Catalyst-free aminobromination of alkenes with N-methyl-p-toluenesulfonamide as nitrogen resource

Article abstract of DOI:10.1016/j.tetlet.2009.12.059

A catalyst-free electrophilic aminobromination system was described with N-methyl-p-toluenesulfonamide (p-TsNHCH₃) and N-bromosuccinimide (NBS) as nitrogen and bromine resources. The reaction can give vicinal haloamines in good yields, excellent regioselectivities, and stereoselectivities under convenient and mild condition. The existence of N-methyl group in the nitrogen resource was found to play an important role in the formation of vicinal haloamine product.

Full text of DOI:10.1016/j.tetlet.2009.12.059

Tetrahedron Letters 51 (2010) 987–989
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Catalyst-free aminobromination of alkenes with
N-methyl-p-toluenesulfonamide as nitrogen resource
c,
Guangqian Zhang a, Guanghui An a, Jun Zheng a, Yi Pan a,b, , Guigen Li
*
*
a School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
b State Key Laboratory of Coordination, Nanjing University, Nanjing 210093, China
c Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409-1061, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A catalyst-free electrophilic aminobromination system was described with N-methyl-p-toluenesulfon-
amide (p-TsNHCH3) and N-bromosuccinimide (NBS) as nitrogen and bromine resources. The reaction
can give vicinal haloamines in good yields, excellent regioselectivities, and stereoselectivities under con-
venient and mild condition. The existence of N-methyl group in the nitrogen resource was found to play
an important role in the formation of vicinal haloamine product.
Received 22 October 2009
Revised 7 December 2009
Accepted 14 December 2009
Available online 16 December 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Aminohalogenation and related reactions of olefins have be-
come an interesting topic in organic synthesis because the result-
ing vicinal haloamines are important building blocks in organic
and medicinal chemistry.1 The products resulting from these pro-
cesses can easily be converted into numerous other derivatives
by replacement of the halogen in intramolecular or intermolecular
reactions. In recent years, several methodologies have been devel-
oped for the aminohalogenation of olefins in the presence of cata-
lysts.2,3 However, there still existed limitations, such as procedural
difficulties, high catalyst loading, necessity of metal or metal salts
as catalysts. In particular, the necessity of metal catalyst limits the
attractiveness of these methodologies in their application for phar-
maceuticals, because removal of the trace of residual metals from
the resulting haloamines products is quite difficult.4 Although sev-
eral nonmetal catalysts have been developed for aminohalogen-
ation reactions recently, these system usually need special
auxiliary reagents, like ionic liquid,5a stoichiometric PhI(OAc)2,5b
sulfuric acid,5c or high pressure of CO2.5d Developing more simple
and efficient aminohalogenation system is still necessary.
and gave the product in 94% yield (Table 1, entry 1). Very low
yields were obtained when acetonitrile, toluene or 1,2-dichloro-
ethane were used as solvent (Table 1, entries 2, 4, and 6). There
was no haloamine product observed at all when the reaction was
carried out in THF or DMF (Table 1, entries 3 and 5). The tempera-
R1
R2
R1
N
Ts
CH2Cl2
45 ºC
R2
Br
+
+
NBS
TsNHMe
R3
R3
1
2
Scheme 1. Catalyst-free aminohalogenation with TsNHMe as nitrogen resource.
Table 1
Aminobromination of styrenea
Br
During our continuous investigation on aminohalogenation we
turned our attentions to develop the catalyst-free aminohalogen-
ation system, which could have great potential in pharmaceutical
chemistry.6,7 In this work we reported, for the first time, a simple
and efficient catalyst-free aminobromination of olefins for the
preparation of vicinal bromoamines with N-methyl-p-toluenesul-
fonamide (p-TsNHCH3) and N-bromosuccinimide (NBS) as nitrogen
and bromine sources (Scheme 1).
+
+
NBS
TsNHMe
N
Ts
1a
2a
Entry
Solvent
Temperature (°C)
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
CH2Cl2
MeCN
THF
45
45
45
45
45
45
25
24
24
24
24
24
24
24
94
11
0
24
0
Initially, styrene was chosen as the model substrate to optimize
the reaction conditions, and the results are shown in Table 1.
