A novel synthesis of β,β-dibromostyrenes

Article abstract of DOI:10.1055/s-2001-18055

A new simple and efficient transformation of aromatic aldehydes to β,β-dibromostyrenes and arylbromoacetylenes is described. The olefination procedure was conducted under mild conditions and in good yields.

Full text of DOI:10.1055/s-2001-18055

PAPER
2081
A Novel Synthesis of b,b-Dibromostyrenes
A
a
N
ovel Synthesis
l
of
b
,
b
e
x
yrenes ey V. Shastin,a Vasily N. Korotchenko,b Valentine G. Nenajdenko,*b Elisabeth S. Balenkovab
Institute of Problems of Chemical Physics, Chernogolovka, Moscow Region, 142432, Russia
b
Moscow State University,, Department of Chemistry,, Leninskie Gory, Moscow 119899, Russia
Fax +7(095)9328846; E-mail: nen@acylium.chem.msu.ru
Received 28 May 2001; revised 26 July 2001
sensitive. Mild conditions and the simplicity of the tech-
nique are favourable features of the reaction.
Abstract: A new simple and efficient transformation of aromatic
aldehydes to b,b-dibromostyrenes and arylbromoacetylenes is de-
scribed. The olefination procedure was conducted under mild con-
ditions and in good yields.
This paper presents the results of the use of carbon tetra-
bromide in this reaction. We found that CBr4 reacted with
Key words: aromatic aldehydes, olefination, dibromostyrenes, hydrazones 1a–i in a similar way to give as target products
copper-carbene complexes, carbon tetrabromide
the corresponding b,b-dibromostyrenes 2a–i (Scheme 2).
Moreover, the corresponding sym-azines were also isolat-
ed as side products.
Olefination of carbonyl compounds, that is, C=O/C=CXY
transformation, is one of the fundamental procedures for
the preparation of substituted alkenes.1 The Wittig reac-
tion and its modifications are the most widely used ways
for this transformation.2 However, the necessity to use
equimolar amounts of phosphoric reagents is a significant
disadvantage. Therefore, new, preferably, catalytic ap-
proaches for the olefination are desirable in modern or-
ganic synthesis.
Scheme 2
b,b-Dibromostyrenes are important reagents in modern
organic synthesis being synthetic precursors of terminal
and unsymmetrical acetylenes,8,9 bromoacetylenes,10,11
and fused heterocycles.12 Recently, various cross-cou-
pling reactions with substituted b,b-dibromostyrenes
were described.13 In the last decade new methods for ste-
reoselective reduction of dibromoalkenes into E-14,15 and
Z-isomers16 of terminal vinyl bromides were elaborated.
Recently, we elaborated a novel non-Wittig approach to-
wards olefination.3,4 The proposed method was based on
the new redox reaction between N-unsubstituted hydra-
zones of aromatic aldehydes and carbon tetrachloride
(Scheme 1). The reaction took place under copper cataly-
sis in the presence of aqueous ammonia to give the corre-
sponding dichloroalkenes in high yields.4,5
We studied the conversion of the wide range of hydra-
zones of aromatic aldehydes bearing various substituents
in the aromatic ring to the corresponding dibromosty-
renes. In general, the reactions proceeded smoothly to
give the target products in good yield (Table 1).
Table 1 Synthesis of Dibromostyrenes
Product
2a
Aryl
Yield (%)
4-ClC6H4
2-ClC6H4
4-FC6H4
84
77
71
92
92
87
57
81
79
2b
Scheme 1
2c
The proposed transformation represented a new general
type of reaction for the formation of new C=C bonds. The
variations of the haloalkanes permitted the preparation of
different types of alkenes. For example, freons CF3CCl3,6
CF2Cl–CFCl2,6 and bromoform7 can be used for stereose-
lective preparation of the corresponding alkenes. It should
be noted that this new procedure is air- and moisture- in-
2d
2-FC6H4
2e
4-BrC6H4
4-CH3C6H4
4-CF3C6H4
2-CF3C6H4
4-CH3 °C6H4
2f
2g
2h
2i
Synthesis 2001, No. 14, 26 10 2001. Article Identifier:
1437-210X,E;2001,0,14,2081,2084,ftx,en;E04101SS.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881

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A. V. Shastin et al.
