Reactions of an indolinonic nitroxide with superoxide radical anion in the presence of alkylhalides. Unexpected formation of a reduced transposed product

Article abstract of DOI:10.1002/jhet.5570400309

This study concerns the reactions of 2-methyl-2-phenyl-3-phenylimino-2,3-dihydroindol-1-oxyl and 2,2,6,6-tetramethylpiperidine-1-oxyl with alkylperoxyls, generated from potassium superoxide and a series of alkylhalides, in order to evaluate possible differences in reactivity with primary, secondary and tertiary alkylperoxyls. To better understand the reactivity of the studied indolinonic aminoxyl in alkaline medium, the investigation was extended to its reactions with potassium hydroxide and potassium tert-butoxide in different solvents.

Full text of DOI:10.1002/jhet.5570400309

May-Jun 2003
459
Reactions of an Indolinonic Nitroxide with Superoxide Radical Anion
in the Presence of Alkylhalides. Unexpected Formation of a Reduced
Transposed Product
Patricia Carloni,* Roberto Vianelli and Lucedio Greci
Dipartimento di Scienze dei Materiali e della Terra, Università Politecnica delle Marche,
Via Brecce Bianche, I-60131 Ancona, ITALY
Received October 29, 2002
This study concerns the reactions of 2-methyl-2-phenyl-3-phenylimino-2,3-dihydroindol-1-oxyl and
2,2,6,6-tetramethylpiperidine-1-oxyl with alkylperoxyls, generated from potassium superoxide and a series
of alkylhalides, in order to evaluate possible differences in reactivity with primary, secondary and tertiary
alkylperoxyls. To better understand the reactivity of the studied indolinonic aminoxyl in alkaline medium,
the investigation was extended to its reactions with potassium hydroxide and potassium tert-butoxide in
different solvents.
J. Heterocyclic Chem., 40, 459 (2003).
Introduction.
studied towards indolinonic and quinolinic aminoxyls
[10,12]. The peroxyls studied in this work were generated
by nucleophilic substitution of superoxide anion on alkyl
halides [13-16]. The obtained results showed that superox-
ide reacts more rapidly with the indolinonic aminoxyl than
with alkyl halides so that the formation of peroxyls and its
reactions with the aminoxyl, even if it occurs, is not the
main process of the reaction. 2,2,6,6-Tetramethyl-
piperidine-1-oxyl (TEMPO), studied for comparison with
indolinonic aminoxyls does not react with peroxyls and
cannot be reduced by superoxide.
The reactions of organic compounds with atmos-
pheric oxygen are some of the most important of all
chemical processes. In fact respiration and combustion
are essential for human life, and autoxidation is becom-
ing of great importance because of its implication in
several pathologies and in deterioration of biological
and organic substrates.
The phenomena proceeds mainly by a free-radical chain
process which involves peroxy radicals. There is an accu-
mulating body of evidence indicating that nitroxide radi-
cals (aminoxyls) protect against these processes. In fact,
aminoxyls are a particular group of antioxidants which
selectively react with potentially toxic free radicals and to
which a SOD (superoxide dismutase) mimic activity has
been attributed [1-3]. Most of these studies have involved
piperidine nitroxides such as 2,2,6,6-tetramethylpiperi-
dine-1-oxyl (TEMPO). However, in recent years, our
group has focused its attention on a different class of
nitroxides, namely indolinonic [4] and quinolinic [5,6].
These aminoxyls have been shown to react efficiently with
all kinds of radicals. They couple with carbon-centered
radicals affording alkylated hydroxylamines [7-10], and
with all oxygen-centered radicals, such as hydroxyl (HO·)
[10,11], alkoxyl (RO·) [7,10,12] and peroxyl (ROO·)
[10,12] radicals, to form paramagnetic and non-paramag-
netic compounds.
Results and Discussion.
The ability of superoxide radical anion to react with
alkylhalides by a nucleophilic reaction has been known
since the seventies [17,18]. In aprotic solvents, primary
alkylhalides react to produce the corresponding dialkylper-
oxide through the formation of the peroxy radical as
shown in Eqs. 1-3 [14,16]. Several studies confirm that
reaction (1) which produces peroxy radicals, is first order
with respect to the substrate and that the rate constant for
this reaction decreases on changing the halide in the order:
primary > secondary >> tertiary [13].
