Stereoselective synthesis of (Z)-β-arylvinyl bromides from anti-2,3-dibromo-3-arylpropanoic acids

Article abstract of DOI:10.3184/174751914X13896335381533

A novel method for the stereoselective synthesis of (Z)-β-arylvinyl bromides in excellent yields by debrominative decarboxylation of anti-2,3-dibromo-3-arylpropanoic acids using NaN₃ was developed. This facile transformation was achieved under room temperature for 1-2 h.

Full text of DOI:10.3184/174751914X13896335381533

JOURNAL OF CHEMICAL RESEARCH 2014
FEBRUARY, 115–117
RESEARCH PAPER 115
Stereoselective synthesis of (Z)-β-arylvinyl bromides from
anti-2,3-dibromo-3-arylpropanoic acids
Wenjing Xva*, Wensheng Zhanga, Fei Zhangb and Chunxiang Kuangc
aSchool of Science, Jiaozuo Teachers’ College, Shanyang Road 998, Jiaozuo 450001, P.R. China
bJiaozuo Vocational Education Center, Huayuan Road 57, Jiaozuo 454001, P.R. China
cDepartment of Chemistry, Tongji University, Shanghai 200092, P.R. China
A novel method for the stereoselective synthesis of (Z)-β-arylvinyl bromides in excellent yields by debrominative decarboxylation
of anti-2,3-dibromo-3-arylpropanoic acids using NaN3 was developed. This facile transformation was achieved under room
temperature for 1–2 h.
Keywords: stereoselective synthesis, (Z)-β-arylvinyl bromide, decarboxylation, NaN3
(Z)-β-Arylvinyl bromides are versatile precursors in
many useful organic transformations including the Stille,1
Suzuki,2,3 Ulmann,4 and Sonogashira5,6 couplings, as well as
the Buchwald7 methodology for stereospecific synthesis of
substituted alkenes. Some efficient methods for the synthesis
of stereoseletive (Z)-β-arylvinyl bromides have been reported.
The most common include Wittig olefination of an aldehyde
with bromomethylene triphenylphosphoran,8–11 boron–bromine
or silicon–bromine exchange of vinyl boronates (boronic
acids)12,13 or vinylsilanes,14 hydroboration-protonolysis of
haloalkynes,15,16 palladium-catalysed reductive removal
of one bromide from 1,1-dibromo-1-alkenes by tributyltin
hydride,17,18 Julia olefination between aromatic aldehydes and
α‑bromomethyl sulfones,19 and debrominative decarboxylation
of cinnamic and acrylic acids dibromides.20–28 Among these
reports, debrominative decarboxylation of cinnamic acid
dibromides using a variety of bases in different organic solvents
might be the most effective, which deserves attention because
the starting substrates are readily available and the procedure
is very convenient. Our group has described a rapid method
for an efficient and stereoselective synthesis of (Z)-β-arylvinyl
bromides from the corresponding 2,3-dibromoalkanoic acids
using a Et3N/DMF system under microwave irradiation.25,26
Functionalised (Z)-β-arylvinyl bromides can be also
formed by using an one-pot synthetic strategy under the
same decarboxylation system.27 We also demonstrated that
diverse range of alkyl and aryl amines.28 Ranu and co-authors
found that basic ionic liquid, [bmIm]OH could be an effective
promoter for the debrominative decarboxylation.29 However,
heating, microwave irradiation or excess organic amines were
needed in most reports.
Besides organic base, NaN3 might be an effective
decarboxylation reagent. We have developed an one-pot
method for the preparation of 4-aryl-1H-1,2,3-triazoles from
anti-3-aryl-2,3-dibromopropanoic acids and NaN3 catalysed
by Pd2(dba)3 and Xantphos in moderate to high yields,30
where the debrominative decarboxylation of anti-3-aryl-2,3-
dibromopropanoic acids by NaN3 giving the (Z)-β-arylvinyl
bromides played a key role in the two-step transformation.
However, the (Z)-β-arylvinyl bromide intermediates were not
isolated in this report.
