A simple, iron-catalyzed, pyridine-assisted hydrogen peroxide epoxidation system

Article abstract of DOI:10.1248/cpb.59.799

A simple and inexpensive system comprised of H₂O ₂-pyridine-FeCl₃ · 6H₂O for the catalysis of olefin epoxidation was established. Intriguingly, the reactivity of this system greatly depends on the amounts of pyridine. Various substrates, including aromatic and aliphatic olefins, were epoxidized by this simple system in moderate to excellent yields.

Full text of DOI:10.1248/cpb.59.799

June 2011
Communication to the Editor
Chem. Pharm. Bull. 59(6) 799—801 (2011)
799
a)
Table 1. Effects of Pyridine Loading on Epoxidation of trans-Stilbene
A Simple, Iron-Catalyzed, Pyridine-
Assisted Hydrogen Peroxide Epoxidation
System
Mingyu JIAO, Hirofumi MATSUNAGA, and
Tadao ISHIZUKA*
b)
c)
Entry
Pyridine (eq)
Yield
Recov. (%)
Faculty of Life Sciences, Kumamoto University; 5–1 Oe-honmachi,
Kumamoto 862–0973, Japan.
Received March 16, 2011; accepted April 5, 2011; published online
April 6, 2011
1
2
3
4
5
0.1
0.25
0.5
1
2
2
2
3
4
20
40
69
82
90
96
94
93
94
78
52
26
12
6
0
3
2
2
d)
6
A simple and inexpensive system comprised of H O -pyri-
e)
2
2
7
8
9
dine-FeCl ·6H O for the catalysis of olefin epoxidation was es-
3
2
tablished. Intriguingly, the reactivity of this system greatly de-
pends on the amounts of pyridine. Various substrates, including
aromatic and aliphatic olefins, were epoxidized by this simple
system in moderate to excellent yields.
a) Reaction conditions: FeCl ·6H O (5 mol%), H O (2 eq), tert-amyl alcohol
10 ml), trans-stilbene (0.5 mmol). b) Isolated yields. c) Recovery yields of trans-
stilbene. d) 10 mol% of FeCl ·6H O was used. e) 3 eq of hydrogen peroxide were
3
2
2
2
(
3
2
used.
Key words hydrogen peroxide; iron(III) chloride; olefin epoxidation;
pyridine; acceleration
combinative system catalyzed the reaction in excellent yield
Epoxides are highly desirable building blocks for the for- within only 30 min. In addition, this system was suitable for
mation of fine chemicals, which are used in the production of other substrates, such as aromatic and aliphatic olefins, both
pharmaceuticals, agricultural chemicals, industrial products of which displayed good reactivity and excellent mass bal-
1
—3)
or synthetic intermediates.
dants. In particular, m-chloroperbenzoic acid (m-CPBA) has
received considerable interest for use in the epoxidation of trans-stilbene 1 was conducted in tert-amyl alcohol at
Peracids are often used as oxi- ance.
At the onset of this work, a model catalytic epoxidation of
29)
4—6)
olefins to obtain the corresponding epoxides.
However, room temperature in the presence of pyridine (Table 1). Use
because of the cost, toxicity, and by-products of m-CPBA, a of 10 mol% resulted in only 20% yield of epoxide 2 (entry
more cost-effective, harmless and clean oxidant is needed. 1), and extending the reaction time did not improve the prod-
Consequently, hydrogen peroxide has been extensively inves- uct yield. Surprisingly, the epoxidation was improved at
27,28)
tigated as an alternative oxidant. Because hydrogen peroxide higher pyridine concentrations (entries 1—5),
and use of
is safe and inexpensive, possesses a high oxygen content, and 50 mol% of pyridine resulted in a good product yield of 69%
generates water as the only by-product, it is a viable candi- (entry 3). To our delight, use of 2 eq of pyridine increased the
7—10)
date for use in epoxidation reactions.
yield to 90% (entry 5). Such a phenomenon was not reported
Metal-catalyzed epoxidations with hydrogen peroxide re- prevously in the protocols of transition metal-catalyzed epox-
1
1—13)
sults in outstanding yields.
