Synthesis and electrochemical Reduction of 2,2′-diaryl-5,5,5′, 5′-tetramethyl-3,3′-bi(pyrrol-3-ylidene)-4,4′(5H,5′H) -dione 1,1′-dioxides

Article abstract of DOI:10.1134/S1070428010030176

2,2′-Diaryl-5,5,5′,5′-tetramethyl-3,3′-bi(pyrrol-3- ylidene)-4,4′(5H,5′H)-dione 1,1′-dioxides containing a carboxy, alkoxycarbonyl, or carbamoyl group in the para position of one or both benzene rings were synthesized. These compounds may be regarded as cyclic dinitrones with conjugated C=C bond. Mild aminolysis of carboxy groups in the title compounds may be used to introduce dinitrone fragments into oligonucleotide or polypeptide structures. Electrochemical reduction of the resulting amides involves reversible oneelectron transfer in the first step at a near-zero potential, which makes it possible to use the title compounds as electrochemically active labels in applied bioorganic electrochemistry.

Full text of DOI:10.1134/S1070428010030176

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2010, Vol. 46, No. 3, pp. 399–405. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © I.A. Khalfina, N.V. Vasil’eva, I.G. Irtegova, L.A. Shundrin, V.A. Reznikov, 2010, published in Zhurnal Organicheskoi Khimii, 2010,
Vol. 46, No. 3, pp. 405–411.
Synthesis and Electrochemical Reduction
of 2,2′-Diaryl-5,5,5′,5′-tetramethyl-3,3′-bi(pyrrol-3-ylidene)-
4,4′(5H,5′H)-dione 1,1′-Dioxides
I. A. Khalfinaa,b, N. V. Vasil’evaa, I. G. Irtegovaa, L. A. Shundrina, and V. A. Reznikova,b
a Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Division, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 9, Novosibirsk, 630090 Russia
e-mail: shundrin@nioch.nsc.ru
b Novosibirsk State University, Novosibirsk, Russia
Received November 11, 2008
Abstract—2,2′-Diaryl-5,5,5′,5′-tetramethyl-3,3′-bi(pyrrol-3-ylidene)-4,4′(5H,5′H)-dione 1,1′-dioxides contain-
ing a carboxy, alkoxycarbonyl, or carbamoyl group in the para position of one or both benzene rings were
synthesized. These compounds may be regarded as cyclic dinitrones with conjugated C=C bond. Mild aminol-
ysis of carboxy groups in the title compounds may be used to introduce dinitrone fragments into oligonu-
cleotide or polypeptide structures. Electrochemical reduction of the resulting amides involves reversible one-
electron transfer in the first step at a near-zero potential, which makes it possible to use the title compounds as
electrochemically active labels in applied bioorganic electrochemistry.
DOI: 10.1134/S1070428010030176
We previously reported [1, 2] on electrochemical
behavior of 2,2′-substituted 5,5,5′,5′-tetramethyl-3,3′-
bi(pyrrol-3-ylidene)-4,4′(5H,5′H)-dione 1,1′-dioxides I
(R = Me, Ph, t-Bu, CF3) which may be regarded as
cyclic dinitrones with conjugated C=C bond. Electro-
chemical reduction of dinitrones in dimethylforma-
mide and acetonitrile is an EE process including two
reversible steps which give rise to long-lived (at room
temperature) radical anions. The latter were charac-
terized by ESR spectroscopy.
(except for trifluoromethyl-substituted derivative) ap-
proach the range typical of redox potentials of ferro-
cene derivatives that are widely used in the recent time
as reporter groups** in oligonucleotides covalently im-
mobilized on the surface of modified microelectrodes
for electrochemical detection of DNA hybridization
[4, 5], in particular while developing DNA microchips
for gene diagnostics [6]. It is quite probable that
dinitrones functionalized at one R substituent may be
promising as reporter labels, which is important from
the viewpoint of extension of a set of reporter groups
with different characteristic potentials [7].
