Mild and efficient debromination of vic-dibromides to alkenes with fecl36h2o/indium system

Article abstract of DOI:10.1080/00397910802531989

The FeCl36H2O/indium system efficiently causes debromination of various dibromides to the corresponding alkenes in good to excellent yields under mild conditions.

Full text of DOI:10.1080/00397910802531989

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Mild and Efficient
Debromination of vic-
Dibromides to Alkenes with
FeCl3·6H2O/Indium System
Byung Woo Yoo a , Jin Woo Choi a & Min Hye Yang a
a Department of Advanced Materials Chemistry ,
Korea University , Jochiwon, Chungnam, South
Korea
Published online: 19 Mar 2009.
To cite this article: Byung Woo Yoo , Jin Woo Choi & Min Hye Yang (2009) Mild and
Efficient Debromination of vic-Dibromides to Alkenes with FeCl3·6H2O/Indium System,
Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 39:8, 1488-1493, DOI: 10.1080/00397910802531989
To link to this article: http://dx.doi.org/10.1080/00397910802531989
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Synthetic Communications1, 39: 1488–1493, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910802531989
Mild and Efficient Debromination of
vic-Dibromides to Alkenes with FeCl3 Á 6 H2O/
Indium System
Byung Woo Yoo, Jin Woo Choi, and Min Hye Yang
Department of Advanced Materials Chemistry, Korea University,
Jochiwon, Chungnam, South Korea
Abstract: The FeCl3 Á 6H2O=indium system efficiently causes debromination of
various dibromides to the corresponding alkenes in good to excellent yields under
mild conditions.
Keywords: Alkene, debromination, ferric chloride, indium
The debromination of vic-dibromides to alkenes is important in organic
synthesis as a double-bond protection–deprotection strategy.[1] Although
reductive debromination of vic-dibromides with various agents has been
the subject of many reports, most of these methods are associated with
limitations regarding low yields, prolonged reaction times, and harsh
reaction conditions.[2] Consequently an efficient and mild procedure for
debromination of vic-dibromides continues to be developed. Because of
the close resemblance of indium to zinc in several respects, including first
ionization, we considered that FeCl3 Á 6H2O=indium system could also be
a useful addition to the conventional method. In recent years, indium
metal has drawn increasing attention for its unique properties such as
low toxicity and high stability in water and air compared with other
metals.[3] In continuation of our interest in exploring the utility of the
metal–metal salt system in organic synthesis,[4] we report here an
Received August 12, 2008.
Address correspondence to Byung Woo Yoo, Department of Advanced
Materials Chemistry, Korea University, Jochiwon, Chungnam 339-700, South
Korea. E-mail: bwyoo@korea.ac.kr
1488

Debromination of vic-Dibromides
1489
efficient and chemoselective method for debromination of vic-dibromides
1 to alkenes 2 with a FeCl3 ꢀ 6H2O=In system in methanol at room
temperature. The reaction can be generalized as Eq. (1). The new reagent
system was generated by the addition of indium powder to a stirred
solution of ferric chloride hexahydrate in methanol under sonication.
We have investigated the reactions of the FeCl3 ꢀ 6H2O=In system with
various vic-dibromides and observed that the debrominations generally
proceeded with high yields and showed selectivity over other labile sub-
stituents. Some control experiments revealed that vic-dibromides could
not be debrominated by ferric chloride hexahydrate or indium alone
under the reaction conditions. The high yields of the debromination pro-
ducts demonstrate the efficiency of this new method. A 2:1 ratio of
indium and FeCl3 ꢀ 6H2O 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. The result of this reduction is summarized in Table 1, where we
examined a series of functionally and sterically diverse vic-dibromides.
Clearly a broad range of functional groups (ester, carboxyl, formyl,
methoxy, chloro, and ketone) was tolerated under the reaction conditions
and only trans olefins were obtained. It was worth commenting that the
sensitive carbonyl group remains intact without any further reduction
under the reaction condition (entries 4–10). In comparison with other
procedures, the present procedure reduces vic-dibromides in higher yields
and showed good chemoselectivity under mild conditions. The notable
advantages of this methodology are mild reaction conditions, short reac-
tion times, high yields, and tolerance of various functional groups. No
overreduction of the produced alkene was observed with any substrate.[5]
All the compounds obtained showed infrared (IR), NMR, and mass spec-
tral data consistent with the structure. Some of the vic-dibromides in the
table are commercially available or could be prepared conveniently from
the corresponding precursors through known olefin halogenation reac-
tions.[6] Although the reaction mechanism is still unclear, the reaction
can be envisaged to proceed in two stages. In the first, iron(III) chloride
is probably reduced by indium to form low-valent iron species, which in
the subsequent step would debrominate vic-dibromides 1 to give the cor-
responding alkenes 2. 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, the elementary

1490
B. W. Yoo, J. W. Choi, and M. H. Yang
Table 1. Reductive debromination of vic-dibromides with FeCl3 ꢀ 6H2O=In
system
Reaction Yield
(%)a
Entry
1
Substrate
Product
time (h)
0.5
95b
2
3
4
1.0
0.5
2.0
90b
93b
89b
5
6
1.5
2.0
91b
88b
7
1.5
85b
8
9
2.0
1.0
91b
92b
(Continued )

