A new facile synthesis of 1,1-dibromo-2-arylethenes

Article abstract of DOI:10.1055/s-2007-984901

Synthetically useful 1,1-dibromo-2-arylethenes were readily prepared in good yields via double bromodesilylation of the easily accessible 1,1-bis(trimethylsilyl)-2-arylethenes using N-bromosuccinimide under mild conditions. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-984901

LETTER
2061
A New Facile Synthesis of 1,1-Dibromo-2-arylethenes
New
F
acile Sy
i
nthesis
o
of 1,1-Dibro
t
mo-2-
r
a
rylethenes Pawluć, Grzegorz Hreczycho, Jędrzej Walkowiak, Bogdan Marciniec*
Department of Organometallic Chemistry, Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60780 Poznan, Poland
Fax +48(61)8291508; E-mail: marcinb@amu.edu.pl
Received 23 May 2007
configurationally defined trisubstituted alkenes such as
Abstract: Synthetically useful 1,1-dibromo-2-arylethenes were
triarylethenes,2b 2-aryl-1,1-dialkynylethenes8a,b or (E)-3-
readily prepared in good yields via double bromodesilylation of the
easily accessible 1,1-bis(trimethylsilyl)-2-arylethenes using N-
methyl-3-en-1-ynes.8c 1,1-Dibromo-2-arylethenes can
also be used as precursors to internal alkynes2b and both
bromosuccinimide under mild conditions.
symmetric and unsymmetric 1,3-diynes9 (Scheme 1).
Key words: 1,1-dibromo-1-alkenes, bromodesilylation, halogena-
tion, organometallic reagents, silicon derivatives
1,1-Dibromo-2-arylethenes are usually prepared by
Wittig-type olefination of aryl aldehydes with triphen-
ylphosphine and carbon tetrabromide.3,10a More recently,
they have also been formed via tandem oxidation–Wittig
reaction of activated benzyl alcohols10b or through the
intermediacy of hydrazones.10c However, the necessity to
use equimolar amounts of phosphoric reagents and/or car-
bon tetrabromide limits the appeal of these methodologies
as a result of their toxicity.
1,1-Dibromo-2-arylethenes are valuable synthetic tools in
organic chemistry. They can serve as precursors for the
preparation of aryl acetamides,1a aryl acetic acids,1b,c
amidines,1b 1-bromo-1-alkynes,2 terminal alkynes
(Corey–Fuchs protocol),3 aryl methyl ketones,4 etc. In ad-
dition, 1,1-dibromo-2-arylethenes have been largely em-
ployed as substrates for the stereoselective synthesis of
geometrically pure (E)-5 and (Z)-b-bromostyrenes.6 Gem-
inal dibromostyrenes can be also used as equivalents of
(Z)-1-aryl-1-bromo-1-alkenes7a,b and (Z)-2-bromo-1,3-
butadienes7c in Pd-catalyzed coupling reactions. More-
over, it is well established that the stereospecific
palladium-catalyzed cross-coupling of 1,1-dibromo-2-
arylethenes in a sequential manner provides access to
Substituted styrylsilanes have been recognized as useful
synthetic reagents since the carbon–silicon bonds are
readily cleaved by various electrophiles in a regio- and
stereoselective manner.11 It was found that electrophilic
bromination of these compounds proceeded with molecu-
lar bromine12a–c or N-bromosuccinimide (NBS)12d,e to
give the corresponding styryl bromides or bis(2-bromo-
ethenyl)arenes with retention of configuration. Although
Ar
R
O
R
Ar
H
Ar
Me
R
Ar
Br
Ar
R
R1
R1
Br
R2
N
Ar
R2
Ar
Ar
Br
O
Br
OH
Ar
Ar
R
O
Br
H
Ar
Ar
H
Br
Ar
R
Scheme 1
SYNLETT 2007, No. 13, pp 2061–2064
1
3
.0
8
.2
0
0
7
Advanced online publication: 17.07.2007
DOI: 10.1055/s-2007-984901; Art ID: G15407ST
© Georg Thieme Verlag Stuttgart · New York

2062
Piotr Pawluć et al.
LETTER
Me
O
Me
Me
Si
Si
1) RuHCl(CO)(PPh3)3, 120 °C
2) MeMgI, THF, 65 °C
ArI, Pd(OAc)2,
CH2=CHSiMe2Cl
Me3Si
Me3Si
Ar
Et3N, pentane, r.t.
