Efficient aziridination of α,β-unsaturated ketones with O-(2,4-dinitrophenyl)-hydroxylamine

Article abstract of DOI:10.1080/00397911.2010.541968

The aziridination of α,β-unsaturated ketones with O-(2,4-dinitrophenyl)-hydroxylamine and tertiary amine was developed. trans-Aziridines were obtained exclusively in good yields. The reaction is proposed to occur via an aminimide intermediate. Copyright T

Full text of DOI:10.1080/00397911.2010.541968

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Efficient Aziridination of α,β-
Unsaturated Ketones with O-(2,4-
Dinitrophenyl)-hydroxylamine
Jin-jia Wang a , Jin-hua Lao a , Xue-ming Li a , Rui-jiong Lu a , Hui
Miao a & Ming Yan a
a Institute of Drug Synthesis and Pharmaceutical Process, School of
Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou, China
Accepted author version posted online: 17 Nov 2011. Version of
record first published: 03 Feb 2012
To cite this article: Jin-jia Wang, Jin-hua Lao, Xue-ming Li, Rui-jiong Lu, Hui Miao & Ming Yan
(2012): Efficient Aziridination of α,β-Unsaturated Ketones with O-(2,4-Dinitrophenyl)-hydroxylamine,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 42:11, 1577-1584
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Synthetic Communications1, 42: 1577–1584, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.541968
EFFICIENT AZIRIDINATION OF a,b-UNSATURATED
KETONES WITH O-(2,4-DINITROPHENYL)-
HYDROXYLAMINE
Jin-jia Wang, Jin-hua Lao, Xue-ming Li, Rui-jiong Lu,
Hui Miao, and Ming Yan
Institute of Drug Synthesis and Pharmaceutical Process, School of
Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou, China
GRAPHICAL ABSTRACT
Abstract The aziridination of a,b-unsaturated ketones with O-(2,4-dinitrophenyl)-
hydroxylamine and tertiary amine was developed. trans-Aziridines were obtained exclus-
ively in good yields. The reaction is proposed to occur via an aminimide intermediate.
Keywords Aziridination; O-(2,4-dinitrophenyl)-hydroxylamine; a,b-unsaturated ketone
INTRODUCTION
Aziridines are important structural units in many drugs and natural
products.[1] They are also valuable intermediates for the synthesis of a wide range
of nitrogen-containing products.[2] A number of synthetic methods for aziridines
have been developed.[3] Among them, the synthesis of N-unsubstituted aziridines is
extremely important, considering the flexibility for further functionalization at the
nitrogen atom. In 1980, Ikeda and coworkers reported the first direct aziridination
of chalcones via hydrazinium salts.[4] Then Xu, Armstrong, and their coworkers
improved this method with different hydrazinium salts and bases.[5,6] These reactions
were assumed to proceed via the conjugate addition of the aminimide intermediates
and consequent ring-closure steps.[4,5] Shi,[7] Armstrong,[8] and coworkers further
developed the method by in situ combination of tertiary amines, amino transfer
reagents, and bases. The hydrazinium salts generated in situ were deprotonated to
provide aminimide intermediates. O-Mesitylenesulfonylhydroxylamine (MSH) and
O-(diphenylphosphinyl)hydroxylamine (DPPH) were used as the amino transfer
reagents (Scheme 1). However, MSH is highly unstable and requires special
Received October 18, 2010.
Address correspondence to Ming Yan, School of Pharmaceutical Sciences, Sun Yat-sen University,
Guangzhou 510006, China. E-mail: yanming@mail.sysu.edu.cn
1577

