Stereo- and regioselective zinc-mediated ring-opening of epoxides with diselenides

Article abstract of DOI:10.1055/s-2005-865224

Two convenient rapid, efficient, stereoselective and highly regioselective methods for the synthesis of β-hydroxy selenides by the direct opening of epoxides with diselenides in acetonitrile in the presence of either Zn/AlCl ₃ or zinc powder in

Full text of DOI:10.1055/s-2005-865224

1316
LETTER
Stereo- and Regioselective Zinc-Mediated Ring-Opening of Epoxides with
Diselenides
Zinc-Mediated
Ri
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xides
w
ith
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D
iselenides man Movassagh,* Mojgan Shamsipoor
Department of Chemistry, K. N. Toosi University of Technology, P. O. Box 15875-4416, Tehran, Iran
Fax +98(21)2853650; E-mail: bmovass1178@yahoo.com
Received 6 January 2005
The anion can then react, under mild and atmospheric
Abstract: Two convenient rapid, efficient, stereoselective and
highly regioselective methods for the synthesis of b-hydroxy se-
lenides by the direct opening of epoxides with diselenides in aceto-
nitrile in the presence of either Zn/AlCl3 or zinc powder in aqueous
conditions, with different classes of epoxides to give b-
hydroxy selenides, formed via trans-opening of the ep-
oxides, in moderate to excellent yields (Scheme 1).
sodium hydroxide solution are described. These methods appear to Table 1 shows the results obtained in the reactions of a
be competitive with the other methods previously reported.
series of representative epoxides with diphenyl- and
dibenzyl diselenides in the presence of Zn/AlCl3 system in
anhydrous acetonitrile (method A), compared with the re-
sults obtained in the presence of zinc powder and aqueous
sodium hydroxide in acetonitrile (method B).
Key words: b-hydroxy selenides, diselenides, epoxides, zinc, zinc
selenolate
b-Hydroxy selenides are valuable selenium intermediates
in organic synthesis;1 they can be converted to allylic al-
cohols, olefins, bromohydrins, vinyl selenides and ep-
oxides.2–5 Several methods are available for the
preparation of b-hydroxy selenides. These hydroxy com-
pounds have been found as the addition products of sele-
nenic acids to olefins with a good regioselectivity.6 The
SN2 displacement of bromine from b-bromoselenides by
hydroxide ion is another stereoselective method.7 The
alkaline hydrolysis of b-acetoxyselenides has been de-
scribed.8 A convenient method for the synthesis of b-hy-
droxy selenide uses N-phenylselenophthalimide (NPSP)
in the presence of water.9 Another important method is the
reaction of aldehydes and ketones with selenium-
stabilized carbanions.10 The reduction11 or nucleophilic
addition of Grignard reagents,11 alkyllithium, a-seleno-
alkyllithiums12 to a-selenoaldehydes or b-selenoketones
provide other methods for access to b-hydroxy selenides.
R2SeSeR2, Zn
O
R1CHCH2SeR2
OH
R1CHCH2OH
SeR2
+
R1
MeCN, 82 °C
1
2
3
Scheme 1
From the results in Table 1 it is quite evident that, in the
case of unsymmetrical epoxides, the reaction proceeds
with a remarkable regioselectivity because in most cases
selenolate anions exclusively attack the less hindered car-
bon of the epoxide to give the regioisomer (2, Scheme 1).
The exceptions are given by styrene oxide (entries 13 and
14) and 1,2-epoxy-3-phenoxypropane (entry 15) where
mixtures of the two regioisomers are obtained. Under neu-
tral conditions, styrene oxide reacted with diphenyl dise-
lenide to give regioisomers (2h) and (3h) in 64:36 ratio
(83% total isolated yield); whereas, the same reaction un-
der alkaline conditions gave the two regioisomers (2h)
and (3h) as an 80:20 mixture (81% total isolated yield).
This regioselectivity is presumably due to partial stabili-
zation of developing positive charge at the more hindered
site of the epoxide. In the reaction of 1,2-epoxy-3-phen-
oxypropane with diphenyl diselenide under both reaction
conditions, while only one regioisomer (2i) was obtained
in alkaline medium (entry 16), equal quantities of both re-
gioisomers were detected under neutral conditions. The
reactions are completely anti-stereoselective as shown by
the reactions carried out on cyclohexene- and cyclooctene
oxides (entries 8–12), where no trace of the syn-adducts
were detected by 1H NMR spectroscopy.
The SN2 ring-opening of epoxides, using selenolate an-
ions, is a common method for preparing b-hydroxy se-
lenides. This method provides an excellent preparative
route to allylic alcohols via selenoxide elimination.2 Other
effective reagents for epoxide-opening include phenyl tri-
methylsilyl selenide,13 aluminum selenolates,14 selenobo-
ranes,15 and benzeneselenol in the presence of alumina.16
Attack by the selenolates generally occurs at the less hin-
dered epoxide carbon and is anti stereospecific. In cyclic
systems, a strong preference for approach from the axial
direction may outweigh other factors.
Herein, we report that alkyl and arylselenide ions can be
easily generated from the corresponding diselenides in the
presence of either Zn/AlCl3 under neutral conditions or
with zinc powder in aqueous sodium hydroxide solution.
When diselenides were reacted with Zn/AlCl3 in dry
MeCN (method A), the zinc powder almost disappeared
within 1.5 hours; this indicates a reductive cleavage of the
Se-Se bond17 leading to the zinc selenolate [(R2Se)2Zn]
intermediate which further undergoes nucleophilic attack
SYNLETT 2005, No. 8, pp 1316–1318
1
7.
0
5.
2
0
0
5
Advanced online publication: 21.04.2005
DOI: 10.1055/s-2005-865224; Art ID: D00605ST
© Georg Thieme Verlag Stuttgart · New York

