Electrooxidation of alcohols in N-oxyl-immobilized silica gel/water disperse system: Approach to totally closed system

Article abstract of DOI:10.1055/s-0028-1087987

Electrooxidation of alcohols in a disperse system with N-oxyl-immobilized silica gel as a disperse phase and an aqueous NaBr/NaHCO₃ solution as a disperse medium proceeded smoothly to give the corresponding carbonyl compounds. The N-oxyl-immobilized silica gel 1 was prepared by silane-coupling method. Recycling of both the aqueous solution and the N-oxyl-immobilized silica gel 1 was performed successfully. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-0028-1087987

PAPER
903
Electrooxidation of Alcohols in N-Oxyl-Immobilized Silica Gel/Water
Disperse System: Approach to Totally Closed System
E
M
lectrooxidation of Al
a
Department of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Tsushima-Naka 3-1-1,
Okayama, Okayama 700-8530, Japan
Fax +81(86)2518079; E-mail: tanaka95@cc.okayama-u.ac.jp
Received 25 September 2008; revised 11 November 2008
+
–
[
Br ] species (Br , OBr , etc.), which move into CH Cl
2 2 2
Abstract: Electrooxidation of alcohols in a disperse system with
N-oxyl-immobilized silica gel as a disperse phase and an aqueous
layer to oxidize N-oxyl. N-Oxyl is thus separated from the
electrodes and direct oxidation/reduction of N-oxyl would
be avoided, and as a result, this electrooxidation was per-
NaBr/NaHCO solution as a disperse medium proceeded smoothly
3
to give the corresponding carbonyl compounds. The N-oxyl-immo-
bilized silica gel 1 was prepared by silane-coupling method. Recy- formed successfully in a simple undivided cell.
cling of both the aqueous solution and the N-oxyl-immobilized
As another site-separation system, we reported a silica
silica gel 1 was performed successfully.
1
1
gel/water disperse system. Silica gel has some good fea-
tures: 1) silica gel is stable in neutral to basic aqueous so-
Key words: alcohols, oxidations, solid-phase synthesis, electron
transfer
1
2
lution, such as an aqueous NaHCO (pH ca. 9) employed
3
for the electrolysis medium, 2) silica gel has wide surface
2
area (480–540 m /g) and large pore volume (0.74–0.84
cm /g) to adsorb organic substrates and products efficient-
Oxidation of alcohols to the corresponding carbonyl com-
pounds is one of the most fundamental transformations,
3
ly in water, and 3) the surface of the silica gel can be easily
1
–4
5–7
and many inorganic and organic oxidants have been
developed. Chemical oxidation processes using these ox-
idants, however, are not environmentally benign because
they usually consume an excess amount of these oxidants
and generate a massive amount of wastes. In contrast,
electrochemical processes are one of the most promising
candidates for environmentally benign processes because
they can be performed only by passing a required electric-
ity without any chemical oxidants. Direct electrooxidation
of alcohols, however, cannot be efficiently achieved be-
cause of the high over-potential. In 1983, Semmelhack re-
ported the first N-oxyl-mediated electrooxidation of
13
modified by using silane-coupling reagents. In the silica
gel-disperse system, N-oxyl and the substrates were ad-
sorbed on the silica gel, and direct electron transfer be-
tween N-oxyl/substrates and the electrodes did not occur.
The electrooxidation can be performed in water, that is,
free from organic solvents. The products can be easily ob-
tained by filtration and rinsing of the silica gel with a
small amount of acetone after the electrolysis. During the
workup process, most of the N-oxyl was eluted off from
the silica gel, and the carbonyl products were always con-
taminated with the N-oxyl. Immobilization of N-oxyl on
the silica gel would be a simple cure for this problem: the
N-oxyl-immobilized silica gel and an aqueous disperse
medium can be easily recovered and used repeatedly;
8
alcohols. In this reaction, N-oxyl was oxidized to the cor-
responding N-oxoammonium at low potential (ca. 0.4 V
vs. Ag/AgNO ), and the N-oxoammonium oxidized alco-
3
thereby, offering a totally closed system as outlined in
hols to give the corresponding carbonyl compounds.
Since N-oxyl was regenerated in this process, a catalytic
amount of N-oxyl was enough to complete the oxidation.
14,15
Scheme 1.
Herein, we describe the totally closed sys-
tem for electrooxidation of alcohols in an aqueous dis-
perse system with an N-oxyl-immobilized silica gel 1 as a
N-Oxyl-mediated electrooxidation reactions including disperse phase.
enantioselective methods have been investigated eagerly.9
N-Oxyl-immobilized silica gel 1 was prepared as follows
To execute the electrooxidation in high current efficiency,
electroreduction of the N-oxoammonium on the cathode
should be excluded. For this purpose, a divided cell was
usually used to separate N-oxyl (and/or N-oxoammoni-
um) from the cathode. This method was, however, not
necessarily satisfactory in terms of operational simplicity.
