aziridinate olefins. However, the reaction took a different
course in furnishing 1,2-bromoamine as the sole product. In
this letter, we wish to report, for the first time, a practical
process for the regio- and stereospecific aminobromination
of various olefins catalyzed by Cu, V, and Mn salts with
Table 1. Aminobromination of Styrene with TsNH
2
and NBS:
Effect of Catalystsa
yieldb (%)
sr. no.
catalyst
t (h)
product
1
2
no catalyst
CuI
24
2
1:2 (60:40)
20
92
85
71
65
58
64
65
30
90
91
97
p-toluenesulfonamide (TsNH
bromine sources, respectively.
When styrene was reacted with TsNH
and NBS (1.1 molar equiv) in the presence of catalytic CuI
5 mol %) in CH Cl , the corresponding aminobrominated
2
) and NBS as amine and
1
1
1
1
1
1
1
1
1
1
2
3
CuCl ‚2H O
2
2
2.5
4
4
CuCN
2
(1.0 molar equiv)
5
Cu(OAc)2
5
6
NiCl2‚6H2O
Ni(OAc)2‚4H2O
Co(OAc)2‚4H2O
FeCl3
8
(
2
2
7
6
product was obtained in high yield with excellent regio-
selectivity (>99%). Surprisingly, when Mn(III)-salen [N,N′-
bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminoman-
ganese(III) chloride] was employed as catalyst, a reversal
in regiochemical product was observed without affecting the
yield and selectivity (Scheme 1). Simple olefins such as
8
6
9
12
2
10
11
MnSO4
V2O5
Mn(III)-salenc
2
1
2
1
a
Reaction conditions: styrene (2.0 mmol), TsNH2 (2 mmol), NBS (2.2
b
mmol), catalyst (5 mol %), CH2Cl2 (5 mL), 25 °C. Yields refer to isolated
product after column chromatography. c N,N′-Bis(3,5-di-tert-butylsalicylidene)-
1,2-cyclohexanediaminomanganese(III) chloride.
Scheme 1a
Mn(III)-salen was employed as the catalyst under the reaction
conditions. The yield and regioselectivity was found to be
excellent in all the styrenic substrates studied (Table 3).
R,â-Unsaturated carbonyl compounds represent the most
synthetically useful substrate classes for various olefin
oxidative reactions. Particularly, the vicinal aminobromina-
tion of R,â-unsaturated carbonyl compounds affords func-
tionalized aminobrominated compounds, which can be
converted to numerous useful organic molecules by replacing
the bromine atom with a series of nucleophiles. Hence, a
variety of R,â-unsaturated carbonyl compounds were sub-
jected to aminobromination under the present catalytic
conditions, affording products in high yields with excellent
control over regio- and diastereoselectivity (Table 4).
a
Reagents and conditions: (i) styrene (2 mmol), TsNH
mmol), N-bromosuccinimide (2.2 mmol), CuI (5 mol %), CH
5 °C; (ii) styrene (2 mmol), TsNH (2 mmol), N-bromosuccinimide
2.2 mmol), Mn(III)-salen complex (5 mol %), CH Cl , 25 °C.
2
(2
2
Cl
2
,
2
(
2
2
2
styrene and cyclohexene gave very slow reaction with poor
regioselectivity and yield in the absence of catalyst.
With this encouraging result, a systematic study was
undertaken to screen various metal catalysts for the amino-
bromination process. Among the various transition metal salts
screened, we found that CuI, MnSO
effective in catalyzing the aminobromination of styrene in
CH Cl as solvent (Table 1). However, other solvents such
as CHCl , benzene, CCl , or toluene except alcoholic ones
4 2 5
, and V O were proven
(
8) General experimental procedure for aminobromination of olefins: To
a mixture of olefin (2 mmol), Cu, V, or Mn catalyst (5 mol %), and TsNH2
0.342 g, 2 mmol) was added slowly via solid addition funnel CH2Cl2 (5
2
2
(
3
4
mL) and NBS (0.392 g, 2.2 mmol), with stirring at 25 °C. The reaction
was monitored by TLC. After completion of the reaction, the solution was
diluted with EtOAc (15 mL) and washed with water and brine. The organic
layer was dried over anhydrous Na2SO4 and concentrated under reduced
pressure to give crude product, which was purified by column chromatog-
raphy with silica gel packing, using pet. ether and EtOAc as eluents to
afford pure product. (()-trans-3-(4-Chlorophenyl)-3-bromo-2-(p-toluene-
sulfonamido)propiophenone (3e): mp 168-170 °C. H NMR (CDCl3): δ
2.31 (s, 3H), 5.00 (d, J ) 6.21 Hz, 1H), 5.43-5.52 (m, 1H), 5.66 (d, J )
1
(
5
1
are found to be equally good for the aminobromination
process.
A variety of olefins with varied functional groups can be
subjected to this reaction. For all of the cases which we
examined, the regioselectivity has been completely controlled
1
0.11 Hz, exchangeable with D2O, 1H), 6.98-7.26 (m, 6H), 7.39-7.50
1
as revealed by the crude H NMR analysis of the products.
13
m, 5H), 7.87 (d, J ) 8.48 Hz, 2H). C NMR (CDCl3): δ 21.28, 49.98,
9.65, 126.66, 128.57, 128.98, 129.20, 129.89, 133.97, 134.71, 135.48,
Further, the regioselectivity of the product was determined
+
35.63, 137.17, 143.13, 197.05. MS m/z (% rel intensity): 493 (M , 3),
by MS spectroscopy analysis in which two prominent
412 (6), 388 (32), 307 (50), 288 (73), 155 (33), 117 (45), 105 (100), 91
73), 77 (73), 65 (23). (()-trans-Ethyl-3-(4-methoxyphenyl)-3-(p-toluene-
(
+
+
fragmented ions, [ArCHNHTs] and [CHRBr] , were clearly
identified. Meanwhile, it is also remarkable to note that
exclusive formation of anti-isomers has been observed in
all the 1,2-disubstituted olefins (Table 2).
1
sulfonamido)-2-bromopropionate (4a): mp 117-119 °C. H NMR
(
CDCl3): δ 1.17 (t, J ) 6.31 Hz, 3H), 2.34 (s, 3H), 3.74 (s, 3H), 4.11 (q,
J ) 6.31 Hz, 2H), 4.42 (d, J ) 6.25 Hz, 1H), 4.79-4.87 (dd, J ) 10.21
and 6.25 Hz, 1H), 6.26 (d, J ) 10.21 Hz, exchangeable with D O, 1H),
2
6
2
1
.67-6.72 (d, J ) 9.41 Hz, 2H), 7.00-7.13 (m, 4H), 7.57 (d, J ) 9.41 Hz,
H). 13C NMR (CDCl3): δ 13.52, 21.13, 47.19, 54.98, 59.43, 62.26, 113.61,
26.88, 128.17, 128.98, 137.32, 142.80, 159.26, 168.09. MS m/z (% rel
However, a noteworthy feature of the aminobromination
process is the reversal in regioselectivity observed when
+
intensity): 455 (M , 1), 410 (1), 370 (2), 290 (60), 155 (40), 134 (27), 91
(100), 65 (30).
862
Org. Lett., Vol. 5, No. 6, 2003