–
–
•
•
O
O
+ RX → RO + X
(1)
(2)
(3)
2
2
–
–
•
•
+ RO → RO + O
2
2
2
2
–
–
RO + RX → ROOR + X
2
Because primary, secondary and tertiary alkyl radicals
and their correponding peroxyls could be involved during
polymer and biological autoxidation chain, and because
aminoxyls may be used to inhibit this process, the aim of
this work was to test different types of peroxyl radicals
with an indolinonic and a piperidinic aminoxyl to under-
stand if the different structure of the alkyl moiety of the
peroxy radical may influence its reactivity and the path of
the reaction. Up to date, due to their commercial availabil-
ity, only tert-butyl and cumyl peroxyls [12] have been
This reaction was therefore used to generate different
kinds of peroxy radicals and to test their reactivity towards
aminoxyls. As a source of superoxide radical, potassium
superoxide was used, and to improve its dissolution in
organic solvents, a 18-crown-6-ether (1,4,7,10,13,16-hexa-
oxacyclooctadecane) was added to the reaction mixture
[19]. Dry benzene was chosen as solvent to avoid the prob-
lems connected with the use of high boiling solvents (such
as dimethylsulfoxide) [14] and with the presence of traces of
water that rapidly reacts with superoxide radical anion [16].

460
P. Carloni, R. Vianelli and L. Greci
Vol. 40
The studied aminoxyls were 2-methyl-2-phenyl-3-
methyl-2-phenyl-1,2-dihydroindol-3-ylidene)-pheny-
lamine], 6 [(1-alkyl-2-methyl-2-phenyl-1,2-dihydroindol-
3-ylidene)-phenylamine] and 7 ((1-alkyl-2-methyl-1H-
indol-3-yl)-methyl-phenylamine) could be attributed to the
interaction of the superoxide with the starting indolinonic
aminoxyl 1 and to the basicity of the medium.
In fact, quinoneimine-N-oxide 2 and alkoxy substituted
aminoxyls like 3 or 3' are formed when tert-butyl or cumyl
peroxyl were reacted with indolinonic aminoxyl 1 [10,12].
The detection of these compounds is therefore evidence
for the formation of peroxyl and alkoxyl radicals (the latter
generated from the coupling of two peroxyradicals and the
decomposition of the formed tetroxide [20]).
phenylimino-2,3-dihydro-indol-1-oxyl (indolinonic
aminoxyl) 1 and the commercial 2,2,6,6-tetramethyl-
piperidine-1-oxyl (TEMPO). The reactions were
performed using the following reagents ratio: aminoxyl (1
mmole), potassium superoxide (10 mmoles), alkylhalide
(100 mmoles).
The low yields of quinoneimine-N-oxide 2 and alkoxy
substituted aminoxyls 3 and 3' suggest that peroxy radicals
may undergo other competitive reactions. In fact, they
could be reduced by the superoxide to their corresponding
anions (Eqn. 2), which react with excess alkyl halide
affording dialkylperoxides (Eqn. 3) [14,16]. Peroxy radi-
cals are rather good oxidants and it may be assumed that
7
-1 -1
their reduction rate constant by superoxide is ≥ 10 M s
[15]; the redox process is thus in competition with the
6
-1 -1
attack on the indolinonic ring (k ≈ 10 M s ) [12] which
leads to the formation of the quinoineimine N-oxide 2.
Moreover, the distribution of the reaction products indi-
cates that superoxide can also reduce indolinonic
aminoxyl 1. This supposition is supported by the redox
In the case of indolinonic aminoxyl 1 with all the alkyl-
halides used (2-iodo-2-methypropane, 2-chloropropane, 2-
iodopropane, 2-iodobutane, iodoethane, iodomethane) the
conversion is not very high and many products are formed.
The isolated products are reported in Figure 1 while their
yields are reported in Table 1.
potential of the aminoxyl (E = -0.10 V vs. NHE) [21]
1/2
5
-1 -1
which suggests a high rate constant (7 x 10 M s ) [21]
for this reaction.
