Synthesis of oxazoles from α,β-unsaturated carbonyl compounds through 2-acylaziridines

Article abstract of DOI:10.1134/S107042800908020X

Oxidative addition of N-aminophthalimide to benzylideneacetone and chalcones followed by thermolysis of the arising 2-aryl-3-acyl-1- phthalimidoaziridines led to the formation of 2,5-disubstituted oxazoles in an overall yield 30-55%. Electron-donor substi

Full text of DOI:10.1134/S107042800908020X

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2009, Vol. 45, No. 8, pp. 1229−1240. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © E.V. Beletskii, M.A. Kuznetsov, 2009, published in Zhurnal Organicheskoi Khimii, 2009, Vol. 45, No. 8, pp. 1237−1248.
Synthesis of Oxazoles from α,β-Unsaturated Carbonyl Compounds
through 2-Acylaziridines
E. V. Beletskii and M. A. Kuznetsov
St. Petersburg State University, St. Petersburg, 198504 Russia
e-mail: mak@mail.wplus.net
Received October 1, 2008
Abstract—Oxidative addition of N-aminophthalimide to benzylideneacetone and chalcones followed by thermolysis
of the arising 2-aryl-3-acyl-1-phthalimidoaziridines led to the formation of 2,5-disubstituted oxazoles in an overall
yield 30–55%. Electron-donor substituents in the aryl fragment of 2-aryl-3-aroyl-1-phthalimidoaziridines accelerate
their conversion into oxazoles, and similar substituents in the aroyl fragment retard this process. The possibility
was demonstrated of going over to oxazoles from α,β-unsaturated carbonyl compounds via 2-acyl-1-
sulfonylaziridines employing chloramine-B. However ethyl 2 cyanocinnamate reacted with chloramine-B with the
rupture of the C=C bond and the formation of N-benzylidene-benzenesulfamide.
DOI: 10.1134/S107042800908020X
The conversion of 2-acylaziridines into oxazoles was
described 49 years ago [1]. It was shown that at 220°C
in the vaporizer of the gas chromatograph 2 benzoyl-1-
tert-butyl-3-phenylaziridine materially completely (to
96%) decomposed into 2,5 diphenyl-oxazole. Later the
2,5-diphenyloxazole was also obtained at the photolysis
of this aziridine however in a lower yield (38%) [2].
the synthesis of oxazoles, compounds exhibiting versatile
biological activity [4], and also widely used in the organic
synthesis [5], for instance, like latent equivalent of a carb-
oxy group [6] or azadiene components in the Diels–Alder
reaction [7].
Therefore the target of this research was the establish-
ment of the preparative possibility of the transition from
α,β-unsaturated carbonyl compounds to oxazoles via
2-acyl-1 phthalimidoaziridines lacking an additional
electron-acceptor moiety. We selected as objects of the
study easily available compounds like benzylideneacetone
(Ia), chalcones Ib–If, vinylmethyl ketone (Ig), and ester
of cynnamic acid Ih which by oxidative addition of
N-aminophthalimide were converted into the cor-
responding N-phthalimidoaziridines IIa–IIh (Scheme 1).
Some years later a report appeared on the formation
of oxazoles from 2 acylaziridines under far milder condi-
tions [3]. It turned out that if 1-phthalimidoaziridines had
at the C2 atom two electron-acceptor groups, at least
one of these groups was a carbonyl, and to the C3 was
attached an aryl substituent, these compounds already at
20–80°C decomposed along two competing routes leading
to oxazolines and oxazoles. Therewith the oxazoles
fraction in the reaction mixture grew with increasing
temperature.
Yields of N-phthalimidoaziridines II were 52–75%,
except for adduct IIg with vinyl methyl ketone (35%).
Aziridines IIa, IIf–IIh were not previously described or
were just mentioned in the literature, and compounds IIb–
IIe were not always adequately described, therefore they
all were characterized by the data of elemental analysis,
NMR and mass spectra.
Thus up till now the fundamental possibility of oxazoles
preparation from 2 acyl-1-phthalimidoaziridines was
shown only for a narrow choice of compounds containing
an additional electron-acceptor moiety. Meanwhile the
conversion of α,β-unsaturated carbonyl compounds into
aziridines with an appropriate leaving group on the nitrogen
atom combined with subsequent thermolysis of these
aziridines might become a general two-stage method of
Owing to the slow in the NMR time scale inversion of
the endocyclic nitrogen characteristic of N-aminoaziridine
1229

BELETSKII, KUZNETSOV
1230
Scheme 1.
R1 = Ph, R2 = Me (a), Ph (b), p-MeOC6H4 (c), p-NO2C6H4 (d); R2 = Ph, R1 = p-MeOC6H4 (e), p-NO2C6H4 (f); R1 = Me, R2 = H
(g); R1 = Ph, R2 = OEt (h).
derivatives [8] the middle region of the 1H NMR spectra
(δ 2.8–5.6 ppm) of compounds IIa–IIf and IIh contains
two pairs of doublets corresponding to the protons of the
aziridine rings of two invertomers (in the spectrum of
aziridine IIg the signals of the methylene protons of two
invertomers are overlapping). The observed vicinal
coupling constants (4.4–5.8 Hz) indicate the trans-position
of the aziridine protons which is not surprising for the
configuration of the double bond is always retained at
the oxidative aziridination. The content of the minor
invertomer varies from 2% for 3-(4-nitrophenyl)-sub-
stituted aziridine IId to 15% for 3 methyl derivative IIg,
with a common value of 6–7%. The comparison of the
substituents at the carbon atoms of the aziridine ring
suggests that in all events the prevailing invertomer
contains the phthalimide group in the cis-position with
respect to the smaller COR2 group.
The thermolysis of aziridines IIa–IIf in toluene solu-
tion at 140–170°C in pressure-tight vessels for 1–5 h led
to the formation of the corresponding oxazoles IIIa–IIIf
in 54–86% yields. All the latter compounds were already
known, and we identified them by comparison of their
melting points and/or NMR spectra with the published
data.
By analogy with the mechanism advanced in [3] we
assume that in the thermolysis of aziridines II first occurs
the conrotatory opening, probably reversible, of the C–C
bond in the three-membered ring giving azomethine ylides
of U- or W-type. U-Azomethine ylide A may undergo
further cyclization into the corresponding 4-oxazoline (2,3-
dihydrooxazole) IV and also a transfer of the hydrogen
atom marked in the scheme to the oxygen of the
phthalimide moiety resulting in the elimination of a phthal-
imide molecule from the azomethine ylide. The new
1,3-dipole (nitrile ylide B) arising in this process may
further undergo cyclization directly into oxazole III
(Scheme 2).
The signals of the aziridine protons belonging to the
major and minor invertomers differ notably and regularly
in chemical shifts. For instance, in the 1H NMR spectra
of aziridines IIb–IIf prepared from chalcones the signals
of the major invertomer are located at δ 4.37–4.40 and
4.65–4.75 ppm, and those of the minor invertomer, in the
region δ 3.65–4.32 and 5.48–5.56 ppm. These differences
originate from the relative location of the phthalimide
fragment and its effect on the chemical shifts (deshielding
of the syn-proton [8]). In the 13C NMR spectra the carbon
atoms of the aziridine ring give rise to signals around δ
50 ppm.
For W-dipole C both these processes are impossible
for the sterical reasons. It probably either suffers
cyclization into the initial aziridine, or undergoes
stereoisomerization at the C–N bonds into the azomethine
ylides of S-type, one of which is able to cyclize into
oxazoline, and another to eliminate the phthalimide
molecule converting into nitrile ylide.
From the thermolysis products of aziridine IIa we
additionally isolated in a low yield 5-methyl-2-phenyl-3-
phthalimido-2,3-dihydrooxazole (IVa), the cyclization
Mass spectra of N-phthalimidoaziridines IIb–IIf
alongside the peaks of molecular ions contain character-
istic peaks originating from the presence in their molecules
of a phthalimide fragment: [M – 146]+ ([M – PiN]+),
[M – 147]+ ([M – PiNH]+), [147]+ ([PiNH]+), [146]+
([PiN]+), and [104]+ ([C6H4CO]+). In the mass spectra
of aziridines IIb–IIf also peaks [M – ArCO]+ and
[ArCO]+ are observed.
1
product of the U-azomethine ylide A. In the H NMR
spectrum of this compound a multiplet in observed in the
region δ 7.7–7.9 ppm showing the retention of the
phthalimide fragment. The protons of the oxazoline ring
appear as doublets at δ 6.8 and 8.0 ppm with a char-
acteristic long-range coupling constant 3 Hz. In the
13C NMR spectrum the signal of C2 atom is observed at
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 8 2009

