Rapid, highly efficient and stereoselective deoxygenation of epoxides by ZrCl4/NaI

Article abstract of DOI:10.1016/j.tetlet.2005.04.005

An effective and highly chemoselective method is described for the rapid deoxygenation of different epoxides to the corresponding olefins using ZrCl ₄/NaI in anhydrous CH₃CN, in excellent yields and with retention of relative stereochemistry.

Full text of DOI:10.1016/j.tetlet.2005.04.005

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 4107–4110
Rapid, highly efficient and stereoselective deoxygenation of
epoxides by ZrCl /NaI
4
*
Habib Firouzabadi, Nasser Iranpoor and Maasoumeh Jafarpour
*
Chemistry Department, College of Sciences, Shiraz University, Shiraz 71454, Iran
Received 21 December 2004;revised 30 March 2005;accepted 4 April 2005
Available online 20 April 2005
Abstract—An effective and highly chemoselective method is described for the rapid deoxygenation of different epoxides to the
corresponding olefins using ZrCl
4 3
/NaI in anhydrous CH CN, in excellent yields and with retention of relative stereochemistry.
Ó 2005 Published by Elsevier Ltd.
The ability of transition metals to mediate organic reac-
tions either catalytically or stoichiometrically constitutes
one of the most powerful strategies to achieve both
which may affect other sensitive functional groups in the
1
molecule.
4
1
selectivity and efficiency in synthetic chemistry. How-
In the course of our research on new applications of
ZrCl in organic synthesis, we have explored its use as
ever, the choice of mediator is important with respect
to environmental and economic considerations. For
example, TiCl is an efficient mediator in organic reac-
4
an effective catalyst for highly chemoselective trans-
5
1
thioacetalization of acetals. Very recently, we have
employed ZrCl /NaI as an efficient reagent for chemo-
4
tions, however, its applications are limited considerably
by its high toxicity and its requirement for special
4
1
6
selective iodination of alcohols. Now, we introduce
ZrCl /NaI as an expedient reagent for immediate and
2
3
handling. ZrCl4 is less costly, easily available and
4
4
relatively safe [LD [ZrCl , oral rat] = 1688 mg/kg].
5
stereospecific deoxygenation of epoxides to olefins in
excellent yields (Scheme 1).
0
4
4
+
Additionally, Zr
(
with a high charge-to-size ratio
22.22 e m ) enables reactions with high to excellent
2
À10 5
4
+
yields due to strong coordination of Zr . Thus, zirco-
nium(IV) compounds are excellent catalysts or reagents
in synthetic chemistry, as evidenced by their increasing
7
commercial use for this purpose.
The results given in Table 1 illustrate the high efficiency
of this protocol for the deoxygenation of structurally
different epoxides in short reaction times. Complete con-
version of diverse epoxides, carrying alkyl, aryl, ether,
carbonyl, ester and hydroxyl groups a or b to the oxi-
rane ring, were all converted in excellent yields.
6
It is well-known that epoxides are versatile intermediates
8
in organic chemistry. The deoxygenation of epoxides to
olefins allows the use of the oxirane ring as a protective
Among the epoxides we have studied, cis-stilbene oxide
deoxygenation required the longest reaction time
(15 min). We suggest that this retardation is caused by
9
group for double bonds. Thus, it is an important proto-
1
0
col to control olefin stereochemistry, for conversion
of biomass-derived substrates to useful organic com-
À
the requirement for attack by the large I on the epoxide
ring, which encounters pronounced steric hindrance
from the phenyl groups present in the molecule.
1
1
pounds and also for structural analysis of natural
1
2
products. Relatively few general methods exist for
1
3
removing oxygen atoms from epoxides. Most of them
require expensive reagents and harsh reaction conditions
R2
O
R4
R2
R4
ZrCl /NaI
4
Keywords: Zirconium tetrachloride;Sodium iodide;Epoxide;
Deoxygenation.
dry CH CN
3
*
Corresponding authors. Tel.: +98 711 2284822;fax: +98 711
280926;e-mail addresses: firouzabadi@chem.susc.ac.ir;iranpoor@
chem.susc.ac.ir
R1
R3
R1
R3
2
Scheme 1.
0
040-4039/$ - see front matter Ó 2005 Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2005.04.005

