TsNBr2 promoted decarboxylative bromination of α,β-unsaturated carboxylic acids

Article abstract of DOI:10.1016/j.tetlet.2018.11.041

A rapid process for decarboxylative bromination of α,β-unsaturated carboxylic acids have been developed using N,N-dibromo-p-toluenesulfonamide (TsNBr₂). Treatment of cinnamic acids with TsNBr₂ in presence of potassium carbonate in acetonitrile produces corresponding β-bromostyrenes at room temperature. Exclusive formation of (E)-β-bromostyrenes was observed in a stereoselective manner within a very short period of time (5–15 min). This method was further extended for obtaining 1-bromoalkynes from corresponding propiolic acids. Instantaneous formation of bromoalkynes was observed when the reaction was carried out in presence of DBU as a base in acetonitrile at room temperature. A wide variety of cinnamic acids and propiolic acids could be converted to corresponding β-bromostyrenes and 1-bromoalkynes respectively under mild reaction condition with high to excellent yield.

Full text of DOI:10.1016/j.tetlet.2018.11.041

Accepted Manuscript
TsNBr2 promoted decarboxylative bromination of α,β-unsaturated carboxylic
acids
Debojit Hazarika, Prodeep Phukan
PII:
S0040-4039(18)31379-0
https://doi.org/10.1016/j.tetlet.2018.11.041
TETL 50426
DOI:
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
30 August 2018
12 November 2018
13 November 2018
Please cite this article as: Hazarika, D., Phukan, P., TsNBr2 promoted decarboxylative bromination of α,β-
unsaturated carboxylic acids, Tetrahedron Letters (2018), doi: https://doi.org/10.1016/j.tetlet.2018.11.041
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Graphical Abstract
Leave this area blank for abstract info.
TsNBr2 promoted decarboxylative bromination
of α,β-unsaturated carboxylic acids
Debojit Hazarika and Prodeep Phukan
COOH
R1
R3
COOH
R2
Br
O
R1
R3
Br
S O
R2
K2CO3, CH3CN,
DBU, CH3CN,
instantaneous,
rt
N
Br
Br
5-15 min,
rt
11 examples
76-93% yield
13 examples
72-92% yield
wide functional group tolerance

TsNBr2 promoted decarboxylative bromination of α,β-unsaturated
carboxylic acids
Debojit Hazarika and Prodeep Phukan*
Department of Chemistry, Gauhati University, Guwahati, 781014, Assam, India
E-mail: pphukan@yahoo.com
Abstract: A rapid process for decarboxylative bromination of α,β-unsaturated carboxylic acids
have been developed using N,N-dibromo-p-toluenesulfonamide (TsNBr2). Treatment of cinnamic
acids with TsNBr2 in presence of potassium carbonate in acetonitrile produces corresponding β-
bromostyrenes at room temperature. Exclusive formation of (E)-β-bromostyrenes was observed
in a stereoselective manner within a very short period of time (5-15 min). This method was
further extended for obtaining 1-bromoalkynes from corresponding propiolic acids.
Instantaneous formation of bromoalkynes was observed when the reaction was carried out in
presence of DBU as a base in acetonitrile at room temperature. A wide variety of cinnamic acids
and propiolic acids could be converted to corresponding β-bromostyrenes and 1-bromoalkynes
respectively under mild reaction condition with high to excellent yield.
Key words: decarboxylative bromination, TsNBr2, β-bromostyrene, 1-bromoalkyne, cinnamic
acid, propiolic acid

