Cyanoaroylation of imines bearing a thiazole ring using potassium hexacyanoferrate(II) as an eco-friendly cyanide source

Article abstract of DOI:10.3184/174751912X13518642070088

The efficient and environmentally friendly cyanoaroylation of imines bearing a thiazole ring via a one-pot three-component condensation of N-arylidenethiazol-2-amines, aroyl chlorides and potassium hexacyanoferrate(II) is described. This protocol has the advantages of using an eco-friendly cyanide source, a simple work-up procedure and affords high yields of products.

Full text of DOI:10.3184/174751912X13518642070088

JOURNAL OF CHEMICAL RESEARCH 2012
RESEARCH PAPER 709
DECEMBER, 709–711
Cyanoaroylation of imines bearing a thiazole ring using potassium
hexacyanoferrate(II) as an eco-friendly cyanide source
Zheng Li*, Pengxian Niu, Rongzhi Li, Yupeng Zhang, Ben Ma and Jingya Yang
College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, P. R. China
The efficient and environmentally friendly cyanoaroylation of imines bearing a thiazole ring via a one-pot three-com-
ponent condensation of N-arylidenethiazol-2-amines, aroyl chlorides and potassium hexacyanoferrate(II) is described.
This protocol has the advantages of using an eco-friendly cyanide source, a simple work-up procedure and affords
high yields of products.
Keywords: green chemistry, N-aroylaminonitrile, multicomponent reaction, potassium hexacyanoferrate(II)
α-Aminonitriles are important intermediates for the synthesis
of a wide variety of amino acids, amides, diamines, and
nitrogen-containing heterocycles.1–5 Therefore, they have con-
siderable applications in the organic chemical industry which
include, medicines, pesticides, dyestuffs, pigments, liquid
crystals and polymer materials. The most general synthetic
method for α-aminonitriles is the cyanation of imines via
the Strecker reaction. At present, many reagents are employed
for the cyanation of imines and include HCN,6,7 KCN,8
TMSCN,9–12 (EtO)2P(O)CN,13 Et2AlCN,14 Bu3SnCN,15,16
MeCOCN,17 acetone cyanohydrin,18 and ethyl cyanofor-
mate.19,20 However, these cyanating agents are strongly toxic
chemicals which are unsafe and environmentally unfriendly.
Potassium hexacyanoferrate(II), K4[Fe(CN)6], is non-toxic
and is even used in the food industry for metal precipitation. In
addition, it has been described as an anti-agglutinating auxil-
iary for table salt (NaCl). K4[Fe(CN)6] is a by-product from the
coal chemical industry and commercially available on a ton
scale, and is even cheaper than KCN. Recently, K4[Fe(CN)6]
has been used as a cyanide source for some substitution reac-
tions to synthesise benzonitriles,21–38 aroyl cyanides,39 benzyl
cyanides,40–41 and cinnamonitriles.42 Our current research inter-
ests have focused on the cyanation of unsaturated compounds
including C=O, C=N and/or C=C functions by nucleophilic
addition reactions using K4[Fe(CN)6] as an eco-friendly cya-
nide source.43–47 As an extension of this research we now report
the cyanoaroylation of N-arylidenethiazol-2-amines via a
one-pot three-component procedure using K4[Fe(CN)6] as a
nucleophilic reagent.
= R2 = H). It was found that the catalyst played a crucial role in
the one-pot three-component reaction. No cyanobenzoylation
products were observed in the absence of a catalyst. Some
bases such as pyridine, hydroxylamine, sodium hydroxide,
piperazine hexahydrate, 4-dimethylaminopyridine (DMAP),
and 1,4-diazabicyclo[2.2.2]octane (DABCO) were employed
but in each case a very low yield of product was obtained.
However, it was found that the reaction gave the desired
product in high yield when triethylamine was employed as a
catalyst.
