Organoselenium-catalyzed baeyer-villiger oxidation of α,β-unsaturated ketones by hydrogen peroxide to access vinyl esters

Article abstract of DOI:10.1002/adsc.201400957

By carefully screening the organoselenium pre-catalysts and optimizing the reaction conditions, simple dibenzyl diselenide was found to be the best pre-catalyst for Baeyer-Villiger oxidation of (E)-α,β-unsaturated ketones with the green oxidant hydrogen peroxide at room temperature. The organoselenium catalyst used in this reaction could be recycled and reused several times. This new method was suitable not only for methyl unsaturated ketones, but also for alkyl and aryl unsaturated ketones. Therefore, it provided a direct, mild, practical, highly functional group-tolerant process for the chemoselective preparation of the versatile (E)-vinyl esters from the readily available (E)-α,β-unsaturated ketones. A possible mechanism was also proposed to rationalize the activity of the organoselenium catalyst in the presence of hydrogen peroxide in this Baeyer-Villiger oxidation reaction.

Full text of DOI:10.1002/adsc.201400957

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DOI: 10.1002/adsc.201400957
Organoselenium-Catalyzed Baeyer–Villiger Oxidation of
a,b-Unsaturated Ketones by Hydrogen Peroxide to Access
Vinyl Esters
Xu Zhang,a,b Jianqing Ye,a Lei Yu,a,b,c,* Xinkang Shi,b Ming Zhang,a Qing Xu,a,b,*
and Mark Lautensc
a
School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou, Jiangsu 225002, Peopleꢀs Republic of
China
Fax : (+86)-514-8797-5244; phone: (+86)-136-6529-5901; e-mail: yulei@yzu.edu.cn
College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, Zhejiang 325035, Peopleꢀs Republic of
b
China
Fax : (+86)-577-8668-9302; phone: (+86)-138-5774-5327; e-mail: qing-xu@wzu.edu.cn
Davenport Laboratories, Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON, M5S 3H6,
c
Canada
Received: October 2, 2014; Revised: December 26, 2014; Published online: && &&, 0000
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201400957.
Abstract: By carefully screening the organoseleni-
um pre-catalysts and optimizing the reaction condi-
tions, simple dibenzyl diselenide was found to be
the best pre-catalyst for Baeyer–Villiger oxidation
of (E)-a,b-unsaturated ketones with the green oxi-
dant hydrogen peroxide at room temperature. The
organoselenium catalyst used in this reaction could
be recycled and reused several times. This new
method was suitable not only for methyl unsaturat-
ed ketones, but also for alkyl and aryl unsaturated
ketones. Therefore, it provided a direct, mild, prac-
tical, highly functional group-tolerant process for
the chemoselective preparation of the versatile (E)-
vinyl esters from the readily available (E)-a,b-unsa-
turated ketones. A possible mechanism was also
proposed to rationalize the activity of the organose-
lenium catalyst in the presence of hydrogen perox-
ide in this Baeyer–Villiger oxidation reaction.
transition metal-catalyzed dehydrogenative or oxida-
tive cross-coupling of carboxylic acids with alkenes
(method B),[6] as well as the Baeyer–Villiger oxidation
of the readily available a,b-unsaturated ketones, as
recently reported by del Amo et al. by using oxone as
the oxidant (method C).[7]
The transition metal-catalyzed addition reaction
has the advantages of high atom economy and the use
of the readily available carboxylic acids as the starting
materials, but it needs relatively expensive alkynes as
substrates, toxic metal catalysts and ligands. In some
cases it is difficult to achieve high regio- and stereo-
Keywords: Baeyer–Villiger oxidation; hydrogen
peroxide; organoselenium catalysis; a,b-unsaturated
ketones; vinyl esters
Vinyl esters are important compounds that have been
widely used in organic synthesis,[1] medicinal chemis-
try,[2] polymer and materials science,[3] and food
chemistry.[4] Methods for vinyl ester synthesis have
been well-established in the literature, which mainly
include the transition metal-catalyzed addition of car-
boxylic acids to alkynes (Scheme 1, method A),[5]
Scheme 1. Methods for vinyl ester synthesis.