1578
J.-J. WANG ET AL.
Scheme 1. Amino transfer reagents MSH, DPPH, and DNPH.
cautions.[9] DPPH is a better amino transfer reagent, but it is more expensive.[10] We
speculate that O-(2,4-dinitrophenyl)-hydroxylamine (DNPH),[11] readily available
from N-hydroxyphthalimide and 1-chloro-2,4-dinitrobenzene, is a cheap and stable
amino transfer reagent. The application of DNPH can provide a more practical
method for the aziridination of a,b-unsaturated ketones. The experiment results
are reported in this article.
Initially, the aziridination of chalcone with DNPH was studied. N-Methylmor-
pholine (NMM) and NaOH were used as the tertiary amine and base respectively. A
series of solvents were screened, and the results are summarized in Table 1. The reac-
tions in less polar solvents, such as toluene, CH2Cl2, and tetrahydrofuran (THF),
afforded 2a in poor yields (Table 1, entries 1–3). However, the reaction in acetonitrile
gave 2a in 81% yield after 24 h (Table 1, entry 4). Further study indicated that
dimethylformamide (DMF) is a better solvent. The product 2a was obtained in
85% yield after 2.5 h (Table 1, entry 5). The importance of the tertiary amine was
Table 1. Effect of reaction solvents and tertiary aminesa
Entry
Solvent
Amine
Time (h)
Yieldb (%)
1
2
Toluene
CH2Cl2
THF
NMM
NMM
NMM
24
24
24
24
2.5
24
24
4
16
38
18
81
85
—
—
72
75
79
85
88
3
4
CH3CN
DMF
DMF
NMM
NMM
5
6
—
Morpholine
NMP
7
DMF
DMF
8
9
DMF
DMF
Triethylamine
DABCO
NMM
4
10
11c
12d
2.5
4
CH3CN
CH3CN
NMM
9
aThe reactions were carried out with chalcone (0.25 mmol), amine (0.26 mmol), DNPH (0.37 mmol), and
NaOH (0.5 mmol) in solvent (4 mL) at room temperature.
bIsolated yield after column chromatography.
cMSH (2.0 equiv) was used, and the yield was reported in Ref. 7.
dDPPH (1.05 equiv) was used, and the yield was reported in Ref. 8a.

SYNTHESIS OF N-UNSUBSTITUTED AZIRIDINES
1579
confirmed by the fact that no product 2a was obtained in the absence of NMM
(Table 1, entry 6). In addition, morpholine is completely ineffective (Table 1, entry
7). The results support the reaction mechanism via aminimide intermediates. Other
tertiary amines are also efficient. N-Methylpyrrolidine (NMP), triethylamine, and
1,4-diazabicyclo[2.2.2]octane (DABCO) provided 2a in 72–79% yields (Table 1,
entries 8–10). For a comparison, the yields obtained with MSH and DPPH are also
listed (Table 1, entries 11 and 12).[7,8a] Comparable yields were achieved with these
three amino transfer reagents; however, less reaction time was required by DNPH.
A variety of a,b-unsaturated ketones were examined in the reaction, and the
results are summarized in Table 2. In general, 4-substitutions at b-phenyl group of
chalcone were tolerated very well. Good yields were achieved for 4-methyl, 4-meth-
oxy, 4-chloro, and 4-bromo substituted chalcones (Table 2, entries 1–5); however,
4-nitro substitution significantly decreased the yield (Table 2, entry 6). 2-Chloro-
substituted chalcone gave satisfactory yield (Table 2, entry 7). b-(2-Thiophenyl)-
and b-1-naphthyl-a,b-unsaturated ketones afforded the corresponding aziridines in
good yields (Table 2, entries 8 and 9). b-tert-Butyl-a,b-unsaturated ketone is appli-
cable, but in lower yield (Table 2, entry 10). On the other hand, the substitutions
at 1-phenyl group of chalcone are also tolerable (Table 2, entries 11 and 12).
Actually, 4-methoxy substituted substrate 1k provided the product in better yield.
The reaction of benzylidene acetone provided complex products, from which no azir-
idine product was obtained (Table 2, entry 13). Methyl cinnamate was found to be
unreactive in this reaction (Table 2, entry 14).
Table 2. Aziridination of a,b-unsaturated ketonesa
Entry
R1
R2
Time (h)
Yieldb (%)
1
2
1a, Ph
1b, 4-MePh
1c, 4-MeOPh
1d, 4-ClPh
1e, 4-BrPh
1f, 4-NO2Ph
1g, 2-ClPh
1h, 2-Thiophenyl
1i, 1-Naphthyl
1j, t-Bu
Ph
Ph
2.5
2.5
8
2a, 85
2b, 85
2c, 81
2d, 83
2e, 81
2f, 39
2g, 80
2h, 78
2i, 81
2j, 65
2k, 95
2l, 82
—
3
Ph
Ph
4
2
5
Ph
Ph
2
6
1.5
2
7
Ph
Ph
8
3
9
Ph
Ph
2
10
11
12
13
14
7
1k, Ph
1l, Ph
4-MeOPh
4-ClPh
Me
5
1.5
8
Ph
Ph
OMe
8
—
aThe reactions were carried out with chalcone (0.25 mmol), NMM (0.26 mmol), DNPH (0.37 mmol),
and NaOH (0.5 mmol) in DMF (4 mL) at room temperature.
bIsolated yield after column chromatography.

