Clean and selective oxidation of alcohols catalyzed by ion-supported TEMPO in water

Article abstract of DOI:10.1016/j.tet.2005.10.022

Three different types of ion-supported TEMPO catalysts are synthesized and their catalytic activity in the chemoselective oxidation of alcohols is investigated. These new catalysts show high catalytic activity in water and can be reused for the next run by extraction of products. Recycling experiments exhibit that ion-supported TEMPO can be reused up to five times without loss of catalytic activity. This system offers a very clean, convenient, environmentally benign method for the selective oxidation of alcohols.

Full text of DOI:10.1016/j.tet.2005.10.022

Tetrahedron 62 (2006) 556–562
Clean and selective oxidation of alcohols catalyzed
by ion-supported TEMPO in water
*
Weixing Qian, Erlei Jin, Weiliang Bao and Yongmin Zhang
Department of Chemistry, Xi Xi Campus, Zhejiang University, Hangzhou, Zhejiang 310028, People’s Republic of China
Received 25 March 2005; revised 9 October 2005; accepted 11 October 2005
Available online 22 November 2005
Abstract—Three different types of ion-supported TEMPO catalysts are synthesized and their catalytic activity in the chemoselective
oxidation of alcohols is investigated. These new catalysts show high catalytic activity in water and can be reused for the next run by
extraction of products. Recycling experiments exhibit that ion-supported TEMPO can be reused up to five times without loss of catalytic
activity. This system offers a very clean, convenient, environmentally benign method for the selective oxidation of alcohols.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
either based on inorganic13 or organic supports.4a,b,14 This
polymer-supported TEMPO, however, in some cases will
result in decreasing activity or extending reaction time after
recycling.4a,15
Chemoselective oxidation of alcohols to carbonyl com-
pounds is an important reaction in organic synthesis
and many methods for this transformation have been
documented in the literature in view of its importance.1
Recently the use of metal-free catalysts for selective
oxidation of organic compounds is attracting more and
more attention because these metal-free catalysts are
beneficial from both economic and environmental view-
points. Moreover, they are readily able to tether to a support
covalently and obviate the problem of metal leaching.2 In
the area of metal-free catalytic alcohol oxidations stable free
nitroxyl radicals, such as 2,2,6,6-tetramethylpiperidine-1-
oxyl (TEMPO), play an increasingly important role in
organic synthesis.3 Usually, efficient methods for the
transformation of alcohols to carbonyl compounds or
carboxylic acids under mild conditions include the use of
1 mol% of TEMPO as a catalyst and a stoichiometric
amount of a terminal oxidant. Many different terminal
oxidants have been developed in this reaction including
sodium hypochlorite,4 [bis(acetoxy)iodo]benzene,5
m-CPBA,6 sodium bromite,7 trichloroisocyanuric acid,8
oxone,9 iodine10 and oxygen in combination with CuCl11
or NaNO2.12 Although these oxidants are successful for
efficient alcohol oxidation, separation of the TEMPO from
products needs tedious workup procedures. To simplify the
product isolation and catalyst recovery the use of polymer-
supported catalysts seems alternative. Various polymer-
supported TEMPO or its derivatives have been synthesized
In the last decade ionic liquids have attracted considerable
attention as an alternative reaction medium, which
represents interesting properties such as high thermal
stability, negligible vapor pressure, high loading capacity
and easy recyclability. Various chemical reactions can be
performed in ionic liquids.16 One of the attractive features
of ionic liquids in organic synthesis is that the structures
with the cationic or anionic components can be modified
according to requirement, so that they can be adapted to
special applications. Recently, increasing attention has been
focused on the use of ionic liquids as a means of
immobilizing catalysts, facilitating products separation
and providing an alternative to recycle the catalysts, and
several publications that present their potential in catalysis
have been demonstrated.17 More recently, a TEMPO-
derived task-specific ionic liquid for oxidation of alcohols
by the Anelli protocol has been described.18 In this paper, we
wish to report three different types of ion-supported TEMPO
catalysts for the oxidation of alcohols by an ion-supported
hypervalent iodine reagent 1-(4-diacetoxyiodobenzyl)-3-
methyl imidazolium tetrafluoroborate19 [dibmin]C[BF4]K in
water and examine their catalytic activity in different cases.
2. Results and discussion
Keywords: Alcohols; Oxidation; Ion-supported TEMPO; Catalysis;
Hypervalent iodine reagent.