Torii and co-workers reported electrooxidation of alco-
hols in an N-oxyl/bromide salt double mediatory system
16
(
Scheme 2). Isocyanic acid 3-(triethoxysilyl)propyl es-
ter (4) was allowed to react with 4-amino-2,2,6,6-tetra-
methylpiperidine-1-oxyl (5) in benzene (30 mL) at room
temperature for 9 hours to yield a red benzene solution of
the corresponding urea compound 6. To the solution was
added silica gel, and the resultant mixture was heated to
reflux gently for 61 hours without stirring. After filtration,
the benzene solution was colorless. The silica gel was
washed with hot benzene by using Soxhlet extractor for
eight hours to give the N-oxyl immobilized silica gel 1.
The color of the silica gel turned into pale orange. Ele-
mental analysis revealed that approximately 0.6 millimole
of N-oxyl was immobilized per gram of modified silica
gel.
1
0
using CH Cl /H O two-phase solution. In the aqueous
2
2
2
phase, bromide anion is oxidized at the anode to generate
SYNTHESIS 2009, No. 6, pp 0903–0908
x
x
.
x
x
.2
0
0
9
Advanced online publication: 02.03.2009
DOI: 10.1055/s-0028-1087987; Art ID: F20808SS
Georg Thieme Verlag Stuttgart · New York
©

9
04
M. Kuroboshi et al.
PAPER
OH
O
silica
gel
unmodified
silica gel
Si (CH2)3NHCH(O)NH
N O•
R1
R2
O
1
recycle
acetone
silica gel 1
N-oxyl-immobilized
silica gel
filtration
rinse
1
electrolysis
recycle
evaporation
O
aqueous media
filtrate
washings
wavenumber (cm–1
)
totally closed system
Figure 1 Infrared spectra of silica gel and N-oxyl-immobilized sili-
ca gel 1 (KBr)
R1
R2
Scheme 1 Electrooxidation of alcohols in water by using N-oxyl-
immobilized silica gel
hours (2.5 F/mol) at 0 °C under vigorous stirring. The
mixture was filtered, and the silica gel was rinsed for sev-
eral times with acetone. The organic washings were con-
centrated in vacuo and the residue was passed through a
short column (SiO , hexane–EtOAc, 5:1) to afford 4-chlo-
2
H2N
N
O•
5
roacetophenone (3a) in 83% yield. It is interesting to note
that neither the starting material 2a nor the product 3a was
detected in the aqueous filtrate, indicating that most of
them were adsorbed on the silica gel during the electroly-
sis and the oxidation of 2a had mainly occurred on the sil-
ica gel.
(
EtO)3Si(CH2)3NCO
benzene
r.t., 9 h
4
H
H
silica gel
(
EtO)3Si
N
N
3
benzene
reflux, 61 h
O
N
Table 1 Effects of Halide Ions on the N-Oxyl-Mediated Electro-
oxidation of Alcohols
O •
6
OH
O
washing with
O
O
1
silica
gel
H
H
benzene using
Si
N
N
2
0 wt% NaX/aq sat NaHCO3
undivided cell, (Pt)-(Pt)
3
Soxhlet extractor
8
h
O
N
0
°C, 30 mA, 2.5 F/mol
Cl
Cl
O •
1
2a
3a
Scheme 2 Preparation of N-oxyl-immobilized silica gel 1
Yield 3a (%)a
Recovered 2a (%)a
Entry
NaX
1
2
3
NaBr
NaCl
NaI
–
94
64
2
–
Infrared spectrum of the N-oxyl-immobilized silica gel 1
is shown in Figure 1. Compared with the IR spectrum of
the unmodified silica gel, new adsorption bands appeared
28
97
49
–
1
at 2979 and 2943 cm , ascribable to carbon–hydrogen
stretching vibrations of N-oxyl moiety. The stretching
band of C=O bond of the urea group also appeared at 1569
4
38
a
–1
Determined by GC analysis by using acetophenone as an internal
standard.
cm . These results show that the N-oxyl moiety was im-
mobilized on the silica gel through the urea bond.