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Table 1. Catalyst and condition screening.[a]
selectivities by this method.[5] Dehydrogenative or ox-
idative cross-coupling reactions are attractive alterna-
tives because of the available and cheaper starting al-
kenes, but they require expensive and toxic metal cat-
alysts and excess amounts of additives. In addition,
these reactions also suffer from limited scope and low
generality due to competitive side-reactions such as
allylic rearrangement.[6] Therefore, the Baeyer–Villig-
er oxidation seems to be a preferable process for its
directness and the ready availability of the a,b-unsa-
turated ketones from aldol condensation reactions.
However, the only method known to date has disad-
vantages including limited substrate scope and the
use of excess potassium monopersulfate triple salt
[KOS(O)2OOH·KHSO5·1/2KHSO4·1/2K2SO4),[7,8]
which inevitably produces large amounts of solid
waste and thus low applicability at the industrial
level. Therefore, better methods that use greener oxi-
dants for the Baeyer–Villiger method are highly desir-
able.
Entry
Cat.
(mol%)
H2O2
[equiv.]
T
Yield
[%][c]
[oC][b]
1
2
3
4
5
6
7
8
(PhS)2 (5)
(PhSe)2 (5)
(PhTe)2 (5)
4
4
4
4
4
4
4
4
4
4
4
4
4
3
5
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
40
33[f]
71 (67)[f]
0[g]
–
0
(ArSe)2 (5)[d]
SeO2 (5)
48–84[f]
58[f]
PhSeR (5)[e]
(c-C6H11Se)2 (5)
(PhCH2Se)2 (5)
(PhCH2Se)2 (5)
(PhCH2Se)2 (5)
(PhCH2Se)2 (2)
(PhCH2Se)2 (10)
(PhCH2Se)2 (5)
(PhCH2Se)2 (5)
0–68[f]
88
9
92 (85)
90
10
11
12
13
14
15
50
72[g]
81[f]
r.t.
r.t.
r.t.
r.t.
67[g]
75[f]
Generating water as the only by-product, hydrogen
peroxide (H2O2) is a green oxidant that has been
widely applied in chemical industry. During our ongo-
ing studies on green synthetic methods,[9,10] we have
achieved practical accesses to many useful com-
pounds, such as the bioactive 4-methylenebutan-
87
[a]
The mixture of 1a (1 mmol), aqueous H2O2 (30% w/w),
and a catalyst in MeCN (2 mL) was stirred for 24 h and
then monitored by GC-MS analysis by using biphenyl as
the internal standard.
[b]
[c]
r.t.=room temperature (ca. 258C).
ACHTUNGTRENNUNG
olides,[10a] nitriles,[10b] and trans-1,2-cyclohexane-
GC yields are shown outside the parenthesis; isolated
yields inside the parenthesis. The yields, based on 1a, are
average yields obtained from three reactions.
Ar=4-FC6H4, 3-FC6H4, 2-FC6H4, 3,5-(CF3)2C6H3, 4-
CH3OC6H4, 4-(CH3)2NC6H4 or 1-C10H8.
R=Et, i-Pr, Ph or Br.
Reactions incomplete.
Unidentified by-products observed.
diol[10c,d] through the organoselenium-catalyzed reac-
tions with H2O2. Although organoselenium-catalyzed
Baeyer–Villiger reactions are known, they are limited
to simple ketones and aldehydes.[11] To the best of our
knowledge, an organoselenium-catalyzed Baeyer–Vil-
liger oxidation of a,b-unsaturated ketones has not
been reported. We thus envisioned that organoseleni-
um catalysts[10–13] might also effect the Baeyer–Villiger
oxidation of a,b-unsaturated ketones for the synthesis
[d]
[e]
[f]
[g]
of vinyl esters by using H2O2 as the oxidant kylphenyl selenides, and dialkyl diselenides (en-
(Scheme 1, method D).
