Oxidative cleavage of aryl epoxides to benzaldehydes catalyzed by VO(acac)2

Article abstract of DOI:10.1016/j.tetlet.2015.12.064

This work reports a novel method for the oxidative cleavage of aryl epoxides to the corresponding aldehydes, catalyzed by the complex vanadyl acetylacetonate, VO(acac)₂, without adding any oxidizing agent. This complex proved to be efficient for the oxidative cleavage of several aryl epoxides in moderate to good yields.

Full text of DOI:10.1016/j.tetlet.2015.12.064

Tetrahedron Letters 57 (2016) 520–522
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Tetrahedron Letters
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Oxidative cleavage of aryl epoxides to benzaldehydes catalyzed by
VO(acac)2
⇑
Sara C. A. Sousa, Ana C. Fernandes
Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
This work reports a novel method for the oxidative cleavage of aryl epoxides to the corresponding
aldehydes, catalyzed by the complex vanadyl acetylacetonate, VO(acac)2, without adding any oxidizing
agent. This complex proved to be efficient for the oxidative cleavage of several aryl epoxides in moderate
to good yields.
Received 25 September 2015
Revised 9 December 2015
Accepted 15 December 2015
Available online 17 December 2015
Ó 2015 Elsevier Ltd. All rights reserved.
Keywords:
Epoxides
Cleavage
Aldehydes
Oxo-vanadium complexes
Introduction
Results and discussion
Epoxides are one of the most useful and versatile substrates in
organic synthesis due to their high reactivity and easy availability
through a wide variety of methods. Although, there are few meth-
ods reported in the literature for oxidative cleavage of epoxides to
aldehydes,1 these methodologies include the reaction with
aqueous sodium periodate2 or aqueous sodium paraperiodate
(Na3H2IO6)3 or iodosylbenzene (PhIO).4 In contrast, several proce-
dures have been developed for the conversion of epoxides to alde-
hydes or ketones by rearrangement catalyzed by Lewis acids.5–10
High valent oxo-complexes have an extreme relevance to oxida-
tion catalysis,11–14 such as in epoxidation of olefins, and more
recently they have been also successfully applied in the reduction
or deoxygenation of a large variety of organic compounds.13–16
In 2011, we reported a novel method for the deoxygenation of
several epoxides to the corresponding olefins in moderate to good
yields catalyzed by oxo-rhenium complexes without adding any
reducing agents.17 In continuation of our work on the use of
oxo-complexes for the deoxygenation of organic compounds, we
decided to investigate the deoxygenation of aryl epoxides
catalyzed by high valent oxo-vanadium, oxo-molybdenum and
oxo-tungsten complexes.
In order to compare the catalytic activity of several oxo-com-
plexes, the oxidative cleavage of 4-chlorostyrene oxide was carried
out in the presence of the catalysts VO(acac)2, MoO2Cl2,
WO2Cl2, MoO2Cl2(H2O)2,18 MoO2Cl2(dmso)2,18 MoO2Cl2(acac)2 and
MoO2Cl2(dmf)218 in reflux of toluene under air atmosphere (Table 1).
The reactions performed with the catalysts MoO2Cl2, MoO2(acac)2
and WoO2Cl2 were carried out under nitrogen atmosphere and in
reflux of dry toluene. The progress of the reactions was monitored
by thin layer chromatography and by 1H NMR.
The best result was obtained using the catalyst VO(acac)2
(10 mol %), affording the 4-chlorobenzaldehyde in 57% yield after
24 h (Table 1, entry 1). Using only 5 mol % of this catalyst, the
aldehyde was obtained in 15% yield, after 24 h (Table 1, entry 2).
The oxo-molybdenum and oxo-tungsten complexes catalyzed the
oxidative cleavage of 4-chlorostyrene oxide in moderate to low
yields (Table 1, entries 3–8). No reaction occurs in the absence of
catalyst (Table 1, entry 9).
The influence of the solvent on the oxidative cleavage of epox-
ides catalyzed by VO(acac)2 (10 mol %) was also explored using
trans-stilbene oxide as the test substrate. Toluene was the best
solvent at reflux temperature, affording the benzaldehyde in 85%
yield after 6 h (Table 2, entry 1). At room temperature, no reaction
was observed (Table 2, entry 2). The reaction performed in acetoni-
trile gave moderate yield of benzaldehyde, but the reaction
required 24 h (Table 2, entry 3). In benzene, p-xylene, tetrahydro-
furan, dichloromethane and chloroform, the aldehyde was
obtained in low yields (Table 2, entries 4–8).
⇑
Corresponding author. Tel.: +351 218419264; fax: +351 218464455.
E-mail address: anacristinafernandes@tecnico.ulisboa.pt (A.C. Fernandes).
http://dx.doi.org/10.1016/j.tetlet.2015.12.064
0040-4039/Ó 2015 Elsevier Ltd. All rights reserved.

