Reactions of some arenes and pyrazoles in MeCN under conditions of undivided-cell electrolysis

Article abstract of DOI:10.1023/A:1014023310543

As exemplified for the first time by pyrazole and its 4-nitro and 3,5-dimcthyl derivatives, N-arylation of pyrazoles can be performed under conditions of undivided-cell amperostatic electrolysis (Pt electrodes, McCN) of systems containing the pyrazolate anion and (or) pyrazole, arene (benzene, 1,4-dimethoxybenzene, or xylene), and a supporting electrolyte. In the case of electrolysis involving 1,4-dimethoxybenzene as arene, N-arylation followed simultaneously three routes to form an ortho-substitution product (1,4-dimethoxy-2-(pyrazol-1-yl)benzene), an ipso-substitution product (4-methoxy-1-(pyrazol-1-yl)benzene), and an ipso-bisaddition product (1,4-dimethoxy-1,4-di(pyrazol-1-yl)cyclohexa-2,5-diene) in a total current yield of up to 50%. The acid-base properties of the pyrazolcs under study affect the ratio of the N-arylation products and govern the required composition of the starting reaction mixture. In the case of a stronger base, such as 3,5-dimethylpyrazole, N-arylation with 1,4-dimethoxybenzene occurred even in the pyrazole-arene-tetraalkylammonium perchlorate system, whereas N-arylation of 4-nitropyrazole (a weaker base) proceeded only in the presence of the pyrazolate anion or another base, viz., sym-collidine. Oxidation of arene to the radical cation is the key anodic reaction. Not only the pyrazolate anion, but also highly basic pyrazole or a solvate complex of weakly basic pyrazole with collidine can serve as a nucleophilic partner in subsequent transformations of these radical cations.

Full text of DOI:10.1023/A:1014023310543

1274
Russian Chemical Bulletin, International Edition, Vol. 50, No. 7, pp. 1274—1279, July, 2001
Reactions of some arenes and pyrazoles in MeCN under conditions
of undivided-cell electrolysis
V. A. Chauzov,« V. Z. Parchinsky, E. V. Sinelshchikova, and V. A. Petrosyan
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5328. E-mail: petros@cacr.ioc.ru
As exemplified for the first time by pyrazole and its 4-nitro and 3,5-dimethyl derivatives,
N-arylation of pyrazoles can be performed under conditions of undivided-cell amperostatic
electrolysis (Pt electrodes, MeCN) of systems containing the pyrazolate anion and (or)
pyrazole, arene (benzene, 1,4-dimethoxybenzene, or xylene), and a supporting electrolyte. In
the case of electrolysis involving 1,4-dimethoxybenzene as arene, N-arylation followed
simultaneously three routes to form an ortho-substitution product (1,4-dimethoxy-2-(pyrazol-
1-yl)benzene), an ipso-substitution product (4-methoxy-1-(pyrazol-1-yl)benzene), and an
ipso-bisaddition product (1,4-dimethoxy-1,4-di(pyrazol-1-yl)cyclohexa-2,5-diene) in a total
current yield of up to 50%. The acid-base properties of the pyrazoles under study affect the
ratio of the N-arylation products and govern the required composition of the starting reaction
mixture. In the case of a stronger base, such as 3,5-dimethylpyrazole, N-arylation with
1,4-dimethoxybenzene occurred even in the pyrazole—arene—tetraalkylammonium perchlor-
ate system, whereas N-arylation of 4-nitropyrazole (a weaker base) proceeded only in the
presence of the pyrazolate anion or another base, viz., sym-collidine. Oxidation of arene to the
radical cation is the key anodic reaction. Not only the pyrazolate anion, but also highly basic
pyrazole or a solvate complex of weakly basic pyrazole with collidine can serve as a
nucleophilic partner in subsequent transformations of these radical cations.
Key words: paired electrosynthesis, N-arylation, pyrazoles, azoles, azolate anions.
