Regio- and stereo-controlled isomerization of 1,2-diaroyl-3-aryl aziridines to the corresponding N-((Z)-1-oxo-1,3-diphenylprop-2-en-2-yl) benzamide

Article abstract of DOI:10.1007/s13738-014-0416-8

Regio- and stereo-controlled isomerization of 1,2-diaroyl-3-aryl aziridines to the corresponding N-((Z)-1-oxo-1,3-diphenylprop-2-en-2-yl) benzamide in the presence of diethyl thiourea in room temperature is described. A plausible mechanism has been proposed. The structures of the products were confirmed by X-ray analysis.

Full text of DOI:10.1007/s13738-014-0416-8

J IRAN CHEM SOC
DOI 10.1007/s13738-014-0416-8
ORIGINAL PAPER
Regio- and stereo-controlled isomerization of 1,2-diaroyl-3-aryl
aziridines to the corresponding N-((Z)-1-oxo-1,3-diphenylprop-2-
en-2-yl) benzamide
•
Heshmat A. Samimi Bohari M. Yamin
•
Marzieh Soltani
Received: 9 November 2013 / Accepted: 15 January 2014
Ó Iranian Chemical Society 2014
Abstract Regio- and stereo-controlled isomerization of
1,2-diaroyl-3-aryl aziridines to the corresponding N-((Z)-1-
oxo-1,3-diphenylprop-2-en-2-yl) benzamide in the pre-
sence of diethyl thiourea in room temperature is described.
A plausible mechanism has been proposed. The structures
of the products were confirmed by X-ray analysis.
aziridines via C–C bond cleavage (leading to azomethine
ylides) or C–N bond cleavage is strongly influenced by the
nature of the substituents present in them and also the
conditions employed [19, 25, 26].
Although a large variety of 1-aroylaziridines are known
to be readily isomerized into oxazolines under the different
conditions [9, 19, 26–45], a literature survey reveals that a
few examples of the isomerization of the 2-aryl keto-azir-
idines have been reported up to now [22, 46–50].
Keywords Aziridine Á Regio- and stereo-controlled Á
Isomerization Á N-((Z)-1-oxo-1,3-diphenylprop-2-en-2-yl)
benzamide
Our study in the transformation of the aziridine ring
[51–56] to regio-isomers of oxazoline (via C–N bond
cleavage), oxazoles (via C–C bond cleavage), or alkenes
leads to the following new reactions (Scheme 1).
Introduction
The present paper describes the results of our studies in
the isomerization of 1,2-diaroyl-3-aryl aziridines to the
corresponding N-((Z)-1-oxo-1,3-diphenylprop-2-en-2-yl)
benzamide by a C–N bond cleavage.
The earliest example of the isomerization of an aziridine
was described by Gabriel and Stelzner [1] The reaction lay
dormant until the late 1950s when a number of workers
confirmed and extended the reaction [2–5]. The reaction
was further extended to a large variety of the different
aziridines [6–8].
Our initial studies were to explore the ring expansion of
N-acyl ketoaziridines using thiourea derivatives, because
primarily we assumed that thiourea similar to iodide [51]
would attack aziridine ring and make a ring expansion
reaction, but our result shows that the reaction proceeds via
a isomerization to the corresponding N-((Z)-1-oxo-1,3-
diphenylprop-2-en-2-yl) benzamide.
Various functionalized aziridines are isomerized by
thermal or non-thermal [9–11], acids or nucleophilic
reagents [12–21] and or photochemical [22–24]. In addi-
tion, it is well known that the isomerization of the different
We prepared trans-2-benzoyl-3-(4-chlorophenyl) aziri-
dines (1a) via Gabriel-Cromwell procedure [57]. Then
4-nitrobenzoyl chloride was added to a solution of trans-2-
benzoyl-3-(4-chlorophenyl) aziridines (1a) in the presence
of Et3N in CH2Cl2 at 0 8C to furnish 2-benzoyl-1-(4-ni-
trobenzoyl)-3-(4-chlorophenyl) aziridines (2a) (Scheme 2).
After completion of the reaction (monitored by TLC ana-
lysis), diethyl thiourea was added to the mixture and stirred
continuously for 30 h at room temperature. In this stage,
TLC analysis confirmed the formation of a new compound.
The crude product was purified by column chromatography
Electronic supplementary material The online version of this
article (doi:10.1007/s13738-014-0416-8) contains supplementary
material, which is available to authorized users.
