Chemoselective hydrogen peroxide oxidation of primary alcohols to aldehydes by a water-soluble and reusable iron(iii) catalyst in pure water at room temperature

Article abstract of DOI:10.1039/c6nj03793c

Hydrogen peroxide oxidation of primary alcohols to aldehydes is described, which is catalyzed by a novel, reusable and water-soluble FeCl₃ complex in situ-formed with quaternary ammonium salt-functionalized 8-aminoquinoline. This reaction exhibits unique chemoselectivity and broad functional-group tolerance, and it can operate efficiently in pure water at room temperature.

Full text of DOI:10.1039/c6nj03793c

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Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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DOI: 10.1039/C6NJ03793C
Journal Name
ARTICLE
Chemoselective hydrogen peroxide oxidation of primary alcohols
to aldehydes by a water-soluble and reusable iron(III) catalyst in
pure water at room temperature
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
b
DOI: 10.1039/x0xx00000x
Qi Yan, Ye Chen Fang, Yun Xue Jia and Xin Hong Duan*
www.rsc.org/
Hydrogen peroxide oxidation of primary alcohols to aldehydes is described, which is catalyzed by a novel, reusable and
water-soluble FeCl complex in situ-formed with quaternary ammonium salt-functionalized 8-aminoquinoline. The reaction
3
exhibits unique chemoselectivity and broad functional-group tolerance, and it can operate efficiently in pure water at
room temperature.
described lack of chemoselectivity towards primary alcohols,
but also control the overoxidation of aldehydes to carboxylic
acids, a major competitive reaction that occurs in the oxidation
Introduction
The oxidation of primary alcohols to aldehydes, especially its
chemoselective oxidation in the presence of secondary
alcohols is a crucial process to synthesize fragrances and food
additives as well as many intermediates. Such reaction occurs
typically with stoichiometric use of environmentally-harmful
oxidants, such as CrO and MnO . Because of high atom
efficiency and formation of water as the sole by-product,
hydrogen peroxide (H O ) has been used as a green oxidant in
transition metal-catalyzed oxidation reactions. In comparison
with other catalysts (Pd, Cu, Ru, etc.), the inexpensive and
9a,b,10
of primary alcohols.
selectivity that cannot be attained in organic solvents.
Water offers unique reactivity and
11
1
Therefore, we anticipated that the use of water instead of
organic solvents required in alcohol oxidations (e.g., MeCN,
CH Cl ) could lead to an iron(II/III)-catalyzed H O -oxidation of
2 2 2 2
primary alcohols to aldehydes with high chemoselectivity.
Moreover, the use of pure water as solvent is an ideal process
of green chemistry, as water is the cleanest, safest and
cheapest solvent.
2
3
2
2
2
3
4
relatively non-toxic iron in combination with H O has recently
2
5
2
attracted interest as catalytic oxidation system.
Iron(II/III) complexes are able to selectively catalyse various
6
oxidation reactions, such as sulfide oxidation, hydroxylation,
epoxidation, etc., and in particular several type of iron
catalysts have been recently developed for the oxidation of
7
,8
alcohols using H O as an oxidant. For example, nano--
2
2
7a,b
7c
7d
Fe O ,
[
[Fe(II)(N-N) ](OTf) ,
[Fe(II)(Me-Pic)3],
2
3
3
2
7e
Fe(II)(imine) (OTf) ], a μ-oxo diiron(III) complex of N3Py-
phenol ligand and Fe(III) complexes based on BTC and
PPh /Schiff base ligands were effective catalysts for the
2
2
7f
7g
7h
3
Scheme 1 The in situ-formed FeCl /L2 complex and its chemoselectivity.
