Trichloroisocyanuric Acid Mediated Oxidative Dehydrogenation of Hydrazines: A Practical Chemical Oxidation to Access Azo Compounds

Article abstract of DOI:10.1055/s-0039-1690052

A highly efficient, metal-free, chemical oxidation of hydrazines has been implemented using environmentally friendly TCCA as oxidant. This benign protocol provides straightforward access to a wide range of azo compounds in THF in excellent yield. Altogether, 35 azo compounds were obtained in this way and scale-up preparations were performed. Additionally, a plausible mechanism was also proposed. Step-economical process, mild reaction conditions, operational simplicity, high reaction efficiency, and easy scale-up highlight the practicality of this methodology.

Full text of DOI:10.1055/s-0039-1690052

SYNTHESIS
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©
Georg Thieme Verlag Stuttgart · New York
2020, 52, A–J
paper
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en
Synthesis
Y. Su et al.
Paper
Trichloroisocyanuric Acid Mediated Oxidative Dehydrogenation of
Hydrazines: A Practical Chemical Oxidation To Access Azo Compounds
Yingpeng Su*
Xuan Liu
0
0
0
0-0
0
0
2-
4
3
9
6-4
1
9
8
O
R1
NH
NH
R2
NH
R2
NH
R1
Jie Yu
Metal-free oxidation
Highly efficient procedure
Easy operation
Guiyan Cao
Rong Zhang
Yanan Zhao
Danfeng Huang
Ke-Hu Wang
Congde Huo
Yulai Hu
Environmental-friendly
condition
TCCA
O
R1
Gram-scale synthesis
N
N
R2
N
N
R2
R1
College of Chemistry and Chemical Engineering, Northwest Normal
University, 967 Anning East Road, Lanzhou 730070, P. R. China
suyp51@nwnu.edu.cn
21 examples
14 examples
1
2
Received: 04.11.2019
Accepted after revision: 23.12.2019
Published online: 22.01.2020
the reductive coupling reaction of nitro compounds, the
oxidation of hydrazines and so on (Scheme 1).
1d,13
Among
DOI: 10.1055/s-0039-1690052; Art ID: ss-2019-h0614-op
these methods for preparing azo compounds, the straight-
forward and efficient routes mainly relied on the oxidation
of hydrazines. In this regard, various types of oxidants
Abstract A highly efficient, metal-free, chemical oxidation of hydra-
zines has been implemented using environmentally friendly TCCA as ox-
idant. This benign protocol provides straightforward access to a wide
range of azo compounds in THF in excellent yield. Altogether, 35 azo
compounds were obtained in this way and scale-up preparations were
performed. Additionally, a plausible mechanism was also proposed.
Step-economical process, mild reaction conditions, operational simplic-
ity, high reaction efficiency, and easy scale-up highlight the practicality
of this methodology.
14
have been involved toward such useful scaffolds, such as
1
4a–h
hypervalent heavy metallic oxidants,
O /metal co-oxi-
2
12b,14i–k
14l,m
dant,
H O /heavy metallic salt oxidant,
elemental
2
2
14n
or NBS,14o hypervalent iodine compounds.
9h,14p
Br2
Very
recently, several elegant and benign methods to achieving
azo compounds have been developed. Balaraman and co-
workers realized a photocatalyzed dehydrogenation of dia-
rylhydrazines with dual-transition-metal (Ru and Co) cata-
Key words trichloroisocyanuric acid, dehydrogenation, hydrazines,
azo compound, chemical oxidation
14x
lysts, thus providing a benign method to azobenzenes.
Afterward, the Fan group also used the organic dye (Acr-
+
As well known, the azo group is a crucial structural unit
Me ) as the photocatalyst to obtaining azobenzenes via an
1
2
14y
distributed in dyes and pigments, pharmaceuticals, food
environmentally friendly strategy. Very recently, the Xia
1c
3
2e,4
additives, organic reaction reagents and materials.
For
and Wu group reported a photoredox-catalyzed procedure
to access azobenzenes from diarylhydrazines using eosin Y
as the catalyst. Meanwhile, they also realized the intercon-
version from azobenzenes to hydrazine derivatives. Be-
sides the photo-promoted oxidative dehydrogenation of
hydrazines, Huang and co-workers employed a novel, green
and efficient electrochemical dehydrogenation of hydra-
instance, methyl red and methyl orange, azobenzene deriv-
5
atives, are utilized as dyes and indicators; Prontosil, an aro-
14z
matic azo compound, is not only a simply dye, but also
more important it was the first synthetic antibacterial sul-
fonamide. Furthermore the dialkyl azodicarboxylates, such
as diethyl azodicarboxylate (DEAD) and diisopropyl azodi-
carboxylate (DIAD), are essential reagents in the Mitsunobu
zines in an undivided cell to give azo compounds with a
broad substrate scope.
6
14aa
reaction and versatile reactants in organic transforma-
Although many efforts have been
7
tions. Doubtlessly, their importance and the utilizations of
devoted to the synthesis of azo compounds, given the im-
portance of azo compounds and the production practicality,
it is still actively appealing to develop alternative and envi-
ronmental friendly approaches for preparing azo com-
pounds.
azo compounds have impelled the development of efficient
preparative routes to these privileged compounds.8 The
classical methods for the synthesis of azo compounds in-
9
clude the oxidative coupling reaction of anilines, the cou-
10
11
pling reactions of diazonium salts, the Mills reaction,
©
2020. Thieme. All rights reserved. Synthesis 2020, 52, A–J
Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B
Synthesis
Y. Su et al.
Paper
the reaction rate without improving the yield (entry 7).
With these benign conditions in hand, we set out to further
evaluate this reaction by varying the solvent (entries 8–14).
As indicated in Table 1, this oxidative dehydrogenation took
place in various common solvents to yield the desired azo-
benzene in moderate to good yields. Toluene, DCM, acetoni-
trile, and DMF gave 3a in moderate to good yields (entries
8–11). To our great delight, using aprotic ethers as solvent
+
N2
H2N
NH2
Oxidative
Coupling
Diazo
Coupling
EWG
+
EDG
NO
Mills
Reaction
R2
+
1N
R
N
R
Oxidative
Reductive
Coupling
H
N
R2 Dehydrogenation
[O]
NO2
R1
N
(entries 12–14), such as Et O, THF and methyl tert-butyl
2
H
Photocatalysis Oxidation;
ether (MTBE), dramatically improved the reaction to gener-
ate desired product in excellent yields, especially THF gave
the best result of 97% yield (entry 13). Afterwards, several
control experiments were performed on this oxidative re-
action in THF using 0.34, 1.0, and 1.5 equiv of TCCA to give
[
O] Electrochemical Oxidation;
Chemical Oxidation:
Hypervalent heavy metal oxidants,
Br2/Py, NBS, PIDA ......