SYNTHESIS OF OXAZOLES FROM α,β-UNSATURATED CARBONYL COMPOUNDS
1231
Scheme 2.
R2 = Me (a), OEt (h).
δ 107 ppm, of C4 atom, around δ 126–129 ppm, of C5
atom, at δ 160 ppm.
failed to obtain by this method an oxazole lacking a
substituent at the C2 atom.
The estimation of the effect of the electronic character
of substituents in the acylaziridines on the rate of their
conversion into oxazoles we performed the thermolysis
of mixtures of aziridines IIb–IIf with various substituents
in the aryl and the aroyl fragments. The change in the
ratio of these aziridines in the course of the thermolysis
was monitored by 1H NMR spectroscopy. As a result it
turned out, that the rate of consumption of initial aziridines
decreased in the series (IIc)> (IIb) > (IId), and also in
the series (IIf) > (IIb) > (IIe). Consequently, the
decomposition of aziridines is accelerated by introducing
electron-donor groups in the aryl substituent or electron-
acceptor groups in the aroyl substituent. This fact suggests
that in the rate-limiting stage of the reaction on the carbon
atom attached to the aryl substituent appears a partial
positive charge, and on the carbon atom at the aroyl
substituent, a partial negative charge.
Aziridine IIg did not visibly change even after heating
for 5 h at 180°C. The low reactivity of this compound is
apparently due to the fact that the hydrogen atom unlike
the aryl substituents of aziridines IIa–IIf cannot stabilize
the transition state of the reaction by the conjugation with
the orbitals of the opening C–C bond.
The heating of ester IIh at 160°C resulted in its
complete decomposition. However we failed to isolate
from the reaction mixture the expected heterocyclic
compounds apparently due to their instability during the
chromatography on silica gel. The only substance obtained
from this experiment after column chromatography was
benzaldehyde (52%), probably formed by the hydrolysis
of the initially arising 5-ethoxy-oxazoline (IVh).
These findings are well consistent with the assumption
that the limiting stage of the whole process is the cleavage
of the aziridine C–C bond resulting in the azomethine
ylide. In the first approximation in the π-system of
azomethine ylide the positive charge is localized on the
nitrogen, and the negative charge is distributed between
the fragments 1 and 2. Due to the different nature of
substituents the distribution of the negative charge is
evidently unsymmetrical: It should be larger on fragment
2. Inasmuch as in the initial aziridine all the three parts of
the molecule formally bear no charge, in the transition
state the negative charge on fragment 2 also should be
larger. Therewith in the transition state because of the
large angle between the axis of the orbital of the unshared
Thus in the majority of cases it is actually possible to
go over from α,β-unsaturated carbonyl compounds to
oxazoles in two steps with the overall yield 30–52%.
Therewith the close values of yields were obtained for
2,5-diaryloxazoles both with electron-donor and electron-
acceptor aromatic substituents. The good yield of oxazole
IIIa suggests that this method might be suitable for the
synthesis of other and alkyl-substituted oxazoles. Yet we
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 8 2009

BELETSKII, KUZNETSOV
1232
electron pair and the orbitals of the opening σ-bond, and
consequently, because of their small overlapping, the
nitrogen atom should bear only a small positive charge,
and its main fraction should be located on fragment 1. In
keeping with this reasoning the donor substituents in the
aryl ring accelerate the reaction, and in the aroyl ring
retard it.
of the aziridine proton in the region δ 5.0 ppm. In the 13C
NMR spectra the signals of the aziridine carbons in the
region δ 50–60 ppm and of two carbonyl atoms of
indandione at δ 190 ppm are easy to identify. Due to the
typical for the sterically loaded phthalimidoaziridines slow
rotation of the phthalimide fragment around the N–N bond
in the 13C NMR spectrum of compound IIl the signals of
phthalimide atoms Ca at δ 130 ppm and NCO around δ
165 ppm are considerably broadened, and in the spectrum
of compound IIk the NCO signal coincides with the base
line. In the mass spectra of phthalimidoaziridines Ik and
Il the molecular ion peak is weak or lacking, but peaks
characteristic of phthalimidoaziridins [M – 147]+ ([M –
PiNH]+), [147]+ ([PiNH]+), and [104]+ ([C6H4CO]+) are
present.
R1
1
O
2
R2
II
N
PiN
We further attempted to extend the already tested
procedure to the conversion of conformationally rigid
spiro-joined benzylideneindandiones Ii–Il into the cor-
responding fused oxazoles. By analogy with the behavior
of 3-aryl-2,2-dibenzoyl-1-phthalimidoaziridines [3] we
expected that the corresponding aziridines would be far
more active than their 2,3-disubstituted analogs, and their
conversion into oxazoles would occur in milder conditions.
We failed to obtain the corresponding spiroaziridines
from arylideneindandiones Ii and Ij with electron-donor
groups in the aryl ring. Yet at the oxidative addition of
N aminophthalimide to the para-tolyl derivative Ij the
TLC monitoring of the reaction mixture showed the
disappearance of the initial compound and the presence
of a single product. Assuming that this was the desired
aziridine we left the mixture standing for two days at
room temperature hoping to obtain the product of its
decomposition, the corresponding oxazole. Finally the 1H
NMR spectrum revealed the presence in the solution of
a single compound containing a methyl group, but it turned
out to be not oxazole but p-toluic aldehyde. In the reaction
However another side of the high reactivity of these
phthalimidoaziridines proved to be their low stability: we
succeeded to obtain pure spiroaziridines only from
compounds Ik and Il with electron-acceptor groups in
the aryl substituent. Evidently like in the previous reaction
series the introduction of these groups into the aryl
substituent retards the opening of the aziridine ring
(Scheme 3).
1
mixture with compound Ii according to the H NMR
spectrum alongside the p methoxybenzaldehyde (43%
of the overall intensity of the methoxy groups) another
product containing methoxy groups was present in a
significant amount (about 30% of the overall intensity of
the methoxy groups) that we failed to isolate due to its
instability.
Compounds Ik and Il are stable in crystals, but in
solutions they decomposed even at room temperature.
Their composition is confirme by elemental analysis, and
their structure, by mass and NMR spectra which show
that both aziridines exist in the form of a single invertomer,
evidently with the syn-location of the phthalimide group
The boiling in benzene of nitro-substituted spiroaziridine
IIl resulted in the formation of a product insoluble in
common organic solvents, whose composition and mass
1
and the aziridine hydrogen. In the H NMR spectra of
these compounds the characteristic signal is the singlet
Scheme 3.
O
O
O
PiNNH2,
Pb(OAc)4
C6H4X-p
C6H4X-p
D
N
N
O
O
O
IIj, IIl
C6H4X-p
NPi
Ii_Ij
IIIl
X = MeO (i), Me (j), Cl (k), NO2 (l).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 8 2009

