Facile one-pot synthesis of α-bromoketones from olefins using bromide/bromate couple as a nonhazardous brominating agent

Article abstract of DOI:10.1016/j.tetlet.2009.03.047

A new method for the preparation of α-bromoketones from olefins using bromide/bromate couple as a nonhazardous brominating agent has been developed. Several α-bromoketones were successfully prepared from a variety of olefins by this method. This procedure is an alternative to conventional molecular bromine.

Full text of DOI:10.1016/j.tetlet.2009.03.047

Tetrahedron Letters 50 (2009) 2529–2532
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Facile one-pot synthesis of a-bromoketones from olefins using bromide/
bromate couple as a nonhazardous brominating agent
b,
Rajendra D. Patil a, Girdhar Joshi a, Subbarayappa Adimurthy a, , Brindaban C. Ranu
*
*
a Central Salt and Marine Chemicals Research Institute, Council of Scientific and Industrial Research, G. B. Marg, Bhavnagar 364 002, Gujarat, India
b Department of Organic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new method for the preparation of
nonhazardous brominating agent has been developed. Several
pared from a variety of olefins by this method. This procedure is an alternative to conventional molecular
bromine.
a
-bromoketones from olefins using bromide/bromate couple as a
-bromoketones were successfully pre-
Received 19 January 2009
Revised 6 March 2009
Accepted 10 March 2009
Available online 13 March 2009
a
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Alkenes
Bromide/bromate couple
a-Bromoketones
Bromine-free procedure
a
-Bromoketones are versatile intermediates in organic synthe-
Our continuous efforts to achieve maximum bromide atom effi-
ciency and minimize waste generation, as well as elimination of
the use of hazardous liquid bromine led us to develop a versatile
brominating reagent, a bromide–bromate couple, and we have al-
ready demonstrated a few useful applications.8
sis.1 Numerous methods have been developed for the preparation
of a-bromoketones from ketones with liquid bromine in the pres-
ence of protic and Lewis acids.2 Bromine is hazardous with associ-
ated risks in handling and transport. However, it is still being used
by industry as well as academia due to its easy availability, low
cost, and lack of a better alternative. A few other alternative proce-
Herein, we report further results using this brominating re-
agent for the direct synthesis of
a-bromoketones from olefins
dures for
a-bromination of carbonyl compounds avoiding liquid
bromine involve N-bromosuccinimide (NBS)3 and 4,4-dibromo-
2,6-di-tert-butyl-cyclohexa-2,5-dienone.4 Nevertheless, these bro-
minating reagents have some limitations including their low atom
efficiency and use of molecular bromine for their preparation.
Table 1
Optimization of reaction conditions for
a-bromoketone synthesis
O
Br
OH
Br
Solvent
A survey of the existing literature revealed that
tones have been synthesized mainly from ketones.2–4 Surprisingly,
we have found limited reports for the preparation of -bromoke-
tones from olefins.5 The direct conversion of alkenes to
-chlorok-
etones is reported with chromyl chloride.6 However, the same
strategy for -bromoketones is not explored in the literature.
a-bromoke-
+
2 BrOH
+
+
R.T.
Br
Br
5
1
2
3
4
a
a
Entry
Solvent
Time (h)
Product ratioa
3
4
5
a
1
2
3
4
5
6
Dioxane
Acetonitrile
THF
CH2Cl2
Et2O
8
8
8
8
8
8
7.5
7.5
8
71
40
3
—
13
—
60
61
36
17
47
39
19
3
60
11
10
52
12
8
24
77
76
8
1
2
3
Despite the fact that, the reactions of olefins with NBS is well
documented in the literature to obtain bromohydrins,7 it is seldom
extended to get
a-bromoketones. As olefins substituted with a
variety of functionalities are easily accessible we assumed that a
convenient procedure from olefins using an alternative mild bro-
minating agent will be appreciated.
DMSO
7b
8c
9d
Dioxane
Dioxane
Dioxane
a
* Corresponding authors. Fax: +91 278 2567562 (S.A.); tel.: +91 3324734971; fax:
+91 33 24732805 (B.C.R.).
E-mail addresses: sadimurthy@yahoo.com (S. Adimurthy), ocbcr@iacs.res.in (B.C.
Ranu).
GC yields unless otherwise stated.
Isolated yield with 2.5 equiv of BrOH.