This work: TCCA
Scheme 1 Classical approaches to the synthesis of azo compounds
Table 1 Optimization of Oxidative Dehydrogenation of 1a with TCCAa
Among various categories of oxidants, trichloroisocy-
anuric acid (TCCA) has emerged as an extremely convenient
oxidant as well as a versatile chlorinating reagent or radical
initiator in synthesis, due to its stability, commercial avail-
ability, cheapness, harmless, easy handling, mild reaction
conditions, and environmentally benign attributes.15
Hence, it has been proved to be an efficient safe alternative
to toxic heavy-metal reagents and expensive organometal-
lic catalysts for a wide range of oxidations, such as, transfor-
H
N
solvent
air, r.t.
N
+
TCCA
N
N
H
1
a
2
3a
Entries
Molar ratio of 1a/2 Solvent
Time (min) Yield (%)b
1c
2c
1.0:0.34
1.0:1.0
1.0:1.5
1.0:2.0
1.0:1.5
1.0:2.0
1.0:2.5
1.0:2.0
1.0:2.0
1.0:2.0
1.0:2.0
1.0:2.0
1.0:2.0
1.0:2.0
1.0:0.34
1.0:1.0
1.0:1.5
1.0:2.0
1.0:1.0
1.0:2.0
1.0:2.0
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
toluene
DCM
18
15
9
52
65
72
78
76
85
84
65
66
71
86
91
97
91
50
55
76
63
58
95
94
16
3
c
mation of alcohols to carboxyl compounds, oxidative aro-
17
4c
5
6
7
8
9
matizations via dehydrogenations, asymmetric epoxida-
6
18
tions and others. In continuation of our interest in the
10
6
19
applications of TCCA in chemical transformations, herein,
we report the oxidative dehydrogenation of hydrazines
with this benign oxidant to provide azo compounds. The
environmental benign reaction conditions, high reaction ef-
ficiency, and remarkable practicality on a gram scale are sa-
lient features of our investigation.
3
20
15
25
15
13
15
14
42
35
25
32
30
15
16
10
MeCN
DMF
Our investigation began by optimizing the oxidative de-
hydrogenation conditions of diphenylhydrazine (1a) with
TCCA (Table 1). Initially, the model substrate 1a was treated
with 0.34 equiv of TCCA in ethanol (entry 1) at room tem-
perature. Gratifyingly, this dehydrogenation was efficiently
accomplished in 18 min to give desired azobenzene 3a in
11
12
13
14
2
Et O
THF
MTBE
THF
THF
THF
THF
THF
THF
THF
15
16
52% yield. To improve the yield of 3a, the amount of TCCA
was increased and a modest yield improvement was ob-
served (entries 2–4). What is intriguing is that the conver-
sions (monitored by TLC) under these conditions were al-
most quantitative and the azo compound was the sole
product. We speculated that hypochlorous acid was formed
during the aqueous workup, which led to chlorination
and/or oxidation of the reaction mixture. Such undesired
reactions may cause erosion of the yields. Hence, after com-
pletion of the reactions (entries 5–7), we concentrated the
reaction mixture to dryness without aqueous workup and
purified the crude product directly. To our delight, this vari-
ation improved the yield to 85% (entry 6). However, further
increasing the amount of TCCA to 2.5 equiv only enhanced
1
1
1
2
7
8d
9e
0e
21f
a
Reaction conditions: 1a (0.3 mmol), solvent (1.5 mL), r.t., air; concentra-
tion of the reaction mixture and direct purification of the crude product by
chromatography (silica gel).
Isolated yield.
The reaction were quenched with water.
N (3.0 equiv) was added and the reaction was carried out at 0 °C.
CO (3.0 equiv) was added.
The reaction was carried out under argon atmosphere.
b
c
d
Et
3
e
f
K
2
3
©
2020. Thieme. All rights reserved. Synthesis 2020, 52, A–J

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Synthesis
Y. Su et al.
Paper
the desired 3a in 50%, 55%, and 76% yields (entries 15–17).
However, when compared with the conditions using 2.0
equiv of TCCA (entry 13), reducing the ratio of TCCA in-
creased the reaction time and led to unidentified side reac-
tions with a dramatic deterioration in yield. Next the acid
binding agents Et N and K CO were added to try to reduce
3
2
3
Table 2 Scope of Diphenylhydrazines for Oxidative Dehydrogenationa,b
R2
R2
H
N
THF
r.t.
N
+
TCCA
N
N
H
R1
R1
N
1
2
3
Cl
F
Br
N
N
N
N
N
N
N
Cl
F
Br
3
a
3b
91% yield, 13 min
3c
3d
9
7% yield, 15 min;
89% yield, 14 min
89% yield, 16 min
Scale-up: 97% yield, 18 min, 954
mg
CH3
I
CF3
OCH3
N
N
N
N
N
N
N
N
H3C
I
F3C
3
H CO
3
e
3f
92% yield, 12 min
3g
3h
9
1% yield, 17 min
92% yield, 14 min
82% yield, 12 min
F
Cl
Cl
N
N
Cl
N
N
N
N
N
N
Cl
Cl
3i
3jc
3k
3l
87% yield, 14 min
81% yield, 16 min
88% yield, 16 min
89% yield, 16 min
CF3
Br
I
OCH3
N
N
N
N
N
N
N
N
3m
3n
3o
3p
92% yield, 14 min
93% yield, 14 min
93% yield, 14 min
88% yield, 11 min
CF3
N
N
N
N
N
N
N
N
N
Cl
CF3
Cl
3q
3r
3s
3t
90% yield, 13 min
91% yield, 12 min
82% yield, 12 min
93% yield, 14 min
Cl
Cl
N
N
3u
93% yield, 13 min
a
b
c
Reaction conditions: 1 (0.3 mmol), TCCA (2; 0.6 mmol), THF (1.5 mL), r.t.
Isolated yield.
The reaction was carried out at –10 °C.
©
2020. Thieme. All rights reserved. Synthesis 2020, 52, A–J

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Synthesis
Y. Su et al.
Paper
the consumption of TCCA (entries 18–20). Disappointingly,
these variations did not decrease the ratio of TCCA. The ad-
timized conditions consisted of performing the oxidative
dehydrogenation reaction of hydrazines with TCCA (2.0
equiv) at room temperature using THF as the solvent.
dition of Et N resulted in severe exotherm, which was be-
3
lieved to lead to many side-reactions. Even when the reac-
tion was carried out at 0 °C, this oxidative reaction with 2.0
equiv of TCCA just gave 63% yield of azo compound 3a after
With the optimum reaction conditions in hand, we pro-
ceeded to investigate the suitability of substrates. As shown
in Table 2, symmetrical substituted diphenylhydrazines
bearing substituents with different electronic properties
were firstly submitted to the dehydrogenation. As expect-
ed, a series of bis(4-substituted phenyl)hydrazines 1a–1h
were found to function very well in this reaction and gave
excellent yields of the corresponding products 3a–3h (82–
97%). In particular, the electron-donating group (Me, OMe)
substituted bis(p-tolyl)hydrazine (1g) and bis(4-methoxy-
phenyl)hydrazine (1h) were also compatible with this pro-
tocol and gave the desired products 3g and 3h in good
32 min (entry 18). On the other hand, employing 1.0 or 2.0
equiv of TCCA with 3.0 equiv of inorganic base K CO nei-
2
3
ther improved nor reduced the reaction results (entries 19
and 20). These preliminary results indicate that the addi-
tion of base did not improve the reaction or decrease the
amount of TCCA. Finally, this oxidative dehydrogenation
was carried out under an argon atmosphere in THF (entry
21). The results indicated that oxygen is not responsible for
this oxidation. Considering the above investigations, the op-
Table 3 Scope of 2-Phenylhydrazine-1-carboxylates for Oxidative Dehydrogenationa,b
H
N
R
N
R
N
H
THF
r.t.
