Mechanism of autoreduction of 2,2,6,6-tetramethyl-1,4-dioxopiperidinium cation in alkaline medium

Article abstract of DOI:10.1134/S1070428011060066

Autoreduction of 2,2,6,6-tetramethyl-1,4-dioxopiperidinium ion to nitroxyl radical in alkaline medium involves a number of parallel and consecutive reactions. The primary products of the reaction of 2,2,6,6-tetramethyl-1,4- dioxopiperidinium with hydroxide ion are three nitroso compounds and N-hydroxy-2,2,6,6-tetramethylpiperidine N-oxide. Isomerization of the nitroso compounds and elimination of acetone from the N-oxide give cyclic hydroxylamines which reduce the initial cation to nitroxyl radical, being oxidized to nitrones. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S1070428011060066

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2011, Vol. 47, No. 6, pp. 869–876. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © V.A. Golubev, V.D. Sen’, 2011, published in Zhurnal Organicheskoi Khimii, 2011, Vol. 47, No. 6, pp. 854–861.
Mechanism of Autoreduction of 2,2,6,6-Tetramethyl-
1,4-dioxopiperidinium Cation in Alkaline Medium
V. A. Golubev and V. D. Sen’
Institute of Chemical Physics Problems, Russian Academy of Sciences,
pr. Akad. Semenova 1, Chernogolovka, Moscow oblast, 142432 Russia
e-mail: senvd@icp.ac.ru
Received April 25, 2010
Abstract—Autoreduction of 2,2,6,6-tetramethyl-1,4-dioxopiperidinium ion to nitroxyl radical in alkaline
medium involves a number of parallel and consecutive reactions. The primary products of the reaction of
2,2,6,6-tetramethyl-1,4-dioxopiperidinium with hydroxide ion are three nitroso compounds and N-hydroxy-
2,2,6,6-tetramethylpiperidine N-oxide. Isomerization of the nitroso compounds and elimination of acetone from
the N-oxide give cyclic hydroxylamines which reduce the initial cation to nitroxyl radical, being oxidized to
nitrones.
DOI: 10.1134/S1070428011060066
Stable nitroxyl radicals give rise to redox triad con-
sisting of oxoammonium cation R2N+=O, nitroxyl radi-
cal R2N–O·, and hydroxylamine R2N–OH (Scheme 1),
which possesses a unique set of parameters. Properties
of two-electron redox couple R2N+=O/R2N–OH and
one-electron redox couples R2N+=O/R2N–O· and
R2N–O·/R2N–OH were utilized in such processes as
selective oxidation of alcohols [1–5], design of chem-
ical current sources with improved parameters [6, 7],
suppression of oxidative stress in living organisms [8],
and even DNA-mediated signaling by base excision
repair enzymes [9]. Oxoammonium derivatives of
nitroso ureas were found to exhibit a strong antitumor
activity [10, 11].
nium salts are the corresponding nitroxyl radicals, it
was presumed [12] that hydroxide ion acts as reducing
agent in this reaction. Nevertheless, the equilibrium
constant calculated from the reduction potentials of
2,2,6,6-tetramethyl-1-oxopiperidinium ion (0.75 V
[14]) and hydroxyl radical OH· (1.89 V [15]) is very
small, K1 = k1/k–1 ≈ 5×10–20 (Scheme 2).
Scheme 2.
k1
+ OH–
R2N
· ·
O + HO
R2N
O
k–1
If k–1 ≈ 1010 l mol–1 s–1, k1 should be equal to ~5×
10–10 l mol–1 s–1, so that the rate of direct electron
transfer from OH– to the cation will be negligibly low.
An alternative mechanism implies that reduction of
oxopiperidinium salts involves intermediate formation
of amine hydroperoxide R2NO2H (Scheme 3).
Scheme 1.
2e–, H+
R2N
O
R2N OH
e–
e–, H+
Scheme 3.
