Iron-Enabled Utilization of Air as the Terminal Oxidant Leading to Aerobic Oxidative Deoximation by Organoselenium Catalysis

Article abstract of DOI:10.1002/adsc.201801163

In contrast to conventional organoselenium-catalyzed oxidation reactions that require peroxide oxidants such as hydrogen peroxide, in this work we found that, addition of a low loading of iron (II) could enable the successful utilization of air as the terminal oxidant in organoselenium-catalyzed oxidative deoximation reaction of ketoximes. This led to a new mild and relatively green aerobic oxidative deoximation method. Control reactions and X-ray photoelectron spectroscopy (XPS) analysis suggest that iron is crucial in the catalytic cycle, working to prohibit the deactivation of selenium catalyst through an iron-catalyzed aerobic oxidation of low valent selenium species by air to the active high valent selenium species. Since air can be utilized as the terminal oxidant, this work may contribute to the advance of organoselenium catalysis. (Figure presented.).

Full text of DOI:10.1002/adsc.201801163

Title: Iron-Enabled Utilization of Air as the Terminal Oxidant Leading to
Aerobic Oxidative Deoximation by Organoselenium Catalysis
Authors: Chao Chen, Xu Zhang, Hongen Cao, Fang Wang, Lei Yu, and
Qing XU
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201801163
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10.1002/adsc.201801163
Advanced Synthesis & Catalysis
UPDATE
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Iron-Enabled Utilization of Air as the Terminal Oxidant
Leading to Aerobic Oxidative Deoximation by Organoselenium
Catalysis
Chao Chen,†,a Xu Zhang,†,a Hongen Cao,†,a Fang Wang,a,b Lei Yu,a,* and Qing Xua,c,*
a
Guangling College and Institute of Pesticide of School of Chemistry and Chemical Engineering and School of
Horticulture and Plant Protection, Yangzhou University, Yangzhou 225002, China
Fax: (+86)-514-87975244; phone: (+86)-13665295901; e-mail: yulei@yzu.edu.cn; xuqing@yzu.edu.cn.
Yangzhou Polytechnology Institute, Yangzhou, Jiangsu 225127, China
College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, Zhejiang 325035, China
b
c
Fax: (+86)-577-8668-9302; phone: (+86)-138-5774-5327; e-mail: qing-xu@wzu.edu.cn.
†
These authors contributed equally to this work.
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.
it is on the other hand explosive and may become a
dangerous reagent especially in large scale reactions.
Therefore, new synthetic methods that can assemble
the advantages of organoselenium catalysis and
aerobic oxidation (using air or O2 as the oxidant
instead of H2O2) are highly desirable in the field as
this may resolve the remaining issues in Se-catalyzed
oxidation reactions.[7a,7b,7f]
Abstract. In contrast to conventional organoselenium-
catalyzed oxidation reactions that require peroxide oxidants
such as hydrogen peroxide, in this work we found that,
addition of a low loading of iron (II) could enable the
successful utilization of air as the terminal oxidant in
organoselenium-catalyzed oxidative deoximation reaction
of ketoximes. This led to a new mild and relatively green
aerobic oxidative deoximation method. Control reactions
and X-ray photoelectron spectroscopy (XPS) analysis
suggest that iron is crucial in the catalytic cycle, working to
prohibit the deactivation of selenium catalyst through an
iron-catalyzed aerobic oxidation of low valent selenium
species by air to the active high valent selenium species.
Since air can be utilized as the terminal oxidant, this work
may contribute to the advance of organoselenium catalysis.