N
+
TCCA
R1
R1
1
2
3
O
O
O
N
N
N
N
O
N
O
N
O
F
Br
O2N
3
v
3w
3x
94% yield, 15 min;
9
2% yield, 13 min
91% yield, 15 min
Scale-up: 96% yield, 20 min, 950 mg
O
O
O
N
Cl
Cl
N
N
N
O
N
O
N
O
H3C
H3CO
3y
3zc
3aac
92% yield, 12 min
90 % yield, 7 min
86% yield, 9 min
O
N
O
N
O
N
N
O
N
O
N
O
Br
O2N
H3C
3ab
3ac
3adc
93% yield, 14 min
95% yield, 16 min
88% yield, 7 min
O
O
O
N
N
N
N
O
N
O
N
O
H3CO
O2N
O2N
3
aec
3af
95% yield, 16 min
3ag
8
5% yield, 7 min
95% yield, 16 min
O
N
O
N
N
O
N
N
O2N
O2N
3ah
3ai
88% yield, 15 min
91% yield,13 min
a
b
c
Reaction conditions: 1 (0.3 mmol), TCCA (2; 0.6 mmol), THF (1.5 mL), r.t.
Isolated yield
THF was replaced by heptane/EtOH (2:1).
©
2020. Thieme. All rights reserved. Synthesis 2020, 52, A–J

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Synthesis
Y. Su et al.
Paper
yields without any chlorination byproducts. Electronic ef-
fects seemed to have no remarkable influence on these de-
hydrogenation processes.
drogenation and reacted to generate desired azo com-
pounds in excellent yields (91–95% yields). Additionally, 2-
phenylhydrazine-1-carboxamide 1ai was also efficiently
dehydrogenated, affording the desired azo compound 3ai in
91% yield. However, electron-donating substituents (Me,
OMe) in the para-position of the phenyl ring of 2-phenylhy-
drazine-1-carboxylates were substantially affected their re-
activity. Under the standard conditions, hydrazines 1z, 1aa,
1ad and 1ae gave complexes instead of the desired prod-
ucts. To avoid this limitation, we adjusted reaction parame-
ters, such as reaction temperature, concentration, and sol-
vent, to decrease the reactivity and oxidation ability of
TCCA. Gratifyingly, replacing THF by the co-solvent mixture
heptane/EtOH (2:1) resulted in the corresponding azo com-
pounds 3z, 3aa, 3ad, and 3ae in good yields (85–90% yields).
Finally, the gram-scale reaction of representative hydrazine
1x were also carried out in THF to prepare 3x in 96% yield.
To gain further insight into the reaction mechanisms of
this TCCA-based direct oxidative dehydrogenation of vari-
ous hydrazines, common control experiments were per-
formed. Firstly, the oxidative dehydrogenations of 1a
worked equally well under an argon atmosphere (Table 1,
entry 21). This result indicates that oxygen is not the con-
tributing oxidant in this oxidative dehydrogenation proce-
dure. Then the oxidative dehydrogenation reaction of 1a
was performed in the presence of radical scavengers TEM-
PO and BHT (Scheme 2), but the reaction retains its reactiv-
ity to form 3a. These results indicate that this oxidative de-
hydrogenation excludes a radical process. Additionally, the
reaction of 1a under the standard conditions in THF was
Then, hindered bis(3- and 2-chlorophenyl)hydrazines 1i
and 1j were employed to investigate the hindrance effect on
this conversion. Interestingly, bis(3-chlorophenyl)hydra-
zine (1i) was suitable reactant for this reaction, leading to
the expected azobenzene 3i in 87% yield. However, under
the standard conditions, substrate 1j merely gave desired 3j
in very low yield together with some unidentified byprod-
ucts. To overcome this problem, the reaction temperature
was varied to decrease the reactivity of TCCA. We were
pleased to find that when the reaction was carried out at
–10 °C, the expected product 3j was obtained in 81% yield.
Furthermore, a wide range of unsymmetrical 1-(substitut-
ed phenyl)-2-phenylhydrazines 1k–1u possessing various
substituents on the phenyl ring were employed in this
transformation. Unsymmetrical 1-(monosubstituted phe-
nyl)-2-phenylhydrazines, with F, Cl, Br, I, CF , Me, and OMe
3
1k–1s and even 1-(disubstituted phenyl)-2-phenylhydra-
zines 1t–1u both behaved as well as the symmetrical
bis(substituted phenyl)hydrazines bearing electron-with-
drawing groups, regardless of the position of the substitu-
ent in the phenyl ring, see 1r and 1s. Notably, 1-(2-chloro-
phenyl)-2-phenylhydrazine (1s) smoothly provided azo
compound 3s in 82% yield without variation of the reaction
temperature (compared with 1j). Additionally, in order to
prove the synthetic potential of this transformation, a
gram-scale reaction of 1a in THF was executed to obtain 3a
without reduction in the yield.
Encouraged by these positive results of oxidative dehy-
drogenation, we next sought to extend this benign method-
ology to various substituted 2-phenylhydrazine-2-carbox-
ylates. As shown in Table 3, various alkyl (ethyl, Bn, i-Bu,
t-Bu and 9-fluorenylmethyl) 2-phenylhydrazine-1-carbox-
ylates bearing different substituents in the para-position of
the phenyl ring 1v–1ah were studied. It was found that the
different alkyl groups were tolerated in this oxidative dehy-
1
monitored by H NMR spectroscopy. Analysis of this reac-
tion mixture revealed the presence of cyanuric acid.
