Methyltrioxorhenium catalyzed synthesis of dinitrones from primary diamines and non-enolizable aldehydes

Article abstract of DOI:10.2174/157017811796504873

Green Chemistry is the design of chemicals and processes that reduce or eliminate the use and generation of hazardous substances, and consequently reduce the risk to human health and the environment. Nitrones have various applications, such as building bl

Full text of DOI:10.2174/157017811796504873

Letters in Organic Chemistry, 2011, 8, 495-499
495
Methyltrioxorhenium Catalyzed Synthesis of Dinitrones from Primary
Diamines and Non-Enolizable Aldehydes
Reza Najjar*,a and Kazem D. Safab
aPolymer Research Laboratory, Faulty of Chemistry, University of Tabriz, 5166616471, Tabriz, Iran
bOrganosilicon Research Laboratory Faulty of Chemistry, University of Tabriz, 5166616471, Tabriz, Iran
Received January 28, 2011: Revised April 25, 2011: Accepted April 25, 2011
Abstract: Green Chemistry is the design of chemicals and processes that reduce or eliminate the use and generation of
hazardous substances, and consequently reduce the risk to human health and the environment. Nitrones have various ap-
plications, such as building blocks in the synthesis of natural and biologically active compounds and molecular weight
regulators in radical polymerization. In this work, dinitrones were successfully synthesized in a one-pot process from pri-
mary diamines and proper aromatic aldehydes employing methyltrioxorhenium (MTO) as catalyst and urea-hydrogen per-
oxide adduct (UHP) as oxidizing agent. Diamines, such as 1,6-diaminohexane and 1,12-diaminododecane were reacted
with benzaldehydes bearing various substituent, such as 4-chloro, 4-nitro, 4-methoxybenzaldehyde, and also furfural. The
resulting N,N'-bis (benzylidene)-1,6-hexanediamine N,N'-dioxides or N,N'-bis (benzylidene)-1,12-dodecanediamine N,N'-
dioxides (or substituted benzylidenes) were separated with 45-60 % yields. The main advantage of the one-pot process is
the elimination of need for several separation and purification steps and reduction in consumption of chemicals and waste
1
production. The products selectively were characterized by H-NMR, 13C-NMR, FT-IR spectroscopies, and elemental
analysis (CHNS).
Keywords: Dinitrones, green chemistry, methyltrioxorhenium (MTO), one-pot reaction, urea-hydrogen peroxide (UHP).
INTRODUCTION
In another work, aldimines have been photochemically
oxidized to nitrones, over TiO2 particles suspended in
acetonitrile in the presence of oxygen [15]. The wavelength
of light used in this photooxidation has been 350 nm.
During the last few decades, many scientists in different
fields have drawn special attention to the nitrones, due to
their successful application as building blocks in the synthe-
sis of various natural and biologically active compounds,
stable nitroxyl radicals, and other important products [1].
Among those products some are designed for special pur-
poses such as spin traps [2, 3] for the study of radical proc-
esses including those that take place in biological systems,
sensors and probes for monitoring acid-base, redox, and free
radical processes [4], or some used as modifiers and regula-
tors of molecular weight in radical polymerization [5]. The
1,3-dipolar cycloaddition reaction with other proper com-
pounds, is one of the most popular reactions of nitrones,
leading to a very versatile range of products [6]. Nitrones
have been synthesized using different methods, such as oxi-
dative routes including oxidation of imines, amines, and hy-
droxylamines [7], or non oxidative methods, including con-
densation of substituted hydroxyl amines with carbonyls [8],
use of oximes [9], nitro [10], and nitroso compounds [11].
For oxidation of imines, reagents such as metachloroperben-
zoic acid [12] or potassium peroxymono sulfate [13]. have
been used as oxidants. Recently, hydrogen peroxide has been
used for the oxidation of chiral imines to access a new series
of calix[4]arene derivatives with one or two nitrone groups
on the upper rim. The imine intermediates used for this reac-
tion, were prepared via amination of the diformyl derivatives
of the calix[4]arenes [14].
