PhI(OAc)2/I2 induced aziridination of alkenes with TsNH2 under mild conditions

Article abstract of DOI:10.1016/j.tetlet.2008.05.143

The aziridination of alkenes with the direct use of p-toluenesulfonamide (TsNH₂) was achieved by using PhI(OAc)₂ and I₂ under mild conditions. The reaction affords aziridines in moderate to good yields, and offers good man

Full text of DOI:10.1016/j.tetlet.2008.05.143

Tetrahedron Letters 49 (2008) 4925–4928
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PhI(OAc)2/I2 induced aziridination of alkenes with TsNH2 under mild conditions
a
b
a,
Renhua Fan a, , Dongming Pu , Jianhong Gan , Bing Wang
*
*
a Department of Chemistry, Fudan University, 220 Handan Road, Shanghai 200433, China
b College of Food Science, Shanghai Fisheries University, 334 Jungong Road, Shanghai 200090, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The aziridination of alkenes with the direct use of p-toluenesulfonamide (TsNH2) was achieved by using
PhI(OAc)2 and I2 under mild conditions. The reaction affords aziridines in moderate to good yields, and
offers good manipulability by avoiding the use of the expensive metal catalyst and the unstable and
explosive PhI@NTs.
Received 14 January 2008
Revised 20 May 2008
Accepted 30 May 2008
Available online 4 June 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Aziridines are important three-membered heterocyclic sub-
structures in many biologically natural products, and are useful
intermediates in organic synthesis.1 As the powerful substrates,
they can undergo various nucleophilic ring-opening reactions to
afford the expected amine derivatives.1,2 Metal-catalyzed transfer
of nitrene to olefins is a well-established protocol for the prepara-
tion of aziridines.3 N-Tosyliminophenyliodinane (PhI@NTs) has
been widely used as the nitrene source,4 but it suffers from its
unstability, explosibility, and commercial unavailability. Although
chloramine-T,5 bromamine-T,6 azides,7 and nitrido complexes8
can also be used in the aziridination of olefins, the direct aziridin-
ation from sulfonamides has attracted more and more attention
recently.9 In most of the cases, heavy metal catalysts are required
to realize the aziridination. Che et al. reported an efficient metal-
free aziridination using hypervalent iodine,10 but the reaction is
restricted to the use of aminophthalimide and aminobenzooxazo-
lone. More recent work by Minakata described a metal-free aziri-
dination from sulfonamides using t-BuOI.11 As a part of our
program to develop the synthetic application of sulfonamides in
the presence of hypervalent iodine,12 we report herein the results
regarding the aziridination of alkenes with the direct use of p-tol-
uenesulfonamide (TsNH2) induced by PhI(OAc)2 and I2 under mild
conditions (Scheme 1).
using of PhI(OAc)2 and K2CO3 in ClCH2CH2Cl. However, when
0.2 equiv of tetrabutylammonium iodide (TBAI) was added as the
phase-transfer catalyst, trace aziridine 3a was detected from the
reaction. When 2 equiv of Bu4NI were used, aziridine 3a could be
isolated in 10% yield (Scheme 2). Control experiments showed that
no aziridine was formed when Bu4NBr or Bu4NCl was used.
Compounds 1a and 2a were isolated as the byproducts of the
reaction. Compound 2a was supposed to be generated from the
iodoacetoxylation of styrene via an acetyl hypoiodite (AcOI) inter-
mediate, which was formed from the reaction of PhI(OAc)2 with
Bu4NI. It was well known that acetyl hypoiodite could also be
formed from the reaction of PhI(OAc)2 with I2.13 So iodine (I2)
was used instead of Bu4NI in the further reaction as shown in
Table 1.
Aziridine 3a was obtained in 18% yield when 1 equiv of I2 was
introduced into the reaction (Table 1, entry 2). The increase of
the amount of I2 decreased the yield of aziridine (entry 3). The re-
sult obtained with 0.5 equiv of I2 was comparable to that with
1 equiv of I2 (entry 4), but the reaction could not be completed
when the amount of I2 was decreased to 0.25 equiv (entry 5).
When the amounts of TsNH2 and K2CO3 (ratio 1:2) were increased,
the yield of aziridine 3a increased (entries 6 and 7). The ratio of
TsNH2 with K2CO3 in 1:2 was essential to the reaction (entries
7–10). No aziridine was detected from the reaction in the absence
of base. Aziridine 3a was isolated in 76% yield when 3 equiv
of PhI(OAc)2 were used (entry 11). Furthermore, the control
The aziridination of styrene with TsNH2 was chosen to establish
the reaction conditions. No aziridination was observed with the
R2
R1
R4
R3
Ts
N
PhI(OAc)2, I2, t-BuOK
(1.4 equiv) TsNH2
(1.5 equiv) PhI(OAc)2
(2.8 equiv) K2CO3
R2
R1
R4
R3
+
TsNH2
Ts
NHTs
OAc
N
(2 equiv) Bu4NI
3
+
I
I
+
Ph
Ph
Ph
Ph
ClCH2CH2Cl, r.t.
Scheme 1. PhI(OAc)2/I2 induced aziridination of alkenes with p-toluenesulf-
3a
10%
1a
15%
2a
onamide.
22%
* Corresponding authors. Tel.: +86 21 6564 3462; fax: +86 21 6510 2412 (R. Fan).
E-mail address: rhfan@fudan.edu.cn (R. Fan).
Scheme 2. PhI(OAc)2/Bu4NI induced aziridination of styrene with p-toluenesulf-
onamide.
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.05.143