4108
H. Firouzabadi et al. / Tetrahedron Letters 46 (2005) 4107–4110
a
Table 1. Deoxygenation of epoxides using ZrCl
4
/NaI in anhydrous CH
3
CN
Entry
Epoxide
Product
GC yield (%)
100
Isolated yield (%)
93
Time (min)
<1
O
1
b
2
96
97
90
87
<1
<1
O
3
O
O
O
b
4
100
95
92
87
<1
<1
O
O
O
O
5
6
7
8
9
100
100
100
100
88
87
90
90
<1
<1
<1
<1
O
O
Cl
Cl
O
O
O
O
O
O
O
O
O
1
0
1
95
98
88
90
<1
<1
O
O
b
1
OH
OH
O
O
b
c
90
1
2
3
82
94
15
3
O
b
c
1
100
a
The molar ratio of epoxide: NaI:ZrCl
4
was 1:2:0.5.
b
17,18
The epoxides in entries 2, 4 and 11–13 were prepared according to the literature.
c 1
H NMR yield.
In all the reactions, the immediate development of a
deep brown colour was observed which is consistent
with the generation of molecular iodine in the reaction
mixture. By considering this observation, we suggest a
mechanism for the reaction (Scheme 2).
In order to show the advantages of the presented meth-
od, in Table 2, we have compared some of the results ob-
tained by other methods with those using the ZrCl /NaI
4
system.
In conclusion, we have reported that ZrCl /NaI is a safe,
4
The important feature of this method is its high stereo-
specificity as demonstrated by the deoxygenation of cis-
stilbene oxide to cis-stilbene and trans-stilbene oxide to
trans-stilbene (entries 12 and 13).
inexpensive and highly efficient reagent for rapid chemo-
selective deoxygenation of various epoxides in excellent
yields. We have also found that the reaction proceeded
with absolute stereospecificity.
The chemoselectivity of the method is also noteworthy,
as exemplified by a molecule which carries both an epox-
ide ring and a hydroxyl group (entry 11). Deoxygenation
of the epoxide ring proceeded well in high yield, the
hydroxyl group remaining intact.
Typical procedure: To a solution of styrene oxide
(0.120 g, 1 mmol) and NaI (0.3 g, 2 mmol) in dry
CH CN (2 ml) solid ZrCl (0.116 g, 0.5 mmol) was
added in several portions. The mixture was stirred at
reflux and the progress of the reaction was monitored
3
4