Solvents also had a dramatic effect on the one-pot three-
component reaction of N-benzylidenethiazol-2-amine, benzoyl
chloride and K4[Fe(CN)6] under triethylamine catalysis. It was
found that some solvents such as Et2O, THF and PhMe sup-
pressed the reaction. However, when n-hexane, MeOH, EtOH
and CH2Cl2 were employed the desired product was obtained
in moderate to high yield. In particular the reaction in CH2Cl2
afforded the product in highest yield (Table 1).
In the light of these findings, a variety of substituted aroyl
chlorides and N-arylidenethiazol-2-amines were examined
for the cyanoaroylation reactions using K4[Fe(CN)6] under tri-
ethylamine catalysis (Scheme 1 and Table 2). Aroyl chlorides
and N-arylidenethiazol-2-amines bearing electron-donating
or electron-withdrawing groups readily participated in the
reactions to afford the desired products in high yield. The
substituents on the aryl rings have no obvious effect on the
yields of products.
A plausible mechanism for the cyanoaroylation reaction is
shown in Scheme 2. Thus K4[Fe(CN)6] first reacts with the
aroyl chlorides to form an aroyl cyanide, which then combines
with triethylamine to give intermediate A. The latter reacts
further with N-arylidenethiazol-2-amines to generate interme-
diate B which finally loses triethylamine to yield the cyanoaro-
ylation products.
Results and discussion
In our previous work48 to investigate one-pot three-component
reactions of carbonyl compounds, amines, and potassium
hexacyanoferrate(II), in the presence of benzoyl chloride as a
promoter, the imine produced in situ afforded hydrocyanation
products. As an extension of this work to investigate the direct
cyanation of imines bearing a thiazole ring under the similar
conditions, quite different cyanoaroylation products were
isolated. Therefore, in order to confirm these observations
the cyanation of imines, containing a thiazole moiety, with
K4[Fe(CN)6] was studied in more detail.
In summary, an efficient and environmentally friendly
method for the cyanoaroylation of imines bearing a thiazole
ring through the one-pot three-component condensation of
N-arylidenethiazol-2-amines, K4[Fe(CN)6] and aroyl chlorides
using triethylamine as a catalyst in CH2Cl2 has developed. The
significant features of this protocol are the use of non-toxic,
inexpensive K4[Fe(CN)6] as a cyanide source to replace the
traditional strongly toxic and volatile cyanating agents. The
simplicity of reaction and work-up procedure, the high yield,
and avoiding the use of heavy metal catalysts are noteworthy.
The reactions were first conducted using N-benzylidenethi-
azol-2-amine and benzoyl chloride as substrates (Scheme 1, R1
Scheme 1 Cyanoaroylation of imines bearing thiazole ring.
* Correspondent. E-mail: lizheng@nwnu.edu.cn

710 JOURNAL OF CHEMICAL RESEARCH 2012
Table1 Theeffectofsolventsontheyieldofcyanobenzoylation
Cyanoaroylation of imines bearing a thiazole ring using K4[Fe(CN)6]
as a cyanide source; general procedure
producta
A mixture of K4[Fe(CN)6] (0.4 mmol) and aroyl chloride (2 mmol)
was heated at 160 °C for 4 h. Then the reaction system was cooled to
room temperature and triethylamine (0.2 mmol) and the N-arylidene-
thiazol-2-amine (2 mmol) in CH2Cl2 (5 mL) were added. The resulting
mixture was stirred at room temperature for 4 h. After completion of
the reaction (TLC), the mixture was filtered to remove the solids, and
the filtrate was concentrated and isolated by column chromatography
using ethyl acetate and petroleum ether (b.p. 60–90 °C) (1:10) as
eluent to give pure products. Analytical data for the products (Table 2)
are given below.
N-[Cyano(phenyl)methyl]-N-(thiazol-2-yl)benzamide (entry 1):
White solid; m.p. 133–135 °C; IR (KBr, νmax/cm−1): 2244 (CN), 1670
(C=O); 1H NMR (CDCl3, 400 MHz): δ 7.48–6.99 (m, 12H, ArH and
ThH), 6.98 (s, 1H, CH); 13C NMR (CDCl3, 100 MHz): 169.6, 159.0,
139.1, 133.1, 131.7, 131.6, 129.3, 128.9, 128.7, 128.2, 127.3, 118.9,
115.9, 52.6. Anal. Calcd for C18H13N3OS: C, 67.69; H, 4.10; N, 13.16.
