Deoxygenation of carbonyl compounds using an alcohol as an efficient reducing agent catalyzed by oxo-rhenium complexes

Article abstract of DOI:10.1039/c5gc02777b

This work describes the first methodology for the deoxygenation of carbonyl compounds using an alcohol as a green solvent/reducing agent catalyzed by oxo-rhenium complexes. The system 3-pentanol/ReOCl₃(SMe₂)(OPPh₃) was successfully employed in the deoxygenation of several aryl ketones to the corresponding alkenes and also in the deoxygenation of aryl aldehydes to alkanes with moderate to excellent yields. The catalyst ReOCl₃(SMe₂)(OPPh₃) can also be used in several catalytic cycles with good activity.

Full text of DOI:10.1039/c5gc02777b

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ARTICLE
Deoxygenation of Carbonyl Compounds using an Alcohol as
Efficient Reducing Agent Catalyzed by Oxo-rhenium Complexes
*
Joana R. Bernardo and Ana C. Fernandes
Received 00th January 20xx,
Accepted 00th January 20xx
This work describes the first methodology for the deoxygenation of carbonyl compounds using an alcohol as green
solvent/reducing agent catalyzed by oxo-rhenium complexes. The system 3-pentanol/ReOCl
3 2 3
(SMe )(OPPh ) was
successfully employed in the deoxygenation of several aryl ketones to the corresponding alkenes and also in the
DOI: 10.1039/x0xx00000x
deoxygenation of aryl aldehydes to alkanes with moderate to excellent yields. The catalyst ReOCl
3 2 3
(SMe )(OPPh ) can also
www.rsc.org/
be used in several catalytic cycles with good activity.
alkanes, there are very few methodologies for the selective
direct deoxygenation of ketones to alkenes. One example
consist in the method reported by Carney which is a
modification of the Clemmensen reduction using amalgamated
Introduction
During the last few years, many efforts were carried out to
discover and to develop new green chemical processes for the
deoxygenation of organic compounds. In particular, the
reductive deoxygenation of carbonyl compounds to the
corresponding alkanes or alkenes has attracted considerable
attention given its many applications in fine-chemical synthesis
1
9
zinc and formic acid in reflux of ethanol. The Shapiro reaction
also provides a convenient method to convert ketones into a
plethora of olefinic substances in high yields, by reaction of
ketones with (phenylsulfonyl)hydrazine, forming the
corresponding hydrazones, which react with a strong base,
1
and pharmaceutical industry. The deoxygenation of carbonyl
2
0
such as n-butyllithium, producing the olefins.
The
compounds from biomass resources is also an important
process and has been a key target in chemical engineering and
biofuel production, due to the concerns about diminishing
fossil fuel sources, increasing fuel prices, global warming, and
deoxygenation of tetralones and indanones to the
corresponding alkenes can also be afforded using an alcohol
2
1
and acid catalysis.
Oxo-rhenium complexes have been applied in the
2
,3
environmental pollution.
2
2
deoxygenation of many organic compounds
2
such as
25
aromatic nitro compounds,
Generally, the reduction of carbonyl group to the
corresponding methylene derivative can be carried out by
3
24
sulfoxides,
epoxides,
2
N-oxides and alcohols.
6
24d,24e,27
4
chemical methods such as Clemmensen reduction, Wolff-
Very recently, we developed
5
Kishner reduction, NaBH
6
7
the first methodology for the direct reductive deoxygenation
aryl ketones to the corresponding alkanes or to a mixture of
4
-CF
3 2
CO H, HI-Phosphorus, TMSCl–
8
Zn, GaCl
9
SiClH, InCl -TMSCl, PMHS-Pd/C, PMHS-
10
11
3
-Me
2
3
13
1
2
14
3 3
InBr -Et SiH, Raney nickel-2-
alkane
PhSiH
and
/ReOCl (SMe
alkene
)(OPPh
using
the
systems
Pd(OAc)
2
,
PMHS-B(C
6
F
5
)
3
,
28
1
5
3
3
2
3
)
and PhSiH
3
3 3 2
/ReOCl (PPh ) .
propanol. However, due to the harsh conditions of some of
these methodologies, they are restricted for the
deoxygenation of compounds containing other functional
groups. There are also number of catalytic protocols for the
deoxygenation of carbonyls employing molecular hydrogen
After, our group developed another very efficient method for
the selectively deoxygenation of aryl ketone to alkenes using
2
9
2 2 2 2 3
MoO Cl (H O) as catalyst and PhSiH as reducing agent.
