Selective oxidation of N-alkyl imines to oxaziridines using UHP/maleic anhydride system

Article abstract of DOI:10.1055/s-2002-31903

Several structurally differentiated N-alkyl imines were oxidized to their corresponding oxaziridines using UHP/maleic anhydride system. Oxidation reaction was performed under mild conditions and oxaziridines were obtained in good to excellent yields.

Full text of DOI:10.1055/s-2002-31903

LETTER
933
Selective Oxidation of N-Alkyl Imines to Oxaziridines using UHP/Maleic
Anhydride system
Selective
Oxidation
o
f
f
N
-Alky
a
l
Imines r Asgarian Damavandi,a Bahador Karami,a Mohammad Ali Zolfigol*b
a
Faculty of Chemistry, University of Teacher Training, Tehran, I. R. Iran
b
Chemistry Department, College of Science, Bu-Ali Sina University, Hamadan, Zip Code 65174, Post Box No. 4135, I. R. Iran
E-mail: Zolfi@basu.ac.ir
Received 28 February 2002
peroxide and urea] is the best candidate for this purpose.
A survey of the literature revealed that UHP I is an inex-
pensive, stable, and easy to handle source of pure H2O2.13
In the last few years, several reports appeared on the use
of UHP in the oxidations, namely for the conversion of
amines to nitroalkane,14 Baeyer–Villiger oxidations of ke-
tones to lactones,15 oxidations of sulfides to sulfones,16
oxidation of aromatic aldehydes,17 aromatization of 1,4-
dihydropyridines,18 selective oxidation of uracil and ade-
nine derivatives,19 epoxidation of alkenes,20 and conver-
sion of pyridines to pyridine N-oxides under different
conditions.21,22 Thus, in this article we wish to report a
simple, cheap and convenient method for the effective
conversion of N-alkyl imines 1 to their corresponding ox-
aziridines 2 under mild conditions (Scheme).
Abstract: Several structurally differentiated N-alkyl imines were
oxidized to their corresponding oxaziridines using UHP/maleic an-
hydride system. Oxidation reaction was performed under mild con-
ditions and oxaziridines were obtained in good to excellent yields.
Key words: UHP, N-alkyl imines, oxaziridines
Oxaziridines are useful aprotic oxidizing reagents for a
large variety of substrates. The aprotic nature of these re-
agents has made possible the facile synthesis of extremely
acid-sensitive species such as -siloxy epoxides1 and
sulfenic acids.2 In recent years, the asymmetric oxidation
of prochiral centers to the desired optically active prod-
ucts by using chiral oxaziridines have received consider-
able attention.3
A good range of N-alkyl imines 1 were subjected to the
oxidation reaction in the presence of UHP I, and maleic
anhydride in methanol. The oxidation reactions were per-
formed under mild conditions at 0 °C with good to excel-
lent yields (Scheme). The reactions were completed after
40–50 min. Highly pure oxaziridines 2 were finally ob-
tained after removing of solvent.23,24
Several methods have been employed for the oxidation of
imines into the corresponding oxaziridines. The most
general reagent is m-chloroperbenzoic acid.4,5 Other
oxidizing
agents
such
as
buffered
oxone®
(2KHSO5 KHSO4 K2SO4)6, in situ generation of sulfonic
or carboxylic peracids,7 and molecular oxygen in the pres-
ence of transition-metal complexes8 have been also used.
Although a variety of reagents are capable of affecting
these oxidations,1–8 as far as we know this transformation
is not so easy and is a tricky step because these com-
pounds are very sensitive to the oxidizing agents and re-
action conditions. However, most of the reported reagents
produce by-products, which either destroy, or are difficult
to remove from the sensitive oxaziridines. For example,
m-chloroperbenzoic acid is expensive and large-scale ox-
idations are sometimes contaminated with bis-(m-chlo-
roperbenzoyl) peroxide, which complicates product
purification. Meanwhile, we also know that imines are
susceptible to hydrolysis in aqueous media.1–8 For these
reasons an oxidizing reagent that would avoid these diffi-
culties was sought. Therefore, we were interested in find-
ing a new reagent or reagent system to overcome the
above limitations and we have investigated a number of
different reaction conditions based upon the in situ gener-
ation of H2O2. In continuing our studies on the application
of oxone® (2KHSO5 KHSO4 K2SO4)9–11 and H2O2 we
found that UHP12 [I an addition compound of hydrogen
Scheme
Unlike N-alkyl imines 1a–f. (Table, entries 1–6) N-aryl
imines (Table, entries 7 and 8) were converted to the cor-
responding nitrones. The remaining of conjugation in N-
aryl imines may be the main reason why nitrones are
formed instead of oxaziridines. We hope that the de-
scribed method due to the its non-toxicity makes the UHP/
Synlett 2002, No. 6, 04 06 2002. Article Identifier:
1437-2096,E;2002,0,06,0933,0934,ftx,en;G03502ST.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0936-5214

