of base sen-
sitive functional groups. Noteably, the halogen atoms linked to the aromatic ring were maintained in the
structures of the products under the amination reaction conditions.
Received 29 December 2012
Revised 11 March 2013
Accepted 15 March 2013
Available online 26 March 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Nitrile
Aminopyridines
Buchwald–Hartwig amination
Palladium
The amination of heteroaryl halides is of central importance in
the synthesis of pharmaceutically relevant molecules.1 Compared
to other methods, the Buchwald–Hartwig amination has become
a central enabling technology in the formation of N-heteroaryl
products, and the development of the palladium-catalyzed amina-
tion of pyridinyl halides with strikingly catalyzed systems has pro-
ceeded well.2 Many chemists have developed efficient ligands and
catalyzed systems to achieve the amination of pyridinyl halides
such as Buchwald and co-workers’ biaryldialkyl-phosphanes,3 Har-
twig and co-workers’ CyPF-tBu,4 Nolan and Organ et al.’s NHC-
based palladium precatalysts and carbene ligands,5 Stradiotto
Mark’s Mor-DalPhos,6 Verkade’s TAP ligands,7 and several classical
diphosphane ligands (BIANP, XantPhos, Dppf, and so on).8
Small molecules containing nitrile and amino groups which are
easily converted into other functional groups are important com-
ponents of many pharmaceuticals.9 However, the amination of
pyridinyl halides with nitrile group seems to be not easy. Due to
that the amination condition usually needs a stronger base and a
higher temperature, the nitrile group might be easily destructed
under such conditions.10 Hence, the synthesis of nitrile substituted
aminopyridines has potential challenges by Buchwald–Hartwig
amination, especially for the commercially cheap and easily avail-
able 2-chloropyridine derivatives. Only one literature reported the
amination of 2,5-dichloroisonicotinonitrile with moderate yields.11
PCy2
PCy2
PCy2
O
N
O
L3
DavePhos
L1 SPhos
L2
XPhos
N
PPh2
PPh2
Fe
Pd
O
Cl
PPh2
PPh2
L3
L4 XantPhos
A Cyclopalladated Catylst
(rac)-BINAP
Scheme 1. The structure of different ligands and catalysts.
We were then interested in the synthesis and application of func-
tional pyridinyl derivatives.12 In this Letter, we report the synthesis
of nitrile substituted 2-arylaminopyridines from nitrile substituted
2-chloropyridines.
To evaluate the catalytic activity of the combination of different
catalysts and ligands (Scheme 1), the coupling of 2-chloroisonico-
tinonitrile 1 and aniline 2 was chosen as a model reaction in
⇑
Corresponding authors. Tel.: +1 732 253 7326; fax: +1 732 253 7327 (Y.W.).
E-mail addresses: wyj@zzu.edu.cn (Y. Wu), yusheng.wu@tetranovglobal.com
(Y. Wu), yushengwusp@yahoo.com (Y. Wu).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.03.085

3234
S. Guo et al. / Tetrahedron Letters 54 (2013) 3233–3237
Table 1
Table 3
Optimization of the Pd-catalyzed cross-coupling of 2-chloroisonicotinonitrile with
Buchwald–Hartwig amination of 2-chloroisonicotinonitriles with aminesa,b
anilinea
CN
CN
2 mol% Pd(OAc)2
3 mol% BINAP
CN
H2N
CN
H2N
Pd source
Ligand
R
R
Cs2CO3, dioxane
80 oC, 4 h
N
Cl
N
H
N
Cs2CO3, 1,4-dioxane
N
N
H
N
Cl
1
2
3
1
2
3
Entry
Amine
Product
Yield of 3b (%)
Entry
Pd source
Ligand
T (°C)
GC yield of 3b (%)
O
O
1
2
3
4
5
6
7
8
9
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
A
PdCl2
Pd2(dba)3
ꢀ
( )BINAP
L1
L2
L3
80
80
80
80
80
80
80
80
120
93
20
30
10
Trace
Trace
60
90
0
H
N
H2N
NC
1
2
3
4
5
90
N
N
3a
2a
L4
ꢀ
NO2
H
N
NC
( )BINAP
( )BINAP
ꢀ
90
80
60
86
H2N
H2N
NO2
2b
3b
a
Reaction conditions: 2-chloroisonicotinonitrile (1.0 mmol), aniline (2.0 mmol),
Pd (2 mol %), ligand (3 mol %), Cs2CO3 (1.4 mmol), 1,4-dioxane (2 mL), 4 h, Ar
atmosphere.
NO2
H
N
NC
NC
b
Detected by GC.