H. A. Samimi (&) Á M. Soltani
Department of Chemistry, Faculty of Sciences, The University of
Shahrekord, P. O. Box 115, Shahrekord, Iran
e-mail: samimi-h@sci.sku.ac.ir
B. M. Yamin
School of Chemical Sciences and Food Technology, Universitiy
Kebangsaan Malaysia, UKM, 43500 Bangi, Selangor, Malaysia
123

J IRAN CHEM SOC
Ar1
Ar3
O
N
NH2
Ar2
O
N
N
S
ii
i
Ar1
i
O
Ar1
O
H
Ar2
N
Ar2
O
Ar1
Ar3
i
Ar2
NHCOAr3
O
Ar1
i
i
O
N
O
H
Ar2
Ar2
Ar1
O
This work
Ar2
Ar1
i) via C-N bond cleavage ii) C-C bond cleavage
Scheme 1 Conversion of aziridines to other compounds
Fig. 1 X-ray crystal structures of 3a
(silica gel, EtOAc/hexane: 1/4) to provide N-((Z)-1-oxo-1-
phenyl-3-(4-chlorophenyl)prop-2-en-2-yl)-4-nitro benzam-
ide (3a) (57 %). In a separate experiment, a sample of 2a
was prepared via reported procedure [51] and separated as
a pure compound and treated with diethyl thiourea in
CH2Cl2. The reaction afforded the same product (3a)
(95 %). In other attempt, a mixture of 2a in CH2Cl2 in the
room temperature and absence of diethyl thiourea was
stirred for 30 h and the reaction mixture was monitored by
TLC analysis, but 2a was recovered unchanged; no isom-
erization to 3a was detected.
in good yields (Table 1). The experimental results are
included in Table 1. All the products were characterized by
1H, 13C NMR and IR spectra.
According to the outline in Scheme 3, in a C–N bond
cleavage of aziridine, there are two routes for isomerization
of N-acyl ketoaziridines via addition–elimination reaction
using diethyl thiourea.
In route A, the N-(3-oxo-1,3-diaryl-propenyl)-benzam-
ide (Z-4) will be formed, whereas route B will lead to the
N-((Z)-1-oxo-1,3-diarylprop-2-en-2-yl) benzamide (Z-3).
Based on the X-ray crystallographic analysis11 as shown in
Fig. 1, path B prevails to produce the product.
1
Since the spectral data (e.g., H and 13C NMR, IR, and
elemental analysis) were not conclusive to assign the ste-
reochemistry of the product, X-ray crystallographic ana-
lysis was conducted on 3a to verify product structure.
X-ray analysis of the representative product 3a (Fig. 1)
confirms the diastereoselectivity of the reaction.
In this pathway, the aryl moiety at position 3 makes it a
suitable position for nucleophilic attack by diethyl thio-
urea. Therefore, the isomerization involves initial attack by
diethyl thiourea on an aziridinyl carbon adjacent to the aryl
group with concurrent breaking of the three-membered ring
(C2–N bond) to form an intermediate B.
The results of this study revealed that isomerization
reaction in the presence of thiourea (NH2CSNH2)
(25 mol % catalyst) gave a mixture of products (3a) with
only a moderate yield (36 %) of 3a.
In a subsequent step, negatively charged oxygen
abstracts the hydrogen adjacent to aroyl group synchronous
with elimination of diethyl thiourea affords Z-3. The same
stereochemistry is generalized for all other products. As
shown in Scheme 3, path B prevails to produce Z-isomer as
a sole product.