4926
R. Fan et al. / Tetrahedron Letters 49 (2008) 4925–4928
Table 1
The screening experiments of reaction conditionsa
Ts
N
NHTs
OAc
PhI(OAc)2, I2
,
base
+
Ph
TsNH2
+
+
I
I
solvent
0.5-1 hr
Ph
Ph
Ph
1a
2a
3a
Entry
TsNH2 (equiv)
PhI(OAc)2 (equiv)
I2 (equiv)
Base (equiv)
Solvent
Temp. (°C)
1ab (%)
2ab (%)
3ab (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
1.4
1.4
1.4
1.4
1.4
2
3
3
3
3
3
3
3
3
3
3
3
3
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
3
4
3
3
3
3
3
3
3
0
1
2
K2CO3 (2.8)
K2CO3 (2.8)
K2CO3 (2.8)
K2CO3 (2.8)
K2CO3 (2.8)
K2CO3 (4)
K2CO3 (6)
K2CO3 (3)
K2CO3 (0)
K2CO3 (9)
K2CO3 (6)
K2CO3 (6)
K2CO3 (6)
t-BuOK (6)
KOH (6)
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl, 4 Å MS
ClCH2CH2Cl, 4 Å MS
ClCH2CH2Cl, 4 Å MS
ClCH2CH2Cl, 4 Å MS
EtOAc, 4 Å MS
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
0
0
32
16
31
13
35
24
32
31
21
13
12
10
12
10
0
0
41
65
30
21
7
6
7
48
10
5
0
18
9
21
7
43
56
35
0
12
76
72
83
88
35
0
0.5
0.25
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
8
Trace
Trace
Trace
0
12
Trace
0
0
0
0
15
5
Et3N (6)
t-BuOK (6)
t-BuOK (6)
t-BuOK (6)
t-BuOK (6)
t-BuOK (6)
t-BuOK (6)
t-BuOK (6)
t-BuOK (6)
23
11
0
0
0
44
78
0
0
0
Toluene, 4 Å MS
THF, 4 Å MS
DMF, 4 Å MS
DMSO, 4 Å MS
CH3CN, 4 Å MS
3
3
3
3
3
3
3
3
3
3
0
0
ClCH2CH2Cl, 4 Å MS
ClCH2CH2Cl, 4 Å MS
24
Trace
28
3
50
Tracec
a
All reactions were conducted in 1 mmol scale.
Isolated yield based on styrene.
Product 4a was isolated in 62% yield.
b
c
experiment showed that no aziridination occurred in the absence
of PhI(OAc)2. When 4 Å MS was added as the additive, the yield
of 3a increased to 83% (entry 13). t-BuOK was also a good base
for the reaction (entry 14), while a significantly lower yield was ob-
tained with the using of KOH as the base (entry 15). When Et3N
was used, no aziridine was formed in the reaction (entry 16). No
product was detected when THF, DMF, DMSO, or CH3CN was used
as solvent while the reaction could proceed in AcOEt and toluene
with varied efficiency (entries 17–22). Drastic decrease in the yield
of aziridine occurred when the reaction was cooled to 0 °C (entry
23), or warmed up to 50 °C (entry 24). A diamination product 4a
was isolated in 62% yield when the reaction was warmed up to
50 °C. Diamination 4a could also be formed when the reaction
was left for a longer time (48 h) at room temperature (Scheme
3). Masuyama et al. reported a diamination reaction of alkenes
by using chloramine-T in the presence of tin(II) iodide at a higher
temperature (50 °C).5a
(3 equiv) PhI=NTs
(0.5 equiv) I2
NHTs
I
Ph
Ph
ClCH2CH2Cl, r.t.
1a
Ts
NHTs
(1 equiv)
t-BuOK
N
I
X
Ph
ClCH2CH2Cl, r.t.
Ph
1a
3a
Scheme 4. Control experiments.
The scope of the PhI(OAc)2/I2 induced aziridination of alkenes
was explored under the optimized conditions (Table 2).14 These
reactions proceeded smoothly and afforded the corresponding
aziridines in moderate to good yields. The electronic nature of
the substituents on the styrene could be either electron-donating
or electron-withdrawing (entries 2–4). When E- and Z-stilbene
were employed, cis-aziridine 3e was isolated as the major isomer
in both cases (entries 5 and 6). The reaction of E-1-(3-chloro-
prop-1-enyl)-benzene also gave a cis-aziridine (entry 7), but a mix-
ture of cis and trans products was obtained in the case of
E-cinnamyl propionate (entry 8). Indene and 1,2-dihydronaphtha-
lene were also good substrates for the aziridination (entries 9 and
10). For the reactions of cyclic and acyclic aliphatic olefins, 1 equiv
of I2 was required to accelerate the reactions (entries 11–16).
In summary, we have developed a PhI(OAc)2 and I2 induced
aziridination of alkenes with the direct use of p-toluenesulfon-
amide under mild conditions. The procedure offers good manipula-
bility by avoiding the use of the expensive metal catalyst and the
unstable and explosive PhI@NTs. The further investigation of the
scope, mechanism, synthetic applications, and asymmetric reac-
tions is ongoing and will be reported in due course.
In order to get some clues of the reaction pathway, the reaction
of styrene with N-tosyliminophenyliodinane in the presence of
iodine was carried out. No aziridine 3a was formed, but the reac-
tion gave byproduct 1a in 62% yield. Byproduct 1a was treated
with t-BuOK, but no intramolecular cyclization was observed
(Scheme 4).
(3 equiv) PhI(OAc)2
(0.5 equiv) I2
NHTs
(6 equiv)
t
-BuOK
+
Ph
TsNH2
NHTs
o
ClCH2CH2Cl, 4A MS
25 oC, 48 hr
Ph
3 equiv.
4a
72%
Scheme 3. PhI(OAc)2/I2 induced diamination of styrene.