Based on our control experimental results as well as
other reports,1
6a,20
the most plausible mechanism is pro-
posed in Scheme 3. Initially, the heterolytic cleavage of
TCCA (2) gives chlorinium ion (4) and dichlorocyanuric acid
anion 5. Subsequent electrophilic addition of hydrazine 1
with in situ formed chlorine cation 4 leads to N-chlorohy-
drazine cation 6, which transfers a proton to intermediate
(
a)
Standard conditions
in THF
H
N
O
OH
N
Cl
Cl
O
N
N
N
N
N
N
H
N
O
N
HO
N
OH
1a
3a
O
Cl
10
1
equiv
14 min, 85% yield
TEMPO (6.3 equiv)
2, TCCA
O
N
O
O
Cl
Cl
O
Cl
Cl
O
– 2Cl+
+
(
b)
N
R
N
N
N
HN
NH
+
2H
Standard conditions
in THF
H
N
O
O
N
H
O
N
H
O
Cl
N
N
N
H
OH
4
5
8
9
tBu
tBu
H
H
Cl
N
1
a
3a
N
R'
N
R'
– HCl
N
R'
R'
R
N
N
H
6
R
N
H
R
N
1
equiv
14 min, 87% yield
Cl
Me
BHT (6.3 equiv)
H
1
7
3
Scheme 2 Control experiments
Scheme 3 Plausible reaction mechanism
©
2020. Thieme. All rights reserved. Synthesis 2020, 52, A–J

F
Synthesis
Y. Su et al.
Paper
anion 5 to generate N-chlorohydrazine 7 and dichloro-
cyanuric acid 8. Final N-chlorohydrazine 7 eliminates HCl to
produce the desired azo compound 2. Meanwhile, the inter-
mediate dichlorocyanuric acid 8 takes part in the subse-
quent similar process to furnish cyanuric acid 10 via isom-
erization of the isocyanuric acid intermediate 9.
In conclusion, we have developed an efficient, metal-
free, and benign method for the oxidation of hydrazines
leading to diverse azo compounds using commercial and
environmentally friendly TCCA as chemical oxidant. This
oxidative dehydrogenation protocol exhibits a reasonably
broad substrate scope and good functional group compati-
bility. Meanwhile, the gram-scale preparation of azo com-
pounds makes this benign protocol very practical and with
more applications in the future. Additional studies on other
mild oxidations mediated by TCCA are underway in our
group.
HRMS (ESI): m/z [M + H]+ calcd for C12H F N : 219.07283; found:
9
2
2
219.07283.
(
E)-1,2-Bis(4-chlorophenyl)diazene (3c)14aa
Orange solid; yield: 67 mg (89%); mp 190–191 °C.
1H NMR (400 MHz, CDCl
):  = 7.88–7.84 (m, 4 H), 7.50–7.47 (m, 4 H).
C NMR (100 MHz, CDCl ):  = 150.8, 137.2, 129.4, 124.2.
3
1
3
3
HRMS (ESI): m/z [M + H]+ calcd for C12H Cl N : 251.01373; found:
9
2
2
251.01373.
E)-1,2-Bis(4-bromophenyl)diazene (3d)14aa
(
Orange solid; yield: 91 mg (89%); mp 203–204 °C.
1
H NMR (400 MHz, CDCl ):  = 7.79 (d, J = 8.4 Hz, 4 H), 7.65 (d, J = 8.4
3
Hz, 4 H).
13
C NMR (100 MHz, CDCl ):  = 151.3, 132.4, 125.8, 124.4.
3
HRMS (ESI): m/z [M + H]+ calcd for C12H Br N : 338.91270; found:
9
2
2
338.91272.
(E)-1,2-Bis(4-iodophenyl)diazene (3e)
Orange solid; yield: 119 mg (91%); mp >230 °C.
All solvents were dried according to standard methods prior to use.
All reagents were obtained from commercial suppliers and used
without further purification unless otherwise noted. Silica gel col-
umn chromatography was carried out using silica gel 60 (300–400
mesh). Analytical TLC was performed using silica gel (silica gel 60
1
H NMR (400 MHz, CDCl ):  = 7.88–7.85 (m, 4 H), 7.66–7.62 (m, 4 H).
3
13C NMR (100 MHz, CDCl
HRMS (ESI): m/z [M + H]+ calcd for C12H I N : 434.88496; found:
):  = 151.7, 138.4, 124.5, 98.1.
3
9
2
2
434.88495.
1
13
F254). TLC plates were analyzed by exposure to UV light. H and
NMR spectra were recorded at 400 MHz or 600 MHz and 100 MHz or
C
(
E)-1,2-Bis[4-(trifluoromethyl)phenyl]diazene (3f)14aa
Orange solid; yield: 88 mg (92%); mp 101–102 °C.
1
50 MHz, respectively. NMR experiments were carried out in CDCl
3
1
and are reported relative to internal TMS ( = 0.00 for H NMR), resid-
1
13
1H NMR (400 MHz, CDCl
ual CHCl3 ( = 7.26 for H NMR and  = 77.00 for C NMR). Melting
points are uncorrected. HRMS were recorded on Q-Exactive and Mi-
cro TOF-QII mass instrument (ESI). All starting materials were pre-
pared according to literature procedures: 1a, 1b–1h, 1i–1j, 1k–
1
3
):  = 8.03 (d, J = 8.4 Hz, 4 H), 7.80 (d, J = 8.0
Hz, 4 H).
13
C NMR (100 MHz, CDCl ):  = 154.0, 133.0 (q, J = 32 Hz), 126.4 (q,
3
21
13c
22
J = 4 Hz), 123.8 (q, J = 270 Hz), 123.3.
1
3c
23
u, 1v–1ai.
HRMS (ESI): m/z [M + H]+ calcd for C14H F N : 319.06644; found:
9
6
2
319.09012.
Azo Compounds 3; General Procedure
To a 10-mL flame-dried round-bottom flask equipped with a stirrer
bar were added hydrazine 1 (0.3 mmol) and THF (1.5 mL). Then TCCA
E)-1,2-Di-p-tolyldiazene (3g)14aa
(
Orange solid; yield: 59 mg (92%); mp 140–142 °C.
2
(2.0 equiv) was added in portions and the resulting mixture was
1
H NMR 400 MHz, (CDCl ):  = 7.81 (d, J = 8.4 Hz, 4 H), 7.30 (d, J = 8.0
stirred at r.t. until all the starting material had been completely con-
sumed (TLC monitoring; for reaction times see Tables 2 and 3). The
mixture was evaporated under reduced pressure and the residue was
purified by column chromatography (heptane/EtOAc 20:1–3:1) to ob-
tain the desired azo compound 3.
3
Hz, 4 H), 2.42 (s, 6 H).
13C NMR (150 MHz, CDCl ):  = 150.8, 141.2, 129.7, 122.7, 21.5.
3
HRMS (ESI): m/z [M + H]+ calcd for C14H15N : 211.12298; found:
2
211.12305.
(
E)-1,2-Diphenyldiazene (3a)14aa
(
E)-1,2-Bis(4-methoxyphenyl)diazene (3h)14aa
Orange solid; yield: 54 mg (97%); mp 67–68 °C.
1
Orange solid; yield: 60 mg (82%); mp 163–165 °C.
