Substitution of a nitro group by diazonium salts in σH-Adducts of carbanions to mono-nitrobenzenes. Formation of substituted azobenzenes and indazoles

Article abstract of DOI:10.1016/j.tet.2021.132186

σ^H-Adducts formed at low temperature from nitrobenzene derivatives and carbanions stabilized by cyano, alkoxycarbonyl or sulfonyl groups react with benzenediazonium salts as nucleophiles, forming a new C–N bond preferentially at carbon atom bearing the nitro group. The so-formed intermediates eliminate HNO₂ molecule under action of base, yielding substituted azobenzenes. Adducts of secondary carbanions, stabilized by cyano or sulfonyl groups to the ortho positions of nitrobenzenes, cyclize in situ to substituted indazoles. Some ortho σ^H-adducts of 1-chloroethyl phenyl sulfone carbanion add diazonium cations at meta position to the nitro group. In this case, the subsequent elimination of HCl leads to azo compounds retaining the nitro group in its original position.

Full text of DOI:10.1016/j.tet.2021.132186

Tetrahedron xxx (xxxx) xxx
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Substitution of a nitro group by diazonium salts in s
H-Adducts of
carbanions to mono-nitrobenzenes. Formation of substituted
azobenzenes and indazoles
a
,
Zbigniew Wrobel *, Bogdan Wilk b, Andrzej Kwast a
ꢀ
a Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 00-266, Warsaw, Poland
b Monmouth University, 400 Cedar Ave, West Long Branch, NJ, 07764, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
s
H-Adducts formed at low temperature from nitrobenzene derivatives and carbanions stabilized by
Received 25 February 2021
Received in revised form
17 April 2021
Accepted 20 April 2021
Available online xxx
cyano, alkoxycarbonyl or sulfonyl groups react with benzenediazonium salts as nucleophiles, forming a
new CeN bond preferentially at carbon atom bearing the nitro group. The so-formed intermediates
eliminate HNO2 molecule under action of base, yielding substituted azobenzenes. Adducts of secondary
carbanions, stabilized by cyano or sulfonyl groups to the ortho positions of nitrobenzenes, cyclize in situ
to substituted indazoles. Some ortho
s
H-adducts of 1-chloroethyl phenyl sulfone carbanion add diazo-
nium cations at meta position to the nitro group. In this case, the subsequent elimination of HCl leads to
azo compounds retaining the nitro group in its original position.
© 2021 Elsevier Ltd. All rights reserved.
Keywords:
Nitroarenes
Carbanions
s
H-adducts
Azo compounds
1. Introduction
Oxidation of s
H-adducts with external oxidants, sometimes also
spontaneously, leads to products of the oxidative substitution of
hydrogen (ONSH) [4]. Nucleophiles containing X-leaving groups in
Addition of nucleophilic species to the aromatic ring of electron-
poor arenes is one of the elementary processes fundamental to the
chemistry of aromatic compounds. It was convincingly proved that
the addition of typical nucleophilic reagents, namely carbon, oxy-
gen or nitrogen anions to electrophilic arenes, proceeds preferen-
the nucleophilic center enable b-elimination of HX from s
H-ad-
ducts to give products of Vicarious Nucleophilic Substitution (VNS)
[1,3,5]. Intramolecular redox process involving vicinal adjacent
nitro group is often followed by subsequent transformations [6a-d].
In case of the ortho addition of anilide nucleophiles it leads to
substitution of hydrogen along with the formation of substituted 2-
nitrosodiarylamines [6e]. Nitroso compounds were also produced
tially in activated, unsubstituted positions giving s
H-adducts [1,2].
The addition is essentially reversible, so unless the equilibrium is
shifted strongly to the right or any subsequent transformation
leading to a stable product is not fast enough, the
mation may go unnoticed, giving other processes a chance to pro-
ceed. Stable
H-adducts formed from polynitrobenzenes or
strongly electrophilic heterocyclic compounds are well known and
also investigated presently [3]. The study of transformations of sH
s
H-adduct for-
after acidic workup of irreversibly formed s
H-adducts of mono-
nitroarenes with some organolithium and Grignard reagents [7].
Less common transformations are cine and tele substitutions which
have been reviewed [8].
s
-
s
H-Adducts of carbon nucleophiles to nitroarenes are negatively
adducts formed as intermediates in the reactions of nucleophiles
with less reactive mononitroarenes has a much shorter history, but
several reviews and chapters in monographs have been devoted to
them [1,3]. It has been found that these unstable adducts can be
converted into stable products in several synthetically significant
ways (Scheme 1).
charged species with a charge spread on the nitro group and con-
jugate carbon atoms of the ring. This makes them weakly basic and
nucleophilic molecules that are prone to react with external or
internal electrophilic reagents. Intramolecular trapping of a nega-
tively charged carbon atom of the ring by a side chain isonitrile
group is an interesting way for the synthesis of isoindoles [9].
Recently a report on intramolecular SN2 substitution of phenyl-
selenone group with a carbon atom forming cyclopropane ring on
the C1eC2 bond of 1-nitronaphtalene was reported [10].
* Corresponding author.
ꢀ
E-mail address: zbigniew.wrobel@icho.edu.pl (Z. Wrobel).
https://doi.org/10.1016/j.tet.2021.132186
0040-4020/© 2021 Elsevier Ltd. All rights reserved.
H-Adducts of carbanions to mono-
ꢀ
Please cite this article as: Z. Wrobel, B. Wilk and A. Kwast, Substitution of a nitro group by diazonium salts in
s
nitrobenzenes. Formation of substituted azobenzenes and indazoles, Tetrahedron, https://doi.org/10.1016/j.tet.2021.132186

ꢀ
Z. Wrobel, B. Wilk and A. Kwast
Tetrahedron xxx (xxxx) xxx
to nitrobenzene (2a) was chosen. 4-Bromobenzenediazonium salt
(3a) was used in preliminary experiments and found to be a
potentially effective electrophilic agent in the intended reaction.
The reaction was completed with the addition of a second base to
form the substituted azobenzene final product (Scheme 2).
To find the best reaction conditions, a short series of scrutinizing
experiments were performed. The reaction was carried out under
various conditions which differed in the solvent, temperature and
base added (Table 1).
In all the cases, a solution of nitrobenzene and the nitrile was
added into a cooled solution of t-BuOK. This should result in for-
mation of a s
H-adduct of the carbanion at position 4 of nitroben-
Scheme 1. Principal transformations of
interactions with electrophiles.
s
H-adducts of mononitroarenes and possible
zene. Then the diazonium salt was added, followed by addition of
the base (1 equiv. of t-BuOK in THF or an excess of neat Et3N). The
reaction was quenched with aqueous NH4Cl at the reaction tem-
perature or, after removing the cooling bath, at room temperature.
In all the reactions, the desired product (4a) was formed, although
in rather low to moderate yield. Depending on the reaction con-
ditions, 4a was accompanied by numerous side-products, mainly
5a and 6a as shown in Fig. 1. Thus, under unsuitable conditions, the
reaction course was quite complicated. The best results were ob-
tained when the reaction was carried out in a solvent of low po-
larity (THF) and a strong base was used, even at low temperature
(conditions A, G, H). A weak base (Et3N) is not effective under these
conditions and requires higher temperature reached before the
quench (condition F).
