A convenient synthesis of 2,2-dibromo-1-arylethanones by bromination of 1-arylethanones with the H2O2-HBr system

Article abstract of DOI:10.1055/s-2006-926386

1-Arylethanones and related compounds are brominated in dioxane with the H₂O₂-HBr_aq system, resulting in the replacement of two hydrogen atoms in the methyl group with bromine. The reaction is also accompanied by bromination of the aromatic ring provided that the latter contains electron-donating substituents. The reaction proceeds rapidly (20 min) and results in complete conversion of ketones to give 2,2-dibromo-1- arylethanones in yields up to 86%. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-926386

PAPER
1087
A Convenient Synthesis of 2,2-Dibromo-1-arylethanones by Bromination of
1-Arylethanones with the H2O2–HBr System
S
ynthesis of 2,2-D
l
ibrom
o
e
-1-aryletha
x
none
s
ander O. Terent’ev,* Sergey V. Khodykin, Igor B. Krylov, Yuri N. Ogibin, Gennady I. Nikishin
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky Prospect 47, 119991 Moscow, Russia
Fax +7(95)1355328; E-mail: terentev@ioc.ac.ru
Received 27 June 2005
O
O
O
O
Abstract: 1-Arylethanones and related compounds are brominated
in dioxane with the H2O2–HBraq system, resulting in the replace-
ment of two hydrogen atoms in the methyl group with bromine. The
reaction is also accompanied by bromination of the aromatic ring
provided that the latter contains electron-donating substituents. The
reaction proceeds rapidly (20 min) and results in complete conver-
sion of ketones to give 2,2-dibromo-1-arylethanones in yields up to
86%.
Br
Br
Br
+
+
Br
Br
Br
1
2
3
4
Scheme 1
fold molar excess of H2O2 (run 2), the yield of 3 decreased
to 78%, and monobromoketone 2 remained unconsumed.
A decrease in the amount of HBr (run 3), a decrease in the
reaction time to 8 min (run 4), or lowering of the reaction
temperature to 50 °C (run 5) also lead to a decrease in the
yield of dibromoketone 3.
Key words: acetophenones, 1-arylethanones, 2,2-dibromo-1-aryl-
ethanones, bromination, hydrogen peroxide
2,2-Dibromo-1-arylethanones are used in organic synthe-
sis primarily for the construction of heterocyclic
structures1–3 and small rings,4–6 for the preparation of
compounds with a double7–9 or triple10 bond, and in reac-
tions with phosphorous esters11,12 and thiols.13,14 Most of
the known methods for the synthesis of 2,2-dibromo-1-
arylethanones are based on bromination of acetophenones
with molecular bromine8,11,15–18 and its complex com-
pounds.19,20
Bromination of ketone 1 in acetic acid in the presence of
sulfuric acid afforded dibromoketone 3 in 43% yield and
tribromoketone 4 in 48% yield. The formation of product
4 is the first example of the preparation of 2,2,2-tribromo-
1-phenylethanone in an acidic medium in a satisfactory
yield. The use of a larger amount of H2O2 did not lead to
a considerable increase in the conversion of acetophenone
1 to tribromoketone 4. Alternative procedures for the syn-
thesis of tribromoketone 4 are based on bromination of
acetophenone in acetic acid in the presence of bases,39,40
In the last two decades, chlorination and bromination of
organic compounds with HCl or HBr combined with per-
oxides have developed extensively.21–38 These methods
are most actively used for halogenation of arenes,22–26,28–36
alkenes,21,23 and ketones.37,38
Table 1 Bromination of Ketone 1 with the H2O2–HBr Systema
As part of our continuing studies on the use of hydrogen
peroxide in organic synthesis, in particular the halogena-
tion of ketones,38 we report the results of bromination of
1-arylethanones with the H2O2–HBr system. The influ-
ence of experimental conditions on the selectivity of bro-
mination and the yield of 2,2-dibromo-1-phenylethanone
was revealed using acetophenone (1) as an example
(Scheme 1, Table 1). The reaction was carried out by add-
ing 35% aqueous hydrogen peroxide to a refluxing solu-
tion of ketone 1 in dioxane (acetic acid) and 48%
hydrobromic acid for one minute. Then the mixture was
refluxed with stirring for 20 minutes. The reaction afford-
ed dibromoketone 3 as the major product and mono- (2)
and tribromoketones (4) as by-products.