N
N
NO2
2c
3c
CN
H
N
dioxane at 80 °C in the presence of Cs2CO3 as base (as shown in Ta-
ble 1). The monophosphine ligands L1, L2, and L3 (6 mol %) were
found much less active, with only 20%, 30%, and 10% yields ob-
tained, respectively (Table 1, entries 2–4). The diphosphane ligand,
2,20-bis(diphenylphosphino)-1,10-binaphthyl ( )-BINAP gave 3 in
93% yield (Table 1, entry 1). When the other diphosphane ligand
(Xantphos L4) was used, lower yield was obtained (Table 1, entry
5). Three sources of palladium [Pd(OAc)2, PdCl2 (4 mol %), and
Pd2(dba)3] were examined and all afforded the amination product
in good yields (93%, 60%, and 90%, respectively) (Table 1, entries 1,
7, and 8). Thus commercially cheaper Pd(OAc)2 was then chosen as
palladium source. In the absence of Pd source, no cross-coupling
products were obtained (Table 1, entry 9), which proved the mech-
anism of the reaction was not traditional SNAr approaches. It was
noticed that employing a lower catalyst loading (1 mol %) resulted
in a noticeable decrease in coupling efficiency. Additionally, our
laboratory once reported the amination of aryl chlorides in water
H2N
H2N
CN
2d
3d
CH3
NC
NC
NH
N
CH3
2e
3e
H
N
CH3
H2N
CH3
N
6
81
2f
3f
NH
OMe
NC
NC
NC
N
7
8
71
70
NH2
H2N
OMe
3g
2g
Cl
Cl
H
N
catalyzed by cyclopalladated ferrocenylimine complex
A
(Scheme 1).13 At the present condition, the catalyst A was found
N
Cl
Cl
less active (Table 1, entry 6).
2h
3h
H
N
Table 2
9
87
75
H2N
N
Screening of bases and solvents for Buchwald–Hartwig amination of 2-chloroisonic-
2i
otinonitrile with anilinea
3i
H
CN
CN
NC
NC
N
F
H2N
Pd(OAc)2, BINAP
10
H2N
H2N
F
N
N
2j
Base, Solvent
3j
N
N
H
N
Cl
H
N
Br
1
2
3
40 (75)c
Br
11
12
13
Entry
Base
Solvent
Yield of 3b (%)
2k
3k
1
2
3
4
5
6
7
8
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
NaO-t-Bu
K2CO3
1,4-Dioxane
DME
Toluene
t-BuOH
DMSO
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
93
85
60
6
Trace
0
Br
H
N
NC
NC
80c
H2N
N
N
Br
2l
3l
Br
H
30
80
N
K3PO4
83c
H2N
a
Reaction conditions: 2-chloroisonicotinonitrile (1.0 mmol), aniline (2.0 mmol),
Pd (OAc)2 (2 mol %), BINAP (3 mol %), base (1.4 mmol), solvent (2 mL), 80 °C, 4 h, Ar
Br
2m
3m
atmosphere.
b
Detected by GC.

S. Guo et al. / Tetrahedron Letters 54 (2013) 3233–3237
3235
2 mol % Pd(OAc)2, and 3 mol % BINAP in 1,4-dioxane in the pres-
ence of 1.4 equiv Cs2CO3 at 80 °C under Ar atmosphere. Though
the second generation catalyst for the amination (Pd–BINAP com-
plex) was discovered long ago,14 it still has the specific and splen-
did value.15
Table 3 (continued)
Entry
Amine
Product
Yield of 3b (%)
H
N
With the optimized condition, the couplings of 2-chloroisonico-
tinonitrile 1 with various anilines 2a–2o were investigated. The re-
sults were listed in Table 3. The amination proceeded smoothly
with high yields with electron-withdrawing substituted anilines
(Table 3, entries 1–3). To further reveal the compatibility of the
condition, 4-aminobenzonitrile 2d was chosen and tested (Table 3,
entry 4) which was found that the nitrile group was also tolerated.
The introduction of functional groups such as a methoxyl, methyl
group at ortho-, meta-, or para-substituted anilines had not much
effect on the yields of the desired amines (3e–3g). We also ob-
served that the fluoro and chloro groups did not participate in
the coupling reaction when it is substituted in the anilines (Table 3,
entries 8–10). The bromo-groups in the substituted anilines were
also intact as the examples of Table 3, entries 11 and 12, although
the yields were low. It was found that DMSO was more effective
than 1,4-dioxane in the coupling of the bromo-substituted anilines
with 2-chloroisonicotinonitrile (Table 3, entry 13). Unfortunately,
electron-deficient oxazol-2-amine (Table 3, entry 15) was discov-
ered to be the uniquely challenging coupling partner for which
only trace amount of the desired product was detected by GC–
MS after extended reaction times and changed with various bases.
The coupling of other nitrile substituted 2-chloropyridines and
4-bromoaniline was then studied under the optimized condition.
The nitrile substituted 2-chloropyridines were found to have sim-
ilar reactivity to substrate 1 and were effective coupling partners
with the bromo-substituted anilines (Table 4). As the result, 2-
chloronicotinonitrile 4a, 6-chloro-4-methoxynicotinonitrile 4b,
and 6-chloropicolinonitrile 4c all produced the desired products
5a–5c in excellent yields (Table 4, entries 1–3).