Those reaction conditions were then applied for the reactions of
selected carbanions stabilized by CN, COOR and ArSO2 groups. At
first, tertiary compounds were chosen since they are known to add
to nitrobenzenes selectively at para position, if available, thus the
formation of isomeric ortho adducts was avoided (Table 2).
tert-Butyl ester of phenylacetic acid was expected to react at
para position, similarly to the tertiary nitriles, due to its bulkiness.
However, while under condition F, the reactions gave multicom-
ponent mixtures. Positive results were achieved when they were
carried out in DMF with Et3N or t-BuOK used as a base (condition C
or D). These conditions were found rather unfavorable for the ni-
triles (Table 1). The addition proceeded at position para to the nitro
group and the products, azo compounds 4i and 4j, were isolated in
relatively good yield (Table 2, entries 10 and 11). Also, tertiary
benzyl sulfones reacted better in DMF (condition C) than in THF.
Thus, it is apparent that there are no optimal reaction conditions for
every class of CH-acids and particular reactions were not further
optimized. The yields obtained were rather low due to the several
by-products, which only in a few cases were formed individually in
sufficient amounts for identification (Table 2, entries 4 and 5).
The results show the crucial role of the added base. In the
absence of base or when a weak base is operating at low temper-
ature, other processes take place in parallel and they can dominate
over the main course (Table 1). The formation of substituted
The reaction of s
H-adduct with an external electrophilic reagent
requires that the adduct is stable under the reaction conditions and
formed in high concentration so that the starting, stronger nucle-
ophile does not compete with the adduct. Those requirements are
met for adducts formed irreversibly by addition of Grignard re-
agents or silyl enol ethers in which case O-silylated adducts are
formed. Both types of adducts easily react with bromine giving
geminal bromonitrocyclohexadiene intermediates susceptible to
elimination of HBr or HNO2 [11]. For typical, stabilized carbanions
or their hetero analogues, the requirements are easily satisfied with
strongly electrophilic arenes such as polynitrobenzenes or nitro
compounds of low aromaticity. It was found, however, that equi-
librium of the addition of some carbanions to mononitrobenzene
derivatives, when carried out in polar solvents at low temperature,
lies shifted strongly to the right and s
H-adducts are formed in high
concentration [4]. This finding was successfully exploited in the
ONSH reactions mentioned above [4] and in the cine substitution of
the nitro group with some sulfone-stabilized carbanions [12]. Ac-
cording to our best knowledge, no other electrophiles than proton
or halogens have been successfully used for trapping s
H-adducts of
carbanions to regular mononitrobenzenes. Our goal was to find
other external electrophiles which would take advantage of the
nucleophilic feature of the ring carbon atoms of such s
H-adducts to
form a new stable bond. The most promising electrophiles seemed
to be benzenediazonium salts which were found earlier to add to
nitronate anions [13] and stable adducts formed from hydride,
alkoxylate or enolate anions and polynitroarenes[14aec] or 9-
nitroantracene [14d] that could be finally transformed to azo
compounds [14]. This proved their high reactivity to such type of
weak nucleophiles.
2. Results and discussion
As
phenylpropionitrile anion (1a- generated from 1a using t-BuOK)
a model s a product of the addition of 2-
H-adduct,
Scheme 2. The model reaction of the
s
H-adduct of 1a and 2a with diazonium salt 3a.
2

ꢀ
Z. Wrobel, B. Wilk and A. Kwast
Tetrahedron xxx (xxxx) xxx
Table 1
Screening of the reaction conditionsa.
Entry
Solvent
Temperature ꢀC
Base
Final temperature ꢀC
Condition
4a %
5a %
6a %
1
2
3
4
5
6
7
8
THF
THF
DMF
DMF
THF
THF
THF
THF
ꢁ100
ꢁ100
ꢁ60
ꢁ60
ꢁ78
ꢁ78
ꢁ78
ꢁ78
t-BuOK
none
t-BuOK
Et3N
Et3N
Et3N
ꢁ100
ꢁ100
r.t.
A
B
C
D
E
F
G
H
53b
26
25
20
20
59
55
60
e
e
29
13
12
30
<2
2
2
20
19
5
<2
6
r.t.
ꢁ78
r.t.
t-BuOK
t-BuOK
ꢁ78
r.t.
<2
<2
a
b
Yields measured by GC. Isolated yield
Fig. 1. The identified by-products in the reactions of diazonium salts with s
H-adducts of 1a-e and 2a-h (Table 2).
Table 2
Formation of s
H-adducts and their reactions with diazonium salts 3.
Entry
CH-Acid
Y
Nitroarene
X
Diazonium salt
Z
Product
R1
R2
1
2
3
Conditiona
No
Yieldb
%
1
2
3
4
5
6
7
8
CN
CN
CN
CN
CN
CN
CN
CN
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
4-ClC6H4
Cl
Me
Me
Me
Me
Me
Me
Me
i-Pr
Me
H
1a
1a
1a
1a
1a
1a
1a
1b
1a
1c
1c
1d
1e
1e
1e
1e
1e
H
H
H
H
2a
2a
2a
2a
2b
2b
2c
2a
2d
2a
2d
2a
2e
2e
2f
4-Br
3a
3b
3c
3d
3a
3a
3a
3a
3a
3a
3a
3a
3a
3b
3a
3a
3a
A
F
F
F
F
H
F
H
H
D
C
F
I
4a
4b
4c
4d
4e
4e
4f
4g
4h
4i
53
42
47
31c
21d
42
31
34
20
51
41
31
30e
27f
39
32
30
4-NO2
3-NO2
4-OMe
4-Br
4-Br
4-Br
4-Br
4-Br
4-Br
4-Br
4-Br
4-Br
4-NO2
4-Br
4-Br
2-OMe
2-OMe
3-Cl
H
2-Cl
H
9
CN
10
11
12
13
14
15
16
17
CO2t-Bu
CO2t-Bu
SO2Ph
SO2Ph
SO2Ph
SO2Ph
SO2Ph
SO2Ph
H
2-Cl
H
4j
Me
Me
Me
Me
Me
Me
4k
7a
7b
7c
7d
7e
2,4-Cl2
2,4-Cl2
4-CF3
4-Cl
4-F
Cl
Cl
Cl
Cl
I
I
I
I
2g
2h
4-Br
a
Reaction conditions as in Table 1. Condition I: same as D except that the initial temperature was ꢁ40 ꢀC.
Isolated yield.
4-Methoxyazobenzene (6b) was isolated in 10% yield.
4-Bromo-20-methoxyazobenzene (6c) was isolated in 26% yield.
Additionally 8a (Fig. 1) was formed in 33% yield.
b
c
d
e
f
Additionally 8b (Fig. 1) was formed in 26% yield.
azobenzenes 4 and 7 is believed to proceed according to the
accompanies these reactions when potentially oxidizing reagents
are present in the reaction mixture. In this case, there are starting
nitroarenes and, particularly, diazonium salts which can play the
role of a powerful electron acceptor [15]. The fact that this process
is remarkably efficient when the base is absent or operates inef-
fectively could be explained by the assumption of reversibility of
the formation of 10 (Scheme 3), which means that it dissociates to
form 9 and the diazonium cation. Alternatively, intermediate 10
could be believed to form irreversibly, as an unstable, not isolable
intended reaction scheme (Scheme 2). However, additional note-
worthy observations can be made. First, azo compound 4a is
formed in a considerable amount even in the absence of a
concluding base, or when a weak base is used at low temperature.