Found: C, 67.55; H, 4.09; N, 13.11%.
Entry
Solvent
Reaction time/h
Yield/%b
1
2
3
4
5
6
7
Et2O
THF
8
8
8
4
4
4
4
0
0
0
10
52
63
88
PhMe
n-hexane
MeOH
EtOH
CH2Cl2
a Reaction conditions: N-benzylidenethiazol-2-amine (2 mmol),
benzoyl chloride (2 mmol), K4[Fe(CN)6] (0.4 mmol) and triethyl-
amine (0.2 mmol) in 5 mL of solvent for 8 h.
b Isolated yield.
Table 2 Synthesis of N-aroylaminonitriles using K4[Fe(CN)6]
as a cyanide sourcea
N-[Cyano(4-tolyl)methyl]-N-(thiazol-2-yl)benzamide (entry 2):
White solid; m.p. 96–98 °C; IR (KBr, νmax/cm−1): 2247 (CN), 1671
Entry
R1
R2
Yield/%b
M.p./oC
1
(C=O); H NMR (CDCl3, 400 MHz): δ 7.46–6.97 (m, 11H, ArH
1
2
H
4-CH3
3,4-(CH3)2
4-Cl
H
88
75
81
70
78
82
88
79
84
89
90
79
84
89
133–135
96–98
94–96
and ThH), 6.94 (s, 1H, CH), 2.25 (s, 3H, CH3); 13C NMR (CDCl3,
100 MHz): 169.6, 159.0, 139.3, 139.2, 133.2, 131.6, 129.6, 128.6,
128.2, 127.3, 119.0, 116.0, 52.3, 21.1. Anal. Calcd for C19H15N3OS: C,
68.45; H, 4.53; N, 12.60. Found: C, 68.31; H, 4.55; N, 12.56%.
N-[Cyano(3,4-dimethylphenyl)methyl]-N-(thiazol-2-yl)benzamide
(entry 3): White solid; m.p. 94–96 °C; IR (KBr, νmax/cm−1): 2249 (CN),
H
3
H
H
4
113–115
112–114
135–137
103–105
96–98
5
H
4-CH3
4-CH3
4-CH3
3-CH3
3-CH3
3-CH3
4-F
4-Cl
4-Cl
4-Cl
6
4-CH3
3,4-(CH3)2
H
1
7
1671 (C=O); H NMR (CDCl3, 400 MHz): δ 7.46–6.98 (m, 10H,
ArH and ThH), 6.92 (s, 1H, CH), 2.15 (s, 6H, CH3); 13C NMR (CDCl3,
100 MHz): 169.6, 159.1, 139.1, 138.0, 137.4, 133.3, 131.5, 130.1,
128.9, 128.6, 128.4, 128.2, 124.6, 118.9, 116.1, 52.3, 19.7, 19.5. Anal.
Calcd for C20H17N3OS: C, 69.14; H, 4.93; N, 12.09. Found: C, 69.23;
H, 4.95; N, 12.12%.
8
9
4-CH3
3,4-(CH3)2
3,4-(CH3)2
H
4-CH3
3,4-(CH3)2
74–76
10
11
12
13
14
103–105
113–115
125–126
152–154
146–148
N-[Cyano(4-chlorophenyl)methyl]-N-(thiazol-2-yl)benzamide
(entry 4): White solid; m.p. 113–115 °C; IR (KBr, νmax/cm−1): 2245
1
a Reaction condition: N-arylidenethiazol-2-amine (2 mmol),
aroyl chloride (2 mmol), K4[Fe(CN)6] (0.4 mmol) and triethylamine
(0.2 mmol) in 5 mL of CH2Cl2 for 8 h.