The route for the synthesis of ion-supported TEMPO
catalysts was depicted in Scheme 1. Starting from the
commercially available 4-hydroxyl-TEMPO (1), reaction
*
Corresponding author.
e-mail: wlbao@css.zju.edu.cn
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doi:10.1016/j.tet.2005.10.022

W. Qian et al. / Tetrahedron 62 (2006) 556–562
557
Scheme 1. Synthesis of ion-supported catalysts 4, 6, and 7. Reaction conditions: (i) 1.0 equiv NaH, 1.5 equiv 1,4-dibromobutane, acetone, rt, 25%; (ii)
1.1 equiv 1-methylimidazole, CH3CN, 60 8C, 97%; (iii) 1.5 equiv NaBF4, acetone, refluxing, 86%; (iv) 1.1 equiv 2-chloroacetyl chloride, 1.1 equiv pyridine,
CH2Cl2, 5 8C to rt, 80%; (v) 1.1 equiv 1-methylimidazole, CH3CN, 60 8C, 98%; (vi) 1.5 equiv NaBF4, acetone, refluxing, 85%; (vii) 1.1 equiv imidazole,
1.1 equiv K2CO3, acetone, rt; (viii) 1.1 equiv NaBF4, 82%.
with 1,4-dibromobutane (2) as a linker in acetone afforded
4-(2,2,6,6-tetramethyl-1-oxyl-4-piperidoxyl)butyl bromide
(3) in 25% yield.20 Quaternization of 1-methylimidazole
with 3 and subsequent anion exchange with NaBF4 gave the
desired ion-supported TEMPO catalyst (4) in 97 and 86%
yields, respectively. To raise the yield in the first step,
catalyst (6) was synthesized with chloroacetyl chloride (5)
as a linker instead of 1,4-dibromobutane 2 and the yield
reached to 80%. The rest steps were analogous to the
catalyst 4. As to symmetrical catalyst (7), we wanted to
make imidazolium cation have higher loading capacity,
reaction of imidazole with 2 equiv bromide 3 in the
presence of K2CO3 and subsequent metathesis with
NaBF4 in one pot afforded the ion-supported diradical 7 in
good yield, which was purified by silica gel chromato-
graphy. These ion-supported catalysts are insoluble in low
polar organic solvents such as ethers or hexanes but are
soluble in CH2Cl2 and highly soluble in water and ionic
liquids. They are ideal candidates for aqueous homogeneous
catalysis.
After three ion-supported TEMPO catalysts were obtained,
the catalyst 4 was chosen as a candidate to investigate its
catalytic activity in combination with various terminal
oxidants in water.21 Table 1 listed the results. The
ion-supported TEMPO catalyst 4 proved to be an effective
one for the selective oxidation of 4-methoxylbenzyl
alcohol except for oxidant peracetic acid, giving 4-
methoxylbenzyl aldehyde in good to excellent yields and
short reaction times under mild conditions (a 1:1.2 ratio of
alcohol/oxidant). It showed similar catalytic activity to that
of free TEMPO (Table 1, entry 6). Using PhI(OAc)2 as a
terminal oxidant, the reaction did not work well because of
poor solubility of PhI(OAc)2 in water. Both I2 and NaOCl
showed effective oxidants. The reaction proceeded fast and
gave excellent yields. However, in the case of I2, a slight
Table 1. Oxidation of 4-methoxybenzyl alcohol catalyzed by an ion-supported TEMPO 4 in water
Entry
Oxidant
Time (min)
Yield (%)a
1
2
3
4
5
6
CH3CO3H
PhI(OAc)2
I2
NaOCl
[dibmim]C[BF4]K
[dibmim]C[BF4]K
600
120
40
3
6
6
25
70
98
96
98
97b
a Isolated yields after chromatographic purification unless otherwise noted.
b Free TEMPO was used as a catalyst.

558
W. Qian et al. / Tetrahedron 62 (2006) 556–562
excess of I2 would contaminate the products, and in the
TEMPO-bleach protocol introduced by Anelli et al.
CH2Cl2 usually was used as a biphasic system4c and
chlorinated byproducts could be formed.9 After screening
several terminal oxidants listed in Table 1, we found
[dibmin]C[BF4]K to be suitable for the reaction conducted
in water, which based on the following reasons: (a) readily
dissolving in water due to its ion-type structure; (b) acting
as a role of phase transfer catalyst (PTC) to some extent to
facilitate substrate dissolving in water; (c) most part of the
oxidant, which was reduced easily precipitated out from
water and recovered by filtration after the products
extracted by Et2O (the oxidant can be reoxidized by
peracetic acid). The ion-supported TEMPO catalyst 4
remained in filtrate, which could be reused for next run
after reloading the substrates and the oxidant
[dibmin]C[BF4]K.