tries 6–9).[14] Surprisingly, in contrast to previous work
We initiated our study on the oxidation of (E)-ben- employing electron-deficient diaryl diselenides,[10b,c,11]
zalacetone 1a by H2O2 by using various organoseleni- we found that dialkyl diselenides exhibited much
um compounds as the catalysts. As shown in Table 1, higher activities than other organoselenium catalysts
1a was initially treated with 4 equiv. of H2O2 at room in the Baeyer–Villiger oxidation. As shown in
temperature in the presence of diphenyl dichalcoge- Table 1, dicyclohexyl diselenide afforded 88% GC
nides (PhY)2 (entries 1–3,Y=S, Se, Te). The results yield of 2a (entry 8) and the simple and readily avail-
showed that the selenium analogue (PhSe)2 was able dibenzyl diselenide (PhCH2Se)2 gave 2a in the
a much more effective catalyst than corresponding highest GC yield of 92% (entry 9, 85% isolated
(PhS)2 and (PhTe)2, affording a single product in 71% yield). With the best catalyst in hand, other parame-
GC yield (entry 1). The product was then isolated ters, such as the temperature, the amount of the cata-
(67% yield) and determined to be the desired (E)- lyst and the oxidant H2O2 were examined (entries 10–
styrenyl acetate 2a by NMR spectroscopic analysis. In 15).[14] The results showed that elevated temperatures
contrast, no reaction occurred at all without the cata- and more or less catalyst and oxidant H2O2 were all
lyst (entry 4). Various diaryl diselenides were investi- less effective since lower yields of 2a were obtained
gated, and the results showed different degrees of ac- under these conditions. In summary, the best condi-
tivities to give low to good yields of 2a under the tions used 5 mol% of (PhCH2Se)2, 4 equiv. of H2O2
same conditions (entry 5).[14] We also tested other in- and room temperature in MeCN for 24 h (entry 9).
organic and organic selenium-containing compounds
With the optimized conditions in hand, a variety of
such as selenium dioxide, phenylselenium bromide, al- (E)-a,b-unsaturated ketones were prepared and then
2
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Organoselenium-Catalyzed Baeyer–Villiger Oxidation
Table 2. Baeyer–Villiger oxidation for vinyl ester synthesis.[a]
treated with H2O2 in the presence of 5 mol% of
(PhCH2Se)2 to synthesize the corresponding vinyl
esters. It seems that electron-rich vinyl moieties fa-
vored the Baeyer–Villiger oxidation because sub-
strates bearing electron-donating substituents R1 (en-
tries 1–9) usually gave higher yields of the products
than those with electron-deficient ones (entries 10–
12). Steric properties of the vinylic substituents R1 did
not affect the reaction efficiency very much. Thus,
substrates with higher steric hindrance such as ortho-
substituted and/or bulky groups all gave good to high
yields of the corresponding vinyl esters (entries 4, 6,
8, 9, 12, and 13), which was most possibly because the
reaction site was not at this side. In addition to aryl
R1 groups, conjugated dienyl ketones with vinylic R1
groups (entries 14 and 15), including the natural prod-
uct b-ionone (entry 15), could also be used as the sub-
strates and were smoothly oxidized to give good
yields of the products. It should be mentioned that
vinyl ester 2o is a useful chemical widely applied in
the perfume industry[15a–c] and natural product synthe-
sis.[15d]
Entry R1
R2
Yield [%][b]
1
2
3
4
5
6
7
8
C6H5
4-CH3C6H4
3-CH3C6H4
2-CH3C6H4
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
2a: 85
2b: 78
2c: 80
2d: 75
2e: 64
2f: 88
2g: 84
2h: 81
2i: 84
2j: 76
2k: 70
2l: 80
2m: 75
2n: 78
4-tBuC6H4
2,4,6-(CH3)3C6H2
4-CH3OC6H4
2-CH3OC6H4
9
2,3,4-(CH3O)3C6H2 CH3
10
11
12
13
14
4-ClC6H4
3-ClC6H4
2-ClC6H4
1-C10H7
CH3
CH3
CH3
CH3
CH3
C6H5CH=CH
15
CH3
2o: 78
Since the previous Baeyer–Villiger method using
oxone as the oxidant was limited to the methyl unsa-
turated ketones (R2 =Me only),[7] we then investigat-
ed a,b-unsaturated ketones with different R2 groups
to test and extend the scope of the organoselenium-
catalyzed method. As shown in Table 2, less bulky
linear and more bulky branched alkyl R2 groups (en-
tries 16–18) and normal and more bulky aryl R2
groups (entries 19–23) were tolerated, affording mod-
erate to good yields of the products. The steric prop-
erties of the ketonic R2 groups affected the reaction.
