Triphenylphosphine-mediated eco-friendly synthesis of (Z)-diisopropyl-2- (Cyano(Aryl)Methylene)hydrazine-1,1-dicarboxylates using potassium hexacyanoferrate(II) as a cyanide source

Article abstract of DOI:10.1080/10426507.2012.658983

A triphenylphosphine-mediated synthetic method for (Z)-diisopropyl-2-(cyano (aryl)methylene)hydrazine-1,1-dicarboxylates via one-pot three-component reactions using potassium hexacyanoferrate(II) as a cyanide source was described. This protocol has advantages of no use of strong toxic cyanating agents, high yield, and simple work-up procedure.

Full text of DOI:10.1080/10426507.2012.658983

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Phosphorus, Sulfur, and Silicon and the
Related Elements
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Triphenylphosphine-Mediated Eco-
Friendly Synthesis of (Z)-Diisopropyl-2-
(Cyano(Aryl)Methylene)Hydrazine-1,1-
Dicarboxylates Using Potassium
Hexacyanoferrate(II) as a Cyanide Source
Xiaochun Hu a b , Zhouxing Zhao a & Zheng Li a
a College of Chemistry and Chemical Engineering , Northwest Normal
University , Lanzhou , Gansu , 730070 , P.R. China
b Editorial Department of the University Journal , Northwest Normal
University , Lanzhou , Gansu , 730070 , P.R. China
Accepted author version posted online: 08 Feb 2012.Published
online: 07 Jun 2012.
To cite this article: Xiaochun Hu , Zhouxing Zhao & Zheng Li (2012) Triphenylphosphine-Mediated Eco-
Friendly Synthesis of (Z)-Diisopropyl-2-(Cyano(Aryl)Methylene)Hydrazine-1,1-Dicarboxylates Using
Potassium Hexacyanoferrate(II) as a Cyanide Source, Phosphorus, Sulfur, and Silicon and the Related
Elements, 187:8, 1003-1008, DOI: 10.1080/10426507.2012.658983
To link to this article: http://dx.doi.org/10.1080/10426507.2012.658983
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Phosphorus, Sulfur, and Silicon, 187:1003–1008, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.658983
TRIPHENYLPHOSPHINE-MEDIATED ECO-FRIENDLY
SYNTHESIS OF (Z)-DIISOPROPYL-2-
(CYANO(ARYL)METHYLENE)HYDRAZINE-1,1-
DICARBOXYLATES USING POTASSIUM
HEXACYANOFERRATE(II) AS A CYANIDE SOURCE
Xiaochun Hu,1,2 Zhouxing Zhao,1 and Zheng Li1
1College of Chemistry and Chemical Engineering, Northwest Normal University,
Lanzhou, Gansu 730070, P.R. China
2Editorial Department of the University Journal, Northwest Normal University,
Lanzhou, Gansu 730070, P.R. China
GRAPHICAL ABSTRACT
O
O
O
O
Ph3P (1.0 equiv)
toluene
O
N
N
O
+ K4[Fe(CN)6] +
N
O
N
Ar
Cl
O
O
CN
Ar
Abstract A triphenylphosphine-mediated synthetic method for (Z)-diisopropyl-2-(cyano
(aryl)methylene)hydrazine-1,1-dicarboxylates via one-pot three-component reactions using
potassium hexacyanoferrate(II) as a cyanide source was described. This protocol has
advantages of no use of strong toxic cyanating agents, high yield, and simple work-up
procedure.
Keywords Cyanation; triphenylphosphine; three-component synthesis; potassium hexacyano-
ferrate(II); (Z)-diisopropyl-2-(cyano(phenyl)methylene)hydrazine-1,1-dicarboxylate
INTRODUCTION
(Z)-Diisopropyl-2-(cyano(aryl)methylene)hydrazine-1,1-dicarboxylates were re-
ported to be synthesized via the reactions of aroyl cyanides with diisopropyl azodicarboxy
late and triphenylphosphine in anhydrous toluene under argon at 90 ◦C.1 However,
commercially available aroyl cyanides are limited and comparatively expensive. Espe-
cially, the synthesis of aroyl cyanides had to utilize strong toxic reagents as original
cyanide sources, such as HgCN,2 NaCN,3 CuCN,4 KCN,5 and TMSCN,6 which render
Received 6 December 2011; accepted 15 January 2012.
The authors thank the National Natural Science Foundation of China (21162024) for the financial support
of this work.
Address correspondence to Zheng Li, College of Chemistry and Chemical Engineering, Northwest Normal
University, Lanzhou, Gansu 730070, P.R. China. E-mail: lizheng@nwnu.edu.cn
1003