On the other hand, oxidative deoximation[8] is a
significant transformation in organic, pharmaceutical,
and total synthesis, because the oxime block is an
easily acquired stable functional group that can allow
the utilization of oximation-deoximation strategies in
protection and purification of carbonyl compounds or
in the transformation of other functional groups into
carbonyl group. For example, this protocol has been
successfully employed by Corey et al in the total
synthesis of erythronolide A in 1970s.[9] Deoximation
could also be used in industrial-scale production of
useful carbonyl-containing fine chemicals from non-
carbonyl compounds. Synthesis of spice carvone
from limonene is one of the typical examples
(Scheme 1).[10] However, currently known
deoximation methods usually require explosive
peroxide oxidants such as H2O2,[11] or use potentially
hazardous cyanide-containing catalysts or oxidants,[12]
Keywords: aerobic oxidation; deoximation; iron;
ketoximes; organoselenium catalysis
In the past decades, organoselenium chemistry has
attracted extensive attention because of the unique
chemical and biological activities of the
organoselenium compounds.[1] Since selenium (Se)
compounds are lower in cost than many of the
widely-used noble metal catalysts/ligands, can be
recovered and reused without much deactivation,[2]
and Se itself is an organism-metabolizable and
environmental-friendly element,[3] methods using
organoselenium compounds as the catalysts has also
been unfolding rapidly in recent years.[2,4-7] Besides,
since Se-catalyzed reactions generally do not require
or
use
hazardous
reagents
such
as
hexachlorodisilane[13] or halogenated solvents,[14] or
use excess hydrochloric acid with iron powder,[15] or
use
nitrite/nitrate-containing
catalysts
or
additives.[14,16] Due to the use of the above-mentioned
harsh conditions but relatively greener conditions,[2,4,5] environmentally-unfriendly reagents or catalysts,
organoselenium catalysis may also be of good
potential in industrial application in the future. We
have also reported some Se-catalyzed oxidation
reactions in the past five years,[2,5] in which hydrogen
peroxide (H2O2) had to be employed as the oxidant.
Although H2O2 is known as a relatively clean oxidant
due to generation no other waste than the water,[2,4,5]
these methods inevitably generate large amounts of
wastes. Some even have a very limited scope of the
substrates.[12a] Moreover, although the oxidative
deoximation reaction could also be accomplished by
using enzyme catalysts such as Laccase T.
versicolor,[17] the method has its own limitations,
either. Firstly, the enzyme catalysts are not cheap and
1
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10.1002/adsc.201801163
Advanced Synthesis & Catalysis
can be easily deactivated. Secondly, the method
requires additional use of 15 mol % TEMPO as the
oxidation co-catalyst, which makes the method less
preferable.
Scheme 1. Synthesis of carvone from limonene involving a
key deoximation step.
In our ongoing studies on organoselenium
catalysis,[2,5] we recently found that, addition of a low
loading of Fe(II) can enable the successful utilization
of the safe and economic air as the terminal oxidant
in organoselenium-catalyzed oxidative deoximation
reaction of ketoximes.[18] This finding leads to a facile
aerobic oxidative deoximation method that can be
performed in green solvents under mild conditions.
Herein we disclose the detail of this work.
Figure 1. Evaluation of transition metal salts.
As shown in Figure 1, PhSe(O)OH-catalyzed
oxidative deoximation of (Z)-1-phenylethan-1-one
oxime (1a) was chosen as the model reaction. The
reaction was initially heated in MeCN in open air in
the absence of any metal co-catalysts (entry 1). Only
a low yield of the product acetophenone (2a) was
observed with low conversion of 1a. Since formation
of (PhSe)2 was also observed in the reaction, we
reckoned it might be the over-reduction of the Se
catalyst and its difficulty in re-oxidation to
PhSe(O)OH that caused the termination of the
deoximation reaction.[19] Consequently, to achieve an
effective aerobic re-oxidation reaction of (PhSe)2
with air, various simple metal salts were added as the
co-catalyst. Copper and manganese salts were firstly
tested since they are both well known catalysts for
oxidation reactions. However, Cu(OAc)2, CuCl, and
Mn(OAc)2 (1.25 mol%)[20] did not show obvious
promoting effect on the reaction (entries 2-4). Noble
metal salt RuCl3 also showed no obvious activity in
the reaction (entry 5). Although ceric ammonium
nitrate (CAN) and Co(OAc)2 showed certain
promoting effect, the product yields (34-42%) were
still not satisfactory (entries 6-7). Then, AgNO3 was
found to be a better co-catalyst, affording 2a in 61%
yield (entry 8). Interestingly, the more abundant and
cheaper iron salt Fe(NO3)3 was even more effective,
leading to a higher 67% yield of 2a (entry 9). Further
screenings of the iron salts (entries 9-12) revealed
that FeSO4 is the best co-catalyst, which could afford
2a in 73% yield under the same conditions (entry 12).