In the last years the use of alcohols as green reducing
agents has attracted considerable attention. They proved to be
effective reducing agents for the deoxydehydration of
1
6
2
(H ) using the catalysts Pd-Choline-based ionic liquids,
1
,
7
18
Cu/SiO
2
or Cu30Cr10
/γ
-Al
2
O
3
.
2
Although, H constitutes the
2
7b,30
31
glycols,
compounds
deoxygenation of sulfoxides
and nitro
most atom-efficient and green reducing agent, its use is
generally associated with high pressure, special equipment
and safety precautions to minimize the explosion risk.
3
1a
in the presence of oxo-rhenium and oxo-
molybdenum complexes. To best of our knowledge, there are
no reports of the use of alcohols as reducing agents for the
direct deoxygenation of carbonyl compounds catalyzed by oxo-
complexes.
In contrast to the several methods reported in the
literature for the deoxygenation of carbonyl compounds to
In order to develop new catalyst/reductant systems with
optimum efficiency, selectivity, economy, and ecofriendly we
decided to investigate the deoxygenation of ketones and
aldehydes using an alcohol as green solvent/reducing agent
and an oxo-rhenium complex as catalyst.
*Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa,
Av. Rovisco Pais, 1049-001 Lisboa, Portugal,Tel: 351 218419264;
Fax: 351 218464455, anacristinafernandes@tecnico.ulisboa.pt
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
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Results
Table 2 Direct reductive deoxygenation of 6-methoxytetralone
using different alcohols as reducing agents
The catalytic activity of several oxo-rhenium complexes
was compared in the deoxygenation of the test substrate
a
6
-methoxytetralone using 3-pentanol as reducing agent (Table
). The oxo-rhenium complex ReOCl (SMe )(OPPh ) proved to
1
3
2
3
be the more efficient catalyst at 170°C under air atmosphere.
The best result was obtained using 10 mol% of
b
Entry
Alcohol
Yield (%)
Temp. (°C)
c
ReOCl
3
(SMe
2
)(OPPh
3
), affording the alkene in 98% yield after
1
3-pentanol
3-pentanol
2-pentanol
1-butanol
3-hexanol
2-butanol
glycerol
170
120
170
170
170
170
200
170
170
170
170
170
84 (5)
6
h (Table 1, entry 1). In the presence of 5 mol% of this
2
No reaction
75
catalyst, the alkene was also formed in good yield, but the
reaction required 17 h (Table 1, entry 2). Low yield of alkene
3
c
4
47 (53)
was obtained using 2 mol% of ReOCl
entry 3). The reaction catalyzed by the oxo-complex
ReOCl (PPh (5 mol%) gave the alkene in 67% yield (Table 1,
entry 4). Moderate to low yields of alkene were observed in
the deoxygenation catalyzed by complexes ReOBr (PPh
ReIO (PPh , ReOCl (dppm) and MTO (Table 1, entries 5-8). No
3 2 3
(SMe )(OPPh ) (Table 1,
d
e
5
39 (35) (18)
No reaction
No reaction
No reaction
No reaction
No reaction
No reaction
No reaction
3
3 2
)
6
7
3
3 2
) ,
8
Ethylene glycol
2-octanol
2-propanol
Ethanol
2
3
)
2
3
9
reaction was observed in the presence of NaReO
absence of catalyst (Table 1, entry 9 and 10).