1580
J.-J. WANG ET AL.
Scheme 2. Proposed catalytic mechanism.
A catalytic mechanism is proposed (Scheme 2).[7] First, NMM reacts with
DNPH to form the hydrazinium salt (I), which is deprotonated by NaOH to provide
the aminimide (II). The conjugate addition of II to chalcone provides intermediate
III, which undergoes an intramolecular cyclization to give the aziridine product
and regenerate NMM. Although only a catalytic amount of NMM is theoretically
necessary, significantly lower yields were obtained, while substoichiometric amount
of NMM (such as 30 mol% or 50 mol%) was used in our study. Other side reactions
of the aminimide (II) are supposed to account for the loss of NMM in substantial
amounts during the reaction.
In conclusion, we have found that DNPH is an efficient amino transfer reagent
for the aziridination of a,b-unsaturated ketones. Good yields of aziridine products
were obtained for a variety of a,b-unsaturated ketones under mild reaction con-
ditions. The present method provides a practical synthetic route for a number of
N-unsubstituted aziridines.
EXPERIMENTAL
1H NMR and 13C NMR spectra were recorded on Bruker Avance 400 spec-
trometer. Chemical shifts of protons are reported in parts per million downfield from
TMS (d ¼ 0). Chemical shifts of carbon are referenced to the carbon resonances of
the solvent (CHCl3: d ¼ 77.0). Peaks are labeled as singlet (s), doublet (d), triplet (t),
quartet (q), and multiplet (m). Melting points were measured on a WRS-2A melting-
point apparatus and are uncorrected. The high-resolution mass spectroscopic
(HRMS) data were obtained on a Shimadazu LCMS-IT-TOF spectrometer. Infra-
red (IR) spectra were recorded on a Bruker Tensor 37 spectrophotometer. Data
are represented as follows: frequency of absorption (cmꢀ1) and intensity of
absorption (s ¼ strong, m ¼ medium, w ¼ weak). Flash chromatography was per-
formed over silica gel (230–400 mesh), purchased from Qingdao Haiyang Chemical
Co., Ltd.