There are few reports that imines have been reduced to
secondary amines and afterwards the resulting secondary
amines were oxidized to nitrones [16]. The oxidation of sec-
ondary amines to nitrones with excellent yields, also has
been conducted using methyltrioxorhenium (MTO)
-
hydrogen peroxide system [17], or polymer supported MTO-
H2O2 system [18]. The combination of MTO with oxygen
has been proved as another technique for oxidation of secon-
dary amines to nitrones [19]. The oxidation of hydroxy-
lamines containing at least one proton on the ꢀ- carbon
atom, to nitrones has been carried out by different oxidants,
such as air, metachloroperbenzoic acid, hydrogen peroxide,
and metal oxides (such as PbO2, MnO2, HgO) [20]. Among
the non-oxidative methods, condensation of the N-benzyl
hydroxyl amines with different aldehydes and ketones in the
presence of anhydrous magnesium sulfate have resulted in
the successful synthesis of the N-benzylnitrones containing
chiral and achiral sugars [21]. The same method has been
used for preparation of chiral dinitrones by condensation of a
C2-symmetrical chiral dihydroxylamine with different alde-
hydes. The electronic and steric properties of the dinitrones
can be modified by changing the aldehyde component [22].
The activity of dinitrones as Lewis base catalysts was exam-
ined for the asymmetric allylation of aldehydes with allyl-
trichlorosilanes. Dinitrones has been also synthesized via
condensation of N-benzylhydroxylamine with adequate reac-
tants, such as glutaraldehyde. Their intramolecular pinacol
coupling reaction induced with Samarium diiodide (SmI2)
*Address correspondence to this author at the Polymer Research Labora-
tory, Faulty of Chemistry, University of Tabriz, 5166616471, Tabriz, Iran;
Tel: +98-411-3393101; Fax: +98-411-3340191; E-mail: najjar@tabrizu.ac.ir
1570-1786/11 $58.00+.00
© 2011 Bentham Science Publishers

496 Letters in Organic Chemistry, 2011, Vol. 8, No. 7
Najjar and Safa
was carried out, resulting in the formation of cyclic vicinal
diamines with good cis-selectivity [23].
The melting points of products were measured using a Stuart
melting point apparatus from Barloworld Scientific Ltd, UK
(SMP3 model).
N-alkylation of oximes offers a facile non-oxidative
method for the preparation of nitrones [9, 24]. Intramolecular
cyclization of hydroxylaminoalkynes, depending on the rela-
tive position of the hydroxylamino group and acetylenic part
results in the formation of the corresponding 5-, to 7-
membered cyclic nitrones [25].
Nuclear Magnetic Resonance (1H-NMR and 13C-NMR)
spectra of the compounds were recorded in CDCl3 at 25 °C
on a Brucker Avance 400 MHz spectrometer. Chemical
shifts were reported in ppm using tetramethylsilane (TMS)
as internal standard. Coupling constants were reported in
hertz (Hz). Fourier Transform Infrared (FT-IR) spectra of the
compounds were recorded as a thin film on KBr disk using a
Brucker Tensor 27 spectrometer. The required amounts of
the chemicals were weighed to 0.1 mg precision by a balance
from AND, Japan, model HR-200. The elemental analysis
measurements were carried out using a Vario EL analyzer,
from Elementar Analysensysteme GmbH, Germany.
More recently, a great tendency has been observed in
finding green and sustainable processes, to prevent consump-
tion of large amounts of chemicals as well as production of
large volumes of the chemical wastes [26]. A green method
for the synthesis of nitrones has been reported in the litera-
ture [27]. In this method, under the solvent-free conditions in
a ball-mill apparatus, an equimolar mixture of an aldehyde,
N-substituted-hydroxylamine hydrochloride, and NaHCO3
were ball-milled for 0.5-2 h to obtain the corresponding ni-
trones. Using this method, C-aryl and C-alkyl-nitrones were
synthesized without any need for excluding air and moisture.
The yields of the expected products were so high that there
was no need for purification of the products, for example,
nitrones such as N-(2-iodobenzylidene) methylamine N-
oxide, N-benzylidene-tert-butylamine N-oxide, N-(pyridine-
4-ylmethylidene) benzylamine N-oxide, and N-(napht-2-
ylmethylidene) benzylamine N-oxide have been obtained
almost quantitatively.
General Procedure for the Preparation of Dinitrones
5 mL methanol, 750 mg of Na2SO4, and 1 mmol of de-
sired diamine were weighed into a 10 mL round bottom flask
equipped with a magnetic stirrer bar. The content of reaction
flask was then stirred on a magnetic stirrer for few minutes.