The potentials of the first one-electron reduction
peaks of dinitrones I in aprotic solvents are very small
in absolute value.* They become less negative as the
concentration of water in MeCN–H2O mixtures in-
creases and are close to zero in water (relative to a sat-
urated calomel electrode), and the first step of electro-
chemical reduction of dinitrones retains its reversible
and one-electron character [3]. The potentials of
electrochemical reduction of the examined dinitrones
O
R
Me
Me
O
N
N
Me
Me
O
R
O
I
* Electrochemical potentials of first reduction peaks of dinitrones I
(R = Me, Ph, t-Bu, CF3) are, respectively, –0.58, –0.55, –0.52,
and –0.18 V (relative to a saturated calomel electrode) at a plati-
num electrode in a 0.1 M solution of Et4NClO4, v = 0.1 V/s in
MeCN [2] and –0.14, –0.09, –0.08, and 0.19 V in a 0.1 M solu-
tion of LiClO4, v = 0.1 V/s in H2O [3].
R = Me, Ph, t-Bu, F3C, 4-HOCOC6H4, 4-EtOCOC6H4,
4-i-PrNHCOC6H4.
** Introduction of reporter groups (labels) into oligonucleotides
makes it possible to study them by spectrophotometric, electro-
chemical, and other methods.
399

KHALFINA et al.
400
Scheme 1.
R
O
O
R
R
O
Me
O
Me
Me
RCOOR', PhLi
or LiN(Pr-i)2
O
H+, H2O
Me
[O]
N
NH
N
Me
Me
Me
Me
Me
Me
Me
Me
N
Me
Me
R
Me
N
N
N
O
O
OH
OH
II
III
I
Symmetric structure of dinitrones functionalized at
both R substituents could give rise to dimeric struc-
tures (e.g., polypeptide) with a central group capable
of transferring an electron in a reversible mode. On
this basis, artificial biologically important compounds
ensuring reversible electron transport may be designed
in the future.
subsequent reaction of III with (i-Pr)2NH (leading to
the corresponding diisopropylamide [10]) may be
avoided by replacing dimethyl terephthalate by diethyl
terephthalate which is readily soluble in diethyl ether.
When enamino ketone III (Scheme 2) was heated
in aqueous–alcoholic solution of HCl, it underwent
recyclization to 1-hydroxy-4,5-dihydropyrrol-4-one
IV, while the ester group in the para position of the
benzene ring remained unchanged. Acid V was ob-
tained by hydrolysis of IV in the presence of a base
and subsequent neutralization of the reaction mixture.
A standard procedure for the introduction of elec-
trochemically active groups into modified oligonucleo-
tide*** or polypeptide structures is based on aminol-
ysis of the corresponding carboxylic acid esters. There-
fore, the goal of the present work was to synthesize
symmetrical and unsymmetrical dinitrones with R sub-
stituents having a carboxy or alkoxycarbonyl group,
convert them into the corresponding amides (this proc-
ess should simulate covalent binding of dinitrone to
terminal amino groups in linkers of modified oligonu-
cleotides or polypeptides), and examine the ability of
the compounds thus obtained to undergo reversible
one-electron transfer in the first step of electrochem-
ical reduction. As subjects for study we selected dini-
trone derivatives I containing the above substituents in
the para position of the benzene ring.
Oxidative dimerization of dihydropyrrolones IV
and V by the action of manganese(IV) oxide in aceto-
nitrile gave dinitrones Ia and Ib, respectively. The
reaction of ester Ia with isopropylamine under the con-
ditions described in [11] resulted in the formation of
a complex mixture of products; therefore, this reaction
is hardly suitable for the introduction of dinitrone
fragment into oligonucleotide or polypeptide mole-
cules.
In order to obtain dinitrone Ic having one carboxy
group, a mixture of compound V and 2,2-dimethyl-5-
phenyl-3,4-dihydro-2H-pyrrol-3-one 1-oxide (VI) was
subjected to oxidation with MnO2 (Scheme 3). In this
case the yield of unsymmetrical dinitrone Ic was 27%,
i.e., almost twice as low as that reported in [8] for
nitrones with similar reactivities.