Halogenated organic substrates serve as an useful class of synthons for various organic
transformations.1 Synthesis of organic halides via decarboxylative bromination of α,β-
unsaturated carboxylic acids, classically known as the Hunsdiecker reaction, is an important
reaction for organic chemist.2 The original Hunsdiecker reaction and subsequent developments
for enhancing the synthetic utility of the classical reaction itself suffered from major drawbacks
such as low yield of the desired product, high reaction temperature and use of toxic molecular
bromine along with heavy metal salts.3
In past few decades, different methodologies involving radical or electrophilic
halogenium ion pathway were developed to overcome the limitations associated with the
classical processes.4 Stoichiometric combination of a brominating agent and an additive viz.
NBS/PhIO,4c
TBAB/IBX,4d
NBS/LiOAc,4e,4f,4g,4h
NaBr/Oxone,4i
TEAB/PhI(OAc)2,4j
KBr/Selectfluor,4k
LiBr/CAN,4l,4m
bis(collidine)bromine(I)
hexafluorophosphate4n,
ethylenebis(N-methylimidazolium) ditribromide4o etc. were used for oxidative decarboxylative
bromination of cinnamic acids. Roy and coworkers used NBS for bromodecarboxylation both
under transition metal catalyzed and metal-free conditions.5,6 Catalysts based on molybdenum
and tungsten were also used for synthesis of β-bromostyrenes in presence of KBr and H2O2.7,8
Synthetic methodologies assisted by ionic liquid [bmim][Br3]/[bmim]Br, micellar media,
ultrasonic reaction condition and electrolysis phenomena are also prevalent in the literature for
synthesis of β-bromostyrenes from cinnamic acids.9 But the major drawback associated with
most of the protocol corresponds to the variation of reaction yield and time for different
substrates depending upon the substitution pattern. In many cases, electron rich cinnamic acid
produces good yield within a shorter period of time compared to cinnamic acid having electron
withdrawing groups or halo functionalities. In certain cases the assistance of a micro-wave

condition is also necessary for specific substrates to minimize the reaction time for moderate
yield of the desired product.
Telvekar and coworkers achieved considerable success in bromodecarboxylation of both
electron rich and electron poor cinnamic acids using variety of reagent combinations.10 They
explored two different iodine reagents Dess-Martin-Perodinane (DMP) and diphosphorous
tetraiodide (DPTI) respectively as oxidant for promoting the transformation using
tetraethylammonium bromide (TEAB) as the bromine source,.10a-b DMP provided higher yield
for electron rich cinnamic acids at a faster rate whereas DPTI gave good results for electron poor
cinnamic acids and vice-versa. Further extending their bromodecarboxylative protocol, the same
group also reported the transformation of cinnamic acids using NaNO2 as catalyst in presence of
48% aq. HBr.10c However the efficiency of this protocol relies upon the use of O2 as the external
oxidant. So the development of a process which could minimize or overcome the inefficiency of
the existing ones is of utmost importance.
N,N-Dibromo-p-toluenesulfonamide (TsNBr2), an efficient source of electrophilic
bromine, has been established as a powerful and efficient reagent by our group for various
organic transformations.11,12 In continuation of our work on this reagent,12 we are reporting
herewith very fast and mild protocols for bromodecarboxylation reactions using TsNBr2 as
bromine source (Scheme 1).
COOH
R1
R3
COOH
O
Br
R2
R1
R3
Br
S O
DBU, CH3CN,
rt
K2CO3, CH3CN,
rt
R2
N
Br
Br
TsNBr2
Scheme 1. Decarboxylative bromination using TsNBr2.

For the synthesis of β-bromostyrenes, initial investigations were carried out using
cinnamic acid as the model substrate (Table 1). The experiment was carried out by adding
TsNBr2 (1 mmol) to a solution of cinnamic acid (1 mmol) and NaOH (2 mmol) in acetonitrile (2
mL) at room temperature. The reaction produced the desired product in 40% yield after 2h of
reaction (Table 1, entry 1). When NaOH was replaced with equimolar amount of Et3N, the
reaction afforded 57% yield within 1h (Table 1, entry 2).
Table 1. Optimization of reaction condition for synthesis of β-bromostyrene from cinnamic acid.
Br
COOH
TsNBr2
base, solvent,
rt
S. No. Base (equiv.) TsNBr2 (equiv.)
Solvent
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
Ethylacetate
DCM
Time (min) % Yieldb
1
2
NaOH (2)
Et3N (2)
1
1
120
40
57
94c
85
87
92
93
77
89
81
84
60
3
DBU (2)
1
Instantaneous
4
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (1)
K2CO3 (1.5)
K2CO3 (2)
K2CO3 (2)
1
5
5
5
1.05
1.1
1.2
1.1
1.1
1.1
1.1
6
5
7
5
8
15
5
9
10
11
60
20
aReaction condition: cinnamic acid (1mmol), solvent (2 mL), rt; bIsolated yield;
cmixture of cis:trans isomers (1:2).