Second, the product of the oxidative substitution of hydrogen 5a is
a major reaction product under such conditions (Table 1, entries 2
and 5).
Oxidation of the
s
H-adduct is a common process which often
3

ꢀ
Z. Wrobel, B. Wilk and A. Kwast
Tetrahedron xxx (xxxx) xxx
Scheme 3. Plausible routes of the formation of 4, 5 and 6 from s
H-adduct of 1 and 2.
compound that at higher temperature (up to room temperature) or
during workup undergoes energetically favored rearomatization.
This is possible to take place via several plausible routes. The most
obvious is spontaneous elimination of HNO2 leading to 4 without
action of base. On the other hand, homolytic fragmentation of 10 by
departure of the ArN2 radical would allow the nitrocyclohexadiene
radical to rearomatize yielding 5 [15]. Side products 6 were formed
in considerable amounts in the model reaction conducted in DMF
(6a, Table 1, entries 2 and 3) and unexpectedly also in two cases of
the reaction carried out in THF when the nitroarene (2b) or dia-
zonium salt (3d) bear OMe substituent in the benzene ring (6b and
6c, Table 2, entries 4 and 5).
In both reactions, Et3N was used as a base that was allowed to
act up to room temperature (condition F). For the model reaction,
these conditions were equally efficient as those with t-BuOK used
as a base (condition H). In the cases of the methoxy-substituted
reagents, changing the reaction conditions from F to H allowed to
suppress the side process and to increase the yields of the desired
products significantly. This fact and the structure of azo compounds
6, lacking both carbon substituent and a nitro group, suggest that
the way of its formation from intermediate 10 is rather complex
and may involve some radical processes [15]. Thus, additional
research would be necessary to propose a reasonable mechanistic
scheme for this transformation.
Scheme 4. Two pathways of the reaction of diazonium salt 3a with sH-adducts of 1-
chloroethyl phenyl sulfone (1e) and nitroarenes 2.
The addition of ArNþ2 at meta position results in formation of
compound 11, which transforms into 8 by abstraction of two pro-
tons and departure of Clꢁ (steps shown in Scheme 4) or vice versa.
The formation of 8 was observed only in case of ortho-substituted
nitroarene 2e, thus, it can be attributed to the sterically crowded
position occupied by the nitro group. It should be noted that the
conceivable course of the reaction via initially formed VNS product,
followed by its reaction with 3a, was excluded in the separate
experiment. The VNS product obtained from 1e and 2e was sub-
jected to the reaction with 3a under the reaction conditions. The
reaction did not result in 7a, only some unidentified products were
observed.
Anions of secondary, less crowded CH-acids are known to form
s
H-adducts in both ortho and para positions of nitroarenes. To avoid
formation of a mixture of isomeric products, 4-substituted nitro-
benzenes were then selected and reacted with arylacetonitriles and
diazonium salts under condition H, which was most effective in the
reactions of 2-arylpropionitriles. However, the main or exclusive
products of the reactions were not the expected azo compounds 12
but 2,3-diaryl-2H-indazole derivatives 13 (Scheme 5, Table 3).
Apparently, the initially formed azo compounds 12 underwent
base-induced cyclization together with the departure of cyanide
ion. The arylsulfonyl group can also play a role of a leaving group in
the cyclization step (entry 5). The process seems to be analogous to
the cyclization of (2-nitrosophenyl)acetonitriles leading to 2,1-
benzisoxazoles (anthranils) [6a,c,16] (Scheme 5).
Some sterically undemanding tertiary sulfone-stabilized carb-
anions readily add to nitroarene ring at both para and ortho posi-
tions. They form
undergo elimination of HCl (VNS) [5]. On the other hand, the ortho
H-adducts formed from carbanions such as 1-chloroethyl phenyl
s
H-adducts which, in the presence of strong base,
s
sulfone (1e) eliminate HCl relatively slowly. Additionally, when
generated at low temperature, they can be protonated with
aqueous strong acids at position bearing NO2 group, followed by
spontaneous elimination of HNO2 leading to the cine substitution of
nitro group [12]. It was expected that diazonium salt would capture
such ortho s
H-adducts when added prior to base, although further
effect of the base added was difficult to predict. For the reaction of
1e with 4-substituted nitrobenzenes 2, initially applied condition F
was found to be ineffective and complex mixtures of products were
obtained. Better results were achieved when the reactions were
carried out in DMF at ꢁ40 ꢀC and, after addition of Et3N, finished at
room temperature (Table 2, condition I). A short series of reactions
showed that the expected products 7 were formed and the VNS
process did not occur to a noticeable extent. However, in some
cases another unpredicted product 8 (Fig. 1) was created in a
quantity comparable to main product 7 (Scheme 4). Addition of the
diazonium cation to the
s
H-adduct can occur at the partially
negatively charged position ipso or meta to the nitro group. In the
former case, the subsequent elimination of HNO2 but not HCl took
place yielding 7. This demonstrates that rearomatization of the ring,
as a result of NO2 anion departure, is energetically more favorable
than formation of exo-double bond by elimination of HCl.
Scheme 5. Formation of indazoles 13 from nitroarenes 1 and diazonium salts 3.
4

ꢀ
Z. Wrobel, B. Wilk and A. Kwast
Tetrahedron xxx (xxxx) xxx
Table 3
phenylpropanenitrile
phenyldiazene (6a)
(5a)
[19]
[4b],
and
1-(4-bromophenyl)-2-
1-(4-bromophenyl)-2-(2-
Reaction of secondary carbanions with nitroarenes and 3a under condition Ha.
methoxyphenyl)diazene (6b) [19] were identified on the basis of
Entry
CH-acid
Y
Nitroarene
X
Indazole 13
Yieldb
23
the published 1H NMR and MS spectra which were matching.
R
1
2
%
1
2
3
4
5
CN
CN
CN
CN
H
H
H
1f
1f
1f
1g
1h
H
2a
2g
2f
2e
2g
13a
13b
13c
13d
13b
4.2. General procedure for the reactions of CH-acids 1 with
nitroarenes 2 and diazonium salts 3
4-Cl
4-CF3
2,4-Cl2
4-Cl
52
15
36
32
4-OMe
H
TolSO2
The initial and final temperatures, solvents and the added base
are given in Table 1.
a
See Table 1.
Isolated yield.
b
A solution of t-BuOK (112 mg, 1.0 mmol) in dry THF (10.0 mL) or
in dry DMF (6.0 mL) was cooled down under nitrogen to the tem-
perature specified for a particular variant. To that mixture, a solu-
tion of the carbanion precursor 1 (1.0 mmol) in THF (1.0 mL) or DMF
(1.0 mL) was added dropwise, followed by the addition of the
nitroarene 2 (1.0 mmol) in the same manner. The mixture was
stirred at that temperature for 5 min, then a solution of diazonium
When in the reaction of 1f with 2g using weaker base Et3N
(condition F), the intermediate azo compound 12b (X ¼ 4-Cl, Ar1 ¼
Ph, Ar2 [] ¼ 4-BrC6H4) was isolated in 35% yield. Then, it was suc-
cessfully cyclized to 13b in almost quantitative yield under action of
t-BuOK, analogously to condition H.
tetrafluoroborate
3 (1.2 mmol) in cold N-methylpyrrolidone
To our best knowledge, such a transformation is unknown in the
literature so far, thus, it becomes a novel route for the synthesis of
aryl-substituted indazole scaffold.