SYNTHESIS OF OXAZOLES FROM α,β-UNSATURATED CARBONYL COMPOUNDS
1233
spectrum corresponded to the structure of expected
oxazole IIIl. In particular, its mass spectrum contained a
strong peak of molecular ion and no peaks characteristic
of phthalimide derivatives with m/z 146 and 147 indicating
the absence of this fragment in the obtained compound.
The composition of N-benzenesulfonylaziridines Vb
and Ve was confirmed by elemental analyses, and their
structure, by 1H, 13C NMR and mass spectra. In the 1H
NMR spectra in the region δ4.3–4.6 ppm pairs of doublets
corresponding to the protons of the aziridine ring appeared
in due course, and the values of the vicinal coupling
constants (4.4–5.8 Hz) revealed the trans-position of the
aziridine protons. The signals of the aziridine carbon atoms
were observed in the 13C NMR spectra in their usual
region δ ~50 ppm. The molecular ion peaks were absent
from the mass spectra of compounds Vb and Ve, but
appeared the characteristic fragment ions [M – 141]+
([M – C6H5SO2]+). Besides also peaks appeared
corresponding to the fragment [ArCO]+.
Yet as a result of heating spiroaziridine IIk at 80°C
till its complete disappearance from the reaction mixture
(TLC monitoring) after the subsequent chromatographic
separation of the reaction mixture we only obtained an
instable compound whose structure was not established.
Inasmuch as in the transition from unsaturated carbonyl
compounds to oxazoles we used relatively expensive
N-aminophthalimide and lead tetraacetate, and the
phthalimide moiety was not present in the final product
we started to look for cheaper reagents for the preparation
of 2-acylaziridines with a good leaving gtoup at the
nitrogen atom and assumed that this could be an
arylsulfonyl group.
The only products that we succeeded in separating
from the thermolysis of sulfonylaziridines Vb and Ve at
160–170°C were the expected oxazoles IIIb and IIIe,
but their yields were considerably worse than from the
corresponding phthalimidoaziridines. This may be ascribed
to the stronger electron-acceptor properties of the sulfonyl
group compared to the phthalimide moiety that lead to
a greater number of side processes with the opening of
C–N bond. However applying the microwave irradiation
we succeeded in reducing the decomposition temperature
of aziridine Vb to 135°C and hence increasing the yield
of oxazole IIIb nearly 1.5-fold.
In the last decade several publications reported on
the synthesis of tosylaziridines from unsaturated
compounds with the use of chloramine-T. The process
required a catalyst, the role of which played sources of
molecular bromine [9, 10] or iodine [11], and also some
compounds of Cu(I) [12]. However in the most cases
alkenes and styrenes were used as substrates, and only
in [10] the tosylaziridines were obtained from α,β-
unsaturated carbonyl compounds.
It would be interesting to prepare benzenesulfonyl-
aziridines from α,β-unsaturated carbonyl compounds with
an additional electron-acceptor group in the α-position
for by analogy to the corresponding 1-phthalimido-
aziridines [3] it is expectable to convert them into the
oxazoles under mild conditions. It proved however that
both in the presence and in the absence of bromine source
the ethyl 2-cyanocinnamate Im reacted with chlor-amine-
B to give N-benzylidenebenzenesulfamide (VI) and not
aziridine or oxazole (Scheme 5).
Therefore we decided to synthesize sulfonylaziridines
from chalcones and chloramine-B we possessed along
the procedure of [10]. As a result from chalcones Ib and
Ie we actually obtained benzenesulfonylaziridines IVb
and IVd, although in a low yield. Therewith in the
experiments with benzalacetophenone (Ib) we used as
catalyst both pyridinium tribromide [10] and
tetramethylammonium tribromide recommended in [9].
1
According to H NMR of the reaction mixtures the
analytical yields of sulfonylaziridine Vb in both cases
attained ~32% (Scheme 4).
We presume that here first occurs the nucleophilic
attack of the anion of chloramine-B on the electron-
Scheme 4.
O
_
PhSO2NCl(Na), 10 mol% PyH+Br3
D or MW
IIIb, IIIe
Ib, Ie
Ph
C6H4X-p
Vb, Ve
MeCN
N
PhO2S
X = H (b), OMe (e).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 8 2009

BELETSKII, KUZNETSOV
1234
Scheme 5.
_
+
PhSO NCl(Na) xH O, PhCH NMe Cl
SO2Ph
CO2Et
2
2
2
3
Ph
N
Ph
MeCN
CN
Im
VI, 45%
Scheme 6.
_
PhSO2NCl
_
N
PhO2S
Cl
_
PhO2S
N
Δ
CO2Et
CO2Et
CO2Et
Cl
SO2Ph
_
Ph
Ph
Ph
Ph
N
_ ClC(CN)CO2Et
CN
CN
CN
Im
VI
deficient C=C bond of ester Im (Scheme 6). The arising
anion apparently transforms into the anion analogous in
structure to the intermediate suggested for the reaction
of unsaturated compounds with chloramine-T in the
presence of trimethylphenylammonium tribromide [9], but
further instead of intramolecular nucleophilic substitution
of chlorine providing aziridine occurs the cleavage of the
C–C bond facilitated by the high stability of the leaving
anion.
of the solvents (δ 77.16, 39.52, and 1.32 ppm respective-
ly). The assignment of signals in the 13C NMR spectra
was made with the help of DEPT spectra. Mass spectra
were measured on an instrument Finnigan MAT INCOS-
50 (Electron impact, 70 eV, direct admission into the ion
source). Elemental analysis was carried out on an auto-
matic CHN-analyzer HP-185B. The composition of the
reaction mixtures and the purity of compounds obtained
was controlled by TLC on ALUGRAM SIL G/UV254
plates.
Despite these drawbacks we can state that we
suggested and carried out by two examples a two-stage
process of the conversion of α,β-unsaturated carbonyl
compounds into oxazoles with the use of a cheap reagent,
chloramine-B. We regard the results obtained as hopeful
for further research directed to the optimization of this
reaction and the estimation of the range of its applicability.
Yet apparently this reaction is not feasible for the synthesis
of oxazoles with alkenyl and some heteroaromatic and
aromatic substituents with elevated electron density for
they themselves can react with bromine catalyzing the
aziridination stage. Besides the last example shows that
the reaction is hardly suitable for compounds containing
at the C=C bond simultaneously two electron-acceptor
moieties.
The reactions under microwave activation were
performed in a monomode microwave installation
Minotavr (maximum power 200 W) of Lyumeks Co.
N-Aminophthalimide was prepared by procedure [13],
chalcones Ic–If, by general method [14]. Arylidene-
indandiones Ii–Il were kindly provided by Professor of
Voronezh State University Kh.S.Shikhaliev to whom the
authors are deeply grateful. Toluene was dried with metal
sodium [15].Acetonitrile was distilled over phosphorus(V)
oxide [15]. Chloramine-B was dried till constant weight
at 80°C and the pressure 10 mm Hg.
Oxidative addition of N-aminophthalimide to α,β-
unsaturated ketones. General procedure. To a solu-
tion of 6 mmol of unsaturated compound in 20 ml of di-
chloromethane containing a dispersion of 3 g of potassium
carbonate was added while stirring at cooling to 0°C
within 10 min by alternating small portions 972 mg
(6 mmol) of N-aminophthalimide and 2.66 g (6 mmol) of
lead tetraacetate. The mixture was stirred for another
5 min, filtered through a bed of silica gel (1 cm), and
washed with 20 ml of dichloromethane. The solvent was
distilled off in a vacuum, 30 ml of ethyl ether was added
EXPERIMENTAL
1H (300.13 MHz) and 13C (75.47 MHz) NMR spectra
were registered on a spectrometer Bruker DPX-300 from
solutions in CDCl3, DMSO-d6, or CD3CN using for
internal reference in the 1H NMR spectra the signals of
the residual protons of the solvent (δ 7.26, 2.50, and
1.96 ppm), and in the 13C NMR spectra, carbon signals
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 8 2009