14
85
NC
NC
N
2n
N
N
3n
N
O
H
NH2
2o
N
O
15
Trace
N
3o
a
Reaction conditions: 2-chloroisonicotinonitrile (1.0 mmol), amine (2.0 mmol),
Pd(OAc)2 (2 mol %), BINAP (3 mol %), Cs2CO3 (1.4 mmol), 1,4-dioxane (2 mL), 80 °C,
4 h , Ar atmosphere.
b
Isolated yields; average of 2 runs.
Solvent: DMSO replaced for 1, 4-dioxane.
c
To study the effect of solvents and bases on the Buchwald–Har-
twig amination reaction, the coupling of 2-chloroisonicotinonitrile
1 and aniline 2 were chosen as the model reaction by fixing 2 mol %
Pd(OAc)2 and 3 mol % BINAP (Table 2). Several solvents such as
DMF, 1,4-dioxane, t-BuOH, and 1,2-dimethoxyethane (DME) were
examined in the reaction, the best result (93%) was obtained when
1,4-dioxane was used as solvent (Table 2, entry 1). In the case of t-
BuOH, as low as 6% yield was observed (Table 2, entry 4). After
screening several bases, Cs2CO3 was found to be the superior one
(Table 2, entry 1). It was also discovered that only 1.4 equiv of base
was required to obtain the desired compound in good yield. A sim-
ilar result was observed when K3PO4 was used as base (Table 2, en-
try 8). Whereas, NaO-tBu was found to be completely unsuitable, it
led to a trace product (Table 2, entry 6). The reason is that the ni-
trile group was easily destroyed by the stronger base as detected
by LC–MS.
Subsequently, the cross-coupling of benzophenone imine 2p
with various substituted pyridinyl chlorides was investigated.
The results are summarized in Table 5. Benzophenone imine is
As the result, the optimized reaction condition is 1.0 equiv of
the nitrile substituted pyridinyl chlorides, 2.0 equiv amines,
Table 4
Cross-coupling reactions of pyridyl chlorides and aminesa,b
2mol% Pd(OAc)2
3 mol% BINAP
Br
Br
H2N
R
R
Cs2CO3, DMSO
80 oC, 4 h
N
Product
N
N
H
5
N
Cl
Br
4
2
Entry
1
2-Chloropyidines
Amine
Yield of 5 (%)
CN
H2N
CN
83
N
Cl
Br
Br
N
H
2m
2m
2m
4a
5a
H2N
H2N
O
N
O
Br
Br
NC
NC
2
3
88
80
N
Cl
Cl
N
H
4b
5b
NC
N
NC
N
N
H
5c
Br
4c
a
Reaction conditions: pyridyl chlorides (1.0 mmol), amine (2.0 mmol), Pd(OAc)2 (2 mol %), BINAP (3 mol %), Cs2CO3 (1.4 mmol), 1,4-dioxane (2 mL), 80 °C, 4 h , Ar
atmosphere.
b
Isolated yields; average of 2 runs.

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S. Guo et al. / Tetrahedron Letters 54 (2013) 3233–3237
Table 5
Cross-coupling reactions of pyridyl chlorides with benzophenone iminea,b,c
2 mol% Pd(OAc)2
3 mol% BINAP
NH
aqueous HCl
R
R
N
NH2
NH2
Cs2CO3, dioxane
80 oC, 4 h
N
Cl
5
4
2p
Entry
1
2-Chloropyidines
Amine
Product
Yield of 5 (%)
CN
NH
NC
N
72
N
N
Cl
5e
1
2p
NH
CN
CN
2
3
70
85
Cl
N
NH2
4f
5f
2p
NH
O
O
NC
NC
N
Cl
Cl
N
5g
NH2
NH2
2p
4g
NH
NC
N
NC
N
4
80
4h
5h
2p
a
Reaction conditions: pyridyl chlorides (1.0 mmol), amine (2.0 mmol), Pd(OAc)2 (2 mol %), BINAP (3 mol %), Cs2CO3 (1.4 mmol), 1,4-dioxane (2 mL), 80 °C, 4 h , Ar
atmosphere.
b
Isolated as the free amine after hydrolysis of imine with aqueous HCl.
Isolated yields; average of 2 runs.
c
an effective ammonia equivalent16 and the initially formed cou-
pling product can be easily converted into the corresponding free
amine after treating with aqueous HCl or NH2OH–HCl. The cou-
pling of the nitrile substituted pyridinyl chlorides with benzophe-
none imine produced the desired products in good yields after the
deprotection of benzophenone by aqueous HCl Table 5. The nitrile
groups of these substrates were all tolerated with this reaction
condition.
In conclusion, we have identified reaction conditions for the
efficient Pd-catalyzed C–N cross coupling of the nitrile substituted
pyridyl chlorides with a range of arylamines. A variety of function-
alized pyridinyl derivatives could be easily obtained in moderate to
good yields under the optimized conditions. The nitriles at differ-
ent positions of pyridinyl skeletons and halides at the anilines
are all compatible. This method is very useful for the quick synthe-
sis of various amino-substituted pyridinyl nitriles which are a ser-
ies of important pharmaceutical intermediates.
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Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2013.
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