OH
PPh3, Et3N, AgNO3
HO
O
– CH2=CH2
MeCN, 80 °C
Me3Si
72%
Me3Si
87–96%
Me
90%
Scheme 2
the utility of the 1-aryl-2-silylethenes as intermediates in
the stereoselective synthesis of styryl bromides is well
documented, the application of geminally silylated
styrenes in the bromodesilylation process lags far behind
mainly due to the complexity of their synthesis.
Table 1 Synthesis of 1,1-Dibromo-2-arylethenes via Bromo-
desilylation of 1,1-Bis(trimethylsilyl)-2-arylethenesa
NBS (10 equiv)
SiMe3
SiMe3
Br
Ar
Ar
MeCN, r.t., 4–48 h
Br
Recently we have developed a new facile and efficient
protocol for the synthesis of 1,1-bis(silyl)-2-arylethenes
from easily available starting materials using a sequential
procedure: ethylene glycol silylation–one-pot deethen-
ative silylative coupling cyclization13a/Grignard reagent
treatment–Heck coupling13b (Scheme 2).
Entry Ar
Time Product structure
(h)
Yield
(%)b
Br
1
2
3
4
5
Ph
4
72
Br
Br
Br
Having established a method for their selective synthesis
and given synthetic utility of 1,1-dibromo-2-arylethenes
we decided to explore the application of bromodesilyla-
tion procedure to 1,1-bis(trimethylsilyl)-2-arylethenes.
p-MeC6H4
m-MeC6H4
m-MeOC6H4
p-MeOC6H4
4
66
68
88
82
Br
Me
Me
4
24
24
Br
Initial studies were carried out with the 1,1-bis(trimethyl-
silyl)-2-phenylethene. After several attempts, we found
that its reaction with NBS (10 equiv), conducted in an-
hydrous acetonitrile at room temperature for four hours
exclusively afforded the bromodesilylation product, 1,1-
dibromo-2-phenylethene in good (72%) yield (entry 1,
Table 1).
MeO
MeO
Br
Br
Br
Br
To investigate the generality of this reaction, a series of
1,1-bis(silyl)-2-arylethenes bearing various substituents
in the aromatic ring was subjected to similar reaction
conditions. In a typical procedure, the 1,1-bis(silyl)-2-
arylethene was dissolved in acetonitrile at room tempera-
ture and treated with ten equivalents of NBS.14 In general,
the reactions proceeded smoothly under mild conditions
to give the corresponding b,b-dibromostyrenes in good
yields, within 4–24 hours (Table 1).
Br
6
p-NO2C6H4
48
74
Br
O2N
Me
Br
Br
7
8
p-AcC6H4
p-BrC6H4
24
4
90
78
O
Br
In all cases, the monobromodesilylation of 1,1-bis(silyl)-
2-arylethenes took place easily within one hour to form a
mixture of two stereoisomeric 1-bromo-1-silyl-2-
arylethenes (detected by GC–MS), however, the substitu-
tion of the second silyl group by bromine usually required
a longer time (4–48 h) and an increase in the amount of
NBS (from 5 equiv to 10 equiv per silyl group) did not ap-
preciably affect the rate of this process. Moreover, in the
cases of m-tolyl and p-tolyl substituted substrates (entries
2 and 3, Table 1), bromodesilylation was accompanied
with the formation of the corresponding m- and p-bro-
momethyl derivatives (22% and 18% yields, respectively)
via competitive bromination of the methyl substituents in
the phenyl ring. However, they could be easily separated
by column chromatography.
Br
Br
a Reactions performed on a 2-mmol scale with NBS (10 equiv) in
MeCN (20 mL) at r.t.
b Isolated yields of chromatographically pure products.
It is worth noting that 1,1-bis(trimethylsilyl)-2-alkenyl-
ethenes, e.g. 1,1-bis(trimethylsilyl)-4-phenylbuta-1,3-di-
ene under the same reaction conditions led to the selective
formation of the dibrominated products containing 1,3-di-
ene fragments.