SYNTHESIS OF OXAZOLES FROM α,β-UNSATURATED CARBONYL COMPOUNDS
1235
to the residue, and the separated precipitate was filtered
off.
[17, 19]. Mass spectrum, m/z (Irel, %): 368 (2) [M]+, 263
(16) [M – PhCO]+, 222 (13) [M – PiN]+, 167 (10), 116
(10), 106 (14), 105 (100) [PhCO]+, 104 (36) [C6H4CO]+,
103 (13), 77 (82), 76 (50), 51 (31), 50 (31). Found, %:
C 75.1; H 4.44; N 7.41. C23H16N2O3. Calculated, %:
C 75.0; H 4.35; N 7.61.
trans-2-Acetyl-3-phenyl-1-phthalimidoaziridine
(IIa),a mixture of two invertomers in a ratio 94:6. Charge
of reagents 10 mmol each. Yield 2.31 g (75%), white
1
powder, mp 192–193°C (from butanol). H NMR
trans-2-Benzoyl-3-(4-methoxyphenyl)-1-phthal-
imidoaziridine (IIc), mixture of two invertomers in a ratio
93:7. Yield 1.24 g (52%), white powder, mp 154–155°C
spectrum (CDCl3), δ, ppm: 2.47 C and 2.55 C–CH3 of
minor and of major invertomer respectively, overall 3H;
3.72 d (J 4.4 Hz) and 4.37 d (J 4.4 Hz) – NCH of major
invertomer, 4.02 d (J 5.8 Hz) and 4.54 d (J 5.8 Hz) –
NCH of minor invertomer, overall 2H; 7.37–7.43 m (5H,
Ph), 7.66–7.77 m (4H, PiN). 13C NMR spectrum of major
invertomer (CDCl3), δ, ppm: 31.51 (CH3), 49.92 (NCH),
51.07 (NCH), 123.07 (PiN, Cb), 127.06 and 128.60 (Ph,
C° and Cm), 128.52 (Ph, Cp), 130.18 (PiN, Ca), 133.98
(PiN, Cc), 134.91 (Ph, Ci), 164.67 (NCO), 198.50 (CO).
Mass spectrum, m/z (Irel, %): 307 (0.3), 306 (2) [M]+,
265 (11), 264 (62) [M – CH2CO]+, 263 (11) [M –
MeCO]+, 130 (18), 118 (41), 117 (64), 116 (22), 105 (18),
104 (60) [C6H4CO]+, 103 (20), 91 (26), 90 (28), 89 (17),
77 (39), 76 (83), 75 (12), 74 (10), 63 (11), 51 (23), 50
(43), 43 (100) [MeCO]+. Found, %: C 70.5; H 4.63;
N 9.30. C18H14N2O3. Calculated, %: C 70.6; H 4.61; N
9.15. Compound IIa was mentioned in [16], however
none of its characteristics was reported.
1
(ethanol–butanol, 1:1). H NMR spectrum (CDCl3), δ,
ppm: 3.73 s and 3.82 s – MeO of minor and of major
invertomer respectively, overall 3H; 4.21 d (J 5.1 Hz)
and 5.48 (J 5.1 Hz) – NCH of minor invertomer, 4.39 d
(J 4.4 Hz) and 4.65 d (J 4.4 Hz) – NCH of major
invertomer, overall 2H; 6.79 d (J 8.7 Hz) and 6.94 d
(J 8.7 Hz) – C6H4, Hm of minor and of major invertomer
respectively, overall 2H; 7.32 d (J 8.7 Hz) – C6H4, Ho of
minor invertomer and 7.43–7.74 m (Harom), overall 9H;
8.10 d (J 7.4 Hz) and 8.32 d (J 7.2 Hz) – PhCO, Ho of
minor and of major invertomer respectively, overall 2H.
13C NMR spectrum of major invertomer (CDCl3), δ, ppm:
48.55 (NCH), 50.45 (NCH), 55.33 (OMe), 114.11 (p-
C6H4, Cm), 123.08 (PiN, Cb), 127.12 (p-C6H4, Ci), 128.43,
128.68, 128.72, 130.24 (PiN, Ca), 133.53, 133.92 (PiN,
Cc), 137.34 (PhCO, Ci), 159.87 (C–O), 164.59 (NCO),
190.68 (CO). Mass spectrum, m/z (Irel, %): 398 (11) [M]+,
293 (34) [M – PhCO]+, 252 (22) [M – PiN]+, 251 (21)
[M – PiNH]+, 238 (10), 237 (12), 147 (17) [PiNH]+, 146
(31) [PiN]+, 105 (100) [PhCO]+, 104 (29) [C6H4CO]+,
77 (47), 76 (34), 51 (14), 50 (18). Found, %: C 72.4;
H 4.54; N 6.81. C24H18N2O4. Calculated, %: C 72.4; H 4.52;
trans-2-Benzoyl-3-phenyl-1-phthalimidoaziridine
(IIb), mixture of two invertomers in a ratio 94:6. Charge
of reagents 10 mmol each. Yield 2.17 g (60%), white
powder, mp 126–127°C (from ethanol) (mp 121–123°C
[17], 124°C [18]). 1H NMR spectrum (CDCl3), δ, ppm:
4.28 d (J 4.8 Hz) and 5.56 d (J 4.8 Hz) – NCH of minor
invertomer, 4.40 d (J 4.8 Hz) and 4.70 d (J 4.8 Hz) –
NCH of major invertomer, overall 2H; 7.26–7.74 m (12H,
Harom); 8.10 d (J 7.2 Hzb) and 8.32 d (J 7.2 Hz) – PhCO,
H° of major and of minor invertomer respectively, overall
2H. 13C NMR spectrum of major invertomer (CDCl3),
δ, ppm: 48.65 (NCH), 50.58 (NCH), 123.12 (PiN, Cb),
127.17, 128.56, 128.65, 128.72, 128.78, 130.24 (PiN, Ca),
133.59, 133.95 (PiN, Cc), 135.15 (Ci), 137.29 (Ci), 164.57
(NCO), 190.53 (CO). 1H and 13C NMR spectra of major
invertomer are well consistent with the published data
1
N 7.04. H and 13C NMR spectra of compound we
obtained are well consistent with published data [19].
trans-2-Benzoyl-3-(4-nitrophenyl)-1-phthalimido-
aziridine (IId), mixture of two invertomers in a ratio
98:2. Yield 1.52 g (61%), light-yellow powder, mp 192–
193°C (butanol–DMF, 10:1). 1H NMR spectrum (CDCl3),
δ, ppm: 3.65 d (J 5.1 Hz) and 5.53 d (J 5.1 Hz) – aziridine
protons of minor invertomer; 4.39 d (J 5.1 Hz) and
4.75 d (J 5.1 Hz) – aziridine protons of major invertomer,
overall 2H; 7.50–7.71 m (9H), 8.10 d (2H, PhCO, Ho,
13
J 7.3 Hz), 8.26 (2H, p-C6H4, Hm, J 8.7 Hz). C NMR
a Adducts IIa and IIg were first synthesized and described in the
graduation thesis of the student of our team Yu.A. Titarev, St.
spectrum of major invertomer (CDCl3), δ, ppm: 48.83
(NCH), 49.18 (NCH); 123.27, 123.85 (p-C6H4, Cm and
PiN, Cb); 128.16, 128.82, 128.84, 130.05 (PiN, Ca), 133.92,
134.16, 136.89 (PhCO, Ci), 142.49 (p C6H4, Ci), 147.95
(CNO2), 164.40 (NCO), 189.58 (CO). Mass spectrum,
m/z (Irel, %): 413 (0.8) [M]+, 308 (25) [M – PhCO]+, 267
(19) [M – PiN]+, 266 (29) [M –PiNH]+, 212 (29), 178
Petersburg State University.
b Here and hereinafter in the description of the signals of aromatic
substituents appearing as the second order spectra we present the
apparent multiplicity of complex signals and the distance between
the main peaks of the complex multiplets and not the real coupling
constants.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 8 2009