Run
Products (yield, %) b
2
0
3
84
78
42
74
75
4
1
12
2c
3d
4e
5f
7
8
52
16
17
0
traces
traces
a Reaction conditions: addition (1 min) of 35% aq H2O2 soln (3.23 g,
33.3 mmol, a fourfold molar excess with respect to 1) to a refluxing
mixture (92–94 °C) of 48% aq HBr soln (20 mL), dioxane (20 mL),
and 1 (1.00 g, 8.33 mmol), followed by reflux of the reaction mixture
for 20 min.
Our study demonstrated that the highest yield (84%) of di-
bromoketone 3 was achieved in the presence of a fourfold
molar excess of H2O2 (run 1). In the presence of a three-
b The yields are given with respect to the isolated product.
c A threefold molar excess of 35% aq H2O2 (2.42 g, 24.9 mmol) with
respect to 1 was used.
d The amount of HBr soln was 4.0 mL (35 mmol).
e The reaction time was 8 min.
SYNTHESIS 2006, No. 7, pp 1087–1092
x
x
.
x
x
.2
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6
Advanced online publication: 14.03.2006
DOI: 10.1055/s-2006-926386; Art ID: P08705SS
f The temperature was 50 °C.
© Georg Thieme Verlag Stuttgart · New York

1088
A. O. Terent’ev et al.
PAPER
Table 2 Bromination of 1-Arylethanones and Related Compounds
5a–n with the H2O2–HBraq Systema (continued)
bromination of dibromoacetophenone with hexabromocy-
clopentadiene in acetonitrile,41 or the reaction of phenyl-
propiolic acid in the presence of mercury salts.42
Ketone 5
Molar ratio Products 6 and 7
H2O2/5
Yield (%)b
The experimental conditions, which provided a high yield
of dibromoketone 3, were used in bromination of ketones
5a–n containing various substituents in the aromatic moi-
ety (Table 2). The only difference is that the optimal
amount of hydrogen peroxide was determined for the syn-
thesis of each dibromoketone 6a–l.
5
O
O
Br
Br
Br
HO
Br
HO
5e
6e, 86%
As can be seen from Table 2, the hydrogen atoms are most
easily replaced with bromine in ketones 5a–c, which do
not contain electron-withdrawing substituents. To achieve
the highest yields of ketones 6a–c, it is sufficient to use
the molar ratio H2O2/5a–c = 3.5–4 (the stoichiometric co-
efficient of the reaction is 2).
8
O
O
Br
Br
Br
MeO
MeO
5f
6f, 82%
4
5
5
O
O
Br
Br
Bromination of 1-(2-hydroxyphenyl)ethanone (5d), 1-(4-
hydroxyphenyl)ethanone (5e), and 1-(4-methoxyphen-
yl)ethanone (5f), unlike that of ketones 5a–c, involves si-
multaneously the acetyl group and the aromatic ring.
Bromination of a-tetralone (5g) proceeds readily and re-
sults in the replacement of two hydrogen atoms in the
methylene unit.
5g
6g, 84%
O
O
Br
Br
Br
Br
5h
6h, 79%
O
O
O
O
To prepare dibromoketones 6h–k containing the electron-
withdrawing Cl, Br, or NO2 substituents in high yields, it
is necessary to consume a 2.5 times higher amount of hy-
drogen peroxide compared to the stoichiometric value. In
1,4-diacetylbenzene (5l), both acetyl groups are subjected
to bromination. The tetrabromination product, 1,4-bis(di-
bromoacetyl)benzene (6l), was isolated in 71% yield
when the molar ratio was H2O2/5l = 8.
Br
Br
Br
Br
Br
Br
6i, 84%
5i
5
5
8
Cl
Cl
5j
6j, 85%
Bromination of 2-chloro- and 2,4-dichloroacetophenones
5m and 5n afforded tribromoketones 7m and 7n, respec-
tively, as the major reaction product.