Scheme 1b
The data on the possibilities of electrochemical
N-arylation of azoles are scarce. One of the first publi-
cations was devoted to N-phenylation of 3-nitro-1,2,4-
triazole (hereinafter, nitrotriazole). It was found1 that
electrolysis of a system containing the tetramethylam-
monium salt (TMA) of nitrotriazole and benzene in
MeCN in an undivided cell equipped with Pt electrodes
afforded a mixture of isomers of N-phenylnitrotriazole
(Scheme 1a). The addition of nitrotriazole to the mix-
ture subjected to electrolysis led to an increase in the
yield of the target product, which was indicative of
O2N
O2N
N
N
+2e
2
2
+
H2
N
N
N
H
N
–
reduction of nitrotriazole (Scheme 1b) giving rise to an
additional amount of the corresponding N-anions.
1,4-Dimethoxybenzene (DMB) was also used as an
arylating agent.2 Electrolysis of a mixture containing the
TMA salt of nitrotriazole and DMB in MeCN appeared
to generate exclusively the ortho-substitution product in
the anode compartment of a divided cell. The forma-
tion of analogous products was also observed3 upon
electrolysis of a mixture containing tetrazole (or
5-phenyltetrazole), its tetrabutylammonium salt (TBA),
and DMB (or 1,3,5-trimethoxybenzene) in an undi-
vided cell. However, only a product of the replacement
of the methoxy group by the triazole fragment was
identified in the reaction mixture obtained by electroly-
sis of an equimolar mixture of 1,2,4-triazole (hereinaf-
ter, triazole) and DMB. The formation of N-arylation
products with substantially different structures upon elec-
trolysis of structurally similar azoles is evidence for the
ambiguity of the processes and indicates that they can
Scheme 1a
O2N
O2N
N
N
N
PhH
–e
N
N
N
–
O2N
O2N
N
N
N
–e
N
N
N
+
–H
H
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1215—1219, July, 2001.
1066-5285/01/5007-1274 $25.00 ©ꢀ2001 Plenum Publishing Corporation

Russ.Chem.Bull., Int.Ed., Vol. 50, No. 7, July, 2001
1275
Reactions of some arenes and pyrazoles
Scheme 2
simultaneously follow several alternative mechanisms.
This fact gave impetus to further studies in this field.
Since data on the behavior of genetically related pyrazoles
in analogous electrochemical reactions are lacking, we
chose these compounds as objects of our investigation,
which simultaneously opened up the possibility of ex-
tending essentially the experimental basis of these studies.
O2N
N
O2N
O2N
N
2 F
N
N
+
+ PhH
N
H
N
–
Bu4N+
Results and Discussion
ꢀ
Investigation of electrochemical N-arylation of
pyrazoles was carried out in the amperostatic mode in
an undivided cell with the use of Pt electrodes. These
conditions provided paired electrolysis involving the use
of the coupled cathodic-anodic processes.
respectively. The last-mentioned compound existed as
an approximately equimolar mixture of stereoisomers.
Scheme 3
The major aim of the present invstigation was to
reveal general regularities of N-arylation of azoles and
to elucidate the characteristic features of their behavior
associated with the structures of particular compounds.*
At this stage, a search for preparative procedures was
beyond the scope of our study. It should be noted that
electrolysis often affords a mixture of N-arylation prod-
ucts and, generally, each product is obtained in low
yield, some of them being hydrolytically unstable (see
below). For these reasons, we analyzed the resulting
reaction mixtures using a special procedure based on
1H NMR spectroscopy (see the Experimental section).
This approach allowed us not only to reliably establish
the formation of minor products labile under the condi-
tions of isolation (including those formed in the inter-
mediate stages of electrolysis), but also to obtain quanti-
tative information on the compositions of the final
reaction mixtures which provided the basis for estima-
tion of the current yields of individual products without
their isolation.
OMe
O2N
O2N
2 F
N
N
+
+
N
H
N
–
Me4N+
OMe
NO2
NO2
OMe N
N
N
N
MeO
N
N
N
NO2
N
+
+
MeO
OMe
OMe
NO2
!