Dinitrones I are generally synthesized via oxidative
dimerization of dihydropyrrolones formed by recy-
clization of enamino ketones [8]. The latter are pre-
pared by condensation of 2,2,4,5,5-pentamethyl-2,5-di-
hydro-1H-imidazol-1-ol (II) with carboxylic acid ester
in the presence of phenyllithium or lithium diisopro-
pylamide (Scheme 1) [9]. It is seen from Scheme 1 that
substituted carboxylic acid esters may be used to ob-
tain dinitrones having functional groups. As shown in
[10], the reaction of compound II with dimethyl tere-
phthalate in the presence of lithium diisopropylamide
gave the corresponding condensation product at one
ester group in a poor yield (10%). The yield of
enamino ketone III may be increased to 55%, and the
One of the most widely used methods for the intro-
duction of reporter groups into oligonucleotide struc-
tures is based on the activation of the corresponding
carboxylic acids with N-hydroxysuccinimide and sub-
sequent reaction of reactive ester derivative with
amino group in the linker of modified oligonucleotide
at pH ~7. A necessary condition is conservation of
electrochemical properties of the reporter group incor-
porated into oligonucleotide chain. With a view to
simulate such process we synthesized diamide Ie and
amide If by reaction of compounds Ib and Ic, respec-
tively, with N-hydroxysuccinimide in the presence of
N,N′-dicyclohexylcarbodiimide (DCC), followed by
*** Standard modification of oligonucleotides is performed at the
3′- or 5′-terminal groups with aminohexyl linkers (e.g., in
automated phosphamidite synthesis).
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SYNTHESIS AND ELECTROCHEMICAL REDUCTION OF 2,2′-DIARYL-...
401
Scheme 2.
O
O
O
EtO
EtO
HO
(1) OH–
O
(2) H+, H2O
H+, H2O
OH
O
N
N
NH
Me
Me
Me
Me
Me
Me
Me
Me
N
O
O
OH
III
IV
V
MnO2
MnO2
O
O
Me
Me
Me
Me
O
O
N
N
EtO
HO
O
O
O
O
OEt
O
OH
Me
Me
Me
Me
N
N
O
O
O
Ia
Ib
Scheme 3.
O
Ph
Me
Me
O
O
Ph
N
O
Me
Me
O
N
Me
Me
MnO2
N
O
V
+
+
+
Ib
Me
Ph
N
Me
Me
O
N
O
Me
O
Ph
O
COOH
VI
Ic
Id
treatment with isopropylamine in a 1:1 mixture of
acetonitrile with aqueous phosphate buffer (pH 7.01)
(Scheme 4).
is quasi-reversible for monoamide If and irreversible
for diamide If, and their electrochemical reduction is
an EEC process (see figure). The reduction peak
potentials are given in Table 1.
Electrochemical reduction of dinitrones Ia, Ie, and
If was studied by cyclic voltammetry in acetonitrile
and water. The reduction of carboxy derivatives Ib and
Ic was not studied. Electrochemical reduction of di-
ester Ia in acetonitrile was an EE process including
two reversible one-electron transfer steps. In the reduc-
tion of amides Ie and If the first reduction peaks (1C)
were one-electron, reversible (Er1A – Er1C = 0.06 V), and
diffusion-controlled (ip ν–1/2 = const, where ip is the
peak current, and ν is the potential sweep rate). The
second peak corresponding to the formation of dianion
In the electrochemical reduction of dinitrones Ia,
Ie, and If in acetonitrile, the first peak potential corre-
sponds to the formation of radical anions which were
characterized by ESR (Table 2). In all cases, both 14N
nuclei in the N-oxide groups are spectrally equivalent,
and the hyperfine structure (HFS) is represented by
a quintet with an intensity ratio of 1:2:3:2:1 and is
analogous to HFS of the ESR spectrum of radical
anion derived from diphenyl derivative Id [1, 2].
Symmetry violation in going to amide If radical anion
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 3 2010

KHALFINA et al.
402
Scheme 4.