Figure 2. Screening of Se catalysts.
Different organoselenium acid RSe(O)OH were
then screened to further optimize the Se catalyst. As
shown in Figure 2, in comparison with PhSe(O)OH
(entry 1), both electron-enriched and -deficient
ArSe(O)OH were found to be less effective catalysts
(entries 2-4), showing that introduction of electron-
withdrawing and -donating groups is not a preferable
protocol. Aliphatic RSe(O)OH were then investigated.
Although c-C6H11Se(O)OH showed very poor
catalytic activity in the reaction (entry 5), the reaction
2
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10.1002/adsc.201801163
Advanced Synthesis & Catalysis
using EtSe(O)OH as the catalyst interestingly
produced a very high 89% yield of 2a (entry 6). Since
c-C6H11Se(O)OH is sterically more bulky than
EtSe(O)OH, this suggests that the steric properties of
the Se catalysts may affect the reaction greatly (vide
infra). Further evaluation of PhCH2Se(O)OH showed
that it’s a more active catalyst for the reaction,
affording 2a in the highest 92% yield (entry 7). The
reaction was also tested using inorganic Se powder as
the catalyst or without using any Se catalyst (entries
8-9). The contrastive results suggested that Se acid
RSe(O)OH is crucial to achieving a high efficiency of
the aerobic oxidative deoximation reaction.
Solvents were then evaluated (Figure 4). Water
was firstly considered, but was found rather
ineffective (entry 2). Unfortunately, relatively greener
solvents like ethanol and aqueous ethanol (EtOH/H2O
1/1) also gave poor yields of the product (entries 3-4).
Usual organic solvents such as DMSO, DMF, CH2Cl2
and THF were found less effective than CH3CN
(entries 5-8). To our surprise, ethyl acetate (EtOAc),
a cheap, abundant, and relatively green but seldom-
used as a solvent in organic reactions, was observed
to be the best one for the reaction, giving the highest
95% yield of 2a under the standard conditions (entry
9).
Reduced loadings of PhCH2Se(O)OH were also
investigated to enhance the catalyst’s turnover
number (TON) (Figure 3, entries 1-4). However, this
only led to decreased yields of 2a. Similarly,
increased loadings of PhCH2Se(O)OH were also not
Therefore, as demonstrated in Figures 1-4,
performing the reaction in open air at 60 oC in EtOAc
using 5 mol% of PhCH2Se(O)OH and 1.25 mol% of
FeSO4 as the catalysts is the best conditions for this
aerobic oxidative deoximation reaction. These
conditions were then applied to a series of ketoximes
to extend the scope of the method. As shown in Table
1, similar to 1a, ketoximes with either electron-
donating or electron-withdrawing groups substituted
at the ortho-, meta- and para-positions on the phenyl
ring all afforded the corresponding ketones in
excellent yields (entries 2-9), revealing that electronic
and steric properties of the substituents do not affect
the substrate’s reactivity greatly. In addition, 1-
phenylpropan-1-one oxime 1j and 1-phenylbutan-1-
one oxime 1k, substrates with relatively short alkyl
chains, also produced the target ketones 2j and 2k in
high yields under the standard conditions (91-93%)
(entries 10-11). In great contrast, in the cases of
ketoximes with longer alkyl chains such as n-C4H9
and n-C6H13, much lower yields of the products were
obtained (entries 12-13). This is mostly likely due to
the increased steric hindrance derived from the longer
alkyl chains that could prevent the addition of the
catalyst to the C=N bond of the ketoximes according
to the reaction mechanism (vide infra). Thus, even
performing the reactions at a higher temperature of
preferable (entries 6-10). Thus,
5
mol%
PhCH2Se(O)OH was still the best catalyst loading for
the reaction.