3
oxidations of both secondary and primary alcohols to ketones
8a
To achieve these goals, we have recently started exploring
iron(III) catalysts suitable for the chemoselective oxidation of
and aldehydes/acids. In contrast, FeBr
and the Fe(II)-
3
8b
8c
benzimidazoylpyridine,
Fe(III)-phen, as well as Fe(II)-
8
d
primary alcohols to aldehydes in pure water by H O2 as
bis(picoly)amine complexes provided selectivity for the
preferential oxidation of secondary over primary alcohols. Due
to the generally lower reactivity of primary alcohols in
2
oxidant. Considering that ligand solubility is the crucial factor
12
to enhance the activity and selectivity of a catalyst in water,
9
and motivated by the fact that 8-aminoquinolines (AQ) have
oxidation reactions, however, to date few catalytic oxidation
been shown to be strong iron-chelating agents containing the
methods with H O as an oxidant have been reported on the
2
2
13
N-C-C-N linkage, we developed two novel ligands by merging
the AQ skeleton with highly water-soluble quaternary
ammonium salts. Herein, we for the first time report the use of
chemoselective oxidation of primary alcohols to aldehydes in
the presence of secondary alcohols. As such, the development
of an efficient iron(II/III) catalytic system capable of such
transformation is highly required as well as remarkably
challenging, because it must not only overcome the above-
a highly active water-soluble FeCl catalyst in situ-formed with
3
an optimized ligand (L2) for such oxidation reaction in water at
room temperature (Scheme 1). Apart from being an effective
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oxidation in room temperature water, this method has Indeed, the use of L1 or L2 as ligand was shownVietwoAritmiclepOronlvinee
substantial advantages. On the one hand, the catalyst exhibits further the catalyst activity. By contrasDtO, I:th10e.10in39/sCit6uN-Jfo03rm79e3Cd
several types of chemoselectivity, including (1) the oxidation of FeCl3/L2 complex was a much more effective catalyst that led
primary alcohols but not secondary ones, (2) the formation of to complete conversion of 1a into 2a within 1.5 h (Table 1,
aldehydes without overoxidation to carboxylic acids, and (3) entry 6 versus entry 7). Moreover, the optimal mol ratio of
the preferential oxidation of benzylic over aliphatic primary FeCl to L2 was investigated and found to be 1:1 (Table 1,
3
alcohols. On the other hand, the use of pure water as solvent entries 7-9). At this ratio, reduction in the amount of Fe to 2
provides an opportunity for facilitating recycle and reuse of mol% and of H O to 2 mmol almost did not affect the yield
2
2
the catalyst, because when a water-soluble catalyst is used in a (Table 1, entries 10 and 11). However, when the same reaction
biphasic system, the product can be separated by a simple was carried out in MeCN instead of water, the overoxidation
decantation or extraction, and the catalyst solution can be occurred significantly and resulted in a decreased yield (Table
1a,14
recycled and reused.
1, entry 12). Hence, these results show that water as a solvent
favours the activity and selectivity of such a catalytic system.
a
Table 1 Optimization of the reaction conditions.
Result and disscusion
The ligand of L1 or L2 was prepared by a facile procedure. As
shown in Scheme 2, the amidation of AQ led to the formation
of AQ-1, then which was simply quaternized with TEA to give
L1. Moreover, Ligand L2 was obtained in a three step synthesis, Entry
b
Catalyst (mol %)
H
O
2 2
(equiv)
Time (h)
Yield (%)
involving the amination of AQ-1 with DEA, reduction of AQ-2
1
FeCl (3)
3
3
3
3
3
3
3
3
3
3
2
2
8
9
3
3
3
3
3
3
3
3
3
3
3
3
with LiAlH and quaternization of AQ-3 with C H Br. Despite
4
2 5
2
3
4
5
6
7
8
9
1
1
1
FeCl (3) + bpy (3)
3
37
48
62
79
74
92
53
11
90
93
49
the advantage of being easily carried out at room
temperature, this procedure involved the use of CH Cl or DMF
FeCl (3) + AQ (3)
3
2
2
FeCl (3) + AQ-Me (3)
3
as solvent, which is not green.
c
FeCl (3) + AQ-Me (3)
2
FeCl (3) + L1 (3)
3
FeCl (3) + L2 (3)
1.5
5
FeCl (3) + L2 (6)
FeCl (3) + L2 (9)
5
0
1
2
FeCl (2) + L2 (2)
1.5
1.5
2.5
FeCl (2) + L2 (2)
d
FeCl (2) + L2 (2)
a
1
3 2 2
) The catalyst was formed in-situ by stirring FeCl ·6H O and Ligand in 1 mL H O
to give a clear yellow solution after 10 minutes; 2) Reaction conditions: 4-
methylbenzyl alcohol (1a, 1 mmol) and H (30 wt% in H O) were added
dropwise into the above solution at room temperature with stirring within 10
2
O
2
2
b
c
d
minutes. Isolated yield. 10 mol% TBAB was added. The same conditions as in
a, but 1 mL MeCN was used instead of water as the solvent.