4
and in the
10
The deoxygenation of 6-methoxytetralone catalyzed by
ReOCl (SMe )(OPPh ) (5 mol%) was also investigated using
different secondary and primary alcohols as reducing agents
Table 2). 3-Pentanol was the best reducing agent for this
1
1
1
2
3
2
3
Methanol
a
The reactions were carried out with 0.5 mmol of
-methoxytetralone and 2 mL of alcohol. Yields determined by
H NMR spectroscopy using 1,2-dimethoxyethane as internal
standard. Substrate. Yield of Alkane. Yield of Alcohol
(
b
6
reaction, affording the alkene with 84 % yield at 170 °C under
air atmosphere (Table 2, entry 1). At reflux temperature of
1
c
d
e
3-pentanol (120 °C) the reaction did not occur (Table 2, entry
2
). Good yield of alkene (75%) was also observed in the
Table 1 Direct reductive deoxygenation of 6-methoxytetralone deoxygenation of 6-methoxytetralone with 2-pentanol (Table
a
catalyzed by different oxo-rhenium complexes
2, entry 3). The reaction using 1-butanol as reducing agent
only led to moderate yield of alkene (Table 2, entry 4). An
interesting result was observed in the deoxygenation of
6
-methoxytetralone with 3-hexanol that produced the alkene
in 39% yield, along with 35% yield of the alkane and 18% yield
of alcohol (Table 2, entry 5). Finally, the reductions performed
with glycerol, ethylene glycol, 2-butanol and 2-octanol and
with small alcohols such as 2-propanol, ethanol and methanol
did not occur (Table 2, entries 6-12). As reported previously by
b
Entry Catalyst
Catalyst
mol%)
Time
Yield (%)
(
1
2
3
4
5
6
7
ReOCl
ReOCl
ReOCl
ReOCl
3
(SMe
(SMe
(SMe
2
)(OPPh
)(OPPh
)(OPPh
3
)
)
)
10
5
6
98
3
0a
Toste, the reactivity of the different alcohols was dependent
on both size and structure of the alcohol. In general secondary
alcohols gave higher yields than primary alcohols owing to
decreased by-product formation. The reactivity increased as
the carbon chain length of alcohol increased, presumably
because the strong coordination of multiple alcohol molecules
to the rhenium center was prevented.
c
3
2
3
17
17
17
17
17
17
84 (5)
c
3
3
2
3
2
37 (42)
(PPh
(PPh
(PPh
3
)
2
5
67
c
ReOBr
ReIO
3
3
)
2
5
39 (54)
c
2
3
)
2
5
33 (57)
In order to explore the scope and the limitations of this
novel method, we investigated the deoxygenation of several
c
ReOCl
3
(dppm)
5
30 (70)
ketones
and
aldehydes
with
the
system
c
3-pentanol/ReOCl (SMe )(OPPh ) at 170 °C under air
3
2
3
8
9
1
MTO
5
5
−
17
17
17
13 (86)
atmosphere in a closed Schlenk equipped with a J-Young tap,
without using any special pressure-controlling equipment
NaReO
4
No reaction
No reaction
0
Without catalyst
(
Tables 3 and 4). The progress of the reactions was monitored
1
a
by thin layer chromatography and by H NMR spectroscopy.
The best yield of alkene (96%) was obtained in the
deoxygenation of 5-methoxytetralone in the presence of 10
The reactions were carried out with 0.5 mmol of
-methoxytetralone and 2 mL of 3-pentanol. Yield determined by
b
6
1
H
NMR spectroscopy using 1,2-dimethoxyethane as internal
c
standard. Substrate
2
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a
Table 3 Direct reductive deoxygenation of aryl ketones with the system 3-pentanol/ReOCl (SMe )(OPPh )
3
2
3
Entry
Ketone
Product
Catalyst (mol%)
Time (h)
Yield (%)
c
1
2
10
5
6
96
c
17
90
c
3
4
10
5
6
87
d,c
17
82 (5)
c
5
6
10
5
17
17
88
d,b
44 (62)
d,b
7
8
10
10
17
40
48
88 (10)
e,b
36 (64)
d,b
55 (45)
1
1
0
0
9
b
17
40
65
1
1
0
1
d,c
78 (20)
1
0
d,c
1
1
2
3
10
40
40
50 (40)
f,c
1
1
0
50 (25)
1
4
0
40
d,c
5 (35)
6
a
b
1
The reactions were carried out with 0.5 mmol of ketone and 2 mL of 3-pentanol. Yields determined by H NMR spectroscopy using
c
d
e
f
1
,2-dimethoxyethane as the internal standard. Isolated yield. Substrate. Yield of alcohol. Yield of ether.
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3 2 3
mol% of ReOCl (SMe )(OPPh ) after 6 h (Table 3, entry 1). respectively (Table 3, entries 11 and 12). Curiously, the
Using only 5 mol% of this catalyst, the alkene was afforded in reaction of 4′-chloro-2-phenylacetophenone, under the same
9
0% yield after 17 h (Table 3, entry 2). Both reactions of reaction conditions, produced the alkane in 50% yield, along
-methoxytetralone with 10 mol% or with 5 mol% of with 25% yield of the ether, resulting of the reaction with
6
ReOCl
deoxygenation with 10 mol% of catalyst was much faster (6 h) 3-pentanol/ReOCl
Table 3, entries 3 and 4). In contrast, the reduction of the deoxygenation of isobutyrophenone, giving the alkene (65%
-methoxytetralone required 10 mol% of ReOCl (SMe )(OPPh yield) (Table 3, entry 14).