O
O
Br
Br
O2N
O2N
Table 2 Bromination of 1-Arylethanones and Related Compounds
5a–n with the H2O2–HBraq Systema
5k
6k, 78%
O
O
Br
Br
Ketone 5
Molar ratio Products 6 and 7
H2O2/5
Br
Yield (%)b
Br
O
O
O
4
O
6l, 71%
5l
Br
5
5
Cl
O
Cl
O
Cl
O
Br
Br
Br
O
Br
Br
6a, 85%
6b, 82%
Br
5a
5b
5c
3.5
3.5
8
O
O
5m
6m, 7% 7m, 79%
Br
Br
Cl
O
Cl
O
Cl
O
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
O
5n
6n, 31% 7n, 55%
a Reaction conditions: Rapid addition (1 min) of 35% aq H2O2 to a re-
fluxing mixture of 48% HBraq (20 mL), dioxane (20 mL), and 5a–n
(1.00 g, 7.46–5.03 mmol), followed by reflux of the reaction mixture
for 20 min.
6c, 84%
OH
O
OH
O
b The yields are given with respect to the isolated product.
Br
Br
Br
Br
5d
6d, 83%
Synthesis 2006, No. 7, 1087–1092 © Thieme Stuttgart · New York

PAPER
Synthesis of 2,2-Dibromo-1-arylethanones
1089
It is known that the acid-catalyzed halogenation of ke- tribromination products 7m and 7n in yields of 79% and
tones begins with the protonation of the carbonyl oxygen 55%, respectively (Table 2).
atom, followed by deprotonation of the resulting interme-
Apparently, this behavior of 2-chloro-substituted ace-
tophenones during bromination is attributable to the fact
that, in the enol form, repulsion between the chlorine atom
and the hydroxy (a) or dibromomethylene (b) group caus-
es the C(OH)CBr2 group to twist about the Ar–C bond,
with the result that conjugation between the double bond
diate (A) to form enol B, which reacts with a halogenating
agent, for example, with bromine.43 Then, the second and
third hydrogen atoms are more slowly replaced to give the
structures F and I (Scheme 2). Bromination with HOBr,
H2OBr+ occurs via a similar mechanism.44,45
Electron-withdrawing substituents in the aromatic ring of the enol and the aromatic ring is disrupted (Figure 1).
decrease the basicity of the oxygen atom, which hinders In this case, the double bond of the enol is brominated
the formation of intermediates (A, D, G), resulting in a de- without the influence of the aromatic ring (which is char-
crease in the concentrations of the corresponding enols acteristic of aliphatic ketones) to form tribromoketones.
(B, E, H). In this process, brominating agents are partially
consumed in side reactions. Since the amount of the bro-
OH
CBr2
OH
Cl
Cl
CBr2
OH
minating reagents in the system is proportional to the
amount of H2O2 used, bromination of ketones 5h–k con-
taining electron-withdrawing substituents requires the use
of a higher excess of hydrogen peroxide (compared to ke-
tones 1 and 5a–c).
CBr2
a
b
c
Figure 1
The successive replacement of hydrogen atoms with halo-
gen (structures C and F) in bromination of ketones gives
rise to the electron-withdrawing effect of the CH2Br and
CHBr2 groups, which decreases the basicity of the oxygen
atom, hinders its protonation, and, as a consequence, pre-
vents the introduction of the second and, particularly,
third bromine atom.
This repulsion is absent in acetophenones containing the
2-unsubstituted aromatic ring (c). As a result, conjugation
of the enol double bond with the p-electron system of the
aromatic ring is retained, which, apparently, stabilizes the
system and hinders further bromination.
To summarize, we developed a convenient procedure for
the synthesis of dibromoacetophenones and related com-
pounds, which can be prepared in yields up to 86% by bro-
mination of acetophenones with the H2O2–HBraq system.
The method is practically feasible, allows the precise con-
trol of the amount of oxidizing agent, and uses a simple
apparatus. Besides, the synthesis is safer compared to bro-
mination of acetophenones with molecular bromine.
Apparently, bromination of ketone 1 in acetic acid in the
presence of sulfuric acid leads to an increase in the con-
centration of the intermediates A, D, and G and, conse-
quently, of enols B, E, and H. It is also possible that, under
these conditions, HOBr derived from HBr and H2O2,46 is
transformed into the reactive protonated form H2OBr+. As
a result, tribromoketone 4 was prepared in moderate yield.
HBr + H2O2 = HOBr + H2O
HBrO + HBr = H2O + Br2
HBrO + H+ = H2OBr+
The high reactivity of the H2OBr+ species was supported
by the results of the studies27,47 which demonstrated that
the relative electrophilicity of bromine in the series
H2OBr+/Br2/HOBr is 106/103.8/1.