1
H NMR (400 MHz, CDCl ):  = 7.94–7.91 (m, 4 H), 7.55–7.45 (m, 6 H).
3
H NMR (400 MHz, CDCl ):  = 7.88 (d, J = 8.8 Hz, 4 H), 7.00 (d, J = 9.2
3
1
3
C NMR (100 MHz, CDCl ):  = 152.6, 131.0, 129.1, 122.8.
Hz, 4 H), 3.88 (s, 6 H).
3
HRMS (ESI): m/z [M + H]+ calcd for C12H11N : 183.09167; found:
13
2
C NMR (150 MHz, CDCl ):  = 161.5, 147.1, 124.3, 114.1, 55.5.
3
183.09171.
HRMS (ESI): m/z [M + H]+ calcd for C14H15N O : 243.11280; found:
2
2
243.11281.
(
E)-1,2-Bis(4-fluorophenyl)diazene (3b)14aa
Orange solid; yield: 60 mg (91%); mp 100–101 °C.
E)-1,2-Bis(3-chlorophenyl)diazene (3i)9f
(
1
H NMR (400 MHz, CDCl ):  = 7.93–7.89 (m, 4 H), 7.21–7.15 (m, 4 H).
Orange solid; yield: 66 mg (87%); mp 97–99 °C.
3
1
3
1
C NMR (100 MHz, CDCl ):  = 164.3 (d, J = 250 Hz), 148.9 (d, J = 2.0
H NMR (400 MHz, CDCl ):  = 7.91–7.89 (m, 2 H), 7.85–7.83 (m, 2 H),
3
3
Hz), 124.8 (d, J = 9.0 Hz), 116.0 (d, J = 23 Hz).
7.48–7.47 (m, 4 H).
©
2020. Thieme. All rights reserved. Synthesis 2020, 52, A–J

G
Synthesis
Y. Su et al.
Paper
13
13
C NMR (150 MHz, CDCl ):  = 153.1, 135.2, 131.2, 130.2, 122.6,
C NMR (150 MHz, CDCl ):  = 154.4, 152.4, 132.2 (q, J = 33 Hz),
3
3
1
21.9.
131.8, 129.2, 126.3 (q, J = 4.5 Hz), 123.9 (q, J = 271.5 Hz), 123.2, 123.0.
HRMS (ESI): m/z [M + H]+ calcd for C13H10F N : 251.07906; found:
HRMS (ESI): m/z [M + H]+ calcd for C12H Cl N : 251.01373; found:
9
2
2
3
2
251.01382.
251.07856.
(E)-1,2-Bis(2-chlorophenyl)diazene (3j)
(E)-1-(4-Methoxyphenyl)-2-phenyldiazene (3p)14aa
Orange solid; yield: 62 mg (81%); mp 130–132 °C.
Orange solid; yield: 56 mg (88%); mp 53–54 °C.
1
1
H NMR (400 MHz, CDCl ):  = 7.79–7.76 (m, 2 H), 7.58–7.56 (m, 2 H),
H NMR (400 MHz, CDCl ):  = 7.94–7.87 (m, 4 H), 7.52–7.42 (m, 3 H),
3
3
7.44–7.34 (m, 4 H).
7.02 (d, J = 8.8 Hz, 2 H), 3.89 (s, 3 H).
13
13
C NMR (150 MHz, CDCl ):  = 148.8, 135.8, 132.2, 130.7, 127.4,
C NMR (100 MHz, CDCl ):  = 162.0, 152.7, 147.0, 130.3, 129.0,
3
3
118.1.
124.7, 122.5, 114.2, 55.6.
HRMS (ESI): m/z [M + H]+ calcd for C12H Cl N : 251.01373; found:
HRMS (ESI): m/z [M + H]+ calcd for C13H13N O: 213.10224; found:
9
2
2
2
251.01384.
213.10223.
(
E)-1-(4-Fluorophenyl)-2-phenyldiazene (3k)14aa
(E)-N,N-Dimethyl-4-(phenyldiazenyl)aniline (3q)
Orange solid; yield: 53 mg (88%); mp 77–79 °C.
Orange solid; yield: 61 mg (90%); mp 115–116 °C.
1
1
H NMR (600 MHz, CDCl ):  = 7.94–7.89 (m, 4 H), 7.51–7.43 (m, 3 H),
H NMR (400 MHz, CDCl ):  = 7.90–7.83 (m, 4 H), 7.49–7.45 (m, 2 H),
3
3
7.19–7.15 (m, 2 H).
7.39–7.35 (m, 1 H), 6.76 (d, J = 9.2 Hz, 2 H), 3.08 (s, 6 H).
13
13
C NMR (150 MHz, CDCl ):  = 164.3 (d, J = 250.5 Hz), 152.4, 149.1 (d,
C NMR (100 MHz, CDCl ):  = 153.2, 152.4, 143.6, 129.3, 128.9,
3
3
J = 3.0 Hz), 131.0, 129.1, 124.8 (d, J = 9.0 Hz), 122.8, 116.0 (d, J = 22.5
124.9, 122.2, 111.5, 40.3.
Hz).
HRMS (ESI): m/z [M + H]+ calcd for C14H16N : 226.13387; found:
226.13398.
3
HRMS (ESI): m/z [M + H]+ calcd for C12H10FN : 201.08225; found:
2
201.08244.
(
E)-1-(3-Chlorophenyl)-2-phenyldiazene (3r)
(
E)-1-(4-Chlorophenyl)-2-phenyldiazene (3l)14aa
Orange solid; yield: 59 mg (91%); mp 64–65 °C.
Orange solid; yield: 58 mg (89%); mp 86–87 °C
1
H NMR (600 MHz, CDCl ):  = 7.92–7.89 (m, 3 H), 7.83–7.81 (m, 1 H),
3
1
H NMR (400 MHz, CDCl ):  = 7.92–7.84 (m, 4 H), 7.54–7.46 (m, 5 H).
7.52–7.46 (m, 3 H), 7.43–7.41 (m, 2 H).
3
13
13
C NMR (100 MHz, CDCl ):  = 152.4, 150.9, 136.9, 131.2, 129.3,
C NMR (150 MHz, CDCl ):  = 153.4, 152.3, 135.1, 131.5, 130.6,
3
3
129.1, 124.1, 122.9.
130.1, 129.1, 123.0, 122.3, 121.7.
HRMS (ESI): m/z [M + H]+ calcd for C12H10ClN : 217.05270; found:
HRMS (ESI): m/z [M + H]+ calcd for C12H10ClN : 217.05270; found:
2
2
217.05270.
217.05273.
(
E)-1-(4-Bromophenyl)-2-phenyldiazene (3m)14aa
(E)-1-(2-Chlorophenyl)-2-phenyldiazene (3s)
Orange solid; yield: 72 mg (92%); mp 87–88 °C.
Orange oil; yield: 53 mg (82%).
