Highly efficient Pd-catalyzed cyanation of aryl chlorides and arenesulfonates with potassium ferrocyanide in aqueous media

Article abstract of DOI:10.1007/s10562-010-0385-1

A highly improved Pd-catalyzed cyanation of aryl chlorides to corresponding benzonitriles was demonstrated in aqueous media. Moreover, Pd-catalyzed cyanation of aryl tosylates and benzenesulfonates with K₄[Fe(CN) ₆] was developed under the similar conditions, which extended application scope of the cyanation. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-010-0385-1

Catal Lett (2010) 139:56–60
DOI 10.1007/s10562-010-0385-1
Highly Efficient Pd-Catalyzed Cyanation of Aryl Chlorides
and Arenesulfonates with Potassium Ferrocyanide
in Aqueous Media
Junli Zhang
Yuan Zhang
Jun Huang
•
Xiaorong Chen
Kunling Xu Yanpeng Yu
•
•
Tongjie Hu
•
•
•
Received: 21 April 2010 / Accepted: 31 May 2010 / Published online: 12 June 2010
Ó Springer Science+Business Media, LLC 2010
Abstract A highly improved Pd-catalyzed cyanation of
aryl chlorides to corresponding benzonitriles was demon-
strated in aqueous media. Moreover, Pd-catalyzed cyanation
of aryl tosylates and benzenesulfonates with K [Fe(CN) ]
[6], and acetone cyanohydrins [7] are required. Recently, an
attractive improvement was made by Beller and coworkers.
Nontoxic, inexpensive, and easily handled K [Fe(CN) ]
4
6
was, for the first time, introduced as a cyanide source to the
cyanation reaction [8–10]. Afterwards, further modifica-
tions of the protocol were reported for Pd and Cu catalyzed
cyanation of aryl halides with K [Fe(CN) ] [11–16].
4
6
was developed under the similar conditions, which extended
application scope of the cyanation.
4
6
Keywords Cyanation Á Palladium Á Aryl chlorides Á
Benzonitriles Á Potassium ferrocyanide Á Water
Pd-catalyzed cross-coupling of aryl chlorides is highly
desirable as aryl chlorides typically more inexpensive than
aryl bromides and iodides, although activation of aryl
chlorides was more difficult [17–19]. The use of aryl
arenesulfonates including aryl tosylates (ArOTs) and ben-
zenesulfonates (ArOBs) as electrophiles in cross-coupling
chemistry is favorable because they can be prepared from
readily available, inexpensive phenols [20, 21]. Further-
more, aryl arenesulfonates are easy to handle because they
are stable towards hydrolysis and are highly crystalline.
Unfortunately, their improved stability translates into sig-
nificantly reduced reactivity in transition-metal-catalyzed
cross-coupling reactions. Aside from use of aryl bromides
and iodides, Pd catalyzed cyanation of aryl chlorides with
K [Fe(CN) ] is not generally applicable because of the
1
Introduction
Benzonitriles are important building blocks of dyes, natural
products, herbicides, agrochemicals, and pharmaceuti-
cals.[1] In addition, nitriles are versatile intermediates in
synthetic organic chemistry, since they can be easily con-
verted into other functional groups, such as carboxylic
acids, amides, amines and aldehydes [2]. For these reasons,
much attention has been given to the development of
efficient and practical methods for the synthesis of nitriles.
An elegant method for the preparation of benzonitriles is
the transition-metal-mediated cyanation of aryl halides.
Typically, toxic inorganic or organic cyanide sources, such
4
6
harsh conditions used [8–10]. Therefore, the development
of an efficient Pd catalyzed cyanation of aryl chlorides with
K [Fe(CN) ] under mild conditions remains important.
as alkali cyanides [3], Zn(CN) [4], CuCN [5], TMSCN
2
4
6
Furthermore, to our knowledge, arenesulfonates as elec-
trophiles have never been applied in Pd catalyzed cyana-
tion reaction with K [Fe(CN) ] or other cyanide sources.
JJ .. ZH hu aa nn gg Á(&X.)Chen Á T. Hu Á Y. Zhang Á K. Xu Á Y. Yu Á
College of Chemistry and Chemical Engineering, State Key
Laboratory of Materials-Oriented Chemical Engineering,
Nanjing University of Technology, Nanjing 210009, China
e-mail: junhuang@njut.edu.cn
4
6
Recently, we have reported Pd-catalyzed C–O coupling
reaction of aryl chlorides and bromides with phenols [22].