(1.0 mL) was added over ca 3e4 s. The mixture was stirred for
5 min, then neat Et3N (0.5 mL) or a solution of t-BuOK (112 mg,
1.0 mmol) in THF (2.0 mL) was added. After 5 min the reaction was
quenched by pouring the mixture into saturated aqueous NH4Cl
(50 mL) or, prior to that, the cooling bath was removed and the
mixture was allowed to reach room temperature. After the quench,
the resulting mixture was diluted with water (200 mL) and
extracted with EtOAc (3 ꢂ 50 mL). The extracts were washed with
water (3 ꢂ 100 mL) and dried with Na2SO4. For the results shown in
Table 1, to a 1/10 part of the products solution was added an
appropriate amount of diphenylmethyl phenyl sulfone as an in-
ternal standard and the GC analysis was performed. For preparative
purposes, the dried solution was evaporated and the residue was
separated by column chromatography (SiO2, hexane/DCM). For
analytical purposes, the solid products were recrystallized from i-
PrOH or hexane/EtOAc.
3. Conclusion
The nucleophilic reactivity of unstable s
H-adducts formed from
stabilized carbanions and substituted nitrobenzenes, so far limited
to reactions with protons and bromine, has been extended to the
reactions with diazonium salts forming new CeN bonds. The
coupling takes place preferentially at carbon atom bearing the nitro
group or, in certain cases, also at other conjugated position. Less
crowded adducts of secondary carbanions stabilized by cyano or
sulfonyl groups are formed at ortho positions of nitrobenzenes and
cyclize to substituted indazoles as a result of departure of those
stabilizing groups. Carbanion generated from 1-chloroethyl phenyl
sulfone, suitable for the VNS reaction with nitrobenzenes, forms
ortho s
H-adducts that add diazonium cations at carbon bearing the
4.2.1. 2-{4-[(4-Bromophenyl)diazenyl]phenyl}-2-
phenylpropanenitrile 4a
nitro group and, in case of ortho-substituted nitrobenzenes, also at
the conjugated meta position. The subsequent elimination of HCl
leads to azo compounds retaining the nitro group in its original
position.
Obtained from 1a, 2a and 3a, condition A. Yield: 207 mg (53%);
orange crystals, mp. 132e133 ꢀC. 1H NMR (500 MHz, CDCl3)
d 2.15
(s, 3H), 7.31e7.43 (m, 5H), 7.52e7.55 (m, 2H), 7.63e7.67 (m, 2H),
7.78e7.81 (m, 2H), 7.88e7.91 (m, 2H); 13C NMR (125 MHz, CDCl3)
4. Experimental section
d 28.1, 46.1,123.0,123.3,124.4, 125.7,126.6,127.5,128.2,129.0,132.4,
140.7, 144.2, 151.2, 151.8; MS (EI) m/z 392 (18), 391 (55), 390 (17),
389 (55, [M]þ), 206 (100), 190 (38), 155 (51), 157 (50); HRMS (EI) m/
z calcd for C21H16N739Br 389.0528; found, 389.0526.
4.1. General remarks
Melting points were recorded in open capillary and are uncor-
rected. The 1H and 13C NMR spectra of all compounds studied were
measured at temperature 298 K in CDCl3 or deuterated dimethyl
sulfoxide (DMSO-d6) solutions with a Varian vnmrs-600 or Varian
vnmrs-500 using tetramethylsilane (TMS) as the internal standard.
Mass spectra (EI, 70 eV) were obtained on an AutoSpec Premier
(Waters) spectrometer. For ESIþ and ESI- measurements, a Maldi
SYNAPT G2-S HDMS (Waters) was used. Accurate mass measure-
ments were obtained using magnetic sector mass analyzer (EI) or
TOF analyzer (ESI). Silica gel Merck 60 (230e400 mesh) was used
for column chromatography. GC analyses were performed on a
Hewlett Packard HP6890 GC system with HP5 column and FID
(carrier gas e helium) THF was distilled from sodium/benzophe-
none ketyl prior to use. DMF was dried over CaH2, distilled and
stored over molecular sieves.
4.2.2. 2-{4-[(4-Nitrophenyl)diazenyl]phenyl}-2-
phenylpropanenitrile 4b
Obtained from 1a, 2a and 3b, condition F. Yield: 150 mg (42%);
orange crystals, mp. 145e146 ꢀC; 1H NMR (500 MHz, CDCl3)
d 2.16
(s, 3H). 7.33e7.44 (m, 5H), 7.56e7.60 (m, 2H), 7.95e7.98 (m, 2H),
8.02e8.05 (m, 2H), 8.37e8.41 (m, 2H); 13C NMR (125 MHz, CDCl3)
d
28.0, 48.2,122.8,123.5,123.8,124.7,126.6,127.7,128.3,129.1,140.5,
145.4, 148.9, 151.7, 155.5; MS (EI) m/z 356 (67, [M]þ), 206 (100), 190
(28); HRMS (EI) m/z calcd for
C21H16N4O2 356.1273; found,
356.1273.
4.2.3. 2-{4-[(3-Nitrophenyl)diazenyl]phenyl}-2-
phenylpropanenitrile 4c
Obtained from 1a, 2a and 3c, condition F. Yield: 167 mg (47%);
Sulfone 1d [17] and 1e [18] were obtained following published
procedures. Remaining compounds 1, nitroarenes 2 and diazonium
salts 3 were commercial reagents and were used without additional
purification.
red oil. 1H NMR (500 MHz, CDCl3)
d 2.16 (s, 3H), 7.32e7.44 (m, 5H),
7.56e7.59 (m, 2H), 7.72 (t, J ¼ 8.1 Hz, 1H), 7.95e7.97 (m, 2H),
8.24e8.27 (m, 1H), 8.32e8.35 (m, 1H), 8.73 (t, J ¼ 2.1 Hz, 1H). 13
C
NMR (125 MHz, CDCl3)
d 28.0, 46.2, 117.1, 122.9, 123.7, 125.2, 126.6,
The
known
by-products:
2-(4-nitrophenyl)-2-
127.7, 128.2, 129.1, 129.3, 130.0, 140.5, 145.1, 149.0, 151.4, 152.9; MS
5

ꢀ
Z. Wrobel, B. Wilk and A. Kwast
Tetrahedron xxx (xxxx) xxx
(EI) m/z 356 (59, [M]þ), 206 (100), 190 (35); HRMS (EI) m/z calcd for
(m, 2H), 7.62e7.65 (m, 2H), 7.76e7.79 (m, 2H), 7.84e7.88 (m, 2H);
C
21H16N4O2 356.1273; found, 356.1278.