Figure 3. Evaluation of catalyst loading.
o
80 C, it was still difficult to improve the products’
yields (entries 12-13, yields in parenthesis). Diaryl
ketoximes 1n-r were then investigated. Regardless of
the substituents on both phenyl rings, all substrates
gave the ketone products in excellent yields (entries
14-18). Contrarily, the
reaction of 3,4-
dihydronaphthalen-1(2H)-one oxime 1s was less
efficient, giving 2s in a lower yield of 45% under the
standard conditions (entry 19). This may also
attributed to the steric hindrance of the fused phenyl
moiety according to the reaction mechanism (vide
infra); whereas, a higher 66% yield of 2s could be
obtained by performing the reaction at a higher
temperature (entry 19, yield in parenthesis). Most
likely due to the same reason and also the volatile
nature of product cyclohexanone 2t, although a
moderate GC yield of 2t could be observed, the
reaction of cyclohexanone oxime (1t) only gave 2t in
a lower isolated yield (entry 20).
Figure 4. Evaluation of solvents.
Substrate scope of the method was further
investigated by employing more complex substrates
with other functional groups. Thus, the deoximation
3
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10.1002/adsc.201801163
Advanced Synthesis & Catalysis
20[c,d]
21
2t: 22 (47[e])
reaction of 1-(thiophen-2-yl)ethan-1-one oxime (1u)
bearing a hetroaryl group also proceeded smoothly
under the standard conditions to give 2u in a good
yield (entry 21). With a more bulky phenyl group
than 1u, the reaction of phenyl(thiophen-2-
yl)methanone (1v) became more sluggish and gave
only a moderate yield of 2v in an extended reaction
time (entry 22). Employing the same protocol, ethyl
2-(2-aminothiazole-4-yl)-2-hydroxyiminoacetate 1w,
an important pharmaceutical intermediate bearing
sulphur, nitrogen, and ester groups, also afforded the
desired product 2w in a moderate yield (entry 23).
Moreover, oximes 1x and 1y bearing amide and non-
aryl ether groups could also produce the
corresponding carbonyl compounds 2x and 2y under
similar conditions (entries 24-25), albeit the yields of
the products were not high. This is most likely due to
the great steric hindrance generated from these
complex substrates.
1t
:
2u: 83
1u
:
22[c]
23[c]
2v: 68[f]
1v
:
2w: 50 [d,f,g]
1w
:
24[c]
2x: 36
2y: 21
1x:
Table 1. Substrate scope of the Se/Fe co-catalyzed aerobic
25
oxidative deoximation reaction.[a]
1y
:
[a] 1 mmol of 1, 5 mol % of PhSe(O)OH, 1.25 mol % of
FeSO4 and 2 mL of EtOAc were employed.
[b] Isolated yields based on 1.
[c] Reactions incomplete.
Entry
1
1: R1, R2
2: yield (%)[b]
2a: 95
1a: Ph, Me
[d] 80 oC.
2
1b: 4-MeC6H4, Me
1c: 3-MeC6H4, Me
1d: 2-MeC6H4, Me
1e: 4-MeOC6H4, Me
1f: 4-ClC6H4, Me
1g: 3-ClC6H4, Me
1h: 2-ClC6H4, Me
1i: 4-NO2C6H4, Me
1j: Ph, C2H5
2b: 90
[e] GC yield.
[f] 48 h.
[g] EtOH was used as the solvent instead of EtOAc.
3
2c: 91
4
2d: 88
5
2e: 89
To probe whether the present Se/Fe-catalyzed
method can be extended to aldoximes to transform
the oxime group to aldehyde group, benzaldehyde
oxime (1z) was also investigated under the standard
conditions [Eq. (1)]. However, in addition to the
generation of 42% target benzaldehyde (2z), the
dehydration by-product benzonitrile (3z) was also
obtained in 34% yield. This result suggests that the
present method may not be suitable for
transformation of aldoximes to aldehydes.