934
J. A. Damavandi et al.
LETTER
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A.; Keypour, H.; Salehzadeh, S. Synth. Commun. 2001, 31,
1661.
Table Oxidation of N-Alkyl Imines 1 to the Corresponding Oxazir-
idines 2 and of N-Aryl Imines to the Corresponding Nitrones with a
Combination of UHP I and Maleic Anhydride in Methanol at 0 °C
Entry Substrate
Product
Time
(min)
Yielda
(%)
1
2
3
4
5
6
7
1a
1b
1c
1d
1e
1f
2a
2b
2c
2d
2e
2f
40
40
45
50
50
50
40
95
95
93
90
80
80
85
(12) Zolfigol, M. A.; Bagherzadeh, M.; Chehardoli, G.;
Mallakpour, S. E.; Mamaghani, M. J. Chem. Res. (S) 2001,
390.
(13) Cooper, M. S.; Heaney, H.; Newbold, A. J.; Sanderson, W.
R. Synlett 1990, 533.
8
40
95
(14) Ballini, R.; Marcantoni, E.; Petrini, M. Tetrahedron Lett.
1992, 33, 4835.
(15) (a) Astodillo, L.; Galindo, A.; Gonzalez, A. G.; Mansilla, H.
Heterocycles 1993, 36, 1075. (b) Uchida, T.; Katsuki, T.
Tetrahedron Lett. 2001, 42, 6911.
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6607.
a Isolated yields.
(18) Perez, J. M.; Lopez-Alvardo, P.; Pascual-Alfonso, E.;
Avendano, C.; Menendez, J. C. Tetrahedron 2000, 56, 4575.
(19) Salandino, R.; Carlucci, P.; Danti, M. C.; Crestini, C.;
Mincione, E. Tetrahedron 2000, 56, 10031.
maleic anhydride system a reagent of choice for replacing
transition metals-based oxidants.25–27
In conclusion, practical and efficient oxidation of N-alkyl
imines was achieved using the present methodology. The
UHP, with easy preparation and handling can act as a safe,
stable and efficient reagent for this transformation under
mild conditions. We believe that the present methodology
is an important addition to existing methodologies.
(20) (a) Pietikainen, P. J. Mol. Cat. A: Chem. 2001, 165, 73.
(b) Kureshy, R. I.; Khan, N. H.; Abdi, S. H. R.; Patel, S. T.;
Jasra, R. V. Tetrahedron: Asymmetry 2001, 12, 433.
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41, 2299.
(23) Yields refer to isolated pure products. The oxidation
products were characterized by comparison of their spectral
(IR, 1H NMR, and 13C NMR) and physical data with the
authentic samples.
Acknowledgement
(24) Oxidation of N-benzylphenyl imine(1a) to 2-benzyl-3-
phenyl oxaziridine(2a) with UHP/maleic anhydride system.
A typical procedure: A suspension of compound 1a (0.390 g,
2 mmol), I (0.188 g, 2 mmol), maleic anhydride (0.176 g, 2
mmol) in methanol (8 mL) was stirred at 0 °C. The progress
of the reaction was monitored by TLC (eluent, EtOAc–n-
hexane, 1:5). The reaction was completed after 40 min. The
reaction mixture was filtered and the filtrate was passed
through a short pad of silica gel. Methanol was removed
under reduced pressure. Highly pure oxaziridine(2a) was
obtained in 95% yield (0.354 g). (FT-NMR 500 MHz)
CDCl3: ppm 4.03–4.22 (dd, 2 H), 4.8 (s, 1 H), 7.45–7.6 (m,
10 H).7a
Financial support for this work by the research affairs of University
of Teaching Training, Tehran, I. R. Iran, and also Bu-Ali Sina Uni-
versity, Hamadan, I. R. Iran, are gratefully acknowledged.
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Synlett 2002, No. 6, 933–934 ISSN 0936-5214 © Thieme Stuttgart · New York