On the bases of these suggestions, it may be hypothe-
sized that indolinonic aminoxyl 1 is reduced to 2-methyl-
2-phenyl-3-phenylimino-2,3-dihydroindol-1-ol anion 8,
Table 1
which reacts with the alkyl halide through a S 2 mecha-
N
Reaction products yields for the reaction of indolinonic aminoxyl 1 in
benzene, with potassium superoxide in the presence of different alkyl
halide and 18-crown-6 ether.
nism affording alkoxyamine 4 as shown in Scheme 1.
t
i
i
i
Products a= Bu I b= Pr Cl b'= Pr I c= Bu I d= EtI e= MeI
/
1
2
3
3'
4
5
6
7
50
8
/
38
2
/
22
3
3
3
23
8
29
11
5
/
8
21
/
/
13
3
3
15
2
3
11
8
/
/
/
52
/
/
/
/
3
/
12
12
/
9
53
/
48
11
3
53
18
7
/
/
/
/
6
7
The formation of amine 5 could be explained by the well
known disproportionation reaction of the starting
indolinonic aminoxyl 1 [22], but this process may be
excluded on the basis of the yields of compounds 5 and 2,
which are higher for 5 in all cases, instead of the 1:1 ratio
observed in disproportionation reactions. These data sug-
gest that the mechanism concerning the formation of 5 is
completely different.
Only the quinoneimine-N-oxide 2 (3-phenylimino-2-
methyl-1-oxy-2-phenyl-2,3-dihydroindol-5-one) and the
alkoxy substituted aminoxyls 3 and 3' (5- or 7-alkoxy-2-
methyl-2-phenyl-3-phenylimino-2,3-dihydroindol-1-oxyl)
isolated in very low yields can prove the formation of per-
oxyradicals [10,12], whereas the formation of the
alkoxyamine 4 [(1-alkoxy-2-methyl-2-phenyl-1,2-dihydro-
indol-3-ylidene)-phenylamine] and of the amines 5 [(2-
In order to obtain more information on the formation of
amine 5, and supposing that the basicity of the reaction

May-Jun 2003
Reactions of an Indolinonic Nitroxide with Superoxide Radical Anion
461
medium can influence the mechanism of the reaction,
indolinonic aminoxyl 1 was reacted in the presence of
iodomethane with potassium superoxide, potassium tert-
butoxide and potassium hydroxide in dimethylsufoxide at
room temperature. In all cases, compound 5 was isolated
and identified. In addition, amine 5 treated with the above
alkali in dimethylsulfoxide gave rise to a pink-red solution
which gives a well resolved epr signal, stable for hours
(Figure 2) and attributed to radical anion 9 or to the corre-
sponding deprotonated radical anion 10 (Scheme 2) on the
basis of its hyperfine coupling constants (Figure 2) which
are in agreement with other similar anions [23].
Since amine 5 in alkali gives rise to an acid-base equilib-
rium, it remains difficult to state with certainty if the radi-
cal anion observed is 9 or 10 and if the reduction of the
amine occurs before or after deprotonation (see Scheme 2).
On the basis of these results the following mechanism
can be put forward for the main reaction. Anion 8 in the
reaction mixture gives rise to an acid-base equilibrium
forming hydroxylamine 12 (2-methyl-2-phenyl-3-
phenylimino-2,3-dihydroindol-1-ol) (it cannot be excluded
that in these conditions alkyl halides undergo elimination
to give an alkene thus acting as a proton source). This in
turn may react with superoxide radical anion affording rad-
ical anion 13, which then generates anion 11 [(2-methyl-2-
phenyl-1,2-dihydroindol-3-ylidene)-phenylamine anion]
by elimination of an hydroxy radical (Scheme 3).
Protonation of this anion leads to the formation of amine 5.
Concerning with the formation of amine 6, it can be rea-
sonably formed by nucleophilic substitution of anion 11 on
the alkylhalide. In fact, the reaction of amine 5 with potas-
sium hydroxide in the presence of iodomethane in
dimethylsulphoxide leads to the formation of amine 6 (see
Experimental). The formation of this compound, observed
only when the alkyl halides used were iodomethane and
iodoethane, suggests that nucleophilic substitution in this
case takes place only with primary alkyl halides.