To expand the scope of this novel methodology, several
2-aroyl-3-arylaziridines (1a–g) were reacted with acyl
chloride to afford the 1,2-diaroyl-3-arylaziridines which
were isomerized to 3a–g in the presence of diethyl thiourea
Scheme 2 Acylation of
2-benzoyl-1-(4-
nitrobenzoyl)aziridines (2a) and
reaction with diethyl thiourea
O2N
H
O
N
O
O
Ph
O
H
i
ii
N
Ph
1a
HN
Cl
O
2a
Ph
Cl
Cl
NO2
i) 4-NO2C6H5COCl/CH2Cl2/Et3N/0 OC-RT
ii) ENHCSNHEt/CH2Cl2/RT
3a
123

J IRAN CHEM SOC
Table 1 Synthesis of the derivatives of N-((Z)-1-oxo-1,3-diphenylprop-2-en-2-yl) benzamide (3a–g) via isomerization of N-acyl keto-aziridines
in the presence of diethyl thiourea
Ar3
O
H
N
NHCOAr3
O
Ar1
H
O
i
N
ii
Ar1
O
Ar1
Ar2
Ar2
Ar2
3a-g
1a-g
2a-g
i) ArCOCl/CH2Cl2/Et3N/0 °C-RT ii) ENHCSNHEt / RT °C
Entry
Ar1
Ar2
Ar3
Yield (%)a
a
b
c
d
e
f
4-ClC6H4
3-NO2C6H4
C6H5
C6H5
4-NO2C6H4
4-NO2C6H4
4-NO2C6H4
4-NO2C6H4
4-NO2C6H4
C6H5
95
92
67
93
89
83
69
C6H5
C6H5
3-NO2C6H4
2,4-Cl2C6H3
C6H5
4-ClC6H4
4-ClC6H4
C6H5
g
4-ClC6H4
4-ClC6H4
C6H5
General conditions: reactions were performed in CH2Cl2 using a ratio of 1:3:0.0.25 for aziridine/Et3N/diethyl thiourea. Reaction time for
consuming all of the starting materials was 30 h
a
Isolated yield
H
Ar3
N
Ar3
H
O
O
O
Ar2
Ar1
O
O
Ar3CONH
Ar1
O
N
N
S
H
Ar2
1
Route A
Ar2
Ar2
Ar1
H
Ar1
H
H
C1-N cleavage
S
A
Ar3
O
Z-4, not formed
EtHN
EtHN
NHEt
NHEt
N
O
Ar1
Ar3
Ar3
H
O
O
Ar2
Ar2
O
RouteB
H
O
O
2
N
H
N
S
C2-N cleavage
NHCOAr3
Ar1
Ar2
Ar1
Ar2
Ar1
H
H
S
Z-3, formed
B
EtHN
EtHN
NHEt
NHEt
Scheme 3 Plausible mechanism for the product formation
It is striking to note that the rearrangement of 2–3
occurred in a regio- and stereo-selective manner, and it is
suggested that the regioselectivity entirely depends on the
stereo-electronic nature of the substituents on aziridinyl
carbons (phenyl and benzoyl). It means diethyl thiourea
prefers to attack on carbon-bearing phenyl.
phenyl-3-benzoylaziridine (2), Although it has been
reported that the thermal isomerization of 2 gives rise to
another rearrangement in high yield [47] our result also
shows that compound 2 in refluxing p-xylene afforded 5f
via a C–C bond cleavage in moderate yield (61 %)
(Scheme 4).
Encouraged by the results obtained with the isomeri-
zation of 2–3 in room temperature, it was felt necessary
to reinvestigate the thermal isomerization of trans-2-
Finally, we explored the regio- and stereo-controlled
isomerization of N-acyl keto-aziridines in the presence of
diethyl thiourea for synthesis of the derivatives of N-((Z)-1-
123

J IRAN CHEM SOC
J = 8.8 Hz, 2H), 8.07 (d, J = 8.8 Hz, 2H), 7.83 (dd,
J = 1.2, 7.6 Hz, 2H), 7.64 (dt, J = 1.2, 7.6 Hz, 1H), 7.52
(t, J = 7.6 Hz, 2H), 7.43 (d, J = 8.4 Hz, 2H), 7.37 (d,
J = 8.4 Hz, 2H), 6.88 (s, 1H) ppm; 13C NMR (400 MHz,
CDCl3): d 193.8, 163.3, 150.0, 138.3, 136.1, 135.7, 133.1,
132.2, 132.1, 132.0, 130.7, 129.8, 129.2, 128.7, 128.6,
124.0 ppm. Anal. Calcd for C22H15ClN2O4: C, 64.95; H,
3.72; N, 6.89 %. Found: C, 64.93; H, 3.75; N, 6.71 %.
Ph
O
PhCO2
Ph
H
N
Heat
N
O
CHPh
Ph
5f
Ph
2f
Scheme 4 Thermal rearrangement of 2f to 1,4-diphenyl-4-benzoy-
loxy-2-azabutadie (5f)
X-ray crystal structure analysis for 3a
oxo-1,3-diphenylprop-2-en-2-yl) benzamide. A possible
mechanism for this isomerization was proposed.