"
Previously, it has been demonstrated1,3 that the
system containing azole, its tetraalkylammonium salt,
and arene is appropriate for use in electrochemical
N-arylation in an undivided cell. Actually, we found
that electrolysis of a solution of 4-nitropyrazole (herein-
after, nitropyrazole), its TBA salt, and benzene taken in
a molar ratio of 1 : 0.5 : 10 in MeCN afforded 4-nitro-
1-phenylpyrazole (1) in 7.5% current yield (Scheme 2).
However, electrolysis of the system consisting of
nitropyrazole, its TBA salt, and DMB taken in a molar
ratio 1 : 0.5 : 1 performed under the same conditions
gave an unexpected result. It was found that the solu-
tion obtained after electrolysis contained (Scheme 3) a
mixture of three N-arylation products, viz., ortho- and
ipso-substitution products and an ipso-bisaddition prod-
uct, namely, 1,4-dimethoxy-2-(4-nitropyrazol-1-yl)ben-
zene (2) (7% current yield), 4-methoxy-1-(4-nitro-
pyrazol-1-yl)benzene (3) (7%), and 1,4-dimethoxy-1,4-
di(4-nitropyrazol-1-yl)cyclohexa-2,5-diene (4) (27%),
The size of the tetraalkylammonium cation exerts
only a slight effect on the course of the reaction. Thus,
electrolysis with the use of the TMA salt of nitropyrazole
instead of TBA afforded products 2, 3, and 4 in 10, 8,
and 28% yields, respectively. However, a decrease in the
content of the nitropyrazole salt in the starting mixture
led to a change in the ratio of the final products. For
example, when nitropyrazole, its TMA salt, and DMB
were taken in a ratio of 1.25 : 0.25 : 1, compounds 2, 3,
and 4 were obtained in 8, 4, and 43% current yields,
respectively. It should be noted that products 2, 3, and
4 were not formed in the absence of nitropyrazole or its
TMA salt in this system. The reasons for this fact are
discussed below.
The reaction with the use of p-xylene instead of
DMB proceeded differently (according to the data from
1H NMR spectroscopy of the reaction mixture) to give
an N-benzylation product, viz., 1-p-methylbenzyl-4-
nitropyrazole (5), in low yield (the current yield was
3%) along with other compounds (Scheme 4).
* We believe that the solution of these problems will enable one
to found conditions and the scope of azoles promising for
preparative electrochemical N-arylation.
Both the published data and the above-considered
results of N-arylation of azoles assume the necessary

1276
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 7, July, 2001
Chauzov et al.
Scheme 4
performed under analogous conditions gave rise only to
the ipso-bisaddition product in 25% current yield.
Moreover, triazole possessing similar acid-base prop-
erties (pKa = 10.04, pKb = 2.45) in an analogous
reaction system produced only the ipso-bisaddition prod-
uct (34% current yield) although, according to the
published data,3 electrolysis under similar conditions
resulted only in the ipso-replacement of the methoxy
group in DMB by the 1-triazole fragment.
Based on the results obtained, some regularities of
the processes under study were revealed. Thus, it is
evident that oxidation of DMB (E1/2 = 1.25 V) rather
than of the azole substrate (E1/2 > 1.75 V) is the major
anodic reaction. Moreover, the adduct of highly basic
azoles with the radical cation of DMB is, apparently,
the key intermediate involved in subsequent conversions
giving rise to the final N-arylation products.
NO2
NO2
+
+
N
N
N
H
N
–
Me4N+
N
N
Me
NO2
2 F
+
Me
Me
#
Scheme 5
OMe
OMe
Me
N
N
H
2 F
Bu4NClO4
+
N
Me
N
H
OMe
OMe
Hence, it is not surprising that electrolysis of sub-
stantially less basic azoles, such as nitropyrazole
(pKa = 9.64, pKb = –2.0), nitrotriazole (pKa = 5.98,
pKb = –3.65), 3,5-dimethyl-4-nitropyrazole (hereinaf-
ter, dimethylnitropyrazole, pKa = 10.65, pKb = –0.45),
and tetrazole (pKa = 4.9, pKb = –2.68), in the absence
of the corresponding azole salts afforded N-arylation
products (the reaction mixtures were analyzed by
1H NMR spectroscopy) only in trace amounts. In the
case under consideration, the formation of the corre-
sponding N-anions at a cathode (see Scheme 1b) is,
apparently, suppressed by anodic generation of protons.