Further modification of the reaction condition using DBU as base could produce corresponding
β-bromostyrene instantaneously with a yield of 94% (Table 1, entry 3). However, the product
was found to compose of a mixture of both the isomers E and Z in the ratio 2:1 respectively.
Hence, the reaction was further examined in presence of 2 equivalent of K2CO3. This particular
variation of the reaction condition led to exclusive formation of trans isomer of the desired β-
bromostyrene (85%) within 5 min (Table 1, entry 4) at room temperature. In presence of DBU,
the reaction is likely to proceed via formation of a carbocation intermediate4s where consecutive
decarboxylation leads to the formation of a mixture of cis-trans isomers. Whereas, using K2CO3
as the base, a bromonium ion intermediate is expected where ring opening and decarboxylation
occurs in a concerted manner. Next the reaction was investigated by varying the amount of
TsNBr2 and base to enhance the performance of the reaction (Table 1, entries 5-9). With 1.1
equivalent of TsNBr2, the reaction provided 92% of β-bromostyrene (Table 1, entry 6). However
with lower amount of K2CO3, diminishing yield of the desired product was observed (Table 1,
entries 8-9). Effect of solvent in the reaction yield was also investigated using solvents like
ethylacetate and DCM which produced inferior results with longer reaction time (Table 1, entries
10-11).
Having the optimized reaction condition in hand, the process was extended to a variety of
cinnamic acids (Table 2).13 From Table 2, it can be seen that the reaction completes within a very
short time to produce corresponding β-bromostyrenes with excellent yield. The type and position
of different functional groups in the aromatic ring do not have significant effect on the yield and
reaction time. Cinnamic acids having both electron donating and electron withdrawing groups in
the aromatic ring gave the desired product in excellent yield within a short time. Comparable
reactivity was also observed for different halo-substituted cinnamic acids under the optimized
reaction condition (Table 2, 1c-1f). Moreover cinnamic acid having substitution in the double

bond also gave the desired product in high yield (Table 2, 1m). The method was found to be
highly stereoselective producing exclusively the trans-isomer (E-isomer) of the desired product.
Stereoselectivity was confirmed by analyzing the NMR spectral data and comparing with those
reported in the literature.
Table 2. Substrate scope for synthesis of β-bromostyrene
COOH
Br
Br
TsNBr2 (1.1equiv.)
K2CO3 (2 equiv.),
CH3CN (2 mL), rt,
5-15 min
R
R
1a-m
Br
Br
Br
1a, 5 min, 92%
1b, 5 min, 91%
1c, 5 min, 87%
Br
Br
Br
F
Br
Cl
1d, 5 min, 88%
1e, 10 min, 84%
1f, 5 min, 83%
Br
Br
Br
Br
Cl
NO2
Cl
F
1g, 10 min, 85%
1h, 5 min, 80%
1i, 15 min, 72%
Br
Br
O
O
Cl
1j, 5 min, 78%
1k, 10 min, 80%
Br
Br
O
O
1l, 15 min, 81%
1m, 15 min, 86%