·
R2N
O
R2N
O
+ OH–
R2N OOH
Obviously, stability of compounds in the above
triad and the absence of side reactions are necessary
conditions for effective utilization of their redox prop-
erties. However, even the first study on oxopiperidini-
um salts [12] revealed their ability to undergo auto-
reduction in aqueous solution, which is also typical of
other strong organic oxidants [13]. Taking into account
that the main products of autoreduction of oxoammo-
OH–
R2N
O
HOO– + R2N OH
2R2N
·
O + H2O2
The hypothesis, according to which 4-methoxy-
2,2,6,6-tetramethyl-1-oxopiperidinium bromide in al-
kaline medium is reduced almost quantitatively to the
corresponding radical while OH– is oxidized to H2O2
in a high yield, was confirmed in [16]. However, we
869

GOLUBEV, SEN’
870
Scheme 4.
O
O
O
Me
Me
O
O
N
O
Me
O
Me
NaOH
+
+
+
Me
Me
Me
Me
Me
ClO4
Me
Me
Me
Me
N
O
–NaClO4
N
Me
Me
N
O
N
O
Me
Me
Me
O
·
Me
O
Me
I
II
III
IV
Me
Me
O
N
O
O
O
Me
Me
Me
O
Me
O
N
CH2
Me
Me
Me
Me
+
Me
Me
+
+
+
+
Me
Me
Me
Me
Me
Me
O
N
N
N
N
OH
Me
Me
H
H
Me
O
O
O
O
NO3
V
VI
VII
VIII
IX
did not observe formation of H2O2 and O2 in this
reaction [17]. In addition, hydrogen peroxide is known
[18–20] to be very readily oxidized with oxopiperi-
dinium ions in neutral and alkaline media; therefore, it
cannot be formed as final product in reactions of oxo-
piperidinium salts with alkali. On the other hand, study
on the kinetics and products of autoreduction of
2,2,6,6-tetramethyl-1,4-dioxopiperidinium perchlorate
(I) in acid medium showed [21] that partial (up to
~65%) reduction of 2,2,6,6-tetramethyl-1,4-dioxopi-
peridinium ion to nitroxyl radical occurs with partici-
pation of fragmentation products generated from 1-hy-
droxy-2,2,6,6-tetramethyl-4-oxopiperidine 1-oxide
which is formed in turn via reaction of the cation with
water.
the first step, the following reactions are possible:
(1) proton abstraction form the methylene or methyl
group in cation Ia by the action of hydroxide ion,
which leads to nitroso compounds X and XI, and
(2) addition of OH– ion to cation Ia with formation of
nitroso compound XII and N-hydroxypiperidine
N-oxide XIII (Scheme 5).
Preferential formation of nitroso compound X is
favored by inductive effect of the carbonyl group on
the methylene protons in Ia and by conjugation in the
C=C–C=O bond sequence in molecule X; therefore,
the amount of X is larger by a factor of 28 than the
amount of nitroso compound XI. At a temperature
below 50°C liquid nitroso derivative X is converted
into colorless stable dimer IV. Dimer IV and monomer
X in solution occur in equilibrium with each other. The
equilibrium is displaced toward dimer IV at a tempera-
ture not exceeding 0°C, whereas monomer X prevails
The goal of the present work was to study auto-
reduction of salt I in alkaline medium. When an aque-
ous suspension of perchlorate I was treated with an
equimolar amount of alkali at ~20°C, almost complete
conversion of the salt was achieved during the time
necessary for its dissolution. Analysis of the resulting
product mixture by HPLC showed the presence of
radical II and ~20 more compounds some of which
were isolated and identified (Scheme 4). The major
products (80–86% on the initial cation) were radical II,
dihydropyrrole N-oxide III, diazene N,N′-dioxide IV,
and acetone (yield 41, 15, 25, and 15 mol %, respec-
tively). Perchlorate ion is not consumed in the reaction,
and it can be recovered completely in the form of
NaClO4 or KClO4.
1
above 30°C. According to the H NMR data, the equi-
librium constant K = [X]2/[IV] in CDCl3 is 1.9×10–3 at
0.6°C, 0.57 at 25°C, and 17.8 mol/l at 58°C.
Nitroso compound X is unstable both in the liquid
state and in solution and is gradually converted into
a mixture of products (Scheme 5). Disproportionation
of X gives nitro compound V, and its isomerization
leads to N-hydroxypyrrolidine XIV. The isomerization
occurs through intermediate A and is accompanied by
two-electron reduction of the nitroso group. Analogous
isomerization of unsaturated nitroso compounds to
cyclic hydroxylamines was reported previously [22].
N-Hydroxypyrrolidine XIV reduces two cation Ia
species to radical II and is thus oxidized to dihydro-
pyrrole N-oxide VI as final product.