Scheme 2 The ligand preparation. Reaction conditions: (a) BrCH
2
COBr, TEA, DCM,
rt, 3h; (b) TEA, Me CO, rt, 8h; (c) DEA, K CO , DMF, rt, 12h; (d) LiAlH , THF, rt, 4h;
2
2
3
4
With the above optimized conditions in hand, we next
investigated the substrate scope of the in situ-formed FeCl3/L2
(
2 5 2
e) C H Br, Me CO, rt, 24h.
To explore the catalytic activity and selectivity of the new complex and its chemoselectivity.
iron (III) catalysts, a typical reaction was carried out by using 4-
The oxidation of various benzylic primary alcohols were
methylbenzyl alcohol (1a) as a model substrate and 30 wt% examined under the optimized conditions. As shown in Table
H O as oxidant (Table 1). In the absence of ligand, this FeCl - 2, alcohols (1b ) were smoothly oxidized to aldehydes (2b ) in
-
j
-j
2
2
3
catalyzed reaction proceeded rather sluggishly in water at water at room temperature with little formation of carboxylic
room temperature, and a noticeable overoxidation to 4- acids. Functionalized alcohols containing halogens (F or Cl),
methylbenzoic acid was also observed after 8 h (Table 1, entry ethers, ester and di-N-methylated aniline underwent clean and
1
). The screening of ligands showed that 2,2’-bipyridine (bpy
,
efficient oxidations in excellent yields (Table 2, entries 1 and 3-
Table 1, entry 2), which was reported as an attractive ligand 8). 4-Biphenylmethanol and 1-naphthyl carbinol were also
4b,11a
for the copper-mediated O oxidation of alcohols,
worked compatible with the reaction conditions (Table 2, entries 2 and
AQ-Me, Table 9). Thus, this catalytic system showed broad substrate scope
, entries 3 and 4). Because the use of TBAB as an additive led and remarkable functional group tolerance. In addition, the
to an increased yield in the FeCl3/AQ-Me catalytic system catalyst was shown to be efficient for the selective oxidation of
Table 1, entry 5), we reasoned that L1 or L2, a water-soluble heteroaromatic primary alcohols. Under the above-optimized
2
less efficiently than AQ and N-Methylated AQ
(
1
(
ligand based on the quaternization of AQ-Me, should facilitate conditions, substrates including indole (1k), pyridine (1l),
much more an efficient catalytic oxidation of primary alcohols. brominated thiophene (1m) and substituted furfural (1n) were
2
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converted to exclusively the corresponding aldehydes (2k
-
n
)
underwent facile oxidation to the corresponding aldehydes
(4a-4c) in good yields. Interestingly, the C=C double bonds did
View Article Online
DOI: 10.1039/C6NJ03793C
(Table 2, entries 10-13), which suggested that functional group
tolerance extends to this class of educts. It is worthwhile that not be affected and the overoxidation to carboxylic acids also
after 5 h, both activated and non-activated secondary alcohols did not occur during the reactions. On the other hand, the
(
1o and 1p) were essentially unreactive at room temperature present procedure proved to be very easy to scale up by
o
or even at 80 C, and therefore can be recovered in high yields performing entry 3 on a 10-mmol scale, and found that the
Table 2, entries 14 and 15). Moreover, the presence of 1o did yield was almost identical to that obtained on a 1-mmol scale.
not affect the oxidation rate and yield of a primary alcohol (1b Different from most of the reported iron catalytic systems
Table 2, entry 16). Therefore, these results displayed that such that were often limited to activated benzylic and/or allylic
(
,
catalyst is exclusively active towards primary alcohols.
primary alcohol oxidations, this FeCl3/L2 complex was capable
of catalysing the oxidation of non-activated aliphatic primary
alcohols 3d-3f to the corresponding aldehydes 4d-4f (Table 3,
a
Table 2 The oxidation of benzylic primary alcohols to aldehydes.
entries 4-6), albeit after longer reaction times in comparison
with benzylic primary alcohols. As a result, even in the
presence of an aliphatic primary alcohol group, the
chemoselective oxidation of a benzylic one could be achieved
by the appropriate choice of the reaction time.
b
Entry
Substrate
Product
Time, Yield
1
2
3
4
5
6
7
8
R = 2-OCH (1b)
2b
2c
2d
2e
2f
2h, 87%
2h, 91%
3h, 89%
3h, 94%
3h, 82%
3h, 73%
3h, 85%
3h, 86%
3
= 4-Ph (1c)
= 3-Cl (1d)
a
Table 3 Representative examples of allylic and aliphatic primary alcohol oxidations.