Dichloromethane was proved to be the best solvent for this system,
Toluene
DMF
ClCH2CH2Cl
CH2Cl2
18
13
a
Conditions: 1.2 mmol of 1a, 1 mmol of p-TsNHMe, and 1.4 mmol of NBS in
solvent (3 mL).
* Corresponding authors. Tel.: +86 25 83592846; fax: +86 25 83309123 (P.Y.).
E-mail address: yipan@nju.edu.cn (Y. Pan).
b
Isolated yields after chromatographic purification.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.12.059

988
G. Zhang et al. / Tetrahedron Letters 51 (2010) 987–989
Table 2
Br
Aminobromination of olefins with TsNHMe and NBSa
CH2Cl2
45 ºC
+
+
TsNH2
NBS
HN
Ts
R1
R1
N
Ts
1a
CH2Cl2
17% yield
Scheme 2. Aminohalogenation with TsNH2/NBS.
R2
+
+
NBS
TsNHMe
R2
R3
45 ºC, 24 h
R3
Br
1
2
Entry
1
Substrate
Product
Yieldb (%)
94
After obtaining the optimized reaction conditions, the scope
and limitation of this system were then examined. Varieties of al-
kenes were subjected to the current aminobromination system,
and the results were presented in Table 2.8 The current catalyst-
free system can be suitable for both aliphatic alkenes and aromatic
alkenes, resulting in the corresponding haloamines in good yields.
Especially for the aromatic alkenes, excellent yields were obtained
(Table 2, entries 1–6). A cyclic olefin, cyclooctene, was also reacted
effectively with TsNHMe/NBS in an acceptable yield (Table 2, entry
8). Long chain aliphatic alkene was also a good substrate for the
current system, affording 52% yield (Table 2, entry 9). Only one re-
gio-isomer was observed for each of these cases. The substrates
showed excellent stereoselectivities, only the anti isomers were
observed for two cyclic substrates (Table 2, entries 7 and 8).
To compare the current aminohalogenation system with previ-
ously reported aminohalogenation system using the combined
TsNH2/NBS as nitrogen and bromine resource,9 we carried out
the reaction between styrene and TsNH2/NBS under the current
reaction conditions (Scheme 2). Only 17% yield of desired halo-
amine product was obtained, and most of the starting materials
were recovered. Comparing to 94% yield obtaining from the reac-
tion with TsNHMe as nitrogen resource, we found that the intro-
duction of N-methyl group into nitrogen resource plays an
important role in the formation of haloamine product.
Br
N
Ts
Br
2a
Me
Cl
2
3
4
97
96
95
N
Me
Cl
Ts
2b
Br
N
Ts
2c
Br
Br
N
Br
Ts
2d
Br
O2N
Cl
5
93
N
O2N
Ts
2e
Cl Br
The mechanism of this reaction is believed to be similar to that
of our previously reported aminohalogenation system.2b–d Firstly,
NBS reacts with p-TsNHMe to form the p-TsNBrMe. The following
step would be the formation of the aziridinium intermediate, and
this positively charged intermediate would be SN2 attacked by a
bromide anion to give the aminohalogenation adducts. The exis-
tence of N-methyl group was believed to stable the aziridinium
intermediate, which can promote the proceeding of reaction. The
regio and stereoselectivity of this reaction can also be explained
well on the basis of this mechanistic hypothesis involving these
key aziridinium intermediates.
The presence of benzyl bromide functionality in the current
haloamine products provided an easy access to other useful organ-
ic blocks by intermolecular reactions (Scheme 3). When the prod-
uct 2a was subjected FeCl2/acetonitrile system10 at room
temperature, vicinal diamine 3a was obtained in 74% yield. Product
2a was also easily to be hydrolyzed by treatment with acetone/
water, resulting in vicinal aminoalcohol 4a with the yield of 92%.