The NMR spectra were recorded on Bruker WM-250 (250.13 MHz
for 1H and 62.9 MHz for 13C) and Bruker AC-200 (200.13 MHz for
1H and 50.32 MHz for 13C) spectrometers in CDCl3 and DMSO-d6.
The TLC analysis was carried out using Silufol UV-254 chromato-
graphic plates. Column chromatography was performed using 63–
200 mesh silica gel (Merck).
The melting points were determined on a Kofler hot-stage apparatus
and are uncorrected.
Bromination of ketones like 2-chloroacetophenone 5m
and 2,4-dichloroacetophenone 5n unexpectedly afforded
O
OH
OH
– H+
O
Br2
Ar C CH3 + H+
Ar C CH3
CH2
Ar C CH2Br
Ar C
– HBr
A
B
C
OH
Ar C CH2Br
OH
CHBr
O
– H+
Br2
+
C
+ H
Ar C
Ar C CHBr2
– HBr
D
E
F
OH
Ar C CHBr2
OH
O
– H+
Br2
F + H+
CBr2
Ar C
Ar C CBr3
– HBr
G
H
I
Scheme 2
Synthesis 2006, No. 7, 1087–1092 © Thieme Stuttgart · New York

1090
A. O. Terent’ev et al.
PAPER
Acetophenones 1 and 5 and 48% aqueous HBr solution were pur-
chased from Aldrich and Acros. A 35% aqueous H2O2 solution and
98% H2SO4 of high-purity grade were used.
1H NMR (200 MHz, CDCl3): d = 1.76–1.89 (m, 4 H, CH2CH2CH2CH2),
2.77–2.88 (m, 4 H, ArCH2), 6.76 (s, 1 H, CH), 7.18 (m, 1 H, Ar-H),
7.77 (m, 2 H, Ar-H).
The solvents of high-purity grade (PE, CHCl3, EtOAc, dioxane,
AcOH, and benzene) were used without additional purification.
13C NMR (62.9 MHz, CDCl3): d = 22.7, 22.8 (CH2CH2CH2CH2),
29.4, 29.8 (ArCH2), 40.2 (CHBr2), 126.6, 128.1, 129.7, 130.5,
138.1, 145.2 (Ar), 185.9 (C=O).
2,2-Dibromo-1-(4-methylphenyl)ethanone (6a); Typical Proce-
dure for the Bromination of Ketones 1 and 5a–5n
2,2-Dibromo-1-(2-naphthyl)ethanone (6c)
Ketone 5a (1.00 g, 7.46 mmol) was dissolved in a mixture of 48%
aq HBr soln (20 mL, 29.8 g, 0.177 mol) and dioxane (20 mL) and
was heated to reflux (92–94 °C). A 35% aq H2O2 soln (2.91 g, 33.4
mmol) in dioxane (2 mL) was added with stirring for 1 min. The re-
action mixture was refluxed with stirring for 20 min, cooled to r.t.,
diluted with H2O (30 mL), and extracted with CHCl3 (4 × 30 mL).
The combined organic extracts were washed with H2O (4 × 15 mL),
dried over MgSO4, filtered, and concentrated.
Pale-yellow crystals; yield: 84%; mp 100–101.5 °C (lit.49 mp 101–
102 °C); Rf = 0.31 (PE–EtOAc, 94:6).
1H NMR (250 MHz, CDCl3): d = 6.89 (s, 1 H, CH), 7.55–7.70 (m,
2 H, Ar-H), 7.86–8.01 (m, 3 H, Ar-H), 8.06–8.11 (m, 1 H, Ar-H),
8.62 (s, 1 H, Ar-H).
13C NMR (62.9 MHz, CDCl3): d = 39.9 (CHBr2), 124.7, 127.2,
127.9, 128.1, 128.9, 129.5, 129.8, 131.8, 132.2, 136.0 (Ar-CH),
186.0 (C=O).
2,2-Dibromo-1-(4-methylphenyl)ethanone (6a) was isolated from
the reaction mixture by column chromatography (PE–EtOAc,
94:6); the yield was 1.85 g (85%).
Anal. Calcd for C12H8Br2O: C, 43.94; H, 2.46; Br, 48.72. Found: C,
43.49; H, 2.38; Br, 48.88.