Next, we investigated electrooxidation of alcohols in the
N-oxyl-immobilized silica gel/water disperse system. A
typical procedure is as follows (Table 1, entry 1): In a bea-
ker-type undivided cell were placed 1-(4-chlorophe-
nyl)ethyl alcohol (2a), N-oxyl-immobilized silica gel 1,
and acetone. The mixture was stirred for three minutes,
and then most of acetone was removed by evaporation un-
The presence of NaBr was indispensable for efficient
oxidation, since the yield of 3a decreased to 38% in the
absence of NaBr. In the place of NaBr, neither sodium
chloride nor sodium iodide could be efficiently used (en-
tries 2 and 3); 3a was formed only in 64% and 2%, respec-
tively.
der reduced pressure. To the residual solid was added an A plausible mechanism is shown in Scheme 3. At the an-
+
aqueous solution of saturated sodium hydrogen carbonate ode, bromide ion is oxidized to give [Br ] species. The
+
containing sodium bromide (20 wt%). Two Pt electrodes [Br ] species oxidizes N-oxyl 1¢ immobilized on silica gel
2
(
1.5 × 1.0 cm ) were immersed into the reaction mixture, to give N-oxoammonium 7, which in turn oxidizes alcohol
and a constant current (30 mA) was supplied for 2.23 2a on the silica gel to give 3a. Conproportionation of the
Synthesis 2009, No. 6, 903–908 © Thieme Stuttgart · New York

PAPER
Electrooxidation of Alcohols
905
thus generated N-hydroxylamine intermediate 8 via 7 re- Table 2 Recovery and Reuse of the N-Oxyl-Immobilized Silica Gel
a
generates 1¢. It is noteworthy that chloride salts did not 1 and the Disperse Media
promote the N-oxyl-mediated electrooxidation of alcohols
OH
O
1
efficiently (undecan-1-ol to undecanal: 10–30% yield) in
1
0
aq NaBr/NaHCO3
undivided cell
(Pt)-(Pt), 0 °C
30 mA, 2.5 F/mol
CH Cl /water two-phase system. Chloride ion would be
2
2
oxidized under the electrooxidation conditions to give
Cl
Cl
+
–
2a
3a
[
Cl ] species, such as ClO in aqueous phase. In the two-
phase system, N-oxyl is dissolved in the organic (CH Cl )
Yield 3a (%)b
Recovered 2a (%)b
2
2
Run
1
+
phase and these [Cl ] species would be hardly transferred
into the organic phase due to its solubility. In this silica
gel-disperse system, since N-oxyl is immobilized on silica
94
92
95
92
93
–
–
–
–
–
2
+
gel dispersed in the aqueous phase, [Cl ] would oxidize
the N-oxyl. Although iodide ion was oxidized to produce
3
+
iodonium species [I ] at anode, the iodonium species
4
could not oxidize N-oxyl effectively, and it might be re-
duced to the iodide ion at the cathode.
5
a
N-Oxyl-immobilized silica gel 1 and the disperse media were recov-
ered and repeatedly used.
Determined by GC analysis using acetophenone as an internal stan-
anode
b
silica gel surface
dard.
Br–
2
OH
+N
O
O
2
OH–
oxyl adsorption system (0.025 mmol), and the bromonium
species [Br ] may react with N-oxyl predominately.
R1
R2
+
7
2
a
2
e–
O
Table 3 Electrooxidation of Alcohols 2 in an Aqueous Silica Gel
–
+
OBr , [Br ]
H2O
2
N
•
Disperse System
R1
R2
1'
a
a
N
OH
3a
Entry Alcohol 2
Y
i
e
l
d
3
(
%
)
R
e
c
o
v
e
r
e
d
2
(
%
)
aqueous phase
8
OH
OH
1
2a
94
–
–
–
4
-ClC6H4
OH
Scheme 3 A plausible mechanism of electrooxidation of alcohol
using N-oxyl-immobilized silica gel in aqueous NaHCO /NaBr
3
2
3
2b 83
Ph
The N-oxyl-immobilized silica gel 1 and the disperse me-
dia (aq NaHCO /NaBr) were recovered after filtration and
2c
83
3
acetone-rinsing, and reused for the next oxidation of 2a.
The results are summarized in Table 2 (entries 2–5). The
activity of 1 remained high even after five runs, and the
ketone 3a was obtained in more than 90% yield by passing
4-MeC6H4
OH
4
5
2d 76b
2
–
4-MeOC6H4
OH
2
.5 F/mol of electricity.
2e
86
The N-oxyl-immobilized silica gel disperse electrolysis
system was successfully applied to the electrooxidation of
secondary alcohols (Table 3, entries 1–6). Oxidation of
secondary alcohols proceeded smoothly to afford the cor-
responding ketones in good to excellent yields. In the case
of alcohol having easily oxidizable aromatic ring, for ex-
ample, 1-(4-methoxyphenyl) group, bromination on the
aromatic ring occurred to afford 3-bromo-4-methoxyace-
tophenone (3d¢) as a by-product (entry 4). Compared to
the N-oxyl adsorption system and N-oxyl-immobilized
Ph
-ClC6H4
Ph
6
7
2f
79c
–
–
4
OH
OH
44d
2g
a
b
c
d
Isolated yields.
-(3-Bromo-4-methoxyphenyl)-1-ethanone (3d¢, 9%).
4-Chlorobenzoic acid (9f, 2%).