PAPER
In some cases, however, olefination was accompanied
with the formation of the corresponding bromoacetylenes
(Scheme 3). Substrates containing strong electron-with-
drawing groups or sterically hindered hydrazones were
prone to conversion to the corresponding bromoacety-
lenes (Table 2).
Scheme 3
Table 2 Formation of the Mixture of Dibromoalkenes and Bro-
moacetylenes
Aryl
Ratioa 2:3
1:1
Total Yield (%)
4-O2NC6H4
2-O2NC6H4
2-BrC6H4
2,6-Cl2C6H3
78
50
77
30
Scheme 4
4:1
4:3
The corresponding azines and bromoform were detected
by 1H NMR investigations of reaction mixture.
5:6
a Determined from 1H NMR data.
In summary, we have elaborated a new non-Wittig ap-
proach to b,b-dibromostyrenes. Mild conditions, simplic-
ity of the experimental technique and high yields of
products are remarkable advantages of the presented
method.
A slight modification of the technique permitted the one-
pot preparation of arylbromoacetylenes 3k–m without
isolation of dibromostyrenes. After nitrogen evolution
had completed, the reaction mixture was treated with
DBU; as a result bromoacetylenes were prepared in pure
form (Table 3).
NMR spectra were recorded on a Varian VXR-400 and Bruker AM
400C spectrometers in CDCl3 with TMS as an internal standard. IR
spectra were obtained with UR-20 spectrometer. Merck 60F254
plates were used for analytical TLC chromatography. Column chro-
matography was performed on silica gel (63–200 mesh, Merck).
Mass-spectra were recorded on a HP5890 mass spectrometer with
the 5989x-G detector.
Table 3 Synthesis of Arylbromoacetylenes
Product
3k
Aryl
Yield (%)
2-O2NC6H4
2-BrC6H4
2,6-Cl2C6H3
66
71
43
Hydrazones of aromatic aldehydes 1a–m were prepared as previ-
ously described.4
3l
Dibromostyrenes; General Procedure
3m
Aq NH3 (25%, 3.33 mL) and Cu2Cl2 (100 mg, 1 mmol) were added
to a solution of the hydrazone (10 mmol) in DMSO (10 mL). Then,
a solution of CBr4 (9.9 g, 30 mmol) in DMSO (20 mL) was added
dropwise over 10 min, maintaining the temperature at about 0 °C.
The reaction mixture was stirred for 4 h, and quenched with H2O
(300 mL). The reaction products were extracted with CH2Cl2 (3 ¥
50 mL), extracts were dried (Na2SO4), CH2Cl2 was evaporated, and
the residue was purified by column chromatography (hexane).
Previously, we proposed a general mechanism of this new
reaction (Scheme 4).5 The key intermediate is the copper-
carbenoid complex I, formed in the reaction of copper (II)
with hydrazone via the corresponding diazoalkane. Simi-
lar copper-carbenoid complexes are universally accepted
as reactive intermediates in many copper-catalysed reac-
tions:17 addition of diazoalkanes to C=C bond,18 and
ylides generation.19 Some stable imidazolyl- and thiaz-
olyl-carbenoid complexes of Cu were recently isolat-
ed.20,21
The known compounds 2a, 2f, 2i were identified by comparison of
their spectral data with those described in the literature.22
1-Chloro-2-(2,2-dibromovinyl)benzene (2b)
Colourless oil; Rf = 0.55 (hexane).
IR: 1610 cm–1.
Intermediate I reacts with a molecule of CBr4 to give the
target alkene and to regenerate the copper(II) (inside the
cycle). Another type of transformation of I is the reaction
with diazoalkane to form sym-azine (outside the cycle).5
The copper oxidation step completes the outside catalytic
cycle.
1H NMR (CDCl3): d = 7.22–7.28 (m, 2 H, Ar), 7.35–7.39 (m, 1 H,
Ar), 7.54 (s, 1 H, –CH= ), 7.60–7.63 (m, 1 H, Ar).