LETTER
Zinc-Mediated Ring-Opening of Epoxides with Diselenides
1317
Table 1 Reaction of Epoxides with Diselenides in the Presence of Zinc under Neutral and Alkaline Conditions
Entry
R1 or epoxide
CH3
R2
Ph
Methoda
Reaction time (h)
Productb,c
Yield (%)d
1
2
A
B
1.5
0.5
2a21
2a
90
91
3
4
n-C6H13
HOCH2
ClCH2
Ph
Ph
A
B
3
1
2b21
2b
61
86
5
6
A
B
4
1
2c21
2c
76
80
7
Ph
Ph
A
3
2d22
70
8
9
A
B
5
3
68
65
SePh
OH
O
2e20
10
11
12
Ph
Ph
A
B
2
0.5
78
80
SePh
O
OH
2f20
PhCH2
B
4
60
SeCH2Ph
OH
2g23
13
14
Ph
Ph
Ph
A
B
4
1
2h/3h20
2h/3h
83e
81f
15
16
PhOCH2
A
B
1.5
0.5
2i/3i24
2i
91g
91
17
PhOCH2
PhCH2
Ph
B
2
2j24
70
18
19
n-C4H9
A
B
3
1
2k25
2k
70
89
a A: Zn/AlCl3 system in anhyd MeCN; B: Zn in MeCN–NaOH (aq).
b All products are known compounds.
c References of the known compounds.
d Isolated yields.
e Ratio 2h/3h = 1.8:1.
f Ratio 2h/3h = 4:1.
g Ratio 2i/3i = 1:1.
on the epoxide.18 It seems that, in aqueous sodium hy-
droxide medium, zinc selenolate turns into the sodium
salt (R2Se–Na+) which is a more reactive selenolate ion to-
wards nucleophilic ring-opening of epoxides.19 Interest-
ingly, no corresponding diols were detected using this
method.
Acknowledgment
This work was supported by the K. N. Toosi University of
Technology Research Council.
References
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In conclusion, the new method described here appears to
be highly competitive with other methods reported in the
literature, and in some cases better results are obtained,
especially in terms of reaction time and yields.15,20 It has
been shown that the methods here reported are very effec-
tive for the opening of epoxides, with high regioselectivi-
ty, under simple and relatively mild conditions. The other
advantages of these methods are simple work-up, lower
toxicity, and low costs.
Synlett 2005, No. 8, 1316–1318 © Thieme Stuttgart · New York

1318
B. Movassagh, M. Shamsipoor
LETTER
was continued for the specified time (Table 1) without
protection from the atmosphere. Progress of the reaction was
monitored by TLC. After completion of the reaction, the
solvent was evaporated and the residue was acidified to pH
4 with HCl (10%). The organic phase was extracted with
Et2O (2 × 15 mL), dried (Na2SO4), and concentrated. The
pure products were obtained by preparative TLC (silica gel,
eluent, CCl4/Et2O = 2:1) to afford the desired b-hydroxy
selenides.
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8208.
(19) General Experimental Procedure: Method B.
A mixture of diselenide (0.5 mmol) and activated zinc
powder (2.5 mmol) was suspended in MeCN (15 mL). The
mixture was refluxed, with stirring, for 10 min. To this
mixture was added 25% NaOH (3 mL, 18.8 mmol), and the
mixture was stirred for further 5 min, during which time the
yellow solution turned to colorless. Then, the epoxide (1
mmol) was added in one portion to the solution and stirring
was continued for the length of time indicated in Table 1.
When the reaction was complete, the organic solvent was
evaporated, and the residue was acidified to pH 4 with HCl
(10%). The organic layer was extracted with Et2O (2 × 20
mL), dried (Na2SO4), and evaporated. Preparative TLC
yielded the pure products.
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Chem. Res., Synop. 2004, 148. (c) Movassagh, B.;
Mirshojaei, F. Monatsh. Chem. 2003, 134, 831.
(18) General Experimental Procedure: Method A.
A stirred solution of the diselenide (0.5 mmol) in anhydrous
MeCN (15 mL) was treated with activated zinc powder (2.5
mmol). The mixture was refluxed for 1.5 h, during which
time the zinc powder was almost completely consumed.
Then, finely ground anhydrous AlCl3 (1.2 mmol) and the
epoxide (1.5 mmol) were added to the solution and stirring
(20) Sakakibara, M.; Katsumata, K.; Watanabe, Y.; Toru, T.;
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Synlett 2005, No. 8, 1316–1318 © Thieme Stuttgart · New York