The above-considered conclusions were unexpect-
edly confirmed by electrolysis of reaction mixtures con-
taining sym-collidine as an additive. It appeared that the
presence of this base in the electrolyte led to an increase
in the relative content of ipso-bisaddition products.
Moreover, it was demonstrated that the addition of
collidine made it possible to exclude the use of the
tetraalkylammonium salt of pyrazole (as a necessary
component of the reaction mixtures) in the case of
weakly basic and relatively acidic pyrazoles. Thus, in the
case of nitropyrazole (see above), electrolysis of a mix-
ture of nitropyrazole, TBAP, collidine, and DMB taken
in a molar ratio of 1.5 : 0.5 : 0.5 : 1 gave rise to products
2 and 4 in 4 and 52% current yields, respectively,
whereas electrolysis involving dimethylnitropyrazole in-
stead of nitropyrazole afforded the ipso-bisaddition prod-
uct in 28% current yield. An analogous effect was also
observed in reactions of other azoles. In the case of
nitrotriazole, the ipso-bisaddition product was obtained
in 10% current yield, whereas electrolysis involving
tetrazole afforded a mixture of isomeric ortho-substitu-
Me
Me
Me
MeO
N
N
N
N
OMe N
N
+
Me
MeO
Me
OMe
Me
$
%
involvement of tetraalkylammonium salts of azoles, which
simultaneously serve as the supporting electrolyte and
the donor of N-anions of azoles. Apparently, this fact
hinders the involvement of weakly acidic pyrazoles
(pKa > 10)* in N-arylation because salts of these pyrazole
are readily hydrolyzed and carboxylated in the course of
the synthesis, storage, and use. However, we demon-
strated that N-arylation with the use of rather highly
basic pyrazoles proceeded in the absence of the pyrazole
salt as well. In these case, tetrabutylammonium per-
chlorate (TBAP) served as the supporting electrolyte.
Thus, electrolysis of a mixture of 3,5-dimethylpyrazole
(hereinafter, dimethylpyrazole) (pKa = 15.0, pKb = 4.06),
TBAP, and DMB (taken in a molar ratio of 1 : 0.5 : 1) in
MeCN afforded ortho-substitution (6) and ipso-bis-
addition (7) products in 28 and 16% current yields,
respectively (Scheme 5). It should be noted that
N-arylation of pyrazole (pKa = 14.21, pKb = 2.48)
* The pKa and pKb values for azoles given below were published
in the literature.4

Russ.Chem.Bull., Int.Ed., Vol. 50, No. 7, July, 2001
1277
Reactions of some arenes and pyrazoles
tion products similar to that formed in the reaction with
the use of the TBA salt of tetrazole instead of collidine.3
Therefore, the reactions under consideration involved,
apparently, solvate complexes of azoles with collidine or
other proton acceptors formed through a hydrogen bond
rather than azolate anions (which are virtually absent in
the reaction mixture) or azoles, as such, (weakly basic
azoles did not form N-arylation products; see above) as
nucleophiles reacting with radical cations of 1,4-di-
methoxybenzene. Based on the data on the regularities
of N-arylation in the absence of azole salts in the
reaction mixture, the following sequence of the key
stages of this processes can be suggested (Scheme 6).
with free pyrazole is, apparently, favorable for maintain-
ing the current concentration of the nitropyrazolate
anion at the optimum level due to its generation from
nitropyrazole at a cathode.
In conclusion, it should be noted that our studies
demonstrated for the first time the possibility of forma-
tion of a broad spectrum of products upon electro-
chemical N-arylation of azoles. In our opinion, the fact
that the ipso- and ortho-substitution products and
ipso-bisaddition products are structurally similar to the
products obtained by electrochemical cyanation of DMB5
is of fundamental importance. We believe that this fact
is unambiguous evidence for the generality of the pro-
cesses under consideration. For this reason, our further
efforts will focus on elucidation of conditions and pre-
requisites for the predominant formation of products
with particular structures, which can allow one to refine
the mechanisms of these processes and to search for
optimum condition of their preparative synthesis.