to give 88% yield of alkene (Table 3, entry 5). The alkene was The efficiency
also obtained in good yield (88%) in the reaction of -tetralone 3-pentanol/ ReOCl (SMe
with 10 mol% of ReOCl (SMe )(OPPh ) (Table 1, entry 7). deoxygenation of several aryl aldehydes (Table 4). In these
3
(SMe
2
)(OPPh
3
) produced good yields of alkene, but the 3-pentanol (Table 3, entry 13). Finally, the system
3
(SMe )(OPPh ) was also applicable to the
2
3
(
7
3
2
3
)
of
the
system
α
3
2 3
)(OPPh ) was also tested in the
3
2
3
Interestingly, the deoxygenation of the β-tetralone also reactions were obtained the corresponding alkanes, and in
produced the alkene in 36% yield, along with 64% yield of the certain cases, it was observed the formation of the primary
alcohol (Table 3, entry 8).
alcohol and the ethers (Eq. 1).
In the reaction of 4-methyltetralone
was obtained the alkene in 55% yield
after 48
ReOCl (SMe
h
using 10 mol% of
3
2
)(OPPh ) (Table 3, entry 9).
3
The deoxygenation of chromanone was also investigated and
gave the alkene in 65% yield (Table 3, entry 10). The ketones
deoxyanisoin and deoxybenzoin were also deoxygenated,
affording the corresponding alkenes in 78% and 50% yield,
The best result was obtained in the reaction of
2
,4-dichlorobenzaldehyde producing 2,4-dichlorotoluene in
1% yield (Table 4, entry 1). The reduction of
9
a
3 2 3
Table 4 Direct reductive deoxygenation of aldehydes with the system 3-pentanol/ReOCl (SMe )(OPPh )
O
H
3-pentanol, ReOCl (SMe )(OPPh ) (10 mol%)
3
2
3
R
R
1
70 ºC
Entry
1
Aldehyde
Product
Time (h)
Yield (%)
c
1
7
91
2
3
4
5
d,c
1
1
4
7
7
0
75 (19)
c
66
d,b
50 (40)
e,b
4
0 (50)
1
7
6
7
c
f,b
1
1
7
7
79 (10)
f,c
79 (16)
a
b
1
The reactions were carried out with 0.5 mmol of aldehyde and 2 mL of alcohol. Yields determined by H NMR
c
d
e
f
spectroscopy using 1,2-dimethoxyethane as the internal standard. Isolated yields. Yield of ether. Yield of alcohol. Yield
of alkane.
4
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4
-bromobenzaldehyde with this system gave 4-bromotoluene
in 75% yield and 19% yield of ether (Table 3, entry 2). The
deoxygenation of 4-chlorobenzaldahyde afforded
-chlorotoluene as the major product (66% yield), along with
the residual amounts of 4-chlorobenzyl alcohol and ether
Table 3, entry 3). Similarity, from 4-fluorobenzaldehyde was
Table 6 Use of the complex ReOCl (SMe )(OPPh ) as catalyst in
several cycles in the deoxygenation of 2,4-dichlorobenzaldehyde
3
2
3
a
Cl
O
Cl
4
H
3-pentanol, ReOCl
3 2 3
(SMe )(OPPh ) (10 mol%)
1
70 ºC
Cl
Cl
(
b
Catalytic cycle
Time (h)
17
Yield (%)
91
obtained 4-fluorotoluene in 50% yield and the ether in 40%
yield (Table 4, entry 4). In contrast, the reaction of methyl
1
2
3
4
5
6
7
8
4-formylbenzoate produced as the major product the alcohol
24
91
methyl 4-(hydroxymethyl)benzoate in 50% yield and the
deoxygenated product methyl 4-methylbenzoate in 40% yield
24
90
(Table 4, entry 5). Finally, from the reactions of the
24
82
4-(methylthio)benzaldehyde and 4-methylbenzaldehyde,
24
89
containing electron-donating groups, were obtained the
corresponding ethers with excellent yields and the alkanes in
low yields (Table 4, entries 6 and 7). The results obtained
demonstrate that the aldehydes with electron-withdrawing
groups led to best yields of alkanes.
24
88
24
85
24
71
a
In order to study the possible use of the complex
The reactions were carried out by successive additions of
0
3
.5 mmol of 2,4-dichlorobenzaldehyde to reaction mixture in
mL of 3-pentanol. Yields determined by H NMR spectroscopy
3 2 3
ReOCl (SMe )(OPPh ) as catalyst in several cycles, we carried
b
1
out successive reactions by sequential addition of fresh
substrate 6-methoxytetralone to the reaction mixture, using
using 1,2-dimethoxyethane as the internal standard.
