Regioselective synthesis of vic-halo alcohols and symmetrical or unsymmetrical vic-dihalides from epoxides using triphenylphosphine -N-halo imides

Article abstract of DOI:10.1139/v05-261

A simple, novel, and highly regioselective cleavage of epoxides into vicinal halo alcohols and symmetrical or unsymmetrical dihalides is described using different stoichiometries of triphenylphosphine (PPh₃) and N-halo succinimide (NXS) or N-halo saccharine (NXSac).

Full text of DOI:10.1139/v05-261

6
9
Regioselective synthesis of vic-halo alcohols and
symmetrical or unsymmetrical vic-dihalides from
epoxides using triphenylphosphine – N-halo
imides
Nasser Iranpoor, Habib Firouzabadi, Roya Azadi, and Farzaneh Ebrahimzadeh
Abstract: A simple, novel, and highly regioselective cleavage of epoxides into vicinal halo alcohols and symmetrical
or unsymmetrical dihalides is described using different stoichiometries of triphenylphosphine (PPh ) and N-halo
3
succinimide (NXS) or N-halo saccharine (NXSac).
Key words: N-halo succinimide (NXS), N-halo saccharine (NXSac), triphenylphosphine (PPh ), epoxide, vic-halo
3
alcohol, symmetrical dihalide, unsymmetrical dihalide.
Résumé : On a effectué un nouveau clivage simple et hautement régiosélectif d’époxydes qui conduit à des halogé-
noalcools et des dihalogénures symétriques et non symétriques vicinaux et qui a été réalisé en utilisant des stoechiomé-
tries diverses de triphénylphosphine, de N-halogénosuccinimide (NXS) ou de N-halogénosaccharine (NXSac).
Mots clés : N-halogénosuccinimide (NXS), N-halogénosaccharine (NXSac), triphénylphosphine (PPh ), époxyde, halo-
3
génoalcool vicinal, dihalogénure symétrique, dihalogénure non symétrique.
[
Traduit par la Rédaction] Iranpoor et al. 75
Introduction
(24), and acyl methylimidazolium halide ([AcMIm]X) (25)
are among the reagents used for this transformation. Al-
though there are many methods reported for the conversion
of epoxides into vicinal halo alcohols, their conversion to
symmetrical or unsymmetrical vic-dihalides is rarely found
in the literature. The use of reagents such as PPh –CCl (26)
Epoxides are suitable starting materials for the preparation
of different functional groups (1). Owing to the importance
of vicinal halo alcohols in organic synthesis (2, 3), diverse
methods have been developed for their preparation from
epoxides. The conventional reagents for epoxide ring open-
ing to halo alcohols are hydrogen halides and hypohalite–
water (4). However, the disadvantages of these procedures
are an intolerance to acid-sensitive moieties and by-product
formation (5). A great effort has been made in the last few
years to find milder procedures for converting epoxides into
halo alcohols. For example, silyl halides can be added to
epoxides to give O-silyl protected halo alcohols (6). Other
methods include the use of a halogen and triphenyl-
3
4
and PPh –X (X = Cl, Br) (27) is reported for the prepara-
3
2
tion of symmetrical vic-dihalides and PPh –X (X = Cl, Br)
3
2
followed by using HCl–THF for the preparation of unsym-
metrical vic-dihalides (27).
Results and discussion
Recently, we reported a method for the preparation of vic-
phosphine (PPh ) (7), or disubstituted borane halogenides
halo alcohols or symmetrical or unsymmetrical dihalides
3
(
8), β-bromo bis(dimethylamino)borane (9), monochloro-
(28) from epoxides using a combination of PPh –DDQ–
3
borane – dimethyl sulfide (10), Li M X (M = Ni, Cu, Ti)
R NX (X = Cl, Br, I). In conjunction with this research and
n
n
n
4
(
11), and MX (12). Also, different metal salts (13–17) in
in continuation of our previous work on the use of PPh – N-
n
3
the presence of halide ions, TMSCl, and phosphaferrocene
as the catalyst (18); lithium halides in the presence of silica
gel or Amberlyst 15 (19, 20); a combination of elemental
halogen and 2-phenyl-2-(2-pyridyl)imidazolidine (PPI) (21),
phenyl hydrazine (22), or crown ethers (23); PPh –CBr
halo succinimide (NXS) (29), we now introduce a new, mild,
regioselective, and simpler method for the efficient conver-
sion of epoxides to vic-halo alcohols or symmetrical or un-
symmetrical vic-dihalides. In this method, epoxides in the
presence of PPh –NXS or PPh – N-halo saccharine
3
4
3
3
(
NXSac) are converted to vic-halo alcohols or symmetrical
or unsymmetrical vic-dihalides depending on the molar ratio
and the type of halo imide used (Scheme 1).