Products 2–4, 6a–c, 6f–h, 6k–n, 7m, and 7n were isolated from the
reaction mixture by column chromatography. Products 6i and 6j
were isolated by recrystallization of a crude product from PE. Prod-
ucts 6d and 6e were isolated by recrystallization from PE–EtOAc.
2,2-Dibromo-1-(3,5-dibromo-2-hydroxyphenyl)ethanone (6d)
Slightly yellow crystals; yield: 83%; mp 118–119.5 °C (lit.50 120–
121 °C); Rf = 0.13 (PE–EtOAc, 94:6).
1H NMR (250 MHz, CDCl3): d = 6.70 (s, 1 H, CH), 7.91 (s, 1 H, Ar-
H), 7.98 (s, 1 H, Ar-H), 11.92 (s, 1 H, OH).
Influence of Experimental Conditions on Bromination of 1
(Table 1)
By analogy with the general procedure, experiments were carried
out with the use of 48% aq HBr soln (4.0 mL, 35 mmol) and with
the use of a threefold molar excess of 35% aq H2O2 soln (2.42 g,
24.9 mmol) with respect to 1; the reaction time was decreased to
8 min, and the reaction was performed at 50 °C (Table 1).
2,2-Dibromo-1-(3,5-dibromo-4-hydroxyphenyl)ethanone (6e)
White crystals; yield: 86%; mp 104–105 °C (lit.50 105–106 °C);
Rf = 0.1 (PE–EtOAc, 94:6).
1H NMR (250 MHz, CDCl3): d = 6.54 (s, 1 H, CH), 6.40–6.65 (br s,
1 H, OH), 8.23 (s, 2 H, Ar-H).
13C NMR (62.9 MHz, CDCl3): d = 38.7 (CHBr2), 110.3 (CBr, Ar),
125.3 (CC=O), 134.1 (Ar-CH), 154.5 (COH, Ar), 182.7 (C=O).
The reaction performed by analogy with the general procedure in
HOAc (20 mL) instead of dioxane in the presence of H2SO4 (5.0
mL, 94 mmol) afforded dibromoketone 3 and tribromoketone 4 in
yields of 43% and 48%, respectively.
Anal. Calcd for C8H4Br4O2: C, 21.27; H, 0.89; Br, 70.75. Found: C,
21.33; H, 0.84; Br, 70.71.
2-Bromo-1-phenylethanone (2)
Pale-yellow crystals; yield: 52%; mp 49–51 °C.
1H NMR (200 MHz, CDCl3): d = 4.48 (s, 2 H, CH2Br), 7.45–7.67
(m, 3 H, Ar-H), 7.95–8.04 (m, 2 H, Ar-H).
2,2-Dibromo-1-(3-bromo-4-methoxyphenyl)ethanone (6f)
Slightly yellow crystals; yield: 82%; mp 104–105 °C (lit.50 102 °C);
Rf = 0.16 (PE–EtOAc, 94:6).
1H NMR (200 MHz, CDCl3): d = 3.98 (s, 3 H, CH3), 6.67 (s, 1 H,
CH), 6.96 (d, J = 8.7 Hz, 1 H, Ar-H), 8.04 (dd, J = 8.7, 2.3 Hz, 1 H,
Ar-H), 8.26 (d, J = 2.3 Hz, 1 H, Ar-H).
13C NMR (50 MHz, CDCl3): d = 39.5 (CHBr2), 56.7 (CH3), 111.3
(Ar-CH), 112.3, 124.2 (Ar-C), 131.1, 135.0 (Ar-CH), 160.5
(COCH3), 183.7 (C=O).
2,2-Dibromo-1-phenylethanone (3)
White crystals; yield: 84%; mp 35–36 °C (lit.48 mp 35.5–36 °C);
Rf = 0.28 (PE–EtOAc, 94:6).
1H NMR (250 MHz, CDCl3): d = 6.71 (s, 1 H, CH), 7.46–7.57 (m,
2 H, Ar-H), 7.58–7.69 (m, 1 H, Ar-H), 8.09 (m, 2 H, Ar-H).
Anal. Calcd for C9H7Br3O2: C, 27.94; H, 1.82; Br, 61.96. Found: C,
28.20; H, 1.78; Br, 62.06.
2,2,2-Tribromo-1-phenylethanone (4)
White crystals; yield: 12%; mp 64–65.5 °C (lit.39 mp 65–66 °C);
Rf = 0.37 (PE–EtOAc, 94:6).