And here we reported a general and efficient Pd catalyzed
cyanation of aryl chlorides in aqueous media. More-
over, Pd catalyzed cyanation of aryl arenesulfonates with
T. Hu
College of Chemistry and Chemical Engineering,
Jiangsu University, Zhenjiang, Jiangsu 212013, China
K [Fe(CN) ] towards corresponding benzonitriles was
4
6
developed firstly under similar conditions (Scheme 1).
1
23

Highly Efficient Pd-Catalyzed Cyanation of Aryl Chlorides and Arenesulfonates
57
CN
prepared aryl nitriles are commercial available and iden-
tified by comparison (GC/MS) with authentic samples
X
Pd/Ligand
K [Fe(CN) ]3H O
R
R
4
6
2
H O/1,4-dioxane
2
(purchased from Aladdin Reagent, Alfa-Aesar and Sigma–
X=Cl,OTs,OBs
Aldrich Company).
Scheme 1 Pd-catalyzed cyanation of aryl chlorides, tosylates (OTS)
and benzenesulfonates (OBS) with potassium hexacyanoferrate(II)
2.3 Typical Procedure for Pd-Catalyzed Cyanation
of Aryl Chlorides and Arenesulfonates
Xphos (Scheme 2, L2) was an excellent ligand devel-
oped by Buchwald for activation of aryl chlorides and
arenesulfonates [23]. And recently, sulfonated Xphos
An oven-dried pressure tube, which was equipped with a
magnetic stir bar, was charged with Pd(OAc)
0.0150 mmol), Ligand, (L1: 15.7 mg or L2: 14.3 mg,
0.030 mmol), K [Fe(CN) ].3H O (105.6 mg, 0.25 mmol),
base (K CO , 34.55 mg, 0.25 mmol for aryl chlorides;
(3.4 mg,
2
(
Xphos-SO Na: L1) as a water soluble ligand was also
3
synthesized and applied for Suzuki and Sonogashira cou-
pling reactions in aqueous media [24]. Reactions conducted
in aqueous media are attractive since water is nontoxic,
nonflammable, and inexpensive, and is easily separated
from organic products. The utilization of water as a solvent
in transition-metal-catalyzed coupling reactions often
greatly facilitates the workup procedure and avoids drying
solvents and starting materials. As K [Fe(CN) ] was solu-
4
6
2
2
3
138.20 mg, 1.0 mmol for aryl arenesulfonates). The tube
was evacuated and backfilled with argon (the process was
repeated a total of 3 times) and then the aryl chloride or
arenesulfonate (1.00 mmol, if liquid) and 1,4-dioxane/water
(1:1) 2.0 mL were added via syringe (aryl chlorides or
arenesulfonates that were solids at room temperature were
added with the palladium catalyst and ligand). The pressure
tube was sealed and the mixture was stirred for 10 h under
the noted temperature. After cooled to room temperature,
4
6
ble in water but insoluble in most organic solvents, we
conducted the Pd-catalyzed cyanation of aryl chlorides and
arenesulfonates with K [Fe(CN) ] in aqueous media.
4
6
1
00 lL hexadecane and 10 mL diethyl ether were added.
The organic layer was separated, dried over anhydrous
MgSO , filtered through Celite, and analyzed by GC.
2
Experimental
4
For 4-chlorobenzoic acid, the cooled reaction mixture was
carefully acidified with dilute aqueous HCl (1.0 M, 2.0 mL),
extracted with 10 mL diethyl ether. The organic phase was
added 100 lL hexadecane and then analyzed by GC.
2
.1 Reagents
All reagents were purchased from Aladdin Reagent,
Sigma–Aldrich Company and Alfa-Aesar Company with-
out further purification. XPhos (L2), SPhos (L3), L4, L5
and L6 were purchased from Beijing InnoChem Co. Ltd
3 Results and Discussion
[
25]. And XPhos-SO Na (L1) was prepared following the
3
literature method [24]. The aryl arenesulfonates were pre-
pared from their corresponding phenols with p-toluene-
sulfonyl chloride or benzenesulfonyl chloride in the
presence of triethylamine in CH Cl according to the lit-
3.1 Pd-Catalyzed Cyanation of 4-Chloroanisole
with K [Fe(CN) ]
4
6
Pd-catalyzed cyanation of 4-chloroanisole with K [Fe(CN) ]
4 6
2
2
erature method [21, 23, 26–31].