The formation of a complex mixture of products is
the result of a number of parallel and consecutive
reactions. Let us consider these reactions separately. In
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 6 2011

MECHANISM OF AUTOREDUCTION OF 2,2,6,6-TETRAMETHYL-1,4-DIOXOPIPERIDINIUM
871
Scheme 5.
V
VI
2Ia –2II
Me
O
O
N
O
O
Me
Me
CH2
–H2O
N
HO
N
H
Me
Me
Me
Me
Me
Me
XIV
Me
O
X
A
2Ia
XIV
VI
–2II
O
O
O
O
2Ia
HO–
Me
Me
+
Me
Me
Me
–H2O
–2II
Me
Me
Me
CH2
Me
Me
Me
Me
N
O
N
O
N
N
Me
HO
XV
O
Ia
XI
XVII
O
O
2Ia
CH2
CH2
Me
Me
Me
Me
–2II
O
N
N
N
HO
O
Me
Me
XVI
XVIII
Me
Me
OH
O
O
O
2Ia
XII
III
N
–Me2CO
–2II
Me
Me
Me
Me
N
HO O–
XIII
OH
Me
Me
XX
OH
N
OH
O
Me
Me
Me
Me
2Ia
Me
Me
OH
VII
Me
Me
–2II
Me
Me
Me
N
N
OH
OH
Me
OH
OH
XIX
O
XIIa
XIXa
isomers VI, XVII, and XVIII, only the former was
detected; dihydropyrrole N-oxide VI can also be
formed from nitroso compound X (see above).
Nitroso compound XII was not isolated from the
reaction mixture, but its formation follows from the
isolation of dihydropyrrole N-oxide VII. The trans-
formation of XII into VII is likely to follow a path
shown in Scheme 5. Enol tautomer of XII (nitroso
As shown previously [23], nitroso compound XI is
unstable, and it was not isolated as individual sub-
stance. The corresponding dimer was detected by
HLPC as an impurity in diazene N,N′-dioxide IV (see
Experimental). Isomerization of XI can give rise to
three cyclic hydroxylamines XIV–XVI which are
oxidized to the corresponding cyclic nitrones VI,
XVII, and XVIII with cation Ia. Among three possible
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 6 2011

GOLUBEV, SEN’
872
Scheme 6.
O
O
Me Me
Me Me
N
O
O
N
Ia
X
+
II
Me
Me
Me Me
Me
Me
Me Me
–II
N
O
O
N
O
O
Me
Me
Me
Me
·
XXI
XXII
O
N
Me Me
Me Me
Me
N
Me
O
O
HO–
HO
N
N
2Ia
VIII
Me
Me
Me Me
Me
Me
Me
–Me2CO
–2II
O
O
O
Me
HO O–
XXIII
XXIV
compound XIIa) undergoes isomerization into N-hy-
droxydihydropyrrole XIX which is oxidized with
cation Ia to N-oxide VII. Assuming that all molecules
of nitroso compound XII are converted into dihydro-
pyrrole N-oxide VII, the rate of formation of XII
should be lower by a factor of 18 than the rate of
formation of nitroso compound X.
As a result of complex processes, cation Ia is partly
converted into 2,2,6,6-tetramethylpiperidin-4-one
(XXVI) and nitrate ion. Triacetonamine XXVI is
formed via four-electron reduction of cation I with
acetone according to a scheme proposed previously
[14, 24] (Scheme 7). Mechanism of four-electron
oxidation of the oxoammonium group in Ia to NO–3 ion
is not clear. Presumably, precursor of NO3– is nitrous
acid which can be formed by fragmentation of N-oxide
XIII. By special experiment we found that salt I
oxidizes NaNO2 to NaNO3, thus being reduced to
radical II.
As shown previously [21], N-hydroxypiperidine
N-oxide XIII is unstable; it decomposes into acetone
and 1-hydroxy-5,5-dimethylpyrrolidin-3-one (XX).
Oxidation of the latter with cation Ia yields dihydro-
pyrrole N-oxide III. In keeping with the fraction of III
among autoreduction products of salt I, the rate of its
formation from Ia is lower by a factor of 1.7 than the
rate of formation of nitroso compound X.