Time,
Yield
Entry
Substrate
Product
= 3,4-(OCH
= 4-NO (1f)
= 2-F (1g)
= 4-N(CH
= 4-COOCH
2
O) (1e)
b
2
2g
2h
2i
5
81 %
h
1
3
)
2
(1h)
(1i)
3a
3b
4a
4b
3
5
8
h
4 %
2
9
2j
3h, 83%
3h, 80%
(1j)
5
8
85 %
h
8 %
1
0
2k
3
4
c
(1k)
3
3
c
4c
7
71 %
h
1
1
1
1
2
3
2l
2h, 79%
3h, 77%
(1l)
d
e
4d
2m
2n
(1m)
7 h
7
5
5 %
3
4e
4f
3h, 88%
(
1n)
7
7
h
9 %
6
c
5
9
h, trace
3f
1
1
4
2o
1% recovery
a
Reaction conditions: the in situ-formed FeCl
3
/L2 complex (2 mol%) in 1 mL H
2
O,
(1o)
b
substrate (1 mmol), H
Isolated yield. Reaction was performed on a 10-mmol scale: 3c (10 mmol), H
2
O
2
2
(30 wt% in H O, 2 mmol) at room temperature.
c
c
5
8
h, trace
2
O
2
5
6
2p
2b
2
(30 wt% in H O, 20 mmol) at room temperature, 8 h.
9% recovery
(
1p)
d
1
1b + 1o
2h, 85%
The possibility of this chemoselectivity was investigated by a
O, competition between benzylic and aliphatic primary alcohol
a
Reaction conditions: the in situ-formed FeCl
3
/L2 complex (2 mol%) in 1 mL H
O, 2 mmol) at room temperature.
Isolated yield. Apart from at room temperature, heating at 80 C was also
2
b
substrate (1 mmol), H
2
O
2
(30 wt% in H
2
oxidation. Thus, a mixture of 1a and 3f in a molar ratio of 1:1
was subjected to the FeCl3/L2-catalyzed oxidation. Whereas
the oxidation of 1a was almost complete within 3 h to give an
c
o
d
performed. A mixture of 1b and 1o in a molar ratio of 1:1 was used.
8
%
2 % isolated yield of 2a, the unreacted 3f was recovered in 89
yield (Scheme 3, eq. 1). Based on the results, we next turned
In addition to benzylic primary substrates, allylic primary
alcohols were also amenable to such oxidation. Representative
examples were illustrated in Table 3, entries 1-3, where (s)-
to the synthetically more useful case of intramolecular
competition between benzylic and aliphatic primary alcohols.
perillyl alcohol (3a) and (E)-cinnamyl alcohols (3b and 3c
)
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Therefore, the oxidation of diol (3g) was carried out under the General Methods
View Article Online
DOI: 10.1039/C6NJ03793C
same conditions. As expected, the chemoselective oxidation
All reagents were obtained from Sigma-Aldrich Chemical Co. or
took place efficiently to afford the benzaldehyde 4g in 91 %
yield, where the aliphatic primary alcohol group remained
completely intact (Scheme 3, eq. 2).
1
Alfa Aesar. H-NMR spectra were recorded on a Bruker Avance
DPX 400 (400 MHz) spectrometer at 400 MHz using CDCl or
3
D2O as the solvent. The chemical shifts are reported in δ (ppm)
values. Coupling constants are reported in hertz (Hz). The
following abbreviations are used to designate the
multiplicities: s = singlet, d = doublet, t = triplet, q = quartet
13
and m = multiplet. C-NMR spectra were recorded on a Bruker
Avance DPX 400 (400 MHz) spectrometer at 100 MHz using
CDCl or D O as the solvent. Elemental analyses were obtained
3
2
on an Elementar Vario EI.