O
O
Me
Me
Me
Me
O
O
N
N
(1) N-Hydroxysuccinimide, DCC
(2) i-PrNH2
HO
i-PrNH
O
O
O
O
X
Y
Me
Me
Me
Me
N
N
O
O
Ib, Ic
Ie, If
X = COOH (b), H (c); Y = CONHPr-i (e), H (f).
I, μA
I, μA
(a)
–60
–100
Ie
If
2C
2C
1C
1C
–30
–50
0
0
30
0.5
50
0.5
0.0
–0.5
–1.0
E, V
0.0
–0.5
–1.0
E, V
I, μA
I, μA
(b)
–40
–20
Ie
If
1C
–10
0
1C
–20
0
10
20
20
0.5
0.0
–0.5
–1.0
E, V
0.5
0.0
–0.5
–1.0
E, V
Cyclic voltammograms for the reduction of dinitrones Ie and If in (a) acetonitrile and (b) water [v = 0.2 V/s; for dinitrone Ie in H2O,
v = 1 V/s]; the second potential sweep cycle is shown with dashed line.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 3 2010

SYNTHESIS AND ELECTROCHEMICAL REDUCTION OF 2,2′-DIARYL-...
403
Table 1. Peak potentials for electrochemical reduction of dinitrones Ia, Id, Ie, and If in acetonitrile and watera
Compound no.
R
Solvent
Er1C,b V
Er1A, V
Er2C, V
Er2A, V
Ia
Ie
C6H4COOEt-4
MeCN
MeCN
H2O
–0.48
–0.49
–0.07
–0.53
–0.08
–0.55
–0.09
–0.42
–0.43
–0.01
–0.46
–0.02
–0.49
–0.03
–0.98
–1.03
–
–0.88
C6H4CONHPr-i-4b
–
–
If
C6H4CONHPr-i, Phb
MeCN
H2O
–1.01
–
–0.90
–
Id
Ph
MeCN [2]
H2O [3]
–1.05
–
–0.95
–
a
Potential sweep rate v = 0.1 V/s; supporting electrolyte Et4NClO4 (0.1 M) for MeCN or LiClO4 (0.1 M) for H2O; saturated calomel
electrode as reference.
See figure.
b
does not affect spectral equivalence of the N→O nitro-
gen atoms, and no hyperfine coupling with protons in
the benzene rings and nitrogen nuclei in the amide
groups is observed due to essential noncoplanarity of
the benzene and pyrrole rings contributing mainly to
the singly occupied molecular orbital of the radical
anion (cf. [1]); in this case, benzene rings may be
regarded as linkers.
termined at the Microanalysis Laboratory, Novosibirsk
Institute of Organic Chemistry, Siberian Division,
Russian Academy of Sciences. Silica gel (5–100 μm)
manufactured at the Novosibirsk Institute of Organic
Chemistry was used for column and preparative thin-
layer chromatography. 2,2,4,5,5-Pentamethyl-2,5-dihy-
dro-1H-imidazol-1-ol (II) was synthesized according
to the procedure described in [12].
Cyclic voltammograms for the reduction of dini-
trones Ie and If in water (see figure) in the potential
sweep range from 0.5 to –0.8 V display a single
reversible one-electron peak with a near-zero potential
(Table 1). Introduction of a carbamoyl group into the
para position of one or two benzene rings does not
affect the potential of the first reduction peak to an ap-
preciable extent. The first reduction step of compounds
Ie and If retains its reversible and one-electron char-
acter both in acetonitrile and in water, whereas low
reduction potentials make it possible to use dinitrones
Ie and If as electrochemically active groups in applied
bioorganic electrochemistry.