primary alcohols (Table 2, entries 1–4 and 6) gave excellent
yields of the corresponding aldehydes in very short reaction
times (6–40 min) without any noticeable overoxidation to
the carboxylic acids. This methodology is mild and
compatible with several functional groups other than the
hydroxyl group. For example, the ester linkage of ethyl
4-(hydroxymethyl)benzoate (Table 2, entry 6) remained
intact. Cinnamyl alcohol (Table 2, entry 5) was oxidized to
the corresponding aldehyde in 97% yield and no double-
bond addition product was found. For the oxidation of
benzylic secondary alcohols (Table 2, entries 12–15), the
reaction afforded excellent yields but required 15–120 min
for completion. The oxidation was relatively slow for the
aliphatic primary and secondary alcohols (Table 2, entries
7–11), but the good yields could be obtained by extending
reaction times. Notably, from the results, as expected,
obtained in experiment, the catalytic activity for the catalyst
4 is the same as that for catalyst 6 (Table 2, entries 2, 5 and
13). The symmetric catalyst 7 gives the same yields as
catalyst 4 or 6 in almost half reaction times and exhibits
catalytic activities two times greater than catalyst 4 or 6
alone under similar conditions (Table 2, entries 5, 7–9 and
11), which implies this ion-supported catalyst with higher
loading capacity would be more economic and potential in
organic synthesis.
Next, we examined the oxidation of a variety of primary
and secondary alcohols in the presence of 5 mol% of
ion-supported TEMPO (4, 6 or 7) catalysts employing
1.2 mol equiv of [dibmin]C[BF4]K as a terminal oxidant.
Under these conditions, of all most alcohols were
quantitatively oxidized to carbonyl compounds within
330 min in good to excellent yields (Table 2). Benzylic
Table 2. Oxidation of alcohols catalyzed by ion-supported TEMPO catalysts (4, 6 or 7) using [dibmim]C[BF4]K as terminal oxidant in water
Entry
Substrate
Product
Catalyst
Time (min)
6
Yield (%)a
97b
1
2
4
4
6
6
6
98
98
3
4
4
15
10
97
4
5
97b
4
6
7
60
60
20
98
97
98
6
7
4
40
90
4
7
240
90
86
85
8
9
4
7
4
7
240
120
330
180
95b
93
85b
88
10
11
4
300
86
4
7
300
120
80
78
12
13
4
120
90b
4
6
30
30
99
98
14
15
4
4
30
15
98
99
a Isolated yields after chromatographic purification unless otherwise noted.
b Yields were determined by GC.

W. Qian et al. / Tetrahedron 62 (2006) 556–562
559
To examine whether the catalytic activity of ion-supported
TEMPO 6 decreases in recycling we compared it with
the catalyst 4 under the same conditions described above
using 4-methoxybenzyl alcohol as a substrate. The results
are listed in Table 3. It was found that almost constant yields
were obtained in five subsequent runs for both catalysts. No
induction period was observed upon recycling of catalysts 4
and 6.4a It suggested that the ester linkage of catalyst 6
probably was stable in reaction processes.
pressure and water (30 mL) was added to dissolve the solid.
The aqueous layer was then extracted with methylene
chloride (15 mL!3). The combined organic extracts were
dried over Na2SO4 and concentrated under vacuum to a
small volume. The resulting concentrated solution was
separated by flash chromatography (10:1, petroleum/ethyl
1
acetate) to obtain red oil 1.15 g (25%); H NMR (CDCl3,
3
ppm): dZ1.17 (s, 6H), 1.23 (s, 6H), 1.47 (t, J(H,H)Z
11.6 Hz, 2H), 1.68–1.73 (m, 2H), 1.90–1.96 (m, 4H),
3.42–3.47 (m, 4H), 3.50–3.57 (m, 1H); 13C NMR (CDCl3,
ppm): dZ20.8, 28.6, 29.7, 31.7, 33.8, 44.4, 59.7, 67.0, 70.4;
IR (KBr): nZ2973, 2937, 1459, 1376, 1363, 1245, 1177,
1104 cmK1; MS (ESI): m/z (%): 306 (23.0) [MC], 308
(21.6) [MCC2], 135 (93.2) [C4H8BrC], 137 (92.1)
[C4H8BrCC2], 55 (100.0) [C4HC7 ]. Anal. Calcd for
C13H25BrNO2: C 50.82, H 8.20, N 4.56. Found: C 50.82,
H 8.25, N 4.19.
Table 3. Recyclability of ion-supported TEMPO catalysts 4 and 6 in the
oxidation of 4-methoxylbenzyl alcohol
Catalyst
Cycle (yield %)a
1
2
3
4
5
4
6
98
98
97
96
96
98
98
97
97
94
a Reaction time 7 min.