3
-pentanol as reducing agent. The reactions were monitored
1
alkane. To examine this hypothesis we decide to carry out the
by H NMR spectroscopy and the results obtained showed that
ReOCl (SMe )(OPPh ) can be used in the first two catalytic
cycles with excellent yields and in 3 cycle with good yield
deoxygenation of alcohols
1 and 3 with the system
3
2
3
th
3-pentanol/ReOCl (SMe )(OPPh ) (10 mol%), obtaining the
3
3
2
corresponding alkene and alkane in 46% and 98% yields,
respectively (Eqs 2 and 3).
(Table 5).
The
catalytic
)(OPPh
spectroscopy, in several cycles in the deoxygenation of
,4-dichlorobenzaldehyde by sucessive additions of fresh
activity
of
the
oxo-complex
1
ReOCl
3
(SMe
2
3
)
was also studied by
H
NMR
2
substrate to the reaction mixture, showing that this catalyst
can be used in at least 8 cycles with excellent to good yields
(Table 6).
The formation of the alcohol in some reductions suggests
that it could be an intermediate in the deoxygenation of the
carbonyl compound. This result indicates that the
deoxygenation of the carbonyl compounds should proceed in
two steps, where the carbonyl compound is first reduced to
the alcohol, followed by deoxygenation to the alkene or the
The temporal progression of the deoxygenation of
2
,4-dichlorobenzaldehyde
with
the
system
3 2 3
Table 5 Use of the complex ReOCl (SMe )(OPPh ) as catalyst in
a
several cycles in the deoxygenation of 6-methoxytetralone
b
Catalytic cycle
Time (h)
17
Yield (%)
1
2
3
84
81
70
24
24
a
The reactions were carried out by successive additions of
.5 mmol of 6-methoxytetralone to the reaction mixture in 3 mL
0
Fig. 1 Deoxygenation of 2,4-dichlorobenzaldehyde with the system
b
1
of 3-pentanol. Yields determined by H NMR spectroscopy
using 1,2-dimethoxyethane as the internal standard.
3-pentanol/ReOCl
(SMe
)(OPPh
)
(10 mol%) monitored by
3
2
3
1
H NMR spectroscopy
.
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1
) was monitored by H NMR
3
-pentanol/ReOCl
3
(SMe
2
)(OPPh
3
spectroscopy during 17 h.
Figure 1 shows the products observed as a function of
time. The analysis of the graphical indicates that the reduction
of the aldehyde to the corresponding benzyl alcohol is very
fast (30 min), confirming that the alcohol is an intermediate in
the deoxygenation of the aldehyde. The graphical also shows
that the deoxygenation of the 2,4-dichlorobenzyl alcohol is the
limiting step in the direct deoxygenation of the aldehyde to
the alkane, requiring nearly 16 h 30 min.
To confirm the deoxygenation of the carbonyl group by the
reducing agent 3-pentanol, we carried the reaction of
2
,4-dichlorobenzaldehyde with deuterated 3-pentanol
3-pentanol-D) at 170 °C (Eq. 4). However, after 17 h we
observed the formation of the deuterated alkane in low yield
(
6
(10%).
Cl
O
Cl
D
D
D
OH
ReOCl3(SMe2)(OPPh3) (10 mol%)
70 ºC, 17 h
H
+
H
(Eq. 4)
1
1
Fig. 3 H NMR spectra (CDCl
, 400 MHz) of: (a) compound 3;
3
Cl
Cl
6
(b) deuterated alcohol 7.
5
1
The analysis of the H NMR spectrum of the deuterated
alkane
shows a signal at δ 2.32 ppm, integrating only one consisted with the reduction of the carbonyl group with the
proton that confirms the incorporation of the two deuterium incorporation of one deuterium atom (Figure 3b).
6
atoms in the alkane (Fig. 2b).
Then, we decided to follow the reduction of agent (3-pentanol) and the catalyst ReOCl
We also performed the reaction between the reducing
3
(SMe
2
)(OPPh
3
) at
1
2
,4-dichlorobenzaldehyde with 3-pentanol-D by H NMR 170 °C during 17 h, leading to the oxidation of the 3-pentanol
1
13
spectroscopy and we observed the formation of the to 3-pentanone, confirmed by H and C NMR spectroscopy
deuterated alcohol
after 3 h (Eq. 5). We stopped the reaction (see supporting information).
and the alcohol was isolated by column cromatography.