Scheme 6
Anode:
e
ArH
Solution:
–
ArH
Experimental
(AzH)
n
The 1H NMR spectra of solutions of specimens in the
DMSO-d6—CCl4 mixture (1 : 1 v/v) were recorded on a Bruker
AC-300 instrument.
+
–(AzH)
•H
n–1
ArH
AzArH
AzH•Sol
Amperostatic electrolysis of the reagents, supporting salts,
and additives dissolved in MeCN was performed in a 45-mL
glass undivided temperature-controlled (20—21 °C) cell equipped
with a magnetic stirred and axially arranged cylindrical Pt
electrodes of sizes 12.3 cm2 (cathode) and 37.2 cm2 (anode). In
the course of electrolysis, the solution was deaerated with a
stream of argon. The required mode of the process was main-
tained using a B5-50 source of direct current and a coulometer
designed at the Special Design Office of the Institute of Or-
ganic Chemistry of the Russian Academy of Sciences.
+
–HSol
N-Arylation products
Cathode:
H+ + e → 0.5 H2
or
The redox characteristics of the specimens were determined
by cyclic voltammetry and by the rotating disk electrode method
using a PI-50-1.1 potentiostat equipped with a PR-8 program-
ming device. In both cases, 2-mm Pt wire pressed into Teflon
was used as the working electrode. An aqueous saturated calomel
electrode, which was separated from the solution under exami-
nation by a salt bridge filled with a solution of the supporting
electrolyte (a 0.1 M solution of TBAP in MeCN), was used as
the reference electrode.
The specimen of TBAP was prepared by the exchange
reaction of the corresponding bromide with NaClO4 followed
by recrystallization from ethanol. The TBA and TMA salts of
nitropyrazole were synthesized according to a general proce-
dure.3 1,4-Dimethoxybenzene, pyrazole, dimethylpyrazole,
triazole, and tetrazole (98—99% purity) were purchased from
Lancaster. Nitrotriazole,6 nitropyrazole,7 and dimethyl-
nitropyrazole7 were prepared according to procedures reported
previously. The solvent MeCN was purified and dried by
refluxing and distillation over KMnO4 and double distillation
over P2O5 followed by distillation over calcined K2CO3.
Electrolysis (general procedure). The reaction mixture of
the given composition was dissolved in anhydrous MeCN
(45 mL) and placed in a cell. Electrolysis was carried out under
an atmosphere of argon at a controlled current by passing 2 F of
electricity per mole of arene. After completion of electrolysis,
the solvent and the low-boiling reagents were distilled off on a
rotary evaporator at ≤ 100 °C and the residue was analyzed by
[HSol]+ + e → 0.5 H2 + Sol,
ArH is 1,4-dimethoxybenzene;
AzH is pyrazole, 4-nitropyrazole, 3,5-dimethylpyrazole,
3,5-dimethyl-4-nitropyrazole, 1,2,4-triazole,
3-nitro-1,2,4-triazole, or tetrazole;
Sol is collidine.
From the aforesaid it follows that the reactions
presented in Schemes 1a,b reflect only one of the
possible routes leading to N-arylation products. Thus,
electrolysis of a mixture of the readily oxidized TMA
salt of nitropyrazole (E1/2 = 0.81 V) and DMB
(E1/2 = 1.25 V), unlike electrolysis of a system consist-
ing of the TMA salt of nitrotriazole and DMB,2 af-
forded only resinous products. Therefore, the process
depends on the nature of the N anion. The concentra-
tion of the readily oxidized nitropyrazolate anion in the
reaction mixture needs be only as high as that sufficient
for N-arylation to proceed through the reaction of this
anion with the radical cation of DMB, but it must be
lower than that at which electrooxidation of the
nitropyrazolate anion becomes the major process. It
should be noted that under the conditions of paired
electrolysis, the combination of the pyrazolate anion

1278
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 7, July, 2001
Chauzov et al.