Debromination of vic-Dibromides
Table 1. Continued
1491
Reaction Yield
(%)a
Entry
10
Substrate
Product
time (h)
1.0
88b
11
1.5
87b
aIsolated yields.
bThe products are commercially available and were characterized by
comparison of their spectral data with authetic samples.
metal part needs to be more electropositive than the metal part of the salt.
We believe that the present procedure using the FeCl3 ꢀ 6H2O=In system
proceeds through a single-electron transfer (SET) process. We have been
able to demonstrate the utility of the FeCl3 ꢀ 6H2O=In system for effecting
chemoselective debromination of vic-dibromides.
In conclusion, we have discovered that the FeCl3ꢀ6H2O=In system
mediates an efficient and mild conversion of vic-dibromides to the corre-
sponding alkenes. Although the scope and limitations were not fully
established, the present method could be a practical alternative to the
conventional method.
EXPERIMENTAL
1
The H NMR spectra were recorded on a FT-Bruker AF-300 (300 MHz
1
for H NMR; 75 MHz for 13C NMR) using tetramethylsilane (TMS) as
an internal standard. IR spectra were obtained on a Perkin-Elmer 16F
PC Fourier transform (FT)-IR Shimadzu. Thin-layer chromatographic
(TLC) analysis was performed on silica-gel plates (Merck, 60 F-254).
All products were purified by flash-column chromatography using
silica-gel 60 (79–230 mesh, Merck).
General Procedure for the Reaction
A typical procedure for the debromination of vic-dibromides is as
follows: indium powder (230 mg, 2.0 mmol) and iron(III) chloride
hexahydrate (270 mg, 1.0 mmol) were mixed in methanol (4 mL). The

1492
B. W. Yoo, J. W. Choi, and M. H. Yang
resulting mixture was stirred at room temperature for 0.5 h under sonica-
tion to get a solution of the low-valent iron–indium complex. Sonication
was carried out in a Bransonic ultrasonic cleaner bath, which delivered a
A7-KHz ware with a fixed electrical power of 125 W. 1,2-Dibromoethyl-
benzene (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
acetate ¼ 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.
ACKNOWLEDGMENT
This work was supported by a Korea University grant.
REFERENCES
1. Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic Synthesis, 4th ed.;
Longman Group, Ltd., New York, 2007.
2. (a) Buther, T. S.; Detty, M. R. Debromination of vic-dibromides with diorga-
notellurides, 1: Stereoselectivity: Relative rates and mechanistic implications.
J. Org. Chem. 1998, 63, 169–176; (b) Li, C. J.; Harpp, D. N. Bis(triphenylsta-
nyl)telluride: A mild and selective reagent for telluration and debromination.
Tetrahedron Lett. 1990, 31, 6291; (c) Malanga, C.; Mannucci, S.; Lardicci,
L. Carbon-halogen bond activation by nickel catalyst: Synthesis of alkenes
from 1,2-dihalides. Tetrahedron 1998, 54, 1021; (d) Tanata, R.; Negoro, N.;
Yanada, K.; Fujita, T. Reductive dehalogenation of aliphatic vic-dihalides
with metallic samarium in a methanolic medium. Tetrahedron Lett. 1996, 37,
9313; (e) Ranu, B. C.; Guchhait, S. K.; Sarkar, A. Stereoselective debromina-
tion of aryl-substituted vic-dibromide with indium metal. J. Chem. Soc., Chem.
Commun. 1998, 2113; (f) Mathai, I. M.; Sching, K.; Miller, S. I. Stereoselec-
tivity in the debromination of the stilbene dibromides by several metals and
inorganic reductants in several solvents. J. Org. Chem. 1970, 35, 1733.
3. For review see (a) Nair, V.; Ros, S.; Jayan, C. N.; Pillia, B. S. Indium- and
gallium-mediated carbon–carbon bond-forming reactions in organic synthesis.
Tetrahedron 2004, 60, 1959; (b) Lubineau, A.; Auge, J.; Queneau, Y. Water-
promoted organic reactions. Synthesis 1994, 741; (c) Li, C. J. Aqueous
Barbier–Grignard-type reaction: Scope, mechanism, and synthetic application.
Tetrahedron 1996, 52, 5643; (d) Cintas, P. Synthetic organoindium chemistry:
What makes indium so appealing? Synlett. 1995, 1087.
4. (a) Han, J. H.; Choi, K. I.; Kim, J. H.; Yoon, C. M.; Yoo, B. W. Facile
deoxgenation of amine-N-oxides with CoCl2 ꢀ 6H2O-indium system. Synth.

Debromination of vic-Dibromides
1493
Commun. 2006, 36, 415; (b) Yoo, B. W.; Song, M. S.; Park, M. C. Mild and
efficient deoxygenation of sulfoxides with MoCl5=indium system. Synth.
Commun. 2007, 37, 3089; (c) Han, J. H.; Choi, J. W.; Choi, K. I.; Kim, J.
H.; Yoo, B. W. A facile and efficient reduction of nitroarenes with
NiCl2 ꢀ 6H2O=indium. Bull. Korean Chem. Soc. 2006, 27, 1115; (d) Choi, K.
H.; Choi, K. I.; Kim, J. H.; Yoon, C. M.; Yoo, B. W. Mild and efficient
deoxygenation of epoxides with bis(cyclopentadienyl)titanium(IV) dichloride–
indium system. Bull. Korean Chem. Soc. 2005, 26, 1495.
5. Hudlicky, T.; Sinai-Zingde, G.; Natchus, M. G. Selective reduction of a,b-
unsaturated esters in the presence of olefins. Tetrahedron Lett. 1987, 26, 5287.
6. Vogel’s Textbook of Practical Organic Chemistry, 4th ed.; Longman
Group, Ltd., New York, 1978.