Afterwards, 2.05 mmol of required aldehyde was added to
the reaction mixture. Stirring was continued until completion
of the reaction, which was monitored by almost complete
disappearance of the aldehyde on the TLC plate. The reac-
tion mixture was then cooled to 0 °C and stirred for few
minutes. Subsequently, 0.04 mmol (10 mg) of MTO catalyst
(2 mol % relative to aldehyde; 4 mol % relative to the dia-
mine) and 566 mg (3 equivalents) of UHP as oxidizing agent
were added to the stirred reaction mixture. The reaction was
continued for the times mentioned in Table 1. The reaction
mixture was filtered to remove the sodium sulfate, and the
filtrate was washed with a few milliliters of methanol. The
solvent (methanol) was then removed under reduced pres-
sure. CH2Cl2 was added to the resulting residue, and stirred
for 5 minutes. The un-dissolved urea was filtered off. Re-
moval of the solvent leaves the crude product which was
purified on silica gel TLC plates. The yields of the products,
which in most of the cases were white to pale yellow solids,
are given in Table 1.
In this work, we report a facile one-pot method for the
synthesis of the dinitrones. The main advantage of the pre-
sented method is that it is one-pot, which avoids several
separation and workup steps, and the use of large amounts of
solvents. Hence, it is a green method. Using this simple
method, several dinitrones were prepared via catalytic oxida-
tion of diimines, which have been formed in situ by the reac-
tion of primary diamines with different aromatic aldehydes
(Scheme 1). The products were characterized using different
spectroscopic methods such as nuclear magnetic resonance
(1H-NMR, and 13C-NMR), Fourier Transform Infrared (FT-
IR) spectroscopies and elemental analysis (CHNS).
MATERIALS AND METHODS
Methyltrioxorhenium (MTO, containing 71 wt % rhe-
nium), urea-hydrogen peroxide adduct (UHP, 97 %), and
1,12-diaminododecane (97 %) were purchased from Aldrich
Chemical Co, and used without any further purification. 1,6-
Diaminohexane (99 %, Merck) was sublimated in vacuum at
45 °C. Benzaldehyde (99 %, Merck), 4-methoxybenzal-
dehyde (98 %, Merck), and furan-2-carboxaldehyde (98 %,
Aldrich) were distillated in vacuum shortly before use. 4-
Chlorobenzaldehyde (98 %, Merck) and 4-nitrobenzaldehyde
(98 %, Merck) were sublimated in vacuum at temperatures
slightly higher than their melting temperature (respectively,
at 55 °C and 110 °C) [28].
RESULTS AND DISCUSSION
The results concerning the experiments of the one-pot
synthesis of dinitrones from primary diamines and aromatic
aldehydes via condensation-oxidation reaction using methyl-
trioxorhenium (MTO) as catalyst (Scheme 1), are given in
the Table 1.
MTO
O-
O-
UHP
R - CHO + H2N-(CH2)n-NH2
R
N+
N+
R
MeOH
rt
n
-
R = C6H5- , p-NO2-C6H4-, p-Cl-C6H4 , p-MeO-C6H4- or 2-furyl-
Methanol used as solvent was refluxed over -and distil-
lated over calcium sulfate, and freshly used for the reaction.
Ethyl acetate was of high purity grade and distillated before
use. High purity grade dichloromethane was refluxed over
calcium chloride for 6 h, and then distillated. Petroleum
ether was fractionally distillated and the light fraction boiling
at 40-60 °C was separated and used as solvent in this work.
n = 6 or 12
Scheme 1.
The experiments carried out here, are very simple,
straightforward, and without any need for the special cares,
such as removal of oxygen from the reaction medium. The

Methyltrioxorhenium Catalyzed Synthesis of Dinitrones
Letters in Organic Chemistry, 2011, Vol. 8, No. 7
497
reactants have been mixed at room temperature in a few mil-
liliters of methanol as solvent, which has been known as one
of the benign and environmentally friendly solvents. The
oxidant used in this study was solid urea hydrogen peroxide
(UHP), which nevertheless has a relatively high content of
hydrogen peroxide (36.2 %). It is a very safe and stable oxi-
dizing agent compared to the anhydrous hydrogen peroxide
[29], and can be stored at room temperature without any de-
crease in its oxygen content, even for a period of twelve
months. The reaction was catalyzed by 2 mol % of MTO
relative to aldehyde functional group. To facilitate the reac-
tion between aldehyde and amine, anhydrous sodium sulfate
has been added to the reaction medium to absorb the water
released during imine formation.