As an extension to the present study we have found that
our method can be also applied to the bromination of
tetrasilyl derivative of 1,4-divinylbenzene,15 easily ob-
tained by Heck arylation of 1,1-bis(trimethylsilyl)ethene
with 1,4-diiodobenzene (Scheme 3).16
Synlett 2007, No. 13, 2061–2064 © Thieme Stuttgart · New York

LETTER
New Facile Synthesis of 1,1-Dibromo-2-arylethenes
2063
SiMe3
Br
Me3Si
NBS (20 equiv)
MeCN, r.t., 24 h
Br
(Me3Si)2C=CH2
I
I
AgNO3, Et3N
Pd(OAc)2, PPh3
MeCN, 80 °C, 2 h
SiMe3
Br
Me3Si
Br
9
10
96%
89%
Scheme 3
(12) (a) Eisch, J. J.; Foxton, M. W. J. Org. Chem. 1971, 36, 3520.
(b) Miller, R. B.; McGarvey, G. J. Org. Chem. 1978, 43,
4424. (c) Brook, M. A.; Neuy, A. J. Org. Chem. 1990, 55,
3609. (d) Tamao, K.; Akita, M.; Maeda, K.; Kumada, M.
J. Org. Chem. 1987, 52, 1100. (e) Nagao, M.; Asano, K.;
Umeda, K.; Katayama, H.; Ozawa, F. J. Org. Chem. 2005,
70, 10511.
(13) (a) Pawluc, P.; Marciniec, B.; Hreczycho, G.; Gaczewska,
B.; Itami, Y. J. Org. Chem. 2005, 70, 370. (b) Pawluc, P.;
Hreczycho, G.; Marciniec, B. J. Org. Chem. 2006, 71, 8676.
(14) A Typical Procedure for the Synthesis of 1,1-Dibromo-2-
arylethenes and Spectroscopic Data of Selected
Products: N-Bromosuccinimide (3.55 g, 20 mmol) was
added to the solution of the corresponding 1,1-bis(silyl)-2-
arylethene (2 mmol) in anhyd MeCN (20 mL) and the
suspension was stirred at r.t. for the appropriate time (see
Table 1). The solvent was then evaporated and the mixture
was extracted with n-hexane (50 mL). After extraction with
an aqueous solution of Na2S2O3 (5%, 50 mL) the organic
layer was concentrated and the crude product was preloaded
on to silica. 1,1-Dibromo-2-arylethenes were purified by
silica chromatography, eluting with n-hexane–EtOAc
(25:1).
In conclusion, a new application of 1,1-bis(trimethyl-
silyl)-2-arylethenes to the synthesis of useful 1,1-di-
bromo-2-arylethenes via NBS-based bromodesilylation is
described. Mild conditions, good functional group com-
patibility and the simplicity of the experimental technique
of this new non-Wittig approach to 1,1-dibromo-2-
arylethenes are favorable features of the reaction.
Acknowledgment
This work was made possible by a grant (PBZ-KBN 118/T09/17)
from the Ministry of Science and Higher Education (Poland).
References and Notes
(1) (a) Shen, W.; Kunzer, A. Org. Lett. 2002, 4, 1315. (b) Huh,
D. H.; Jeong, J. S.; Lee, H. B.; Ryu, H.; Kim, Y. G.
Tetrahedron 2002, 58, 9925. (c) Li, P.; Alper, H. J. Org.
Chem. 1986, 51, 4354.
(2) (a) Zapata, A. J.; Ruiz, J. J. Organomet. Chem. 1994, 479,
C6. (b) Shen, W.; Wang, L. J. Org. Chem. 1999, 64, 8873.
(c) Lin, S. T.; Lee, C. C.; Liang, D. W. Tetrahedron 2000,
56, 9619.
(3) Corey, E. J.; Fuchs, P. L. Tetrahedron Lett. 1972, 13, 3769.
(4) Wang, L.; Li, P.; Yan, J.; Wu, Z. Tetrahedron Lett. 2003, 44,
4685.
(5) (a) Hirao, T.; Masunaga, T.; Ohshiro, Y.; Agawa, T. J. Org.
Chem. 1981, 46, 3745. (b) Abbas, S.; Hayes, C. J.; Worden,
S. Tetrahedron Lett. 2000, 41, 3215. (c) Kuang, C.;
Senboku, H.; Tokuda, M. Tetrahedron 2002, 58, 1491.
(d) Ranu, B. C.; Samanta, S.; Guchhait, S. K. J. Org. Chem.
2001, 66, 4102. (e) Horibe, H.; Kondo, K.; Okuno, H.;
Aoyama, T. Synthesis 2004, 986.
