Iron(III) chloride catalyzed formation of aryl hydrazides from electron-rich arenes and azodicarboxylates

Article abstract of DOI:10.1055/s-0033-1338585

Iron(III) chloride-catalyzed direct amination of electron-rich arenes with azodicarboxylates gives the corresponding aryl hydrazides in moderate to good yields within two minutes under mild conditions. This method will serve as an important tool for the s

Full text of DOI:10.1055/s-0033-1338585

PAPER
▌757
paper
Iron(III) Chloride Catalyzed Formation of Aryl Hydrazides from Electron-
Rich Arenes and Azodicarboxylates
Synthesis of Aryl Hydrazides
Zhiyong Wang,*a Xiaoxiao Xing,a Lijun Xue,a Yan Xiong,a Ling Fang*b
a
School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044, P. R. of China
Fax +86(23)65102531; E-mail: zwang@cqu.edu.cn
b
School of Environmental and Biological Engineering, Chongqing Technology and Business University, Chongqing 400067, P. R. of China
Received: 30.10.2013; Accepted after revision: 19.12.2013
with which they can change their oxidation state and their
Abstract: Iron(III) chloride-catalyzed direct amination of electron-
distinct Lewis acid character, iron catalysts have been
rich arenes with azodicarboxylates gives the corresponding aryl hy-
used in several protocols for the synthesis of various or-
drazides in moderate to good yields within two minutes under mild
conditions. This method will serve as an important tool for the syn-
ganic compounds through the formation of carbon−car-
thesis of bioactive nitrogen-containing products and pharmaceuti- bon or carbon−heteroatom bonds.7,8 In a prominent case,
cals.
iron has been shown to be an efficient catalyst for the al-
kenylation of simple arenes with aryl-substituted alkynes,
Key words: catalysis, iron, aminations, arenes, hydrazides
giving new C−C bonds from aromatic C–H bonds.8b
We recently demonstrated that iron(III) chloride is a high-
ly effective catalyst for Friedel−Crafts reactions of elec-
tron-rich arenes with imines or aziridines.8f We therefore
set out to look for a new transformation using this catalyst
system, with the aim of demonstrating its wide range of
potential applications. Here, we describe the results from
our attempts to develop a new iron(III) chloride catalyzed
direct amination of electron-rich arenes with azodicarbox-
ylates under mild conditions.
Functionalized aryl hydrazides and their derivatives are
useful intermediates for the synthesis of nitrogen-contain-
ing heterocycles and bioactive medicinal and agrochemi-
cal compounds.1 Consequently, a variety of protocols
have been developed for synthesizing aryl hydrazides
from azodicarboxylates.1,2 Among these, the conventional
protocols involve aminations of aryllithium reagents,3a,b
aryl Grignard reagents,3b or arylzinc halides3c with azodi-
carboxylates. Alternatively, Lewis acids or Brønsted
acids can be used as efficient catalysts for reactions of
electron-rich arenes with azodicarboxylates.4 In an impor-
tant contribution to this field, Zhang and co-workers de-
scribed the first example of a catalytic direct amination of