H. Firouzabadi et al. / Tetrahedron Letters 46 (2005) 4107–4110
4109
Cl
Cl
ZrCl3
ZrCl3
R2 O+ R4
ZrCl2
R4
R2
R1
O
R4
R2
R1
R2
R1
R4
R3
O
I
NaI
-I2
+
ZrOCl2
Cl-
-Cl-
-
R3
R1 I- R3
R3
I-
Cl
Cl
ZrOCl
R4
ZrOCl
ZrO
R4
R2
R1
O
R2
O+
R4
R2
R1
R2
R1
R4
R3
O
NaI
-I2
-Cl-
+
ZrO2
Cl-
-
R3
R1 I- R3
R3
I
I-
Scheme 2.
Table 2. Comparison of the ZrCl
Substrate ZrCl [Co(salen)
NaI min
4
/NaI system with previously reported methods for deoxygenation of epoxides
14j
14o
À
+10o
4
/
2
]/ MoO(Et dtc)
h [yield (%)]
2
2
LReO
3
/
13b
LiI/
Amberlyst 15
(EtO) P(O)TeNa
2
[n-Bu SnAlMe ] Li
3 3
13f
Na(Hg)
13g
PPh
3
h [yield (%)]
h [yield (%)]
[
yield (%)] h [yield (%)]
h [yield (%)] h [yield (%)]
O
a
b
<
1 [100]
1 [100]
—
2 [32]
—
3 [85]
—
—
—
O
<1 [100]
6 [100]
36 [92]
—
42 [88]
O
c
d
e
f
15 [90]
24 [100]
—
2 [33]
8 [93]
—
6 [88]
a
b
c
d
e
f
The product was a mixture of 2-phenylethanol and styrene.
The product was the halohydrin.
cis-Stilbene.
The product was a mixture of cis-stilbene, trans-stilbene and 1,2-diphenylethanol.
trans-Stilbene.
34% trans-stilbene, 66% cis-stilbene.
by GC. After less than 1 min, the reaction mixture was
diluted with cold water (10 ml) and ether (10 ml). The
organic layer was separated and washed with a solution
of Na S O (aq 10%, 10 ml), and then H O (10 ml). The
2. Lewis, R. J., Sr. Hawley’s Condensed Chemical Dictionary;
Suneel Galgotia: New Delhi, 1998.
3
4
. Riley, J. P.;Chester, R. Introduction to Marine Chemistry;
Academic: New York, 1971.
. Lewis, R. J. S. R. Dangerous Properties of Industrial
Materials, 8th ed.;Van Nostrand Reinhold: New York,
2
2
3
2
organic layer was separated and dried over anhydrous
Na SO . Evaporation of the solvent under reduced pres-
2
4
1
989;Vol. 3.
sure at room temperature gave the pure olefin (0.097 g,
3%) (Table 1, entry 1). In the case of low boiling prod-
5
. Huheey, J. E. Inorganic Chemistry: Principles of Structure
and Reactivity, 3rd ed.;Harper & Row: Singapore, 1990,
Chapter 7.
9
ucts (Table 1, entries 3, 6, 7, 8 and 9) liquid air cooled,
bulb-to-bulb distillation was used for purification.
6. Bora, U. Synlett 2003, 1073–1074, and references cited
therein.
7
. Moles, P. J. http://www.zrchem.com.
8. Smith, J. G. Synthesis 1984, 629–656.
. (a) Kraus, G. A.;Thomas, P. J. J. Org. Chem. 1988, 53,
395–1397;(b) Johnson, W. S.;Plummer, M. S.;Pulla
Reddy, S.;Bartlett, W. R. J. Am. Chem. Soc. 1993, 115,
15–521.
Acknowledgements
9
1
Support for this work by Iran TWAS Chapter at ISMO
and Shiraz University research council is highly
appreciated.
5
1
0. (a) Sharpless, K. B.;Umbreit, M. A.;Nieh, M. T.;Flood,
T. C. J. Am. Chem. Soc. 1972, 94, 6538–6540;(b) Umbreit,
M. A.;Sharpless, K. B. Org. Synth. 1981, 60, 29;(c)
Dowd, P.;Kang, K. Chem. Commun. 1974, 384–385;(d)
Hudrlik, P. F.;Peterson, D.;Rona, R. J. J. Org. Chem.
1975, 40, 2263–2264;(e) Rosenblum, M.;Saidi, M. R.;
Madhavarao, M. Tetrahedron Lett. 1975, 16, 4009–4012;
(f) Reetz, M. T.;Plackky, M. Synthesis 1976, 199–200;
References and notes
1
. Trost, B. M. In Transition Metal Organic Reactions;
Beller, M., Bolm, C., Eds.;Wiley-VCH: D-69469, Wein-
heim, Germany, 1998.