SYNTHESIS OF N-UNSUBSTITUTED AZIRIDINES
1581
Commercial reagents were used as received. Analytical-grade solvents and
commerically available reagents were used without further purification. DNPH
was prepared according to the literature procedures.[12]
General Procedure for the Aziridination of a,b-Unsaturated Ketones
with DNPH
NMM (0.26 mmol) was added to a solution of DNPH (0.38 mmol) in DMF
(4 mL) at room temperature. The mixture was allowed to stir for 15 min, and then
NaOH (0.5 mmol) and chalcone (0.25 mmol) were added. The mixture was stirred
until the thin-layer chromatographic (TLC) analysis indicated the complete con-
sumption of chalcone. The reaction mixture was diluted with EtOAc (30 mL) and
washed with saturated brine. The organic layer was dried over anhydrous Na2SO4
and concentrated in vacuum. The crude mixture was purified by flash chromato-
graphy over silica gel (AcOEt=petroleum ether ¼ 1=8) to give the aziridine product.
Phenyl(3-phenylaziridin-2-yl)methanone (2a)
White solid; mp 98–99 ꢁC (lit. 100–101 ꢁC[5]). IR (KBr): 3222 (m), 1660 (s),
1449 (m), 1413 (m), 1264 (s). NMR data are in agreement with reported values.[8a]
1H NMR (400 MHz, CDCl3): d 8.00–7.99 (m, 2H), 7.63–7.59 (m, 1H), 7.51–7.47
(m, 2H), 7.37–7.31 (m, 5H), 3.51 (dd, J ¼ 8.0, 2.0 Hz, 1H), 3.18 (dd, J ¼ 9.2,
2.0 Hz, 1H), 2.69–2.65 (br m, 1 H). 13C NMR (100 MHz, CDCl3): d 195.7, 138.3,
135.9, 133.8, 128.8, 128.5, 128.3, 127.9, 126.2, 44.1, 43.5. HRMS (ESI) calcd. for
C15H12NO (M ꢀ H)ꢀ: 222.0919; found: 222.0916.
Phenyl(3-p-tolylaziridin-2-yl)methanone (2b)
White solid; mp 106–107 ꢁC (lit. 106–107 ꢁC[5]). IR (KBr): 3222 (m), 1660 (s),
1449 (m), 1264 (m), 1231 (m). NMR data are in agreement with reported values.[8a]
1H NMR (400 MHz, CDCl3): d 8.00–7.98 (m, 2H), 7.63–7.59 (m, 1H), 7.50–7.46 (m,
2H), 7.26 (d, J ¼ 8.0 Hz, 2H), 7.17 (d, J ¼ 8.0 Hz, 2H), 3.49 (d, J ¼ 2.0 Hz, 1H), 3.15
(d, J ¼ 2.4 Hz, 1H), 2.65 (br s, 1H), 2.36 (s, 3H) 13C NMR (100 MHz, CDCl3): d
195.8, 137.7, 136.0, 135.4, 133.8, 129.2, 128.8, 128.3, 126.1, 44.2, 43.5, 21.2. HRMS
(ESI) calcd. for C16H14NO (M ꢀ H)ꢀ: 236.1075; found: 236.1071.
(3-(4-Methoxyphenyl)aziridin-2-yl)(phenyl)methanone (2c)
Orange oil. IR (KBr): 3228 (m), 1660 (s), 1517 (s), 1252 (s). NMR data are in
agreement with reported values.[8a] 1H NMR (400 MHz, CDCl3): d 8.00–7.94 (m,
2H), 7.62–7.58 (m, 1H), 7.49–7.45 (m, 1H), 7.30–7.25 (m, 2H), 6.90–6.88 (m, 2H),
3.80 (s, 3H), 3.47 (d, J ¼ 2.0 Hz, 1H), 3.13 (d, J ¼ 1.6 Hz, 1H), 2.67 (br s, 1H).
13C NMR (100 MHz, CDCl3): d 195.7, 159.4, 135.9, 133.7, 130.4, 128.8, 128.3,
127.3, 114.0, 55.3, 44.1, 43.3. HRMS (ESI) calcd. for C16H14NO2 (M ꢀ H)ꢀ:
252.1025; found: 252.1019.