Figure 2. Epr spectra of radical anion 9 or 10 in dimethylsulphoxide, (a)
experimental, (b) simulated. H.f.c.cs: a (C4)=10.03; a (C6)=9.85;
H
H
It is worth noting that in the reaction with iodomethane
and iodoethane, amine 7 (see Table 1) was also obtained.
This involves migration of the methyl group from C-2 to
the exocyclic nitrogen and alkylation of the endocyclic
nitrogen. 1,2-Migrations involving anions are rare; 1,3
migrations seem to be impossible. Nevertheless, based on
the assumption that anion 11 could be a suitable intermedi-
ate for rearrangement, the reaction of amine 5 with potas-
sium superoxide or potassium hydroxide which could
afford anion 11, was carefully performed with the aim of
obtaining a rearranged compound; however only the start-
ing amine was quantitatively recovered. The same reaction
carried out in the presence of iodomethane affords mainly
amine 6, as previously described. Since this compound
a (C5)=2.45; a
=0.99 Gauss.
N-exo
H
Scheme 2
does not undergo any change under alkaline
treatment, we

462
P. Carloni, R. Vianelli and L. Greci
Vol. 40
a Janssen Chimica commercial reagent grade product and used as
purchased. 18-Crown-6 ether (1,4,7,10,13,16-hexaoxacyclooc-
tadecane), was an Aldrich commercial reagent grade product and
was crystallized according to the literature [25]. 1-Alkoxy-2-
methyl-2-phenyl-1,2-dihydroindol-3-ylidene)-phenylamine 4a,
4b, 4d and 4e [8], amines 5 [(2-methyl-2-phenyl-1,2-dihydroin-
dol-3-ylidene)-phenylamine] [26,27] and 7e [methyl-phenyl-
(1,2-dimethyl-1H-indol-3-yl)-amine] [26], and 3-phenylimino-2-
methyl-1-oxy-2-phenyl-2,3-dihydroindol-5-one 2 [12], were
characterised by comparison with authentic samples.
are unable to suggest a likely mechanism for the formation
of amines 7d and 7e.
In the reaction of TEMPO with potassium superoxide in
the presence of all the alkyl halides used, the starting
aminoxyl was totally recovered after reaction workup. To
confirm that this aminoxyl does not react with the peroxy
radicals which could be formed, further experiments were
carried out. tert-Butylperoxyradicals were generated by
hydrogen abstraction of lead dioxide on tert-butylhydroper-
oxide [10,12], but also in this case, only unreacted TEMPO
was recovered when the reaction was carried out in benzene.
However when acetone was used as solvent, 1-(2,2,6,6-
tetramethylpiperidin-1-yloxy)-propan-2-one was isolated.
The formation of this product can be ascribed to the cou-
pling of the nitroxide function with the acetonyl radical
formed by hydrogen abstraction of the tert-butoxyradicals
(generated from the decomposition of tert-butylperoxy radi-
cal [20]) on the solvent [10,11]. Experimental results con-
firm that the lower oxidation power of TEMPO (E1/2= -0.58
V vs. NHE) [21], with respect to indolinonic aminoxyl 1,
does not permit electron transfer with superoxide [21].
General Procedure for the Reaction of Aminoxyl with Potassium
Superoxide and Alkyl Halide in Benzene.
Potassium superoxide (227 mg, 3.2 mmol) was added to a solu-
tion of 169 mg (0.64 mmol) of 18-crown-6 ether in 20 ml of
benzene; to the mixture, 32 mmol of alkyl halide followed by 0.32
mmol of aminoxyl were added. The reaction mixture was stirred
for 24 hrs; then 10 ml of distilled water were added and the mixture
was neutralized with 10% hydrochloric acid. The reaction was
extracted with methylene chloride, dried over sodium sulphate and
concentrated to a small volume. The residue was chromatographed
on preparative plates eluting with cyclohexane/ethyl acetate 9:1. In
the case of indolinonic aminoxyl 1, the products were isolated in
the following order: amine 6 ((1-alkyl-2-methyl-2-phenyl-1,2-
dihydroindol-3-ylidene)-phenylamine), alkoxyamine 4, amine 7
((1-alkyl-2-methyl-1H-indol-3-yl)-methylphenylamine),
indolinonic aminoxyl 1, 5-alkoxy substituted aminoxyl 3 (5-
alkoxy-2-methyl-2-phenyl-3-phenylimino-2,3-dihydroindol-1-
oxyl), 7-alkoxy substituted aminoxyl 3' (7-alkoxy-2-methyl-2-
phenyl-3-phenylimino-2,3-dihydroindol-1-oxyl), amine 5 and
quinoneimine N-oxide 2; yields are reported in Table 1. With
TEMPO only the starting aminoxyl was recovered in all cases.