1004
X. HU ET AL.
the reactions unsafe and environmentally unfriendly. Therefore, there is a need to explore
environmentally benign cyanating agents and simple procedures for the synthesis of
(Z)-diisopropyl-2-(cyano(aryl)methylene)hydrazine-1,1-dicarboxylates.
Potassium hexacyanoferrate (II), K4[Fe(CN)6], is nontoxic and is even used in the
food industry for metal precipitation. In addition, it has been described as an antiagglu-
tinating auxiliary for table salt (NaCl).7 K4[Fe(CN)6] is commercially available on a ton
scale and is even cheaper than KCN. Very recently, K4[Fe(CN)6] has been proved to
be an efficient cyanide source for the cyanation of halogenated arenes to benzonitriles,8
the cyanation of aroyl chlorides to aroyl cyanides,9 the cyanoaroylation of aldehydes to
cyanohydrin esters,10 the Strecker reactions to α-aminonitriles,11 the arylcyanation of in-
ternal alkynes to β-arylalkenylnitriles,12 and the nucleophilic addition-elimination of α,α-
dibromoacetophenones to 2-aryl-3,3-dibromoacrylonitriles.13 However, the cyanation of
N N containing compounds was not investigated.
Multicomponent reactions (MCRs) are more and more popular and effective.14 Re-
cently, MCRs have emerged as a highly valuable synthetic tool in the context of modern
drug discovery. The atom economical and convergent character, the simplicity of a one-pot
procedure, the possible structural variations, the accessible complexity of the molecules, as
well as the very large number of accessible compounds are among the described advantages
of MCRs. Thus, they are perfectly amenable to automation for combinatorial synthesis.
Herein, we wish to report the triphenylphosphine-mediated one-pot three-component
eco-friendly synthesis of (Z)-diisopropyl-2-(cyano(aryl)methylene)hydrazine-1,1-dicarbo
xylates using potassium hexacyanoferrate(II) as a cyanide source.
RESULTS AND DISCUSSION
Initially, the one-pot three-component synthesis of (Z)-diisopropyl-2-(cyano
(phenyl)methylene)hydrazine-1,1-dicarboxylate was attempted using benzoyl chloride,
potassium hexacyanoferrate(II), and diisopropyl azodicarboxylate as model substrates
under different conditions (Scheme 1). It was found that the reaction could only take
place in the presence of triphenylphosphine as a promoter. After conducting the reactions
under different conditions, the best result was obtained by using 0.2 equiv of potassium
hexacyanoferrate(II) to react with one equiv of diisopropyl azodicarboxylate and one equiv
of benzoyl chloride, which indicated that all CN− of potassium hexacyanoferrate(II) could
be efficiently utilized in the reaction. In addition, one equiv of triphenylphosphine was
also required for the reaction in toluene. In addition, it was also found that the product
structure had Z-selectivity, which was determined by comparing the product spectra with
the literature data.1
O
O
O
O
Ph3P (1.0 equiv)
toluene
O
N
N
O
+ K4[Fe(CN)6] +
N
O
N
Ar
Cl
O
O
CN
Ar
Scheme 1 Synthesis of (Z)-diisopropyl-2-(cyano(aryl)methylene)-hydrazine- 1,1-dicarboxylates.