1582
J.-J. WANG ET AL.
(3-(4-Chlorophenyl)aziridin-2-yl)(phenyl)methanone (2d)
Pale yellow solid; mp 88–89 ꢁC (lit. 88–89 ꢁC[5]). IR (KBr): 3221 (m), 1658 (s),
1492 (m), 1267 (s). NMR data are in agreement with reported values.[7] 1H NMR
(400 MHz, CDCl3): d 8.00–7.97 (m, 2H), 7.65–7.60 (m, 1H), 7.52–7.48 (m, 2H),
7.35–7.29 (m, 4H), 3.46 (d, J ¼ 2.4 Hz, 1H), 3 (d, J ¼ 2.0 Hz, 1H), 2.67 (br s, 1H).
13C NMR (100 MHz, CDCl3): d 195.4, 136.9, 135.8, 133.9, 133.7, 128.9, 128.7,
128.3, 128.0, 44.1, 42.8. HRMS (ESI) calcd. for C15H11NOCl (M H)ꢀ: 256.0529;
found: 256.0520.
(3-(4-Bromophenyl)aziridin-2-yl)(phenyl)methanone (2e)
White solid; mp 109–111 ꢁC (lit. 110–111 ꢁC[5]). IR (KBr): 3219 (m), 1660 (s),
1
1596 (w), 1388 (m), 1268 (m). H NMR (400 MHz, CDCl3): d 7.99–7.97 (m, 2H),
7.65–7.60 (m, 1H), 7.52–7.47 (m, 4H), 7.26–7.24 (m, 2H), 3.46–3.45 (m, 1H),
3.14–3.13 (m, 1H), 2.67 (br s, 1H). 13C NMR (100 MHz, CDCl3): d 195.4, 137.4,
135.8, 133.9, 131.7, 128.9, 128.3, 127.9, 121.8, 44.1, 42.8. HRMS (ESI) calcd. for
C15H11NOBr (M ꢀ H)ꢀ: 300.0024; found: 300.0014.
(3-(4-Nitrophenyl)aziridin-2-yl)(phenyl)methanone (2f)
Yellow solid; mp 131–132 ꢁC (lit. 142–143 ꢁC5). IR (KBr): 3264 (m), 1662 (s),
1599 (m), 1515 (s), 1344 (m). NMR data are in agreement with reported values.[7]
1H NMR (400 MHz, CDCl3): d 8.23–8.21 (m, 2H), 8.00–7.98 (m, 2H), 7.67–7.63
(m, 1H), 7.56–7.50 (m, 4H), 3.52 (dd, J ¼ 8.0, 2.0 Hz, 1H), 3.27 (dd, J ¼ 9.2,
2.0 Hz, 1H), 2.80–2.76 (br m, 1H). 13C NMR (100 MHz, CDCl3): d 194.8, 147.6,
145..8, 135.6, 134.2, 129.0, 128.3, 127.1, 123.8, 44.2, 42.3. HRMS (ESI) calcd. for
C15H11N2O3 (M ꢀ H)ꢀ: 267.0770; found: 267.0767.
(3-(2-Chlorophenyl)aziridin-2-yl)(phenyl)methanone (2g)
Pale yellow solid; mp 91–92 ꢁC (lit. 92–94[5]). IR (KBr): 3197 (m), 1666 (s), 1598
(w), 1417 (m), 1385 (m), 1228 (m). NMR data are in agreement with reported
values.[7] 1H NMR (400 MHz, CDCl3): d 8.07–8.06 (m, 2H), 7.65–7.61 (m, 1H),
7.56–7.49 (m, 3H), 7.37 (dd, J ¼ 7.6, 1.6 Hz, 1H), 7.32–7.24 (m, 2H), 3.46 (d,
J ¼ 1.6 Hz, 1H), 3.40 (d, J ¼ 2.0 Hz, 1H), 2.62 (s, 1H). 13C NMR (100 MHz, CDCl3):
d 195.9, 136.0, 135.8, 134.2, 133.9, 129.1, 128.9, 128.8, 128.5, 127.6, 127.0, 42.8, 41.5.
HRMS (ESI) calcd. for C15H11NOCl (M ꢀ H)ꢀ: 256.0529; found: 256.0522.
Phenyl(3-(thiophen-2-yl)aziridin-2-yl)methanone (2h)
White solid; mp 108–110 ꢁC. IR (KBr): 3207 (m), 1661 (s), 1449 (m), 1399 (m),
1
1261 (m). H NMR (400 MHz, CDCl3): d 8.03–8.01 (m, 2H), 7.65–7.61 (m, 1H),
7.53–7.49 (m, 2H), 7.23 (dd, J ¼ 5.2, 0.8 Hz, 1H), 7.10 (dd, J ¼ 3.2, 0.4 Hz, 1H),
6.99 (dd, J ¼ 5.2, 3.6 Hz, 1H), 3.62 (dd, J ¼ 8.0, 2.4 Hz, 1H), 3.41 (dd, J ¼ 9.2,
2.0 Hz, 1H), 2.81–2.76 (br m, 1H). 13C NMR (100 MHz, CDCl3): d 195.1, 143.1,