Conclusions.
The yields reported in Table 1 for compounds 2 and 3,
ascribed to the interaction of peroxyls or its derivatives
with indolinonic aminoxyl 1, clearly show that all
alkylperoxyls (primary, secondary and tertiary) behave in a
similar way and that the decomposition of peroxyls with
hydrogens in α position to the peroxy group gives rise to
alkoxy radicals in accordance with the last literature
reports [24]. Moreover, aromatic aminoxyls such as 1 in
alkaline medium undergo reduction with subsequent
deoxygenation to the corresponding amines while aliphatic
aminoxyls such as TEMPO do not react with peroxyls and
cannot be reduced by superoxide.
2-Methyl-2-phenyl-3-phenylimino-5-(2-propyloxy)-2,3-dihydro-
indol-1-oxyl (3b).
This compound was obtained as dark green solid; ir: 1644,
-1
N
H
1581, 1469, 1417, 1331, 1258 cm ; epr: a (NO·) = 10.1, a
H
N
(H4, H6) = 1.0, a (H7) = 3.1, a (NPh) = 0.95 gauss; ms: m/z
371 (M , 91 %); 356 (70); 329 (72); 313 (81); 77 (100); hrms
+
calcd for C
H N O 371.4612, found 371.4615.
24 23 2 2
EXPERIMENTAL
5-(2-Butoxy)-2-methyl-2-phenyl-3-phenylimino-2,3-dihydro-
indol-1-oxyl (3c).
Ir spectra were recorded on a Nicolet Fourier Transform
Infrared 20-SX spectrophotometer equipped with a Spectra Tech
"Collector" for DRIFT measurements or on a Perkin Elmer 298
This compound was obtained as brown solid; ir: 1644, 1581,
-1
N
H
1469, 1420, 1331, 1258 cm ; epr: a (NO·) = 10.1, a (H4,
H
N
+
1
13
H6) = 1.1, a (H7) = 2.9, a (NPh) = 0.9 gauss; ms: m/z 385 (M ,
12 %); 370 (28); 329 (25); 313 (42); 77 (100); hrms calcd for
Infrared Spectrometer. H nmr and C nmr spectra were
recorded at room temperature in deuterochloroform on a Varian
Gemini 200 spectrometer (δ in ppm referred to tetramethylsi-
lane). Mass spectra were recorded on a Carlo Erba QMD 1000
C
H
N O 385.4882, found 385.4883.
25 25
2 2
5-Ethoxy-2-methyl-2-phenyl-3-phenylimino-2,3-dihydroindol-
1-oxyl (3d).
+
spectrometer in EI mode and high resolution mass spectra on a
VG7070-E 5000 spectrometer with PFK as the resolution and
calibration standard. Epr spectra were recorded on a Varian E4
spectrometer interfaced with a computer. Elemental analyses of
the new compounds were performed with a Carlo Erba CHNSO
E.A. 1108 elemental analyser.
This compound was obtained as dark green solid; ir: 1644,
-1
N
H
1581, 1469, 1417, 1329, 1258 cm ; epr: a (NO·) = 10.0, a
H
N
(H4, H6) = 1.0, a (H5 or H7) = 3.0, a (N Ph) = 0.85 gauss; ms:
+
m/z 357 (M , 71 %); 341 (42); 329 (7); 313 (18); 77 (100); hrms
1,2-Dihydro-2-methyl-2-phenyl-3-phenylimino-3H-indole-1-
oxyl 1 was prepared according to literature methods [4]. 2,2,6,6-
Tetramethylpiperidine-1-oxyl (TEMPO), potassium superoxide,
potassium tert-butoxide, tert-butylhydroperoxide, potassium
hydroxide and all the alkylhalides were Aldrich commercial
reagent grade products and used as purchased. Lead dioxide was
calcd for C
H N O 357.4342, found 357.4340.
