Microwave-mediated debromination of vicinal/-dibromides

Article abstract of DOI:10.1080/00397910500334496

Debromination of vicinal-dibromides to E-alkenes is reported using inorganic solid supports (silica gel or acidic alumina) under microwave irradiation. Copyright Taylor & Francis LLC.

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Microwave‐Mediated Debromination of
vicinal‐Dibromides
a
a
Jitender M. Khurana & Arpita Agrawal
a
Department of Chemistry , University of Delhi , Delhi, India
Published online: 15 Aug 2006.
To cite this article: Jitender M. Khurana & Arpita Agrawal (2006) Microwave‐Mediated Debromination
of vicinal‐Dibromides, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 36:2, 207-209, DOI: 10.1080/00397910500334496
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Synthetic Communications , 36: 207–209, 2006
Copyright # Taylor & Francis LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500334496
Microwave-Mediated Debromination of
vicinal-Dibromides
Jitender M. Khurana and Arpita Agrawal
Department of Chemistry, University of Delhi, Delhi, India
Abstract: Debromination of vicinal-dibromides to E-alkenes is reported using
inorganic solid supports (silica gel or acidic alumina) under microwave irradiation.
Keywords: Debromination, inorganic solid support, microwaves, stereoselective,
vic-dibromides
The olefins can be regenerated from vicinal-dibromides with a variety of
[
1]
reagents and the overall bromination/debromination process represents a
[2]
means of protection and deprotection of olefins. Our group has reported
solvolytic stereoselective debromination of vic-dibromides by N,N-dimethyl-
[
3,4]
[5]
and hexamethylphosphoramide (HMPA) without the
formamide (DMF)
aid of any reagent. Different methods
tion have their own advantages and disadvantages.
[
6,7]
reported in literature for debromina-
We report herein the first study on stereoselective debromination of vic-
dibromides (I) adsorbed on inorganic solid support (silica gel or acidic
[
8]
alumina) under microwave irradiation to give the corresponding E-olefins
II) (Fig. 1). Microwave-mediated debromination has been carried out on a
variety of vic-dibromides (Table 1) within periods of 1–5 min.
(
Figure 1. Debromination of vicinal-dibromides under microwave irradiation.
Received in India July 11, 2005
Address correspondence to Jitender M. Khurana, Department of Chemistry, Univer-
sity of Delhi, Delhi 110007, India. Fax: 91-11-27666605; E-mail: jmkhurana@
chemistry.du.ac.in
2
07

Table 1. Reactions of vic-dibromides under microwave irradiation on inorganic solid support
Silica gel
Acidic alumina
Isolated yield
(%) (II)
Time
(min)
Isolated yield
(%) (II)
Time
(min)
S. No.
Substrates
1
2
3
4
5
6
7
8
9
meso-Stilbene dibromide (Ia)
dl-Stilbene dibromide (Ib)
2
2
95
84 (89)
2
2
96
84 (91)
a
b
meso-4-Chlorostilbene dibromide (Ic)
meso-4-Methylstilbene dibromide (Id)
4
90
91
92
82
96
95
81
84
—
—
21
4
96
95
96
86
98
98
81
85
—
—
37
3
3
0
meso-4,4 -Dichlorostilbene dibromide (Ie)
5
5
meso-4-Methoxystilbene dibromide (If)
meso-a,b-Dibromosuccinic acid (Ig)
dl-a,b-Dibromosuccinic acid (Ih)
trans-1,2-Dibromocyclooctane (Ii)
trans-1,2-Dibromocyclohexane (Ij)
Dihydrocinnamic acid dibromide (Ik)
Cholesterol dibromide (Il)
1
1
1
1
1
1
2
10
2
10
1
1
1
1
0
1
2
3
c
c
—
—
d
d
—
—
meso-Stilbene dichloride (Im)
2
2
a
b
c
Yield in bracket is HPLC yield. 11% Z-stilbene was also formed.
Yield in bracket is HPLC yield. 9% Z-stilbene was also formed.
Starting material recovered.
d
Decomposition of starting material was observed.

vicinal-Dibromide Debromination
209
TYPICAL PROCEDURE
meso-Stilbene dibromide (0.5 g), dichloromethane (5 ml), and silica gel or
acidic alumina (2 g) were mixed thoroughly in a beaker. The adsorbed
material was dried and then exposed to microwave irradiation. After 2 min,
the residue was extracted with ethyl acetate (3 ꢀ 10 ml). The combined
ethyl acetate extract was dried over anhyd. MgSO , filtered, and concentrated
4
[9]
to afford E-stilbene (0.25 g, 95%); mp 1228C, lit. mp 1248C.
ACKNOWLEDGMENT
A. A. thanks CSIR, New Delhi, India, for providing a Junior Research
Fellowship.
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