The structure of the isolated compounds was deter-
mined on the basis of their elemental compositions and
1H and 13C NMR, IR, UV, and mass spectra (see Ex-
perimental). Except for triacetonamine nitrate (IX) and
dihydropyrrole N-oxide VII, the mass spectra of all
compounds contained the corresponding molecular ion
peaks. Salt IX displayed no molecular ion peak, but
that belonging to triacetonamine, m/z 155, was present.
The molecular ion of N-oxide VII is unstable and is
not observed in the mass spectrum, which is typical of
compounds containing a tertiary hydroxy group [25].
Elimination of methyl radical from [M]+ gives frag-
ment ion with m/z 170. In the mass spectrum of
N-oxide VIII, apart from [M]+ with m/z 296, ion peaks
corresponding to piperidine (m/z 170) and dihydropyr-
role fragments (m/z 127) were observed.
Compounds formed as a result of transformations
shown in Scheme 5 may be involved in further reac-
tions with each other. For example, N-oxide VIII is
likely to be formed via reaction of nitroso compound X
with radical II according to Scheme 6. Addition of
radical II to X gives radical XXI which was obtained
previously by oxidation of II with xenon difluoride
[23]. Cation Ia reversibly oxidizes radical XXI to
cation XXII, and addition of hydroxide ion to the latter
gives N-oxide XXIII. Elimination of acetone molecule
from XXIII produces hydroxypyrrolidine XXIV
whose oxidation with Ia yields final dihydropyrrole
N-oxide VIII.
Scheme 7.
Me
Me
Me
O
O
Me
O
O
N
O
O
NH
Ia
+
+
–H+
Me
Me
H
Me
CHO
Me Me
Me Me
XXVI
Me
XXV
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 6 2011

MECHANISM OF AUTOREDUCTION OF 2,2,6,6-TETRAMETHYL-1,4-DIOXOPIPERIDINIUM
873
The structure of dihydropyrrole N-oxide VI was
confirmed by the 13C NMR spectrum recorded using
DEPT 135 pulse sequence. The spectrum showed the
presence of three methyl groups, two methylene
groups, and four quaternary carbon atoms in molecule
VI. Isomeric N-oxides XVII and XVIII were charac-
terized by different ratios of the corresponding carbon
atoms. The double C=C bond in molecule VI is cross-
conjugated with the carbonyl and N-oxide moieties;
therefore, it displayed in the UV spectrum two strong
absorption bands with their maxima at λ 229 and
291 nm. The IR spectrum of a dilute solution of VII in
carbon tetrachloride lacked absorption band assignable
to free hydroxy group, which may be due to formation
of strong intramolecular hydrogen bond between the
hydroxy proton and oxygen atom of the carbonyl or
N-oxide group. Compound VIII possesses an asym-
through N-oxide XIII. By contrast, hydroxide ion
better abstracts protons; therefore, autoreduction of Ia
through nitroso derivatives predominates in alkaline
medium. Taking into account high nucleophilicity of
hydroxide ion, the rate of reactions with its participa-
tion is incomparably higher than the rate of reactions
with H2O as nucleophile. Primary products of the
above reactions undergo further transformations lead-
ing to numerous products. Such autoreduction mechan-
ism is likely to be general for all oxopiperidinium salts.
Stability of the latter to autoreduction is determined by
both acidity of the medium and nature of substituents
therein.
EXPERIMENTAL
The IR spectra were recorded on a Specord 75 IR
spectrometer. The UV spectra were measured on
a Specord UV-Vis spectrophotometer. The NMR spec-
tra were recorded from solutions in CDCl3 on a Bruker
1
metric carbon atom and is racemic. In the H NMR
spectrum of VIII recorded at a temperature below 5°C,
all methyl groups and methylene protons in the piper-
idine fragment gave different signals.