1H NMR spectroscopy. The current yields were determined
with respect to the two-electron conversion of the arene loaded*
by comparing the integral intensities of the signals of the
products (the CH protons of the azole and aromatic fragments
and the protons of the OCH3 groups), which were unambigu-
ously identified** and were observed (in most cases) as singlets,
and the intensities of the signals of the tetrabutyl- or tetra-
methylammonium cation of the supporting salt with the known
concentration (the protons of the CH2 and CH3 groups). It
should be noted that analysis of the composition of the reac-
tion mixture thus performed made it possible to found
ipso-bisaddition products, which have not been detected previ-
ously in the case of N-arylation of azoles with DMB2,3 due,
apparently, to their tendency to undergo hydrolysis giving rise
to hemiketals (and then azole, methanol, and 1,4-benzoquinone)
in the course of isolation and purification.
Electrolysis of a mixture of nitropyrazole, the TBA salt of
nitropyrazole, and benzene (p-xylene). A solution of nitro-
pyrazole (2 mmol), the TBA salt of nitropyrazole (1 mmol),
and benzene (p-xylene) (20 mmol) in anhydrous MeCN (45 mL)
was placed in a cell and electrolysis was carried out at a current
of 250 mA. After completion of electrolysis, the reaction mix-
ture was treated according to a standard procedure and ana-
lyzed by 1H NMR spectroscopy, which showed that 4-nitro-1-
phenylpyrazole8 (1) was obtained as the final product (the
current yield was 7.5%). 1H NMR, δ: 7.42 (t, 1 H, CH arom.);
7.53 (t, 2 H, CH arom.); 7.94 (d, 2 H, CH arom.); 8.36 and
9.55 (both s, 1 H each, CH of pyrazole).
1 H each, CH of pyrazole). 1H NMR of compound 4a, δ: 3.28
(s, 6 H, CH3O); 6.60 (s, 4 H, C6H4); 8.17 and 9.00 (both s,
1 H each, CH of pyrazole). 1H NMR of compound 4b, δ: 3.33
(s, 6 H, CH3O); 6.73 (s, 4 H, C6H4); 8.11 and 8.94 (both s,
1 H each, CH of pyrazole).
Electrolysis of a mixture of dimethylpyrazole, TBAP, and
DMB. A solution of dimethylpyrazole (2 mmol), TBAP
(1 mmol), and DMB (2 mmol) in MeCN (45 mL) was placed
in a cell and electrolysis was carried out at a current of 50 mA.
The reaction mixture was treated as described above and ana-
1
lyzed by H NMR spectroscopy, which showed that the reac-
tion afforded 1,4-dimethoxy-2-(3,5-dimethylpyrazol-1-yl)ben-
zene (6) (the current yield was 28%) and a mixture (∼1 : 1) of
stereoisomers of 1,4-dimethoxy-1,4-di(3,5-dimethylpyrazol-
1-yl)cyclohexa-2,5-diene (7a,b) (16%). 1H NMR of compound
6, δ: 2.14 and 2.20 (both s, 6 H, 2 CH3); 3.70 and 3.78 (both s,
6 H, 2 CH3O); 5.90 (s, 1 H, CH of pyrazole); 6.81 (m, 1 H,
CH arom.); 6.97—7.07 (m, 2 H, CH arom.). 1H NMR of
compound 7a, δ: 2.08 and 2.10 (both s, 6 H, 2 CH3); 3.13 (s,
6 H, CH3O); 5.85 (s, 1 H, CH of pyrazole); 6.40 (s, 4 H,
1
C6H4). H NMR of compound 7b, δ: 2.44 and 2.45 (both s,
6 H, 2 CH3); 3.19 (s, 6 H, CH3O); 5.88 (s, 1 H, CH of
pyrazole); 6.50 (s, 4 H, C6H4).