23 21 2 2
5-Methoxy-2-methyl-2-phenyl-3-phenylimino-2,3-dihydroindol-
1-oxyl (3e).
This compound was obtained as dark green solid; ir: 1645,
1581, 1470, 1417, 1331, 1258 cm ; epr: a (NO·) = 10.1, a
-1
N
H

May-Jun 2003
Reactions of an Indolinonic Nitroxide with Superoxide Radical Anion
463
H
N
Anal. Calcd. For C
C, 84,64; H, 6,77; N, 8,49.
H N : C, 84,63; H, 6,79; N, 8,58. Found:
23 22 2
(H4, H6) = 1.1, a (H7) = 2.9, a (NPh) = 0.9 gauss; ms: m/z 343
+
(M , 100 %); 328 (77); 313 (48); hrms calcd for C
343.4073, found 343.4070.
H N O
22 19 2 2
Reaction of Indolinonic Aminoxyl 1 with Potassium Superoxide
2-Methyl-2-phenyl-3-phenylimino-7-iso-propyloxy-2,3-dihydro-
in Benzene.
indol-1-oxyl (3'b).
The reaction was carried out as previously described above
omitting the alkyl halide. Products 1, 5 and 2 were isolated in the
described order and yields are reported in Table 1.
This compound was obtained as dark red solid; ir: 1644, 1581,
-1
N
H
1465, 1417, 1331, 1260 cm ; epr: a (NO·) = 9.6, a (H4, H6) =
H
N
+
1.0, a (H5) = 3.3, a (NPh) = 0.82 gauss; ms: m/z 371 (M , 10
Reaction of Indolinonic Aminoxyl 1 with Potassium Superoxide,
or Potassium tert-Butoxide or Potassium Hydroxide in
Dimethylsulfoxide in the Presence of 2-Iodopropane.
%); 356 (67); 329 (12); 313 (100); hrms calcd for C
371.4612, found 371.4610.
H N O
24 23 2 2
7-Ethoxy-2-methyl-2-phenyl-3-phenylimino-2,3-dihydroindol-
Base (potassium superoxide, potassium tert-butoxide or 1 pel-
let of potassium hydroxide) (1.6 mmol) was added to a solution
of 16 mmol of 2-iodopropane and 0.16 mmol of aminoxyl 1 in
2.5 ml of dimethylsulfoxide. The reaction mixture was stirred for
24 hrs; then 5 ml of distilled water were added and the mixture
was neutralized with 10% hydrochloric acid. The reaction was
extracted with ethylacetate, dried over sodium sulphate and con-
centrated to a small volume. The residue was chromatographed
on preparative plates eluting with cyclohexane/ethyl acetate 9:1.
In all cases amine 5 was isolated in 70-80% yield.
1-oxyl (3'd).
This compound was obtained as dark red solid; ir: 1644, 1583,
-1
N
H
1469, 1417, 1331, 1258 cm ; epr: a (NO·) = 10.0, a (H4,
H
N
H6) = 1.0, a (H5 or H7) = 3.0, a (NPh) = 0.85 gauss; ms: m/z
+
357 (M , 71 %); 341 (42); 329 (7); 313 (18); 77 (100); hrms
calcd for C
H N O 357.4342, found 357.4343.
23 21 2 2
1-(2-Butoxy)-2-methyl-2-phenyl-1,2-dihydroindol-3-ylidene)-
phenylamine (4c).
This compound was obtained as yellow solid; ir: 1660, 1600,
-1
1
Reaction of Amine 5 with Potassium Hydroxide and
Iodomethane in Dimethylsulfoxide.