Procedures for the synthesis of ligands and substrates
15
N-methyl-8-aminoquinoline
(AQ-Me)
8
-Aminoquinoline (AQ, 0.65 g, 4.5 mmol) and CH I (0.85 g,
3
6
4
.0 mmol) were dissolved in 15 mL DMF, then K CO (0.63 g,
2 3
.5 mmol) was added to the solution and stirred at room
Scheme 3 The chemoselective oxidation of a benzylic primary alcohol in the
presence of an aliphatic one. Reaction conditions: the in situ-formed FeCl
3
/
L2
complex (2 mol%) in 1 mL H
mmol).
2 2 2 2
O, 1a, 3f or 3g (1 mmol), H O (30 wt% in H
O, 2
temperature for 24 hours. After a routine workup including
that the reaction mixture was extracted with EtOAc (3 × 10
In this procedure, recovery of the water-soluble FeCl3/L2 mL), dried over Na SO , and concentrated in vacuo, the
2 4
complex was easy and efficient (by solvent extraction of the desired product of AQ-Me was afforded as a light yellow oil by
water layer after separating the organic layer). Furthermore, purification with silica gel flash chromatography (0.48g, 67 %
1
this catalyst was reused several times without obvious loss of yield). H-NMR (400 MHz, CDCl
): δ 8.77 (q, J = 5.8 Hz, 1H),
3
activity, as shown in Table 4.
8.09 (q, J = 9.9 Hz, 1H), 7.48 (t, J = 15.8 Hz, 1H), 7.40 (q, J = 12.4
Hz, 1H), 7.11 (q, J = 9.1 Hz, 1H), 6.71 (d, J = 7.6 Hz, 1H), 6.23 (s,
a
13
Table 4 Reusability of the catalyst in the oxidation of 1a.
br, 1H), 3.09 (s, 3H). C-NMR (100 MHz, CDCl ): δ 146.80,
3
1
1
45.90, 138.31, 135.98, 128.61, 127.89, 121.38, 113.70,
04.14, 30.06.
Run
1
2
3
Time (h)
1.5
95
1.5
89
b
2
b
16
Yield (%)
78
2-bromo-N-(quinolin-8-yl)acetamide
(
AQ-1
)
a
Reaction was carried out on a 1- mmol scale. Isolated yield.
AQ (0.65 g, 4.5 mmol) and Et N (0.46 g, 4.5 mmol) were
3
dissolved in 15 mL CH Cl , then bromoacetyl bromide (0.91 g,
2
2
4
.5 mmol) in 5 mL CH Cl was added dropwise to the solution
2 2
Conclusions
and stirred at room temperature for 3 hours. After a routine
workup including that the reaction mixture was extracted with
CH Cl (3 × 20 mL), dried over CaCl and concentrated in vacuo,
In summary, we have developed a novel water-soluble
iron(III) catalyst that is highly efficient, chemoselective and
reusable for primary alcohol oxidations. It has demonstrated
that in water at room temperature, the in situ-formed FeCl3/L2
complex catalyses the H O -oxidation of primary alcohols to
2
2
2
the desired product of AQ-1 was afforded as an off-white solid
0.87g, 95% yield), which was used in the next step without
further purification.
(
2
2
aldehydes in good to high yields and where secondary alcohols
do not react. The major advantages of this method apart from
a very popular room-temperature water as solvent is that it
enables the oxidation of a broad range of primary alcohols,
including benzylic, allylic and aliphatic derivatives, and is not
only highly selective for conversion of primary alcohols to
aldehydes with little formation of carboxylic acids, but which
also exhibits selectivity for a benzylic primary alcohol even in
the presence of an aliphatic one.