We now describe the use of NaN3/DMF system for the
synthesis of stereoselective (Z)-β-arylvinyl bromides
2
by debrominative decarboxylation of anti-2,3-dibromo-3-
arylpropanoic acids 1 at room temperature (Scheme 1). This
method might be an alternative to the previous report due to
its convenience, excellent yields and mild reaction condition
without the use of either microwave irradiation or excess
organic amines.
A possible mechanism for this conversion is shown in
Scheme 2. The mild condition and high efficiency should be
attributed to the release of HN3 from the system by alkalisation
of –CO2H during the formation of intermediates A, which
favours the reaction equilibrium shifting, hence, promoting the
following debrominative decarboxylation process.
stereoselective
(Z)-4-(2-bromovinyl)benzenesulfonamides
could be afforded by microwave-induced simultaneous
debrominative decarboxylation and sulfamation of anti-2,3-
dibromo-3-(4-chlorosulfonylphenyl)propanoic acid using a
Br
NaN3 (1.1eq.)
Ar
CO2H
Ar
Br
DMF
rt, 1 - 2 h
Br
1
2
Scheme 1
Ο
O
Br
Ar
NaN3
- NaBr
Ar
Br
H
H
CO2H
Br
Ar
Br
CO2
HN3
Br
A
2
1
Scheme 2
* Correspondent. E-mail: jzszzws@163.com
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116 JOURNAL OF CHEMICAL RESEARCH 2014
(Z)-β-Bromostyrene (2a):14,26 Colourless oil; IR (neat) 1611, 1594,
1488, 928, 768 cm–1; 1H NMR (400 MHz, CDCl3): δ=6.43 (1H, d,
J=8.2 Hz), 7.07 (1H, d, J=8.2 Hz), 731–7.40 (3H, m), 7.66–7.69 (2H, m).
(Z)-β-Bromo-4-methylstyrene (2b):22,26 Colourless oil; IR (neat)
1603, 1557, 1490, 945 cm–1. 1H NMR (400 MHz, CDCl3): δ=2.36
(3H, s), 6.36 (1H, d, J=7.9 Hz), 7.02 (1H, d, J=7.9 Hz), 7.17 (2H, d,
J=7.9 Hz), 7.58 (2H, d, J=7.9 Hz).
Results and discussion
Our initial attempt began with the debrominative
decarboxylation of anti-2,3-dibromo-3-arylpropanoic acid
1a. The experiment was carried out with 1a (1 mmol), NaN3
(1.1 mmol) in DMF. The reaction mixture was stirred at room
temperature for 1 h. The expected product 2a was afforded in
94% yield (Table 1, entry 1). Various solvents were examined to
optimise the yield and stereoselectivity of 2. It was found that
CH2Cl2 and THF were less satisfactory as solvents than DMF.
While DMF turned out to be the most effective solvent for the
stereocontrolled preparation of (Z)-β-arylvinyl bromides, the
dropwise addition of compound 1 in DMF to the suspension of
NaN3 in DMF was also necessary for the reaction efficiency.
Other dibromo-3-arylpropanoic acids besides 1a were
employed successfully using the same conditions for 1–2 h
(entries 2–8). This reaction system proved to be applicable
for aromatic ring bearing both electron-donating groups such
as Me (entry 2) and electron-withdrawing groups like F, Cl,
Br and CO2Me, affording products 2b–g in 80–94% yields
(entries 3–7). The steric hindrances of the substituents like
Cl on the ortho-position of the aromatic ring (entry 6) did
not alter the efficiency of the reaction. Interestingly, anti-2,3-
dibromo-3-(4-(chlorosulfonylphenyl)propanoic acid 1h could
smoothly convert to the corresponding (Z)-4-(2-bromovinyl)
benzenesulfonyl azide 2h in a high yield of 95% when 2.2 equiv.
of NaN3 was used (entry 8).
(Z)-β-Bromo-4-fluorostyrene (2c):26 Colourless oil; IR (neat) 1609,
1
1510, 1327, 1230 cm–1. H NMR (400 MHz, CDCl3): δ=6.38 (1H, d,
J=8.2 Hz), 6.97–7.07 (3H, m), 7.61–7.67 (2H, m).