was investigated as a model reaction in aqueous media
firstly. The catalyst loading was optimized and 4-methoxy-
benzonitrile was obtained in excellent yield (96% yield)
under 120 °C in water/1,4-dioxane (1:1) (Table 1, entries
2
.2 Analytical Methods
Gas chromatography analyses were performed on a Hewlett
Packard 5890 instrument with a FID detector and Hewlett
Packard 24 m 9 0.2 mm i.d. HP-5 capillary column. All
1–4). Excess of base (1.0 equiv. of K
2 3
CO ) was not necessary
(Table 1, entry 5). K PO and KOH were also good bases for
3
4
the transformation, and similar yields were achieved
Scheme 2 Ligands used for
cyanation of 4-chloroanisole
PPh2
PCy2
i-Pr
PCy2
PCy2
OMe
t-Bu
t-Bu
with K [Fe(CN)
4
6
]
Fe
L4
P
i-Pr
i-Pr MeO
PCy2
i-Pr
PPh2
N
i-Pr
SO3Na
L1(XPhos-SO3Na)
L3(SPhos)
L5
L6
L2(XPhos)
123

5
8
J. Zhang et al.
Table 1 Pd-catalyzed cyanation of 4-chloroanisole with K
4
[Fe(CN)
6
]
Table 2, the 4-methoxybenzonitrile was obtained in 62%
and 35% yields with L3 and L6 respectively (Table 2, entry
3, 6). L4 and L5 were not suitable ligands for the
Pd-cyanation reaction (Table 2, entries 4–5).
Cl
CN
Pd catalyst
K [Fe(CN) ].3H O
4
6
2
MeO
MeO
3.2 Pd-Catalyzed Cyanation of Aryl Chlorides
Entry T ( °C) Ligand/Pd(OAc)
mol%/mol%)
2
Ligand Conv.% Yield%
with K [Fe(CN) ]
6
4
(
1
2
3
4
5
6
7
8
9
1
1
1
1
120
120
120
120
120
120
120
120
120
120
120
120
100
1.0/1.0
2.0/1.0
3.0/1.0
3.0/1.5
3.0/1.5
3.0/1.5
3.0/1.5
3.0/1.5
3.0/1.5
3.0/1.5
2.0/1.0
3.0/1.0
3.0/1.5
L1
L1
L1
L1
L1
L1
L1
L1
L1
L2
L2
L2
L2
37
91
96
99
83
97
96
14
10
99
82
90
77
20
89
94
Next, various aryl chlorides were tested with K [Fe(CN) ]
4 6
under optimized reaction conditions (Table 3). All the
cyanation reactions proceeded smoothly towards the cor-
responding benzonitriles in good to excellent yields by L2/
96
a
74
Pd(OAc)2 or L1/Pd(OAc) . The Pd-catalyzed cyanation
2
b
c
gave excellent yields (89–100%) for the aryl chlorides
insensitive to base and high temperature (Table 3, entries
1–10, 12, 15 and 16). The reactions of the activated aryl
chlorides were easier and they can be carried out at 100 °C
95
91
d
4
6
e
(Table 3, entries 6–11, 13, 14). The cyanation of 4-chlo-
0
1
2
3
98
74
90
74
robenzoilic acid and 4-chloronitrobenzene require excess
of base (1.0 equiv. K CO ) (Table 3, entries 9 and 12).
2
3
The reactions of aryl chlorides with functional groups
sensitive to base and high temperature, such as aldehydes,
ketones and nitriles afforded the corresponding benzonitr-
iles in good yields due to the mild reaction conditions
(Table 3, entry 11, 13, and 14). To the best of our
knowledge, benzonitriles with aldehyde, ketone and nitrile
groups were first time synthesized from the corresponding
aryl chlorides with K [Fe(CN) ]. The aqueous media
Reaction conditions: 4-chloroanisole, 1.0 mmol; K
0.25 equiv.; K CO , 0.25 equiv.; water/1,4-dioxane (1:1) 2.0 mL as
solvents; 10 h; conversions and yields were determined by GC using
4
[Fe(CN)
6
]Á3H
2
O,
2
3
hexadecane as the internal standard
a
K
2
CO
3
(1.00 equiv)
b
c
d
e
K
3
PO
4
was used as base (0.25 equiv.)
KOH was used as base (0.25 equiv.)
.0 mL water and 1.0 equiv TBAB as solvents
4
6
improved the reaction dramatically under mild conditions,
and extended the application scope.