In the case of electrolysis of a mixture of pyrazole, TBAP,
and DMB performed under analogous conditions, a mixture
(∼1 : 1) of stereoisomers of 1,4-dimethoxy-1,4-di(pyrazol-
1-yl)cyclohexa-2,5-diene (8a,b) was detected (the current yield
was 25%). 1H NMR of compound 8a, δ: 3.13 (s, 6 H, CH3O);
6.33 (t, 1 H, CH of pyrazole); 6.53 (s, 4 H, C6H4); 7.47 and
Electrolysis with the use of p-xylene instead of benzene was
carried out analogously. Among the reaction products,
1-(p-methylbenzyl)-4-nitropyrazole (5) was identified (the cur-
1
7.93 (both d, 1 H each, CH of pyrazole). H NMR of com-
pound 8b, δ: 3.2 (s, 6 H, CH3O); 6.27 (t, 1 H, CH of pyrazole);
6.64 (s, 4 H, C6H4); 7.44 and 7.85 (both d, 1 H each, CH of
pyrazole).
1
rent yield was 3%). H NMR, δ: 2.55 (s, 3 H, CH3); 4.69 (s,
2 H, CH2); 7.10 (dd, 4 H, CH arom.); 8.30 and 9.10 (both s,
1 H each, CH of pyrazole).
In the case of electrolysis of a mixture of triazole, TBAP,
and DMB performed under analogous conditions, a mixture
(∼1 : 1) of stereoisomers of 1,4-dimethoxy-1,4-di(1,2,4-triazol-
1-yl)cyclohexa-2,5-diene (9a,b) was detected (the current yield
was 34%). 1H NMR of compound 9a, δ: 3.20 (s, 6 H, CH3O);
6.59 (s, 4 H, C6H4); 7.92 and 8.72 (both s, 1 H each, CH of
triazole). 1H NMR of compound 9b, δ: 3.30 (s, 6 H, CH3O);
6.70 (s, 4 H, C6H4); 7.88 and 8.61 (both s, 1 H each, CH of
triazole).
Electrolysis of a mixture of nitropyrazole, TBAP, sym-col-
lidine, and DMB. A solution of nitropyrazole (3 mmol), TBAP
(1 mmol), collidine (1 mmol), and DMB (2 mmol) in MeCN
(45 mL) was placed in a cell and electrolysis was carried out at
a current of 50 mA. After completion of electrolysis, the
reaction mixture was treated as described above and analyzed
by 1H NMR spectroscopy, which showed that the reaction
afforded compound 2 (the current yield was 4%) and a mixture
(∼1 : 4) of stereoisomers 4a,b (52%).
Electrolysis of a mixture of nitropyrazole, the TMA salt of
nitropyrazole, and DMB. A solution of nitropyrazole (2 mmol),
the TMA salt of nitropyrazole (1 mmol), and DMB (2 mmol)
in MeCN (45 mL) was placed in a cell and electrolysis was
carried out at a current of 50 mA. After completion of elec-
trolysis, the reaction mixture was treated as described above
and analyzed by 1H NMR spectroscopy, which showed that the
reaction afforded 1,4-dimethoxy-2-(4-nitropyrazol-1-yl)benzene
(2) (the current yield was 10%), 4-methoxy-1-(4-nitropyrazol-
1-yl)benzene (3) (8%), and a mixture (∼1 : 1) of stereoisomers
of 1,4-dimethoxy-1,4-di(4-nitropyrazol-1-yl)cyclohexa-2,5-di-
ene (4a,b) (28%). 1H NMR of compound 2, δ: 3.79 and 3.91
(both s, 6 H, 2 CH3O); 7.04—7.20 (m, 2 H, CH arom.); 7.31
(m, 1 H, CH arom.); 8.30 and 9.02 (both s, 1 H each, CH of
1
pyrazole). H NMR of compound 3, δ: 3.85 (s, 3 H, CH3O);
7.05 and 7.85 (both d, 4 H, C6H4); 8.33 and 9.39 (both s,
In the case of electrolysis of a mixture of dimethyl-
nitropyrazole, TBAP, sym-collidine, and DMB performed un-
der analogous conditions, a mixture (∼1 : 3) of stereoisomers of
1,4-dimethoxy-1,4-di(3,5-dimethyl-4-nitropyrazol-1-yl)cyclo-
hexa-2,5-diene (10a,b) was detected (the current yield was
* In the case of electrolysis of nitropyrazole performed in the
presence of excess benzene and p-xylene, the current yield was
determined with respect to azole.