1
A III instrument (500 MHz for H). Signals in the
NMR spectra were assigned using DEPT pulse
sequences and by comparing with the spectra of struc-
turally related compounds. The mass spectra (electron
impact, 70 eV) were obtained on a Finnigan GC–MS
system. The melting points were determined on
a PHMK hot stage. HPLC analysis was performed
using a Milikhrom chromatograph equipped with a 2×
64-mm column (Separon C18, 5 μm) and a UV detec-
tor (λ 200, 240, and 270 nm); eluent 50% aqueous
methanol; retention volumes Vr, μl: II, 290; III, 210;
IV, 4400; V, 810; VI, 480; VII, 320; VIII, 950; IX,
165; X, 1450; dimer of XI, 3070. 4-Nitrotoluene was
used as internal standard for quantitative measure-
ments (Vr = 1280 μl). Preparative separation of com-
ponents was performed using a 10×250-mm column
charged with Separon C18 (7 μm), an HPP-5001
pump, and an LCD-2563 UV detector (λ 254 nm);
eluent 50% aqueous methanol; Vr, ml: II, 30; III, 19.2;
V, 98.3; VI, 54; VII, 40; VIII, 116; X, 182. The
amount of liberated acetone was determined by GLC
on an LKhM-80 chromatograph equipped with a 3×
1500-mm column (stationary phase Separon BD-1,
100 μm; 159/175°C; carrier gas nitrogen, flow rate
30 ml/min); retention time of acetone 240 s.
Diazene N,N′-dioxide IV was assigned the structure
of trans isomer, for its IR spectrum contained a strong
absorption band at 1258 cm–1 (ε = 460), typical of
trans-dimers of nitroso compounds [26]. The vinylcar-
bonyl fragments in nitroso compound X, dimer IV, and
nitro compound V have trans configuration. This fol-
lows from the intensity of the corresponding absorp-
tion band in the UV spectra of these compounds,
λmax ~240 nm (ε ≈ 15000 l mol–1 cm–1). Such intensity
is typical of trans-vinyl ketones, while the corre-
sponding value for cis-vinyl ketones is ε ≈ 8000 l×
mol–1 cm–1 [27].
Thus the results of our studies on the reduction of
2,2,6,6-tetramethyl-1,4-dioxopiperidinium perchlorate
(I) in alkaline and acid [21] media show that its
autoreduction is initiated by hydroxide ion and water.
These nucleophiles add to cation Ia with formation of
N-oxide XIII and nitroso compound XII or abstract
a proton from methylene or methyl group in Ia with
formation of unsaturated nitroso compounds X and XI.
Elimination of acetone molecule from N-oxide XIII or
redox isomerization of nitroso compounds gives cyclic
hydroxylamines which reduce cation Ia via two-elec-
tron transfer process to N-hydroxypiperidine [21], thus
being oxidized to cyclic nitrones. The reaction of
N-hydroxypiperidine with cation Ia yields radical II.
The rate of addition of water molecule to the oxoam-
monium group of cation Ia is higher than the rate of
proton abstraction by the same nucleophile. Therefore,
the main process in acid medium is autoreduction
2,2,6,6-Tetramethyl-1,4-dioxopiperidinium per-
chlorate (I) was synthesized from 2,2,6,6-tetramethyl-
4-oxopiperidin-1-oxyl (II) according to the procedure
described in [28] and was purified by reprecipitation
from acetonitrile with diethyl ether.
Reaction of 2,2,6,6-tetramethyl-1,4-dioxopiperi-
dinium perchlorate (I) with sodium hydroxide.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 6 2011

GOLUBEV, SEN’
874
A mixture of 2.3 g (8.53 mmol) of perchlorate I and
90 ml of water was stirred for 4 min at ~20°C, and
90 ml of aqueous sodium hydroxide (c = 0.1 M) was
added to the resulting suspension. The originally
yellow mixture instantaneously turned light green, and
a blue emulsion (nitroso compounds) separated. After
addition of a few crystals of dimer IV, the emulsion
solidified to colorless crystals. The mixture was stirred
for ~15 min at ~20°C and was left to stand for ~3 h in
a refrigerator for complete crystallization. The precip-
itate, 342 mg, was filtered off, washed with water, and
dried. According to the HPLC data, it contained
325 mg (22.5 mol % calculated on the initial cation Ia)
of dimer IV, 2 mg (0.1 mol %) of nitro compound V,
and 11 mg (0.8 mol %) of (assumingly) nitroso com-
pound XI dimer.
6.03 m (2H, CH). 13C NMR spectrum (25°C), δC, ppm:
20.69 (C1, C14), 24.57 (6-CH3, 9-CH3), 27.72 (2-CH3,
13-CH3), 50.61 (C5, C10), 76.57 (C6, C9), 123.97 (C3,
C12), 155.31 (C2, C13), 196.32 (C4, C11). Mass spec-
trum, m/z (Irel, %): 338 (0.2) [M]+, 335 (1.0), 285 (1.1),
235 (1.1), 169 (6.2) [X]+, 147 (2.0), 119 (1.5), 97 (2.0),
84 (5.4), 83 (100).