Thus, a,b-unsaturated ketones with more bulky R2
groups usually afforded lower yields of the products
than those with less bulky R2 groups (entries 16–18:
yields 2r<2q<2p; entries 19–23: yields 2w–v<2s–u).
Similarly, the electronic properties of R2 also affected
the reaction. Thus, aryl R2 with electron-rich substitu-
ents afforded higher yields of the products than the
one with the unsubstituted phenyl group (entries 19
16
17
18
19
20
21
22
23
24
25
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
c-C6H11
n-C4H9
CH2CH(CH3)2 2q: 75
t-Bu
C6H5
4-CH3C6H4
4-CH3OC6H4
1-C10H7
2-C10H7
4-ClC6H4
CH3
2p: 84
2r: 64
2s: 75
2t: 76
2u: 84
2v: 70
2w: 62
2x: NR[c]
2y: NR[c,d]
[a]
The mixture of 1a (1 mmol), aqueous H2O2 (30% w/w,
4 mmol), and (PhCH2Se)2 (0.05 mmol) in MeCN (2 mL)
was stirred at room temperature (ca. 258C) for 24 h.
Isolated yields based on 1.
No reaction occurred.
The reaction was also investigated at 40–808C, but no re-
action occurred either.
[b]
[c]
[d]
and 20: yields 2t–u>2s). No product could be ob- soluble in water, the product and the catalyst could
tained from the reaction of an a,b-unsaturated ketone be separated by a simple extraction after the reaction.
bearing an electron-deficient R2 (entry 24). In addi- The organic layer containing the product was concen-
tion, we also investigated the reactions of the aliphat- trated and purified through the usual procedure;
ic unsaturated ketones such as (E)-4-cyclohexylbut-3- while the aqueous layer containing the organoseleni-
en-2-one, but no reaction occurred under the standard um species was concentrated under vacuum and re-
conditions or at elevated temperatures (entry 25).
dissolved by adding MeCN into the flask. Catalyst re-
The above results revealed the generality of the or- covery was achieved by transferring the MeCN solu-
ganoselenium-catalyzed Baeyer–Villiger oxidation tion into a new reaction tube and recharging the tube
method, showing its practicability and potentials in with the same amounts of 1 and H2O2. The mixture
synthetic applications. On the other hand, as certain was then stirred under the standard conditions and
organoselenium catalysts were recyclable and reusa- the results are summarized in Figure 1. It was shown
ble in our previous work,[10b,c] we further investigated that generally moderate to good yields of the vinyl
the possibility of catalyst recovery and reuse. Since esters could be obtained by using the recycled orga-
the organoselenium pre-catalyst (PhCH2Se)2 was noselenium catalyst. The decreasing product yields
mostly oxidized by H2O2 to organoselenium acids could be attributed to loss of the catalyst during the
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C(O)-C(R2) bond via path b. This chemoselective
À
C C cleavage reaction led to a rearrangement of 4 to
give stereodefined (E)-vinyl esters 2 and seleninic
acid 5,[16] which was then oxidized by H2O2 to regen-
erate the active organoselenium species 3.[10,11,16]
In conclusion, we have developed a simple and
straightforward method for the preparation of the
useful (E)-vinyl esters through the organoselenium-
catalyzed chemoselective Baeyer–Villiger oxidation of
the a,b-unsaturated ketones by using H2O2. This new
method has the advantages of mild conditions, high
functional group tolerance, recyclability and reusabili-
ty of the organoselenium catalyst while generating
water as the only by-product. Investigations on other
synthetic methods based on the organoselenium-cata-
Figure 1. Results of catalyst recovery and reuse.
recovery process. In addition, based on our own expe- lyzed oxidations are underway.
riences and the literature,[10,11] it might also be attrib-
uted to deactivation of the catalyst due to the forma-
tion of catalytically inactive organoselenium species Experimental Section
during the reactions. Although decreasing product
yields were inevitable, Figure 1 illustrates that the re- General Procedure for the Preparation of Vinyl
cycled organoselenium catalyst was still effective for Esters (E)-2
five cycles.