Nevertheless, although the idation, including dipicolinic acid and amine or imidazole
1
4)
15,16)
superior metal catalysts like Re or Pt
have excellent derivative systems. It indicates that pyridine acts as different
reactivity, the disadvantages of these metals cannot be way from dipicolinic acid or imidazole derivatives, leading to
ignored—namely, their high cost and quantitative insuffi- a different mechanism in FeCl -catalyzed hydrogen peroxide
3
ciency. Thus, our research focus has been on iron salts, epoxidation. Further increases in the pyridine equivalent did
which are relatively inexpensive compared with other transi- not affect the product yield obviously (entries 8, 9). As ex-
tion metals, due to their natural abundance. Furthermore, pected, increasing the amount of iron catalyst improved
30)
iron salts have little risk to human health and are commer- the yield (entry 6), and vice versa. In the absence of
17—21)
cially available.
FeCl ·6H O, no reaction was observed when using 2 eq of
3 2
Beller and co-workers performed epoxidation of olefins in pyridine, suggesting that the FeCl ·6H O plays an indispen-
3
2
a reaction system comprised of FeCl ·6H O and H O , em- sable role in this epoxidation system. It should be noted that
3
2
2
2
ploying dipicolinic acid and an amine to activate the reaction. the mass balance of this reaction system was ca. 96%, which
This method afforded the correspongding epoxides in good indicates minimal side reactions of the epoxide product.
22—26)
to excellent yields.
Recently, they also reported a sim-
To elucidate the effects of pyridine on the ability to coordi-
pler system that uses imidazole derivatives, rather than dipi- nate to iron species, activation following addition of pyridine
27,28)
colinic acid and amines,
as ligands. However, the reactiv- to the FeCl -aromatic amine-assisted epoxidation system was
3
ity of this system was moderate, and the ligands which re- investigated (Table 2).
sulted in relatively high yields had to be synthesized ad hoc
Imidazole and its derivatives, which are good ligands, are
before use because of commercial inavailability. Moreover its commonly employed in transition metal-catalyzed epoxida-
31,32)
versatility regarding the use of different olefin substrates was tion.
limited.
However, when we performed our model epoxida-
tion reaction with imidazole 3 instead of pyridine, the yields
We performed a more economical and practical H O -oxi- were unsatisfactory and tended to decrease with increasing
27,28)
2
2
dized epoxidation of trans-stilbene 1 with a catalytic iron salt amounts of imidazole (entries 1—4). Intriguingly, when an
and a different ligand. This simple, FeCl ·6H O and pyridine excess amount of pyridine was added to the imidazole–FeCl3
3
2
∗
To whom correspondence should be addressed. e-mail: tstone@gpo.kumamoto-u.ac.jp
© 2011 Pharmaceutical Society of Japan

8
00
Vol. 59, No. 6
Table 2. Effects of the Combination of Additive and Pyridine on the
Epoxidation of trans-Stilbene
Table 3. Pyridine–FeCl -Catalyzed Epoxidation of Different Olefin Sub-
strates
3
a)
a)
b)
Entry
Additive
Pyridine : Additive
Yield
(%)
b)
Entry
Substrate
Conv. (%)
94
Yield (%)
(mol% : mol%)
1
2
3
4
5
6
Imidazole (3)
0 : 5
0 : 10
0 : 30
0 : 100
190 : 10
195 : 5
0 : 10
0 : 200
195 : 5
0 : 60
16
24
15
6
55
78
18
6
61
0
62
74
0
1
2
1
90
3
3
3
3
10
36
64
56
28
49
56
c)
3
3
10
c)
7
N-Methylimidazole (4)
8
9
4
4
4
5
11
12
10
11
12
13
14
2,6-Lutidine (5)
63
75
83
91
44
50
58
70
5
5
170 : 30
195 : 5
190 : 10
195 : 5
2,2ꢀ-Bipyridyl (6)
Phenanthroline (7)
6
13
14
15
0
d)
7
a) Reaction conditions: see Table 1. b) Isolated yields. c) See ref. 28.
d)
8
complex, the catalytic activity was dramatically restored, giv-
ing the epoxides in good yields (entries 5, 6). Similar phe-
nomena were also observed for the N-methylimidazole (4)
a) Reaction conditions: see Table 1. b) Isolated yields. c) 20 mol% of
FeCl ·6H O was used. d) Calculated from H-NMR after distillation of solvent.
