342
K. Kikushima et al. / Tetrahedron Letters 51 (2010) 340–342
Table 2 (continued)
Entry
Substrate
OTBS
AlBr3 (mol %)
120
Methoda
B
Product
Isolated yield (%)
Quant
OTBS
10
1h
3i
Br
11
12
120
120
C
D
99
76
Br
7Br
7
Br
13
14
120
120
C
E
3j
93
98
Br
Br
Br
4k
Br
OMe
MeO
MeO
15
120
E
4l
97
OMe
Br
a
Method A: a substrate (0.50 mmol), NH4VO3 (0.025 mmol), and AlBr3 in 1,4-dioxane under atmospheric oxygen at 80 °C for 8 h. Method B: a substrate (0.50 mmol),
NH4VO3 (0.025 mmol), and AlBr3 in ether under atmospheric oxygen at rt for 18 h. Method C: a substrate (0.50 mmol), NH4VO3 (0.025 mmol), AlBr3 (0.60 mmol), and Bu4NBr
(0.60 mmol) in MeCN under atmospheric oxygen at 50 °C for 18 h. Method D: a substrate (0.50 mmol), NH4VO3 (0.025 mmol), AlBr3 (0.60 mmol), and KBr (5.0 mmol) in MeCN
under atmospheric oxygen at 50 °C for 18 h. Method E: a substrate (0.50 mmol), NH4VO3 (0.025 mmol), AlBr3 (0.60 mmol), and Bu4NBr (0.60 mmol) in MeCN under
atmospheric oxygen at 80 °C for 18 h.
b
Together with 2-bromo-6-formylphenol (13%).
tyne was observed to give the trans-dibromides 4k and 4l, respec-
tively (entries 14 and 15). These findings suggest the involvement
of a bromonium cation-like species as an intermediate for anti-
bromination.
References and notes
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Acknowledgments
One of the authors K.K. acknowledges a JSPS fellowship for
young scientists, and expresses special thanks for the Global COE
(center of excellence) Program ‘Global Education and Research
Center for Bio-Environmental Chemistry’ of Osaka University.
Supplementary data
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