4110
H. Firouzabadi et al. / Tetrahedron Letters 46 (2005) 4107–4110
(
9
g) Dervan, P. B.;Shippey, M. A. J. Am. Chem. Soc. 1976,
8, 1265–1266;(h) Vedejs, E.;Fuchs, P. L. J. Am. Chem.
14. (a) Caputo, R.;Mangoni, L.;Neri, O.;Palumbo, G.
Tetrahedron Lett. 1981, 22, 3551–3552;(b) Mangette, J.
E.;Powell, D. R.;West, R. J. Chem. Soc., Chem. Commun.
1993, 1348–1349;(c) Mangette, J. E.;Powell, D. R.;
Calabrese, J. C.;West, R. Organometallics 1995, 14, 4064–
4073;(d) Mangette, J. E.;Powell, D. R.;Firman, T. K.;
West, R. J. Organomet. Chem. 1996, 521, 363–370;(e)
Ogawa, A.;Miyake, J.;Murai, S.;Sonoda, N. Tetrahedron
Lett. 1985, 26, 669–672;(f) Dittmer, D. C.;Zhang, Y.;
Discordia, R. P. J. Org. Chem. 1994, 59, 1004;(g) Alper,
H.;DesRoches, D. Tetrahedron Lett. 1977, 18, 4155–4158;
(h) Hayasi, Y.;Schwartz, J. Inorg. Chem. 1981, 20, 3473–
3476;(i) Sato, M.;Oshima, K. Chem. Lett. 1982, 157;(j)
Moloy, K. G. Inorg. Chem. 1988, 27, 677–681;(k) Sarmah,
P.;Barua, N. C. Tetrahedron Lett. 1988, 29, 5815–5816;(l)
Whinnery, L. L., Jr.;Henling, L. M.;Bercaw, J. E. J. Am.
Chem. Soc. 1991, 113, 7575–7582;(m) Isobe, H.;Bran-
chaud, B. P. Tetrahedron Lett. 1999, 40, 8747–8750;(n)
Ukaji, Y.;Fujisawa, T. Tetrahedron Lett. 1988, 29, 5165–
5168;(o) Clive, D. L. J.;Menchen, S. M. J. Org. Chem.
1980, 45, 2347–2354.
Soc. 1973, 95, 822–825;(i) Yamada, K.;Goto, S.;Nagase,
H.;Kyotani, Y.;Hirata, Y. J. Org. Chem. 1978, 43, 2076–
2
077;(j) Sonnet, P. E. Synthesis 1980, 828–830;(k) Clive,
D. L. J.;Denyer, C. V. J. Chem. Soc., Chem. Commun.
973, 253;(l) Calo, V.;Lopez, L.;Mincuzzi, A.;Pesce, G.
1
Synthesis 1976, 200–201;(m) Behan, J. M.;Johnstone, R.
A. W.;Wright, M. J. Chem. Soc., Perkin Trans. 1 1975,
1216–1217;(n) Suzuki, H.;Fuchita, T.;Iwasa, A.;
Mishina, T. Synthesis 1978, 905–908;(o) Matsubara, S.;
Nonaka, T.;Okuda, Y.;Kanemoto, Sh.;Oshima, K.;
Nozaki, H. Bull. Chem. Soc. Jpn. 1985, 1480–1483;(p)
Ogawa, A.;Miyake, J. I.;Murai, Sh.;Sonoda, N.
Tetrahedron Lett. 1985, 26, 669–672.
1
1
1
1. Carbohydrates as Organic Raw Materials II;Descotes, G.,
Ed.;VCH: New York, 1993.
2. Shoppee, C. W.;Sternhell, S.;Taylor, W. C.
Chem. 1966, 19, 1265–1269.
Aust. J.
3. (a) Gable, K. P.;Brown, E. C. Synlett 2003, 2243–2244;
b) Gable, K. P.;Brown, E. C. Organometallics 2000, 19,
44–946;(c) Gable, K. P.;Zhuravlev, F. A.;Yokochi, A.
(
9
15. (a) Firouzabadi, H.;Iranpoor, N.;Karimi, B.
Synlett
F. T. Chem. Commun. 1998, 779–780;(d) Antonioletti, R.;
Bovicelli, P.;Fazzolari, E.;Righi, G. Tetrahedron Lett.
1999, 319–320;(b) Firouzabadi, H.;Iranpoor, N.;Karimi,
B. Synlett 1999, 321–323.
2
000, 41, 9315–9318;(e) Wang, X.;Woo, L. K. J. Org.
16. Firouzabadi, H.;Iranpoor, N.;Jafarpour, M. Tetrahedron
Lett. 2004, 45, 7451–7454.
17. Mohajer, D.;Rezaeifard, A. Tetrahedron Lett. 2002, 43,
1881–1884.
Chem. 1998, 63, 356–360;(f) Isobe, H.;Branchaud, B. P.
Tetrahedron Lett. 1999, 40, 8747–8749;(g) Righi, G.;
Bovicelli, P.;Sperandio, A. Tetrahedron 2000, 56, 1733–
1737;(h) Patra, A.;Bandyopadhyay, M.;Mal, D. Tetra-
hedron Lett. 2003, 44, 2355–2357.
18. Kim, Y. H.;Hwang, J. P.;Gak Yang, S. Tetrahedron Lett.
1997, 38, 3009–3012.