In conclusion, we reported a first catalyst-free aminohalogen-
ation system with TsNHMe as the nitrogen resource and NBS as
bromine resource. The TsNHMe was found to be a good nitrogen
resource for aminohalogenation reaction, and can react with vari-
eties of alkenes to form haloamine product in good to excellent
6
7
97
N
Ts
2f
Br
69c
N
( )
Ts
Ts
2g
Br
N
8
9
43c
52
( )
2h
Br
N
Ts
2i
a
Conditions: 1.2 mmol of alkenes, 1 mmol of p-TsNHMe, and 1.4 mmol of NBS in
CH2Cl2 (3 mL) at 45 °C for 24 h.
b
Isolated yields after chromatographic purification.
Only anti-product was observed, estimated by crude 1H NMR.
c
ture was also found to have an effect on the formation of halo-
amine product, because only 13% yield was obtained when the
reaction was carried out at 25 °C.
O
Br
OH
FeCl2•4H2O
NH
acetone/H2O
MeCN
N
N
Ts
Ts
N
Ts
4a
92% yield
3a
74% yield
2a
Scheme 3. Nucleophilic substitutions.

G. Zhang et al. / Tetrahedron Letters 51 (2010) 987–989
989
N-(2-Bromo-2-(4-chlorophenyl)ethyl)-N,4-dimethylbenzenesulfonamide
isolated as
= 3448, 1596, 1491, 1048, 1158, 1089, 985, 828, 746, 715, 547 cmÀ1
NMR (300 MHz, CDCl3): d = 7.63 (d, J = 6.6 Hz, 2H), 7.39–7.30 (m, 6H), 5.12 (dd,
J = 6.6, 8.7 Hz, 1H), 3.67 (dd, J = 6.6, 14.4 Hz, 1H), 3.54 (dd, J = 8.7, 14.4 Hz, 1H),
2.60 (s, 3H), 2.43 (s, 3H) ppm. 13C NMR (75 MHz, CDCl3): d = 143.8, 137.5, 134.7,
134.5, 129.9, 129.5, 129.1, 127.3, 57.7, 50.6, 36.8, 21.6 ppm. MS (ESMS/
[M+Na]+): calcd for C16H17BrClNO2SNa: 425.97; found 426.17.
(2c)
yield without use of any catalyst. The introduction of N-methyl
group into nitrogen resource was found to be very important for
this aminohalogenation system, and can promote the formation
of haloamine product.
a
white solid (387 mg, 96% yield); mp 81–82 °C. IR (KBr):
m
.
1H
Acknowledgments
N-(2-Bromo-2-(4-bromophenyl)ethyl)-N,4-dimethylbenzenesulfonamide
isolated as white solid (425 mg, 95% yield); mp 108–110 °C. IR (KBr):
= 3461, 1596, 1489, 1346, 1158, 984, 821, 664, 551 cmÀ1 1H NMR (300 MHz,
CDCl3): d = 7.62 (d, J = 8.4 Hz, 2H), 7.48 (d, J = 6.6 Hz, 2H), 7.33–7.29 (m, 4H),
5.10 (dd, J = 6.6, 8.7 Hz, 1H), 3.66 (dd, J = 6.6, 14.7 Hz, 1H), 3.53 (dd, J = 8.7,
14.7 Hz, 1H), 2.60 (s, 3H), 2.43 (s, 3H) ppm. 13C NMR (75 MHz, CDCl3):
d = 143.9, 138.0, 134.4, 132.0, 129.9, 129.8, 127.4, 122.9, 57.6, 50.6, 36.8,
21.6 ppm. MS (ESMS/[M+Na]+): calcd for C16H17Br2NO2SNa: 469.92; found
470.00.
(2d)
a
We gratefully acknowledge the financial support from the Na-
tional Natural Science Foundation of China (No. 20772056, to
Y.P.). This work was also partially supported by research funds to
Y.P. from the Qing-Lan Program of Jiangsu Province and the Kua-
Shi-Ji Program of the Education Ministry of China. The Jiangsu
333 program (for Pan) was also acknowledged.
m
.