Isolated yield with 3.0 equiv of BrOH.
Reaction with NBS.
b
c
d
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.03.047

2530
R. D. Patil et al. / Tetrahedron Letters 50 (2009) 2529–2532
Table 2
Synthesis of various
a-bromoketones from olefins
Entry
Substrate
Time (h)
Isolated yields (%)
Bromohydrin
Ref.
10
10
2i
Bromoketone
Dibromo
O
60
Br
OH
1
2
3
4
5
6
7
7.5
6
12
01
Br
Br
Br
O
87
OH
Br
11
02
Br
Br
Br
OH
Br
O
6
86
Br
10
01
Br
Br
OH
O
Br
t-Bu
Cl
t-Bu
t-Bu
Cl
6
82
11
02
t-Bu
Cl
Br
Br
Br
OH
O
77
Br
Cl
Br
6.5
6.5
15
12
02
11
11
2e
Br
Br
Br
Br
O
OH
Br
Br
68
25
03
Br
Br
Br
Br
Br
O
OH
40
09
01
Br
Br
Br
NO2
NO2
NO2
NO2
O
OH
Br
Br
8
7
77
15
02
10
8a
Br
Br
O
O
OHO
Br
O
Br
O
9
10
8
64
10
03
Br
Br
O
Br
OH
Br
07
10
C4H9
50
17
Br
Br
C4H9
C4H9
C4H9
O
O
O
OH
OH
OH
Br
Br
Br
11
12
13
C6H13
C7H15
C8H17
7
68
20
04
03
Br
Br
Br
Br
Br
C6H13
C7H15
C6H13
C7H15
C6H13
C7H15
13
13
64
70
08
07
10
Br
Br
Br
Br03
C8H17
C9H19
C8H17
C9H19
C8H17
C9H19
O
OH
Br
Br
Br
14
15
16
7.5
14
15
Br 70
07
06
03
C9H19
O
Br
C10H21
OH
C10H21
Br
Br
Br
82
02
C10H21
C10H21
O
Br
OH
C12H25
Br
Br
03
Br 65
08
C12H25
C12H25
C12H25

R. D. Patil et al. / Tetrahedron Letters 50 (2009) 2529–2532
2531
Ref.
Table 2 (continued)
Entry
Substrate
Time (h)
Isolated yields (%)
Bromohydrin
Bromoketone
Dibromo
O
OH
C14H29
Br
Br
03
Br
17
18
19
14
14
8
Br 67
09
C14H29
C14H29
C14H29
O
OH
Br
Br
03
Br
C16H33
65
Br08
C16H33
C16H33
C
16H33
O
Br
Br
OH
Br
46
07
06
8b
8b
Br
O
OH
Br
20
9
46
07
06
Br
Br
Br
under ambient conditions. In our earlier communication,8a we
showed the generation of active species BrOH by reacting
bromide–bromate and acid in the ratio of 2:1:3, respectively
(Eq. 1):
were performed under these optimized conditions in dioxane, un-
less otherwise required.9
When we carried out the reaction of styrene with N-bromosuc-
cinimide7 (2.1 equiv) under identical conditions the desired prod-
uct (3) was obtained only in 36% yield (Table 1, entry 9). This
study further supports the significance of the present reagent for
2Brꢀ þ BrOꢀ3 þ 3Hþ ! 3BrOH
ð1Þ
obtaining
Several alkenes were subjected to this procedure to produce the
corresponding -bromoketones (Table 2). 4-Methyl styrene and in-
dene (Table 2, entries 2 and 3.) showed high selectivity to provide
4-methyl- -bromoacetophenone and 2-bromo-indan-1-one in 87%
a-bromoketones directly from olefins in good yields.