2,2-Dibromo-3,4-dihydronaphthalen-1(2H)-one (6g)
White crystals; yield: 84%; mp 57.5–59 °C (lit.51 mp 59–60 °C);
Rf = 0.31 (PE–EtOAc, 94:6).
1H NMR (200 MHz, CDCl3): d = 3.02–3.15 (m, 4 H, CH2CH2),
7.22–7.41 (m, 2 H, Ar-H), 7.49–7.59 (m, 1 H, Ar-H), 8.10–8.17 (m,
1 H, Ar-H).
13C NMR (50 MHz, CDCl3): d = 29.1 (ArCH2), 45.6 (ArCH2CH2),
67.4 (CBr2), 126.9, 127.0, 128.5, 129.8, 134.3, 141.9 (Ar), 183.9
(C=O).
1H NMR (250 MHz, CDCl3): d = 7.42–7.52 (m, 2 H, Ar-H), 7.53–
7.66 (m, 1 H, Ar-H), 8.28–8.39 (m, 2 H, Ar-H).
2,2-Dibromo-1-(4-methylphenyl)ethanone (6a)
Pale-yellow crystals; yield: 85%; mp 97–98 °C (lit.49 mp 98–
99 °C); Rf = 0.41 (PE–EtOAc, 94:6).
1H NMR (250 MHz, CDCl3): d = 2.43 (s, 3 H, CH3), 6.72 (s, 1 H,
CH), 7.30 (d, J = 7.9 Hz, 2 H, Ar-H), 7.97 (d, J = 7.9 Hz, 2 H, Ar-
H).
2,2-Dibromo-1-(3-bromophenyl)ethanone (6h)
Pale yellow crystals; yield: 79%; mp 42.5–44 °C (lit.20 mp 43–
44 °C); Rf = 0.31 (PE–EtOAc, 94:6).
2,2-Dibromo-1-(5,6,7,8-tetrahydronaphthalen-2-yl)ethanone
(6b)
Pale-yellow crystals; yield: 82%; mp 55–56 °C (lit.49 mp 55.5–
56.5 °C); Rf = 0.34 (PE–EtOAc, 94:6).
Synthesis 2006, No. 7, 1087–1092 © Thieme Stuttgart · New York

PAPER
Synthesis of 2,2-Dibromo-1-arylethanones
1091
1H NMR (250 MHz, CDCl3): d = 6.69 (s, 1 H, CH), 7.37 (m, 1 H,
Ar-H), 7.71 (m, 1 H, Ar-H), 7.98 (m, 1 H, Ar-H), 8.15 (m, 1 H, Ar-
H).
13C NMR (50 MHz, CDCl3): d = 41.2 (CBr3), 126.7, 129.9, 130.1
(Ar-CH), 131.5, 133.2, 137.5 (CC=O, C-Cl), 184.5 (C=O).
13C NMR (62.9 MHz, CDCl3): d = 39.6 (CHBr2), 123.2 (CBr),
128.2, 130.3, 132.5 (Ar-CH), 134.4 (CC=O), 137.3 (Ar-CH), 184.7
(C=O).
Acknowledgment
This study was financially supported by the Federal Program for the
Support of Leading Scientific Schools of the Russian Federation
(Grant No. 02121-2003-3) and the Russian Science Support Foun-
dation.
2,2-Dibromo-1-(4-bromophenyl)ethanone (6i)
White crystals; yield: 84%; mp 92–93 °C (lit.49 mp 93–94 °C);
Rf = 0.38 (PE–EtOAc, 94:6).
1H NMR (250 MHz, CDCl3): d = 6.61 (s, 1 H, CH), 7.64 (d, J = 8.7
Hz, 2 H, Ar-H), 7.96 (d, J = 8.7 Hz, 2 H, Ar-H).
References
13C NMR (75.5 MHz, CDCl3): d = 39.4 (CHBr2), 129.7, 129.9
(CBr, CC=O), 131.2, 132.3 (Ar-CH), 185.1 (C=O).
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2,2-Dibromo-1-(4-chlorophenyl)ethanone (6j)
White crystals; yield: 85%; mp 92.5–93.5 °C (lit.49 mp 93–94 °C);
Rf = 0.33 (PE–EtOAc, 94:6).
