A new method for stereoselective bromination of stilbene and chalcone in a water suspension medium

Article abstract of DOI:10.1039/a906967d

Bromination reactions of (E)-stilbene and (E)-chalcone in a water suspension medium proceeded efficiently and stereoselectively, and the reaction products were collected easily by filtration. The Royal Society of Chemistry 1999.

Full text of DOI:10.1039/a906967d

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A new method for stereoselective bromination of stilbene and
chalcone in a water suspension medium
Koichi Tanaka,a Ryusuke Shiraishia and Fumio Toda*b
a Department of Applied Chemistry, Faculty of Engineering, Ehime University, Matsuyama,
Ehime 790-8577, Japan
b Department of Chemistry, Faculty of Science, Okayama University of Science, 1-1 Ridai-cho,
Okayama 700-0005, Japan
Received (in Cambridge, UK) 27th August 1999, Accepted 23rd September 1999
Table 1 Bromination reactions of (E)-stilbene 1 in solution, gas/solid,
solid/solid and water suspension media
Bromination reactions of (E)-stilbene and (E)-chalcone in
a water suspension medium proceeded efficiently and
stereoselectively, and the reaction products were collected
easily by filtration.
Conditions
Time/h
Yield (%)
meso-2:rac-3a
CH2Cl2
Gas/solid
Solid/solid
Water suspension
12
64
168
15
98
20
71
88
84:16b
62:38b
100:0
The addition reaction of bromine to olefin is still difficult to
control in most cases. For example, the reaction of (E)-stilbene
1 with bromine in CH2Cl2 gives a 84:16 mixture of meso-2 and
100:0
a The ratio was determined by 13C NMR, see ref. 1. b Data from ref. 1.
Table 2 Bromination reactions of (E)-chalcone 4a with 7 in solution,
solid/solid and water suspension media
Conditions
Time/h
Yield (%)
erythro-5a:threo-6aa
CH2Cl2
Solid/solid
Water suspension
0.5
4
1.5
90
89
90
86:14
100:0
100:0
a The ratio was determined by 1H NMR, see ref. 5.
Table 3 Bromination reaction of (E)-chalcone 4a in the solid state
Reagents
Time/h
Yield (%)
erythro-5a:threo-6aa
7
8
9
4
4
168
89
91
83
100:0
100:0
100:0
rac-3.1 Treatment of crystalline 1 with bromine vapor gives 2
and 3 in a 62:38 mixture in only 20% yield, although the reac-
tion proceeds without passing through any liquid phases.1 We
have now found that the bromination reaction of 1 and chal-
cone 4 could be controlled perfectly when carried out in the
solid state by mixing both powdered 1 or 4 and solid bromin-
ating reagent 7. More interestingly, the bromination reactions
proceeded more efficiently and selectively when carried out in a
water suspension medium and the products were collected
easily by filtration. This method has a big advantage as no
organic solvent is necessary during the reaction and separation
of the product. This provides a new simple, efficient and
stereoselective bromination procedure.
After keeping a mixture of powdered 1 and powdered 7 at
room temperature for 168 h in the solid state, water was added
to the reaction mixture and then the product was isolated by
filtration to give only meso-2 in 71% yield (Table 1). Bromin-
ation reaction of chalcone 4 with 7 in the solid state was also
found to proceed efficiently and stereoselectively. For example,
when a mixture of powdered 4a and powdered 7 was kept in the
solid state for 4 h at room temperature, erythro-5a was obtained
exclusively in 89% yield (Table 2). As well as 7, phenyltrimethyl-
ammonium tribromide 8 was also effective for stereoselective
bromination of 4a, but the sterically bulky reagent 9 takes a
long time for the reaction to go to completion (Table 3).
a The ratio was determined by 1H NMR, see ref. 5.
efficiently and conveniently. For example, a suspension of both
powdered 1 and 7 in a small amount of water was stirred at
room temperature for 15 h. The reaction mixture was filtered
and air-dried to give meso-2 in 88% yield (Table 1). Bromin-
ation of chalcones 4a–c was also found to proceed very effi-
ciently and selectively in a water suspension medium. For
example, a suspension of powdered chalcone 4a and 7 in a small
amount of water was stirred at room temperature for 1.5 h to
give erythro-5a in 90% yield. Similar treatment of 4b and 4c
with 7 in a water suspension gave erythro-5b and 5c in 90 and
87% yield, respectively (Table 4).
It has been reported that gas/solid bromination of a single
crystal of 4,4Ј-dimethylchalcone 4b, which crystallizes in a
chiral space group (P212121), yields optically active erythro-5b in
6% ee.2 The enantioselectivity of the asymmetric bromination
of 4b was found to improve when the reaction was carried
out in a water suspension medium. For example, when the
powdered chiral crystal of 4b, which shows a (Ϫ)-Cotton effect
in the solid-state CD spectrum,3 was stirred in a small amount
of water containing 7 for 3 h, optically active adduct (Ϫ)-5b in
13% ee was obtained in 73% yield.
Very interestingly, bromination of the crystalline powder of 1
with 7 in a water suspension medium proceeded much more
Enantioselective bromination of cyclohexene in the inclusion
crystal of 11 with optically active host compound 10 was also
J. Chem. Soc., Perkin Trans. 1, 1999, 3069–3070
This journal is © The Royal Society of Chemistry 1999
3069