7
Based on these results, we suggest that the deoxygenation
of the carbonyl compounds with the system
Cl
O
Cl
D
OH
H
D
OH
ReOCl
3
(SMe
2
)(OPPh
3
) (10 mol%)
3 2 3
3-pentanol/ReOCl (SMe )(OPPh ) involves the oxidation of the
(Eq. 5)
H
+
170 ºC, 3 h
3-pentanol to the corresponding 3-pentanone and the
Cl
Cl
7
5
hydride transfer from the 3-pentanol to the carbonyl group as
confirmed by the incorporation of the deuterium atom in the
1
The H NMR spectrum of deuterated alcohol
7
presents a
signal at δ 4.71 ppm that integrates one proton, which is
alcohol 7. Finally, occurs the deoxygenation of the alcohol by
reaction with another molecule of 3-pentanol.
Comparing this novel methodology using the system
3
3 2 3
-pentanol/ReOCl (SMe )(OPPh ) with the other methods
developed by our group for the deoxygenation of carbonyl
28,29
compounds,
we conclude that this novel procedure is more
economical, environmental friendly using an alcohol as a green
solvent/reducing agent instead of a silane. Furthermore, this
method is also more efficient and selective for the
deoxygenation of ketones to the corresponding alkenes that
the method catalyzed by the same oxo-rhenium complex
3 2 3 3
ReOCl (SMe )(OPPh ) employing PhSiH as reducing agent,
which produced a mixture of alkane and alkene in the reaction
of several substrates, being the alkene the minor product.
Conclusions
We have developed the first methodology for the
deoxygenation of ketones to the corresponding alkenes and
for the deoxygenation of aldehydes to alkanes using an
alcohol as a green solvent/reducing agent catalyzed by the
oxo-rhenium complex ReOCl (SMe )(OPPh ) in moderate to
3
2
3
1
Fig. 2 H NMR spectra (CDCl
3
, 400 MHz) of: (a) compound 4;
excellent yields. This procedure has some advantages over the
(
b) deuterated alkane 6.
6
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other reported in the literature that use toxic hydride reagents
7
8
9
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4
1
2
or molecular hydrogen (H ), its use is generally associated with
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This novel method is also chemoselective and the catalyst
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2, 182-184
1 A.Volkov, K. P. J. Gustafson, C.-W. Tai, O. Verho, J.-E. Bäckvall
1
these advantages make this catalytic protocol a green and
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and H. Adolfsson, Angew. Chem. Int. Ed., 2015, 54, 1-6.
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1
1
4 N. Sakai, K. Nagasawa, R. Ikeda, Y. Nakaike and T.
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Experimental
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6 C. V. Doorslaer, J. Wahlen, P. G. N. Mertens, B. Thijs, P.
931.
General procedure for the deoxygenation of carbonyl
1
compounds
-pentanol/ReOCl
The solution of ReOCl
with the
(SMe )(OPPh
2 3
(SMe )(OPPh ) (5-10 mol%) and
system
Nockemann, K. Binnemans and D. E. De Vos, ChemSusChem,
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carbonyl compound (0.5 mmol) in 3-pentanol (2 ml) was
stirred at 170 °C under air atmosphere in a closed Schlenk
equipped with a J-Young tap without using any special
pressure-controlling equipment (the reaction times are
indicated in Tables 3 and 4 and all reaction temperatures
refer to bath temperatures). The reaction mixture of the less
volatile products was evaporated and purified by silica gel
column chromatography with n-hexane. The yields of more
volatile deoxygenated products were determined directly by
8 J. Ma, S. Liu, X. Kong, X. Fan, X. Yan and L. Chen, Res. Chem.
Intermed, 2012, 38, 1341-1349.
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H NMR spectroscopy using 1,2-dimethoxyethane as the
2
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Acknowledgements
This research was supported by Fundação para a Ciência e
Tecnologia (FCT) through project PTDC/QUI-QUI/110080/2009.
Joana R. Bernardo thanks FCT for grant (SFRH/BD/90659/2012).
Authors thank the project UID/QUI/00100/2013 and the Portuguese
NMR Network (IST-UTL Center) for providing access to the NMR
facilities.
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Graphical Abstract
The catalytic system 3-pentanol/ReOCl
deoxygenation of carbonyl compounds.
3 2 3
(SMe )(OPPh ) was very efficient for the