BELETSKII, KUZNETSOV
1236
(11), 165 (18), 147 (28) [PiNH]+, 130 (28), 116 (13), 115
(11), 106 (61), 105 (71) [PhCO]+, 104 (27) [C6H4CO]+,
103 (28), 102 (46), 89 (37), 77 (100), 76 (43), 75 (49), 74
(37), 64 (11), 63 (38), 62 (19), 51 (74), 50 (83), 39 (29),
38 (12), 37 (10). Found, %: C 66.9; H 3.76; N 10.2.
C23H15N3O5. Calculated, %: C 66.8; H 3.63; N 10.2.
1H and 13C NMR spectra of compound we obtained are
well consistent with published data [19].
123.90 (C6H4, Cm and PiN, Cb); 127.11, 128.75, 128.83,
129.82, 130.02 (PiN, Ca), 134.18 (PiN, Cc), 134.51 (Ci),
141.69 (C6H4, Ci), 150.42 (CNO2), 164.54 (NCO), 189.08
(CO). Mass spectrum, m/z (Irel, %): 413 (11) [M]+, 267
(25) [M – PiN]+, 266 (55) [M – PiNH]+, 264 (45), 251
(12), 252 (39), 236 (42), 221 (22), 220 (18), 206 (10), 178
(11), 165 (31), 151 (46), 150 (14), 147 (55) [PiNH]+, 132
(19), 131 (19), 130 (43), 120 (23), 117 (61), 106 (45), 105
(14), 104 (56) [C6H4CO]+, 103 (64), 102 (29), 92 (42), 91
(21), 90 (64), 89 (93), 77 (84), 76 (61), 75 (69), 74 (57),
64 (26), 63 (72), 62 (27), 52 (17), 51 (28), 50 (100), 39
(50), 38 (28), 37 (21). Found, %: C 66.6; H 3.80; N 10.2.
C23H15N3O5. Calculated, %: C 66.8; H 3.63; N 10.2.
trans-2-(4-Methoxybenzoyl)-3-phenyl-1-phthal-
imidoaziridine (IIe), mixture of two invertomers in a ratio
94:6. We used 1.33 equiv of N-aminophthalimide and lead
tetraacetate. Yield 1.30 g (54%), glassy substance.
1H NMR spectrum (CDCl3), δ, ppm: 3.87 s and 3.89 s
(3H, OMe) – MeO of major and of minor invertomer
respectively, overall 3H; 4.27 d (J 5.1 Hz) and 5.50 d
(J 5.1 Hz) – NCH of minor invertomer, 4.37 d (J 4.4 Hz)
and 4.70 d (J 4.4 Hz) – NCH of major invertomer, overall
2H; 6.99 d (J 8.7 Hz) and 7.05 d (J 8.7 Hz) – C6H4, Hm
of major and of minor invertomer respectively, overall
2H; 7.37–7.74 m (9H); 8.08 d (J 8.7 Hz) and 8.32 d
(J 7.2 Hz) – C6H4, Ho of major and of minor invertomer
respectively, overall 2H. 13C NMR spectrum of major
invertomer (CDCl3), δ, ppm: 48.40 (NCH), 50.05 (NCH),
55.49 (OMe), 113.99 (C6H4, Cm), 123.04 (PiN, Cb),
124.65 (Ci), 127.13, 128.43, 128.59, 130.22 (PiN, Ca),
131.05, 133.86 (PiN, Cc), 135.22 (Ci), 163.99 (CO),
164.54 (NCO), 188.53 (CO). Mass spectrum, m/z (Irel,
%): 398 (4) [M]+, 263 (27) [M – MeOC6H4CO]+, 252
(34) [M – PiN]+, 251 (24) [M – PiNH]+, 237 (11), 197
(48), 146 (29) [PiN]+, 136 (84) [MeOC6H4CO]+, 135 (75),
130 (14), 116 (20), 107 (30), 105 (20), 104 (94) [C6H4CO]+,
103 (27), 102 (14), 92 (49), 90 (38), 89 (22), 77 (93), 76
(100), 75 (23), 74 (21), 64 (30), 63 (31), 51 (29), 50 (69),
39 (19). Found, %: C 72.2; H 4.59; N 7.02. C24H18N2O4.
Calculated, %: C 72.4; H 4.52; N 7.04. 1H and 13C NMR
spectra of compound we obtained are well consistent
with published data [19].
2-Acetyl-1-phthalimidoaziridine (IIg), mixture of
two invertomers in a ratio 85:15 in CDCl3, 93:7 in DMSO-
d6. Charge of reagents 10 mmol each. Vinyl methyl ketone
was used in 10% excess. Yield 810 mg (35%), white
1
powder, mp 136–137°C (ethanol). H NMR spectrum,
δ, ppm, in CDCl3: 2.34 s and 2.52 s – CH3 of major and
of minor invertomer respectively, overall 3H; 2.80–
2.82 m (2H) – NCH2 of both invertomers; 3.16 t
(J 6.5 Hz) and 3.48 t (J 5.8 Hz) – NCH of major and of
minor invertomer respectively, overall 1H; 7.69–7.79 m
(4H, PiN); in DMSO-d6: 2.19 s and 2.42 s – CH3 of
major and of minor invertomer respectively, overall 3H;
2.84–2.87 m (2H) – NCH2 of both invertomers; 3.25 d.d
(J1 8.3, J2 5.5 Hz) and 3.69 t (J 5.8 Hz) – NCH of major
and of minor invertomer respectively, overall 1H; 7.81 C
(4H, PiN). 13C NMR spectrum (CDCl3), δ, ppm, major
invertomer: 27.19 (CH3), 36.58 (NCH2), 46.28 (NCH),
123.28 (PiN, Cb), 129.97 (PiN, Ca), 134.34 (PiN, Cc),
164.52 (NCO), 202.90 (CO); minor invertomer: 31.52
(CH3), 36.80 (NCH2), 42.07 (NCH), 123.01 (PiN, Cb),
133.95 (PiN, Cc).
Ethyl trans-3-phenyl-1-phthalimidoaziridine-2-
carboxylate (IIh), mixture of two invertomers in a ratio
93:7. Charge of reagents 5 mmol each. Yield 850 mg
(57%), colorless crystals, mp 96–97°C (ether–hexane,
1:1). 1H NMR spectrum (CDCl3), δ, ppm: – 1.28 t
(J 7.3 Hz) and 1.37 t (J 6.5 Hz) – CH3 of major and of
minor invertomer respectively, overall 3H; 3.53 d
(J 5.1 Hz) and 4.40 d (J 5.1 Hz) – NC2H and NC3H of
major invertomer, 4.07 d (J 5.8 Hz) and 4.59 d
(J 5.8 Hz) – NCH of minor invertomer, overall 2H;
4.19 q (J 7.3 Hz) and 4.36 q (J 6.5 Hz) – CH2 of major
and of minor invertomer respectively, overall 2H; 7.37–
7.78 m (9H). 13C NMR spectrum of major invertomer
(CDCl3), δ, ppm: 13.90 (CH3), 46.28 (NCH), 49.47
(NCH), 62.05 (OCH2), 123.08 (PiN, Cb), 127.19, 128.59
trans-2-(4-Nitrobenzoyl)-3-phenyl-1-phthalimido-
aziridine (IIf), mixture of two invertomers in a ratio 94:6.
Yield 1.81 g (73%), light-yellow crystalline powder, mp
1
183–184°C (butanol–DMF, 10:1). H NMR spectrum
(CDCl3), δ, ppm: 4.32 d (J 5.1 Hz) and 5.50 d (J 5.1 Hz) –
NCH of minor invertomer, 4.38 d (J 5.1 Hz) and 4.68 d
(J 5.1 Hz) – NCH of major invertomer, overall 2H; 7.38–
7.54 m (5H), 7.65–7.74 m (4H), 8.26 d (2H, C6H4,
J 8.7 Hz); 8.37 d (J 8.7 Hz) and 8.53 d (J 8.7 Hz) –
C6H4, signals of major and of minor invertomer respec-
tively, overall 2H. 13C NMR spectrum of major invertomer
(CDCl3), δ, ppm: 49.05 (NCH), 51.11 (NCH); 123.24,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 8 2009