6
2f: 92
7
2g: 89
8
2h: 90
9
2i: 83
10
11
12[c]
13[c]
14
15
16
17
18
19[c]
2j: 91
1k: Ph, n-C3H7
2k: 93
1l: Ph, n-C4H9
2l: 36 (44)[d]
2m:27(35)[d]
2n: 96
1m: Ph, n-C6H13
1n: Ph, Ph
1o: 4-MeC6H4, 4-MeC6H4
2o: 96
1p: 4-MeOC6H4, 4-MeOC6H4 2p: 80
Control reactions were then investigated to help
understanding the mechanism of this interesting
Se/Fe co-catalyzed aerobic oxidative deoximation
reaction (Table 2). Initially, addition of water as the
free radical scavenger or azodiisobutyronitrile (AIBN)
as the free radical initiator to the reaction of 1n was
found unable to affect the reaction greatly (Table 2,
entries 1-2), suggesting that a free-radical mechanism
can be excluded. In contrast to the preceding aerobic
conditions (condition screening section and Table 1),
1q: 4-ClC6H4, 4-ClC6H4
1r: 4-FC6H4, 4-FC6H4
2q: 85
2r: 93
2s: 45 (66)[d]
1s
:
4
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10.1002/adsc.201801163
Advanced Synthesis & Catalysis
a control reaction under N2 gave a very low yield of
the product 2n (entry 3); whereas, addition of a
stoichiometric amount of PhCH2Se(O)OH under N2
could improve the product yield to 80% (entry 4).
These results indicated that an oxidant, either air or
PhCH2Se(O)OH, is indispensible in the reaction.
contrast, in the spectra of the sample with FeSO4
added (Figure 5B), the low valent Se2+ species
disappeared almost completely and a high selectivity
(96%) for the high valent Se4+ species [corresponds to
PhCH2Se(O)OH] could be observed. This suggested
that Se2+ could be effectively oxidized to Se4+ by air
in the presence of FeSO4. Moreover, after correcting
the C1s peak to 284.8 eV, the Se4+ peaks were at
58.95 eV and 59.59 eV, while the Se2+ peaks were at
55.93 eV and 56.57 eV (Figure 5A). These peaks
shifted to 58.38 eV, 59.02 eV, 56.01 eV, and 56.95
eV, respectively, after the addition of FeSO4 (Figure
5B). These shifts suggest that an interaction between
Se and Fe might have occurred, which may further
contribute to the Fe-catalyzed aerobic oxidation of
low valent Se species.
Table 2. Control reactions for Se/Fe co-catalyzed aerobic
oxidative deoximation reaction.[a]
[b]
Entry Catalyst (mol%), additive (mol%), atm.[b] 2n
%
1
2
PhCH2Se(O)OH (5), FeSO4 (1.25), H2O 90
(100), open air
PhCH2Se(O)OH (5), FeSO4 (1.25), 89
AIBN (50), open air
3[c]
4
PhCH2Se(O)OH (5), FeSO4 (1.25), N2
10
PhCH2Se(O)OH (100), FeSO4 (1.25), N2 80
5
6
7
8[c]
9[c]
PhCH2Se(O)OH (100), N2
PhCH2Se(O)OH (5), H2O2 (100), N2
H2O2 (100), N2
FeSO4 (100), N2
Fe2(SO4)3 (100), N2
84
92
17
trace
18
[a] 1 mmol of 1n in 2 mL of EtOAc.
[b] Isolated yield based on 1n.
[c] Reactions incomplete.
Moreover, in reactions using stoichiometric
amounts of PhCH2Se(O)OH or H2O2 as the oxidant
(entries 5-6), it was found FeSO4 is not needed. In
contrast, the reaction with stoichiometric amount of
H2O2 alone without adding Se and Fe catalysts
afforded only a poor yield of the product (entry 7).