2,6-Dimethyl-2-nitrosohept-5-en-4-one (X) was
formed upon melting of dimer IV. Light blue liquid.
UV spectrum (MeCN), λmax, nm (ε, l mol–1 cm–1): 240
(15400), 322 (72), 670 (26). IR spectrum (CHCl3), ν,
cm–1: 1621 and 1688 (C=C–C=O), 1566 (N=O).
1H NMR spectrum (58°C), δ, ppm: 1.26 s (6H, CH3),
1.86 d (3H, CH3, J = 0.9 Hz), 2.08 d (3H, CH3, J =
0.8 Hz), 3.00 s (2H, CH2), 6.00 m (1H, CH). 13C NMR
spectrum (58°C), δC, ppm: 20.70 (C7), 21.42 (C1,
2-CH3), 27.57 (6-CH3), 50.31 (C3), 96.92 (C2), 124.0
(C5), 155.95 (C6), 197.10 (C4).
The aqueous phase contained (HPLC) 590 mg
(40.6 mol %) of radical II, 33 mg (2.3 mol %) of
nitroso compound X, 159 mg (14.7 mol %) of N-oxide
III, and 72 mg (14.5 mol %) of acetone. The aqueous
solution was extracted with chloroform (5×15 ml), and
the extract was dried over Na2SO4 and evaporated
under reduced pressure to obtain 1.05 g of a mixture of
products as a dirty green liquid which was dissolved in
45 ml of diethyl ether. The solution was left to stand
for 24 h at ~20°C, and 32 mg (1.7 mol %) of triaceton-
amine nitrate (IX) was filtered off. The filtrate was
evaporated, and the residue was subjected to chroma-
tography in a 10 × 250-mm column charged with
Separon C18 (5 μm). A ~200-mg portion was separated
at once using first 300 ml of 30% MeOH and then
50% MeOH as eluent. As a result we obtained 550 mg
(38 mol %) of radical II, 154 mg (14 mol %) of
N-oxide III, 14 mg (1 mol %) of nitroso compound X,
22 mg (1.5 mol %) of N-oxide VI, 8 mg (0.5 mol %)
of nitro compound V, 32 mg (1.3 mol %) of N-oxide
VIII, and 21 mg (1.4 mol %) of N-oxide VII.
2,6-Dimethyl-2-nitrohept-5-en-4-one (V). Dimer
IV, 169 mg, was dissolved on heating in 10 ml of
acetonitrile, and the light blue solution was left to
stand for 3 days at 36°C. The solution was evaporated,
and the residue was passed through a 30×50-mm
chromatographic column charged with silica gel L
(63–70 μm) using chloroform–hexane (1:4) as eluent
to remove tars. A fraction containing nitro compound
V was collected. It was evaporated to obtain 80 mg of
a mixture of nitro and nitroso compounds. The mixture
was subjected to chromatography on a 10×250-mm
column (Silasorb 600, 7 μm; chloroform–hexane, 1:4);
Vr. 21 ml (X), 30 ml (V). As a result, we isolated 42 mg
of nitro compound V as colorless crystals with mp 40–
40.5°C. UV spectrum (MeCN), λmax, nm (ε, l×
mol–1 cm–1): 240 (15000), 317 (64). IR spectrum
(CHCl3), ν, cm–1: 1696, 1628 (C=C–C=O); 1550, 1366
1
(NO2). H NMR spectrum, δ, ppm: 1.67 s (6H, CH3),
1.90 d (3H, CH3, J = 1.15 Hz), 2.13 d (3H, CH3, J =
1.1 Hz), 3.09 s (2H, CH2), 6.02 m (1H, CH). 13C NMR
spectrum, δC, ppm: 20.9 (C7), 26.5 (C1, 2-CH3), 27.8
(6-CH3), 52.2 (C3), 85.1 (C2), 123.2 (C5), 157.8 (C6),
195.1 (C4). Mass spectrum, m/z (Irel, %): 185 (0.8)
[M]+, 149 (0.5), 138 (1.9), 123 (1.6), 110 (4.9), 83
(100). Found, %: C 58.15; H 8.25; N 7.49. C9H15NO3.