To a reaction tube, 1 mmol of a,b-unsaturated ketone 1,
0.05 mmol of (PhCH2Se)2 (17 mg) and 4 mmol of H2O2
The mechanism of this chemoselective Baeyer–Vil-
liger oxidation reaction was then considered. Based
(0.46 g, 30% aqueous) in 2 mL of MeCN were added in
on our previous organoselenium-catalyzed reac-
tions[10] and the literature,[11] a possible mechanism is
illustrated in Scheme 2. The pre-catalyst (RSe)2 might
be oxidized by H2O2 to give the highly oxidative orga-
noseleninoperoxoic acid 3 via hydrolysis of the initial-
ly generated organoseleninoperoxoic anhydride
[RSe(O)O]2O, which has been observed by 77Se NMR
turn. The mixture was then stirred at room temperature.
After 24 h, 5 mL of water were added and the liquid was ex-
tracted 3ꢂ with EtOAc (5 mL). The combined organic layer
was then dried over anhydrous Na2SO4 and the solvent was
evaporated under vacuum. The residue was separated by
flash column chromatograohy (eluent: petroleum ether/
EtOAc 8:1) to afford the corresponding vinyl esters 2.
studies.[10a,16] Then, selective nucleophilic O H addi-
À
Detailed Procedure for Catalyst Recycling and Reuse
tion of 3 might take place at the C=O bond of the
a,b-unsaturated ketones 1, giving the key intermedi-
ate 4.[10,11] Clearly, this step was influenced by the
steric properties of the adjacent R2 group more than
that of the remote R1, which was in good agreement
with the results obtained in Table 2. In the next step,
due to the presence of the sterically less bulky vinyl
The procedure for organoselenium-catalyzed oxidation of 1a
with H2O2 to 2a was performed as above. After extraction
and separation of the organic layer and the aqueous layer,
the combined organic layer was sent to GC analysis and pu-
rified as above. The aqueous layer was concentrated on
a rotary evaporator. The residue was then washed with
1 mL of MeCN and transferred into a new reaction tube. To
the reaction tube containing the recycled catalyst were
added a solution of 1 mmol of 1a and 4 mmol of H2O2
(0.46 g, 30%, aqueous) in 1 mL of MeCN. The mixture was
then stirred at room temperature and treated, purified and
analyzed as above.
À
moiety and its activation on the C(vinyl) C(O) bond,
À
selective C C bond cleavage took place at the
À
C(vinyl) C(O) bond via path a rather than at the
Acknowledgements
We thank NNSFC (21202141, 20902070, 51273172), Priority
Academic Program Development of Jiangsu Higher Educa-
tion Institutions, and ZJNSF for Distinguished Young Schol-
ars (LR14B020002) for financial support. We also thank the
analysis center of Yangzhou University for assistance.
Scheme 2. Possible mechanism for the organoselenium-cata-
lyzed Baeyer–Villiger oxidation of a,b-unsaturated ketones.
4
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Chen, Adv. Synth. Catal. 2013, 355, 73–80.
[10] Our recent publications on organoselenium catalysis:
a) L. Yu, Y. Wu, H. Cao, X. Zhang, X. Shi, J. Luan, T.
Chen, Y. Pan, Q. Xu, Green Chem. 2014, 16, 287–293;
b) L. Yu, H. Li, X. Zhang, J. Ye, J. Liu, Q. Xu, M. Laut-
ens, Org. Lett. 2014, 16, 1346–1349; c) L. Yu, J. Wang,
T. Chen, Y. Wang, Q. Xu, Appl. Organomet. Chem.
2014, 28, 652–656; d) L. Yu, J. Wang, T. Chen, K. Ding,
Y. Pan, Chin. J. Org. Chem. 2013, 33, 1096–1099.
[11] Selected articles on organoselenium catalysis: a) F.
Chen, C. K. Tan, Y.-Y. Yeung, J. Am. Chem. Soc. 2013,
135, 1232–1235; b) D. W. Tay, I. T. Tsoi, J. C. Er,
G. Y. C. Leung, Y.-Y. Yeung, Org. Lett. 2013, 15, 1310–
1313; c) J. Trenner, C. Depken, T. Weber, A. Breder,
Angew. Chem. 2013, 125, 9121–9125; Angew. Chem.