(Z)-β-Bromo-4-chlorostyrene (2d):26 Colourless oil; IR (neat) 1616,
1580, 1490, 1010, 725 cm–1. 1H NMR (400 MHz, CDCl3): δ=6.45 (1H,
d, J=7.9 Hz), 7.12 (1H, d, J=7.9 Hz), 7.34 (2H, d, J=8.2 Hz), 7.62 (2H,
d, J=8.2 Hz).
(Z)-β-Bromo-4-bromostyrene (2e):26 Colourless oil; IR (neat) 1616,
1
1575, 1495, 1013 cm–1. H NMR (400 MHz, CDCl3): δ=6.45 (1H, d,
J=8.2 Hz), 6.98 (1H, d, J=8.2 Hz), 7.48 (2H, d, J=8.6 Hz), 7.54 (2H, d,
J=8.6 Hz).
(Z)-β-Bromo-2-chlorostyrene (2f):26 Colourless oil; IR (neat) 1616,
1589, 1461, 1435, 949 cm–1. 1H NMR (400 MHz, CDCl3): δ=6.59 (1H,
d, J=8.2 Hz), 7.23–7.31 (3H, m), 7.37–7.44 (1H, m), 7.80–7.84 (1H, m).
(Z)-Methyl-4-(β-bromovinyl)benzoate (2g):26 M.p. 43–44 °C (hexane,
lit: 43–44°C); IR (film) 1716, 1605, 1579, 961 cm–1. 1H NMR (400 MHz,
CDCl3): δ=3.93 (3H, m), 7.56 (1H, d, J=8.2 Hz), 7.12 (1H, d, J=8.2 Hz),
7.74 (2H, d, J=8.6 Hz), 8.04 (2H, d, J=8.6 Hz).
(Z)-4-(β-Bromovinyl)benzenesulfonyl azide (2h): Light yellow
liquid. IR (KBr): 2128, 1601, 1479, 1369, 1173 cm–1. 1H NMR
(400 MHz, CDCl3): δ 6.70 (1H, d, J=8.3 Hz), 7.16 (1H, d, J=8.3 Hz),
7.89 (2H, d, J=8.5 Hz), 7.96 (2H, d, J=8.5 Hz). 13C NMR (125 MHz,
CDCl3): δ 111.06, 127.45, 129.92, 130.56, 137.48, 141.43.
Table 1 Synthesis of (Z)-β-arylvinyl bromides 2 using NaN3/DMF system
Entry
Ar
Product
Time/h Yield of 2/% a,b
Conclusion
1
2
3
4
5
6
7
8c
C6H5
1a
1b
1c
1d
1e
1f
2a
2b
2c
2d
2e
2f
1
94
97
94
93
95
91
92
95
In conclusion, we have developed a new method for the synthesis
of (Z)-β-arylvinyl bromides by debrominative decarboxylation
of anti-2,3-dibromo-3-arylpropanoic acids using NaN3/DMF
system under mild conditions.
4-Me-C6H4
4-F-C6H4
1
2
4-Cl-C6H4
4-Br-C6H4
2-Cl-C6H4
1.5
1.5
2
4-MeO2C-C6H4
4-ClO2S-C6H4
1g
1h
2g
2h
2
2
This work was supported by the National Natural Science
Foundation of China (No. 21272174), Program for Science
& Technology Innovation Talents in Universities of Henan
Province (No. 2011HASTIT032), Foundation of Henan
Scientific and Technological Committee (No. 132300410206,
No. 132300410167), Foundation of Henan Educational
Committee (No. 14B150056) and Foundation of Jiaozuo
Scientific and Technological Bureau (No. 2012017).
aIsolated yields based on anti-2,3-dibromo-3-arylpropanoic acids 1.
bZ/E>98%, determined by 1H NMR.
c2.2 equiv. of NaN3 was used.
Experimental
Melting points were recorded using a WRS-1B digital melting point
apparatus and are uncorrected. H NMR and 13C NMR spectra were
1
Received 25 November 2013; accepted 31 December 2013
Paper 1302304 doi: 10.3184/174751914X13896335381533
Published online: 5 February 2014
recorded using Bruker DPX-400 spectrometer in CDCl3 with SiMe4
as an internal standard. Commercially obtained reagents were used
without further purification. All reactions were monitored by TLC
with HuanghaiGF254 silica gel coated plates. Column chromatography
was carried out using 300–400 mesh silica gel at medium pressure.
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