The reaction of BrOH with olefins to provide
a
-bromoketones is
investigated. To optimize the reaction conditions we initiated our
studies with styrene 1 as a representative olefin in different sol-
vents at room temperature. When the reaction was carried out with
1,4-dioxane as solvent with 2.0 equiv of brominating reagent, the
a
a
and 86% isolated yields. These transformations are associated with
undesired products during bromination using HBr/H2O2.10 When
this methodology was applied to 3-nitro styrene (Table 2, entry
products
a-bromoacetophenone 3, 2-bromo-1-phenylethanol 4,
and styrene dibromide 5 were obtained in 71%, 17%, and 12% yields,
respectively (GC) (Table 1, entry 1). When the reaction was per-
formed in acetonitrile, the yield of product 3 was reduced to 40%
(entry 2), bromohydrin 4 being the major product in 47% along with
8% of product 5. Whereas THF, dichloromethane, and diethyl ether
provided desired product 3 in 3%, 0%, and 13% yields, respectively,
and products 4 and 5 are obtained as major ones. When the reaction
was conducted in dimethylsulfoxide (DMSO) at room temperature,
the reaction does not yield bromoketone; however, it gave bro-
mohydrin (4) as the major product (60% isolated yield) and dibromo
derivative (5) in 8% yield and the rest constituted unidentified bro-
mo impurities (entry 6). To optimize the amount of the reagent 2,
we performed two reactions in dioxane employing 2.5 and 3.0 equiv
of reagent 2. The gradual increase of the reagent from 2 to 2.5 and
3 equiv gave the desired product (3) in 60% and 61% isolated yields,
respectively (entries 7 and 8). The results clearly indicate that the
best yield of the desired product could be obtained in dioxane with
2.1 equiv of reagent BrOH. Therefore the following experiments
7) the corresponding 3-nitro-a-bromoacetophenone was obtained
in 40% yield. Such deactivated substrates are reported to be tedious
by other methods.3a The internal olefins stilbene and chalcone
were smoothly converted to 2-bromo-1,2-diphenyl-ethanone and
2-bromo-1,3-diphenylpropane-1,3-dione, respectively, in good
yields (Table 2, entries 8 and 9). Under the same experimental con-
ditions straight chain as well as cyclic olefins underwent bromina-
tions without any difficulty to provide the corresponding
a-
bromoketones in moderate to good yields (Table 2, entries 10–20).
As indicated in Eq. 1, the active species BrOH reacts with olefins
to provide bromohydrin8a which further reacts with another equiv-
alent of BrOH to give the corresponding
lined in Scheme 1.
a-bromoketones as out-
In conclusion, the bromide/bromate couple in aqueous acidic
medium serves as an efficient and green reagent for the synthesis
of the a-bromoketone by direct oxybromination of olefins avoiding
HO
Br
BrOH
H
R
+
R
Br
O
Br
Br + + OH-
Br
+
O
H
O
R
OH-
+
-H2O
Br
R
R
Br
Br
-HBr
O
R
Scheme 1. Proposal of the mechanism for the synthesis of a-bromoketones from olefins.

2532
R. D. Patil et al. / Tetrahedron Letters 50 (2009) 2529–2532
addition of the acid, stirring was continued for further 4 h (TLC). The product
was extracted with CH2Cl2 (3 ꢁ 25 ml). The combined organic layers were
washed with aqueous Na2S2O3 and dried over Na2SO4. Evaporation of solvent
left the crude product which was purified by column chromatography over
silica gel (ethyl acetate–hexane 5:95) to afford the pure white solid product
(1.15 g, 5.76 mmol) 2-bromo-1-phenyl-ethanone 3 in 60% yield; melting point
48 °C, (Lit 48.8–49.3 °C).10 The side products, styrene bromohydrin 4 (0.31 g,
hazardous molecular bromine. In addition, this procedure offers
significant improvements with regard to reaction conditions (room
temperature), good yields, and user-friendly operations compared
to conventional methods. These results also highlight the signifi-
cant scope for the synthesis of a-bromoketones from easily acces-
sible olefins, which is inadequately reported in the literature.
12%) and styrene dibromide
5 (0.022 g, 1%) were also obtained. The
spectroscopic data (IR, 1H NMR and 13C NMR) are in good agreement with
the reported values.10
Acknowledgment
2-bromo-1-(4-tert-butylphenyl) ethanone (Table 2, entry 4): Yellow oil. IR:
m
max (Neat). 3042, 2965, 2870, 1680, 1605, 1566, 1465, 1428, 1407, 1365, 1284,
We gratefully acknowledge DST, New Delhi, India, for the finan-
cial support of this project under the Green Chemistry Task Force
scheme [No. SR/S5/GC-02A/2006].