** The spectral characteristics of compounds 2—7 used for
identification are lacking in the literature and were determined
based on the results of analysis of the 1H NMR spectra of the
following structurally similar compounds using the ACD/labs
program: 3-nitro-1-phenyl-1,2,4-triazole,1 1,4-dimethoxy-
2-(3-nitro-1,2,4-triazol-1-yl)benzene,2 1,4-dimethoxy-2-(N-tet-
razolyl)benzene and 4-methoxy-1-(triazol-1-yl)benzene,3
1,1,4,4-tetramethoxycyclohexa-2,5-diene and 1,4-dicyano-1,4-
dimethoxycyclohexa-2,5-diene,5 and 4-nitro-1-phenyl- and
1-benzyl-4-nitropyrazoles.8
1
28%). H NMR of compound 10a, δ: 2.39 and 2.45 (both s,
6 H, 2 CH3); 3.25 (s, 6 H, CH3O); 6.52 (s, 4 H, C6H4).
1H NMR of compound 10b, δ: 2.32 and 2.45 (both s, 6 H,
2 CH3); 3.31 (s, 6 H, CH3O); 6.62 (s, 4 H, C6H4).
In the case of electrolysis of a mixture of nitrotriazole,
TBAP, sym-collidine, and DMB performed under analogous
conditions, a mixture of stereoisomers (or isomers with respect
to the N atom) of 1,4-dimethoxy-1,4-di(3-nitro-1,2,4-
triazolyl)cyclohexa-2,5-diene (11) was detected (the current

Russ.Chem.Bull., Int.Ed., Vol. 50, No. 7, July, 2001
1279
Reactions of some arenes and pyrazoles
yield was 10%). 1H NMR, δ: 3.36 and 3.41 (both s, 6 H,
CH3O); 6.72 and 6.84 (both s, 4 H, C6H4); 9.04 and 9.14
(both s, 1 H, CH of nitrotriazole).
nukleofil´noe zameshchenie" [Abstrs. of Papers, All-Union Conf.
on Aromatic Nucleophilic Substitution], Novosibirsk, 1989, 91
(in Russian).
3. Kai Hu, M. E. Niyazymbetov, and D. H. Evans, Tetrahedron
Lett., 1995, 36, 7027.
4. J. Catalan, J. L. M. Abbaud, and J. Elguero, Adv. Heterocycl.
Chem., 1987, 41, 250.
5. N. L. Weinberg, D. H. Marr, and C. N. Wu, J. Am. Chem.
Soc., 1975, 97, 1499.
6. L. I. Bagal, M. S. Pevzner, A. N. Frolova, and N. I.
Sheludyakova, Khim. Geterotsikl. Soedin., 1970, 259 [Chem.
Heterocycl. Compd., 1970 (Engl. Transl.)].
7. R. Hüttel, F. Büchele, and P. Jochum, Chem. Ber., 1955,
88, 1377.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 00-03-
32870a) and by the Russian Federation Government
Program "Leading Scientific Schools" (Project No. 00-
15-97328).
References
1. V. A. Petrosyan, M. E. Niyazymbetov, M. S. Pevzner, and
B. I. Ugrak, Izv. Akad. Nauk SSSR, Ser. Khim., 1988, 1643
[Bull. Acad. Sci. USSR, Div. Chem. Sci., 1988, 37, 1458
(Engl. Transl.)].
8. J. A. Burton, A. R. Katritzky, M. Konya, and H. O. Tarhan,
J. Chem. Soc., Perkin Trans 2, 1974, 389.
2. M. E. Niyazymbetov, L. V. Mikhal´chenko, and V. A.
Petrosyan, Tez. dokl. Vsesoyuzn. konf. "Aromaticheskoe
Received January 25, 2001;
in revised form March 7, 2001