755, 695 cm ; H NMR: δ 0.84 (2H, m, CH -CH(O)-CH -CH );
3
2
3
0.85 (3H, t, CH -CH(O)-CH -CH , J = 7.3 Hz); 1.24 (3H, d,
3
2
3
CH -CH(O)-CH -CH , J = 6.1 Hz); 1.93 (s, 3H, Ind-CH ); 3.55
3
2
3
3
Potassium hydroxide (1 pellet) was added to a solution of 16
mmol of iodomethane and 0.16 mmol of amine 5 in 2.5 ml of
dimethylsulfoxide. The reaction mixture was stirred for 24 hrs;
then 5 ml of distilled water were added and the mixture was neu-
tralized with 10% hydrochloric acid. The reaction was extracted
with ethylacetate, dried over sodium sulphate and concentrated to
a small volume. The residue was chromatographed on prepara-
tive plates eluting with cyclohexane/ethyl acetate 9:1 and product
6e was isolated in 63% yield.
(1H, m, CH -CH(O)-CH -CH ); 6.38 (1H, d, H7, J = 7.7 Hz);
3
2
3
6.64 (1H, t, H6, J = 7.2 Hz); 6.78 (2H, bd, arom.); 7.1 (2H, m,
arom.); 7.35 (6H, m, arom.); 7.54 (2H, m, arom.) ppm; ms: m/z
+
370 (M , 41 %); 298 (100).
Anal. Calcd. For C
H N O: C, 81.05; H, 7.07; N, 7.56.
25 26 2
Found: C, 81.03; H, 7.09; N, 7.48.
1-Ethyl-2-methyl-2-phenyl-1,2-dihydroindol-3-ylidene)-phenyl-
amine (6d).
Reaction of Amine 5 with Potassium Superoxide or Potassium
Hydroxide in Dimethylsulfoxide.
This compound was obtained as yellow solid, mp 85-87 °C; ir:
-1
1
1653, 1601, 1481, 1317 cm
; H NMR: δ 1.16 (3H, t,
-NCH CH , J = 7.1 Hz); 1.92 (3H, s, Ind-CH ); 3.18 (1H, dq,
2
3
3
Potassium superoxide (1.6 mmol) or 1 pellet of potassium
hydroxide was added to a solution of 0.16 mmol of amine 5 in
2.5 ml of dimethylsulfoxide. The reaction mixture was stirred for
24 hrs; then 5 ml of distilled water were added and the mixture
was neutralized with 10% hydrochloric acid. The reaction was
extracted with ethylacetate, dried over sodium sulphate and
concentrated to a small volume. In all cases only the starting
amine was recovered.
-NCH CH , J = 14.2 and 7.2 Hz); 3.39 (1H, dq, -NCH CH , J =
2
3
2
3
14.2 and 7.2 Hz); 6.34 (2H, m, arom.); 6.71 (1H, m, arom.); 7.07
(1H, tt, arom., J = 7.4 and 1.2 Hz); 7.3 (8H, m, arom.) ppm; ms:
+
m/z 326 (M , 76 %); 311 (36); 297 (100); 282 (54).
Anal. Calcd. For C
H N : C, 84,63; H, 6,79; N, 8,58. Found:
23 22 2
C, 84,62; H, 6,81; N, 8,50.
1,2-Dimethyl-2-phenyl-1,2-dihydro-indol-3-ylidene)-phenyl-
amine (6e).
Reaction of Amine 6 with Potassium Hydroxide in
This compound was obtained as yellow solid, mp 89-91 °C; ir:
Dimethylsulfoxide.
-1
1
1653, 1601, 1481, 1317 cm ; H NMR: δ 1.89 (3H, s, Ind-CH );
3
Potassium hydroxide (1 pellet) was added to a solution of
0.16 mmol of amine 6e in 2.5 ml of dimethylsulfoxide. The
reaction mixture was stirred for 24 hrs; then 5 ml of distilled
water were added and the mixture was neutralized with 10%
hydrochloric acid. The reaction was extracted with ethylacetate,
dried over sodium sulphate and concentrated to a small volume,
where only the starting amine was recovered.
2.84 (3H, s, -NCH ); 6.35 (2H, m, arom.); 6.66 (1H, d, arom., J =
3
8.1 Hz); 6.76 (2H, m, arom.); 7.08 (1H, tt, arom., J = 7.4 and 1.2
+
Hz); 7.31 (8H, m, arom.) ppm; ms: m/z 312 (M , 59 %); 297
(100); 282 (53).
Anal. Calcd. For C
H N : C, 84,58; H, 6,45; N, 8,97. Found:
22 20 2
C, 84,59; H, 6,47; N, 8,93.