4.2.2. 1-Methyl-3-(4-(2,2,6,6-tetramethyl-1-oxyl-4-piper-
idoxyl)butyl)imidazolium bromide. Under stirring,
0.922 g (3 mmol) of 4-(2,2,6,6-tetramethyl-1-oxyl-4-piper-
idoxyl)butyl bromide was slowly added to a solution of
0.295 g (3.6 mmol) of 1-methylimidazole in 1 mL of
acetonitrile. The mixture was stirred for 6 h at 60 8C.
After cooling to room temperature, 5 mL ether was added to
the mixture causing precipitation of 1-methyl-3-(4-(2,2,6,
6-tetramethyl-1-oxyl-4-piperidoxyl)butyl)imidazolium
bromide as a red solid. This solid was recovered by filtration
and washed with ether twice. The yield was 1.13 g (97%).
Mp: 71–73 8C; 1H NMR (DMSO-d6, ppm): dZ1.03 (s, 6H),
1.07 (s, 6H), 1.22–1.24 (m, 2H), 1.42–1.47 (m, 2H),
1.78–1.82 (m, 4H), 3.40 (t, 3J(H,H)Z6.4 Hz, 2H),
3. Conclusion
In conclusion, we have successfully developed three ion-
supported TEMPO catalysts and examined their catalytic
activities. These low molecular weight catalysts displayed
the same selectivities and activities as those of free TEMPO.
The symmetric catalyst 7 noticeably increased the rate of
oxidation of alcohols. Their combination with an ion-
supported oxidant [dibmin]C[BF4]K afforded an easy
workup and environmentally benign catalyst system for
mild and selective oxidation of primary and secondary
alcohols to carbonyl compounds. Both catalysts and oxidant
could be recovered and recycled, and almost no waste was
produced.
3
3.49–3.54 (m, 1H), 3.86 (s, 3H), 4.19 (t, J(H,H)Z7.2 Hz,
2H), 7.74 (s, 1H), 7.80 (s, 1H), 9.19 (s, 1H); 13C NMR
(DMSO-d6, ppm): dZ20.9, 26.6, 27.1, 32.8, 36.2, 45.0,
49.0, 58.3, 66.8, 70.4, 122.6, 124.0, 136.9; IR (KBr):
nZ3087, 2974, 2938, 1632, 1572, 1463, 1363, 1171,
1097 cmK1; MS (ESI): m/z (%): 309 (8.5) [MCKBrK],
124 (100.0) [C9H1C6], 123 (66.4) [C7H1C5], 81 (59.8)
[C4H5NC2 ], 55 (65.8) [C3H5NC], 42 (53.6) [C2H4NC].
Anal. Calcd for C17H31BrN3O2: C 52.44, H 8.03, N 10.79.
Found: C 52.09, H 8.09, N 10.98.
4. Experimental
4.1. General
1H and 13C NMR spectra were determined in CDCl3 or
DMSO-d6 on a Bruker 400 MHz spectrometer with TMS as
the internal standard. IR spectra were recorded on a Bruker
Vector-22 infrared spectrometer. C, H, N were analyzed on
a Carlo Erba 1110 elemental analyzer. GC–MS analyses
were performed on a Hewlett-Packard 5973 instrument
(column: HP-5 30 m!0.25 mm!0.25 mm). All melting
points were uncorrected. The columns were handpacked
with silica gel H60 (w400). Reactions were carried out
under atmosphere.