Ethyl 4-[2-(1-hydroxy-2,2,5,5-tetramethylimid-
azolidin-4-ylidene)acetyl]benzoate (III). A solution
of 1 g (6.4 mmol) of N-hydroxydihydroimidazole II in
20 ml of anhydrous diethyl ether was added with stir-
ring under argon to a solution of phenyllithium pre-
pared from 2 ml (19.2 mmol) of bromobenzene and
0.29 g (38.4 mmol) of metallic lithium in 30 ml of
anhydrous diethyl ether. The mixture was stirred for
30 min, cooled to –10°C, a solution of 3.5 g
(15.8 mmol) of diethyl terephthalate in 15 ml of anhy-
drous diethyl ether was added in one portion, and the
mixture was stirred first for 30 min at –5°C and then
for 1.5 h at 20°C. The mixture was treated with 10 ml
of water, the organic phase was separated, and the
aqueous phase was extracted with diethyl ether (3×
30 ml). The extracts were combined with the organic
phase and dried over MgSO4, the solvent was distilled
off, the residue was diluted with 10 ml of hexane, and
the precipitate of III was filtered off and purified by
The synthesis of monoamide derivatives If from the
corresponding carboxylic acid through intermediate
N-hydroxysuccinimide ester may be regarded as
a method for the introduction of a dinitrone fragment
into molecules of modified oligonucleotides with
a terminal amino group with a view to obtain DNA
markers containing a novel electrochemically active
reporter group.
Table 2. Isotropic hyperfine coupling constants for radical
anions derived from dinitrones Ia, Ie, and If in acetonitrile
EXPERIMENTAL
Compound no.
R
aH, G
The IR spectra were recorded in KBr on a Bruker
Vector 22 spectrometer. The H NMR spectra were
measured on a Bruker AV-300 instrument from solu-
tions in CDCl3. The elemental compositions were de-
Ia
Ie
If
C6H4COOEt-4
4.320
4.320
4.275
1
C6H4CONHPr-i-4
C6H4CONHPr-i-4, Ph
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KHALFINA et al.
404
column chromatography using chloroform as eluent.
Yield 55%, mp 171–173°C. IR spectrum, ν, cm–1:
3200–3500 (OH), 3303 (NH), 1703 (C=O, ester), 1607
residue was purified by preparative thin-layer chroma-
tography using ethyl acetate as eluent. Yield 82%,
mp 230–235°C. IR spectrum, ν, cm–1: 1720 (C=O,
1
1
(C=O). H NMR spectrum, δ, ppm: 1.39 t (3H,
ester; C=C–C=O). H NMR spectrum, δ, ppm: 1.39 t
CH2CH3, J = 7.1 Hz), 1.42 s (6H, 2-CH3), 1.48 s (6H,
5-CH3), 4.38 q (2H, CH2CH3, J = 7.1 Hz), 4.86 br.s
(OH), 5.66 s (1H, =CH) 7.89 d (2H, o-H, J = 8.3 Hz),
8.06 d (2H, m-H, J = 8.3 Hz). Found, %: C 65.01;
H 7.25; N 8.49. C18H24N2O4. Calculated, %: C 65.06;
H 7.23; N 8.43.
(6H, CH2CH3, J = 7.2 Hz), 1.40 s (12H, CH3), 4.39 q
(4H, CH2CH3, J = 7.2 Hz), 7.67 br.s (4H, o-H), 8.11 br.s
(4H, m-H). Found, %: C 65.89; H 5.51; N 5.21.
C30H30N2O8. Calculated, %: C 65.93; H 5.49; N 5.13.
4-{3-[2-(4-Carboxyphenyl)-5,5-dimethyl-1-oxido-
4-oxo-4,5-dihydro-3H-pyrrol-3-ylidene]-5,5-dimeth-
yl-1-oxido-4-oxo-4,5-dihydro-3H-pyrrol-2-yl}ben-
zoic acid (Ib) was synthesized in a similar way by
oxidation of compound V. Yield 80%, decomposes
above 270°C. IR spectrum, ν, cm–1: 3400 (OH), 1720
Ethyl 4-(1-hydroxy-5,5-dimethyl-4-oxo-4,5-dihy-
dro-1H-pyrrol-2-yl)benzoate (IV). A suspension of
0.3 g (1.1 mmol) of enamino ketone III in a mixture of
5.5 ml of ethanol and 5.5 ml of 10% hydrochloric acid
was kept for 72 h at 20°C (until the precipitate dis-
solved completely). The solvent was distilled off under
reduced pressure (2 mm) at room temperature, the
residue was diluted with 3 ml of hexane, and the
precipitate was filtered off and purified by preparative
thin-layer chromatography using chloroform–ethyl
acetate (1:1) as eluent. Yield 87%, mp 120–122°C. IR
spectrum, ν, cm–1: 1760, 1563 (C=O, C=N), 1714
1
(C=C–C=O), 1700 (COOH). H NMR spectrum, δ,
ppm: 1.38 s (12H, CH3), 7.83 br.s (8H, Harom). Found,
%: C 63.71; H 4.48; N 5.68. C26H22N2O8. Calculated,
%: C 63.67; H 4.49; N 5.71.
