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Petrosyan et al.
Pt electrodes (the anode and cathode were of 37.2 and 12.3 cm2,
respectively). In some cases, a mixture of azole (2 mmol) and its
salts (1 mmol) was used instead of azole itself (see Table 1 and 2).
Solution of Bu4NClO4 (0.022 M) served as a supporting electroꢀ
lyte. After passing of 2 F of electricity per 1 mol of arene, the
electrolysis was stopped, the solvent was evaporated on a rotary
evaporator at room temperature (25—30 Torr), and the residue
(due to elimination of two molecules of NP) lead to biꢀ
phenyl 13 (Scheme 6).
Scheme 6
1
was analyzed by H NMR. The current yields were determined
by calculation on the twoꢀelectron transformation of the starting
arene by comparison of the integral intensities of characteristic
singlets of the products (the protons of the OMe and Me groups)
and signals of tetrabutylammonium cation of the electrolyte salts
of known concentration (the protons of the CH2 and Me groups).
Examples of isolation of the target products, their spectral
characteristics, and elemental analysis data are given below.
1,3ꢀDimethoxyꢀ4ꢀ(tetrazolꢀ1(2)ꢀyl)benzenes (see Table 1,
entry 14). The residue after evaporation of the solvent (20—35 °C,
25 Torr) was treated with diethyl ether, the ethereal extract was
concentrated in vacuo, after chromatographic purification of the
residue on silica gel (benzene), a mixture of indicated isomers
was obtained (330 mg, 80%). Found (%): C, 62.15; H, 5.88;
N, 32.07. C9H10N4. Calculated (%): C, 62.05; H, 5.79; N, 32.16.
1H NMR, δ: 3.81—3.92 (m, 6 H, 2 MeO); 6.60—6.78 (m), 7.38
(d), 7.56 (d) (3 H, C6H3); 8.76, 9.34 (both s, 1 H each, H tetraꢀ
zole). The product isolated in entry 15 had the same spectrum.
1,3ꢀDimethoxyꢀ4ꢀ(3ꢀnitroꢀ1,2,4ꢀtriazolꢀ1ꢀyl)benzene. Simꢀ
ilar treatment of the dry residue (see Table 1, entry 12) led to the
target product (220 mg, 44%). Found (%): C, 54.98; H, 4.70;
N, 25.63. C10H10N4O2. Calculated (%): C, 55.04; H, 4.62;
N, 25.68. 1H NMR, δ: 3.85, 3.92 (both s, 3 H each, 2 MeO); 6.66
(d), 6.78 (s), 7.60 (d) (3 H, C6H3); 8.96 (s, 1 H, H triazole). The
reaction mixture obtained in entry 11 contained product with
the same spectrum.
AzH = NP
In conclusion, anodic azolation of isomeric 1,2ꢀ and
1,3ꢀDMB can be described in the framework of the same
mechanism as for azolation of 1,4ꢀDMB (see Scheme 1).
The structure of starting azoles, arenes, and the intermeꢀ
diately formed arenonium cations determine efficiency of
either step of the process. This is indicated by the absence
of the ipsoꢀbisaddition product of the type 7 in the azolaꢀ
tion of 1,3ꢀDMB or formation of products 11 only in the
azolation of 1,2ꢀDMB with the mixture of T and CL.
On the whole, the studied anodic azolation of 1,2ꢀ,
1,3ꢀ, and 1,4ꢀDMB proceeding through the formation of
arenonium cation of the ipsoꢀstructure as a key intermediꢀ
ate is very unusual electrochemical process, which should
be considered as electroinduced nucleophilic aromatic subꢀ
stitution proceeding through the formation of the Wheꢀ
land complex.
1,3ꢀDimethoxyꢀ4ꢀ(4ꢀnitropyrazolꢀ1ꢀyl)benzene. Similar
treatment of the dry residue (see Table 1, entry 9) led to the
target product (240 mg, 48%). Found (%): C, 60.63; H, 5.61;
N, 19.12. C11H12N3O2. Calculated (%): C, 60.54; H, 5.54;
N, 19.25. 1H NMR, δ: 3.85, 3.94 (both s, 3 H each, 2 MeO); 6.52
(d), 6.72 (s), 7.57 (d) (3 H, C6H3); 8.21, 8.81 (both s, 2 H,
H pyrazole). The reaction mixture obtained in entry 8 contained
product with the same spectrum.
Products from entries 1, 3—6 (see Table 1), and entry 1 (see
Table 2) were not isolate.
1H NMR spectra of reaction mixtures obtained in entries 1
and 3 exhibited the following signals, δ: 2.01, 2.11 (both s, 3 H
each, 2 Me); 3.84 (br.s, 6 H, 2 MeO); 5.81 (s, 1 H, H pyrazole);
6.51—6.61 (m, 3 H, C6H3), which were assigned to 1,3ꢀdiꢀ
methoxyꢀ4ꢀ(3,5ꢀdimethylpyrazolꢀ1ꢀyl)benzene based on analysis of
the simulated 1H NMR spectra of compounds using the ACDlabs
program. Such an approach has been used by us earlier.11
1H NMR spectra of reaction mixtures obtained in entries 4—6
(see Table 1) exhibited the following signals, δ: 3.84, 3.90 (both s,
3 H each, 2 MeO); 6.59 (d), 6.60 (s), 7.54 (d) (3 H, C6H3); 7.90,
8.60 (both s, 2 H, H triazole), which were assigned to 1,3ꢀdiꢀ
Experimental
1
H NMR spectra were recorded in the mixture DMSOꢀd6—
—CCl4 (1 : 1 v/v) on a Bruker ACꢀ300 spectrometer. Commerꢀ
cial DMP, T, TA, P, CL (Lancaster, purity 98—99%), 1,3ꢀDMB,
1,2ꢀDMB (Aldrich, purity 99%), and glacial acetic acid (pure
for analysis grade) were used in this work; NTA and NP were
synthesized according to the described procedures.9 Tetramethꢀ
ylꢀ and tetrabutylammonium salts of NP, NTA, and Т were
obtained according to the known procedure.10
1
methoxyꢀ4ꢀ(1,2,4ꢀtriazolꢀ1ꢀyl)benzene. H NMR spectra of reꢀ
Electrochemical experiments were performed using a source
of the direct current B5ꢀ50 according to the following proceꢀ
dure: a mixture of DMB (2 mmol), azole (3 mmol) with the
additive (if necessary) of AcOH (3 mmol) or CL (1 mmol) (see
Table 1 and 2) was dissolved in MeCN (45 mL) and subjected to
galvanostatic electrolysis (I = 50 mA) in an undivided cell with
action mixtures obtained in entry 1 (see Table 2) exhibited the
following signals, δ: 3.89, 3.91 (both s, 6 H, 2 MeO); 7.02 (m, 1 H,
H arom.); 7.35—7.50 (m, 1 H, H arom.); 7.62 (m, 1 H, H arom.);
8.81, 9.82 (both s, 1 H each, H tetrazole), which were assigned
to isomers 1,2ꢀdimethoxyꢀ4ꢀ(tetrazolꢀ1ꢀyl)benzene and 1,2ꢀdiꢀ
methoxyꢀ4ꢀ(tetrazolꢀ2ꢀyl)benzene.