electron-deficient arenes with azodicarboxylates.5 How-
ever, their modified method used air-sensitive and expen-
sive gold(III) chloride as a catalyst, which detracts from
the synthetic appeal of this transformation. Mandal and
co-workers recently described a ruthenium chloride-cata-
lyzed direct amination of arenes with azodicarboxylates;
this method can be applied to amination of a broad spec-
trum of arenes, including those with certain electron-
withdrawing groups, which give modest to low yields.4k
Recently, transition metal-catalyzed coupling reactions of
arylboronic acids with azodicarboxylates to give aryl-
substituted hydrazines have been developed.6 Although
these methods are useful, the development of new meth-
ods that do not involve expensive reagents or harsh condi-
tions is desirable to provide an environmentally friendly
catalytic system for the direct amination of arenes.
First, we examined the use of iron(III) chloride (5 mol%)
as a catalyst for the reaction of mesitylene (1a) with diiso-
propyl azodicarboxylate (2a) in nitromethane at room
temperature (Table 1, entry 1). Gratifyingly, this reaction
was completed within two minutes, affording the desired
product 3a in 95% yield. A similar yield (91%) was ob-
tained when iron(III) chloride hexahydrate was used as
the catalyst instead of the anhydrous salt (entry 2). Other
iron salts, such as iron(III) sulfate, iron(III) nitrate nona-
hydrate, tris(acetylacetonato)iron, or iron(II) sulfate hep-
tahydrate, were ineffective catalysts for the formation of
aryl hydrazide 3a (entries 3–6). Moderate yields of the de-
sired product 3a were obtained by using iron(II) chloride
or iron(II) triflate as the catalyst (entries 7 and 8, respec-
tively). An evaluation of various solvents did not produce
any better results (entries 9–11). When aqueous hydro-
chloric acid (20 mol%) was used as the catalyst, none of
the desired product was obtained (entry 12). These results
confirm the high catalytic activity of iron(III) chloride.
Next, we examined the substrate scope of the iron-cata-
lyzed direct amination of simple arenes with azodicarbox-
ylates under the optimized reaction conditions (Table 1,
entry 1). As shown in Table 2, this method was effective
for electron-rich arenes, and the catalyst was highly effi-
cient in this reaction. Almost all reactions of electron-rich
arenes were complete within two minutes and gave mod-
erate to excellent isolated yields of the corresponding aryl
hydrazides 3. For example, amination of naphthalene and
1-methoxynaphthalene in the presence of 5 mol% of the
In the last decade, iron salts have attracted the attention of
synthetic organic chemists because of their ready avail-
ability, environmental friendliness, and low cost, along
with their exceptional reactivity.7 Because of the ease
SYNTHESIS 2014, 46, 0757–0760
Advanced online publication: 28.01.2014
0
0
3
9
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7
8
8
1
1
4
3
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DOI: 10.1055/s-0033-1338585; Art ID: SS-2013-H0704-OP
© Georg Thieme Verlag Stuttgart · New York