13C NMR (CDCl3): d = 92.76 (=CBr2), 126.44, 129.36, 129.60,
129.96, 132.95, 133.94, 134.62.
Synthesis 2001, No. 14, 2081–2084 ISSN 0039-7881 © Thieme Stuttgart · New York

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A Novel Synthesis of b,b-Dibromostyrenes
2083
Anal. Calcd for C8H5Br2Cl: C, 32.42; H, 1.70. Found: C, 32.63; H,
1.72.
Arylbromoacetylenes; General Procedure
A solution of the hydrazone (10 mmol) in DMSO (10 mL) was treat-
ed as described for the dibromostyrenes. After 4 h, a solution of
DBU (4.5 mL, 30 mmol) in DMSO (20 mL) was added dropwise
over 10 min, maintaining the temperature at 20 °C. The reaction
mixture was stirred for 3 h. The reaction products were isolated as
described for the dibromostyrenes.
1-(2,2-Dibromovinyl)-4-fluorobenzene (2c)
Colourless oil; Rf = 0.60 (hexane).
IR: 1620 cm–1.
1H NMR (CDCl3): d = 6.97 (dd, 2 H, J = 8.6, 8.6 Hz, Ar), 7.33 (s, 1
H, –CH=), 7.43 (dd, 2 H, J = 8.6, 4.3 Hz, Ar).
1-(Bromoethynyl)-2-nitrobenzene (3k)
13C NMR (CDCl3): d = 90.03 (=CBr2), 115.10 (J = 21.6 Hz, C-3,5),
130.92 (J = 7.6 Hz, C-2,6), 131.98 (C-1), 136.36 (–CH=), 163.20
(J = 248.7 Hz, C–F).
Colourless crystals; mp 94–95 °C.
Rf = 0.10 (hexane).
1H NMR (CDCl3): d = 7.48 (ddd, 1 H, J = 8.5, 8.2, 1.4 Hz, Ar), 7.58
(ddd, 1 H, J = 8.5, 7.8, 1.2 Hz, Ar), 7.64 (dd, 1 H, J = 7.8, 1.4 Hz,
Ar), 8.03 (dd, 1 H, J = 8.2, 1.2 Hz, Ar).
Anal. Calcd for C8H5Br2F: C, 34.32; H, 1.80. Found: C, 34.05; H,
1.76.
13C NMR (CDCl3): d = 58.78 (∫CBr), 75.30 (∫C–Ar), 118.03,
1-(2,2-Dibromovinyl)-2-fluorobenzene (2d)
Colourless oil; Rf = 0.60 (hexane).
IR: 1620 cm–1.
1H NMR (CDCl3): d = 7.06 (dd, 1 H, J = 9.7, 8.7 Hz, Ar), 7.15 (dd,
1 H, J = 7.9, 7.6 Hz, Ar), 7.32 (m, 1 H, Ar), 7.54 (s, 1 H, –CH=),
7.76 (dd, 1 H, J = 7.9, 7.6 Hz, Ar).
124.66, 129.05, 132.88, 135.37, 150.05 (C-NO2).
MS (EI, 70 eV): m/z (%) = 226 (7) [M+], 170 (13) [C7H6Br]+, 90
(100) [C7H6]+.
Anal. Calcd for C8H4BrNO2: C, 42.51; H, 1.78. Found: C, 42.67; H,
2.01.
13C NMR (CDCl3): d = 92.70 (=CBr2), 107.76 (J = 94.6 Hz, C-1),
116.19 (J = 21.4 Hz, Ar), 124.51 (Ar), 129.94 (Ar), 130.73 (Ar),
131.05 (J = 9.2 Hz, –CH=), 160.34 (J = 250.3 Hz, C–F).
1-Bromo-2-(bromoethynyl)benzene (3l)
Colourless oil; Rf = 0.55 (hexane).
1H NMR (CDCl3): d = 7.17 (ddd, 1 H, J = 8.2, 8.1, 1.8 Hz, Ar), 7.23
(ddd, 1 H, J = 8.2, 8.1, 1.4 Hz, Ar), 7.44 (dd, 1 H, J = 8.1, 1.8 Hz,
Ar), 7.54 (dd, 1 H, J = 8.2, 1.4 Hz, Ar).