R. Fan et al. / Tetrahedron Letters 49 (2008) 4925–4928
4927
Table 2 (continued)
Table 2
PhI(OAc)2/I2 induced aziridination of alkenes with p-toluenesulfonamidea
Entry
15
Alkene
Aziridine
3b (%)
(3 equiv) PhI(OAc)2
NTs
3n (48)d
Ts
N
(0.5 equiv) I2
R2
R1
R4
R3
R2
R1
R4
R3
(6 equiv)
t-BuOK
+
TsNH2
o
ClCH2CH2Cl, 4A MS
NTs
3
0.5-2 hr
16
3o (52)d
Entry
Alkene
Aziridine
3b (%)
a
NTs
Ph
All reactions were conducted in 1 mmol scale.
Isolated yield based on styrene.
1
3a (88)
3b (65)
b
c
Ph
H3C
Cl
The ratio determined by 1H NMR.
One equivalent of I2 was used.
d
NTs
2
H3C
Acknowledgements
NTs
3
3c (78)
3d (58)
Financial support from National Natural Science Foundation
of China (20702006), the Shanghai Rising-Star program
(07QA14007), and Fudan University is gratefully acknowledged.
Cl
NTs
4
5
References and notes
F
F
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Ph
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CH2OOCEt
8
9
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10
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3j (62)d
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NTs
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12
13
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3k (58)d
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14. Representative experimental procedure and spectroscopic data for 3a:
A
solution of TsNH2 (513 mg, 3 mmol) in anhydrous ClCH2CH2Cl was treated
with t-BuOK (672 mg, 6 mmol) and 4 Å MS. After 10 min, PhI(OAc)2 (966 mg,
3 mmol) was added, and the resulted mixture was stirred at room temperature
for 1 h. Styrene (104 mg, 1 mmol) and I2 (127 mg, 0.5 mmol) were added. After
styrene disappeared (determined by TLC, about 0.5 h), the mixture was
filtered with Celite. The crude product was purified by flash column
chromatography to provide the corresponding product. 2-phenyl-
1-tosylaziridine 3a: 1H NMR (400 MHz, CDCl3)
d 7.80 (d, J = 8.2 Hz, 2H),
7.20–7.40 (m, 7H), 3.75 (dd, J = 7.2, 4.4 Hz, 1H), 2.90 (d, J = 7.2 Hz, 1H), 2.40 (s,
3H), 2.35 (d, J = 4.5 Hz, 1H).