1194, 1104, 1008, 992, 847, 733, 665, 643, 578. 1H NMR (CDCl3-500 MHz)—(d):
1.32 (s,9H), 4.43 (s, 2H), 7.47 (d, 2H, J = 8.5 Hz), 7.91 (d, 2H, J = 8.5 Hz) ppm. 13C
NMR (CDCl3-125 MHz) (d): 30.9, 31.2, 35.1, 125.7, 128.8, 131.2, 157.6,
190.7 ppm. HRMS Calcd for C12H15BrO [M+1]+: 255.0384; Found: 255.0385.
1-Bromo-hexan-2-one (Table 2, entry 10): Colorless liquid. IR: mmax (Neat).
2956, 2931, 2859, 1718, 1462, 1403, 1377, 1255, 1124, 1057, 758, 631. 1H NMR
(CDCl3-500 MHz)—(d): 0.66 (s, 3H), 1.08 (d, 2H, J = 5.0 Hz), 1.34 (s, 2H), 2.40 (s,
2H), 3.65 (s, 2H) ppm. 13C NMR (CDCl3-125 MHz) (d): 13.7, 22.1, 25.8, 34.4,
39.5, 202.1 ppm. HRMS Calcd for C6H11BrO [M+1]+: 179.0071; Found:
179.0072.
Supplementary data
Characterization data for products at entries 4, 10, 11 and 13–
18 in Table 2. Copies of 1H NMR and 13C NMR of all products listed
in Table 2. Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tetlet.2009.03.047.
1-Bromo-octan-2-one (Table 2, entry 11): yellow oil. IR: mmax (Neat). 2930,
2858, 1716, 1464, 1213, 1055, 878, 671, 487. 1H NMR (CDCl3-500 MHz)—
(d) = 0.89 (s, 3H), 1.29 (s, 6H), 1.61 (s, 2H), 2.65 (s, 2H), 3.89 (s, 2H) ppm. 13C
NMR (CDCl3-125 MHz) (d): 13.9, 22.4, 23.8, 28.6, 31.4, 34.3, 39.8, 202.2 ppm.
LRMS Calcd for C8H15BrO [M]+: 207.0384; Found: 207.0385.
References and notes
1-Bromo-decan-2-one (Table 2, entry 13): Pale yellow oil. IR: mmax (Neat). 2928,
2857, 1719, 1462, 1401, 1065, 894, 634. 1H NMR (CDCl3-500 MHz)—(d): 0.87 (s,
3H), 1.29 (d, 10H, J = 4 Hz), 1.61 (t, 2H, J = 7 Hz), 2.64 (t, 2H, J = 7 Hz), 3.89 (s,
2H) ppm. 13C NMR (CDCl3-125 MHz) (d): 14.0, 22.6, 23.8, 29.0, 29.2, 31.7, 34.3,
39.8, 202.1 ppm. HRMS Calcd for C10H19BrO [M]+: 235.0697; Found: 235.0698.
1-Bromo-undecan-2-one (Table 2, entry 14): White crystalline solid melting
point observed 40-41 °C. IR: mmax (Neat). 2925, 2854, 1719,1468, 1406, 1243,
1128, 1086, 1038, 719, 693, 638, 469. 1H NMR (CDCl3-500 MHz)—(d): 0.87 (t,
3H, J = 7 Hz), 1.28 (t, 12H, J = 6 Hz), 1.62 (t, 2H, J = 3.5 Hz), 2.64 (t, 2H, J = 7 Hz),
3.88 (s, 2H) ppm. 13C NMR (CDCl3-125 MHz) (d): 14.1, 22.6, 23.8, 29.0,29.2,
29.3, 29.4, 31.8, 34.3, 39.8, 202.3 ppm. Elemental Anal. Calcd for C11H21BrO is C,
53.02; H, 8.49. Found: C, 53.26; H, 9.21. LRMS Calcd for C11H21BrO [M]+:
249.19; Found: 248.67.
1-Bromo-dodecan-2-one (Table 2, entry 15): White crystalline solid melting
point observed 41–42 °C. IR: mmax (Neat). 2925, 2855, 1720, 1468, 1408, 1238,
1128, 1090, 1049, 719, 693, 639. 1H NMR (CDCl3-500 MHz)—(d): 0.88 (t, 3H,
J = 6 Hz), 1.27 (s, 14H), 1.61 (t, 2H, J = 7 Hz), 2.64 (t, 2H, J = 7 Hz), 3.89 (s,
2H) ppm. 13C NMR (CDCl3-125 MHz) (d): 14.1, 22.7, 23.8, 29.0, 29.3, 29.4, 29.6,
31.9, 34.3, 39.8, 202.2 ppm. Elemental Anal. Calcd for C12H23BrO is C, 54.76; H,
8.81. Found: C, 55.03; H, 9.09. LRMS Calcd for C12H23BrO [M]+: 263.21; Found:
262.68.