TRIPHENYLPHOSPHINE-MEDIATED ECO-FRIENDLY SYNTHESIS
1005
Table 1 Synthesis of (Z)-diisopropyl-2-(cyano(aryl)-methylene)hydrazine-1,1-dicarboxylates using potassium
hexacyanoferrate(II) as a cyanide source
Entry
Ar
C6H5
Yield (%)a
mp (lit.) (oC)
1
2
3
4
5
6
7
8
9
80
70
74
80
86
88
82
85
84
68
40–42 (Oil)1
Oil
50–52
Oil (Oil)1
80–82
82–83 (81–83)1
112–114
118–120
102–104
40–42 (Oil)1
2-CH3C6H4
3-CH3C6H4
2-ClC6H4
3-ClC6H4
4-ClC6H4
3-NO2C6H4
4-NO2C6H4
4-IC6H4
10
aIsolated yields.
Under the optimal conditions, various substituted aroyl chlorides were examined for
the one-pot three-component synthesis. The results are shown in Table 1. It was found
that aroyl chlorides bearing electron-withdrawing substituents such as chloro, iodo, and
nitro groups on the aromatic ring gave the corresponding products in high yield (Table 1,
entries 4–9). In contrast, aroyl chlorides bearing electron-donating group such as methyl
on the aromatic ring gave the corresponding products in slightly lower yield under similar
conditions (Table 1, entries 2–3). For ortho-substituted aroyl chlorides, the corresponding
products were obtained in slightly lower yield than meta- or para-substituted ones, pre-
sumably due to the steric effect (Table 1, entries 2, 4). Heteroaroyl chloride, such as furoyl
chloride, was also very efficient for the three-component synthesis (Table 1, entry 10).
CONCLUSION
An efficient triphenylphosphine-mediated one-pot three-component eco-friendly syn-
thetic method for (Z)-diisopropyl-2-(cyano(aryl)methylene)hydrazine-1,1-dicarboxylates
using potassium hexacyanoferrate(II) as a cyanide source has been developed. The pro-
tocol has advantages of no use of strong toxic cyanating agents, high yield, and simple
work-up procedure.
EXPERIMENTAL
IR spectra were recorded using KBr pellets on an Alpha Centauri FTIR spectropho-
1
tometer. H NMR and 13C NMR spectra were recorded on a Mercury-400BB instrument
using CDCl3 as solvent and Me4Si as internal standard. Mass spectra were recorded by
electron spray ionization (ESI). Elemental analyses were performed on a Vario El Elemen-
tal Analysis instrument. Melting points were observed in an electrothermal melting point
apparatus. Potassium hexacyanoferrate(II) was dried at 80 ◦C under vacuum for 24 h and
finely powdered prior to use.

1006
X. HU ET AL.
General Procedure for the Preparation of (Z)-Diisopropyl-2-(cyano(aryl)
methylene)hydrazine-1,1-dicarboxylates
The mixture of aroyl chloride (10 mmol) and potassium hexacyanoferrate(II)
◦
(0.84 g, 2 mmol) was heated at 160 C for 3 h. After cooling to room temperature,
triphenylphosphine (2.62 g, 10 mmol) and diisopropyl azodicarboxylate (2.02 g, 10 mmol)
in 20 mL of toluene were added. The resulting mixture was further stirred at 90 ◦C for 1 h.
Then, the solid was removed by filtration, the filtrate was evaporated off the solvent, and the
residue was subjected to silica gel flash column chromatography (ethyl acetate, petroleum
ether, 1:20) to obtain pure products. The analytical data for representative products are
given below.
(Z)-Diisopropyl-2-(cyano(2-methylphenyl)methylene)hydrazine-
1,1-dicarboxylate (2)
1
Oil. H NMR (CDCl3, 400 MHz): δ 7.72–7.31 (m, 4H, Ph-H), 5.19–5.13 (m, 2H,
CH), 2.62 (s, 3H, CH3), 1.38 (d, J = 6.2 Hz, 12H, CH3), 13C NMR (CDCl3, 100 MHz):
δ 149.8, 148.3, 138.5, 131.9, 131.8, 130.3, 129.3, 126.1, 110.2, 72.6, 21.3, 21.0; IR (KBr,
cm−1): 3064 (s), 2985 (s), 2225 (w), 1798 (s), 1763 (s), 1600 (s), 1456 (s), 1375 (s), 1307
(s), 1235 (s), 1093 (s), 910 (s). MS (ESI): m/z 332 (M++1). Anal. Calcd. for C17H21N3O4:
C, 61.62; H, 6.39; N, 12.68. Found: C, 61.70; H, 6.40; N, 12.64.
(Z)-Diisopropyl-2-(cyano(3-methylphenyl)methylene)hydrazine-
1,1-dicarboxylate (3)
◦
1
Colorless solid. mp: 50–52 C. H NMR (CDCl3, 400 MHz): δ 7.85–7.31 (m, 4H,
Ph-H), 5.19–5.13 (m, 2H, CH), 2.42 (s, 3H, CH3), 1.38 (d, J = 6.8 Hz, 12H, CH3). 13C NMR
(CDCl3, 100 MHz): δ 150.3, 146.5, 138.9, 134.0, 130.2, 128.8, 128.1, 125.2, 109.7, 72.8.
21.5, 21.1. IR (KBr) νmax/cm−1: 2985 (s), 2937 (s), 2228 (w), 1798 (s), 1762 (s), 1564 (s),
1465 (s), 1375 (s), 1307 (s), 1235 (s), 1094 (s), 911 (m). MS (ESI): m/z 332 (M++1). Anal.
Calcd. for C17H21N3O4: C, 61.62; H, 6.39; N, 12.68. Found: C, 61.53; H, 6.38; N, 12.72.
(Z)-Diisopropyl-2-(cyano(3-chlorophenyl)methylene)hydrazine-
1,1-dicarboxylate (5)
◦
1
Colorless solid. mp: 80–82 C. H NMR (CDCl3, 400 MHz): δ 8.03–7.69 (m, 4H,
Ph-H), 5.20–5.14 (m, 2H, CH), 1.38 (d, 12H, J = 6.0 Hz, CH3). 13C NMR (CDCl3,
100 MHz): δ 150.4, 142.7, 135.4, 133.0, 131.5, 130.3, 128.5, 127.4, 109.5, 73.4, 21.7. IR
(KBr, cm−1): 2980 (m), 2919 (m), 2222 (w), 1715 (s), 1591 (m), 1468 (m), 1382 (m), 1264
(s), 1104 (s), 920 (m). MS (ESI): m/z 352 (M++1). Anal. Calcd. for C16H18ClN3O4: C,
54.63; H, 5.16; N, 11.94. Found: C, 54.76; H, 5.16; N, 11.90.
(Z)-Diisopropyl-2-(cyano(3-nitrophenyl)methylene)hydrazine-
1,1-dicarboxylate (7)
◦
1
Colorless solid. mp: 112–114 C. H NMR (CDCl3, 400 MHz): δ 8.54–7.73 (m,
4H, Ph-H), 5.12–5.05 (m, 2H, CH), 1.38 (d, 12H, J = 7.2 Hz, CH3). 13C NMR (CDCl3,
100 MHz): δ 150.5 143.3, 137.5, 130.6, 127.5, 127.2, 116.4, 114.1, 109.5, 73.7, 21.6. IR