1
1
H NMR (400 MHz, CDCl ):  = 7.93–7.90 (m, 2 H), 7.82–7.79 (m, 2 H),
H NMR (400 MHz, CDCl ):  = 7.99–7.97 (m, 2 H), 7.71–7.69 (m, 1 H),
3
3
7.67–7.63 (m, 2 H), 7.55–7.47 (m, 3 H).
7.57–7.50 (m, 4 H), 7.42–7.33 (m, 2 H).
13
13
C NMR (100 MHz, CDCl ):  = 152.4, 151.3, 132.3, 131.3, 129.1,
C NMR (150 MHz, CDCl ):  = 152.8, 148.7, 135.3, 131.6, 131.5,
3
3
125.3, 124.3, 122.9.
130.7, 129.1, 127.3, 123.3, 117.6.
HRMS (ESI): m/z [M + H]+ calcd for C12H10BrN : 261.00219; found:
HRMS (ESI): m/z [M + H]+ calcd for C12H10ClN : 217.05270; found:
2
2
261.00217.
217.05270.
(
E)-1-(4-Iodophenyl)-2-phenyldiazene (3n)14z
(E)-1-[3,5-Bis(trifluoromethyl)phenyl]-2-phenyldiazene (3t)
Orange solid; yield: 87 mg (93%); mp 105–106 °C.
Orange solid; yield: 89 mg (93%); mp 70–71 °C.
1
1
H NMR (400 MHz, CDCl ):  = 7.92–7.83 (m, 4 H), 7.68–7.62 (m, 2 H),
H NMR (400 MHz, CDCl ):  = 8.36 (s, 2 H), 7.99–7.96 (m, 3 H), 7.57–
3
3
7.54–7.46 (m, 3 H).
7.55 (m, 3 H).
13
13
C NMR (100 MHz, CDCl ):  = 152.7, 152.1, 138.6, 131.6, 129.4,
C NMR (100 MHz, CDCl ):  = 152.8, 152.0, 132.7 (q, J = 34 Hz),
3
3
1
24.7, 123.2, 97.9.
132.5, 129.3, 123.8 (q, J = 4 Hz), 123.4, 123.1 (q, J = 271 Hz), 123.0 (d,
J = 4 Hz).
HRMS (ESI): m/z [M + H]+ calcd for C12H10IN : 308.98832; found:
2
308.98822.
HRMS (ESI): m/z [M + H]+ calcd for C14H F N : 319.06644; found:
9
6
2
319.06644.
(
E)-1-Phenyl-2-[4-(trifluoromethyl)phenyl]diazene (3o)14aa
(E)-1-(2,4-Dichlorophenyl)-2-phenyldiazene (3u)
Orange solid; yield: 70 mg (93%); mp 95–96 °C.
1
Orange solid; yield: 70 mg (93%); mp 107–108 °C.
H NMR (600 MHz, CDCl ):  = 7.98 (d, J = 8.4 Hz, 2 H), 7.95–7.93 (m, 2
3
H), 7.76 (d, J = 8.4 Hz, 2 H), 7.54–7.50 (m, 3 H).
©
2020. Thieme. All rights reserved. Synthesis 2020, 52, A–J

H
Synthesis
Y. Su et al.
Paper
1
Ethyl (E)-2-(4-Methoxyphenyl)diazene-1-carboxylate (3aa)14i
H NMR (400 MHz, CDCl ):  = 7.96–7.94 (m, 2 H), 7.66 (d, J = 8.8 Hz, 1
3
H), 7.56 (d, J = 2.4 Hz, 1 H),7.54–7.47 (m, 3 H), 7.30 (dd, J = 8.8, 2.0 Hz,
Orange oil; yield: 54 mg (86%).
1
H).
1
H NMR (400 MHz, CDCl ):  = 7.99–7.95 (m, 2 H), 7.03–6.99 (m, 2 H),
3
13
C NMR (100 MHz, CDCl ):  = 152.6, 147.1, 137.1, 136.2, 131.8,
3
4.51 (q, J = 7.2 Hz, 2 H), 3.91 (s, 3 H) 1.47 (t, J = 7.2 Hz, 3 H).
130.4, 129.2, 127.7, 123.4, 118.4.
13
C NMR (100 MHz, CDCl ):  = 164.6, 162.1, 146.1, 126.5, 114.5, 64.2,
3
HRMS (ESI): m/z [M + H]+ calcd for C12H Cl N : 251.01373; found:
9
2
2
55.7, 14.2.
251.01375.
HRMS (ESI): m/z [M + H]+ calcd for C10H13N O : 209.09207; found:
2
3
209.09203.
Ethyl (E)-2-(4-Fluorophenyl)diazene-1-carboxylate (3v)14i
Orange oil; yield: 55 mg (92%).
Benzyl (E)-2-(4-Bromophenyl)diazene-1-carboxylate (3ab)
1
H NMR (400 MHz, CDCl ):  = 8.00–7.96 (m, 2 H), 7.27–7.19 (m, 2 H),
3
Orange solid; yield: 89 mg (93%); mp 75–76 °C.
4.52 (q, J = 7.2 Hz, 2 H), 1.47 (t, J = 7.2 Hz, 3 H).
1
H NMR (400 MHz, CDCl ):  = 7.80–7.75 (m, 2 H), 7.66–7.64 (m, 2 H),
3
13
C NMR (100 MHz, CDCl ):  = 166.1 (d, J = 255 Hz), 161.9, 148.1 (d,
3
7.49–7.46 (m, 2 H), 7.43–7.35 (m, 3 H), 5.46 (s, 2 H).
J = 3 Hz), 126.2 (d, J = 9.0 Hz), 116.5 (d, J = 23 Hz), 64.5, 14.1.
HRMS (ESI): m/z [M + H]+ calcd for C H FN O : 197.07208; found:
13
C NMR (100 MHz, CDCl ):  = 161.8, 150.2, 134.2, 132.6, 128.9,
3
9
10
2
2
128.9, 128.7, 128.7, 125.1, 70.0.
197.07207.
+
HRMS (ESI): m/z [M + H] calcd for C14H12BrN O : 319.00767; found:
2
2
319.00052.
Ethyl (E)-2-(4-Bromophenyl)diazene-1-carboxylate (3w)14i
Orange oil; yield: 70 mg (91%).
Benzyl (E)-2-(4-Nitrophenyl)diazene-1-carboxylate (3ac)
1
H NMR (400 MHz, CDCl ):  = 7.82–7.79 (m, 2 H), 7.69–7.67 (m, 2 H),
3
Orange solid; yield: 81 mg (95%); mp 116–118 °C.
4.53 (q, J = 7.2 Hz, 2 H), 1.47 (t, J = 7.2 Hz, 3 H).
1
H NMR (600 MHz, CDCl ):  = 8.39–8.37 (m, 2 H), 8.05–8.02 (m, 2 H),
3
13
C NMR (100 MHz, CDCl ):  = 161.9, 150.2, 132.7, 128.9, 125.1, 64.6,
3
7.49–7.48 (m, 2 H), 7.43–7.38 (m, 3 H), 5.49 (s, 2 H).