4.2.3. 1-Methyl-3-(4-(2,2,6,6-tetramethyl-1-oxyl-4-piper-
idoxyl)butyl)imidazolium tetrafluoroborate. The
1-methyl-3-(4-(2,2,6,6-tetramethyl-1-oxyl-4-piperidoxyl)-
butyl)imidazolium bromide obtained above 1.17 g (3 mmol)
was added to a suspension of NaBF4 (0.495 g, 4.5 mmol) in
acetone (5 mL). The mixture was then stirred under the
refluxing for 72 h. The sodium bromide precipitate was
removed by filtration and the filtrate concentrated by rotary
evaporation. The yield was 1.02 g (86%), red viscous oil; 1H
NMR (DMSO-d6, ppm): dZ1.05 (s, 6H), 1.08 (s, 6H), 1.25
4.2. Synthesis of catalysts (4, 6, and 7)
The bromide, chloride, and tetrafluoroborate salts of ion-
supported TEMPO were prepared by modification of
published literature procedures.22
3
(t, J(H,H)Z10.8 Hz, 2H), 1.43–1.47 (m, 2H), 1.81–1.87
(m, 4H), 3.41 (t, 3J(H,H)Z6.4 Hz, 2H), 3.50–3.55 (m, 1H),
3
4.2.1. 4-(2,2,6,6-Tetramethyl-1-oxyl-4-piperidoxyl)butyl
bromide. To a solution of 4-hydroxy-TEMPO (2.58 g,
0.015 mol) in anhydrous acetone (25 mL) was added NaH
(0.6 g, 0.015 mol) and the resulting slurry stirred for 10 min
at room temperature. 1,4-Dibromobutane (4.86 g,
0.0225 mol) was then added and stirred for 3 h at room
temperature. The acetone was removed under reduced
3.85 (s, 3H), 4.18 (t, J(H,H)Z7.2 Hz, 2H), 7.68 (s, 1H),
7.74 (s, 1H), 9.06 (s, 1H); 13C NMR (DMSO-d6, ppm):
dZ20.8, 26.6, 27.1, 32.7, 36.1, 44.9, 49.1, 58.5, 66.9, 70.3,
122.6, 124.0, 136.9; IR (KBr): nZ3159, 2937, 2938, 1575,
1465, 1364, 1170, 1060 cmK1; MS (ESI): m/z (%): 309 (1.0)
[MCKBFK4 ], 137 (78.2) [C8H13NC2 ], 83 (100.0)
[C4H7NC2 ], 55 (70.2) [C3H5NC], 42 (99.0) [C2H4NC].

560
W. Qian et al. / Tetrahedron 62 (2006) 556–562
Anal. Calcd for C17H31BF4N3O2: C 51.53, H 7.89, N 10.60.
Found: C 51.15, H 7.96, N 10.62.
6H), 1.24 (s, 6H), 1.53 (t, 3J(H,H)Z11.2 Hz, 2H), 1.90–1.94
(m, 2H), 3.90 (s, 3H), 5.02–5.08 (m, 1H), 5.21 (s, 2H), 7.71
(s, 2H), 9.05 (s, 1H); 13C NMR (DMSO-d6, ppm): dZ20.7,
32.3, 36.3, 43.6, 49.9, 58.6, 69.3, 1237, 124.1, 138.1, 166.8;
IR (KBr): nZ2978, 2940, 1753, 1580, 1467, 1225, 1179,
1061 cmK1; MS (ESI): m/z (%): 98 (68.2) [C5H8NOC], 82
(46.2) [C4H6N2C], 55 (94.3) [C4H7C], 41 (100.0) [C2H3NC].
Anal. Calcd for C15H25BF4N3O3: C 47.14, H 6.59, N 10.99.
Found: C 46.86, H 6.76, N 10.63.
4.2.4. 1,3-Bis(4-(2,2,6,6-tetramethyl-1-oxyl-4-piper-
idoxyl)butyl)imidazolium tetrafluoroborate. To a suspen-
sion of 0.245 g (3.6 mmol) of imidazole and 0.7 g potassium
carbonate in acetone (10 mL) was added 1.84 g (6 mmol) of
4-(2,2,6,6-tetramethyl-1-oxyl-4-piperidoxyl)butyl bromide,
and the mixture was stirred under the refluxing for 48 h. And
then 0.396 g (3.6 mmol) NaBF4 was added to the mixture to
continue stirring for 72 h. The sodium bromide precipitate
was removed by filtration and the filtrate concentrated by
rotary evaporation. The yield was 1.50 g (82%), red viscous
4.3. General procedure for alcohol oxidations
[dibmim]C[BF4]K (353 mg, 0.6 mmol) was added to a
solution of alcohol (0.5 mmol) in 1.5 g of water containing
5% mmol of ion-supported TEMPO. The reaction mixture
was stirred at 30 8C for a given time. The mixture was
extracted with ether (3!8 mL) and concentrated under
reduced pressure. The filtrate could be reused for next run
after the oxidant in reduced form was removed by filtration.
The product was purified by flash column chromatography
using petroleum ether and Et2O as eluent. All products were
commercially available and identified by comparison of the
isolated products with authentic samples.
1
oil; H NMR (DMSO-d6, ppm): dZ1.04 (s, 12H), 1.07 (s,
12H), 1.22–1.26 (m, 4H), 1.37–1.42 (m, 4H), 1.70–1.76 (m,
4H), 1.82–1.86 (m, 4H), 3.37 (t, 3J(H,H)Z6.4 Hz, 4H),
3
3.48–3.52 (m, 2H), 3.96 (t, J(H,H)Z7.2 Hz, 4H), 7.61 (s,
2H), 8.96 (s, 1H); 13C NMR (DMSO-d6, ppm): dZ20.9,
27.0, 28.1, 30.0, 32.5, 32.8, 45.0, 46.2, 56.2, 58.3, 67.0,
68.9, 70.3, 119.6, 129.1, 137.6; IR (KBr): nZ2973, 2935,
2871, 1510, 1464, 1363, 1147, 1108 cmK1; MS (ESI): m/z
(%): 141 (43.2) [C9H19NC], 124 (100.0) [C9H1C6]. Anal.