trone in the second step. Result indicated that, the yield of
the two steps reaction is slightly higher than that of one-pot
reaction (entry 3, Table 1). This implies that the presented
one-pot reaction offers a very useful method for the synthe-
sis of dinitrones, and in price of only a slight decline in the
yield, one can decrease the amount of solvents used for the
reaction by almost 50 %. On the other hand, this observation
proves that the reaction occurs through the formation of
imine by condensation of amine with aldehyde [31]. In the
first step, the oxidation of amine to N-hydroxylamine, with
UHP, is another path mentioned in the literature for the for-
mation of nitrones in one-pot reaction [32]. Then, the subse-
quent condensation of the N-hydroxylamine formed with the
aldehyde leads to the formation of the final product, the dini-
trone [33]. Here, as the oxidant and the catalyst were added
after complete formation of the diimine, it can be concluded
that the imine formation pathway has been the main route for
the formation of the products.
The aldehydes used in this work has been aromatic alde-
hydes bearing different substitutes on the aromatic ring, to-
gether with 1,6–diaminohexane and 1,12–diaminododecane.
The experiment carried out using hexanal, an aliphatic alde-
hyde, which produced a final crude product composed of
many by-products that, their separation was practically very
difficult. A slight excess of aldehyde was added to the reac-
tion medium to ensure the reaction of both amine groups on
each diamine molecule with the aldehyde, and consequently,
formation of the nitrone at both ends of the diamine mole-
cule.
After completion of the reaction, sodium sulfate was fil-
tered off and washed with 2 mL of methanol. The solvent
was then removed from the resulting filtrate at reduced pres-
sure using a rotary evaporator. The residue containing the
product as well as the urea released from the UHP during the
reaction was obtained. It was taken up into 5 mL of dry
dichloromethane, and the undissolved urea was filtered off.
The spectral characteristics observed for the products are
consistent with results from the literature for similar com-
pounds [23, 31]. The spectral data and characterization of
each product are given.
The addition of MTO in the reaction medium leads to an
instantaneous color change to yellow. This was attributed to
the formation of the catalytically active peroxorhenium spe-
cies [30]. The reaction was checked by TLC until almost
complete disappearance of aldehyde. The times required for
completion of reaction in each case are given in Table 1.
Selected Characterization Data of the Products
In most cases, dinitrones produced by simple mixing of
the reactants (one-pot reaction) were obtained with relatively
high yields. The one-pot reaction was compared with the two
steps reaction, namely, synthesis and separation of the di-
imine in the first step, and its subsequent oxidation to dini-
N,N'-bis benzylidene-1,6-hexanediamine N,N'-dioxide (1a)
Yield: 55 %; m.p. 157-159 °C; FT-IR (film CH2Cl2,
1
cm-1): 3065, 2924, 2857, 1633, 1454, 1155, 754, 692; H-
NMR (400 MHz, CDCl3, ꢀ/ppm): 8.21 (m, 4 H), 7.33–7.44
Table 1. MTO Catalyzed Synthesis of Dinitrones from Non-Enolizable Aldehydes and Diamines
MTO
UHP
O-
O-
R - CHO + H2N-(CH2)n-NH2
R
N+
N+
R
MeOH
rt
n
Entry
dinitrone
n
R
Reaction time (h)
Yield (%)
1
2
1a
2b
1a
2a
2b
3a
3b
4a
4b
5a
5b
6
12
6
C6H5-
C6H5-
12
16
-
55
49
3
C6H5-
58(a)
50
4
6
p-NO2-C6H4-
p-NO2-C6H4-
p-Cl-C6H4-
p-Cl-C6H4-
2-Furyl
10
13
11
15
12
14
10
12
5
12
6
45
6
44
7
12
6
52
8
45
9
12
6
2-Furyl
42
10
p-MeO-C6H4-
p-MeO-C6H4-
60
11
12
56
aThe reaction was done in two steps.

498 Letters in Organic Chemistry, 2011, Vol. 8, No. 7
Najjar and Safa
(m, 8 H), 3.93 (t, 3J=7.0 Hz, 4 H, CH2), 2.01 (m, 4 H, CH2),
1.32 (m, 4 H, CH2); 13C-NMR (400 MHz, CDCl3, ꢀ/ppm):
136.3, 131.1, 128.3, 127.5, 67.9, 28.4, 27.8, 26.5; Anal.