aReaction condition: cinnamic acid (1 mmol), TsNBr2 (1.1 mmol),
K2CO3 (2 mmol), CH3CN (2 mL), rt.
A probable mechanistic pathway to explain the decarboxylative bromination mechanism
is illustrated in Scheme 2. Initially, the base abstract the acidic proton to produce the carboxylate
ion intermediate I, which upon subsequent reaction with TsNBr2 results in the formation of
bromonium intermediate II. Simultaneous ring opening of the bromonium ion along with
elimination of carbon dioxide give the trans-β-bromostyrene.4q
O
O
O
Br
K2CO3
Br
-CO2
TsNBr2
OH
O
O
I
II
Scheme 2. Plausible mechanism for decarboxylative bromination of cinnamic acid.
Successful and quick transformation of various cinnamic acids to corresponding vinyl
bromides encouraged us to extend the reaction to propiolic acids. So, we intended to examine the
possibility of decarboxylative bromination of aryl propiolic acids using TsNBr2. 1-Bromoalkynes
serve as important building blocks in organic, material as well as polymer synthesis.14 Compared
to cinnamic acids, methods for decarboxylative bromination of propiolic acids are limited and
only a few are reported in the literature.4p,6b,7b,15 Lee et al established the same protocol using
Oxone/NaBr for decarboxylative bromination of aryl propiolic acids after successful
bromodecarboxylation of cinnamic acids.16 Recently Liu’s group reported copper mediated
synthesis of 1-bromoalkynes from aryl propiolic acids in presence of pyridine under heating
condition.17
While optimizing the reaction condition for cinnamic acid, we observed that using DBU
as the base, the reaction goes for completion instantaneously to form a corresponding isomeric
mixture of cis- and trans- vinyl bromide (Table 1, entry 3). However using propiolic acid as the

starting substrate, it invalidates the stereoselectivity factor. Hence, we examined the possibility
of using DBU in case of propiolic acids. Initial reaction was carried out by treating a solution of
phenyl propiolic acid (1 mmol) in acetonitrile (2 mL) with TsNBr2 (1 mmol) in presence of DBU
(1 mmol) at room temperature which produced corresponding 1-bromoalkyne instantaneously
with 81% yield (Table 3, entry 1).
Table 3. Optimization of reaction condition for synthesis of 1-bromoalkyne from propiolic acid.
TsNBr2
COOH
Br
base, solvent,
rt
S. No. Base (equiv.) TsNBr2 (equiv.) Solvent
Time (min)
% yieldb
81
1
2
3
4
5
6
7
8
9
DBU (1)
DBU (1)
DBU (1)
DBU (1)
DBU (1.2)
DBU (1)
DBU (1)
K2CO3 (1)
Et3N (1)
1
CH3CN Instantaneous
CH3CN Instantaneous
CH3CN Instantaneous
CH3CN Instantaneous
CH3CN Instantaneous
1.05
1.1
1.2
1.2
1.2
1.2
1.2
1.2
87
91
91
90
DCM
EtOAc
CH3CN
CH3CN
10
60
30
60
81
84
87
64
aReaction condition: phenyl propiolic acid (1 mmol); solvent (2 mL), rt; bIsolated yield
Enhancement in the reaction yield was observed by increasing the amount of TsNBr2 to 1.1
mmol, with further increment being ineffective (Table 3, entries 2-4). The amount of base was
also varied which could not afford any remarkable results (Table 3, entry 5). Solvents like DCM
and ethylacetate were also effective but acetonitrile was found to be the better solvent with

respect to reaction time and yield (Table 3, entries 6-7). Investigation of other bases such as
K2CO3 and Et3N were also carried out which failed to produce any better results (Table 3, entries
8-9).
Table 4. Substrate scope for synthesis of 1-bromoalkyne
TsNBr2 (1.1equiv.)
R
COOH
Br
R
Br
DBU (1 equiv.),
CH3CN (2 mL), rt,
instantaneous
2a-k
Br
Br
C3H7
2a, 91%
2b, 87%
2c, 90%
Br
Br
Br
Br
Br
C4H9
Br
2d, 93%
2g, 87%
2e, 91%
2f, 84%
Br
O2N
F
O
2h, 89%
2i, 83%
Br
S
Br
n-C4H9
2k, 80%b
2j, 76%
aReaction condition: propiolic acid (1mmol), TsNBr2 (1.1 mmol), DBU (1 mmol),
CH3CN (2 mL), instantaneous, rt; bReaction time = 30 min
Under the optimized condition, the scope of the reaction was explored. A wide variety of
phenyl propiolic acid having different functionalities could be transformed to corresponding 1-
bromoalkyne in excellent yield (Table 4).18 It was observed that the presence of electron