These results are consistent with the known Se-
catalyzed
oxidative
deoximation
reaction,[2a]
indicating that PhCH2Se(O)OH should be the active
oxidant for the deoximation process and H2O2 or air
as the terminal oxidant for the reaction. It may further
suggest that Fe’s role in the reaction is most likely to
enable the generation of the active oxidant for the
reaction. Meanwhile, control reactions with
stoichiometric amount of FeSO4 or Fe2(SO4)3 alone
led to poor yields of 2n under N2 (entries 8-9),
suggesting that Fe(II) even the more oxidative Fe(III)
are not the active oxidant for the deoximation
reaction. The above contrastive results implied that
Fe most likely works to catalyze the aerobic
oxidation of the reduced low valent Se species for
generation of an active high valent Se oxidant such as
PhCH2Se(O)OH by employing air as the oxidant.
Thereafter, X-ray photoelectron spectroscopy
(XPS) analysis was employed to further disclose the
role of Fe in the catalyst system. As shown in Figure
5, 1 mmol of (PhCH2Se)2 was heated in 2 mL of
EtOAc in air under the standard conditions (60 oC, 24
h) either in the absence or in the presence of 0.25
equiv. of FeSO4. The XPS spectra obtained from the
sample without FeSO4 (Figure 5A) showed that there
is still 24% ratio of the low valent Se2+ species. In
Figure 5. XPS analysis: heating (PhCH2Se)2 in air without
FeSO4 (A) or with 0.25 equiv. of FeSO4 (B) and heating
oxime 1a with 5 mol% PhCH2Se(O)OH under N2 (C).
On the other hand, in addition to the observation of
the generated small amount of (PhCH2Se)2 in the
reaction of 5 mol% of PhCH2Se(O)OH with 1 mmol
5
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10.1002/adsc.201801163
Advanced Synthesis & Catalysis
o
of 1a (2 mL EtOAc, under N2, 60 C, 24 h), XPS
analysis of the reaction residue also clearly showed
the generation of low valent Se species Se2+ (Figure
5C). To confirm that (PhCH2Se)2 was indeed
generated in the above reaction, a tenfold reaction [10
mmol 1a with 0.5 mmol of PhCH2Se(O)OH] was also
carried out under the same conditions and subjected
to purification by column chromatography. As a
result, 5.2 mg of (PhCH2Se)2 could be isolated and
confirmed by comparison with the authentic sample.
These observations clearly confirmed that
PhCH2Se(O)OH could be easily reduced to
(PhCH2Se)2 by the ketoxime substrates.[19]
may firstly occur to give adduct 4, which then
rearranges to afford product ketones 2 and
organoselenium species 5.[2a] Decomposition of 5
may then occur to afford the possible byproduct
hyponitous acid (HNO) and a reduced Se species
PhCH2SeOH.[21] It is known that PhCH2SeOH can be
easily reduced to the more stable and difficult-to-
oxidize diselenides under the reaction conditions,
most likely by the substrates or the solvents.[19] Hence,
only a low yield of the product could be obtained in
the reaction with lone PhCH2Se(O)OH catalyst.
Contrarily, addition of Fe(II) as the catalyst’s
oxidation catalyst can cause a dramatic effect on
improving the catalytic performance of the reaction
by a re-oxidation of the diselenide to the active
oxidant PhCH2Se(O)OH to finally furnish the
catalytic cycle.
The above contrastive results (Figure 5) are
consistent with those of the control reactions (Table
2), clearly supporting the point that Fe’s role in the
reaction should be working as the catalyst for the
aerobic re-oxidation of low valent Se species to high
valent Se species such as PhCH2Se(O)OH. Hence, an
organoselenium-catalyzed
aerobic
oxidative
deoximation reaction could be achieved using air as
the terminal oxidant by using Fe(II) as an effective Se
catalyst’s oxidation catalyst. In this sense, in
comparison with some preceding reports using iron
slats as the catalyst or oxidant,[12,16,18] the role of
FeSO4 in the present reaction is obviously different.