(1-Ethyl-2-methyl-1H-indol-3-yl)-methylphenylamine (7d).
Reaction of 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) with
tert-Butylhydroperoxide and Lead Dioxide in Different Solvents.
This compound was obtained as white solid, mp 145-7 °C; ir:
-1
1
1597, 1496, 1456, 1368, 1339, 1229 cm ; H NMR: δ 1.34 (3H,
t,-NCH CH , J = 7.2 Hz); 3.09 (3H, s,Ph-N-CH ); 4.19 (2H, q,
General Procedure.
2
3
3
-NCH CH , J = 7.2 Hz); 6.68 (2H, m, arom.); 7.28 (12H, m, arom.)
ppm; ms: m/z 326 (M , 100 %); 311 (32); 297 (39); 282 (61).
Lead dioxide (155 mg, 0.64 mmol) was added to a solution of
100 mg (0.64 mmol) of 2,2,6,6-tetramethylpiperidin-1-oxide
2
3
+

464
P. Carloni, R. Vianelli and L. Greci
Vol. 40
[9] P. Stipa, L. Greci, P. Carloni and E. Damiani, Polym.
Degrad. Stab., 55, 323 (1997).
[10] P. Carloni, E. Damiani, M. Scattolini, P. Stipa and L.
Greci, J. Chem. Soc. Perkin Trans. 2, 447 (2000).
[11] E. Damiani, P. Carloni, P. Stipa and L. Greci, Free Radical
Research, 31, 113 (1999).
[12] L. Cardellini, P. Carloni, L. Greci and P. Stipa, Gazz.
Chim. Ital., 119, 621 (1989).
[13] J. San Filippo Jr., C.-I. Chern and J. S. Valentine, J. Org.
Chem., 40, 1678 (1975).
[14] R. A. Johnson, E. G. Nidy and M. V. Merritt, J. Am. Chem.
Soc., 7960 (1978).
[15] C.-I. Chern, R. Di Cosimo, R. De Jesus and J. San Filippo
Jr., J. Am. Chem. Soc., 8, 7317 (1978).
[16] D. T. Sawyer and J. S. Valentine, Acc. Chem. Res., 14, 393
(1981).
[17] M. V. Merritt and D. T. Sawyer, J. Org. Chem., 35, 2157
(1970).
(TEMPO) in 10 ml of solvent (benzene or acetone); to the mix-
ture, a solution of 0.82 ml (6.4 mmol) of tert-butylhydroperoxide
(70% in water) in 5 ml of solvent was added dropwise. The reac-
tion mixture was stirred for 1 hr; then 10 ml of distilled water were
added and the reaction was extracted with methylene chloride,
dried over sodium sulphate and concentrated to a small volume.
The residue was chromatographed on preparative plates eluting
with cyclohexane/ethyl acetate 9:1. When the solvent used was
acetone, besides the starting aminoxyl, 1-(2,2,6,6-tetra-
methylpiperidin-1-yloxy)-propan-2-one (29 %) was recovered.
1-(2,2,6,6-Tetramethylpiperidin-1-yloxy)-propan-2-one.
This compound was obtained as colourless oil; ir: 2900; 1710
-1
1
(C=O); 1455; 1365; 1350; 1125; 1075 cm ; H NMR: δ 1.13
(12H, d, CH ); 1.45 (6H, d, CH ); 2.19 (3H, s, -NOCH C(O)CH );
3
2
2
3
13
4.36 (2H, s, -NOCH C(O)CH ) ppm; C NMR: δ 17.43, 20.61,
27,74, 33.34, 40.07, 60.53, 83.76, 207.4 ppm; ms: m/z 213 (M , 4
%); 198 (52); 156 (23).
2
3
+
[18] R. Dietz, A. E. Forno, B. E. Larcombe, and M. E. Peover,
J. Chem. Soc. (B), 816 (1970).
[19] J. S. Valentine and A. B. Curtis, J. Am. Chem. Soc., 224
(1975).
REFERENCES AND NOTES
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Petrucci and A. Trazza, Tetrahedron, 52, 11257 (1996).
[22] A. R. Forrester and R. H. Thomson, Nature, 203, 74
(1964).
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