Anal. Calcd for C8H5Br2F: C, 34.32; H, 1.80. Found: C, 34.16; H,
1.64.
13C NMR (CDCl3): d = 54.91 (∫CBr), 78.82 (∫C–Ar), 125.77,
1-Bromo-4-(2,2-dibromovinyl)benzene (2e)
Colourless oil; Rf = 0.50 (hexane).
IR: 1600 cm–1.
1H NMR (CDCl3): d = 7.37 (d, 2 H, J = 8.7 Hz, Ar), 7.37 (s, 1 H, –
CH=), 7.46 (d, 2 H, J = 8.7 Hz, Ar).
13C NMR (CDCl3) : d = 90.51 (=CBr2), 122.57, 129.82, 131.54,
134.03, 135.62.
127.03, 129.83, 130.77, 132.47, 133.93.
MS (EI, 70 eV): m/z (%) = 260 (68) [M+], 179 (22) [M+–Br], 100
(63) [M+–2Br], 76 (100) [M+–2Br–2C].
Anal. Calcd for C8H4Br2: C, 36.97; H, 1.55. Found: C, 37.19; H,
1.73.
2-(Bromoethynyl)-1,3-dichlorobenzene (3m)
Colourless oil; Rf = 0.55 (hexane).
1H NMR (CDCl3): d = 7.17 (t, 1 H, J = 7.8 Hz, CH-5), 7.29 (d, 2 H,
J = 7.8 Hz, CH-4,6).
13C NMR (CDCl3): d = 60.99 (∫CBr), 74.40 (∫C–Ar), 127.50,
129.32, 131.12, 137.95.
MS (EI, 70 eV): m/z (%) = 341 (100) [M+], 261 (14) [M+–Br], 180
(55) [M+–Br–HBr], 101 (42) [M+–2Br–HBr].
Anal. Calcd for C8H5Br3: C, 28.19; H, 1.48. Found: C, 28.03; H,
1.39.
1-(2,2-Dibromovinyl)-4-(trifluoromethyl)benzene (2g)
Colourless oil; Rf = 0.60 (hexane).
IR: 1615 cm–1.
1H NMR (CDCl3): d = 7.51 (s, 1 H, –CH=), 7.63 (s, 4 H, Ar).
13C NMR (CDCl3): d = 92.83 (=CBr2), 121.24 (q, J = 274.7 Hz,
CF3), 126.14, 129.38, 132.20 (q, J = 28.2 Hz, C-4), 136.35, 139.54.
MS (EI, 70 eV): m/z (%) = 250 (100) [M+], 169 (28) [M+–Br], 133
(35) [M+–Br–Cl], 98 (71) [M+–Br–2Cl], 74 (32) [M+–Br–2Cl–2C].
Anal. Calcd for C8H3BrCl2: C, 38.45; H, 1.21. Found: C, 38.23; H,
1.34.
Acknowledgement
Anal. Calcd for C9H5Br2F3: C, 32.76; H, 1.53. Found: C, 32.91; H,
1.72.
Financial support from the Russian Fundamental Investigation
Foundation (Grants No. 00-03-32760 and No. 00-03-32763) is gra-
tefully acknowledged.
1-(2,2-Dibromovinyl)-2-(trifluoromethyl)benzene (2h)
Colourless oil; Rf = 0.60 (hexane).
IR: 1615 cm–1.
References
1H NMR (CDCl3): d = 7.40–7.45 (m, 1 H, Ar), 7.53–7.55 (m, 1 H,
Ar), 7.56 (s, 1 H, –CH=), 7.60–7.63 (m, 1 H, Ar), 7.65–7.68 (m, 1
H, Ar).
13C NMR (CDCl3): d = 94.43 (= Br2), 124.45 (q, J = 274.7 Hz,
CF3), 125.83, 126.59, 129.14, 130.38, 131.42, 132.50 (q, J = 28.0
Hz, C-2), 134.97.
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1.44.
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Synthesis 2001, No. 14, 2081–2084 ISSN 0039-7881 © Thieme Stuttgart · New York