SYNTHESIS OF OXAZOLES FROM α,β-UNSATURATED CARBONYL COMPOUNDS
1237
(Cp), 128.62, 130.22 (PiN, Ca), 134.00 (PiN, Cc), 134.51
(Ph, Ci), 164.60 (NCO), 166.17 (COO). Found, %:
C 67.81; H 4.88; N 8.28. C19H16N2O4. Calculated, %:
C 67.86; H 4.76; N 8.33.
anhydrous toluene was heated for 2 h at 170°C. The
precipitate formed on cooling was filtered off and
subjected to chromatography on a column packed with
20 g of silica gel (eluent dichloromethane–ethyl ether,
20:1).Yield 160 mg (60%), yellow powder, mp 207–208°C
(mp 204.5°C [24]). 1H NMR spectrum of compound we
obtained is well consistent with published data [25].
5-Methyl-2-phenyloxazole (IIIa). A solution of
306 mg (1 mmol) of aziridine IIa in 10 ml of anhydrous
toluene was heated for 5 h at 160°C in a glass reactor
with a pressure-tight screw-top. On cooling the reaction
mixture the solvent was distilled off in a vacuum. The
residue was subjected to chromatography on a column
packed with 20 g of silica gel (eluent dichloromethane),
and the main fraction was evaporated in a vacuum. Yield
96 mg (60%). Colorless oily substance (colorless oily
substance [20]). 1H and 13C NMR spectra of compound
we obtained are well consistent with published data [20].
5-(4-Methoxyphenyl)-2-phenyloxazole (IIIe).
A solution of 398 mg (1 mmol) of aziridine IIe in 10 ml of
anhydrous toluene was heated for 4 h at 160°C. The
solvent was distilled off in a vacuum. The residue was
subjected to chromatography on a column packed with
20 g of silica gel (eluent dichloromethane–ethyl ether,
20:1). Yield 180 mg (75%), colorless crystals, mp 83–
84°C (80°C [22]). 1H and 13C NMR spectra of compound
we obtained are well consistent with published data [26].
The small first fraction containing the mixture of
oxazole IIIa and 5-methyl-2-phenyl-3-phthalimido-
2,3-dihydrooxazole (IVa) was evaporated in a vacuum
to the volume of 5 ml, and 10 ml of hexane was added.
The separated precipitate of oxazoline IVa was filtered
5-(4-Nitrophenyl)-2-phenyloxazole (IIIf). A solut-
ion of 413 mg (1 mmol) of aziridine IIf in 10 ml of
anhydrous toluene was heated for 2 h at 160°C. The
solvent was distilled off in a vacuum. The residue was
subjected to chromatography on a column packed with
20 g of silica gel (eluent dichloromethane–ethyl ether,
20:1). The product contained about 5% of unidentified
impurity. Yield 201 mg (76%). Analytically pure sample
was obtained by recrystallization from a mixture ethanol–
butanol, 1:2.Yield 150 mg (56%), yellow powder, mp 197–
1
off. Yield 10 mg (3%). H NMR spectrum (CDCl3), δ,
ppm: 2.10 (3H, CH3), 6.77 d (1H, H4, J 3.0 Hz), 7.36–
7.44 m (5H, Ph), 7.74–7.88 m (4H, PiN), 8.06 d (1H, H2,
J 3.0 Hz). 13C NMR spectrum ( as the difference of
spectra of the mixture of compounds IIIa and IVa and
pure oxazole IIIa) (CDCl3), δ, ppm: 24.09 (Me), 107.26
(C2), 123.48 (PiN, Cb), 125.9 (Co), 126.42 (Cp or C4),
128.46 (Cm), 128.74 (C4 or Cp), 131.70 (PiN, Ca), 134.39
(PiN, Cc), 137.83 (Ci), 159.95 (C5), 167.48 (NCO).
1
198°C (mp 194–196°C [27]). H NMR spectrum of
compound we obtained is well consistent with published
data [25].
2,5-Diphenyloxazole (IIIb). A solution of 368 mg
(1 mmol) of aziridine IIb in 10 ml of anhydrous toluene
was heated for 2 h at 160°C. The solvent was distilled
off in a vacuum. The oily residue was extracted with
hexane which was later distilled off in a vacuum. Yield
191 mg (86%), colorless crystals, mp 73–74°C (mp 72–
74°C [21]). 1H and 13C NMR spectra of compound we
obtained are well consistent with published data [21].
Thermolysis of aziridine IIg. A solution of 230 mg
(1 mmol) of aziridine IIg in 10 ml of anhydrous toluene
was heated for 5 h at 180°C. The solvent was distilled
off in a vacuum. According to the data of H NMR
spectroscopy and TLC the residue contained only the
initial compound.
1
Thermolysis of aziridine IIh. A solution of 336 mg
(1 mmol) of aziridine IIh in 10 ml of anhydrous toluene
was heated for 3 h at 160°C. In keeping with TLC the
initial compound disappeared from the reaction mixture.
The solvent was distilled off in a vacuum. The column
chromatography (eluent dichloromethane) provided 55 mg
(52%) of benzaldehyde that was absent in the reaction
mixture according to 1H NMR spectroscopy.
2-(4-Methoxyphenyl)-5-phenyloxazole (IIIc).
A solution of 398 mg (1 mmol) of aziridine IIc in 10 ml of
anhydrous toluene was heated for 2 h at 140°C. The
solvent was distilled off in a vacuum. The residue was
subjected to chromatography on a column packed with
20 g of silica gel (eluent dichloromethane–ethyl ether,
20:1). Yield 135 mg (54%), colorless crystals, mp 98–
Estimation of substituents effect on the rate of
conversion acylaziridine – oxazole. Weighed portions
of aziridines IIb–IIf were dissolved in 10 ml of anhydrous
toluene and heated at 140°C. After 30 and 60 min of
heating the aziridines ratio in the reaction mixture was
measured by the intensity of the corresponding aziridine
1
99°C (103°C [22]). H and 13C NMR spectra of com-
pound we obtained are well consistent with published data
[23].
2-(4-Nitrophenyl)-5-phenyloxazole (IIId). A
solution of 413 mg (1 mmol) of aziridine IId in 10 ml of
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 8 2009

BELETSKII, KUZNETSOV
1238
protons of the main invertomers in the 1H NMR spectra
(CDCl3) taking into account the fraction of these inverto-
mers.
ing a dispersion of 1 g of potassium carbonate was added
while stirring at cooling to 0°C within 10 min by alternating
small portions 340 mg (2.1 mmol) of N-aminophthalimide
and 930 mg (2.1 mmol) of lead tetraacetate. The mixture
was stirred for another 5 min, filtered, and the solvent
was distilled off in a vacuum. Then 10 ml of dichloro-
methane was added, the solution was filtered through
a bed of silica gel (1 cm), and washed with 20 ml of
dichloromethane. The solvent was distilled off in a vacuum.
The residue was washed with 10 ml of ethyl ethera. Yield
605 mg (79%), white powder, t.decomp. 155–160°C.
1H NMR spectrum (CDCl3), δ, ppm: 5.01 s (1H, CHN),
7.73–8.01 m (10H), 8.27 d (2H, C6H4, Hm, J 8.0 Hz).
13C NMR spectrum (CDCl3), δ, ppm: 54.19 (CN), 57.01
(CHN), 123.42, 123.45, 123.60, 123.62, 129.46, 129.90
(PiN, Ca), 134.49, 136.11, 136.19, 136.22, 137.99, 141.54,
141.96, 148.14 (CNO2), 164.82 (NCO), 189.47 (CO),
190.32 (CO). Mass spectrum, m/z (Irel, %): 439 (0.4)
[M]+, 293 (21), 292 (100) [M – PiNH]+, 262 (10), 190
(41), 147 (36) [PiNH]+, 104 (56) [C6H4CO]+, 103 (16),
77 (11), 76 (77), 75 (21), 74 (20), 62 (14), 50 (48), 39
(11), 38 (11), 37 (10). Found, %: C 65.52; H 3.27;
N 9.30. C24H13N3O6. Calculated, %: C 65.60; H 2.99;
N 9.58.
Run no. 1. Initial mixture of aziridines: 83.3 mg (IIb),
71.9 mg (IIc), 63.6 mg (IId) (molar ratio 1:0.79:0.68).
As analytical the following signals were used: at δ 4.70,
4.65 and 4.75 ppm respectively.After 30 min the ratio of
aziridines was 1:0.30:0.84, after 60 min, 1:0.1:1.15.
Run no. 2. Initial mixture of aziridine: 57.2 mg (IIb),
87.8 mg (IIe) (molar ratio 1:1.42). Analytical signals at
δ 4.40 and 4.37 ppm respectively. After 30 min the ratio
of aziridines was 1:1.66, after 60 min, 1:1.90.
Run no. 3. Initial mixture of aziridine: 57.3 mg (IIb),
68.8 mg (IIf) (molar ratio 1:1.07).Analytical signals at δ
4.40 and 4.38 ppm respectively.After 30 min the ratio of
aziridinee was 1:0.67, after 60 min, 1:0.37.
1-Phthalimido-3-(4-chlorophenyl)spiro[aziridine-
2,2'-indene]-1',3'-dione (IIk). To a solution of 269 mg
(1 mmol) of 2-(4-chlorobenzylidene)indan-1,3-dione (Ik)
in 10 ml of dichloromethane containing a dispersion of
0.5 g of potassium carbonate was added while stirring at
cooling to 0°C within 10 min by alternating small portions
176 mg (1.1 mmol) of N-aminophthalimide and 488 mg
(1.1 mmol) of lead tetraacetate. The mixture was stirred
for another 5 min, filtered through a bed of silica gel
(1 cm), and washed with 20 ml of dichloromethane. The
solution was evaporated to a volume of 5 ml, 10 ml of
ethyl ether was added, and the precipitated product was
filtered off. Yield 329 mg (77%), light-pink powder,
Oxidative addition of N-aminophthalimide to
2-(4-methoxybenzylidene)-indan-1,3-dione (Ii).To
a solution of 132 mg (0.5 mmol)of compound Ii in 5 ml of
a mixture dichloromethane–THF, 1:1, containing a disper-
sion of 1 g of potassium carbonate was added while
stirring at cooling to –15°C within 5 min by alternating
small portions 82 mg (0.5 mmol) of N-aminophthalimide
and 222 mg (0.5 mmol) of lead tetraacetate. The mixture
was stirred for another 5 min, filtered, and kept for
2 days at 5°C in the dark place. According to 1H NMR
spectrum the final reaction mixture contained 43% of
p-methoxybenzaldehyde. By column chromatography on
15 g of silica gel (eluent dichloromethane) 22 mg of
unstable substance was isolated whose structure we
failed to establish.
1
t.decomp. 120–130°C. H NMR spectrum (CDCl3), δ,
ppm: 4.94 s (1H, CHN), 7.36 d (2H, C6H4, J 7.9 Hz),
7.57 d (2H, C6H4, J 7.9 Hz), 7.65–8.00 m (8H). 13C NMR
spectrum (CDCl3), δ, ppm: 54.43 (C–N), 56.10 (CHN);
123.42 and 123.46 (PiN, Cb and C4',7'), 128.47 (C6H4, Co
or Cm), 129.34 (C6H4, Ci or Cp), 129.73 (PiN, Ca and
C6H4, C° or Cm), 134.33 (PiN, CC), 134.91 (C6H4, Ci or
Cp); 135.82 and 135.97 (C5',6'); 190.04 (CO), 190.62
(CO). Mass spectrum, m/z (Irel, %): 283 (10) [M –
PiNH]+, 281 (32) [M – PiNH]+, 190 (18), 147 (33)
[PiNH]+, 114 (16), 104 (72) [C6H4CO]+, 103 (26), 88
(33), 87 (16), 77 (16), 76 (100), 75 (36), 74 (35), 73 (12),
63 (13), 62 (25), 61 (10), 50 (73), 43 (10), 39 (12), 38
(17), 37 (16). Found, %: C 66.9; H 3.08; N 6.32.
C24H13ClN2O4. Calculated, %: C 67.2; H 3.06; N 6.53.
Oxidative addition of N-aminophthalimide to
2-(4-methylbenzylidene)indan-1,3-dione (Ij). To
a solution of 124 mg (0.5 mmol) of compound Ij) in 5 ml
of a mixture dichloromethane–THF, 1:1, containing a dis-
persion of 1 g of potassium carbonate was added while
stirring at cooling to 0°C within 5 min by alternating small
portions 82 mg (0.5 mmol) of N aminophthalimide and
222 mg (0.5 mmol) of lead tetraacetate. The mixture was
stirred for another 5 min. The monitoring by TLC showed
the absence in the reaction mixture of the initial compound
3-(4-Nitrophenyl)-1-phthalimidespiro[aziridine-
2,2'-indene]-1',3'-dione (IIl). To a solution of 488 mg
(1.75 mmol) of 2-(4-nitrobenzylidene)indan-1,3-dione (Il)
in 20 ml of a mixture dichloromethane–THF, 1:1 contain-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 8 2009