SYNTHESIS OF N-UNSUBSTITUTED AZIRIDINES
1583
135.8, 133.9, 128.9, 128.4, 127.2, 125.3, 124.5, 44.9, 40.0. HRMS (ESI) calcd. for
C13H10NOS (M ꢀ H)ꢀ: 228.0483; found: 228.0487.
(3-(Naphthalen-1-yl)aziridin-2-yl)(phenyl)methanone (2i)
Pale yellow solid; mp 146–147 ꢁC (lit. 148–150 ꢁC[8a]). IR (KBr): 3253 (m), 1663
(s), 1595 (m), 1450 (s), 1261 (s). NMR data are in agreement with reported values.[8a]
1H NMR (400 MHz, CDCl3): d 8.07–8.05 (m, 2H), 8.01 (d, J ¼ 8.4 Hz, 1H), 7.91 (d,
J ¼ 8.0 Hz, 1H), 7.83 (d, J ¼ 8.0 Hz, 1H), 7.76 (d, J ¼ 7.2 Hz, 1H), 7.63 (t, J ¼ 6.8 Hz,
1H), 7.61–7.42 (m, 5H), 3.78–3.76 (m, 1H), 3.54–3.53 (m, 1H), 2.72 (br s, 1H). 13C
NMR (100 MHz, CDCl3): d 196.2, 135.9, 134.0, 133.9, 133.4, 131.9, 128.9, 128.8,
128.5, 128.2, 126.4, 125.9, 125.7, 123.9, 122.7, 43.1, 41.9. HRMS (ESI) calcd. for
C19H16NO (M þ H)þ: 274.1232; found: 274.1228.
(3-tert-Butylaziridin-2yl)(phenyl)methanone (2j)
Yellow solid; mp 59–61 ꢁC. IR (KBr): 3264 (m), 2956 (s), 1660 (s), 1596 (w),
1450 (m), 1229 (m). NMR data are in agreement with reported values.[13] 1H
NMR (400 MHz, CDCl3): d 8.04–8.00 (m, 2H), 7.64–7.60 (m, 1H), 7.53–7.27 (m,
2H), 3.37 (s, 1H), 2.04–1.92(m, 2H), 0.99 (s, 9H). 13C NMR (100 MHz, CDCl3): d
197.6, 136.1, 133.5, 128.8, 128.1, 52.6, 36.7, 31.3, 26.7. HRMS (ESI) calcd. for
C13H16NO (M ꢀ H)ꢀ: 202.1232; found: 202.1239.
(4-Methoxyphenyl)(3-phenylaziridin-2-yl)methanone (2k)
White solid; mp 50–51 ꢁC (lit. 50–51 ꢁC[8a]). IR (KBr): 3236 (m), 1650 (s), 1608
(s), 1454 (m), 1260 (s). NMR data are in agreement with reported values.[8a] 1
H
NMR (400 MHz, CDCl3): d 7.98 (d, J ¼ 8.8 Hz, 2H), 7.37–7.29 (m, 5H), 6.94 (d,
J ¼ 9.2 Hz, 2H), 3.86 (s, 3H), 3.46 (d, J ¼ 2.0 Hz, 1H), 3.14 (d, J ¼ 2.0 Hz, 1H),
2.68 (br s, 1H). 13C NMR (100 MHz, CDCl3): d 193.8, 164.1, 138.5, 130.6, 128.9,
128.5, 127.7, 126.1, 114.0, 55.5, 43.6, 43.0. HRMS (ESI) calcd. for C16H14NO2
(M ꢀ H;)ꢀ: 252.1025; found: 252.1027.
(4-Chlorophenyl)(3-phenylaziridin-2-yl)methanone (2l)
Pale yellow solid; mp 75–76 ꢁC (lit. 76–78 ꢁC[5]). IR (KBr): 3245 (m), 1660 (s),
1590 (s), 1354 (s), 1229 (s). NMR data are in agreement with reported values.[8a]
1H NMR (400 MHz, CDCl3): d 7.92 (d, J ¼ 8.4 Hz, 2H), 7.45 (d, J ¼ 8.4 Hz, 2H),
7.37–7.31 (m, 5H), 3.45 (s, 1H), 3.18 (s, 1H), 2.67 (br s, 1H). 13C NMR (100 MHz,
CDCl3): d 194.5, 140.3, 138.1, 134.2, 129.7, 129.1, 128.6, 127.9, 126.1, 44.0, 43.7.
HRMS (ESI) calcd. for C15H11NOCl (M ꢀ H;)ꢀ: 256.0529; found: 256.0533.
ACKNOWLEDGMENTS
We thank National Natural Science Foundation of China (Nos. 20772160 and
20972195) and the Ministry of Health of China (No. 2009ZX09501-017) for financial
support of this study.

1584
J.-J. WANG ET AL.
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