N-(2-Bromo-2-(4-nitrophenyl)ethyl)-N,4-dimethylbenzenesulfonamide
isolated as a yellow gum (384 mg, 93% yield); IR (KBr): = 3450, 1599, 1524,
1346, 1160, 857, 742, 670, 550 cmÀ1 1H NMR (300 MHz, CDCl3): d = 8.21 (d,
(2e)
m
References and notes
.
J = 9.0 Hz, 2H), 7.63 (d, J = 8.4 Hz, 4H), 7.32 (d, J = 8.4 Hz, 2H), 5.21 (t, J = 7.8 Hz,
1H), 3.64–3.62 (m, 2H), 2.62 (s, 3H), 2.43 (s, 3H) ppm. 13C NMR (75 MHz,
CDCl3): d = 148.0, 145.9, 144.1, 134.1, 130.0, 129.3, 127.4, 124.0, 57.5, 49.0,
36.9, 21.5 ppm. MS (ESMS/[M+Na]+): calcd for C16H17BrN2O4SNa: 437.00;
found 437.00.
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Shaughnessy, K. H. Organometallics 2006, 25, 4105; (c) Garrett, C. E.; Prasad, K.
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Timmons, C.; Chen, D.; Xu, X.; Li, G. Eur. J. Org. Chem. 2003, 3850.
8. General aminobromination procedure (Table 2): A mixture of olefins (1.2 mmol),
p-TsNHMe (0.185 g, 1 mmol), and NBS (0.249 g, 1.4 mmol) was added in CH2Cl2
(3 mL) with stirring at 45 °C under nitrogen atmosphere for 24 h. The reaction
was quenched by dropwise addition of saturated aqueous Na2SO3 solution
(3 mL). The organic layer was separated and the aqueous layer was extracted
with EtOAc (3 Â 10 mL). The combined organic layers were washed with water
and brine and dried over by anhydrous Na2SO4 and concentrated under
reduced pressure to give crude product, which was purified by column
chromatography packed with silica gel to afford pure product.
N-(2-Bromo-2-(2-chlorophenyl)ethyl)-N,4-dimethylbenzenesulfonamide
isolated as white solid (391 mg, 97% yield); mp 74–76 °C. IR (KBr):
= 3445, 1596, 1335, 1156, 982, 751, 547 cmÀ1 1H NMR (300 MHz, CDCl3):
(2f)
a
m
.
d = 7.66–7.62 (m, 3H), 7.38–7.25 (m, 5H), 5.66 (dd, J = 7.2, 7.8 Hz, 1H), 3.83 (dd,
J = 7.8, 14.4 Hz, 1H), 3.53 (dd, J = 7.2, 14.4 Hz, 1H), 2.72 (s, 3H), 2.43 (s, 3H) ppm.
13C NMR (75 MHz, CDCl3): d = 143.8, 136.1, 134.4, 133.4, 130.0, 129.9, 129.9,
129.8, 127.6, 127.4, 56.2, 46.1, 36.0, 21.6 ppm. MS (ESMS/[M+Na]+): calcd for
C16H17BrClNO2SNa: 425.97; found 426.08.
N-(1-Bromo-2,3-dihydro-1H-inden-2-yl)-N,4-dimethylbenzenesulfonamide (2g)
isolated as
m
a
white solid (262 mg, 69% yield); mp 127–129 °C. IR (KBr):
= 3441, 1597, 1339, 975, 884, 810, 746, 693, 667, 549 cmÀ1
.
1H NMR
(300 MHz, CDCl3): d = 7.79 (d, J = 6.6 Hz, 2H), 7.38–7.16 (m, 6H), 5.11–5.10 (m,
2H), 3.36–3.28 (m, 1H), 2.85–2.78 (m, 1H), 2.56 (s, 3H), 2.48 (s, 3H) ppm. 13C
NMR (75 MHz, CDCl3): d = 143.7, 141.0, 140.3, 136.1, 129.9, 129.5, 127.9, 127.5,
125.4, 124.5, 66.6, 53.4, 33.8, 29.6, 21.7 ppm. MS (ESMS/[M+Na]+): calcd for
C17H18BrNO2SNa: 404.01; found 403.92.