donating or withdrawing groups in the aromatic ring has no significant impact on the outcome of
the reaction. Heterocyclic and alkyl propiolic acids were also tested, which participated well to
produce the desired products in high yield (Table 4, 2j-k). However, in case of alkyl propiolic
acid, the reaction requires 30 min for completion.
In conclusion, simple and efficient protocols for decarboxylative bromination of α,β-
unsaturated carboxylic acids have been established using TsNBr2 in presence of K2CO3 at room
temperataure. A comparable reactivity pattern was observed for different cinnamic acids
irrespective of the substituent present in the aromatic ring. High stereoselectivity of the reaction
with exclusive formation of E-isomer makes the process more useful. The procedure could
further be extended for the synthesis of 1-bromoalkynes from aryl propiolic acids. The use of
DBU as a base was found to be beneficial for transformation of propiolic acids to corresponding
1-bromoalkyne instantaneously with excellent yield. The significance of the process relies on
very fast, mild and operationally simple reaction conditions along with wide substrates scope and
excellent yield of the desired products.
Acknowledgement
Financial support from SERB, India (Grant No. EMR/2016/007883) is gratefully acknowledged.
DH thanks UGC, India, for BSR fellowship.
References
1. (a) Tsuji, J. Reactions of Organic Halides and Pseudohalides, Transition Metal Reagents and
Catalysts: InnoVations in Organic Synthesis; Wiley: New York, 2000; pp 27. (b) Meijere, A.;

Diederich, F. Metal-Catalyzed Cross-Coupling Reactions; 2nd edn.; Wiley-VCH: Weinheim,
2004; pp 1-916.
2. Hunsdiecker CH. Ber. Dtsch. Chem. Ges. B. 1942; 75: 291-297.
3. Johnson RG, Ingham RK. Chem. Rev. 1956; 56: 219-269.
4. (a) Borah AJ, Yan G. Org. Biomol. Chem. 2015; 13: 8094-8115. (b) Barton DHR, Lather B,
Zard SZ. Tetrahedron Lett. 1985; 26: 5939-5942. (c) Graven A, Jørgensen KA, Dahl S, Stanczak
A. J. Org. Chem. 1994; 59: 3543-3546. (d) Han J, Wei Y. J. Chem. Res. 2012; 247-248. (e)
Chowdhury S, Roy S. J. Org. Chem. 1997; 62: 199-200; (f) Bazin M-A, Kihel LE, Lancelot J–C,
Rault S. Tetrahedron Lett. 2007; 48: 4347-4351. (g) Kuang C, Senboku H, Tokuda M. Synlett
2000; 10: 1439-1442. (h) Kuang C, Yang Q, Senboku H, Tokuda M. Synthesis 2005; 8: 1319-
1325. (i) You H–W, Lee K–J. Synlett 2001; 105-107. (j) Fursule RA, Patil PO, Shewale BD,
Kosalge SB, Deshmukh PK, Patil DA. Chem. Pharm. Bull. 2009; 57: 1243-1245. (k) Ye C,
Shreeve JM. J. Org. Chem. 2004; 69: 8561-8563. (l) Roy SC, Guin C, Maiti C. Tetrahedron Lett.
2001; 42: 9253-9255. (m) Nikishin GI, Sokova LL, Makhaev VD, Kapustina NI. Russ. Chem.
Bull. 2008; 57: 118-123. (n) Homsi F, Rousseau G. J. Org. Chem. 1999; 64: 81-85. (o)
Hosseinzadeh R, Tajbakhsh M, Mavvaji M, Lasemi Z. Res. Chem. Intermed. 2015; 41: 2427-
2436. (p) Homsi F, Rousseau G. Tetrahedron Lett. 1999; 40: 1495-1498. (q) Huang Y–L, Cheng
Y–H, Hsien K–C, Chen Y–L, Kao C–L. Tetrahedron Lett. 2009; 50: 1834-1837. (r) Ganguly
NC, De P, Dutta S. Synthesis 2005; 7: 1103-1108. (s) Tang KG, Kent GT, Erden I, Wu W.
Tetrahedron Lett. 2017; 58: 3894-3896.
5. Chowdhury S, Roy S. Tetrahedron Lett. 1996; 37: 2623-2624.
6. (a) Naskar D, Roy S. Tetrahedron 2000; 56: 1369-1377. (b) Das JP, Roy S. J. Org. Chem.
2002; 67: 7861-7864.