We took oxiranylmethyl phenyl ether (Table 1, entry 1) as
an example and optimized the reaction conditions for its
conversion to vic-bromo alcohol. It was observed that the
Received 30 August 2005. Published on the NRC Research
Press Web site at http://canjchem.nrc.ca on 28 February 2006.
1
2
N. Iranpoor, H. Firouzabadi, R. Azadi, and
F. Ebrahimzadeh. Department of Chemistry, College of
Sciences, Shiraz University, Shiraz, 71454, Iran.
mixture of oxiranylmethyl phenyl ether – PPh – NBS or
3
1
Corresponding author (e-mail: iranpoor@chem.susc.ac.ir).
Corresponding author (e-mail: firouzabibi@chem.susc.ac.ir).
NBSac with the molar ratio of 1:1.2:1.2 in 1% aqueous
acetonitrile at room temperature is suitable for the quantita-
2
Can. J. Chem. 84: 69–75 (2006)
doi:10.1139/V05-261
© 2006 NRC Canada

7
0
Can. J. Chem. Vol. 84, 2006
Scheme 1.
PPh /NXS or NXSac(1.2/1.2) X = Br, Cl, I
PhO
3
PhOCH CH(OH)CH X
O
2
2
r.t.,1% aq. CH CN
3
PPh /NXS or NXSac (2.5/2.5)
3
PhOCH CHXCH X
2
2
reflux, CH CN
3
X = Br, Cl
PhO
'
X = Br, Cl, I
O
PPh /NXS or NXSac(1.2/1.2) and
3
PhOCH CHX'CH X
2
2
PPh /NX'S or NX'Sac (2.5/2.5), reflux, CH CN
3
3
tive conversion of oxiranylmethyl phenyl ether to 1-bromo-
-phenoxy-2-propanol. Aqueous acetonitrile is required to
hydrolyze the intermediate to the corresponding vicinal
halohydrine. Similar reaction conditions were then applied
for the conversion of structurally different epoxides to their
corresponding vic-halo alcohols. The results are shown in
Table 1.
and to introduce a mild and novel method for this
transformation, we applied our method to epoxides. For this
transformation, the successive use of two N-halo imides hav-
ing different halide ions produces the desired unsymmetrical
vic-dihalide in high yield. To optimize the reaction condi-
tions, oxiranylmethyl phenyl ether was added to a mixture of
PPh –NCS or PPh –NCSac with the molar ratio of 1.2:1.2 in
3
3
3
Under these reaction conditions, the ethereal bonds, ester
groups, carbon–carbon double bond, and activated aromatic
ring do not interfere with the formation of halo alcohols and
remain intact. Electronic and steric factors control the orien-
tation of the attack of halide ion. In the case of styrene ox-
ide, owing to electronic factors, the attack of the halide ion
occurs mainly at the more substituted position. However, in
other epoxides that bear alkyl or electron-withdrawing
groups, owing to the combination of steric and electronic
factors, the attack occurs at the less hindered site of the ring
and 1-halo-2 alcohols are produced as the major product
acetonitrile at room temperature. When all the epoxide was
consumed, the mixture was poured into another mixture con-
taining PPh3–NBS or PPh3–NBSac (2.5:2.5) in acetonitrile
and refluxed for 8 h. After completion of the reaction, 2-
bromo-1-chloro-3-phenoxypropane was obtained in 85%
yield (Table 3, entry 2). Since this attempt was successful,
we applied it to the preparation of unsymmetrical vic-
dihalides from other epoxides. By using the proper halide
anion in each step, we could easily control the formation of
vic-dihalides with high regioselectivity. The results obtained
for this study are tabulated in Table 3. In these reactions, as
we expected, in the first step, the first halide ion attacks the
epoxide ring from the same side of the formation of vic-halo
alcohols. In the second step, the resulting halo alcohol reacts
(
Table 1).