Formula C22H15ClN2O4, M = 406.81, Yellow crystal
0.30 9 0.10 9 0.10 mm, a = 10.0267 (5), b = 16.1419
3
(9), c = 23.9254 (14) A, V = 3,872.3(4) A ,
˚
˚
q
Z = 8,
calcd = 1.396 mg cm-3
,
l = 0.229 mm-1
,
Experimental section
˚
orthogonal, k = 0.71073 A, T = 301 K, x and u scans,
3,591 reflections collected ( h, k, l), [I C 2 r(I)],
1,959 independent (Rint = 0.0808) and 1,852 observed
reflections [I C 2 r(I)], 267 refined parameters,
R = 0.0544, wR2 = 0.1260, max residual electron density
General
All yields refer to isolated products after purification by
column chromatography or distillation in vacuum. Products
were characterized by comparison with authentic samples
(IR, 13C and 1H NMR spectra, TLC analysis, melting
0.251 (-0.373) eA-3, Flack parameter 0.0040 (6). Data set
˚
was collected with a Bruker SMART APEX CCD area
detector diffractometer, Absorption correction: multi-scan
(SADABS; Sheldrick, 1996) School of Chemical Sciences
and Food Technology, Universiti Kebangsaan Malaysia,
bohari@pkrisc.cc.ukm.my.
1
points). All H NMR spectra were recorded at 400 MHz
(The central Laboratory of the University of Isfahan,
Isfahan. Iran) in CDCl3 relative to TMS and IR spectra
were recorded on FT Infrared spectroscope JASCO, FT/IR-
6300, The central Laboratory of the University of Isfahan,
Isfahan, I.R. Iran. All solvents used were dried and distilled
according to standard procedures.
N-((Z)-1-oxo-1-phenyl-3-(3-nitrophenyl)prop-2-en-2-yl)-4-
nitrobenzamide (3b)
Yellow solid, m.p. 162–165 °C; IR (KBr): v (cm-1) 3,323,
3,119, 1,643, 1,620, 1,602, 1,528, 1,484, 1,449; H NMR
General procedure for rearrangement of keto-aziridines
1
(1a–f) to (3a–g)
(400 MHz, CDCl3): d 8.63 (br, NH), 8.37–8.35 (m, 2H),
8.26 (d, J = 8.9 Hz, 1H), 8.21–8.16 (m, 2H), 8.07 (t,
J = 8.2 Hz, 1H), 7.88 (dd, J = 7.2, 1.4, Hz, 1H), 7.67 (tt,
J = 7.5, 1.3 Hz, 1H), 7.56 (t, J = 7.8 Hz, 1H), 7.42–7.33
(m, 1H),), 7.26–7.13 (m, 4H) ppm; 13C NMR (400 MHz,
CDCl3): d 193.4, 163.4, 151.3, 148.7, 135.1, 133.1, 131.3,
130.8, 129.5, 128.8, 128.7, 124.2, 123.8, 123.6, 122.7,
121.7 ppm. Anal. Calcd for C22H15N3O4: C, 63.31; H,
3.62; N, 10.07 %. Found: C, 63.28; H, 3.65; N, 10.6 %.
Aroyl chloride (2 mmol) was added drop wise to a solution
of aziridines (1) (2 mmol) and triethylamine (0.6 mL) in
CH2Cl2 (20 mL) at 0 °C. After 2 h, diethyl thiourea was
added and the mixture was stirred at room temperature.
The progress of the reaction was monitored by TLC
(EtOAc-hexane: 1/4). After completion of the reaction,
organic layer was rinsed twice with dilute HCl (10 %) and
water and then dried with anhydrous MgSO4. Evaporation
of the solvent under reduced pressure and subsequent
purification of the residue by column chromatography
(silica gel, EtOAc-hexane: 1/4) provided the derivatives of
N-((Z)-1-oxo-1,3-diphenylprop-2-en-2-yl) benzamide (3a–
f) (67–95 %) (Table 1).
N-((Z)-1-oxo-1-phenyl-3-(phenyl)prop-2-en-2-yl)-4-
nitrobenzamide (3c)
White solid, m.p. 203–205 °C; IR (KBr): v (cm-1) 3,217,
3,067, 1,666, 1,664, 1,598, 1,525, 1,480, 1,447; H NMR
1
N-((Z)-1-oxo-1-phenyl-3-(4-chlorophenyl)prop-2-en-2-yl)-
(400 MHz, CDCl3): d 8.76 (br, NH), 8.29 (d, J = 8.7 Hz,
2H), 8.07 (d, J = 8.6 Hz, 2H), 7.90 (d, J = 7.3 Hz, 2H),
7.62 (t, J = 7.5 Hz, 1H), 7.52–7.48 (m, 4H), 7.43–7.36 (m,
3H), 6.92 (s, 1H) ppm; 13C NMR (400 MHz) (CDCl3) d
193.7, 163.1, 149.9, 138.5, 136.4, 133.5, 133.3, 133.1,
132.9, 129.9, 129.8, 129.4, 128.9, 128.8, 128.5, 123.9 ppm.