(6) (a) Uenishi, J.; Kawahama, R.; Shiga, Y.; Yonemitsu, O.;
Tsuji, J. Tetrahedron Lett. 1996, 37, 6759. (b) Uenishi, J.;
Kawahama, R.; Yonemitsu, O.; Tsuji, J. J. Org. Chem. 1998,
63, 8965.
(7) (a) Xu, C.; Negishi, E. Tetrahedron Lett. 1999, 40, 431.
(b) Shen, W. Synlett 2000, 737. (c) Ogasawara, M.; Ikeda,
H.; Hayashi, T. Angew. Chem. Int. Ed. 2000, 39, 1042.
(8) (a) Lee, H. B.; Huh, D. H.; Oh, J. S.; Min, G.-H.; Kim, B. H.;
Lee, D. H.; Hwang, J. K.; Kim, Y. G. Tetrahedron 2001, 57,
8283. (b) Kabalka, G. W.; Dong, G.; Venkataiah, B.
Tetrahedron Lett. 2005, 46, 763. (c) Shi, J.; Zeng, X.;
Negishi, E. Org. Lett. 2003, 5, 1825.
(9) Shen, W.; Thomas, S. A. Org. Lett. 2000, 2, 2857.
(10) (a) Ramirez, F.; Desai, N. B.; McKelvie, N. J. Am. Chem.
Soc. 1962, 84, 1745. (b) Raw, S. A.; Reid, M.; Roman, E.;
Taylor, R. J. K. Synlett 2004, 819. (c) Shastin, V.;
Korotchenko, V. N.; Nenajdenko, V. G.; Balenkova, E. S.
Synthesis 2001, 2081.
1,1-Dibromo-2-(3-methoxyphenyl)ethene (4): yield:
1
0.514 g, 88%; yellowish oil. H NMR (CDCl3): d = 3.86
(3 H, Me), 6.88–6.96 (m, 2 H), 7.30–7.34 (m, 1 H), 7.60 (s,
1 H, CH=), 7.68–7.72 (m, 1 H). 13C NMR (CDCl3): d = 55.2
(3 H, Me), 89.6 (=CBr2), 110.3, 121.2, 124.2, 128.8, 129.9
(Ar), 132.8 (CH=), 156.4 (>COMe). MS (EI): m/z (%rel.
int.) = 292 (56) [M+], 277 (55), 210 (20), 168 (26), 132 (90),
117 (58), 102 (15), 89 (100), 74 (20), 63 (78). HRMS: m/z
[M+ + 2] calcd for C9H8Br2O: 291.8922; found: 291.8916.
1,1-Dibromo-2-(4-nitrophenyl)ethene (6): yield: 0.454 g,
74%; yellow crystals; mp 105–106 °C. 1H NMR (CDCl3):
d = 7.55 (s, 1 H, CH=), 7.68 (d, J = 8.8 Hz, 2 H, Ar), 8.24 (d,
J = 8.8 Hz, 2 H, Ar). 13C NMR (CDCl3): d = 94.3 (=CBr2),
123.3, 129.1, 134.8 (Ar), 138.5 (CH=), 141.4 (>CNO2). MS
(EI): m/z (%rel. int.) = 307 (52) [M+], 286 (78), 249 (20), 220
(25), 180 (25), 139 (95), 101 (54), 89 (30), 75 (100), 63 (20),
50 (34). HRMS: m/z [M+ + 2] calcd for C8H5Br2NO2:
306.8667; found: 306.8654.
1,1-Dibromo-2-(4-acetylphenyl)ethene (7): yield: 0.547 g,
90%; yellowish crystals; mp 73–74 °C. 1H NMR (CDCl3):
d = 2.60 (3 H, Me), 7.68 (s, 1 H, CH=), 7.30 (d, J = 8.2 Hz,
2 H, Ar), 7.76 (d, J = 8.2 Hz, 2 H, Ar). 13C NMR (CDCl3):
d = 28.9 (Me), 91.8 (=CBr2), 128.0, 135.6, 147.7 (Ar), 148.9
(CH=), 153.3 (Ar), 196.3 (CO). MS (EI): m/z (%rel. int.) =
304 (25) [M+], 289 (100), 261 (20), 180 (25), 129 (15), 101
(30), 75 (30), 50 (20). HRMS: m/z [M+] calcd for
C10H8Br2O: 303.9779; found: 303.9786.