-
In those reports, NO3 works as the catalyst other than
Fe in the deoximation reactions.[12,16,18]
Since (PhCH2Se)2 can be re-oxidized to
PhCH2Se(O)OH by Fe catalysis based on above
findings, we also investigated a few control reactions
using (PhCH2Se)2 as the catalyst instead of
PhCH2Se(O)OH as (PhCH2Se)2 is also readily
available. However, under the standard conditions
using 2.5 mol% (PhCH2Se)2 and 1.25 mol% FeSO4,
only a low yield of 2n was obtained with recovery of
a considerable amount of starting 1n [Eq. (2), entry 1].
Clearly this result cannot compete with those
obtained from PhCH2Se(O)OH, but it may suggest
that the loading of FeSO4 is not adequate. Hence,
reactions with higher loadings of FeSO4 were
investigated [Eq. (2), entries 2-3], which indeed
afforded high yields of 2n as expected. Although
PhCH2Se(O)OH is still the more preferable catalyst
as it require a much lower loading of FeSO4, the
above results also support Fe’s role in the reaction as
a catalyst for aerobic oxidation of low valent Se
species to high valent Se species.
Scheme 2. Possible mechanism of the Se/Fe co-catalyzed
aerobic oxidative deoximation reaction.
In conclusion, by employing a low loading of Fe(II)
as the Se catalyst’s aerobic oxidation catalyst, the
abundant and economic air can be successfully
utilized as the terminal oxidant instead of the
conventionally used peroxide oxidants in the
oxidative deoximation of ketoximes. This led to a
Se/Fe co-catalyzed mild and relatively green aerobic
oxidative deoximation method. Control reactions and
X-ray photoelectron spectroscopy (XPS) analysis
confirmed that Fe is crucial in the catalytic cycle,
working to prohibit the deactivation of the Se catalyst
through a Fe-catalyzed aerobic oxidation of the
generated low valent Se species such as (PhCH2Se)2
by air to the active high valent Se species such as
PhCH2Se(O)OH. Since air can be well utilized as the
terminal oxidant, this work may contribute to the
advance of organoselenium-catalyzed oxidation
reactions. Further extension and applications of the
Fe-facilitated organoselenium-catalyzed aerobic
oxidation reaction are under way in this group.
Based on above results and the literature
knowledge,[2,5,19,21] a plausible mechanism is proposed
for the Se/Fe co-catalyzed aerobic oxidative
deoximation reaction. As shown in Scheme 2,
nucleophilic addition of PhCH2Se(O)OH to oximes 1
Experimental Section
6
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10.1002/adsc.201801163
Advanced Synthesis & Catalysis
General
Meotti, V. C. Borges, G. Zeni, J. B. T. Rocha, C.W.
Nogueira, Toxicol. Lett. 2003, 143, 9–16;
All reagents were purchased with purities >98% and used directly
as received. Solvents are analytical pure (AR) and directly used
without any further treatment. IR spectra were measured on a
Bruker Tensor 27 Infrared spectrometer. NMR spectra were
recorded on a Bruker Avance instrument (400 MHz for 1H NMR)
using CDCl3 as the solvent and Me4Si as the internal standard.
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Chemical shifts for H NMR were referred to internal Me4Si (0
ppm) and J-values shown in Hz. GC-MS analysis were performed
on a Thermofisher Trace ISQ instrument, with initial temperature
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Typical procedure for the deoximation reaction.
The mixture of 1 mmol of ketoxime (1), 0.05 mmol of
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Acknowledgements
We thank NNSFC (21202141, 21672163), Jiangsu Provincial Six
Talent Peaks Project (XCL-090), Priority Academic Program
Development of Jiangsu Higher Education Institutions (PAPD),
Top-notch Academic Programs Project of Jiangsu Higher
Education Institutions (TAPP), and the Nature Science
Foundation of Guangling College (ZKZD17005) for financial
support.
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10.1002/adsc.201801163
Advanced Synthesis & Catalysis
UPDATE
Iron-enabled utilization of air as the terminal
oxidant leading to aerobic oxidative deoximation
by organoselenium catalysis
Adv. Synth. Catal. Year, Volume, Page – Page
C. Chen, X. Zhang, H. Cao, F. Wang, L. Yu,* and
Q. Xu*
9
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