Dioxane dibromide-mediated solvent-free synthesis of vicinal dibromides

Article abstract of DOI:10.1080/00397910601033617

Structurally varied vicinal dibromides have been synthesized in high yield and good purity through highly stereoselective anti-addition of bromine across the olefinic linkages using dioxane dibromide (DD) under solvent-free conditions. Copyright Taylor & Francis Group, LLC.

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Dioxane Dibromide–Mediated Solvent‐Free
Synthesis of Vicinal Dibromides
Subrata Kumar Chaudhuri a , Sanchita Roy a , Manabendra Saha a & Sanjay
Bhar a
a Department of Chemistry, Organic Chemistry Section, Jadavpur University,
Kolkata, India
Version of record first published: 25 Jul 2007.
To cite this article: Subrata Kumar Chaudhuri , Sanchita Roy , Manabendra Saha & Sanjay Bhar (2007):
Dioxane Dibromide–Mediated Solvent‐Free Synthesis of Vicinal Dibromides, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 37:2, 271-274
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Synthetic Communicationsw, 37: 271–274, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910601033617
Dioxane Dibromide–Mediated Solvent-Free
Synthesis of Vicinal Dibromides
Subrata Kumar Chaudhuri, Sanchita Roy, Manabendra Saha,
and Sanjay Bhar
Department of Chemistry, Organic Chemistry Section,
Jadavpur University, Kolkata, India
Abstract: Structurally varied vicinal dibromides have been synthesized in high yield
and good purity through highly stereoselective anti-addition of bromine across the
olefinic linkages using dioxane dibromide (DD) under solvent-free conditions.
Keywords: electrophilic addition, regioselectivity, solid-phase synthesis, stereo-
selectivity
INTRODUCTION
Addition of bromine across the olefinic linkage[1] is an important protocol in
organic synthesis because the brominated products serve as important precur-
sors (through various organometallics) in C-C bond formation reactions.[2]
This is generally accomplished with molecular bromine[3] in various
organic (mainly halogenated) solvents, bromine on g-alumina,[4] N-bromo-
succinimide (NBS) in tetrabutylammonium bromide (TBAB),[5] and many
others. The corrosive, lachrymatory, volatile, and fuming nature of
molecular bromine along with its inherent toxicity cause serious procedural
hazards. Also, the reaction products are generally complicated and contami-
nated with by-products because of various side reactions such as overbro-
mination, oxidative decomposition, and polymeric transformations of the
Received in India June 1, 2006
Address correspondence to Sanjay Bhar, Department of Chemistry, Organic
Chemistry Section, Jadavpur University, Kolkata 700032, India. E-mail:
sanjaybharin@yahoo.com; sssbhar@lycos.com
271

272
S. K. Chaudhuri et al.
Scheme 1.
sensitive substrates and products. As part of our endeavor[6] to develop highly
selective, operationally simple, economically viable, and environmentally
benign methodologies for synthetically important organic transformations,
we report herein improved applications of dioxane dibromide (DD) as
bromine source under solvent-free condition (Scheme 1). Detailed results
are furnished in Table 1.
As delineated in Scheme 1 and Table 1, electrophilic addition of
bromine across various nucleophilic and electrophilic double bonds
produced vicinal dibromides with high anti-diastereoselectivity (determined
from the coupling constants of vicinal protons using Karplus’s equation)
under solvent-free conditions in practically pure form with negligible
formation of by-products. Many of the products serve as commercially[7]
and synthetically[1,3] important intermediates. In the presence of excess (6
eq.) nucleophilic reagents such as water and methanol, ethyl cinnamate
yielded the major product as the vicinal anti-dibromide; about 30% of
methanol addition product and no trace of 1,2-bromohydrin (water-
addition product) were obtained. The COOH group also survived instead
of the Hunsdiecker reaction.[5] An isolated double bond was selectively bro-
minated in the presence of the conjugated one using critically weighed
amount of DD as per the stoichiometric requirement (entry 8 in Table 1).
Similarly, the isolated double bond preferentially underwent bromination
in the presence of activated aromatic ring (entry 9 in Table 1); both the
double bond and the activated ring were brominated when an excess
amount of DD was used (entry 10 in Table 1). It is noteworthy that
phenyl propargyl ether underwent preferential ring bromination in
moderate yield and purity, keeping the triple bond intact (entry 11 in
Table 1). The aforesaid reactions with DD in various organic solvents
have been found to end up with incomplete conversions and the
formation of a considerable amount of by-products. This demonstrates the
very efficacy of the solvent-free protocols compared to their homogeneous
counterparts.
The present solvent-free method using DD provides a good preparative
method for differently substituted synthetically and commercially important
vicinal anti-dibromides with varied functional groups in good yield, high
purity, and excellent selectivity through operationally simple and relatively
green procedures.

Vicinal Dibromides
273
Table 1. Electrophilic anti-addition of bromine across the double bond with dioxane
dibromide under solvent-free conditions
Time Yielda
Entry
1
Substrate
Product
(min)
(%)
10
85[7]
2
3
10
10
82[7]
78[3]
4
5
6
20
15
20
70[3]
85[3]
68
7
8
30
30
76
78
9
10
11
30
30
45
62
80b
66
aYield refers to that of isolated pure racemic products, characterized
spectroscopically.
b2.5 eq. of DD used.

274
S. K. Chaudhuri et al.
EXPERIMENTAL
General Procedure for Bromination Using DD
DD (6.0 mmol) was added in portions to the neat substrate (5 mmol, cooled at
0–58C in ice water) and intimately mixed. The mixture was allowed to attain
the ambient temperature and left for the stipulated time period (as mentioned
in Table 1). Crushed ice was then added to the reaction mixture and filtered (if
the product was solid) or extracted with ether (for a semisolid or liquid mass),
washed successively with saturated aqueous sodium bicarbonate solution and
water, and dried to get the product in almost pure form. The products were
further purified by crystallization, short-path distillation, or filtration chroma-
tography on a short column of silica gel using 5% ethyl acetate–petroleum
ether, if needed.
ACKNOWLEDGMENTS
Financial support from the Council of Scientific and Industrial Research,
Government of India (CSIR), New Delhi [Grant No. 01(1673)/00/EMR-II]
is gratefully acknowledged. S. R. thanks the University Grants Commission
Government of India (UGC), New Delhi, and M. S. thanks CSIR, New Delhi,
for Junior Research Fellowships. The authors express profound thanks to
N. Dutta of the Indian Association for the Cultivation of Science (IACS) for
necessary assistance.
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