4-nitrobenzamide (3a)
Yellow solid, m.p. 187–190 °C; IR (KBr): v (cm-1) 3,380,
3,091, 1,662, 1,590, 1,482, 1,101, 867, 828, 756, 685; H
1
NMR (400 MHz, CDCl3): d 8.37 (br, NH), 8.28 (d,
123

J IRAN CHEM SOC
Anal. Calcd for C22H16N2O4: C, 70.96; H, 4.33; N, 7.52 %.
Found: C, 70.93; H, 4.37; N, 7.50 %.
133.2, 131.3, 131.0, 129.8, 129.3, 128.4, 127.1, 123.7 ppm.
Anal. Calcd for C22H13N2O4: C, 59.88; H, 3.20; N, 6.35 %.
Found: C, 59.71; H, 3.26; N, 6.32 %.
N-((Z)-1-oxo-1-(4-chlorophenyl)-3-(3-nitrophenyl)prop-2-
Acknowledgments We are thankful to Research Council of Shah-
rekord University for supporting this work.
en-2-yl)-4-nitrobenzamide (3d)
White solid, m.p. 246–248 °C; 1H NMR (400 MHz,
CDCl3): d 8.54 (br, NH), 8.40–8.38 (m, 3H), 8.23 (d,
J = 7.5 Hz, 1H), 8.08 (d, J = 8.6 Hz, 2H), 7.87 (d,
J = 8.3 Hz, 2H), 7.77 (d, J = 7.6 Hz, 1H), 7.62–7.54 (m,
3H), 7.08 (s, 1H) ppm; 13C NMR (400 MHz, CDCl3): d
193.4, 163.7, 149.7, 139.4, 137.3, 135.1, 133.1, 132.6,
130.9, 129.1, 128.8, 128.7, 126.2, 124.2, 123.8, 122.3 ppm.
Anal. Calcd for C22H14ClN3O6: C, 58.48; H, 3.12; N,
9.30 %. Found: C, 58.45; H, 3.16; N, 9.2 %.
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White solid, m.p. 197–199; 1H NMR (400 MHz, CDCl3): d
8.50 (br, NH), 8.19 (dd, J = 8.8, 2.1 Hz, 2H), 7.88 (dd,
J = 8.8, 2.1 Hz, 2H), 7.81 (dt, J = 8.6, 2.1 Hz, 2H),
7.45–7.42 (m, 2H), 7.41 (d, J = 8.7 Hz, 1H), 7.17 (d,
J = 8.4, 2.2 Hz, 1H), 6.95 (s, 1H) ppm; 13C NMR
(400 MHz, CDCl3): d; 13C NMR (400 MHz, CDCl3): d
191.9, 162.9, 150.1, 139.9, 138.0, 135.8, 134.9, 134.1,
133.2, 131.3, 131.0, 130.0, 129.9, 129.8, 129.0, 128.6,
127.4, 124.0 ppm. Anal. Calcd for C22H13N2O4: C, 55.55;
H, 2.75; N, 5.89 %. Found: C, 55.53; H, 2.78; N, 5.86 %.
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White solid, m.p. 160–162 °C; 1H NMR (400 MHz,
CDCl3): d 8.33 (br, NH), 7.88 (dd, J = 8.6, 2.1 Hz, 2H),
7.80 (s, 1H); 7.75 (dd, J = 8.4, 2.1 Hz, 2H), 7.86–7.4 (m,
10H), 7.01 (s, 1H) ppm; 13C NMR (400 MHz, CDCl3): d;
13C NMR (400 MHz, CDCl3): d 192.9, 162.9, 139.7, 138.2,
136.8, 134.9, 133.1, 131.2, 131.0, 130.0, 129.9, 129.8,
129.0, 128.6, 126.8, 124.0 ppm. Anal. Calcd for
C22H17NO2: C, 80.71; H, 5.23; N, 4.28 %. Found: C,
80.68; H, 5.25; N, 4.27 %.
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White solid, m.p. 190–192; 1H NMR (400 MHz, CDCl3): d
8.45 (br, NH), 7.90 (dd, J = 8.6, 2.1 Hz, 2H), 7.85 (dd,
J = 8.6, 2.1 Hz, 2H), 7.78 (dt, J = 8.6, 2.1 Hz, 2H),
7.40–7.42 (m, 3H), 7.39 (d, J = 8.4 Hz, 1H), 7.15 (d,
J = 8.4, 2.2 Hz, 1H), 6.94 (s, 1H) ppm; 13C NMR
(400 MHz, CDCl3): d; 13C NMR (400 MHz, CDCl3): d
192.0, 162.8, 150.0, 139.6, 138.1, 135.6, 134.4, 134.0,
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