S. C. A. Sousa, A. C. Fernandes / Tetrahedron Letters 57 (2016) 520–522
521
Table 1
Oxidative cleavage of 4-chlorostyrene oxide by different oxo-complexesa
Table 3
a
Oxidative cleavage of epoxides catalyzed by VO(acac)2
Entry
Catalyst
Catalyst (mol %)
Yieldb (%)
Entry
1
Substrate
Product
Time (h)
6
Yieldb (%)
1
2
3
4
5
6
7
8
9
VO(acac)2
VO(acac)2
MoO2Cl2
WO2Cl2
MoO2Cl2(H2O)2
MoO2Cl2(DMSO)2
MoO2(acac)2
MoO2Cl2(DMF)2
Without catalyst
10
5
57
15
35
23
19
14
5
3
85
83
10
10
10
10
10
10
—
2
3
4
5
6
7
24
24
24
24
24
24
No reaction
a
All reactions were carried out with 1.0 mmol of 4-chlorostyrene oxide.
Yield determined by 1H NMR.
79
68
57
51
46
b
To evaluate the general applicability of this methodology, the
oxidative cleavage of several epoxides catalyzed by 10 mol % of
VO(acac)2 in refluxing toluene under air atmosphere was explored
(Table 3).19 The best result was obtained in the oxidative cleavage
of trans-stilbene oxide, affording the benzaldehyde in 85% yield
after 6 h (Table 3, entry 1). The reaction of trans-stilbene oxide cat-
alyzed by 10 mol % of VO(acac)2 was also carried out under inert
atmosphere (6 h, 83% yield) and with bubbling air (5 h 45 min
84% yield). In both cases the results obtained are similar.
Good yields of benzaldehyde were also observed in the reaction
of ethyl 3-phenylglycidate and trans-1,3-diphenyl-2,3-epoxypro-
pan-1-one (83–79%), but these reactions required longer reaction
times (24 h) (Table 3, entries 2 and 3).
In contrast to the good yield of aldehyde obtained in the reac-
tion of trans-stilbene, the benzaldehyde was formed in 68% yield
in the reaction of cis-stilbene after 24 h (Table 3, entry 4).
4-Chlorobenzaldehyde, benzaldehyde and 4-fluorobenzaldehyde
were obtained in moderate yields (57–46%) from the oxidative
cleavage of 4-chlorostyrene oxide, styrene oxide and 4-fluo-
rostyrene oxide, respectively (Table 3, entries 5–7).
a
All reactions were carried out with 1.0 mmol of epoxide.
Yield determined by 1H NMR.
b
using 10 mol % of VO(acac)2, producing the benzaldehyde in 74%
yield after purification by silica gel column chromatography.
Finally, we observed that these reaction conditions were not
efficient for the deoxygenation of the aliphatic epoxide 1,2-epoxy-
hexane, cyclohexene oxide and 4-chlorophenylglycidyl ether that
produced a residual amount of the corresponding aldehyde.
To evaluate the scalability of the present protocol, the oxidative
cleavage of trans-stilbene oxide was performed on a 10 mmol scale
Conclusion
In conclusion, we developed a novel, practical and efficient
method for the oxidative cleavage of aryl epoxides to the corre-
sponding aldehydes, catalyzed by the oxo-vanadium complex
VO(acac)2 without adding any oxidizing agent. The advantages of
this methodology are: (a) the absence of an oxidizing agent; (b)
moderate to good yields of aldehydes; (c) applicability to a variety
of aryl epoxides; (d) use of a commercial and easy-to-handle catalyst;
(e) easy procedure (the reactions can be carried out under air
atmosphere with readily available equipment).
Table 2
Oxidative cleavage of trans-stilbene oxide catalyzed by VO(acac)2 in different
solventsa
All these features make this procedure one of the easiest, prac-
tical and eco-friendly procedures for the oxidative cleavage of aryl
epoxides reported in the literature, minimizing the use and gener-
ation of hazardous substances than traditional methods.
Further studies to improve the yields of the oxidative cleavage
through catalyst modifications and mechanistic studies, including
computational studies, are now in progress in our group.
Entry
Solvent
Temperature
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
Toluene
Toluene
CH3CN
Benzene
p-Xylene
THF
Reflux
rt
6
24
24
24
42
24
24
24
85
No reaction
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
53
32
29
11
5
Acknowledgments
This research was supported by Fundação para a Ciência e
Tecnologia (FCT) through project PTDC/QUI-QUI/110080/2009.
Sara C.A. Sousa thanks FCT for grant. Authors thank the project
UID/QUI/00100/2013 and the Portuguese NMR Network (IST-UTL
Center) for providing access to the NMR facilities.
CH2Cl2
CHCl3
3
a
All reactions were carried out with 1.0 mmol of trans-stilbene oxide.
Yield determined by 1H NMR.
b