Calcd for C29H53BF4N4O4: C 57.24, H 8.78, N 9.21. Found:
C 56.95, H 8.96, N 9.52.
1
4.3.1. Benzaldehyde. Oil; H NMR (CDCl3, ppm): dZ
4.2.5. 2,2,6,6-Tetramethyl-1-oxyl-4-piperidinyl 2-chloro-
acetate. To a solution of 4.3 g (0.025 mol) 4-hydroxy-
TEMPO and 3.11 g (0.0275 mol) 2-chloroacetyl chloride in
dichloromethane (30 mL) was slowly added 2.18 g
(0.0275 mol) of pyridine under cooling, and the mixture
was standing over night. The precipitate was removed by
filtration and the filtrate was washed with water (30 mL),
10% NaHCO3, then 2 mol dilute HCl and finally water
(30 mL). The solution was dried over Na2SO4 and
concentrated under vacuum to give red solid 4.98 g
7.52–7.56 (m, 2H; Ar-H), 7.62–7.65 (m, 1H; Ar-H),
7.88–7.90 (m, 2H; Ar-H), 10.03 (s, 1H; CHO); IR (neat):
nZ1703 cmK1 (C]O); MS (70 eV): m/z (%): 106 (100)
[MC], 105 (94) [MCKH], 77 (92) [C6HC5 ].
4.3.2. 4-Methoxybenzaldehyde. Oil; 1H NMR (CDCl3,
ppm): dZ3.90 (s, 3H; CH3), 7.01 (d, 3J(H,H)Z7.6 Hz, 2H;
3
Ar-H), 7.85 (d, J(H,H)Z7.6 Hz, 2H; Ar-H), 9.89 (s, 1H;
CHO); IR (neat): nZ1685 cmK1 (C]O); MS (70 eV): m/z
(%): 136 (76) [MC], 135 (100) [MCKH].
1
(80%). Mp: 49–51 8C; H NMR (CDCl3, ppm): dZ1.22
(s, 6H), 1.25 (s, 6H), 1.68 (t, 3J(H,H)Z11.6 Hz, 2H),
1.94–1.98 (m, 2H), 4.02 (s, 2H), 5.11–5.16 (m, 1H); 13C
NMR (CDCl3, ppm): dZ20.4, 31.8, 41.0, 43.5, 59.2, 69.1,
166.8; IR (KBr): nZ2978, 2954, 1753, 1464, 1319, 1177,
1136 cmK1; MS (ESI): m/z (%): 248 (14.5) [MC], 250 (5.2)
[MCC2], 124 (53.9) [C9H1C6], 109 (100), 41 (82.3). Anal.
Calcd for C11H19ClNO3: C 53.12, H 7.70, N 5.63. Found: C
52.99, H 7.73, N 5.54.
4.3.3. 4-Chlorobenzaldehyde. Mp: 46–47 8C; 1H NMR
3
(CDCl3, ppm): dZ7.53 (d, J(H,H)Z8.4 Hz, 2H; Ar-H),
7.83 (d, 3J(H,H)Z8.4 Hz, 2H; Ar-H), 9.99 (s, 1H; CHO); IR
(KBr): nZ1702 cmK1 (C]O); MS (70 eV): m/z (%): 139
(100) [MC], 141 (33) [MCC2].
4.3.4. Furaldehyde. Oil; 1H NMR (CDCl3, ppm): dZ
6.61–6.63 (m, 1H), 7.27–7.30 (m, 1H), 7.70–7.71 (m, 1H),
9.67 (s, 1H; CHO); IR (neat): nZ1675 cmK1 (C]O); MS
(70 eV): m/z (%): 96 (100) [MC], 95 (94) [MCKH], 39 (58)
[C3HC3 ].