1,1-Dibromo-2-(4-bromophenyl)ethene (8): yield: 0.531 g,
78%; colorless oil. 1H NMR (CDCl3): d = 7.60 (d, J = 8.6 Hz,
2 H, Ar), 7.52 (s, 1 H, CH=), 7.71 (d, J = 8.6 Hz, 2 H, Ar).
13C NMR (CDCl3): d = 90.2 (=CBr2), 122.6, 129.8, 132.4,
134.1 (Ar), 135.6 (CH=). MS (EI): m/z (%rel. int.) = 341
(100) [M+], 261 (45), 180 (60), 101 (46), 75 (48), 50 (40).
(11) Fleming, I.; Barbero, A.; Walter, D. Chem. Rev. 1997, 97,
2063.
Synlett 2007, No. 13, 2061–2064 © Thieme Stuttgart · New York

2064
Piotr Pawluć et al.
LETTER
(16) Synthesis of 1,4-Bis[2,2-bis(trimethylsilyl)ethenyl]
HRMS: m/z [M+ + 2] calcd for C9H5Br3: 339.7921; found:
339.7930.
benzene (9): A mixture consisting of palladium(II) acetate
(67.0 mg, 0.30 mmol), triphenylphosphine (157.2 mg, 0.6
mmol), silver nitrate (1.70 g, 10 mmol), 1,4-diiodobenzene
(5 mmol), 1,1-bis(trimethylsilyl)ethane (10 mmol, 1.72 g),
triethylamine (2.80 mL, 20 mmol) and acetonitrile (30 mL)
was placed in a 50-mL, two-necked, round-bottomed flask
equipped with a magnetic stirring bar and reflux condenser.
The suspension was heated in an oil-bath at 80 °C for 2 h.
After cooling to r.t., the reaction mixture was added to H2O
(50 mL) and extracted with pentane (2 × 30 mL). The
combined organic layers were dried (MgSO4) and the crude
product obtained was then purified by column chromatog-
raphy (silica gel, pentane) to give the pure product (2.01 g,
96%) as white crystals. 1H NMR (CDCl3): d = –0.01 (s, 18
H, SiMe), 0.18 (s, 18 H, SiMe), 7.12 (s, 4 H, Ar), 7.72 (s, 2
H, =CH). 13C NMR (CDCl3): d = 0.5 (SiMe), 2.1 (SiMe),
127.4, 141.4 (Ar), 146.3 (CH=), 154.7 (>C=). MS (EI):
m/z (%rel. int.) = 418 (10) [M+], 345 (15), 257 (10), 171
(100), 131 (10), 73 (15). HRMS: m/z calcd for C22H42Si4:
418.2363; found: 418.2348.
(15) Synthesis of 1,4-Bis(2,2-dibromoethenyl)benzene (10):
N-Bromosuccinimide (3.55 g, 20 mmol) was added to the
solution of 1,4-bis[2,2-bis(trimethylsilyl)ethenyl]benzene
(0.418 g, 1 mmol) in anhyd MeCN (50 mL) and the
suspension was stirred at r.t. for 24 h. The solvent was then
evaporated and the mixture was extracted with n-hexane (50
mL). After extraction with aqueous solution of Na2S2O3
(5%, 50 mL) the organic layer was concentrated and the
crude product was preloaded onto silica. 1,4-Bis(2,2-di-
bromoethenyl)benzene was purified by silica gel chromatog-
raphy, eluting with n-hexane–EtOAc (25:1) (0.397 g, 89%;
white crystals; mp 108–109 °C). 1H NMR (CDCl3): d = 7.39
(s, 2 H, CH=), 7.68 (s, 4 H, Ar). 13C NMR (CDCl3): d = 90.4
(=CBr2), 128.4, 132.3 (Ar), 136.2 (CH=). MS (EI):
m/z (%rel. int.) = 446 (100) [M+], 365 (12), 286 (30), 206
(18), 126 (48), 63 (25). HRMS: m/z [M+] calcd for C10H6Br4:
445.7162; found: 445.7176.
Synlett 2007, No. 13, 2061–2064 © Thieme Stuttgart · New York

Copyright of Synlett is the property of Georg Thieme Verlag Stuttgart and its content may not
be copied or emailed to multiple sites or posted to a listserv without the copyright holder's
express written permission. However, users may print, download, or email articles for
individual use.