TRIPHENYLPHOSPHINE-MEDIATED ECO-FRIENDLY SYNTHESIS
1007
(KBr, cm−1): 2984 (m), 2937 (m), 2237 (w), 1770 (s), 1747 (s), 1535 (s), 1356 (s), 1274
(m), 1097 (s), 920 (m), 735 (m). MS (ESI): m/z 363 (M++1). Anal. Calcd. for C16H18N4O6:
C, 53.04; H, 5.01; N, 15.46. Found: C, 52.95; H, 5.02; N, 15.49.
(Z)-Diisopropyl-2-(cyano(4-nitrophenyl)methylene)hydrazine-
1,1-dicarboxylate (8)
Colorless solid. mp: 118–120 ◦C. 1H NMR (CDCl3, 400 MHz): δ 8.31 (d, 2H, J =
8.8 Hz, Ph-H), 8.15 (d, 2H, J = 8.8 Hz, Ph-H), 5.04-4.89 (m, 2H, CH), 1.28 (d, 12H, J
= 6.0 Hz, CH3). 13C NMR (CDCl3, 100 MHz): δ 154.1 152.3 148.5, 135.4, 135.3, 130.0,
123.3, 74.4, 21.3. IR (KBr, cm−1): 2983 (s), 2939 (s), 2234 (w), 1739 (s), 1709 (s), 1596
(s), 1526 (s), 1463 (s), 1345 (s), 1300 (s), 1128 (s), 1095 (s), 900 (s), 858 (m). MS (ESI):
m/z 363 (M++1). Anal. Calcd. for C16H18N4O6: C, 53.04; H, 5.01; N, 15.46. Found: C,
53.11; H, 5.02; N, 15.41.
(Z)-Diisopropyl-2-(cyano(4-iodophenyl)methylene)hydrazine-
1,1-dicarboxylate (9)
Colorless solid. mp: 102–104 ◦C. 1H NMR (CDCl3, 400 MHz): δ 7.80 (d, 2H, J =
8.0 Hz, Ph-H), 7.43 (d, 2H, J = 8.0 Hz, Ph-H), 5.17–5.11 (m, 2H, CH), 1.38 (d, 12H, J =
6.2 Hz, CH3). 13C NMR (CDCl3, 100 MHz): δ 150.4, 143.7, 139.6, 129.5, 129.2, 129.1,
109.4, 73.3, 21.6. IR (KBr, cm−1): 2985 (m), 2934 (m), 2218 (w), 1714 (s), 1664 (m), 1595
(m), 1548 (m), 1471 (m), 1381 (s), 1325 (m), 1169 (m), 1106 (m), 1053 (m), 986 (m), 832
(m). MS (ESI): m/z 444 (M++1). Anal. Calcd. for C16H18IN3O4: C, 43.36; H, 4.09; N,
9.48. Found: C, 43.29; H, 4.08; N, 9.45.
Additional characterization data and a complete set of spectra (1H and 13C NMR and
IR) can be found in the Supplemental Materials (Figures S1–S30).
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