A facile and efficient method for the debromination of vic-dibromides to alkenes with BiCl3/indium system

Full text of DOI:10.5012/bkcs.2010.31.04.791

Communications to the Editor
Bull. Korean Chem. Soc. 2010, Vol. 31, No. 4 791
DOI 10.5012/bkcs.2010.31.04.791
A Facile and Efficient Method for the Debromination of vic-Dibromides to Alkenes
with BiCl3/Indium System
Byung Woo Yoo,* Jong Ho Kim, and Min Hye Yang
Department of Advanced Materials Chemistry, Korea University, Jochiwon, Chungnam 339-700, Korea
*E-mail: bwyoo@korea.ac.kr
Received September 22, 2009, Accepted February 3, 2010
Key Words: Debromination, Alkene, Bismuth, Indium
The vic-dibromide-alkene functional group interconversion
represents a useful step in the double bond protection-depro-
tection strategy.1 To date, several protocols have been utilized
for the debromination of vic-dibromides to alkenes, but some of
these methods are associated with limitations regarding chemo-
selectivity, low yields, prolonged reaction times, and harsh
reaction conditions.2 Consequently an efficient and mild pro-
cedure for debromination of vic-dibromides continues to be
developed. The chemical reactivity of BiCl3/M system (M = Zn,
Fe, Al, Mg) has been the subject of considerable interest and
the reducing ability of these systems has been extensively stu-
died.3 Because of the close resemblance of indium to zinc in
several respects, including first ionization, we reasoned that
BiCl3/indium system could serve as a protocol for the debro-
mination of vic-dibromides. In recent years indium metal has
drawn an increasing attention for its unique properties such as
low toxicity and high stability in water and air compared with
other metals.4 Bismuth(III) chloride is inexpensive, relatively
non-toxic, fairly water insensitive, and environmentally benign
reagent, which have been used as mild Lewis acid catalyst for
synthetic transformations. In continuation to our interest in
exploring the utility of metal-metal salt system in organic syn-
thesis,5 we wish to report here an efficient and mild method
for debromination of vic-dibromides 1 to alkenes 2 with BiCl3/
indium system in methanol at room temperature. The reaction
can be generalized as in eq. 1.6 The new reagent system was
generated by the addition of indium powder to a stirred solu-
tion of bismuth chloride in methanol under sonication.7 To
guage the scope and limitations of this methodology, various
substituted vic-dibromides were subjected to this protocal at
room temperature. We have found that vic-dibromides on treat-
ment with BiCl3/indium system in methanol solution are smoo-
thly converted into the corresponding alkenes in high yields.
with BiCl3 without indium metal, which failed to yield any
desired product. A2 : 1 ratio of indium and BiCl3 was the best
ratio in terms of yield and reaction time. And methanol has
been found to be the most suitable solvent for the reaction.
Table 1. Reductive debromination of vic-dibromides with BiCl3/indium
system
time yield
entry
substrate
product
(hr) (%)a
Br
Br
1
2
3
4
5
0.5
0.5
0.5
1.5
1.5
1.0
2.0
0.5
1.0
2.0
1.0
95
91
94
92
89
86
86
94
90
84
89
Br
Br
Br
O
Br
O
CH3
O
CH3
O
Br
Br
Br
Br
Br
O
O
O
O
6
7
Br
Br
Cl
Cl
O
O
Br
Br
OCH3
OCH3
OMe
OMe
8
Br
O
O
Br
Br
Br
O
O
9
CH3
H
CH3
Br Br
BiCl3/In
Br
Br
C
C
C
C
(1)
O
O
O
MeOH, rt
10
H
1
2
O
11
OH
OH
Br
The high yields of the debromination products demonstrate
the efficiency of this new method. To ensure the role of indium,
a controlled experiment was carried out using vic-dibromides
aIsolated yields. The products are commercially available and were cha-
racterized by comparison of their spectral data with authentic samples.