We also investigated the possibility of converting epoxides
to symmetrical vicinal dihalides using PPh –NXS or PPh –
3
3
with the mixture of PPh –NXS or PPh –NXSac and the sec-
NXSac (X = Cl, Br). For this purpose, oxiranylmethyl
phenyl ether (Table 2, entries 1 and 2) was treated as a
model compound with the PPh –NBS or PPh –NBSac re-
3
3
ond halide anion displaces the hydroxyl group to produce
the desired unsymmetrical dihalide. It was observed that
when one of the nucleophiles was iodide, because of the
possibility of the elimination of IX (X = Cl, Br), alkene for-
mation was a competing pathway and lowered the yield of
vic-dihalides considerably (Table 3, entries 3 and 6).
3
3
agent system using the optimized molar ratio of 2.5:2.5 in
refluxing acetonitrile, and the corresponding dibromide was
obtained in high yield. The use of NCS or NCSac in this
method under the same reaction conditions as used for the
preparation of dibromide offers the possibility of producing
vic-dichlorides. We extended this procedure to other
epoxides to obtain symmetrical vic-dihalides. The results of
this investigation are shown in Table 2.
Although the exact mechanism of these reactions is not
clear, it is suggested that, at first, a positively charged adduct
(I) (31) is formed from the reaction of PPh with NBS
3
(Scheme 2). This positively charged adduct interacts with
the oxygen atom of the epoxide and produces (II). When R-
(–)-styrene oxide, the formation of the corresponding β-
bromohydrin, which did not show any optical rotation, ac-
counts for the formation of the racemic product through the
intermediacy of a benzylic carbocation. Nucleophile attack
of the halide ion on (II) produces the intermediate (III).
This intermediate in the presence of water could produce
triphenylphosphine oxide, succinimide, and the correspond-
ing vic-halo alcohol. Similarly, the attack of another halide
ion on this intermediate produces the corresponding vicinal
symmetrical or unsymmetrical dihalide.
However, the preparation of vic-diiodides by this method
was not successful. This result is in accordance with the
literature (30), which indicates that alkene formation is fa-
voured owing to the ease of elimination of molecular iodine.
In all the reactions of epoxides with PPh –NIS or PPh –
3
3
NISac (2.5:2.5), alkene formation was the only pathway. For
example, the addition of oxiranylmethyl phenyl ether to the
mixture of PPh –NBS or PPh –NBSac (2.5:2.5) in refluxing
3
3
acetonitrile produced allyl phenyl ether as the only product
after 0.5 h. Therefore, the use of a PPh –NIS or PPh –NISac
3
3
mixture offers a new mixed reagent system for the
deoxygenation of epoxides into their corresponding alkenes.
As shown in Table 3, entries 1 and 4, when the first
To overcome the problems of using highly acidic condi-
tions for the conversion of epoxides to vic-dihalides (27),
nucleophile used was bromide,
regioisomers was obtained. It is assumed that, in these cases,
a
mixture of two
©
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Iranpoor et al.
71
Table 1. Conversion of epoxides to vic-halo alcohols with PPh –NXS or PPh –NXSac (X = Br, C1, I) in
3
3
1
% aqueous acetonitrile at room temperature.