4-[3-(5,5-Dimethyl-1-oxido-4-oxo-2-phenyl-4,5-
dihydro-3H-pyrrol-3-ylidene)-5,5-dimethyl-1-oxido-
4-oxo-4,5-dihydro-3H-pyrrol-2-yl]benzoic acid (Ic).
Manganese(IV) oxide, 0.12 g, was added to a solution
of 0.08 g (0.4 mmol) of compound V and 0.1 g
(0.4 mmol) of 2,2-dimethyl-5-phenyl-3,4-dihydro-2H-
pyrrol-3-one 1-oxide (VI) in 5 ml of acetonitrile, and
the mixture was stirred for 1 h at 20°C. The precipitate
of manganese oxides was filtered off and washed with
acetonitrile (2×1 ml), and the filtrate was evaporated
under reduced pressure (2 mm) at room temperature.
Yield 27%, mp 117–120°C. IR spectrum, ν, cm–1: 3440
1
(C=O, ester). H NMR spectrum, δ, ppm: 1.37 t (3H,
CH2CH3, J = 7.0 Hz), 1.60 s (6H, CH3), 4.37 q (2H,
CH2CH3, J = 7.0 Hz), 6.16 s (1H, 3-H), 8.11 br.s
(4H, Harom). Found, %: C 65.45; H 6.20; N 4.99.
C15H17NO4. Calculated, %: C 65.45; H 6.18; N 5.09.
4-(2,2-Dimethyl-1-oxido-3-oxo-3,4-dihydro-2H-
pyrrol-5-yl)benzoic acid (V). A solution of 0.012 g
(0.05 mmol) of compound IV in 0.2 ml of 30% aque-
ous sodium hydroxide was stirred for 2 h at 20°C. The
mixture was acidified with 20% hydrochloric acid to
pH 3, and the precipitate was filtered off and purified
by preparative thin-layer chromatography using aceto-
nitrile as eluent. Yield 80%, decomposes above 150°C.
IR spectrum, ν, cm–1: 3400 (OH), 1766, 1532 (C=O,
1
(OH), 1718 (COOH), 1613 (C=C–C=O). H NMR
spectrum, δ, ppm: 1.45 s (12H, CH3), 7.45 br.s (2H,
o-H), 7.61 br.s (5H, C6H5), 8.20 br.s (2H, m-H). Found,
%: C 67.19; H 4.95; N 6.33. C25H22N2O6. Calculated,
%: C 67.26; H 4.93; N 6.28.
Dinitrones Ib–Id were isolated by preparative thin-
layer chromatography using ethyl acetate as eluent.
The yields of Ib and Id were 53 and 60%, respectively.
1
C=N), 1700 (COOH). H NMR spectrum, δ, ppm:
1.56 s (6H, CH3), 3.80 s (2H, 4-H), 7.67 d (2H, o-H,
J = 8.5 Hz), 8.42 d (2H, m-H, J = 8.5 Hz). Found, %:
C 63.11; H 5.30; N 5.62. C13H13NO4. Calculated, %:
C 63.16; H 5.26; N 5.67.