792 Bull. Korean Chem. Soc. 2010, Vol. 31, No. 4
Communications to the Editor
References
The result of the reaction is summarized in Table 1, where we
examined a series of functionally and structurally various vic-
dibromides. Clearly a broad range of functional group (ester,
carboxyl, aldehyde, methoxy, chloro, and ketone) was tolerated
under the reaction conditions and only trans olefins were obtain-
ed. It was worth commenting that the sensitive carbonyl group
remains intact without any further reduction under the reaction
condition (entries 5-10). In comparison with other procedures,
the present procedure reduced vic-dibromides in higher yields
and showed a good chemoselectivity under mild conditions.
The notable advantages of this methodology are mild reaction
conditions, simple manipulation, high yields, and tolerance of
various functional groups. No over-reduction of the produced
alkene was observed with any substrate.8 Some of the vic-dibro-
mides in the table are commercially available, or could be pre-
pared conveniently from the corresponding precursors through
known olefin halogenation reactions.9 Although the reaction
mechanism is still not clearly understood at this time, the re-
action can be envisaged to proceed in two stages. In the first
bismuth(III) chloride is probably reduced by indium to form
low-valent bismuth species, which in the subsequent step would
debrominate vic-dibromides 1 to give the corresponding alke-
nes 2 through a SET (single electron transfer) process. The
reducing property exhibited by metal-metal salt combinations
proceeds through transfer of one electron from the metal surface
to the substrate. In such combinations elementary metal part
needs to be more electropositive than the metal part of the salt.
The involvement of zero valent bismuth resulting from the trans-
metallation of bismuth chloride with indium metal may be
presumed.10 We have been able to demonstrate the utility of
BiCl3/indium system for effecting chemoselective debromina-
tion of vic-dibromides.
1. Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic Syn-
thesis, 2nd ed.; New York, 1991.
2. (a) Buther, T. S.; Detty, M. R. J. Org. Chem. 1998, 63, 169. (b) Li,
C. J.; Harpp, D. N. Tetrahedron Lett. 1990, 31, 6291. (c) Malanga,
C.; Mannucci, S.; Lardicci, L. Tetrahedron 1998, 54, 1021. (d)
Tanata, R.; Negoro, N.; Yanada, K.; Fujita, T. Tetrahedron Lett.
1996, 37, 9313. (e) Ranu, B. C.; Guchhait, S. K.; Sarkar, A. Chem.
Commun. 1998, 2113. (f) Mathai, M.; Sching, K.; Miller, S. I. J.
Org. Chem. 1970, 35, 1733.
3. (a) Makoto, W.; Hidenori, O.; Kin-ya, A. Tetrahedron Lett. 1986,
27, 4771. (b) Zhen, S.; Jinqi, Z.; Huixian, Z.; Minmin, Y. Tetra-
hedron Lett. 1997, 38, 2733. (c) Makoto, W.; Tomohiro, F.; Mika,
M.; Toshikazu, T.; Norikazu, M. Tetrahedron Lett. 1997, 38, 8045.
(d) Norikazu, M.; Mami, N.; Shunsuke, M.; Tomohiro, F.; Makoto,
W. Bull. Chem. Soc. Jpn. 2000, 73, 689.
4. For review: (a) Nair, V.; Ros, S.; Jayan, C. N.; Pillia, B. S. Tetra-
hedron 2004, 60, 1959. (b) Lubineau, A.; Auge, J.; Queneau, Y.
Synthesis 1994, 741. (c) Li, C. J. Tetrahedron 1996, 52, 5643. (d)
Cintas, P. Synlett 1995, 1087.
5. (a) Han, J. H.; Choi, K. I.; Kim, J. H.; Yoon, C. M.; Yoo, B. W.
Synth. Commun. 2006, 36, 415. (b) Yoo, B. W.; Song, M. S.; Park,
M. C. Synth. Commun. 2007, 37, 3089. (c) Yoo, B. W.; Park, M.
C.; Shin, J. I. Bull. Korean Chem. Soc. 2009, 30, 1927. (d) Yoo, B.
W. ; Choi, J. W. ; Kim, Y. S. Bull. Korean Chem. Soc. 2008, 29, 1655.
6. A typical procedure for the debromination of vic-dibromides is
as follows: Indium powder (230 mg, 2.0 mmol) and bismuth(III)
chloride (315 mg, 1.0 mmol) were mixed in methanol (4 mL). The
resulting mixture was stirred at room temperature for 0.5 hr under
sonicationproducing a solution of the low-valent bismuth-indium
complex. 1,2-Dibromoethylbenzene (264 mg, 1.0 mmol) was then
added to this solution and the reaction mixture was stirred for 30
min at room temperature. The solvent was removed under reduced
pressure and the residue was extracted with ether, washed with
brine, and dried over anhydrous Na2SO4. The crude product was
purified by silica gel column chromatography (hexane:ethyl ace-
tate = 10:1) to afford styrene (99 mg, 95%). All of the products
are commercially available compounds, and their identification
was based on spectral comparison with authentic samples.
7. Sonication were carried out in a BRANSONICultrasonic cleaner
bath, which delivered a 47 KHz wave, with a fixed electrical power
of 125 Watts.
In conclusion, we have demonstrated that BiCl3/indium sys-
temmediates an efficient and mild conversion of vic-dibromides
to the corresponding alkenes. Although the scope and limitations
were not fully established, the present method could be a prac-
tical alternative to the conventional method. Further work on
the application of BiCl3/indium system is in progress.
8. Hudlicky, T.; Sinai-Zingde, G.; Natchus, M. G. Tetrahedron Lett.
1987, 26, 5287.
9. Vogel’s Textbook of Practical Organic Chemistry, 4th ed.; Long-
man Group Limited: 1978; London, p 400.
Acknowledgments. This work was supported by Korea
10. Petrier, C.; Barbosa, D.; Dupuy, C.; Luche, J. L. J. Org. Chem.
1985, 50, 5761.
University Grant.