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Table 4 Bromination reactions of (E)-chalcone 4a–c with 7 in a water
powder of 1 (0.5 g, 2.8 mmol), 7 (1.33 g, 4.2 mmol) and water
suspension medium
(5 ml) was stirred at room temperature for 15 h. The reaction
mixture was filtered, washed with water and air-dried to give
meso-2 as a colorless powder (0.84 g, 88% yield). The crude
crystals thus obtained were recrystallized from toluene to give
pure meso-2 as colorless needles. Data for meso-2; mp 243–
245 ЊC (lit.,1 244–245 ЊC); δH (300 MHz; CDCl3; Me4Si) 7.6–7.2
(10H, m), 5.48 (2H, s); δC (75 MHz; CDCl3; Me4Si) 140.02,
129.02, 128.77, 127.91, 56.08.
Chalcones
Time/h
Yield (%)
erythro-5:threo-6a
4a
4b
4c
1.5
4
2
90
90
87
100:0
100:0
100:0
a The ratio was determined by 1H NMR.
Typical procedure for the bromination reaction of (E)-chalcone in
a water suspension medium
Crystals of 4a were finely powdered by grinding with a pestle
and mortar for a few minutes. A suspension of crystalline
powder of 4a (1.97 g, 9.5 mmol), 7 (3.63 g, 11.4 mmol) and
water (20 ml) was stirred at room temperature for 1.5 h. The
reaction mixture was filtered, washed with water and air-dried
to give erythro-5a as a colorless powder (3.12 g, 90% yield). The
crude crystals thus obtained were recrystallized from toluene to
give pure erythro-5a as colorless needles. Data for erythro-5a;
accomplished [reaction (1)]. When a solution of a mixture of
(Ϫ)-10 and cyclohexene in ether was kept at room temperature
for 12 h, a 2:1 inclusion complex 11 was obtained as colorless
prisms (mp 134–137 ЊC) in 72% yield. When a powdered mix-
ture of 11 and 7 was kept at room temperature in the solid state
for 3 days, (ϩ)-trans-1,2-dibromocyclohexane 12 in 12% ee5
was obtained in 56% yield by distillation of the reaction
mixture.
In conclusion, the bromination reaction of (E)-stilbene 1 and
(E)-chalcones 4 in a water suspension medium provides a simple,
efficient, stereoselective and environmentally benign method
which is superior to previously reported methods.
mp 161–162 ЊC (lit.,4 160 ЊC); ν (C᎐O) 1678 cmϪ1; δH (300 MHz;
᎐
CDCl3; Me4Si) 7.4–8.1 (10H, m), 5.83 (1H, d, J 11.4), 5.65
(1H, d, J 11.4).
References
1 G. Kaupp and D. Matthies, Chem. Ber., 1987, 120, 1897.
2 K. Penzien and G. M. J. Schmidt, Angew. Chem., Int. Ed. Engl., 1969,
8, 608; B. S. Green, D. Rabinovich, Z. Shakked, H. Hope and
K. Swanson, Acta Crystallogr., Sect. B, 1981, 37, 1376.
3 F. Toda, K. Tanaka and M. Kato, J. Chem. Soc., Perkin Trans. 1, 1998,
1315.
4 R. E. Lutz, D. F. Hinkley and R. H. Jordan, J. Am. Chem. Soc., 1951,
73, 4647.
5 The optical purity was determined by GC (Chirasil-dex CB,
Chrompak, The Netherlands).
Experimental
Typical procedure for the bromination reaction of (E)-stilbene in
a water suspension medium
Crystals of 1 were finely powdered by grinding with a pestle
and mortar for a few minutes. A suspension of the crystalline
Communication 9/06967D
3070
J. Chem. Soc., Perkin Trans. 1, 1999, 3069–3070