SYNTHESIS OF OXAZOLES FROM α,β-UNSATURATED CARBONYL COMPOUNDS
1239
and the presence of a single reaction product. The reac-
tion mixture was filtered, and kept for 2 days at 5°C in
the dark place. According to 1H NMR spectrum the only
reaction product containing a methyl group was the
p-toluic aldehyde separated by chromatography on
a column packed with 15 g of silica gel (eluent dichloro-
methane). Yield 47 mg (81%).
trans-1-Benzenesulfonyl-2-(4-methoxybenzoyl)-
3-phenylaziridine (Ve). To a solution of 640 mg
(2.70 mmol) of chalcone Ie in 15 ml of anhydrous
acetonitrile was added 639 mg (3.0 mmol) of chloramine-
B and 95 mg (0.30 mmol)of pyridinium tribromide. The
reaction mixture was kept for 3 days at room temperature.
The solvent was distilled off in a vacuum. The residue
was passed through a short column packed with silica
gel, eluent hexane–ethyl acetate, from 3:1 to 2:1. The
product precipitated from the second fraction was filtered
off. Yield 180 mg (14%), white powder, mp 142–143°C.
1H NMR spectrum (CDCl3), δ, ppm: 3.88 s (3H, OMe),
4.30 d (1H, NCH, J 4.8 Hz), 4.53 d (1H, NCH,
J 4.8 Hz), 6.95 d (2H, C6H4, Hm, J 8.6 Hz), 7.31–7.35 m
(5H, 3-Ph), 7.36–7.43 m (2H, PhSO2, Hm), 7.46–7.56 m
(1H, PhSO2, Hp), 7.85 d (2H, PhSO2, Ho, J 7.6 Hz),
8.05 d (2H, p-C6H4, Ho, J 8.6 Hz). 13C NMR spectrum
(CDCl3), δ, ppm: 47.50 (NCH), 50.17 (NCH), 55.56
(OMe), 114.04 (C6H4, Cm), 127.50, 127.61, 128.59, 128.84,
129.10 (C6H4, Ci), 131.34, 131.38, 132.93 (3-Ph, Ci),
133.29, 139.71 (PhSO2, Ci), 164.36 (CO), 188.32 (C=O).
Mass spectrum, m/z (Irel, %): 252 (50) [M – SO2C6H5]+,
197 (42), 135 (100) [MeOC6H4CO]+, 107 (10), 92 (18),
89 (11), 90 (11), 77 (71), 64 (13), 63 (10), 51 (27), 50
(12). Found, %: C 67.0; H 4.90; N 3.51. C22H19NO4S.
Calculated, %: C 67.2; H 4.83; N 3.56.
Thermolysis of spiroaziridine IIk. A solution of
107 mg (0.25 mmol) of aziridine IIk in 5 ml of anhydrous
toluene was heated for 1.5 h at 80°C. By chromatography
on a column packed with 10 g of silica gel (eluent hexane–
ethyl acetate, from 2:1 to 1:1) 30 mg of unstable substance
was isolated whose structure we failed to establish.
2-(4-Nitrophenyl)-4H-indeno[2,1-d]oxazol-4-one
(IIIl).Asolution of 100 mg (0.23 mmol) of spiroaziridine
IIl in 10 ml of anhydrous benzene was boiled for 5 h.
The precipitate formed was filtered off and washed with
10 ml of ethyl ether. Yield 37 mg (56%), red powder
virtually insoluble in common organic solvents, mp 271–
274°C. Mass spectrum, m/z (Irel, %): 293 (19), 292 (100)
[M]+, 262 (15), 234 (10), 218 (13), 191 (15), 190 (89),
189 (12), 164 (13), 163 (25), 114 (17), 104 (67), 102 (25),
88 (82), 87 (40), 86 (19), 77 (14), 76 (97), 75 (57), 74
(39), 63 (26), 62 (65), 61 (21), 51 (23), 50 (84), 46 (10),
39 (36), 38 (19), 37 (14). Found, %: C 65.67; H 2.77;
N 9.37. C16H8N2O4. Calculated, %: C 65.75; H 2.74;
N 9.59.
Reaction of chloramine-B with ethyl (E)-2-
cyanocinnamate (Im). To a solution of 201 mg (1 mmol)
of ester Im and 23 mg (0.1 mmol) of benzyltrimethyl-
ammonium chloride in 5 ml of acetonitrile was added at
stirring 322 mg (1.2 mmol) of chloramine-B hydrate. The
reaction mixture was stirred for 15 min. The solvent was
distilled off in a vacuum. The residue was passed through
a thin bed of silica gel in a mixture hexane–ethyl acetate,
1:1. The solvent was distilled off in a vacuum. The
reaction mixture was found to contain N-benzylidene-
benzenesulfamide (VI). Yield 45% (by 1H NMR data).
1H NMR spectrum (CDCl3), δ, ppm: 9.08 s (CH=N) (9.07
[28]). 13C NMR spectrum (CDCl3), δ, ppm (published
data are given in parentheses [28]): 127.93 (128.2), 129.11
(129.30), 129.20 (129.34), 131.29 (131.5), 132.25 (132.6),
133.50 (133.7), 134.99 (135.2), 138.32 (138.5), 170.56
(170.7) (CH=N).
trans-2-Benzoyl-1-benzenesulfonyl-3-phenyl-
aziridine (Vb). To a solution of 4.16 g (20 mmol) of
benzylideneacetophenone (Ib) in 50 ml of anhydrous
acetonitrile was added 4.69 g (22 mmol) of chloramine-
B and 620 mg (2.2 mmol) of tetramethylammonium
tribromide. The reaction mixture was stirred for 3 days
at room temperature. The solvent was distilled off in
a vacuum. The residue was passed through a short column
packed with silica gel, eluent eluent hexane–ethyl acetate,
3:1. The precipitated reaction product was filtered off.
Yield 990 mg (14%), white powder, mp 139–140°C.
1H NMR spectrum (CDCl3), δ, ppm: 4.33 d (1H, NCH,
J 4.4 Hz), 4.56 d (1H, NCH, J 4.4 Hz), 7.32–7.36 m (5H,
3-Ph), 7.42–7.65 m (6H), 7.86 d (2H, PhSO2, Ho,
J 7.6 Hz), 8.06 d (2H, PhCO, Ho, J 7.3 Hz). 13C NMR
spectrum (CDCl3), δ, ppm: 47.58 (NCH), 50.26 (NCH),
127.45, 127.59, 128.62, 128.78, 128.86, 128.87, 128.90,
132.78 (3-Ph, Ci), 133.34, 134.08, 135.91 (PhCO, Ci),
139.63 (PhSO2, Ci), 190.18 (CO). Mass spectrum, m/z
(Irel, %): 222 (43) [M – SO2C6H5]+, 167 (21), 105 (100)
[PhCO]+, 90 (14), 89 (24), 77 (97), 51 (41), 50 (12). Found,
%: C 69.3; H 4.71; N 3.79. C21H17NO3S. Calculated, %:
C 69.4; H 4.68; N 3.86.
Thermolysis of sulfonylaziridine Vb. A solution of
182 mg (0.5 mmol) of aziridine Vb in 5 ml of anhydrous
toluene was heated for 1 h at 160°C. The solvent was
distilled off in a vacuum. The residue was passed through
a bed of neutral aluminum oxide (1 cm) and washed with
20 ml of mixture dichloromethane–hexane, 1:1. The
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 8 2009