13C NMR (125 MHz, CDCl3)
d 28.0, 57.9, 81.7, 123.0, 124.3, 125.3,
127.2, 128.5, 128.6, 129.4, 132.3, 138.7, 142.6, 151.36, 151.41, 171.15;
4.2.4. 2-{4-[(4-Methoxyphenyl)diazenyl]phenyl}-2-
phenylpropanenitrile 4d
MS (EI) m/z 452 (13), 450 (13, [M]þ), 351 (64), 349 (62), 165 (60), 57
79
(100); HRMS (ESI) m/z calcd for C
H
24 23
BrN2O2, [M]þ 4500943;
Obtained from 1a, 2a and 3d, condition F. Yield: 106 mg (31%);
found, 450.0939.
orange crystals, mp. 98e100 ꢀC. 1H NMR (500 MHz, CDCl3)
d 2.14 (s,
3H), 3.89 (s, 3H), 6.99e7.03 (m, 2H), 7.31e7.35 (m, 1H), 7.36e7.42
(m, 4H), 7.50e7.53 (m, 2H), 7.84e7.88 (m, 2H), 7.90e7.93 (m, 2H);
4.2.10. tert-Butyl {4-[(4-bromophenyl)diazenyl]-3-
chlorophenyl}(phenyl)acetate 4j
13C NMR (125 MHz, CDCl3)
d
28.1, 46.1, 55.6, 114.3, 122.9, 123.1,
Obtained from 1c, 2d and 3a, condition C. Yield: 199 mg (41%);
124.9, 126.6, 127.4, 128.1, 129.0, 140.9, 143.1, 146.9, 151.1, 162.3.
HRMS (ESI) m/z calcd for C22H20N3O, [MþH]þ 342.1606; found,
342.1608.
red oil. 1H NMR (500 MHz, CDCl3)
d
1.51 (s, 9H), 4.98 (s, 1H),
7.32e7.42 (6H), 7.56e7.57 (m, 1H), 7.67e7.71 (m, 3H), 7.85e7.88 (m,
2H); 13C NMR (125 MHz, CDCl3)
28.0, 57.6, 82.0, 117.4, 124.7, 126.0,
d
127.5, 127.7, 128.5,128.8,130.9, 132.4, 135.7, 138.0, 143.7, 147.4, 151.5,
4.2.5. 2-{4-[(4-Bromophenyl)diazenyl]-3-methoxyphenyl}-2-
phenylpropanenitrile 4e
170.6; MS (EI) m/z 486 (7), 484 (5, [M]þ), 351 (64), 385 (100), 383
79
(83), 165 (50); HRMS (ESI) m/z calcd for C
H
24 22
Br35ClN2O2, [M]þ
Obtained from 1a, 2b and 3a, condition H. Yield: 176 mg (42%);
484.0553; found, 484.0544.
orange crystals, mp.121e122 ꢀC. 1H NMR (600 MHz, CDCl3)
d 2.13 (s,
3H), 3.98 (s, 3H), 6.98 (dd, J ¼ 8.4, 2.0 Hz, 1H), 7.13 (d, J ¼ 1.8 Hz, 1H),
4.2.11. 1-(4-Bromophenyl)-2-{4-[1-(4-chlorophenyl)-1-
(phenylsulfonyl)ethyl]phenyl}diazene 4k
7.31e7.35 (m, 1H), 7.36e7.42 (m, 4H), 7.60e7.63 (m, 3H), 7.75e7.78
(m, 2H); 13C NMR (150 MHz, CDCl3)
d
28.0, 46.4, 56.5, 111.6, 117.4,
Obtained from 1d, 2a and 3a, condition F. Yield: 167 mg (31%);
119.0, 122.9, 124.5, 125.4, 126.6, 128.2, 129.0, 132.3, 140.5, 141.4,
145.8, 151.7, 157.1; MS (EI) m/z 421 (50), 419 (49, [M]þ), 264 (35),
249 (40), 206 (100); HRMS (EI) m/z calcd for C22H18N739Br 419.0633;
found, 419.0637.
orange crystals, mp. 149e150 ꢀC (hexane/EtOAc); 1H NMR
(500 MHz, CDCl3)
d 2.12 (s, 3H), 7.27e7.32 (m, 4H), 7.38 (d,
J ¼ 7.4 Hz, 2H), 7.38 (d, J ¼ 8.6 Hz, 2H), 7.50 (t, J ¼ 7.4 Hz, 1H),
7.62e7.67 (m, 4H), 7.80e7.83 (m, 4H); 13C NMR (125 MHz, CDCl3)
d
26.0, 74.6, 122.5, 124.4, 125.8, 128.2, 128.3, 130.3, 130.9, 132.4,
4.2.6. 2-{4-[(4-Bromophenyl)diazenyl]-2-chlorophenyl}-2-
phenylpropanenitrile 4f
133.6, 134.5, 136.1, 137.5, 141.9, 151.2, 151.8; HRMS (ESI) m/z calcd for
79
C
H
26 20
Br35ClN2O2SNa [MþNa]þ 561.0015; found, 561.0044.
Obtained from 1a, 2c and 3a, condition F. Yield: 132 mg (31%);
orange crystals, mp. 134e135 ꢀC. 1H NMR (500 MHz, CDCl3)
d
2.20
(s, 3H), 7.29 (m, 5H), 7.67e7.68 (m, 2H), 7.81e7.84 (m, 3H),
7.93e7.96 (m, 2H); 13C NMR (125 MHz, CDCl3)
29.3, 45.6, 121.3,
4.2.12. 1-(4-Bromophenyl)-2-(2-methoxyphenyl)diazene 6c
Obtained from 1a, 2b and 3a, condition F, as by-product along
with 4e. Yield 75 mg (26%); orange crystals, mp. 80e81 ꢀC. (lit[21]
d
122.4, 124.6, 124.9, 126.4, 127.8, 128.8, 128.9, 132.5, 135.5, 138.9,
140.4, 151.0, 152.7; MS (EI) m/z 425c(78), 423 (66, [M]þ), 240 (73),
190 (60), 183 (69), 155 (100); HRMS (ESI) m/z calcd for
81.5e82.5 ꢀC); 1H NMR (500 MHz, CDCl3)
d 4.02 (s, 3H), 7.01 (ddd,
J ¼ 8.0, 7.3, 1.2 Hz, 1H), 7.10 (dd, J ¼ 8.4, 1.2 Hz, 1H), 7.46 (dd, J ¼ 8.4,
7.3, 1.7 Hz, 1H), 7.61e7.64 (m, 2H), (dd, J ¼ 8.0, 1.7 Hz, 1H), 7.77e7.80
C
21H15N739Br35Cl 423.0138; found, 423.0137.
(m, 2H); 13C NMR (125 MHz, CDCl3)
d 56.3, 112.8, 116.9, 120.8, 124.4,
125.1, 132.2, 132.9, 142.1, 151.8, 157.1; MS (EI) m/z 292 (30), 290 (31,
4.2.7. 2-{4-[(4-Bromophenyl)diazenyl]phenyl}-3-methyl-2-
phenylbutanenitrile 4g
[M]þ), 186 (20), 185 (29), 184 (22), 183 (29), 157 (40), 155 (41), 135
79
(48), 77 (100); HRMS (ESI) m/z calcd forC
H
13 11
BrN2O [M]þ
Obtained from 1a, 2e and 3a, condition H. Yield: 142 mg (34%);
290.0055; found, 290.0065.
orange oil. 1H NMR (600 MHz, CDCl3)
d
1.11 (d, J ¼ 1.7 Hz, 3H), 1.12
(d, J ¼ 1.7 Hz, 3H), 2.97 (sep, J ¼ 1.7 H, 1H), 7.26e7.29 (m, 1H),
7.33e7.38 (m, 2H), 7.51e7.54 (m, 2H), 7.62e7.67 (m, 4H), 7.75e7.79
4.3. General procedure for the reaction of 1-chloroethyl phenyl
sulfone (1e) or phenylacetonitrile (1f) with nitroarenes 2 and
diazonium salts 3
(m, 2H), 7.85e7.89 (m, 2H); 13C NMR (150 MHz, CDCl3)
d 19.1, 34.9,
59.1, 120.4, 123.3, 124.4, 125.7, 126.7, 127.5, 127.8, 129.0, 132.3, 139.2,
124.9,151.2,151.5; MS (EI) m/z 419 (53), 417 (53, [M]þ), 377 (99), 375
(100), 192 (91)190 (72); HRMS (EI) m/z calcd for C23H20N739Br
417.0841; found, 417.0840.