1
3
2
and 2,6-lutidine (5)–FeCl complexes (entries 7—9, 10—12).
3
By contrast, 2,2ꢀ-bipyridyl (6) and phenanthroline (7)–FeCl3
complexes did not facilitate the epoxidation reaction, and which is economically and environmentally friendly and con-
pyridine did not reactivate the reaction (entries 13, 14). One venient in operation at room temperature and under open-air.
possible explanation for these results is the strong coordina- This simple system is applicable to aromatic and aliphatic
tion of 2,2ꢀ-bipyridyl and phenanthroline to iron species. olefins for the production of the corresponding epoxides in
From Table 2, we assume that pyridine competes with imida- good to excellent yields. Although some of the substrates re-
zole, N-methylimidazole or 2,6-lutidine for coordination to sulted in moderate yields, the unconverted starting material
the iron(III) to form the Fe(III)-pyridine catalyst, which has could be recovered and recycled in subsequent reactions. The
greater activity than either the Fe(III)-(N-methyl)imidazole reactivity of inherently inactive substrates was improved by
or Fe(III)-2,6-lutidine complex. By contrast, 2,2ꢀ-bipyridyl increasing the loading of the FeCl ·6H O catalyst. Intrigu-
3
2
and phenanthroline coordinated tightly to the iron(III), result- ingly, the catalytic activity of Fe(III)-pyridine was highly de-
ing in inactive complexes. pendent on the number of pyridine equivalents added to the
Having optimized the reaction conditions, we proceeded to reaction system. Further studies are in progress.
investigate the scope and limitations of different olefin sub-
References and Notes
strates using 5 mol% of FeCl ·6H O, 2 eq of pyridine and 2
3
2
1
2
)
)
Besse P., Veschambre H., Tetrahedron, 50, 8885—8927 (1994).
Bai D., Jing H., Liu Q., Zhu Q., Zhao X., Catal. Commun., 11, 155—
157 (2009).
eq of H O . Table 3 summarizes the results of the pyridine–
2
2
FeCl -catalyzed epoxidation of various olefin substrates.
3
Thus, the intrinsically inefficient substrate cis-stilbene 10
3) Zhao X., Chen W., Chem. Lett., 39, 527—529 (2010).
4) Machii K., Watanabe Y., Morishima I., J. Am. Chem. Soc., 117,
33,34)
gave the corresponding epoxide in 28% yield (entry 2),
whereas 49% yield was achieved when 20 mol% of FeCl ·
6
691—6697 (1995).
3
35)
5) Jana N. K., Verkade J. G., Org. Lett., 5, 3787—3790 (2003).
6
H O was used (entry 3). Cinnamyl acetate oxide was pro-
2
6
)
Lee S. H., Xu L., Park B. K., Mironov Y. V., Kim S. H., Song Y. J.,
duced in 56% yield from 11 (entry 4) in the absence of side
reactions. Cinnamyl alcohol 12 gave a moderate yield of
Kim C., Kim Y., Kim S.-J., Chem. Eur. J., 16, 4678—4685 (2010).
7) Shu L., Shi Y., J. Org. Chem., 65, 8807—8810 (2000).
8) Neimann K., Neumann R., Org. Lett., 2, 2861—2863 (2000).
44%, showing that our simple and mild pyridine system re-
9)
Yao H., Richardson D. E., J. Am. Chem. Soc., 122, 3220—3221
2000).
sults in chemoselective epoxidation in the presence of hy-
droxy groups (entry 5). 1-Phenylcyclohexene 13 and trans-b-
methylstyrene 14 were epoxidized in 50% and 58% yield, re-
(
10) Rajagopalan B., Wei M., Musie G. T., Subramaniam B., Busch D. H.,
Ind. Eng. Chem. Res., 42, 6505—6510 (2003).
spectively (entries 6, 7). The chemical yield obtained for 1- 11) Sato K., Aoki M., Ogawa M., Hashimoto T., Noyori R., J. Org. Chem.,
6
1, 8310—8311 (1996).
phenylcyclohexene were much higher than the previously re-
ported values. An aliphatic olefin, 4-phenyl-1-butene 15,
also gave a good yield (entry 8).