N-Isopropyl-4-{3-[2-(4-isopropylcarbamoylphen-
yl)-5,5-dimethyl-1-oxido-4-oxo-4,5-dihydro-3H-
pyrrol-3-ylidene]-5,5-dimethyl-1-oxido-4-oxo-4,5-
dihydro-3H-pyrrol-2-yl}benzamide (Ie). A solution
of 0.045 g (0.09 mmol) of dinitrone Ib, 0.04 g
(0.2 mmol) of N,N′-dicyclohexylcarbodiimide, and
0.03 g (0.25 mmol) of N-hydroxysuccinimide in 5 ml
of acetonitrile was stirred for 12 h at 20°C. A solution
of 0.015 ml (0.37 mmol) of isopropylamine in a mix-
ture of 1.5 ml of acetonitrile and 1.5 ml of phosphate
buffer (pH 7.01) was then added, and the mixture was
stirred for 4 h at 20°C. The solvent was distilled off at
20°C under reduced pressure (2 mm), and the residue
Ethyl 4-{3-[2-(4-ethoxycarbonylphenyl)-5,5-di-
methyl-1-oxido-4-oxo-4,5-dihydro-3H-pyrrol-3-yli-
dene]-5,5-dimethyl-1-oxido-4-oxo-4,5-dihydro-3H-
pyrrol-2-yl}benzoate (Ia). Manganese(IV) oxide,
0.01 g, was added to a solution of 0.006 g (0.02 mmol)
of compound IV in 1 ml of chloroform, and the
mixture was stirred for 1 h at 20°C. The precipitate
(manganese oxides) was filtered off and washed with
chloroform (2×1 ml), the filtrate was evaporated under
reduced pressure (2 mm) at room temperature, and the
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SYNTHESIS AND ELECTROCHEMICAL REDUCTION OF 2,2′-DIARYL-...
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was purified by preparative thin-layer chromatography
using acetone as eluent. Yield 21%, mp 145–148°C.
IR spectrum, ν, cm–1: 3325 (NH), 1740, 1635, 1539
(C=C–C=O; C=O, amide). 1H NMR spectrum, δ, ppm:
1.29 d [12H, CH(CH3)2, J = 6.7 Hz], 1.43 br.s (12H,
CH3), 4.29 m [2H, CH(CH3)2], 6.00 br.s (2H, NH),
7.68 br.s (4H, o-H), 7.80 br.s (4H, m-H). Found, %:
C 67.10; H 6.30; N 9.84. C32H36N4O6. Calculated, %:
C 67.13; H 6.29; N 9.79.
ESP-300 radiospectrometer equipped with a double
resonator. Electrochemical reduction of Ia, Ie, and If
in combionation with ESR spectroscopy was per-
formed under oxygen-free conditions at a potential
corresponding to the first reduction peak (298 K) in
a standard three-electrode cell with a platinum cathode
for measurement of ESR spectra of electrochemically
generated paramagnetic species. The working part
(cathode) of the cell was placed into the probe of ESR
spectrometer. Numerical simulation of the ESR spectra
of radical anions was performed using Winsim 2002
program [13] with SIMPLEX multiparameter optimi-
zation algorithm.
4-[5,5-Dimethyl-3-(5,5-dimethyl-1-oxido-4-oxo-
2-phenyl-4,5-dihydro-3H-pyrrol-3-ylidene)-1-oxido-
4-oxo-4,5-dihydro-3H-pyrrol-2-yl]-N-isopropyl-
benzamide (If) was synthesized in a similar way from
dinitrone Ic. Yield 25%, mp 121–123°C. IR spectrum,
ν, cm–1: 3339 (NH), 1721, 1644, 1535 (C=C–C=O;
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 06-03-32859-a).
1
C=O, amide). H NMR spectrum, δ, ppm: 1.27 d [6H,
CH(CH3)2, J = 6.8 Hz], 1.40 s (12H, CH3), 4.28 m
[1H, CH(CH3)2], 6.03 br.s (1H, NH), 7.44 br.s (2H,
o-H), 7.60 br.s (5H, C6H5), 7.80 br.s (2H, m-H). Found,
%: C 68.95; H 6.00; N 8.71. C28H29N3O5. Calculated,
%: C 68.99; H 5.95; N 8.62.
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 3 2010