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S. C. A. Sousa, A. C. Fernandes / Tetrahedron Letters 57 (2016) 520–522
10. Bonchio, M.; Conte, V.; Furia, F. D.; Modena, G. J. Mol. Catal. 1991, 70, 159–164.
References and notes
11. Sutradhar, M.; Martins, L. M. D. R. S.; Guedes da Silva, M. F. C.; Pombeiro, A. J. L.
Coord. Chem. Rev. 2015, 301–302, 200–239.
12. Ligtenbarg, A. G. J.; Hage, R.; Feringa, B. L. Coord. Chem. Rev. 2003, 237, 89–101.
13. Sanz, R.; Pedrosa, M. R. Curr. Org. Synth. 2009, 6, 239–263.
1. Antoniotti, S.; Duñach, E. Synthesis 2003, 2753–2762.
2. Binder, C. M.; Dixon, D. D.; Almaraz, E.; Tius, M. A.; Singaram, B. Tetrahedron
Lett. 2008, 49, 2764–2767.
3. Telvekar, V. N.; Patel, D. J.; Mishra, S. J. Synth. Commun. 2009, 39, 311–315.
4. Havare, N.; Plattner, D. A. Helv. Chim. Acta 2012, 95, 2036–2042.
5. Robinson, M. W. C.; Pillinger, K. S.; Graham, A. E. Tetrahedron Lett. 2006, 47,
5919–5921.
14. Jeyakumar, K.; Chand, D. K. J. Chem. Sci. 2009, 121, 111–123.
15. Sousa, S. C. A.; Fernandes, A. C. Coord. Chem. Rev. 2015, 284, 67–92.
16. Sousa, S. C. A.; Cabrita, I.; Fernandes, A. C. Chem. Soc. Rev. 2012, 41, 5641–5653.
17. Sousa, S. C. A.; Fernandes, A. C. Tetrahedron Lett. 2011, 52, 6960–6962.
18. Arnáiz, F. J.; Agudo, R.; Pedrosa, M. R.; De Cian, A. Inorg. Chim. Acta 2003, 347,
33–40.
19. In a typical experiment, the mixture of aryl epoxide (1.0 mmol) and VO(acac)2
(10 mol %) in toluene (3 ml) was stirred at reflux temperature under air
atmosphere, and the progress of the reaction was monitored by TLC or 1H NMR
spectroscopy (the reaction times are indicated in Tables 1–3). Upon
completion, the yields of the aldehydes were determined by 1H NMR.
6. Suda, K.; Kikkawa, T.; Nakajima, S.; Takanami, T. J. Am. Chem. Soc. 2004, 126,
9554–9555.
7. Karamé, I.; Tommasino, M. L.; Lemaire, M. Tetrahedron Lett. 2003, 44, 7687–
7689.
8. Bhatia, K. A.; Eash, K. J.; Leonard, N. M.; Oswald, M. C.; Mohan, R. S. Tetrahedron
Lett. 2001, 42, 8129–8132.
9. Martínez, F.; del Campo, C.; Llama, E. F J. Chem. Soc., Perkin Trans. 1 2000, 1749–
1751.