22)
12) De Vos D. E., Sels B. F., Reynaers M., Subba Rao Y. V., Jacobs P. A.,
Tetrahedron Lett., 39, 3221—3224 (1998).
1
1
3) Lane B. S., Burgess K., J. Am. Chem. Soc., 123, 2933—2934 (2001).
4) Rudolph J., Reddy K. L., Chiang J. P., Sharpless K. B., J. Am. Chem.
Soc., 119, 6189—6190 (1997).
In conclusion, we established a simple epoxidation system
comprised of the catalytic FeCl –pyridine complex and H O ,
3
2
2

June 2011
801
1
5) Pizzo E., Sgarbossa P., Scarso A., Michelin R. A., Strukul G.,
Organometallics, 25, 3056—3062 (2006).
Chem. Eur. J., 14, 7687—7698 (2008).
27) Schröder K., Tong X., Bitterlich B., Tse M. K., Gelalcha F. G.,
Brückner A., Beller M., Tetrahedron Lett., 48, 6339—6342 (2007).
28) Schröder K., Enthaler S., Bitterlich B., Schulz T., Spannenberg A., Tse
M. K., Junge K., Beller M., Chem. Eur. J., 15, 5471—5481 (2009).
29) The same reaction shown in entry 5, Table 1, was also tried in ethanol,
THF, MeCN and t-BuOH/CH Cl (7/3) in place of t-amyl alcohol to
16) Colladon M., Scarso A., Sgarbossa P., Michelin R. A., Strukul G., J.
Am. Chem. Soc., 128, 14006—14007 (2006).
17) Groves J. T., Nemo T. E., J. Am. Chem. Soc., 105, 5786—5791 (1983).
18) Groves J. T., Myers R. S., J. Am. Chem. Soc., 105, 5791—5796 (1983).
19) White M. C., Doyle A. G., Jacobsen E. N., J. Am. Chem. Soc., 123,
2
2
7
194—7195 (2001).
0) Payeras A. M. I., Ho R. Y. N., Fujita M., Que. L. Jr., Chem. Eur. J., 10,
944—4953 (2004).
give the corresponding epoxide in 0%, 12%, 15% and 91% yields, re-
spectively. Considering the chemical yields and the simplicity of reac-
tion system, we chose t-amyl alcohol as a standard solvent.
2
4
2
2
1) Stephenson N. A., Bell A. T., Inorg. Chem., 46, 2278—2285 (2007).
2) Bitterlich B., Anilkumar G., Gelalcha F. G., Spilker B., Grotevendt A.,
Jackstell R., Tse M. K., Beller M., Chem. Asian J., 2, 521—529
30) 54% yield was achieved with 2.5 mol% of FeCl ·6H O.
31) Anelli P. L., Stefano B., Montranari F., Quici S., J. Chem. Soc., Chem.
Commun., 1989, 779—780 (1989).
3
2
(
2007).
32) Patra R., Chaudhary A., Ghosh S. K., Rath S. P., Inorg. Chem., 49,
2057—2067 (2010).
2
2
2
2
3) Anilkumar G., Bitterlich B., Gelalcha F. G., Tse M. K., Beller M.,
Chem. Commun., 2007, 289—291 (2007).
4) Gelalcha F. G., Bitterlich B., Anilkumar G., Man K. T., Beller M.,
Angew. Chem. Int. Ed., 46, 7293—7296 (2007).
33) Yin G., Danby A. M., Kitko D., Carter J. D., Scheper W. M., Busch D.
H., Inorg. Chem., , 46, 2173—2180 (2007).
34) Mohajer D., Abbasi M., Eur. J. Inorg. Chem., 20, 3218—3224 (2008).
5) Bitterlich B., Schröder K., Tse M. K., Beller M., Eur. J. Org. Chem., 3, 35) 52% yield was achieved when the same reaction was performed for
867—4870 (2008).
3 h.
6) Gelalcha F. G., Anilkumar G., Tse M. K., Brückner A., Beller M.,
4