14.1.
13
C NMR (150 MHz, CDCl ):  = 161.4, 154.2, 150.3, 134.0, 129.1,
3
HRMS (ESI): m/z [M + H]+ calcd for C H BrN O : 256.99202; found:
9
10
2
2
128.8, 128.8, 124.8, 124.3, 70.4.
256.99158.
HRMS (ESI): m/z [M – H]– calcd for C14H10N O : 284.06658; found:
3
4
284.06772.
Ethyl (E)-2-(4-Nitrophenyl)diazene-1-carboxylate (3x)14i
Orange solid; yield: 63 mg (94%); mp 58–59 °C.
Benzyl (E)-2-(p-Tolyl)diazene-1-carboxylate (3ad)
1
H NMR (400 MHz, CDCl ):  = 8.42–8.39 (m, 2 H), 8.08–8.04 (m, 2 H),
3
Orange oil; yield: 68 mg (88%).
4.56 (q, J = 7.2 Hz, 2 H), 1.49 (t, J = 7.2 Hz, 3 H).
1
H NMR (400 MHz, CDCl ):  = 7.85–7.82 (m, 2 H), 7.50–7.47 (m, 2 H),
3
13
C NMR (100 MHz, CDCl ):  = 161.5, 154.2, 150.3, 124.8, 124.2, 65.0,
3
7.42–7.36 (m, 3 H), 7.32–7.29 (m, 2 H), 5.46 (s, 2 H), 2.43 (s, 3 H).
14.1.
13
C NMR (100 MHz, CDCl ):  = 162.1, 149.8, 145.3, 134.5, 129.9,
3
HRMS (ESI): m/z [M + H]+ calcd for C H N O : 224.06658; found:
9
10
3
4
128.8, 128.7, 128.7, 124.0, 69.8, 21.7.
224.06596.
HRMS (ESI): m/z [M – H]– calcd for C15H13N O : 253.09715; found:
2
2
253.09718.
Ethyl (E)-2-(3,4-Dichlorophenyl)diazene-1-carboxylate (3y)14i
Orange solid; yield: 69 mg (92%); mp 43–44 °C.
Benzyl (E)-2-(4-Methoxyphenyl)diazene-1-carboxylate (3ae)
1
H NMR (400 MHz, CDCl ):  = 8.02 (d, J = 2.4 Hz, 1 H), 7.81 (dd,
3
Orange solid; yield: 69 mg (85%); mp 44–45 °C.
J = 8.4, 2.4 Hz, 1 H), 7.64 (d, J = 8.8 Hz, 1 H), 4.53 (q, J = 7.2 Hz, 2 H),
1
H NMR (400 MHz, CDCl ):  = 7.97–7.93 (m, 2 H), 7.50–7.47 (m, 2 H),
3
1.48 (t, J = 7.2 Hz, 3 H).
7.42–7.34 (m, 3 H), 7.00–6.96 (m, 2 H), 5.45 (s, 2 H), 3.88 (s, 3 H).
13
C NMR (100 MHz, CDCl ):  = 161.6, 150.2, 138.1, 134.0, 131.2,
3
13
C NMR (150 MHz, CDCl ):  = 164.7, 162.0, 146.1, 134.6, 128.7,
3
124.6, 123.6, 64.8, 14.1.
128.7, 128.6, 126.5, 114.4, 69.6, 55.7.
HRMS (ESI): m/z [M – H]– calcd for C H Cl N O : 244.98791; found:
9
7
2
2
2
HRMS (ESI): m/z [M + H]+ calcd for C15H15N O : 271.10772; found:
2
3
244.99680.
271.10770.
Ethyl (E)-2-(p-Tolyl)diazene-1-carboxylate (3z)14i
Isobutyl (E)-2-(4-Nitrophenyl)diazene-1-carboxylate (3af)
Orange oil; yield: 52 mg (90%).
Orange solid; yield: 72 mg (95%); mp 41–43 °C.
1
H NMR (400 MHz, CDCl ):  = 7.85 (d, J = 8.4 Hz, 2 H), 7.33 (d, J = 8.4
3
1
H NMR (400 MHz, CDCl ):  = 8.43–8.39 (m, 2 H), 8.08–8.05 (m, 2 H),
3
Hz, 2 H), 4.52 (q, J = 7.2 Hz, 2 H), 2.45 (s, 3 H) 1.47 (t, J = 7.2 Hz, 3 H).
4.28 (d, J = 6.8 Hz, 2 H), 2.21–2.11 (m, 1 H), 1.05 (d, J = 6.8 Hz, 6 H).
13
C NMR (100 MHz, CDCl ):  = 162.2, 149.8, 145.2, 130.0, 123.9, 64.3,
3
13
C NMR (100 MHz, CDCl ):  = 161.7, 154.2, 150.2, 124.8, 124.2, 74.6,
3
21.7, 14.2.
27.8, 18.8.
HRMS (ESI): m/z [M + H]+ calcd for C10H13N O : 193.09715; found:
2
2
HRMS (ESI): m/z [M – H]– calcd for C11H12N O : 250.08223; found:
3
4
193.09712.
250.08266.
©
2020. Thieme. All rights reserved. Synthesis 2020, 52, A–J

I
Synthesis
Y. Su et al.
Paper
tert-Butyl (E)-2-(4-Nitrophenyl)diazene-1-carboxylate (3ag)
2001, 3, 3891. (f) Yamaoka, T.; Makita, Y.; Sasatani, H.; Kim, S.-
I.; Kimura, Y. J. Controlled Release 2000, 66, 187. (g) Singh, A. K.;
Das, J.; Majumdar, N. J. Am. Chem. Soc. 1996, 118, 6185.
Orange solid; yield: 72 mg (95%); mp 135–136 °C.
1
H NMR (400 MHz, CDCl ):  = 8.41–8.37 (m, 2 H), 8.04–8.01 (m, 2 H),
3
(
3) (a) Tang, S.; Deng, Y.-L.; Li, J.; Wang, W.-X.; Wang, Y.-C.; Li, Z.-Z.;
Yuan, L.; Chen, S.-L.; Sheng, R.-L. Chem. Commun. 2016, 52,
4470. (b) Ibrahim, A. A.; Golonka, A. N.; Lopez, A. M.; Stockdill, J.
L. Org. Lett. 2014, 16, 1072. (c) Larraufie, M.-H.; Courillon, C.;
Ollivier, C.; Lacôte, E.; Malacria, M.; Fensterbank, L. J. Am. Chem.
Soc. 2010, 132, 4381. (d) Sha, C.-K.; Hsu, C.-W.; Chen, Y.-T.;
Cheng, S.-Y. Tetrahedron Lett. 2000, 41, 9865.
1.68 (s, 9 H).