4.2.6. 1-Methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxyl-4-
piperidoxyl)ethyl)imidazolium chloride. (This procedure
is similar to the preparation of bromide above). Mp:
1
225–227 8C; H NMR (DMSO-d6, ppm): dZ1.08 (s, 6H),
4.3.5. Cinnamaldehyde. Oil; 1H NMR (CDCl3, ppm): dZ
1.11 (s, 6H), 1.51 (t, 3J(H,H)Z11.6 Hz, 2H), 1.88–1.94 (m,
2H), 3.92 (s, 3H), 5.02–5.07 (m, 1H), 5.28 (s, 2H), 7.77 (s,
2H), 9.22 (s, 1H); 13C NMR (DMSO-d6, ppm): dZ20.7,
32.5, 36.3, 43.8, 49.9, 58.4, 69.3, 123.7, 124.1, 138.1, 166.9;
3
6.73 (dd, J(H,H)Z8.0, 15.6 Hz, 1H; CH), 7.44–7.45 (m,
3H; Ar-H), 7.49 (d, 3J(H,H)Z15.6 Hz, 1H; CH), 7.56–7.58
(m, 2H; Ar-H), 9.71 (d, 3J(H,H)Z8.0 Hz, 1H; CH); IR
(neat): nZ1679 cmK1 (C]O); MS (70 eV): m/z (%): 132
(73) [MC], 131 (100) [MCKH], 103 (56) [C8HC7 ].
IR (KBr): nZ2977, 1747, 1633, 1464, 1223, 1177 cmK1
;
MS (ESI): m/z (%): 124 (34.3) [C6H8N2OC], 82 (100.0)
[C4H6NC2 ], 56 (85.1) [C2H4N2C], 55 (91.2) [C4HC7 ], 42
(84.2) [C2H4NC]. Anal. Calcd for C15H25ClN3O3: C 54.46,
H 7.62, N 12.70. Found: C 54.44, H 7.75, N 12.61.
4.3.6. Ethyl 4-formylbenzoate. Mp: 156–158 8C; 1H NMR
(CDCl3, ppm): dZ1.43 (t, 3J(H,H)Z6.4 Hz, 3H; CH3), 4.42
3
3
(q, J(H,H)Z6.4 Hz, 2H; CH2), 7.96 (d, J(H,H)Z8.4 Hz,
3
4.2.7. 1-Methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxyl-4-
piperidoxyl)ethyl)imidazolium tetrafluoroborate. (This
procedure is similar to the preparation of tetrafluoroborate
2H; Ar-H), 8.21 (d, J(H,H)Z8.4 Hz, 2H; Ar-H), 10.11 (s,
1H; CHO); IR (KBr): nZ3058, 2981, 2924, 1711, 1274,
1102, 733 cmK1; MS (70 eV): m/z (%): 178 (3.3) [MC], 149
(100) [C9H9OC2 ].
1
above). Red oil; H NMR (DMSO-d6, ppm): dZ1.15 (s,

W. Qian et al. / Tetrahedron 62 (2006) 556–562
561
4.3.7. 3-Phenylpropanal. Oil; 1H NMR (CDCl3, ppm): dZ
Acknowledgements
2.77 (t, 3J(H,H)Z7.2 Hz, 2H; CH2), 2.95 (t, 3J(H,H)Z
7.2 Hz, 2H; CH2), 7.18–7.22 (m, 3H; Ar-H), 7.27–7.31
(m, 2H; Ar-H), 9.80 (s, 1H; CHO); IR (film): nZ3029,
2928, 2826, 1726, 1497, 1454, 747, 701 cmK1; MS (70 eV):
m/z (%): 134 (58.0) [MC], 92 (75.3) [C7H8C], 91 (100.0)
[C7HC7 ].
This work was financially supported by the Natural Science
Foundation of China (No. 20225309).
1
References and notes
4.3.8. Hexanal. Oil; H NMR (CDCl3, ppm): dZ0.93 (t,
3J(H,H)Z7.2 Hz, 3H; CH3), 1.27–1.36 (m, 4H; CH2),
1.51–1.58 (m, 2H; CH2), 2.42 (t, 3J(H,H)Z7.2 Hz, 2H;
CH2), 9.77 (s, 1H; CHO); IR (film): nZ2960, 2932, 1718,
1460 cmK1; MS (70 eV): m/z (%): 56 (82.1) [C4HC8 ], 44
(100.0) [C2H4OC].
1. (a) Choudhary, V. R.; Chaudhari, P. A.; Narkhede, V. S. Catal.
Commun. 2003, 4, 171–175. (b) Smith, M. B.; March, J.
March’s Advanced Organic Chemistry: Reaction, Mechanism,
and Structure, 5th ed.; Wiley-Interscience: New York, 2001.
(c) Larock, R. C. Comprehensive Organic Transformations,
2nd ed.; Wiley-VCH: New York, 1999. (d) Muzart, J. Chem.
Rev. 1992, 92, 113–140.
1
4.3.9. Hexan-2-one. Oil; H NMR (CDCl3, ppm): dZ0.91
(t, J(H,H)Z7.2 Hz, 3H; CH3), 1.27–1.36 (m, 2H; CH2),
1.52–1.60 (m, 2H; CH2), 2.14 (s, 3H; CH3), 2.43 (t,
3J(H,H)Z7.2 Hz, 2H; CH2); IR (film): nZ2962, 2936,
1718, 1360, 1169 cmK1; MS (70 eV): m/z (%): 100 (7.8)
[MC], 58 (49.1) [C4H1C0], 43 (100.0) [C2H3OC].