A solution of t-BuOK (56 mg, 0.55 mmol) in dry DMF (6.0 mL)
was cooled down under nitrogen to ꢁ40 ꢀC. To that mixture, a
solution of 1e (102 mg, 0.5 mmol) in DMF (1.0 mL) was added,
followed by the addition of the nitroarene 2 (1.0 mmol) in DMF
(1.0 mL). The mixture was stirred at that temperature for 2 min then
a solution of diazonium tetrafluoroborate 3 (1.2 mmol) in cold N-
methylpyrrolidone (1.0 mL) was added over ca 3e4 s. Neat Et3N
(0.5 mL) was added, the cooling bath was removed and the mixture
was allowed to reach room temperature. The reaction was
quenched by pouring the mixture into saturated aqueous NH4Cl
(50 mL), the resulted mixture was diluted with water (100 mL),
extracted with EtOAc (3 ꢂ 30 mL). The extracts were washed with
water (3 ꢂ 70 mL) and dried with Na2SO4. The solution was evap-
orated and the residue was separated by column chromatography
on SiO2 using hexane/EtOAc mixtures as eluent.
4.2.8. 2-{4-[(4-Bromophenyl)diazenyl]-3-chlorophenyl}-2-
phenylpropanenitrile 4h
Obtained from 1b, 2a and 3a, condition H. Yield: 86 mg (20%);
orange crystals, mp. 90e92 ꢀC (i-PrOH); 1H NMR (500 MHz, CDCl3)
d
2.13 (s, 3H), 7.33e7.38 (m, 2H), 7.39e7.42 (m, 4H), 7.85 (d,
J ¼ 2.1 Hz, 1H), 7.64e7.69 (m, 3H), 7.82e7.85 (m, 2H); 13C NMR
(125 MHz, CDCl3) d 27.9, 45.9, 118.0, 122.5, 124.8, 125.9, 126.5, 128.4,
128.9, 129.2, 132.5, 135.9, 140.0, 145.3, 147.9, 151.4; MS (EI) m/z 425
(85), 423 (67, [M]þ), 240 (66), 183 (71), 155 (100); HRMS (EI) m/z
calcd for C21H15N739Br35Cl 423.0138; found, 423.0134.
4.2.9. tert-Butyl {4-[(4-bromophenyl)diazenyl]phenyl}(phenyl)
acetate 4i
4.3.1. 1-(4-Bromophenyl)-2-{2,4-dichloro-6-[1-chloro-1-
(phenylsulfonyl)ethyl]phenyl}diazene 7a
Obtained from 1c, 2a and 3a, condition D. Yield: 209 mg (51%);
orange crystals, mp.112e114 ꢀC. 1H NMR (500 MHz, CDCl3)
d
1.46 (s,
Obtained from 1e, 2e and 3a along with 8a. Yield: 79 mg (30%);
9H), 4.99 (s, 1H), 7.26e7.29 (m, 1H), 7.31e7.35 (m, 4H), 7.44e7.47
orange crystals, mp. 133e134 ꢀC; 1H NMR (500 MHz, CDCl3)
d 2.18
6

ꢀ
Z. Wrobel, B. Wilk and A. Kwast
Tetrahedron xxx (xxxx) xxx
79
(s, 3H), 7.48 (ddd J ¼ 8.3, 7.0, 0.5 Hz, 2H), 7.56 (dd, J ¼ 2.2, 0.5 Hz,
1H), 7.59 (dd, J ¼ 2.2, 0.5 Hz, 1H), 7.65e7.68 (m, 3H), 7.68e7.70 (m,
C H
Br 35Cl2N2O2S, [M]þ 495.9415; found, 495.9417.
20 15
4H); 13C NMR (125 MHz, CDCl3)
d 28.3, 86.0, 123.9, 124.6, 127.6,
128.6,130.1,131.5,131.7,132.3,132.4,132.7,132.9,134.7,150.0,150.6;
4.8. 1-(4-Bromophenyl)-2-{2-[1-chloro-1-(phenylsulfonyl)ethyl]-4-
fluorophenyl}diazene 7e
79
HRMS (ESI) m/z calcd for
C H
20 14
Br35Cl3N2O2SNa, [MþNa]þ
552.8923; found, 552.8897.
Obtained from 1e, 2h and 3a. Yield: 73 mg (30%); orange crys-
4.4. 1-(4-Bromophenyl)-2-{2,6-dichloro-3-nitro-4-[1-
(phenylsulfonyl)ethyl]phenyl}diazene 8a
tals, mp. 112e113 ꢀC; 1H NMR (500 MHz, CDCl3)
d 2.70 (s, 3H), 7.18
(ddd, J ¼ 9.2, 6.9, 2.7 Hz, 1H), 7.33e7.37 (m, 2H), 7.51e7.55 (m, 2H),
7.57e7.60 (m, 2H), 7.62e7.67 (m, 5H); 13C NMR (125 MHz, CDCl3)
Obtained from 1e, 2e and 3a along with 7a. Yield: 90 mg (33%);
d
28.8, 87.8, 117.9 (d, JFC ¼ 22.5 Hz), 119.1 (d, JFC ¼ 8.7 Hz), 120.1 (d,
orange crystals, mp. 132e133 ꢀC; 1H NMR (500 MHz, CDCl3)
d
1.79
JFC ¼ 26.6), 124.9, 126.0, 128.4, 131.2, 132.5, 133.4, 134.4, 134.5, 148.1
(d, J ¼ 7.0 Hz, 3H), 4.21 (q. J ¼ 7.0 Hz, 1H), 7.54e7.58 (m, 2H),
(d, JFC ¼ 3.5 Hz), 151.2, 163.1 (d, JFC ¼ 252 Hz); MS (EI) m/z (%) 482
7.68e7.74 (m, 5H), 7.83e7.85 (m, 2H), 7.93 (s, 1H); 13C NMR
(4), 480 (3), 343 (39), 341 (100), 339 (84), 304 (100), 224 (54);
79
(125 MHz, CDCl3)
d
15.6, 59.7, 118.8, 124.8, 127.7, 128.4, 128.91,
HRMS (EI) m/z calcd for C H
Br 35ClFN2O2S, [M]þ 479.9710; found,
20 15
128.94, 129.4, 129.5, 132.8, 134.6, 136.5, 149.0, 149.1, 150.7; HRMS
479.9711.
Br35Cl2N3O4SNa, [MþNa]þ 563.9163;
79
(ESI) m/z calcd for C
H
20 14
found, 563.9150.