(CN), 1666 (C=O); H NMR (CDCl3, 400 MHz): δ 7.54–7.06 (m,
11H, ArH and ThH), 6.99 (s, 1H, CH); 13C NMR (CDCl3, 100 MHz):
169.5, 158.9, 139.2, 135.4, 132.8, 131.8, 130.3, 129.1, 128.8, 128.7,
128.2, 119.1, 115.5, 52.0. Anal. Calcd for C18H12ClN3OS: C, 61.10; H,
3.42; N, 11.88. Found: C, 61.18; H, 3.43; N, 11.92%.
b Isolated yield.
N-[Cyano(phenyl)methyl]-N-(thiazol-2-yl)-4-methylbenzamide
(entry 5): White solid; m.p. 112–114 °C; IR (KBr, νmax/cm−1): 2246
Experimental
1
(CN), 1667 (C=O); H NMR (CDCl3, 400 MHz): δ 7.50–7.04 (m,
11H, PhH and ThH), 7.03 (s, 1H, CH), 2.35 (s, 3H, CH3); 13C NMR
(CDCl3, 100 MHz): 169.7, 159.2, 142.4, 139.0, 131.7, 130.1, 129.3,
129.2, 128.9, 128.4, 127.2, 118.7, 115.9, 52.6, 21.5. Anal. Calcd for
C19H15N3OS: C, 68.45; H, 4.53; N, 12.60. Found: C, 68.31; H, 4.54; N,
12.64%.
IR spectra were recorded using KBr pellets on an Alpha Centauri
FTIR spectrophotometer (Shimadzu, Japan). H NMR and 13C NMR
1
spectra were recorded with a Mercury-400BB instrument (Varian,
USA) using CDCl3 as solvent and Me4Si as internal standard. Melting
points were observed using an electrothermal melting point apparatus.
Potassium hexacyanoferrate(II) was dried at 80 °C under vacuum for
24 h and finely powdered prior to use.
N-[Cyano(4-tolyl)methyl]-N-(thiazol-2-yl)-4-methylbenzamide
(entry 6): White solid; m.p. 135–137 °C; IR (KBr, νmax/cm−1): 2245
Scheme 2 The proposed mechanism for the cyanoaroylation of imines bearing a thiazole ring using K4[Fe(CN)6] as a cyanide
source.

JOURNAL OF CHEMICAL RESEARCH 2012 711
1
(CN), 1674 (C=O); H NMR (CDCl3, 400 MHz): δ 7.50–7.03 (m,
The authors thank the National Natural Science Foundation of
China (21162024) and Provincial Natural Science Foundation
of Gansu (1107RJZA189) for financial support of this work.
10H, PhH and ThH), 7.00 (s, 1H, CH), 2.35 (s, 3H, CH3), 2.32 (s, 3H,
CH3); 13C NMR (CDCl3, 100 MHz): 169.7, 159.2, 142.3, 139.2, 139.1,
130.2, 129.5, 129.3, 128.7, 128.4, 127.2, 118.7, 116.1, 52.4, 21.5,
21.1. Anal. Calcd for C20H17N3OS: C, 69.14; H, 4.93; N, 12.09. Found:
C, 69.01; H, 4.91; N, 12.05%.
Received 12 September 2012; accepted 14 October 2012
Paper 1201510 doi: 10.3184/174751912X13518642070088
Published online: 5 December 2012
N-[Cyano(3,4-dimethyl)methyl]-N-(thiazol-2-yl)-4-methylbenza-
mide (entry 7): White solid; m.p. 103–105 °C; IR (KBr, νmax/cm−1):
1
2245 (CN), 1670 (C=O); H NMR (CDCl3, 400 MHz): δ 7.51–7.04
(m, 9H, PhH and ThH), 6.98 (s, 1H, CH), 2.35 (s, 3H, CH3), 2.22 (s,
6H, CH3); 13C NMR (CDCl3, 100 MHz): 169.7, 159.3, 142.3, 139.1,
137.9, 137.3, 130.3, 130.0, 129.3, 129.0, 128.4, 128.3, 124.6, 118.7,
116.2, 52.4, 21.5, 19.7, 19.5. Anal. Calcd for C21H19N3OS: C, 69.78;
H, 5.30; N, 11.63. Found: C, 69.89; H, 5.31; N, 11.68%.