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1-Bromo-tetradecan-2-one (Table 2, entry 16): White solid melting point
observed 54–55 °C. IR: mmax (Neat). 2925, 2853, 1720, 1469, 1410, 1249, 1129,
1097, 1061, 719, 640. 1H NMR (CDCl3-500 MHz)—(d): 0.88 (t, 3H, J = 5 Hz), 1.25
(s, 18H), 1.61 (t, 2H, J = 7.5 Hz), 2.64 (t, 2H, J = 7 Hz), 3.89 (s, 2H) ppm. 13C NMR
(CDCl3-125 MHz) (d): 14.1, 22.7, 23.8, 29.0, 29.36, 29.38, 29.4, 29.62, 29.66,
29.67, 31.9, 34.3, 39.8, 202.2 ppm. Elemental Anal. Calcd for C14H27BrO is C,
57.73; H, 9.34. Found: C, 57.98; H, 7.91. LRMS Calcd for C14H27BrO [M]+:
291.27; Found: 290.74.
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1-Bromo-hexadecan-2-one (Table 2, entry 17): White solid melting point
observed 58–59 °C. IR: mmax (Neat). 2923, 2822, 1720, 1469, 1409, 1254, 1129,
1090, 1034, 718, 640. 1H NMR (CDCl3-500 MHz)—(d): 0.88 (t, 3H, J = 6 Hz), 1.25
(s, 22H), 1.61 (d, 2H, J = 6 Hz), 2.64 (t, 2H, J = 7 Hz), 3.88 (s, 2H) ppm. 13C NMR
(CDCl3): (d): 14.1, 22.7, 23.8, 29.0, 29.3, 29.4, 29.6, 31.9, 34.3, 39.8, 202.2 ppm.
Elemental Anal. Calcd for C16H31BrO is C, 60.18; H, 9.79. Found: C, 60.23; H,
10.72. LRMS Calcd for C16H31BrO [M+ Na]+: 342.31; Found: 341.46.
1-Bromo-octadecan-2-one (Table 2, entry 18): White solid melting point
observed 62-63 °C. IR: mmax (Neat). 2922, 2852, 1725, 1465, 1389, 1249, 1081,
724, 638. 1H NMR (CDCl3-500 MHz)—(d): 0.88 (t, 3H, J = 6 Hz), 1.25 (s, 26H),
1.60 (d, 2H, J = 6.5 Hz), 2.64 (t, 2H, J = 7.5 Hz), 3.88 (s, 2H) ppm. 13C NMR
(CDCl3): (d): 14.1, 22.7, 23.8, 29.0, 29.35, 29.39, 29.4, 29.61, 29.67, 29.69, 29.7,
31.9, 34.3, 39.8, 202.2 ppm. Elemental Anal. Calcd for C18H35BrO is C, 62.24; H,
10.16. Found: C, 62.50; H, 9.93. LRMS Calcd for C18H35BrO [M+Na]+: 370.36;
Found: 369.47.
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while handling.) General procedure for the synthesis of
a-bromoketone from
olefins. Representative procedure for 2-bromo-1-phenyl-ethanone (Table 1, entry
1): To a solution of styrene (1.0 g, 9.6 mmol) in 1,4-dioxane (5.0 mL) was added
an aqueous solution (20 ml) containing a 2:1 mole ratio of NaBr (1.38 g,
13.4 mmol)—NaBrO3 (1.01 g, 6.7 mmol) (2.1 equiv) reagent at room
temperature. To the above mixture, 98% sulfuric acid (10.5 mmol) was added
slowly under stirring at room temperature during 2.5 h. After complete
10. Podgorsek, A.; Stavber, S.; Zupan, M.; Iskra, J. Green Chem. 2007, 9, 1212–1218.
11. Pauchert, C. J.; Behnke, J. In The Aldrich Library of 13C and 1H—FT NMR Spectra, I
ed.; Aldrich Chemical: Milwaukee, USA, 1993, Vol. 2.