Calculated, %: C 58.36; H 8.16; N 7.56. M 185.
2,6,6,9,9,13-Hexamethyl-7,8-diazatetradeca-
2,7,12-triene-4,11-dione 7,8-dioxide (IV) (dimer of
nitroso compound X) was formed in the reaction of
salt I with sodium hydroxide (see above). Yield 25%,
colorless plates (from aqueous acetonitrile), mp 91.5–
92°C; published data: mp 86°C [29], 92°C [23]. UV
spectrum (MeCN), λmax, nm (ε, l mol–1 cm–1): 238.4
(28400), 296 (7800). IR spectrum, ν, cm–1 (ε, l×
mol–1 cm–1): in CHCl3: 1622 (500) and 1692 (390)
[C=C–C=O], 1258 (460) and 1280 (390) [O–N=N–O];
in mineral oil: 1630 and 1688 [C=C–C=O], 1249 and
1258 [O–N=N–O]. 1H NMR spectrum (25°C), δ, ppm:
1.60 s (12H, CH3), 1.86 d (6H, CH3, J = 0.9 Hz),
2.10 d (6H, CH3, J = 0.98 Hz), 3.26 s (4H, CH2),
Nitro compound V formed in the reaction of salt I
with NaOH (see above) was identical in the melting
point and spectral parameters to a sample of V
synthesized from dimer IV as described above.
2,2,6,6-Tetramethyl-4-oxopiperidinium nitrate
(IX). Triacetonamine XXVI, 1 g, was dissolved in
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MECHANISM OF AUTOREDUCTION OF 2,2,6,6-TETRAMETHYL-1,4-DIOXOPIPERIDINIUM
875
4 ml of water, and the solution was neutralized with
dilute (1:4) nitric acid. The mixture was evaporated to
dryness under reduced pressure, and the residue was
recrystallized from acetonitrile. Yield 1.12 g (80%),
colorless crystals; the product sublimes above 150°C
and decomposes without meting above 200°C. UV
spectrum (H2O), λmax, nm (ε, l mol–1 cm–1): 200
(12300), 278 sh (19). IR spectrum (mineral oil), ν,
cm–1: 2300–2800 (N+–H), 1731 (C=O), 1595 (δNH2),
1.4%, colorless crystals, mp 49–50°C (from hexane).
UV spectrum (H2O), λmax, nm (ε, l mol–1 cm–1): 271.6
(17300), 334 sh (75). IR spectrum (CCl4), ν, cm–1
(ε, l mol–1 cm–1): 3431 (OH), 1714 (430) (C=O), 1537
1
(380) (C=N–O). H NMR spectrum, δ, ppm: 1.53 s
(6H, CH3), 1.55 s (6H, CH3), 2.73 s (2H, CH2), 5.62 s
(1H, OH). 13C NMR spectrum, δC, ppm: 25.95 (C1′,
C3′), 26.44 (5-CH3), 47.90 (C4), 70.03 (C2′), 73.17 (C5),
145.73 (C2), 194.25 (C3). Mass spectrum, m/z (Irel, %):
170 (70) [M – CH3]+, 142 (53) [M – CH3 – CO]+, 114
(12), 99 (8), 86 (42), 83 (78), 72 (9), 59 (86), 55 (50),
43 (100). Found, %: C 58.11; H 8.43; N 7.64; O 25.77.
C9H15NO3. Calculated, %: C 58.36; H 8.16; N 7.56;
O 25.91. M 185.
1
1376, 826, 712 (NO3). H NMR spectrum, δ, ppm:
1.59 s (12H, CH3), 2.75 s (4H, CH2), 8.93 s (2H, NH2).
13C NMR spectrum, δC, ppm: 28.23 (CH3), 50.46 (C3,
C5), 60.53 (C2, C6), 202.86 (C4). Mass spectrum, m/z
(Irel, %): 155 (3.2) [XXVI]+, 140 (48.1), 112 (3.9), 98
(15.9), 83 (60.4), 58 (80.5), 56 (15.0), 55 (23.9), 46
(32.4), 42 (100). Found, %: C 49.26; H 8.17; N 12.57.
C9H17NO·HNO3. Calculated, %: C 49.53; H 8.31;
N 12.84. M 218.