758
Z. Wang et al.
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Table 2 Iron(III) Chloride Catalyzed Aminations of Various Arenes
1 with Azodicarboxylates 2
Table 1 Amination of Mesitylene (1a) with Diisopropyl Azodicar-
boxylate (2a) in the Presence of Various Iron Salts
i
R
R
CO2 Pr
HN
N
N
N
HN
FeCl3 (5 mol%)
iPrO2C
Ar
+
N
N
N
[Fe] (5 mol%)
solvent, r.t.
i
MeNO2, r.t.
< 2 min
Ar
R
R
CO2 Pr
+
i
i
1
3
CO2 Pr
2a R = CO2 Pr
2b R = CO2Bn
1a
2a
3a
Product
Ar
R
Yield (%)
Entrya
Catalyst
Solvent
Time
Yieldb (%)
3a
3b
3c
3d
3e
3f
2,4,6-Me3C6H2
CO2i-Pr
CO2i-Pr
CO2i-Pr
CO2i-Pr
CO2i-Pr
CO2i-Pr
CO2i-Pr
CO2i-Pr
CO2Bn
CO2Bn
95
1
2
FeCl3
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
CH2Cl2
DCE
2 min
2 min
2 h
95
2,3,5,6-Me4C6H
2,4,6-(MeO)3C6H2
2,5-(MeO)2C6H3
3,4-(MeO)2C6H3
1-naphthyl
70b
68 (80)c
65
FeCl3·6H2O
Fe2(SO4)3
91
3
–
4
Fe(NO3)3·9H2O
Fe(acac)3
Fe(SO4)2·7H2O
FeCl2
2 h
trace
–
56
5
2 h
81
6
2 h
trace
89
3g
3h
3i
4-methoxy-1-naphthyl
2-MeO-5-IC6H3
2,4,6-Me3C6H2
3,4-(MeO)2C6H3
87
7
2 min
2 min
40d
84
8
Fe(OTf)2
FeCl3
77
9
12 h
26
3j
56
10
11
12
FeCl3
12 h
12 h
12 h
35
a Yields are isolated yields based on the azodicarboxylate 2.
b At r.t. for 30 min.
FeCl3
THF
trace
–
c Fe(OTf)2 catalyst.
HClc
MeNO2
d At r.t. for 24 h.
a Reaction conditions: 2a (0.5 mmol), 1a (1 mmol), catalyst (5 mol%),
solvent (2 mL), r.t.
b Isolated yield based on 2a.
boxylates that is catalyzed by iron(III) chloride and pro-
vides a convenient route for the synthesis of aryl
hydrazides. The protocol has the advantages of providing
high efficiency (reaction times of less than 2 minutes), re-
quiring low-price reactants and catalysts, being environ-
mentally benign, and involving simple experimentally
operations. This method might therefore serve as an im-
portant tool for efficient synthesis of biologically active
nitrogen-contained products and pharmaceuticals.
c 0.1 mmol catalyst (20 mol%).
iron catalyst gave good yields within two minutes (Table
2, 3f and 3g). For the reactions of durene and 1,3,5-tri-
methoxybenzene, yields of the corresponding aryl hydra-
zides 3b and 3c were moderate, even after a prolonged
reaction time. This low yield might be the result of steric
hindrance on the benzene ring. Gratifyingly, however, the
aryl hydrazides 3c could be isolated in 80% yield by using
iron(II) triflate as the catalyst. The reactions of 1,2-di-
methoxybenzene with azidocarboxylates 2 were very
complex, giving mixtures of the monoaminated products
3e or 3j and other unknown products. To our disappoint-
ment, electron-deficient arenes such as chlorobenzene,
fluorobenzene, or iodobenzene were not good partners for
this kind of transformation, even with prolonged reaction
times and increased reaction temperatures. Surprisingly,
amination of 1-iodo-4-methoxybenzene with 2a at room
temperature for 24 hours gave the desired aryl hydrazide
3h in an isolated yield of 40%. With regard to the azodi-
carboxylate reactant, commercially available dibenzyl
azodicarboxylate (2b) reacted with simple arenes 1 to give
the expected products in moderate to good yields (3i,
84%; 3j, 56%). Overall, however, electron-rich arenes are
the most reactive substrates for these aminations.
NMR spectra were recorded with Agilent 400-MR DD2, 600-MR
DD2, and Bruker AV500 spectrometers (400 or 500 MHz for H,
1
100, 125 or 150 MHz for 13C) with CDCl3 as a solvent at 20−25 °C.
High-resolution mass spectra were recorded on a Finnigan
MAT8430 Q-TOF MS spectrometer. IR spectra were recorded as
liquid films on a Bruker Tensor 27 spectrophotometer. Column
chromatography was carried out on silica gel (300−400 mesh), and
TLC analyses were performed on silica gel coated plates
(HSGF254, Yantai Jiangyou Silica Gel Development Co., Ltd.). All
reactions were carried out under argon. All commercial materials
were used without further purification.
Diisopropyl 1-Mesitylhydrazine-1,2-dicarboxylate (3a)5; Typi-
cal Procedure
Azodicarboxylate 2a (0.5 mmol) was added to a stirred solution of
arene 1a (1 mmol) and FeCl3 (5 mol%) in anhyd MeNO2 (3 mL) at
r.t. under argon. When the reaction was complete (TLC, < 2 min),
the reaction was quenched with H2O (10 mL), and the mixture was
extracted with EtOAc (2 × 10 mL). Evaporation of the solvent fol-
lowed by purification of the residue by flash chromatography [silica
gel, PE–EtOAc (8:1)] gave a white solid; yield: 153 mg (95%); mp
90.0–91.0 °C.
In summary, we have developed a novel and simple direct
amination reaction of electron-rich arenes with azodicar-
Synthesis 2014, 46, 757–760
© Georg Thieme Verlag Stuttgart · New York