7. (a) Sinha J, Layek S, Mandal GC, Bhattacharjee M. Chem. Commun. 2001; 1916-1917. (b)
Roya S, Bharb S. Green Chemistry Letters and Reviews 2010; 3: 341-347.
8. Choudary BM, Someshwar T, Kantam ML, Reddy CV. Catal. Commun. 2004; 5: 215-219.
9. (a) Wang C, Bao W, Zhang X. J. Chem. Res. 2005; 617-619. (b) Rajanna KC, Reddy NM,
Reddy MR, Saiprakash PK. J. Dispersion Sci. Technol. 2007; 28: 613-616. (c) Kumar MS,
Rajanna KC, Venkanna P, Venkateswarlu M, Chary VS. Synth. React. Inorg. Met.-Org. Chem.
2016; 46: 642-646. (d) Bi M–X, Qian P, Wang Y–K, Zha Z–G, Wang Z–Y. Chin. Chem. Lett.
2017; 28: 1159-1162.
10. (a) Telvekar VN, Arote ND, Herlekar OP. Synlett 2005; 2495-2497. (b) Telvekar VN,
Chettiar SN. Tetrahedron Lett. 2007; 48: 4529-4532. (c) Telvekar VN, Takale BS. Tetrahedron
Lett. 2011; 52: 2394-2396.
11. (a) Saikia I, Borah AJ, Phukan P. Chem. Rev. 2016; 116: 6837-7042. (b) Rajbongshi KK,
Borah AJ, Phukan P. Synlett 2016; 27: 1618-1634.
12. (a) Phukan P, Chakraborty P, Kataki D. J. Org. Chem. 2006; 71: 7533-7537. (b) Saikia, I.;
Phukan, P. Tetrahedron Lett. 2009; 50: 5083-5087; (c) Saikia I, Chakraborty P, Phukan P.
ARKIVOC 2009; (xiii): 281-286. (d) Saikia I, Kashyap B, Phukan P. Synth. Commun. 2010; 40:
2647-2652. (e) Saikia I, Kashyap B, Phukan P. Chem. Commun. 2011; 47: 2967-2969. (f) Borah
AJ, Phukan P. Chem. Commun. 2012; 48: 5491-5493. (g) Saikia I, Rajbongshi, KK, Phukan P.
Tetrahedron Lett. 2012; 53: 758-761. (h) Borah AJ, Phukan P. Tetrahedron Lett. 2012; 53: 3035-
3037. (i) Rajbongshi KK, Phukan P. Tetrahedron Lett. 2014; 55: 1877; (j) Rajbongshi KK,
Sarma MJ, Phukan P. Tetrahedron Lett. 2014; 55: 5358-5360; (k) Rajbongshi KK, Hazarika D,
Phukan P. Tetrahedron Lett. 2015; 56: 356-358. (l) Saikia I, Chakraborty P, Sarma MJ, Goswami
M, Phukan P. Synth. Commun. 2015; 45: 211-217; (m) Rajbongshi KK, Saikia I, Chanu LD, Roy
S, Phukan P. J. Org. Chem. 2016; 81: 5423-5432; (n) Sarma MJ, Phukan P. Synth. Commun.