13
C NMR (100 MHz, CDCl ):  = 160.5, 154.4, 150.1, 124.7, 124.1, 86.1,
3
27.8.
HRMS (ESI): m/z [M – H]– calcd for C11H12N O : 250.08223; found:
3
4
250.08490.
(
4) (a) Hüll, K.; Morstein, J.; Trauner, D. Chem. Rev. 2018, 118,
9
H-Fluoren-9-ylmethyl (E)-2-(4-Nitrophenyl)diazene-1-carboxyl-
10710. (b) Bandara, H. M. D.; Burdette, S. C. Chem. Soc. Rev.
2012, 41, 1809. (c) Beharry, A. A.; Woolley, G. A. Chem. Soc. Rev.
2011, 40, 4422. (d) Feringa, B. L.; van Delden, R. A.; Koumura, N.;
ate (3ah)
Orange solid; yield: 99 mg (88%); mp 126–128 °C.
1
H NMR (400 MHz, CDCl ):  = 8.43–8.39 (m, 2 H), 8.11–8.07 (m, 2 H),
3
Geertsema, E. M. Chem. Rev. 2000, 100, 1789. (e) Kumar, G. S.;
Neckers, D. C. Chem. Rev. 1989, 89, 1915. (f) Gorostiza, P.;
Isacoff, E. Y. Science 2008, 322, 395. (g) Banghart, M.; Borges, K.;
Isacoff, E.; Trauner, D.; Kramer, R. H. Nat. Neurosci. 2004, 7,
1381. (h) Bushuyev, O. S.; Tomberg, A.; Friščić, T.; Barrett, C. J.
J. Am. Chem. Soc. 2013, 135, 12556. (i) Puntoriero, F.; Ceroni, P.;
Balzani, V.; Bergamini, G.; Vögtle, F. J. Am. Chem. Soc. 2007, 129,
7.79 (d, J = 7.6 Hz, 2 H), 7.68–7.61 (m, 2 H), 7.43 (t, J = 7.6 Hz, 2 H),
7.34 (t, J = 7.2 Hz, 2 H), 4.75–4.72 (m, 2 H), 4.41 (t, J = 7.2 Hz, 1 H).
13
C NMR (100 MHz, CDCl ):  = 161.5, 154.2, 150.4, 142.8, 141.3,
3
128.1, 127.3, 125.1, 124.8, 124.4, 120.2, 70.4, 46.5.
+
HRMS (ESI): m/z [M + Na] calcd for C21H15N O Na: 396.09548; found:
3
4
396.09523.
1
0714. (j) Cisnetti, F.; Ballardini, R.; Credi, A.; Gandolfi, M. T.;
Masiero, S.; Negri, F.; Pieraccini, S.; Spada, G. P. Chem. Eur. J.
004, 10, 2011. (k) Commins, P.; Garcia-Garibay, M. A. J. Org.
Chem. 2014, 79, 1611.
(E)-N,N-Diethyl-2-(4-nitrophenyl)diazene-1-carboxamide (3ai)
2
Orange solid; yield: 68 mg (91%); mp 101–103 °C.
1
H NMR (400 MHz, CDCl ):  = 8.40 (d, J = 8.8 Hz, 2 H), 8.04 (d, J = 8.8
(5) (a) Arslan, T. J. Chem. Res. 2018, 42, 267. (b) Gingell, R.; Bridges,
J. W. Xenobiotica 1973, 3, 599.
(6) (a) Mitsunobu, O. Synthesis 1981, 1. (b) Swamy, K. C. K.; Kumar,
N. N. B.; Balaraman, E.; Kumar, K. V. P. P. Chem. Rev. 2009, 109,
3
Hz, 2 H), 3.61 (q, J = 6.8 Hz, 2 H), 3.52 (q, J = 7.2 Hz, 2 H), 1.34 (t, J = 6.8
Hz, 3 H), 1.20 (t, J = 7.2 Hz, 3 H).
13
C NMR (100 MHz, CDCl ):  = 161.2, 154.7, 149.8, 124.7, 123.9, 41.9,
3
2551.
41.7, 14.4, 12.8.
(
(
(
7) (a) Lau, Y.-F.; Chan, C.-M.; Zhou, Z.; Yu, W.-Y. Org. Biomol. Chem.
2016, 14, 6821. (b) Nair, V.; Biju, A. T.; Mathew, S. C.; Babu, B. P.
Chem. Asian J. 2008, 3, 810.
8) Ling, Y.; Geng, X.; Jiao, N. Green Oxidative Synthesis of Azo, Diazo,
and Azido Compounds, In Green Oxidation in Organic Synthesis;
Jiao, N.; Stahl, S. S., Ed.; John Wiley & Sons: Hoboken, 2019, 221.
9) (a) Saha, A.; Payra, S.; Selvaratnam, B.; Bhattacharya, S.; Pal, S.;
Koodali, R. T.; Banerjee, S. ACS Sustainable Chem. Eng. 2018, 6,
HRMS (ESI): m/z [M + H]+ calcd for C11H15N O : 251.11387; found:
4
3
251.11383.
Funding Information
We are thankful for financial support from the National Natural Sci-
ence Foundation of China (Grant No. 21502154, 21961034,
11345. (b) John, A. A.; Lin, Q. J. Org. Chem. 2017, 82, 9873.
21362033) and the Science and Technology Program of Gansu Prov-
(c) Dutta, B.; Biswas, S.; Sharma, V.; Savage, N.; Alpay, S.; Suib, S.
ince (No. 17JR5RA073).
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Angew. Chem. Int. Ed. 2016, 55, 2171. (d) Seth, K.; Roy, S. R.;
Kumar, A.; Chakraborti, A. K. Catal. Sci. Technol. 2016, 6, 2892.
(
e) Cai, S.; Rong, H.; Yu, X.; Liu, X.; Wang, D.; He, W.; Li, Y. ACS
Catal. 2013, 3, 478. (f) Zhu, Y.; Shi, Y. Org. Lett. 2013, 15, 1942.
g) Okumura, S.; Lin, C.-H.; Takeda, Y.; Minakata, S. J. Org. Chem.
013, 78, 12090. (h) Monir, K.; Ghosh, M.; Mishra, S.; Majee, A.;
Supporting Information
(
2
Supporting information for this article is available online at
https://doi.org/10.1055/s-0039-1690052.
S
u
p
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orti
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g Inform ati
o
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S
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orit
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g Inform ati
o
n
Hajra, A. Eur. J. Org. Chem. 2014, 2014, 1096. (i) Takeda, Y.;
Okumura, S.; Minakata, S. Angew. Chem. Int. Ed. 2012, 51, 7804.
(
(
(
(
(
(
j) Zhang, C.; Jiao, N. Angew. Chem. Int. Ed. 2010, 49, 6174.
k) Grirrane, A.; Corma, A.; García, H. Science 2008, 322, 1661.
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