2
-(Diethylamino)-N-(quinolin-8-yl)acetamide (AQ-2
AQ-1 (0.53 g, 2.0 mmol), Et N (0.18 g, 2.5 mmol) and K CO
3
)
2
2
(0.35g, 2.5 mmol) were added in 10 mL DMF and stirred at
room temperature for 12 hours. After a routine workup
including that the reaction mixture was extracted with EtOAc
(3 × 20 mL), dried over Na SO and concentrated in vacuo, the
2 4
desired product of AQ-2 was afforded as a light yellow oil by
purification with silica gel flash chromatography (0.47g, 91%
yield). H-NMR (400 MHz, CDCl ): δ 11.54 (s, 1H), 8.85 (q, J =
1
3
5
7
.8 Hz, 1H), 8.80 (q, J = 8.9 Hz, 1H), 8.13 (q, J = 9.9 Hz, 1H),
.56-7.51 (m, 2H), 7.49-7.41 (m, 1H), 3.31 (s, 2H), 2.73 (q, 4H),
Experimental
4
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1
3
1
1
1
.18 (t, 6H). C-NMR (100 MHz, CDCl ): δ 171.71, 149.01, concentrated in vacuo) and purification with silica gel flash
3
View Article Online
DOI: 10.1039/C6NJ03793C
o
1
39.66, 136.53, 135.11, 128.59, 127.76, 122.13, 121.99, chromatography (0.33 g, 92 % yield). m.p. 70.1-70.7 C. H-
17.02, 59.53, 49.28, 13.09. NMR (400 MHz, CDCl ): δ 6.90 (s, 1H), 6.79 (d, J = 8.0 Hz, 1H),
3
6
.73 (d, J = 8.0 Hz, 1H), 6.48 (q, J = 15.8 Hz, 1H), 6.20-6.13 (m,
1
1
2
13
N , N -diethyl-N -(quinolin-8-yl)ethane-1,2-diamine (AQ-3
)
1H), 5.93 (s, 2H), 4.25 (q, J = 6.8 Hz, 2H), 2.25 (s, br, 1H). C-
NMR (100 MHz, CDCl ): δ 148.53, 147.79, 131.71, 131.37,
3
AQ-2 (0.52 g, 2.0 mmol) was added in 10 mL anhydrous THF 127.28, 121.68, 108.81, 106.28, 101.60, 64.10.
with LiAlH (0.11 g, 3.0 mmol) and stirred at room temperature
4
for 4 hours. After quenching the reaction with water and 2-((4-(hydroxymethyl)phenyl)(methyl)amino)ethanol (3g
filtration, AQ-3 was afforded as a yellow oil by extraction with
)
EtOAc (3 × 20 mL, which was then dried over Na SO and
The aldehyde of 4g (0.36 g, 2.0 mmol) was added in the 10
2
4
concentrated in vacuo) and purification with silica gel flash mL MeOH with NaBH (0.11 g, 3.0 mmol) and stirred at room
4
1
chromatography (0.42 g, 87 % yield). H-NMR (400 MHz, temperature for 10 hours. After quenching the reaction with
CDCl ): δ 8.72 (q, J = 5.8 Hz, 1H), 8.04 (q, J = 9.9 Hz, 1H), 7.40- water, 3g was afforded as a viscous light yellow oil by
3
7
6
4
1
4
.33 (m, 2H), 7.03 (t, J = 8.1 Hz, 1H), 6.68 (d, J = 7.5 Hz, 1H), extraction with EtOAc (3 × 20 mL, which was then dried over
.40 (s, br, 1H), 3.31 (t, J = 12.8 Hz, 2H), 2.86 (q, 2H), 2.65 (q, Na SO and concentrated in vacuo) and purification with silica
2
4
1
3
1
H), 1.09 (t, 6H). C-NMR (100 MHz, CDCl ): δ 147.40, 145.54, gel flash chromatography (0.34 g, 94 % yield). H-NMR (400
3
38.94, 136.40, 129.22, 128.30, 121.85, 114.22, 105.13, 52.32, MHz, CDCl ): δ 7.23 (d, J = 8.6 Hz, 2H), 6.77 (t, J = 14.2 Hz, 2H),
3
7.66, 41.82, 12.29.
4.56 (s, 2H), 3.80 (t, J = 11.3 Hz, 2H), 3.46 (t, J = 11.4 Hz, 2H),
13
2
.96 (s, 3H), 1.86 (s, br, 2H). C-NMR (100 MHz, CDCl ): δ
3
[
(C H N)-8-NHCOCH NEt ]Br (L1
)
150.28, 130.03, 129.27, 114.18, 113.54, 65.76, 60.59, 55.94,
9.41. Calculated for C H NO : C, 66.27; H, 8.34; N, 7.73.
9
6
2
3
3
10
15
2
Et N (0.25 g, 2.5 mmol) was added in the 20 mL acetone Found: C, 66.25; H, 8.29; N, 7.79.