N-(2-Bromocyclooctyl)-N,4-dimethylbenzenesulfonamide (2h) isolated as a white
solid (161 mg, 43% yield); mp 102–104 °C. IR (KBr):
m
= 3463, 2932, 2855, 1594,
1384, 1227, 1160, 985, 851, 801, 666, 645, 573, 547 cmÀ1
.
1H NMR (300 MHz,
CDCl3): d = 7.76 (d, J = 8.1 Hz, 2H), 7.28 (d, J = 8.1 Hz, 2H), 4.37–4.27 (m, 2H),
2.69 (s, 3H), 2.41 (s, 3H), 2.25–2.16 (m, 2H), 1.95 (m, 1H), 1.64–1.40 (m, 9H)
ppm. 13C NMR (75 MHz, CDCl3): d = 143.1, 137.1, 129.4, 127.6, 56.9, 31.3, 31.1,
28.1, 26.0, 25.0, 25.0, 23.5, 23.5, 21.5 ppm. MS (ESMS/[M+Na]+): calcd for
C16H24BrNO2SNa: 398.06; found 398.08.
N-(2-Bromoheptyl)-N,4-dimethylbenzenesulfonamide (2i) isolated as
solid (188 mg, 52 yield); mp 58–60 °C. IR (KBr): = 3417, 2953, 2857, 1638,
1618, 1384, 1342, 1162, 950, 907, 812, 752, 575, 552 cmÀ1 1H NMR (300 MHz,
a white
m
.
CDCl3): d = 7.68 (d, J = 8.4 Hz, 2H), 7.33 (d, J = 8.4 Hz, 2H), 4.14 (m, 1H), 3.46 (dd,
J = 7.5, 14.1 Hz, 1H), 3.18 (dd, J = 6.3, 14.1 Hz, 1H), 2.81 (s, 3H), 2.44 (s, 3H), 2.00
(m, 1H), 1.74–1.61 (m, 2H), 1.44–1.29 (m, 5H), 0.91 (t, 3H) ppm. 13C NMR
(75 MHz, CDCl3): d = 143.7, 134.3, 129.8, 127.4, 57.2, 53.6, 36.8, 35.6, 31.1, 27.0,
22.5, 21.5, 14.0 ppm. MS (ESMS/[M+Na]+): calcd for C15H24BrNO2SNa: 386.06;
found 386.17.
N-(2-(N,4-Dimethylphenylsulfonamido)-1-phenylethyl)acetamide (3a) isolated as
a white solid (256 mg, 74% yield); mp 132–134 °C. IR (KBr):
m
= 3334, 1650,
1595, 1539, 1444, 1369, 1340, 1166, 941, 771, 705, 659, 578, 552 cmÀ1
.
1H
NMR (300 MHz, CDCl3): d = 7.64 (d, J = 8.4 Hz, 2H), 7.32–7.29 (m, 7H), 6.70
(broad, 1H), 5.11 (m, 1H), 3.46 (dd, J = 6.6, 14.4 Hz, 1H), 3.01 (dd, J = 4.2,
14.4 Hz, 1H), 2.72 (s, 3H), 2.42 (s, 3H), 2.10 (s, 3H) ppm. 13C NMR (75 MHz,
CDCl3): d = 170.3, 143.8, 139.4, 134.6, 129.9, 128.8, 127.8, 127.2, 126.5, 54.9,
51.4, 35.8, 23.3, 21.5 ppm. MS (ESMS/[M+Na]+): calcd for C18H22N2O3SNa:
369.12; found 369.42.
N-(2-Bromo-2-phenylethyl)-N,4-dimethylbenzenesulfonamide (2a) isolated as a
white solid (346 mg, 94% yield); mp 61–63 °C. IR (KBr):
m
= 3418, 1618, 1491,
N-(2-Hydroxy-2-phenylethyl)-N,4-dimethylbenzenesulfonamide (4a) isolated as a
1384, 1334, 1159, 1088, 988, 934, 843, 812, 743, 705, 674, 644, 545 cmÀ1
.