a
Yield (%)b
Entry
Substrate
Product
Time (min)
HO
NBS
NBSac
40
8
93
95
O
Br
1
O
O
Ph
Ph
O
HO
HO
NCS
NCSac
6
15
88
92
O
O
Cl
I
Ph
Ph
O
O
2
3
Ph
Ph
O
NIS
NISac
5
7
90
85
O
O
OH
OH
OH
NBS
NBSac
20
3
82
90
O
O
O
O
O
Br
Cl
I
4
O
O
NCS
NCSac
3
8
95
85
5
6
O
O
O
O
O
O
NIS
NISac
5
3
80
86
O
O
OH
NBS
NBSac
3
3
96
85
Br
Cl
I
7
8
9
O
O
OH
OH
HO
NCS
NCSac
10
6
82
93
O
O
O
NIS
NISac
3
10
90
88
O
O
O
OH
Br
c
Br
Ph
Cl
Ph
NBS
NBSac
30
3
80(16)
90(8)
c
10
Ph
Ph
Cl
I
c
O
HO
OH
OH
NCS
NCSac
3
5
78(18)
85(8)
c
1
1
2
Ph
Ph
HO
O
c
I
NIS
NISac
8
5
80(15)
78(10)
c
1
Ph
Ph
Ph
c
Br
NBS
3
3
65(15)
1
3
4
OH
O
c
NBSac
70(16)
OH
Cl
Br
c
NCS
8
3
75(20)
OH
1
O
O
c
NCSac
66(20)
OH
I
Cl
OH
I
c
NIS
3
65(15)
15
c
NISac
10
76(15)
OH
©
2006 NRC Canada

7
2
Can. J. Chem. Vol. 84, 2006
Table 1 (concluded).
a
Yield (%)b
Entry
Substrate
Product
Time (min)
3
(
)4
c
Br
NBS
69(15)
1
6
O
OH
(
)4
c
NBSac
5
75(20)
(
)4
OH
Cl
Br
(
)4
c
NCS
3
70(18)
OH
Cl
1
7
O
(
)4
c
NCSac
10
75(10)
(
)4
OH
(
)4
c
I
NIS
5
65(25)
O
OH
1
1
8
9
( )4
c
NISac
10
70(20)
(
)4
OH
I
NBS
NBSac
10
8
95
90
Br
O
O
OH
Cl
NCS
NCSac
3
10
87
92
2
0
1
OH
I
NIS
NISac
3
5
90
90
2
O
OH
a
b
c
All the products are known compounds (16, 20, 21, 24, 28) and are identified by their physical or spectral data.
Isolated yield.
Yield % in parentheses shows the formation of the other regioisomer.
the intermediate (a) can release OPPh3 through the
anchimeric assistance of bromide to form the bromonium
ion (b). An attack of the second nucleophile to either side of
perature. TLC monitoring showed the completion of the re-
action after 40 min. (This reaction with 1.2 mmol of NBSac
takes 8 min, Table 1, entry 1.) After evaporation of the sol-
vent, column chromatography of the crude mixture on silica
gel using n-hexane – ethyl acetate afforded 1-bromo-3-
(
b) can produce a mixture of two regioisomers (Scheme 3).
In summary, the present investigation has demonstrated
1
that the use of a PPh –NXS or PPh –NXSac system offers a
phenoxy-2-propanol as a yellow oil in 93% yield. H NMR
3
3
simple, novel, and convenient method for the selective con-
(CDCl , 250 MHz, ppm) δ: 2.6 (d, 1H, J = 5 Hz), 3.6–3.7
3
version of epoxides to either their corresponding vic-halo al-
(m, 2H), 4.07–4.10 (m, 2H), 4.15–4.25 (m, 1H), 6.90–7.10
3
13
cohols or symmetrical or unsymmetrical vic-dihalides.
(m, 3H), 7.3–7.6 (m, 1H). C NMR (CDCl , 62.9 MHz,
3
ppm) δ: 35.0, 69.5, 70.3, 114.5, 121.4, 129.6, 158.1. Mass
spectra m/e (%): 232 ([M + 2], 33.1), 230 ([M], 35.6), 151
Experimental section
(
[M – Br], 20.3).
All the solvents and reagents were purchased from Fluka
Switzerland) or Merck (Germany) Chemical Companies.
(
Typical procedure for the conversion of oxiranylmethyl
phenyl ether to 1,2-dibromo-3-phenoxy propane by
The products were purified by column or thick layer chro-
matography techniques. FT-IR spectra were recorded on a
Shimadzu DR-8001 spectrometer. NMR spectra were recorded
on a Brucker Avance DPX 250 MHz instrument. Mass spec-
tra were recorded on a Shimadzu GC–MS-QP 1000PX.
PPh –NBS
3
PPh (0.654 g, 2.5 mmol) was added to a flask containing
3
NBS (0.443 g, 2.5 mmol) in refluxing acetonitrile. Then
oxiranylmethyl phenyl ether (0.15 g, 1 mmol) was added.