3
solution with AQ-1 (0.53 g, 2.0 mmol) and stirred at room
temperature for 8 hours until a white solid was formed. The Procedure for the alcohol oxidations
resulting white solid was then filtered and washed several
times with acetone to give the pure product L1 (0.71 g, 97 %
FeCl ·6H O (5.4 mg, 20 μmol, 2.0 mol %) and L2 (7.0 mg, 20
3 2
1
yield). H-NMR (400 MHz, D O): δ 8.59 (q, J = 5.7 Hz, 1H), 8.01 μmol, 2.0 mol %) were mixed in 1 mL H O and stirred at room
2
2
(q, J = 9.7 Hz, 1H), 7.92 (d, J = 7.4 Hz, 1H), 7.46 (q, J = 7.9 Hz, temperature to give a yellow clear solution in 20 minutes.
1
H), 7.36-7.31 (m, 2H), 4.24 (s, 2H), 3.52 (q, 6H), 1.28 (t, 9H). After addition of the substrate (1 mmol) into the above
1
3
C-NMR (100 MHz, CDCl ): δ 163.40, 150.33, 139.69, 137.75, solution, the mixture was vigorously stirred and then H O (30
3
2 2
1
7
31.82, 128.69, 126.92, 126.12, 122.65, 121.98, 57.07, 55.30, wt% in water, 2 mmol, 0.2 mL) was added dropwise
-
.67. Calculated for C H N OBr : C, 55.74; H, 6.60; N, 11.47. continuously with a syringe pump in 10 minutes at room
1
7 24 3
Found: C, 55.72; H, 6.64; N, 11.44.
temperature. When the reaction was complete, the aldehyde
layer was separated and rapidly purified with silica gel flash
chromatography to get the desired aldehyde product; the
water layer was recovered by extraction with EtOAc (2 × 10
[
(C H N)-8-NHCH CH NEt ]Br (L2
)
9
6
2
2
3
AQ-3 (0.49 g, 2.0 mmol) and C H Br (0.27 g, 2.5 mmol) were mL) for reuse.
2
5
added in 10 mL acetone and stirred at room temperature for
4 hours until a white solid was formed. Then, the resulting
2
Acknowledges
This research is supported by grants from the Fundamental
Research Funds for the Central Universities (2015ZCQ-LY-03)
and the Beijing Forestry University Student Innovative Program
white solid was filtered and washed several times with
1
acetone to give the pure product L2 (0.61g, 86 % yield). H-
NMR (400 MHz, D O): δ 8.59 (q, J = 5.6 Hz, 1H), 8.09 (q, J = 9.9
2
Hz, 1H), 7.40-7.35 (m, 2H), 7.14 (d, J = 7.8 Hz, 1H), 6.75 (d, J =
7
.6 Hz, 1H), 3.63 (t, 2H), 3.31 (t, 2H), 3.24 (q, 6H), 1.13 (t, 9H).
(X201610022143).
1
3
C-NMR (100 MHz, CDCl ): δ 148.83, 143.11, 138.11, 137.79,
3
1
7
29.32, 128.21, 122.66, 117.10, 107.23, 54.85, 53.81, 36.81,
-
.26. Calculated for C H N Br : C, 57.95; H, 7.44; N, 11.93. Notes and references
1
7 26 3
Found: C, 57.94; H, 7.33; N, 11.95.
E)-3,4-(Methylenedioxy)cinnamyl alcohol (3c
The aldehyde of 4c (0.35 g, 2.0 mmol) was added in the 10
1
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(
)
mL MeOH with NaBH (0.11 g, 3.0 mmol) and stirred at room
4
temperature for 10 hours. After quenching the reaction with
water, 3c was afforded as a white solid by extraction with
EtOAc (3 × 20 mL, which was then dried over Na SO and
2
4
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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PNl ee aws eJ do ou rnn oa tl ao df j uC sht emm ai rs gt ir ny s
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| J. Name., 2012, 00, 1-3
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New Journal of Chemistry
View Article Online
DOI: 10.1039/C6NJ03793C
Graphic Abstract
A novel, water-soluble and reusable FeCl catalyst showed high catalytic activity and
3
2 2
chemoselectivity in the H O -oxidation of primary alcohols into aldehydes.