3
2. Adam, W.; Saha-Moller, C. R.; Ganeshpure, P. A. Chem. Rev.
2001, 101, 3499.
3. De Nooy, A. E. J.; Besemer, A. C.; Van Bekkum, H. Synthesis
1996, 1153–1175.
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Quici, S.; Benaglia, M.; Dell’Anna, G. Org. Lett. 2004, 6,
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1
4.3.10. 4-Hydroxycyclohexanone. Oil; H NMR (CDCl3,
ppm): dZ1.95–2.01 (m, 2H), 2.03–2.08 (m, 2H), 2.28–2.37
(m, 2H), 2.58–2.65 (m, 2H), 3.80 (s, 1H), 4.19–4.23 (m,
1H); IR (KBr): nZ3386 (OH), 1707 cmK1 (C]O); MS
(70 eV): m/z (%): 114 (90.0) [MC], 57 (78.4) [C3H5OC], 55
(100.0) [C3H3OC].
1
4.3.11. 4-Methylcyclohexanone. H NMR (CDCl3, ppm):
dZ1.02 (d, 3J(H,H)Z6.8 Hz, 3H; CH3), 1.37–1.48 (m, 2H),
1.86–1.94 (m, 1H; CH), 1.98–2.02 (m, 2H), 2.34–2.38 (m,
4H); IR (neat): nZ1714 cmK1 (C]O); MS (70 eV): m/z
(%): 112 (43) [MC], 55 (100) [C3H3OC].
7. Inokuchi, T.; Matsumoto, S.; Nishiyama, T.; Torii, S. J. Org.
Chem. 1990, 55, 462–466.
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775,684, 1997; U.S. Patent 5,821,374, 1998. (b) De Luca, L.;
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4.3.12. Acetophenone. 1H NMR (CDCl3, ppm): dZ2.59 (s,
3H; CH3), 7.43–7.47 (m, 2H; Ar-H), 7.54–7.57 (m, 1H; Ar-
3
H), 7.95 (d, J(H,H)Z8.8 Hz, 2H; Ar-H); IR (neat): nZ
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1173–1175.
1686 cmK1 (C]O); MS m/z 120 (MC). MS (70 eV): m/z
(%): 120 (25) [MC], 105 (100) [C7H5OC], 77 (73) [C6HC5 ].
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1
4.3.13. 4-Methoxyacetophenone. Mp: 37–398C; H NMR
(CDCl3, ppm): dZ2.56 (s, 3H; CH3), 3.87 (s, 3H; CH3),
3
3
6.94 (d, J(H,H)Z8.4 Hz, 2H; Ar-H), 7.94 (d, J(H,H)Z
8.4 Hz, 2H; Ar-H); IR (KBr): nZ1677 cmK1 (C]O); MS
m/z 150 (MC). MS (70 eV): m/z (%): 150 (29) [MC], 135
(100) [C8H7OC2 ].
13. (a) Fey, T.; Fischer, H.; Bachmann, S.; Albert, K.; Bolm, C.
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4.3.14. 4-Bromoacetophone. Mp: 50–518C; 1H NMR
3
(CDCl3, ppm): dZ2.59 (s, 3H), 7.61 (d, J(H,H)Z8.4 Hz,
2H; Ar-H), 7.82 (d, 3J(H,H)Z8.4 Hz, 2H; Ar-H); IR (KBr):
nZ1676 cmK1 (C]O); MS m/z 198 (MC), 200 (MC2).
MS (70 eV): m/z (%): 198 (29) [MC], 200 (27) [MCC2],
183 (99) [C7H4OBrC], 185 (100) [C7H4OBrC].
14. (a) Pozzi, G.; Cavazzini, M.; Quici, S.; Benaglia, M.;
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134 8C; 1H NMR (CDCl3, ppm): dZ4.56 (d, 3J(H,H)Z
6.0 Hz, 1H; OH), 5.96 (d, 3J(H,H)Z6.0 Hz, 1H; CH),
7.27–7.34 (m, 5H; Ar-H), 7.38–7.42 (m, 2H; Ar-H),
7.50–7.54 (m, 1H; Ar-H), 7.91–7.93 (m, 2H; Ar-H); IR
(KBr): nZ3417 (OH), 1680 cmK1 (C]O); MS (70 eV): m/z
(%): 212 (3) [MC], 105 (100) [C7H5OC].
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