TLC or GC analysis showed the completion of the conver-
sion of oxiranylmethyl phenyl ether to 1,2-dibromo-3-
phenoxypropane after 3 h. After completion of the reaction,
the solvent was evaporated. 1,2-Dibromo-3-phenoxy propane
was obtained in 88% yield after column chromatography of
Typical procedure for the conversion of oxiranylmethyl
phenyl ether to 1-bromo-3-phenoxy-2-propanol by
PPh –NBS
3
Oxiranylmethyl phenyl ether (0.15 g, 1 mmol) was added
to a flask containing PPh (0.314 g, 1.2 mmol) and NBS
the crude mixture using n-hexane – ethyl acetate (5:1) as
3
1
(
0.213 g, 1.2 mmol) in 1% aq. CH CN (5 mL) at room tem-
eluent. H NMR (CDCl , 250 MHz, ppm) ␦: 3.8–3.9 (m,
3
3
3
Supplementary data for this article are available on the journal Web site (http://canjchem.nrc.ca) or may be purchased from the Depository
of Unpublished Data, Document Delivery, CISTI, National Research Council Canada, Building M-55, 1200 Montreal Road, Ottawa, ON
K1A 0R6, Canada. DUD 4096. For more information on obtaining material refer to http://cisti-icist.nrc-cnrc.gc.ca/irm/unpub_e.shtml.
©
2006 NRC Canada

Iranpoor et al.
73
Table 2. Conversion of epoxides to vic-dihalides with PPh –NXS or PPh –NXSac (X = Br, C1) in
3
3
acetonitrile under reflux conditions.
a
Yield (%)b
88
Entry
1
Substrate
Product
Time (h)
3.5
Br
O
Br
Cl
O
O
Ph
Ph
Ph
Cl
O
2
O
3
90
O
Ph
O
O
Br
Br
3
4
5
3
2
80
87
89
Ph
Ph
Ph
Cl
Cl
Ph
Br
O
O
O
Br
Cl
3.5
O
O
O
Cl
O
O
O
6
2
79
O
Br
Cl
O
O
O
Br
7
8
9
O
5.5
5
82
75
80
O
Cl
O
Br
5
O
Br
1
1
1
1
0
1
2
3
Cl
Br
4
3
78
80
85
O
Cl
Br
O
(
)4
(
)4
O
(
)4
(
)4
Cl
2
Cl
Br
c
4.5
83
O
O
Br
Cl
14
4
88
Cl
a
b
c
All the products are known compounds (28) and are identified by their physical or spectral data.
Isolated yield.
1
The stereochemistry of product was determined by the comparison of its H NMR spectrum with the literature (32).
©
2006 NRC Canada

7
4
Can. J. Chem. Vol. 84, 2006
Table 3. Conversion of epoxides to unsymmetrical vic-dihalides with PPh –NXS of different halides.
3
a
b
c
Entry
1
Substrate
Product
Time (h)
5
Yield (%)
Cl
O
d
O
65
O
O
Br
Ph
Ph
Ph
Ph
Br
I
O
2
3
4
5
Cl
8
8.5
7
85
52
O
Ph
O
O
O
Cl
Ph
Cl
O
O
O
O
O
O
Br
Cl
d
68
O
O
O
Br
9
90
44
O
I
O
O
Cl
6
O
10
O
O
a
All the products are known compounds (28) and are identified by their physical or spectral data.
b
c
These reactions were performed in the presence of PPh –NXSac with similar results.
Isolated yield.
The other isomeric product was also formed in 25% yield.
3
d
Scheme 2.
+
O
O
O PPh
O
3
_
PPh3
_
R
N X + Ph3P
N X
N
+
O
O
O
_
X
R
O
(
I)
(II)
O
HO
O
+
OPPh3
+
X:Cl, Br, I
H O
N H
_
2
Ph PO
N
3
R
X
P
O
P
R
X
h
O
3
/
N
_
X
O
X(
(
X
(
III)
X
')
S
'
)
(X')X
X:Cl, Br
+
OPPh +
3
N H
X':Cl, Br, I
R
X
O
2
H), 4.3–4.4 (m, 3H), 6.9–7.0 (m, 3H), 7.2–7.32 (m, 2H).