BELETSKII, KUZNETSOV
1240
7. Boger, D.L., Chem. Rev., 1986, vol. 86, p. 781.
8. Atkinson, R. and Malpass, J., J. Chem. Soc., Perkin
Trans. 1, 1977, vol. 20, p. 2242.
9. Jeong, J.U., Tao, B., Sagasser, I., Henniges, H., and
Sharpless, K.B., J. Am. Chem. Soc., 1998, vol. 120, p. 6844.
10. Ali, S.I., Nikalje, M.D., and Sudalai, A., Org. Lett., 1999,
vol. 1, p. 705.
solvent was distilled off in a vacuum. The residue was
subjected to chromatography on a column packed with
15 g of silica gel (eluent dichloromethane –ethyl ether,
1:20). We obtained 42 mg (38%) of 2,5-diphenyl-oxazole
(IIIb).
Thermolysis of sulfonylaziridine Ve. A solution of
131 mg (0.33 mmol) of aziridine Ve in 3 ml of anhydrous
toluene was heated for 2 h at 170°C. The solvent was
distilled off in a vacuum. The residue was passed through
a bed of neutral aluminum oxide (1 cm) and washed with
20 ml of mixture dichloromethane–hexane, 1:1. The
solvent was distilled off in a vacuum. The residue was
subjected to chromatography on a column packed with
15 g of silica gel (eluent dichloromethane–ethyl ether,
1:20). We obtained 26 mg (31%) of 5-(4-methoxy-
phenyl)-2-phenyloxazole (IIIe).
11. Ando, T., Kano, D., Minakata, S., Ryu, I., and Koma-
tsu, M., Tetrahedron, 1998, vol. 54, p. 13485.
12. Albone, D.P., Aujla, P.S., Taylor, P.C., Challenger, S., and
Derrick,A.M., J. Org. Chem., 1998, vol. 63, p. 9569; Maire-
na, M.A., Diaz-Requejo, M.M., Belderrain, T.R., Nicasio,
M.C., Trofimenko, S., and Perez, P.J., Organometallics,
2004, vol. 23, p. 253; Martinez-Garcia, H., Morales, D.,
Perez, J., Coady, D.J., Bielawski, C.W., Gross, D.E.,
Cuesta, L., Marquez, M., and Sessler, J.L., Organomettalics,
2007, vol. 26, p. 6511; Bhuyan, R. And Nicholas, K.M.,
Org. Lett., 2007, vol. 9, p. 3957.
Microwave irradiation of sulfonylaziridine Vb.
A solution of 254 mg (0.7 mmol) of aziridine Vb in
a mixture of 4 ml of p-xylene and 0.5 ml of DMF was
irradiated for 1 h with microwave radiation of 180 W
power. The temperature of the reaction mixture attained
135°C. The solution was washed with water (3 × 1 ml).
The solvent was distilled off in a vacuum. The residue
was passed through a bed of neutral aluminum oxide
(1 cm) and washed with 20 ml of mixture dichloro-
methane–hexane, 1:1. The solvent was distilled off in
a vacuum. The residue was subjected to chromatography
on a column packed with 15 g of silica gel (eluent dichloro-
methane –ethyl ether, 1:20). We obtained 84 mg (54%)
of 2,5-diphenyloxazole (IIIb).
13. Drew, N.D.K. and Hatt, N.H., J. Chem. Soc., 1937, p. 16.
14. Metodicheskie ukazaniya k prakticheskim rabotam po
organicheskomu sintezu (Instructions to Practical on
Organic Synthesis), Ogloblin, K.A. and Kostikov, R.R.,
Leningrad: Izd. Leningrad. Gos. Univ., 1982, p. 73.
15. Becker, H., Organicum, New York: Pergamon press, 1973.
16. Li, J., Liang, J.-L., Chan, R.W.H., and Che, C.-M.,
Tetrahedron Lett., 2004, vol. 45, p. 2685.
17. Siu, T. and Yudin, A.K., J. Am. Chem. Soc., 2002, vol. 124,
p. 530.
18. Person, H., Tonnard, F., Foucaud, A., and Fayat, C.,
Tetrahedron Lett., 1973, vol. 14, p. 2495.
19. Krasnova, L.B., Hili, R.M., Chernoloz, O.V., andYudin,A.K.,
ARKIVOC., 2005, p. 26.
20. Herrera,A., Martinez-Alvarez, R., Ramiro, P., Molero, D.,
andAlmy, J., J. Org. Chem., 2006, vol. 71, p. 3026.
21. Crowe, E., Hossner, F., and Hughes, M.J., Tetrahedron,
1995, vol. 51, p. 8889.
REFERENCES
22. Shvaika, O.P., Korzhenevskaya, N.G., and Snagoshchen-
ko, L.P., Khim. Geterotsikl. Soedin., 1985, p. 193.
23. Schuh, K. and Glorius, F., Synthesis, 2007, p. 2297.
24. Makkay, C., Hidisan-Tautean, L. and Ionescu, M., Rev.
Roum. Chim., 1975, vol. 20, p. 643.
25. Pulici, M., Quartieri, F. and Felder, E.R., J. Comb. Chem.,
2005, vol. 7, p. 463.
26. Keni, M. and Tepe, J.J., J. Org. Chem., 2005, vol. 70,
p. 4211.
1. Padwa, A. and Eisenhardt, W., Chem. Commun., 1968,
p. 380.
2. Padwa, A. and Eisenhardt, W., J. Am. Chem. Soc., 1968,
vol. 90, p. 2442; Padwa,A. and Eisenhardt, W., J. Am. Chem.
Soc., 1971, vol. 93, p. 1400.
3. Person, H., Luanglath, K., and Baudru, M., Bull. Soc. Chim.,
1976, vol. 11, p. 1989.
4. Davidson, B.S. Chem. Rev., 1993, vol. 93, p. 1771.
5. Meyers,A., Heterocycles in Organic Synthesis, New York:
Wiley, 1974.
27. Houwing, H.A., Wildeman, J., and van Leusen, A.M.,
Tetrahedron Lett., 1976, vol. 17, p. 143.
6. Wasserman, H.H., McCarty, K.E., and Prowse, K.S., Chem.
Rev., 1986, vol. 86, p. 845.
28. Bowman, R.K. and Johnson, J.S., J. Org. Chem., 2004,
vol. 69, p. 8537.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 8 2009