4.9. {2-[(4-Bromophenyl)diazenyl]-5-chlorophenyl}(phenyl)
acetonitrile 12b
4.5. 1-{2,4-Dichloro-6-[1-chloro-1-(phenylsulfonyl)ethyl]phenyl}-
2-(4-nitrophenyl)diazene 7b
Obtained from 1f, 2g and 3a, condition F. Yield: 143 mg (35%);
orange crystals, mp. 142e143 ꢀC (i-PrOH); 1H NMR (600 MHz,
Obtained from 1e, 2e and 3b along with 8b. Yield: 68 mg (27%);
red crystals, mp. 186e187 ꢀC; 1H NMR (500 MHz, CDCl3)
d
2.25 (s,
CDCl3)
J ¼ 8.8, 1.8 Hz, 1H), 7.59 (d, J ¼ 1.8 Hz, 1H), 7.67e7.70 (m, 2H),
7.75e7.80 (m, 3H); 13C NMR (150 MHz, CDCl3)
36.8, 117.5, 119.3,
d 6.41 (s, 1H), 7.30e7.34 (m, 1H), 7.35e7.40 (m, 4H), 7.44 (dd,
3H), 7.47e7.51 (m, 2H), 7.56 (d, J ¼ 2.2 Hz, 1H), 7.59 (d, J ¼ 2.2 Hz,
1H), 7.65e7.71 (m, 3H), 7.96e7.99 (m, 2H), 8.42e8.44 (m, 2H); 13C
d
NMR (125 MHz, CDCl3)
131.5, 131.6, 132.6, 132.8, 133.1, 134.8, 149.7, 149.8, 154.7; MS (EI) m/z
(%) 499 (2), 497 (2), 358 (55), 356 (56), 323 (75), 321 (100); HRMS
(EI) m/z calcd for
d
27.8, 85.8, 123.6, 123.8, 124.9, 128.6, 130.6,
124.7, 126.6, 127.6, 128.3, 129.2, 129.3, 129.7, 132.6, 135.2, 137.6,
138.4, 146.6, 151.2; MS (EI) m/z 410 (70), 408 (50, [M]þ), 384 (29),
334 (32), 239 (100), 190 (82), 155 (51); HRMS (EI) m/z calcd for
79
C
H
Br35Cl3N3O4S, [M]þ 496.9771;
C
20H13N739Br35Cl 408.9981; found, 408.9981.
20 14
found,496.9775.
4.5.1. 1-{2,6-Dichloro-3-nitro-4-[1-(phenylsulfonyl)ethyl]phenyl}-
2-(4-nitrophenyl)diazene 8b
4.10. 2-(4-Bromophenyl)-3-phenyl-2H-indazole 13a
Obtained from 1e, 2e and 3b along with 7b. Yield: 66 mg (26%);
Obtained from 1f, 2a and 3a, condition H. Yield: 80 mg (23%);
red solid, mp. 121e122 ꢀC (i-PrOH) (lit [20] 118.6e119.3 ꢀC); 1H
orange crystals, mp. 180e182 ꢀC; 1H NMR (500 MHz, CDCl3)
d 1.79
(d, J ¼ 2.2 Hz, 3H), 4.23 (q. J ¼ 7.0 Hz, 1H), 7.55e7.59 (m, 2H),
NMR (500 MHz, CDCl3)
d
7.14 (ddd, J ¼ 8.5, 6.6, 0.8 Hz, 1H),
7.69e7.77 (m, 3H), 7.97 (s, 1H), 8.09e8.12 (m, 2H), 8.43e8.46 (m,
7.31e7.45 (m, 8H), 7.49e7.53 (m, 2H), 7.69 (d, J ¼ 8.5 Hz,1H), 7.78 (d,
2H); 13C NMR (125 MHz, CDCl3)
d
15.6, 59.7, 119.0, 124.0, 124.9,
J ¼ 8.7 Hz, 1H); MS (EI) m/z 350 (98), 348 (100, [M]þ), 268 (63), 134
79
128.5, 128.94, 128.95 129.5, 129.7, 134.7, 136.5, 148.4, 149.2, 150.1,
(37); HRMS (EI) m/z calcd for C H
BrN2, [M]þ 348.0262; found,
19 13
154.6; MS (EI) m/z (%) 508 (5), 369 (75), 367 (100), 122 (54); HRMS
348.0255.
35
(EI) m/z calcd for C
H
20 14
Cl2N4O6S, [M]þ 508.0011; found, 508.0023.
4.6. 1-(4-Bromophenyl)-2-[2-[1-chloro-1-(phenylsulfonyl)ethyl]-4-
4.11. 2-(4-Bromophenyl)-5-chloro-3-phenyl-2H-indazole 13b
(trifluoromethyl)phenyl]diazene 7c
Obtained from 1f, 2g and 3a, condition H, yield 199 mg (52%),
and from 1h, 2g and 3a, condition H; yield 123 mg (32%); creamy
crystals, mp. 178e179 ꢀC (i-PrOH). Obtained also by separate
cyclization of 12b according to the following procedure:
Obtained from 1e, 2f and 3a. Yield: 104 mg (39%); orange
crystals, mp. 146e147 ꢀC; 1H NMR (500 MHz, CDCl3)
d
2.72 (s, 3H),
7.35e7.39 (m, 2H), 7.53e7.63 (m, 4H), 7.68e7.76 (m, 5H), 7.86 (s,
1H); 13C NMR (125 MHz, CDCl3)
28.1, 87.6, 118.1, 123.3 (q,
d
To a cooled solution of azo compound 12b (41 mg, 0.1 mmol) in
dry THF (1.0 mL) was added at ꢁ78 ꢀC under nitrogen a solution of
t-BuOK (12 mg, 0.11 mmol) in dry THF (1.0 mL). The cooling bath
was then removed and the mixture was allowed to reach room
temperature. The mixture was poured into aqueous NH4Cl and
extracted with EtOAc (3 ꢂ 20 mL). The extract was washed with
water and brine and dried with Na2SO4. The solvent was evapo-
rated to dryness to obtain 13b (33 mg, 95%) as a pale pink solid,
pure by TLC and GC, identical with that obtained from 1f, 2g and 3a.
JFC ¼ 273 Hz), 125.2, 126.9, 127.7 (q, JFC ¼ 3.5 Hz), 128.4, 130.1 (q,
JFC ¼ 3.5 Hz), 131.2, 131.3 (q, JFC ¼ 32.9 Hz), 132.2, 132.7, 132.9, 134.5,
79
151.3, 153.8; HRMS (EI) m/z calcd for C
[MþNa]þ 552.9576; found, 552.9562.
H
Br 35Cl2F3N2O2SNa,
21 15
4.7. 1-(4-Bromophenyl)-2-{4-chloro-2-[1-chloro-1-
(phenylsulfonyl)ethyl]phenyl}diazene 7d
Obtained from 1e, 2g and 3a. Yield: 79 mg (32%); orange crys-
1H NMR (500 MHz, CDCl3)
3H), 7.50e7.53 (m, 2H), 7.66 (d, J ¼ 1.4 Hz, 1H), 7.72 (d, J ¼ 9.2 Hz,
1H); 13C NMR (125 MHz, CDCl3)
119.2, 119.3, 122.3, 122.4, 127.2,
d 7.28e7.34 (m, 5H), 7.39e7.46 (m,
tals, mp. 181e184 ꢀC; 1H NMR (500 MHz, CDCl3)
d 2.69 (s, 3H),
7.35e7.39 (m, 2H), 7.45 (dd, J ¼ 8.7, 2.2 Hz, 1H), 7.53e7.59 (m, 4H),
d
7.66 (s, 4H), 7.73 (d, J ¼ 2.2 Hz, 1H); 13C NMR (125 MHz, CDCl3)
128.4, 128.7, 128.9, 129.0, 129.1, 129.5, 132.2, 135.2, 138.9, 147.4; MS
d
28.7, 87.6,118.3,125.0,126.3,128.4,130.9,131.3, 132.5,133.0, 133.2,
(EI) 5 z 384 (100), 382 (83, [M]þ), 302 (22), 268 (26), 267 (26);
79
133.4, 134.5, 136.3, 150.0, 151.2; MS (EI) m/z (%) 498 (2), 496 (1), 359
(45), 357 (92), 355 (60), 322 (100), 320 (80); HRMS (EI) m/z calcd for
HRMS (EI) m/z calcd for C H
Br35ClN2, [M]þ 381.9872; found,
19 12
381.9869.