Typical procedure for the conversion of oxiranylmethyl
phenyl ether to 2-bromo-1-chloro-3-phenoxypropane
1
3
C NMR (CDCl , 62.9 MHz, ppm) δ: 31.7, 46.7, 68.0,
3
1
4
4
13.8, 120.6, 128.6, 156.9. Mass spectra m/e (%): 296 ([M +
], 16.2), 294 ([M + 2], 41.7), 292 ([M], 14.1), 203 ([M +
– PhO], 3.2), 201 ([M + 2 – PhO], 8.7), 199 ([M – PhO], 5.3).
PPh (0.314 g, 1.2 mmol) was added to a flask containing
3
of NCS (0.159 g, 1.2 mmol) in CH CN at room temperature.
3
Then oxiranylmethyl phenyl ether (0.15 g, 1 mmol) was
©
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Iranpoor et al.
75
Scheme 3.
X
R
O
Br
R
Ph PO
3
-OPPh3
PPh /NXS
3
N Ph3P
Br
b)
R
Br
Br
R
O
O
(
a)
(
R
X
Br
gradually added to the reaction mixture over a period of
.5 h. TLC or GC analysis showed the completion of the
conversion of oxiranylmethyl phenyl ether to 1-chloro-3-
phenoxy-2-propanol. Then the reaction mixture was trans-
ferred to another flask containing a solution of PPh3
8. (a) Y. Guindon, M. Therien, Y. Girard, and C. Yoakim. J. Org.
Chem. 52, 1680 (1987); (b) N.N. Joshi, M. Srebnik, and H.C.
Brown. J. Am. Chem. Soc. 110, 6246 (1988).
1
9
. T.W. Bell and J.A. Ciaccio. Tetrahedron Lett. 27, 827 (1986).
0. P. Bovicelli, E. Mincione, and G. Ortaggi. Tetrahedron Lett.
2, 3719 (1991).
1. (a) J.A. Ciaccio, E. Heller, and A. Talbot. Synlett, 248 (1991);
1
1
3
(
0.654 g, 2.5 mmol) and NBS (0.443 g, 2.5 mmol) in
CH CN (5 mL) and refluxed for 8 h to produce 2-bromo-1-
3
(
(
b) M. Shimizu, A. Yoshida, and T. Fujisawa. Synlett, 204
1992); (c) Z.X. Guo, A.H. Haines, and R.J.K. Taylor. Synlett,
chloro-3-phenoxypropane. After completion of the reaction,
the solvent was evaporated. 2-Bromo-1-chloro-3-phenoxy-
propane was obtained in 85% yield after column chromatog-
6
07 (1993).
2. (a) J.S. Bajwa and R.C. Anderson. Tetrahedron Lett. 32, 3021
1991); (b) H. Kotsuki and T. Shimanouchi. Tetrahedron Lett.
7, 1845 (1996).
1
1
raphy of the crude mixture using n-hexane – ethyl acetate
(
3
1
(
(
5:1) as eluent. H NMR (CDCl , 250 MHz, ppm) δ: 3.9–4.0
3
m, 2H), 4.25–4.4 (m, 3H), 6.8–7.1 (m, 3H), 7.2–7.3 (m,
3. Y.-G. Suh, B.A. Koo, J.-A. Ko, and Y.-S. Cho. Chem. Lett.
1
3
2
1
4
H). C NMR (CDCl , 62.9 MHz, ppm) δ: 45.0, 48.1, 68.3,
3
1907 (1993).
14.8, 121.6, 129.6, 157.9. Mass spectra m/e (%): 252 ([M +
], 8.7), 250 ([M + 2], 29.3), 248 ([M], 24), 171 ([M + 2 –
Br] and [M + 4 – 81Br], 7.2), 169 ([M + 2 – Br] and [M –
1
1
1
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7
7
9
81
9
Br], 12.9).
1
1
7. N. Iranpoor and H. Adibi. Bull. Chem. Soc. Jpn. 73, 675
(
2000).
Acknowledgments
8. C.E. Garrett and G.C. Fu. J. Org. Chem. 62, 4534 (1997).
We are thankful to the Organization of Management and
Planning of Iran and the Shiraz University Research Council
for the support of this work.
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2006 NRC Canada