Int. Ed. 2013, 52, 8952–8956; d) F. V. Singh, T. Wirth,
Org. Lett. 2011, 13, 6504–6507; e) S. Santoro, C. Santi,
M. Sabatini, L. Testaferri, M. Tiecco, Adv. Synth. Catal.
2008, 350, 2881–2884; f) S. M. Bennett, Y. Tang, D.
McMaster, F. V. Bright, M. R. Detty, J. Org. Chem.
2008, 73, 6849–6852; g) D. Zhao, M. Johansson, J.-E.
Bꢊckvall, Eur. J. Org. Chem. 2007, 4431–4436; h) A. F.
Barrero, J. F. Q. del Moral, M. M. Herrador, M. Cortꢇs,
P. Arteaga, J. V. Catalꢄn, E. M. Sꢄnchez, J. F. Arteaga,
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Usami, M. Arimoto, Tetrahedron Lett. 2005, 46, 8665–
8668; j) S. R. Mellegaard, J. A. Tunge, J. Org. Chem.
2004, 69, 8979–8981; k) M. A. Goodman, M. R. Detty,
Organometallics 2004, 23, 3016–3020; l) S. R. Melle-
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m) M. D. Drake, M. A. Bateman, M. R. Detty, Organo-
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Vis, I. W. C. E. Arends, R. A. Sheldon, Tetrahedron
2002, 58, 3977–3983; o) G.-J. ten Brink, B. C. M. Fer-
nandes, M. C. A. van Vliet, I. W. C. E. Arends, R. A.
Sheldon, J. Chem. Soc. Perkin Trans. 1 2001, 224–228;
p) G.-J. ten Brink, J.-M. Vis, I. W. C. E. Arends, R. A.
Sheldon, J. Org. Chem. 2001, 66, 2429–2433.
[12] For reviews on green features of organoselenium
chemistry: a) D. M. Freudendahl, S. Santoro, S. A.
Shahzad, C. Santi, T. Wirth, Angew. Chem. 2009, 121,
8559–8562; Angew. Chem. Int. Ed. 2009, 48, 8409–8411;
b) S. Santoro, J. B. Azeredo, V. Nascimento, L. Sancine-
to, A. L. Braga, C. Santi, RSC Adv. 2014, 4, 31521–
31535; c) C. Santi, C. Tidei, Electrophilic selenium/tellu-
rium reagents: reactivity and their contribution to Green
Chemistry, in: The Chemistry of Organic Selenium and
Tellurium Compounds, Vol. 4, (Ed.: Z. Rappoport),
John Wiley & Sons, Chichester, 2013, pp 569–655.
[6] a) D. Yang, S. Ding, J. Huang, K. Zhao, Chem.
Commun. 2013, 49, 1211–1213; b) W. H. Henderson,
Adv. Synth. Catal. 0000, 000, 0 – 0
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Xu Zhang et al.
[13] Selenium is an eco-friendly trace element that can be
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Patent 3,940,499, 1974; Chem. Abstr. 1976, 84, 163170;
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metabolized in organisms: M. P. Rayman, Lancet 2012,
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[14] See the Supporting Information for details.
[15] a) A. O. Pittet, E. M. Klaiber, M. H. Vock, E. J. Shus-
ter, J. Vinals, A. Van Ouwerkerk, B. J. Chant, A. L. Lib-
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[16] Generation of organoselenium species [RSe(O)O]2O, 3
and 5, as well as their generation sequence have all
been confirmed by 77Se NMR studies (see ref.[10a] for
details).
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Adv. Synth. Catal. 0000, 000, 0 – 0
ÝÝ
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COMMUNICATIONS
Organoselenium-Catalyzed Baeyer–Villiger Oxidation of
a,b-Unsaturated Ketones by Hydrogen Peroxide to Access
Vinyl Esters
7
Adv. Synth. Catal. 2015, 357, 1 – 7
Xu Zhang, Jianqing Ye, Lei Yu,* Xinkang Shi, Ming Zhang,
Qing Xu,* Mark Lautens
Adv. Synth. Catal. 0000, 000, 0 – 0
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asc.wiley-vch.de
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These are not the final page numbers!