7

ꢀ
Z. Wrobel, B. Wilk and A. Kwast
Tetrahedron xxx (xxxx) xxx
(b) O.N. Chupakhin, V.N. Charushin, Tetrahedron Lett. 57 (2016) 2665e2672;
(c) O.N. Chupakhin, V.N. Charushin, H.C. van der Plas, Nucleophilic Aromatic
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427e459.
4.12. 2-(4-Bromophenyl)-3-phenyl-5-(trifluoromethyl)-2H-
indazole 13c
Obtained from 1f, 2f and 3a, condition H. Yield: 63 mg (15%);
creamy crystals, mp. 155e157 ꢀC (i-PrOH); 1H NMR (500 MHz,
ꢀ
[4] (a) M. Ma˛kosza, K. Stalinski, Pol. J. Chem. 73 (1999) 151e162;
ꢀ
(b) M. Ma˛kosza, K. Stalinski, Chem. Eur J. 3 (1997) 2025e2031;
CDCl3)
d 7.31e7.38 (m, 4H), 7.44e7.49 (m, 3H), 7.51e7.56 (m, 3H),
(c) W. Adam, M. Ma˛kosza, C.-G. Zhao, K. Surowiec, J. Org. Chem. 65 (2000)
1099e1101.
7.87 (d, J ¼ 9.2 Hz, 1H), 8.01 (s, 1H); 13C NMR (125 MHz, CDCl3)
[5] (a) M. Ma˛kosza, A. Kwast, J. Phys. Org. Chem. 11 (1998) 341e349;
(b) M. Ma˛kosza, K. Wojciechowski, Liebigs Ann. Recueil (1997) 1805e1816;
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(b) W. Danikiewicz, M. Ma˛kosza, J. Org. Chem. 56 (1991) 1283e1286;
d
118.9, 119.6 (q, J ¼ 5 Hz), 120.6, 122.7, 123,2 (q, J ¼ 3 Hz), 124,6 (q,
272 Hz), 124.9, (q, J ¼ 32 Hz), 125.0, 127.3, 128.6, 129.3, 129.6, 132.3,
137.6, 138.7, 149.3; MS (EI) m/z 486 (7), 484 (5, [M]þ), 385 (100), 383
79
(84), 165 (50); HRMS (ESI) m/z calcd for C
H
Br35F3N2, [M]þ [M]þ
20 12
ꢀ
(c) Z. Wrobel, Pol. J. Chem. 72 (1998) 2384e2388;
416.0136; found, 416.0139.
ꢀ
(d) Z. Wrobel, Eur. J. Org Chem. (2000) 521e525;
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(e) Z. Wrobel, A. Kwast, Synthesis (2010) 3865e3872.
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4.13. 2-(4-Bromophenyl)-5,7-dichloro-3-(4-methoxyphenyl)-2H-
indazole 13d
2087e2092.
ꢀ
[8] (a) J. Suwinski, ARKIVOC (i) (2017) 402e435;
ꢀ
ꢀ
(b) J. Suwinski, K. Swierczek, Tetrahedron 57 (2001) 1639e1662.
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J. Chem. Soc., Perkin Trans. 1 (2000) 995e998;
Obtained from 1g, 2e and 3a, condition H. Yield: 162 mg (36%);
creamy crystals, mp. 190e191 ꢀC; 1H NMR (500 MHz, CDCl3)
d 3.86
(b) T.D. Lash, V. Gandhi, J. Org. Chem. 65 (2000) 8020e8026.
[10] D. Antoniak, M. Barbasiewicz, Org. Lett. 21 (2019) 9320e9325.
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5473e5483.
(s, 3H), 6.94e6.97 (m, 2H), 7.21e7.24 (m, 2H), 7.32e7.35 (m, 2H),
7.37 (d, J ¼ 1.7 Hz, 1H), 7.51e7.54 (m, 2H), 7.55 (d, J ¼ 1.7 Hz, 1H); 13
C
NMR (125 MHz, CDCl3)
d 55.4, 114.7, 118.3, 120.7, 122.65, 122.66,
124.1,127.4,127.46,127.47,130.9,132.3,136.6,138.7,145.2,160.2; MS
_
[12] S. Błazej, A. Kwast, M. Ma˛kosza, Tetrahedron Lett. 45 (2004) 3193e3195.
[13] G.A. Russel, R.K. Norris, E.J. Panek, J. Am. Chem. Soc. 93 (1971) 5839e5845.
[14] (a) N.I. Blokhina, I.V. Shakhkel'dyan, Yu M. Atroshchenko, E.N. Alifanova,
S.S. Gitis, A. Ya Kaminskii, D.N. Moiseev, Russ. J. Org. Chem. 37 (2001)
401e403;
(EI) m/z (%) 450 (46), 448 (100), 446 (61); HRMS (ESI) m/z calcd for
79
C
H
20 13
Br35Cl2N2O, [M]þ 445.9588; found, 445.9590.
Declaration of competing interest
(b) YuM. Atroshchenko, N.I. Blokhina, I.V. Shakhkel’dyan, YuD. Grudtsyn,
S.S. Gitis, O.Ya Borbulevich, I.V. Blokhin, A.Ya Kaminskii, O.V. Shishkin,
V.F. Andrianov, Russ. J. Org. Chem. 36 (2000) 684e692;
(c) E.N. Alifanova, YuM. Atroshchenko, A.Ya Kaminskii, S.S. Gitis,
YuD. Grudtsyn, S.N. Nasonov, N.N. Alekhina, L.V. Illarionova, Zh. Org. Khim. 29
(1993) 1412e1418;
(d) I.V. Blokhin, Yu M. Atroshchenko, S.S. Gitis, E.N. Alifanova, A. Ya Kaminskii,
Yu D. Grudtsyn, Yu A. Efremov, V.F. Andrianov, N.I. Blokhina,
I.V. Shakhkel'dyan, Russ. J. Org. Chem. 32 (1996) 1480e1485;
(e) Z.V. Todres, G. Ts Ovsepyan, A. Yu Kosnikov, S.V. Lindeman, Yu
T. Struchkov, J. Org. Chem. USSR 26 (1990) 522e527.
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2021.132186.
[15] C. Galli, Chem. Rev. 88 (1988) 765e792.
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Divers. 19 (2015) 807e816.
[17] J.-L. Zhao, Sh-H. Guo, J. Qiu, X.-F. Gou, Ch-W. Hua, B. Chen, Tetrahedron Lett.
57 (2016) 2375e2378.
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8