2016; 46: 257-262. (o) Rajbongshi KK, Hazarika D, Phukan P. Tetrahedron 2016; 72: 4151-
4158. (p) Hazarika D, Phukan P. Tetrahedron 2017; 73: 1374-1379.
13. General procedure for synthesis of β-Bromostyrene: To a solution of cinnamic acid (1
mmol) in CH3CN (2 mL), TsNBr2 (1.1 mmol) and K2CO3 (2 mmol) was added and stirred at
room temperature. After completion of the reaction (monitored by TLC), water was added. The
aqueous layer was extracted using dichloromethane (30 mL), dried over anhydrous Na2SO4 and
concentrated. The crude product was purified by flash chromatography using petroleum ether as
eleunt.
14. (a) Xie L, Wu Y, Yi W, Zhu L, Xiang J, He W. J. Org. Chem. 2013; 78: 9190-9195. (b) Chen
ZW, Ye D–N, Ye M, Zhou Z–G, Li S–H, Liu L–X. Tetrahedron Lett. 2014; 55: 1373-1375. (c)
Chen Z, Jiang H, Li Y, Qi C. Chem. Commun. 2010; 8049-8051. (d) Trofimov A, Chernyak N,
Gevorgyan V. J. Am. Chem. Soc. 2008; 130: 13538-13539. (e) Okamoto K, Watanabe M, Sakata
N, Murai M, Ohe K. Org. Lett. 2013; 15: 5810-5813. (f) Usanov DL, Yamamoto H. J. Am.
Chem. Soc. 2011; 133: 1286-1289. (g) Tang JS, Tian M, Sheng WB, Guo CC. Synthesis 2012;
44: 541-546. (h) Xue Y–X, Zhu Y–Y, Gao L–M, He X–Y, Liu N, Zhang W–Y, Yin J, Ding Y,
Zhou H, Wu Z–Q. J. Am. Chem. Soc. 2014; 136: 4706-4713. (i) Löppenberg M, Müller H, Pulina
C, Oddo A, Teese M, Jose J, Holl R. Org. Biomol. Chem. 2013; 11: 6056-6070.
15. (a) Ehrlich SJ, Berliner E. J. Am. Chem. Soc. 1978; 100: 1525-1532. (b) Naskar D, Roy S. J.
Org. Chem. 1999; 64: 6896-6897.
16. Lee K–J, Lim KW, Chi DY. Bull. Korean Chem. Soc. 2001; 22: 549-550.
17. Liu Y, Wang W, Han J, Sun J. Org. Biomol. Chem. 2017; 15: 9311-9318.
18. General procedure for synthesis of 1-Bromoalkynes: To a stirred solution of phenyl
propiolic acid (1 mmol) in CH3CN (2 mL), TsNBr2 (1.1 mmol) and DBU (1 mmol) was added at
room temperature. After completion of the reaction, the reaction mixture was diluted with ethyl

acetate and the organic layer was washed with water and dried over anhydrous Na2SO4. The
concentrated crude product was purified by flash chromatography using petroleum ether as
eleunt.

TsNBr2 promoted decarboxylative bromination of α,β-unsaturated
carboxylic acids
Debojeet Hazarika and Prodeep Phukan
Department of Chemistry, Gauhati University, Guwahati-781014, India
Email: pphukan@yahoo.com
Highlights
 Improved synthesis of (E)-β-bromostyrenes with wide substrate scope
 The reaction proceeds rapidly (5-15 min) with high stereoselectivity.
 Propiolic acids produces bromoalkynes instantaneously
 Mild reaction condition at room temperature
 The yields of the products are excellent.