Preparation of aryl-substituted E-homoallylic bromides from cyclopropylcarbinol and PBr3

Article abstract of DOI:10.1080/00397910600602768

An expeditious synthesis of aryl substituted E-homoallylic bromides has been accomplished by the cleavage of cyclopropylcarbinols with phosphorus tribromide. Copyright Taylor & Francis Group, LLC.

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Preparation of Aryl‐Substituted E‐Homoallylic
Bromides from Cyclopropylcarbinol and PBr3
Sanchita Roy a , Sharmistha Guha a , Samit Kumar Dutta a & Sanjay Bhar a
a Department of Chemistry, Organic Chemistry Section, Jadavpur University,
Kolkata, India
Published online: 18 Aug 2006.
To cite this article: Sanchita Roy , Sharmistha Guha , Samit Kumar Dutta & Sanjay Bhar (2006) Preparation of
Aryl‐Substituted E‐Homoallylic Bromides from Cyclopropylcarbinol and PBr3 , Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 36:13, 1919-1922
To link to this article: http://dx.doi.org/10.1080/00397910600602768
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Synthetic Communicationsw, 36: 1919–1922, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600602768
Preparation of Aryl-Substituted
E-Homoallylic Bromides from
Cyclopropylcarbinol and PBr3
Sanchita Roy, Sharmistha Guha, Samit Kumar Dutta,
and Sanjay Bhar
Department of Chemistry, Organic Chemistry Section,
Jadavpur University, Kolkata, India
Abstract: An expeditious synthesis of aryl substituted E-homoallylic bromides
has been accomplished by the cleavage of cyclopropylcarbinols with phosphorus
tribromide.
Keywords: Cleavage, cyclopropane, homoallylic bromide, selectivity
INTRODUCTION
Homoallylic bromides have been obtained in low to moderate yields from the
fragmentation of the cyclopropylcarbinols using anhydrous ZnBr2,[1,2a]
[2b]
HBr,[2a] and MgBr2
but are associated with many products arising from
the Demyanov rearrangement.[3] We report herein PBr3-mediated cleavage
of appropriately substituted cyclopropylcarbinols to accomplish highly
selective synthesis of structurally varied E-homoallylic bromides under mild
conditions, demonstrating the effects of substituents toward the cleavage
pattern.
For this purpose, different b-aryl-a,b-unsaturated enones, obtained
through the base-promoted aldolization[4] between the appropriately substi-
tuted aryl methyl ketones and aryl aldehydes and subsequent dehydration,
Received in India December 26, 2005
Address correspondence to Sanjay Bhar, Department of Chemistry, Organic
Chemistry Section, Jadavpur University, Kolkata 700 032, India. Fax: 91-033-
24146584; E-mail: sanjaybharin@yahoo.com
1919

1920
S. Roy et al.
were cyclopropanated[5] under PTC condition, which on reduction with
NaBH4 furnished cyclopropylcarbinols as a mixture of diastereomers
(Scheme 1).
The present sequence provides excellent access to a plethora of cyclopro-
pylcarbinols bearing the substitution patterns according to one’s choice at both
the carbinol carbon and the cyclopropyl ring. The compounds were then
subjected to substitutive bromination using ethereal PBr3 (Scheme 2); the
results are presented in Table 1.
The relief of ring strain and formation of the conjugated double bond
might be the driving force for this transformation. The cleavage of the cyclo-
propyl ring was probably triggered by the supply of electron density from the
ring to the initially formed electron-deficient center, which was not assisted by
the electron-withdrawing substituents such as COOMe.
In conclusion, the present methodology can serve as an efficient
protocol for the synthesis of aryl-substituted E-homoallylic bromides from
cyclopropylcarbinols.
EXPERIMENTAL
Representative Procedure for the Synthesis of Aryl Substituted
E-Homoallylic Bromide
Phosphorous tribromide (0.1 mL, 285 mg, 1.05 mmol) was added dropwise to
an ice-cold solution of 2,3-cyclopropano-1,3-diphenylpropanol (224 mg,
1.0 mmol) in anhydrous diethyl ether (3 mL) under stirring conditions. The
reaction mixture was allowed to attain the ambient temperature, and stirring
was continued for further 2 h. After the completion of reaction, as monitored
by TLC (silica gel), ice water (2 mL) was added and the organic layer was
diluted with diethyl ether (5 mL); washed successively with distilled water
(3 Â 5 mL), aqueous sodium bicarbonate solution (2 Â 5 mL), and distilled
Scheme 1.

Aryl-Substituted E-Homoallylic Bromides
1921
Scheme 2.
Table 1. Synthesis of aryl substituted E-homoallylic bromides via PBr3-mediated
cleavage of cycloprapane ring
Yielda
(%)
Entry
1
Substrate
Product
74
2
3
78
85
4
69
5
6
79
83
7
74
8[6]
81b
aReaction time 2 h; yield of isolated product, characterized spectroscopically.
bReaction time 8 h.

1922
S. Roy et al.
water (1 Â 5 mL); and dried over anhydrous sodium sulfate. Evaporation of the
solvent furnished the crude product, which was further purified by filtration
chromatography over a short column of silica gel using petroleum ether
(608–808C) as eluent to yield 4-bromo-1,4-diphenyl-1-butene (242 mg, 85%
yield).
1H NMR (300 MHz, CDCl3): d 3.02–3.21 (2H, m, –CH2–), 5.01 (1H, t,
J ¼ 7.2 Hz, –CHBr–), 6.11 (1H, td, J1 ¼ 15.8 Hz, J2 ¼ 7.0 Hz, olefinic-H
b-to –CHBr–), 6.41 (1H, d, J ¼ 15.8 Hz, olefinic-Hg-to –CHBr–), 7.17–7.43
(10H, m, aromatic-H’s).13C NMR (75 MHz, CDCl3): d 43.30 (–CH2–),
54.41 (–CHBr–), 126.05 (olefinic-C b-to –CHBr–), 126.18, 126.21,
127.36, 127.45, 128.44, 128.51, 128.61, 128.65, 128.7, 128.76 (aromatic
CH’s), 133.17 (olefinic-Cg-to –CHBr–), 136.98 (aromatic 48C, connected
to –CHBr–), 141.53 (aromatic 48C, connected to olefinic linkage).
ACKNOWLEDGMENT
This study enjoyed financial support from Council of Scientific and Indus-
trial Research (CSIR), New Delhi [Grant no. 01(1673)/00/EMR-II dated
07-12-2000], which is gratefully acknowledged. Sanchita Roy (S. R.) thanks
University Grants Commission (UGC), Government of India for a junior
research fellowship. Thanks go to Nirmalya Dutta of Indian Association for
the Cultivation of Science (IACS) for necessary assistance.
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