2,2-Dimethyl-4-(2,2,6,6-tetramethyl-4-oxopiper-
idin-1-yloxy)-3,4-dihydro-2H-pyrrol-3-one 1-oxide
(VIII) was formed in the reaction of salt I with NaOH
(see above). Yield 1.3%, colorless crystals, mp 104°C
(from hexane). UV spectrum (MeCN): λmax 275.6 nm
(ε = 20000 l mol–1 cm–1). IR spectrum (CHCl3), ν, cm–1
(ε, l mol–1 cm–1): 3123 (=C–H), 1719 (790) (C=O),
Salt IX formed in the reaction of salt I with NaOH
(see above), was identical in the melting point and
spectral parameters to a sample of IX synthesized from
compound XXVI.
1
1548 (1380) (C=N–O). H NMR spectrum (–5°C), δ,
ppm: 1.13 s, 1.15 s, 1.24 s, and 1.43 s (3H each,
2′-CH3, 6′-CH3); 1.59 s and 1.61 s (3H each, 2-CH3),
2.18 m and 2.21 m (1H each, 3′-H, 5′-H); 2.66 d (1H,
3′-H or 5′-H, J = 13.3 Hz); 2.76 d (1H, 5′-H or 3′-H,
J = 13.5 Hz), 4.47 s (1H, 4-H), 7.11 s (1H, 5-H).
13C NMR spectrum (24°C), δC, ppm: 19.02 (CH3),
26.90 (CH3), 53.55 (C3′, C5′), 77.23 (C2), 79.26 (C2′,
C6′), 85.89 (C4), 130.55 (C5), 194.47 (C3), 207.09 (C4′)
(primed numbers refer to the piperidine ring). Mass
spectrum, m/z (Irel, %): 296 (1.7) [M]+, 281 (3.4) [M –
CH3]+, 199 (3.2), 170 (22.7) [C9H16NO]+, 127 (7.7)
[C6H9NO2]+, 115 (6.3), 114 (100). Found, %: C 60.92;
H 8.27; N 9.27. C15H24N2O4. Calculated, %: C 60.79;
H 8.16; N 9.45. M 296.
5,5-Dimethyl-4,5-dihydro-3H-pyrrol-3-one
1-oxide (III) was formed in the reaction of salt I with
NaOH (see above). Yield 14%, colorless crystals,
mp 42°C (from hexane); published data [21]: mp 41–
1
42°C. H NMR spectrum, δ, ppm: 1.58 s (6H, CH3),
2.82 s (2H, CH2), 7.08 s (1H, CH). 13C NMR spec-
trum, δC, ppm: 26.56 (CH3), 48.74 (C4), 75.58 (C5),
131.89 (C2), 195.69 (C3).
5,5-Dimethyl-2-(prop-1-en-2-yl)-4,5-dihydro-3H-
pyrrol-3-one 1-oxide (VI) was formed in the reaction
of salt I with NaOH (see above). Yield 1.5%, colorless
crystals, mp 53°C (from hexane). UV spectrum
(MeCN), λmax, nm (ε, l mol–1 cm–1): 229 (14000),
291.4 (10700). IR spectrum (CCl4), ν, cm–1 (ε, l×
mol–1 cm–1): 1711 (540) (C=O), 1597 (15) (C=C),
The authors thank A.V. Chernyak for recording the
NMR spectra.
1
1519 (360) (C=N–O). H NMR spectrum, δ, ppm:
1.56 s (6H, CH3), 2.15 d.d (3H, CH3, J = 0.9, 1.55 Hz),
2.75 s (2H, CH2), 5.51 m (1H, CH, J = 1.55, 1.7 Hz),
6.31 m (1H, CH, J = 0.9, 1.7 Hz). 13C NMR spectrum,
δC, ppm: 20.38 (C3′), 26.77 (CH3), 47.64 (C4), 72.67
(C5), 122.76 (C1′), 130.51 (C2′), 139.30 (C2), 195.51
(C3). Mass spectrum, m/z (Irel, %): 167 (38.8) [M]+, 152
(21.4) [M – CH3]+, 150 (3.5) [M – OH]+, 111 (10.1), 83
(100). Found, %: C 64.73; H 7.71; N 8.21. C9H13NO2.
Calculated, %: C 64.65; H 7.84; N 8.38. M 167.
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