2
Water/DMF (1:1) 2.0 ml as solvents
3.3 Pd-Catalyzed Cyanation of 4-Methoxyphenyl
(
Table 1, entry 6, 7). Water with 1.0 equivalent of TBAB and
Tosylate with K [Fe(CN) ]
4
6
water/DMF (1:1) were not effective solvents, and only trace
of product was obtained (Table 1, entry 8, 9). Encouraged by
these results, L2 was used for the Pd catalyzed cyanation of
Since L1 and L2 are suitable supporting ligands for Pd
catalyzed activation of aryl arenesulfonates, we tested our
system for the cyanation of aryl arenesulfonates with
4
-chloroanisole with K [Fe(CN) ] under the same condition.
4 6
We were surprised that L2 exhibited nearly the same activity
and selectivity as L1 for the transformation (Table 1, entry
Table 2 Ligand screening for Pd-catalyzed cyanation of 4-chloro-
1
0), although L2 was not water soluble ligand. Catalyst
4 6
anisole with K [Fe(CN) ]
loadings and reaction temperature were screened for L2/
Entry
Ligand (mol%)
Conv.%
Yield%
Pd(OAc) catalyst system (Table 1, entries 11–13).
2
The aqueous media played an important role for the
cyanation reaction since Pd/L2 catalyst system was not
active for the cyanation of aryl chlorides with K [Fe(CN) ]
1
2
3
4
5
6
L1
L2
L3
L4
L5
L6
98
99
68
22
12
46
96
98
62
0
4
6
in organic solvents [9, 10]. Both K [Fe(CN) ] and K CO
3
4
6
2
were completely soluble in the aqueous media, then the CN
group would be much easier to coordinated with the Pd
center, which improved the activity dramatically.
0
35
Reaction conditions: 4-chloroanisole, 1.0 mmol; K
4
[Fe(CN)
6
]Á3H
2
O,
Since L2 was also excellent ligand for Pd catalyzed
cyanation of 4-chloroanisole with K [Fe(CN) ] in aqueous
0
3
.25 equiv.; K CO , 0.25 equiv.; Pd(OAc) , 1.5 mol%; ligand,
2 3 2
4
6
.0 mol%; water/1,4-dioxane (1:1) 2.0 mL as solvents; 120 °C; 10 h;
media (water/1,4-dioxane), the other ligands (Scheme 2)
were tested for the model reaction (Table 2). As shown in
conversions and yields were determined by GC using hexadecane as
the internal standard
1
23

Highly Efficient Pd-Catalyzed Cyanation of Aryl Chlorides and Arenesulfonates
59
Table 3 Pd-catalyzed cyanation of aryl chlorides with K
4
[Fe(CN)
6
]
Table 4 Pd-catalyzed cyanation of 4-methoxyphenyl tosylate with
[Fe(CN)
K
4
6
]
Cl
CN
Pd/Ligand
OTs
K4[Fe(CN)6] 3H2O
CN
R
K4[Fe(CN)6] 3H2O
R
Pd/Ligand
H2O/1,4-dioxane
R
H2O/1,4-dioxane
MeO
Entry
R
Conv.%
Yield%
Entry
Ligand
Base/substrate
Conv.%
Yield%
1
2
3
4
5
6
7
m-CH
3
O
100
100
96
97
99
91
99
98
1
2
3
4
L1
L1
L2
L2
1/1
94
28
57
6
66
10
22
1
o-CH
p-CH
3
O
0.25/1
1/1
3
m-CH
3
99
0.25/1
o-CH
3
99
a
p-CF
3
98
95
Reaction conditions: 4-methoxyphenyl tosylate, 1.0 mmol; K
3H O, 0.25 equiv.; K CO was used as base; Pd(OAc)
ligand, 3.0 mol%; water/1,4-dioxane (1:1) 2.0 ml as solvents;
4
[Fe(CN)
1.5 mol%;
6
]Á
a
m-CF
3
61
43
2
2
3
2
ac
89
1
1
1
00
75
00
69
00
84
140 °C,10 h; conversions and yields were determined by GC using
hexadecane as the internal standard
a
8
9
o-CF
3
72
ac
99
a
p-NO
2
48
abc
95
a
1
1
0
1
m-NO
2
58
c
9
7
93
Table 5 Pd-catalyzed cyanation of aryl arenesulfonates with
K [Fe(CN) ]
a
4
6
p-CHO
82
00
53
ac
66
X
1
Pd/Ligand
CN
bc
4 6 2
K [Fe(CN) ] 3H O
1
1
1
1
1
2
3
4
5
6
p-COOH
100
100
100
100
100
100
R
H2O/1,4-dioxane
R
a
p-COCH
p-CN
3
62
X=OTs,OBs
a
69
H
98
89
d
1-Naphthyl
Entry
R
X
Conv.%
86
Yield%
65
b
Reaction conditions: aryl chlorides, 1.0 mmol; K
0
4
[Fe(CN)
6
]Á3H
2
O,
1
2
1-Naphthyl
1-Naphthyl
OTs
.25 equiv.; K CO , 0.25 equiv.; Pd(OAc) , 1.5 mol%; L2, 3.0 mol%;
2
3
2
a
8
8
77