Calcd. for C20H24O2N2: C 74.05; H 7.45; N 8.63. Found: C
73.88; H 7.71; N 8.71; Rf = 0.25 (ethyl acetate 2: methanol
1).
(m, 4 H, CH2), 1.34 (m, 4 H, CH2); Rf = 0.25 (ethyl acetate 2:
methanol 1).
N,N'-bis
(furan-2-ylmethylene)-1,12-dodecanediamine
N,N'-dioxide (4b)
Yield: 42 %; m.p. 149-151 °C; FT-IR (film CH2Cl2, cm-
1): 3055, 2919, 2851, 1625, 1610, 1587, 1473, 1274, 1159,
N,N'-bis benzylidene-1,12-dodecanediamine N,N'-dioxide
(1b)
1
1092, 1013, 938, 836; H-NMR (400 MHz, CDCl3, ꢀ/ppm):
8.18 (m, 2 H), 7.29–7.45 (m, 6 H), 3.96 (t, 4 H, CH2), 1.93
(m, 4 H, CH2), 1.29 (m, 16 H, CH2); Rf = 0.3 (ethyl acetate
2: methanol 1).
Yield: 49 %; m.p. 156-158 °C; FT-IR (film CH2Cl2, cm-
1): 3055, 2935, 2875, 1625, 1460, 1189, 1100, 915, 754, 692;
1H-NMR (400 MHz, CDCl3, ꢀ/ppm): 8.23 (m, 4 H), 7.24–
3
3
7.44 (m, 8 H), 3.86 (t, J=7.0 Hz, 4 H, CH2), 1.99 (t, J=7.0
Hz, 4 H, CH2), 1.33 (m, 16 H, CH2); Rf = 0.33 (ethyl acetate
2: methanol 1).
N,N'-bis (4-methoxybenzylidene)-1,6-hexanediamine N,N'-
dioxide (5a)
Yield: 60 %; FT-IR (film CH2Cl2, cm-1): 3057, 2937,
1
N,N'-bis (4-nitrobenzylidene)-1,6-hexanediamine N,N'-
dioxide (2a)
2865, 1641, 1595, 1475, 1275, 1165, 1100, 948, 628; H-
NMR (400 MHz, CDCl3, ꢀ/ppm): 8.2 (m, 4 H), 7.17–7.44
(m, 4 H), 6.95 (m, 2 H), 3.8-3.96 (m, 4 H, CH2), 3.81 (s, 6
H), 1.89 (m, 4 H, CH2), 1.33 (m, 4 H, CH2); Rf = 0.3 (ethyl
acetate 2: methanol 1).
Yield: 50 %; m.p. decomposed at about 130 °C; FT-IR
(film, CH2Cl2, cm-1): 3050, 2984, 2945, 1635, 1584, 1494,
1
1456, 1345, 1210, 1160, 1090, 810; H-NMR (400 MHz,
CDCl3, ꢀ/ppm): 8.24 (m, 4 H), 7.63–7.78 (m, 4 H), 7.26 (m,
2 H), 3.65 (t, 4 H, CH2), 1.57 (m, 4 H, CH2), 1.26 (m, 4 H,
CH2). 13C-NMR (400 MHz, CDCl3, ꢀ/ppm): 132.2, 130.3,
128.7, 127.9, 66.4, 28.4, 26.8, 25.5; Anal. Calcd. for
C20H22O6N4: C 57.97; H 5.35; N 13.52. Found: C 57.81; H
5.88; N 13.41; Rf = 0.26 (ethyl acetate 2: methanol 1).
N,N'-bis
N,N'-dioxide (5b)
(4-methoxybenzylidene)-1,12-dodecanediamine
Yield: 56 %; FT-IR (film CH2Cl2, cm-1): 3055, 2927,
2857, 1639, 1587, 1480, 1279, 1159, 1091, 1010, 951, 833;
1H-NMR (400 MHz, CDCl3, ꢀ/ppm): 8.2 (m, 4 H), 7.17–7.44
(m, 4 H), 6.95 (m, 2 H), 3.8-3.96 (m, 4 H, CH2), 3.81 (s, 6
H), 1.89 (m, 4 H, CH2), 1.33 (m, 4 H, CH2); Rf = 0.37 (ethyl
acetate 2: methanol 1).