1H
colorless gum (281 mg, 92% yield); IR (KBr):
m
= 3511, 3063, 3031, 2924, 1598,
1494, 1454, 1337, 1206, 1160, 1089, 972, 816, 760, 736, 701, 657, 550 cmÀ1
.
1H
NMR (300 MHz, CDCl3): d = 7.64 (d, J = 8.1 Hz, 2H), 7.29–7.45 (m, 7H), 5.15 (dd,
J = 7.2, 8.4 Hz, 1H), 3.73 (dd, J = 7.2, 14.4 Hz, 1H), 3.53 (dd, J = 8.4, 14.4 Hz, 1H),
2.59 (s, 3H), 2.43 (s, 3H) ppm. 13C NMR (75 MHz, CDCl3): d = 143.7, 139.0, 134.6,
129.9, 129.0, 128.9, 128.1, 127.4, 57.7, 51.9, 36.8, 21.6 ppm. MS (ESMS/
[M+Na]+): calcd for C16H18BrNO2SNa: 392.01; found 392.25.
NMR (300 MHz, CDCl3): d = 7.66 (d, J = 6.6 Hz, 2H), 7.39–7.29 (m, 6H), 4.92 (dd,
J = 3.3, 9.0 Hz, 1H), 3.28 (dd, J = 9.0, 14.1 Hz, 1H), 3.02 (dd, J = 3.3, 14.1 Hz, 1H),
2.80 (s, 3H), 2.41 (s, 3H) ppm. 13C NMR (75 MHz, CDCl3): d = 143.7, 141.2, 134.2,
129.8, 128.6, 128.0, 127.4, 126.1, 72.2, 58.3, 36.8, 21.5 ppm. MS (ESMS/
[M+Na]+): calcd for C16H19NO3SNa: 328.10; found 328.25.
N-(2-Bromo-2-(p-tolyl)ethyl)-N,4-dimethylbenzenesulfonamide (2b) isolated as a
white solid (370 mg, 97% yield); mp 92–94 °C. IR (KBr):
m = 3457, 1597, 1384,
9. (a) Wei, J.; Chen, Z.; Lei, W. Org. Lett. 2009, 11, 4216; (b) Wei, J.; Zhang, L.; Chen,
Z. Org. Biomol. Chem. 2009, 7, 3280; (c) Shaikh, T. M.; Karabal, P. U.;
Suryavanshi, G.; Sudalai, G. Tetrahedron Lett. 2009, 50, 2815; (d) Chen, Z.;
Wei, J.; Li, R. J. Org. Chem. 2009, 74, 1371; (e) Wang, Z.; Zhang, Y.; Fu, H. Synlett
2008, 2667; (f) Thakur, V. V.; Talluri, S. K.; Sudalai, A. Org. Lett. 2003, 5, 861.
10. Karabulut, H. R. F.; Kacan, M. Synth. Commun. 2002, 32, 2345.
1346, 1157, 1087, 985, 820, 733, 650, 571 cmÀ1 1H NMR (300 MHz, CDCl3):
.
d = 7.64 (d, J = 8.4 Hz, 2H), 7.32–7.30 (m, 4H), 7.16 (d, J = 7.8 Hz, 2H), 5.13 (dd,
J = 7.2, 8.4 Hz, 1H), 3.71 (dd, J = 7.2, 14.4 Hz, 1H), 3.54 (dd, J = 8.4, 14.4 Hz, 1H),
2.60 (s, 3H), 2.43 (s, 3H), 2.35 (s, 3H) ppm. 13C NMR (75 MHz, CDCl3): d = 143.7,
138.9, 136.1, 134.6, 129.8, 129.6, 127.9, 127.4, 57.6, 52.0, 36.8, 21.6, 21.3 ppm.
MS (ESMS/[M+Na]+): calcd for C17H20BrNO2SNa: 406.03; found 406.17.