N-[Cyano(phenyl)methyl]-N-(thiazol-2-yl)-3-methylbenzamide
(entry 8): White solid; m.p. 96–98 °C; IR (KBr, νmax/cm−1): 2250 (CN),
1671 (C=O); 1H NMR (CDCl3, 400 MHz): δ 7.42–6.97 (m, 11H, PhH
and ThH) 6.96 (s, 1H, CH), 2.25 (s, 3H, CH3); 13C NMR (CDCl3,
100 MHz): 169.8, 158.9, 138.9, 138.8, 133.0, 132.5, 131.7, 129.2,
128.9, 128.7, 128.5, 127.2, 125.1, 118.5, 115.9, 52.6, 21.2. Anal.
Calcd for C19H15N3OS: C, 68.45; H, 4.53; N, 12.60. Found: C, 68.49;
H, 4.52; N, 12.57%.
N-[Cyano(4-tolyl)methyl]-N-(thiazol-2-yl)-3-methylbenzamide
(entry 9): White solid; m.p. 74–76 °C; IR (KBr, νmax/cm−1): 2249 (CN),
1671 (C=O); 1H NMR (CDCl3, 400 MHz): δ 7.42–6.96 (m, 10H, PhH
and ThH), 6.93 (s, 1H, CH), 2.24 (s, 6H, CH3); 13C NMR (CDCl3, 100
MHz): 169.8, 158.9, 139.2, 138.9, 138.7, 133.1, 132.4, 129.5, 128.7,
128.6, 128.4, 127.1, 125.0, 118.6, 116.0, 52.3, 21.2, 21.1. Anal. Calcd
for C20H17N3OS: C, 69.14; H, 4.93; N, 12.09. Found: C, 69.22; H,
4.92; N, 12.12%.
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N-[Cyano(3,4-dimethylphenyl)methyl]-N-(thiazol-2-yl)-3-methyl-
benzamide (entry 10): White solid; m.p. 103–105 °C; IR (KBr,
1
νmax/cm−1): 2249 (CN), 1672 (C=O); H NMR (CDCl3, 400 MHz): δ
7.42–6.96 (m, 9H, PhH and ThH), 6.92 (s, 1H, CH), 2.23 (s, 3H, CH3),
2.14 (s, 6H, CH3); 13C NMR (CDCl3, 100 MHz): 169.8, 159.3, 138.9,
138.6, 137.8, 137.3, 133.1, 132.3, 130.0, 128.9, 128.7, 128.4, 128.3,
125.0, 124.5, 118.5, 116.1, 52.3, 21.2, 19.7, 19.4. Anal. Calcd for
C21H19N3OS: C, 69.78; H, 5.30; N, 11.63. Found: C, 69.69; H, 5.32; N,
11.58%.
N-[Cyano(3,4-dimethylphenyl)methyl]-N-(thiazol-2-yl)-4-fluoro-
benzamide (entry 11): White solid; m.p. 113–115 °C; IR (KBr,
1
νmax/cm−1): 2249 (CN), 1674 (C=O); H NMR (CDCl3, 400 MHz):
δ 7.53–7.00 (m, 9H, PhH and ThH), 6.97 (s, 1H, CH), 2.23 (s, 6H,
CH3); 13C NMR (CDCl3, 100 MHz): 168.6, 165.6, 163.1, 159.4, 139.5,
138.1, 137.4, 130.9, 130.8, 130.1, 129.5, 128.6, 128.5, 124.8, 119.7,
116.0, 115.8, 115.6, 52.0, 19.7, 19.5. Anal. Calcd for C20H16FN3OS: C,
65.74; H, 4.41; N, 11.50. Found: C, 65.67; H, 4.40; N, 11.47%.