N,N'-bis (4-nitrobenzylidene)-1,12-dodecanediamine N,N'-
dioxide (2b)
Yield: 45 %; m.p. decomposed at about 130 °C; FT-IR
(film CH2Cl2, cm-1): 3051, 2990, 2948, 1640, 1591, 1492,
1
1450, 1347, 1204, 1155, 1090, 820; H-NMR (400 MHz,
CONCLUSIONS
CDCl3, ꢀ/ppm): 8.22 (m, 4 H), 7.25–7.42 (m, 6 H), 3.91 (t, 4
H, CH2), 1.97 (m, 4 H, CH2), 1.31 (m, 16 H, CH2); Rf = 0.22
(ethyl acetate 2: methanol 1).
The condensation-oxidation of the aromatic aldehydes
with primary diamines was performed successfully using the
UHP system as an oxidant, and MTO as a catalyst. This one-
pot synthesis produced the corresponding dinitrones in rela-
tively high yields. The method has been proved to be an effi-
cient and useful way to obtain dinitrones. As the reactions
were performed in one step, the consumption of large
amounts of solvents and chemicals, and the production of
large amounts of chemical waste were avoided. Hence, this
method is considered as a green method. It was concluded
that the reaction proceeded through in situ imine formation
and its subsequent oxidation to the dinitrones. Dinitrones
such as N,N'-bis (benzylidene)-1,6-hexanediamine N,N'-
dioxides or N,N'-bis (benzylidene)-1,12-dodecane-diamine
N,N'-dioxides (or substituted benzylidenes) were prepared
with yields of 45-60 %. The structure of the products was
N,N'-bis (4-chlorobenzylidene)-1,6-hexanediamine N,N'-
dioxide (3a)
Yield: 44 %; FT-IR (film CH2Cl2, cm-1): 3043, 2989,
1
2950, 1640, 1585, 1497, 1430, 1210, 1100, 1065, 835; H-
NMR (400 MHz, CDCl3, ꢀ/ppm): 8.19 (m, 4 H), 7.22–7.47
(m, 6 H), 3.91 (t, 3J=7.1 Hz, 4 H, CH2), 1.98 (t, 3J=7.0 Hz, 4
H, CH2), 1.28 (m, 4 H, CH2); Rf = 0.23 (ethyl acetate 2:
methanol 1).
N,N'-bis
(4-chlorobenzylidene)-1,12-dodecanediamine
N,N'-dioxide (3b)
Yield: 52 %; FT-IR (film CH2Cl2, cm-1): 3050, 2995,
1
2940, 1635, 1592, 1487, 1428, 1211, 1095, 1045, 831; H-
1
confirmed by spectroscopic methods such as H-NMR, 13C-
NMR (400 MHz, CDCl3, ꢀ/ppm): 8.21 (m, 4 H), 7.23–7.49
(m, 6 H), 3.88 (t, 3J=7.1 Hz, 4 H, CH2), 1.96 (m, 4 H, CH2),
1.25 (m, 16 H, CH2); Anal. Calcd. for C26H34O2N2Cl2: C,
65.40; H 7.17; N 5.86. Found: C 65.01; H 7.08; N 5.78; Rf =
0.26 (ethyl acetate 2: methanol 1).
NMR, FT-IR spectroscopy and, also elemental analysis
(CHNS).
ACKNOWLEDGEMENT
N,N'-bis (furan-2-ylmethylene)-1,6-hexanediamine N,N'-
dioxide (4a)
The authors would like to thank the financial support of
the Center of Excellence in Clean Chemistry and New Mate-
rials of Faculty of Chemistry, University of Tabriz, Tabriz,
Iran. RN would likes to thank Prof. Dr. Cosima Stubenrauch
for her supports in this project.
Yield: 45 %; m.p. 146-148 °C; FT-IR (film CH2Cl2, cm-
1): 3055, 2930, 2849, 1615, 1607, 1587, 1471, 1270, 1160,
1
1100, 1010, 935, 830; H-NMR (400 MHz, CDCl3, ꢀ/ppm):
8.16 (m, 2 H), 7.28–7.41 (m, 6 H), 3.98 (t, 4 H, CH2), 1.99

Methyltrioxorhenium Catalyzed Synthesis of Dinitrones
Letters in Organic Chemistry, 2011, Vol. 8, No. 7
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