1H NMR (200 MHz, CDCl3): d = 6.68 (s, 1 H, CH), 7.42 (d, J = 8.5
Hz, 2 H, Ar-H), 7.99 (d, J = 8.5 Hz, 2 H, Ar-H).
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Chem. Soc. Jpn. 1976, 49, 829.
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321.
2,2-Dibromo-1-(4-nitrophenyl)ethanone (6k)
Pale-yellow crystals; yield: 78%; mp 62–64 °C (lit.1 mp 60 °C);
Rf = 0.2 (PE–EtOAc, 94:6).
1H NMR (300 MHz, CDCl3): d = 6.65 (s, 1 H, CH), 8.22–8.41 (m,
4 H, Ar-H).
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Chem. USSR (Engl. Transl.) 1992, 28, 902; Zh. Org. Khim.
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1,4-Bis(dibromoacetyl)benzene (6l)
White crystals; yield: 71%; mp 167–169 °C (lit.52 mp 166–168 °C);
Rf = 0.31 (benzene).
(10) Zhdankin, V. V.; Stang, P. J. Tetrahedron Lett. 1993, 34,
1H NMR (250 MHz, DMSO-d6): d = 7.91 (s, 2 H, CH), 8.22 (s, 4 H,
1461.
Ar-H).
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1994, 30, 827.
13C NMR (62.9 MHz, DMSO-d6): d = 43.4 (CHBr2), 129.9 (Ar-
CH), 135.2 (CC=O), 186.4 (C=O).
2,2-Dibromo-1-(2-chlorophenyl)ethanone (6m)53
Slightly yellow liquid; yield: 7%; Rf = 0.44 (PE–EtOAc, 94:6).
1H NMR (200 MHz, CDCl3): d = 6.78 (s, 1 H, CH), 7.34–7.49 (m,
3 H, Ar-H), 7.57–7.64 (m, 1 H, Ar-H).
2,2,2-Tribromo-1-(2-chlorophenyl)ethanone (7m)
Slightly yellow liquid; yield: 79%; Rf = 0.61 (PE–EtOAc, 94:6).
1H NMR (250 MHz, CDCl3): d = 7.32–7.41 (m, 1 H, Ar-H), 7.42–
7.53 (m, 2 H, Ar-H), 7.87–7.92 (m, 1 H, Ar-H).
13C NMR (75.5 MHz, CDCl3): d = 41.7 (CBr3), 126.3, 128.9, 130.0,
131.8 (Ar-CH), 132.0, 133.2, (CC=O, CCl), 185.5 (C=O).
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Okamoto, T. Bull. Chem. Soc. Jpn. 1987, 60, 2667.
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2003, 44, 439.
Anal. Calcd for C8H4Br3ClO: C, 24.56; H, 1.03; Br, 61.26; Cl, 9.06.
Found: C, 24.67; H, 1.12; Br, 61.11; Cl, 9.21.
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Avetisyan, A. A. Russ. J. Org. Chem. 1995, 31, 90; Zh. Org.
Khim. 1995, 31, 100.
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2,2-Dibromo-1-(2,4-dichlorophenyl)ethanone (6n)
White crystals; yield: 31%; mp 27–28.5 °C (lit.54 mp 28.5–29.5 °C);
Rf = 0.36 (PE–EtOAc, 94:6).
1H NMR (250 MHz, CDCl3): d = 6.72 (s, 1 H, CH), 7.37 (d, J = 7.8
Hz, 1 H, Ar-H), 7.48 (s, 1 H, Ar-H), 7.59 (d, J = 7.8 Hz, 1 H, Ar-H).
13C NMR (75.5 MHz, CDCl3): d = 41.8 (CHBr2), 127.7, 130.5,
131.8 (Ar-CH), 132.1, 132.2, 138.9 (CC=O, CCl), 187.5 (C=O)
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2,2,2-Tribromo-1-(2,4-dichlorophenyl)ethanone (7n)55
Oil; yield: 55%; Rf = 0.49 (PE–EtOAc, 94:6).
1H NMR (250 MHz, CDCl3): d = 7.33 (dd, J = 8.5, 2.0 Hz, 1 H, Ar-
H), 7.52 (d, J = 2.0 Hz, 1 H, Ar-H), 7.89 (d, J = 8.5 Hz, 1 H, Ar-H).
V. Tetrahedron Lett. 1998, 39, 6349.
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