N-[Cyano(phenyl)methyl]-N-(thiazol-2-yl)-4-chlorobenzamide
(entry 12): White solid; m.p. 125–126 °C; IR (KBr, νmax/cm−1): 2242
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1
(CN), 1678 (C=O); H NMR (CDCl3, 400 MHz): δ 7.45–7.03 (m,
11H, PhH and ThH), 7.02 (s, 1H, CH); 13C NMR (CDCl3, 100 MHz):
168.6, 159.2, 139.6, 138.0, 131.6, 131.4, 129.8, 129.5, 129.0, 128.8,
127.5, 119.8, 115.7, 52.2. Anal. Calcd for C18H12ClN3OS: C, 61.10; H,
3.42; N, 11.88. Found: C, 61.04; H, 3.41; N, 11.85%.
N-[Cyano(4-tolyl)methyl]-N-(thiazol-2-yl)-4-chlorobenzamide
(entry 13): White solid; m.p. 152–154 °C; IR (KBr, νmax/cm−1): 2240
1
(CN), 1682 (C=O); H NMR (CDCl3, 400 MHz): δ 7.46–7.02 (m,
34 Y.L. Ren, W. Wang, S. Zhao, X.Z. Tian and J.J. Wang, Org. Process Res.
10H, PhH and ThH), 6.99 (s, 1H, CH), 2.27 (s, 3H, CH3); 13C NMR
(CDCl3, 100 MHz): 168.6, 159.2, 139.7, 139.6, 137.9, 131.7, 129.9,
129.7, 128.8, 128.4, 127.5, 119.9, 115.9, 52.0, 21.2. Anal. Calcd for
C19H14ClN3OS: C, 62.04; H, 3.84; N, 11.42. Found: C, 62.14; H, 3.83;
N, 11.38%.
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N-[Cyano(3,4-dimethylphenyl)methyl]-N-(thiazol-2-yl)-4-chloro-
benzamide (entry 14): White solid; m.p. 146–148 °C; IR (KBr,
1
νmax/cm−1): 2239 (CN), 1678 (C=O); H NMR (CDCl3, 400 MHz): δ
7.46–7.02 (m, 9H, PhH and ThH), 6.97 (s, 1H, CH), 2.16 (s, 6H, CH3);
13C NMR (CDCl3, 100 MHz): 168.6, 159.3, 139.6, 138.2, 137.8,
137.5, 131.8, 130.2, 129.8, 128.8, 128.6, 128.6, 124.9, 119.8, 116.0,
52.0, 19.8, 19.5. Anal. Calcd for C20H16ClN3OS: C, 62.90; H, 4.22; N,
11.00. Found: C, 62.79; H, 4.23; N, 12.97%.
41 Y.L. Ren, M.J. Yan, S. Zhao, Y.P. Sun, J.J. Wang, W.P. Yin and Z.F. Liu,
Tetrahedron Lett., 2011, 52, 5107.
42 D. Saha, L. Adak, M. Mukherjee and B.C. Ranu, Org. Biomol. Chem.,
2012, 10, 952.
43 Z.X. Zhao and Z. Li, Eur. J. Org. Chem., 2010, 5460.
44 Z. Li, G.Q. Tian and Y.H. Ma, Synlett, 2010, 2164.
45 Z.X. Zhao and Z. Li, J. Braz. Chem. Soc., 2011, 22, 148.
46 X.C. Hu, Y.H. Ma and Z. Li, J. Organomet. Chem., 2012, 705, 70.
47 X.C. Hu, Z.X. Zhao and Z. Li, Phosphorus, Sulfur Silicon Relat. Elem.,
2012, 187, 1003.
Electronic Supplementary Information
Copies of the IR, 1H and 13C NMR spectra of all the compounds
above are provided in the electronic supplementary informa-
tion available through stl.publisher.ingentaconnect.com/content/
stl/jcr/supp-data.
48 Z. Li, Y.H. Ma, J. Xu, J.H. Shi and H.F. Cai, Tetrahedron Lett., 2010, 51,
3922.

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