water/1,4-dioxane (1:1) 2.0 mL as solvents; 120 °C; 10 h; conver-
sions and yields were determined by GC using hexadecane as the
internal standard
b
OBs
100
93
95
94
94
99
69
98
99
92
71
86
64
91
69
76
a
84
a
b
b
a
The reaction was conducted at 100 °C
3
4
5
6
7
8
9
1
1
1
1
1
1
2-Naphthyl
2-Naphthyl
OBs
OTs
OTs
OTs
OBs
OBs
OTs
OBs
OTs
OTs
OTs
OBs
OBs
90
b
a
1
.0 equiv. K
2
CO
3
was used as base
83
c
L1 was used as ligand (3.0 mol%)
p-CH
o-CH
p-CH
o-CH
H
3
3
3
3
O
O
O
O
66
88
59
86
66
61
60
55
46
89
50
d
1
-Naphthyl chloride as starting aryl chloride
K [Fe(CN) ]. As shown in Table 4, Pd-catalyzed cyanation
4
6
of 4-methoxyphenyl tosylate afforded 4-methoxybenzoni-
trile in 66% yield with L1 and 1.0 equiv. of K CO
0
1
2
3
4
5
H
2
3
o-CH
3
(
Table 4, entry 1). L2 was not suitable for the cyanation
of 4-methoxyphenyl tosylate even with excess of base
Table 4, entry 3, 4).
m-CH
3
p-CH
o-CH
m-CH
3
(
3
3
3
.4 Pd-Catalyzed Cyanation of Aryl Arenesulfonates
with K [Fe(CN) ]
Reaction conditions: aryl arenesulfonates, 1.0 mmol; K
4
[Fe(CN)
6
]Á
4
6
3
3
H O, 0.25 equiv.; K CO , 1.0 equiv.; Pd(OAc) , 1.5 mol%; L1,
2 2 3 2
.0 mol%; water/1,4-dioxane (1:1) 2.0 mL as solvents; 140 °C; 10 h;
Afterwards, several aryl arenesulfonates (aryl tosylates and
benzenesulfonates) were tested for the cyanation with
K [Fe(CN) ] (Table 5). It is interesting that L2 was a better
conversions and yields were determined by GC using hexadecane as
the internal standard
a
2
K CO
3
, 0.25 equiv., L2 was used as ligand (3.0 mol%)
4
6
b
ligand for cyanation of naphthyl arenesulfonates than L1.
Naphthyl chloride as starting aryl chloride
123

6
0
J. Zhang et al.
The cyanation of 1-naphthyl tosylate and benzenesulfonate
gave 1-naphthylcyanide in 77% and 84% yields with L2,
and in 65% and 76% yields with L1 (Table 5, entry 1, 2)
respectively. The cyanation of 2-naphthyl benzenesulfo-
nate and tosylate proceeded towards 2-naphthylcyanide in
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9
0% and 83% yields with L2 (Table 5, entry 3, 4). L1 and
8
L2 have different solublities in the aqueous media, which
affected the activity of the cyanation and hydrolysis of the
products (aryl cyanides) in the aqueous media.
1
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The cyanation of phenyl arenesulfonates with methoxy
and methyl groups gave moderate to good yields of the
corresponding benzonitriles (Table 5, entries 5–15) as the
hydrolysis of the benzonitriles took place under the reac-
tion temperature (140 °C). Owing to the aqueous media,
Pd-catalyzed cyanation of aryl arenesulfonates with
K [Fe(CN) ] was developed firstly. The K [Fe(CN) ] was
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4
6
4
6
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2
3
1
the cyanation of aryl arenesulfonates.
1
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aryl chlorides with K [Fe(CN) ] was developed in aqueous
4
6
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media, which was applicable for extended aryl chlorides in
excellent yields. Moreover, Pd-catalyzed cyanation of aryl
arenesulfonates (aryl tosylates and benzenesulfonates) with
K [Fe(CN) ] was developed firstly under similar reaction
(
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Acknowledgment This work was supported by the National Natural
Science of Foundation of China (grant No. 20802008) and the
foundation from State Key Laboratory of Materials-Oriented Chem-
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