PAPER
Synthesis of Aryl Hydrazides
759
1H NMR (500 MHz, CDCl3): δ = 6.87 (s, 2 H), 6.79–6.70 (m, 1 H),
IR (neat): 3281, 1760, 1721, 1339, 1222, 1058 cm–1.
5.02–4.94 (m, 2 H), 2.30–2.26 (m, 9 H), 1.31–1.15 (m, 12 H).
1H NMR (400 MHz, CDCl3): δ = 7.32–7.16 (m, 11 H), 6.84 (s, 2 H),
5.21–5.09 (m, 4 H), 2.29–2.18 (m, 9 H).
Diisopropyl 1-(2,3,5,6-Tetramethylphenyl)hydrazine-1,2-dicar-
boxylate (3b)5
13C NMR (100 MHz, CDCl3): δ = 156.0, 155.9, 138.1, 136.0, 135.9,
135.8, 135.4, 129.4, 129.2, 128.4, 128.3, 128.2, 128.2, 128.1, 128.0,
127.8, 68.3, 67.7, 20.9, 18.1, 18.0.
White solid; yield: 117 mg (70%); mp 156.5–157.8 °C.
1H NMR (500 MHz, CDCl3): δ = 6.95 (s, 1 H), 6.83–6.74 (m, 1 H),
5.03–4.95 (m, 2 H), 2.23–2.20 (m, 12 H), 1.33–1.15 (m, 12 H).
HRMS (ESI): m/z [M + H]+ calcd for C25H27N2O4: 419.1965; found:
419.1964.
Diisopropyl 1-(2,4,6-Trimethoxyphenyl)hydrazine-1,2-dicar-
boxylate (3c)5
Dibenzyl 1-(3,4-Dimethoxyphenyl)hydrazine-1,2-dicarboxyl-
ate (3j)
Yellow solid; yield: 122 mg (56%); mp 132.1–133.8 °C
IR (neat): 3308, 1722, 1514, 1391, 1249, 1027 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.38–7.31 (m, 10 H), 6.96 (br s, 2
H), 6.78 (d, J = 8.4 Hz, 2 H), 5.20 (s, 2 H), 5.16 (s, 2 H), 3.84 (s, 3
H), 3.78–3.58 (m, 3 H).
13C NMR (150 MHz, CDCl3): δ = 156.1, 155.0, 148.6, 147.9, 135.6,
135.4, 134.6, 128.5, 128.4, 128.3, 128.1, 128.0, 127.8, 116.7, 110.6,
109.6, 68.3, 67.8, 55.9, 55.8.
Pale-yellow solid; yield: 148 mg (80%); mp 113.1–114.8 °C.
1H NMR (500 MHz, CDCl3): δ = 6.94 (br s, 1 H), 6.12 (s, 1 H), 6.11
(s, 1 H), 4.96–4.93 (m, 2 H), 3.83 (s, 3 H), 3.82 (s, 3 H), 3.80 (s, 3
H), 1.30–1.14 (m, 12 H).
Diisopropyl 1-(2,5-Dimethoxyphenyl)hydrazine-1,2-dicarbox-
ylate (3d)
Yellow oil; yield: 110 mg (65%).
IR (neat): 3302, 1721, 1509, 1376, 1226, 1109 cm–1.
1H NMR (500 MHz, CDCl3): δ = 7.11–6.83 (m, 4 H), 4.98–4.95 (m,
2 H), 3.79 (s, 3 H), 3.76 (s, 3 H), 1.32–1.18 (m, 12 H).
HRMS (ESI): m/z [M – H]– calcd for C24H23N2O6: 435.1562; found:
435.1556.
13C NMR (100 MHz, CDCl3): δ = 155.6, 153.3, 148.8, 139.2, 130.7,
115.1, 114.6, 112.0, 70.5, 69.6, 55.9, 55.8, 22.0, 21.9, 21.8.
HRMS (ESI): m/z [M + H]+ calcd for C16H25N2O6: 341.1707; found:
341.1704.
Acknowledgment
Financial support from National Science Foundation Project CQ
(CSTC, 2011BB4054 to Z.W.), Fundamental Research Funds for
the Central Universities (CDJRC11220001 and CQDXWL-2013-
023 to Z.W.), and the Foundation of Chongqing Educational Com-
mittee (KJ130701 to L.F.) is gratefully acknowledged.
Diisopropyl 1-(3,4-Dimethoxyphenyl)hydrazine-1,2-dicarbox-
ylate (3e)
Yellow oil; yield: 95 mg (56%);
IR (neat): 3457, 1718, 1515, 1376, 1249, 1109 cm–1.
1H NMR (500 MHz, CDCl3): δ = 7.04–6.80 (m, 3 H), 5.02–4.98 (m,
2 H), 3.87 (s, 3 H), 3.86 (s, 3 H), 1.28–1.28 (m, 12 H).
13C NMR (150 MHz, CDCl3): δ = 156.0, 154.6, 148.4, 147.3, 135.0,
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis.SnoIufproi
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116.52, 110.5, 109.1, 70.5, 69.8, 55.8, 55.7, 21.8, 21.7.
HRMS (ESI): m/z [M + H]+ calcd for C16H25N2O6: 341.1707; found:
341.1703.
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Yellow solid; yield: 87 mg (40%); mp 120.2–121.9 °C
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Yellow solid; yield: 175 mg (84%); mp 139.5–141.1 °C
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2014, 46, 757–760

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Synthesis 2014, 46, 757–760
© Georg Thieme Verlag Stuttgart · New York