1
3-Phenylpropanoic acid (9g, 17%).
1
7
polymer system, selectivity of formation of 3d was im-
proved [3d/3d¢ = 76:9 (entry 4); adsorption system: 3d/
Under similar conditions, N-oxyl-immobilized silica gel
disperse electrolysis system was applied to the electro-
oxidation of primary alcohols. Oxidation of 4-chlorobenzyl
alcohol (2f) proceeded smoothly to afford 4-chloro-
benzaldehyde (3f) in 79% yield and over-oxidized product,
-chlorobenzoic acid (9f), was barely formed (2%, entry
). 3-Phenylpropanol (2g) gave 3-phenylpropanal (3g,
4%) and 3-phenylpropanoic acid (9g, 17%) (entry 7).
3
d¢ = 42:11; N-oxyl-immobilized polymer: 3d/3d¢/(3-
bromo-4-methoxy)phenyl-1-ethanol/4-bromoanisole =
2:19:12:19]. These results can be explained by assuming
that the amount of N-oxyl-immobilized on the silica gel
0.3 mmol/500 mg) was much more than that in the N-
2
4
6
4
(
Synthesis 2009, No. 6, 903–908 © Thieme Stuttgart · New York

9
06
M. Kuroboshi et al.
PAPER
The electrooxidation of 1,4- and 1,5-diols 10 afforded the (i) N-Oxyl-immobilized silica gel 1 can be easily prepared
corresponding g- and d-lactones 11 in moderate to good by using silane-coupling method using isocyanic acid
yields by passing 4.5 F/mol of electricity (Table 4).
3-(triethoxysilyl)propyl ester.
(
ii) Electrolysis can be performed in a simple undivided
Table 4 Electrooxidation of Diols 10 in Water Using N-Oxyl-
Immobilized Silica Gel 1
a
cell under constant current conditions (self-controlled po-
tential) without use of any organic solvents.
Entry
1
Diol 10
Product 11
Yield 11 Recovered 10
(
iii) Workup process is exceptionally simple; just filtra-
tion, rinsing with acetone, and evaporation.
iv) High current efficiency and good to excellent yields
b
(%)b
(
%)
O
(
OH
OH
88
46
–
of products can be achieved because of high load of N-oxyl
on the silica gel.
O
1
1
0a
0b
1
1
1a
1b
(v) Recycling of aqueous solution (disperse media) and
N-oxyl-immobilized silica gel 1 (disperse phase) was per-
formed successfully.
O
OH
OH
2
3
11
–
O
1H NMR spectra were recorded on a Varian Gemini-200 (200 MHz)
instrument and VXR-600 (600 MHz) instrument. IR spectra were
recorded on a Jasco FT/IR-4100 spectrometer. Unless otherwise
noted, materials were obtained from commercial suppliers and re-
agent grade materials were used without further purification.
OH
OH
O
O
48
59
1
1
0c
OH
11c
O
N-Oxyl-Immobilized Silica Gel 1
A 100 mL two-necked flask fitted with a three-way stopcock was
evacuated to dryness and filled with argon. The flask was charged
with a solution of 3-(triethoxysilyl)propyl isocyanate (4; 2.60 g,
4
–
OH
O
1
0.5 mmol) in benzene (20 mL). To the mixture was added drop-
0d
11d
wise a solution of 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (5;
1.71 g, 10.0 mmol) in benzene (10 mL), and the resultant mixture
was stirred at r.t. for 9 h to yield a benzene solution of the corre-
sponding urea compound 6, which was used for further treatment
without purification. To the solution was added benzene (20 mL)
a
4
.5 F/mol of electricity was passed.
b
Isolated yields.
A plausible mechanism of formation of lactone 11 is as and silica gel (10.0 g), and the resultant mixture was gently heated
follows. One hydroxymethyl group of diol 10 is first oxi- to reflux for 61 h without stirring. The resulting solid was carefully
washed with hot benzene using Soxhlet extractor for 8 h. The resi-
due in the thimble was dried under reduced pressure to afford
N-oxyl-immobilized silica gel 1 (12.8 g); pale orange solid.
dized to give the corresponding hydroxyl aldehyde 12. In-
tramolecular addition of the hydroxyl group to the formyl
group gives the hemiacetal 13. The second oxidation then
occurs to give the corresponding lactone 11 (Scheme 4).
–
1
IR (KBr): 3386, 2979, 2943, 1638, 1569, 1091, 957, 798 cm .
Anal. Calcd for 0.6 mmol N-oxyl/g silica gel: C, 10.80, H, 1.80;
N, 2.52. Found: C, 11.90; H, 1.78; N, 2.60.
CH2OH
CH2OH
CHO
electrooxidation (EO)
Electrooxidation of 1-(4-Chlorophenyl)ethyl Alcohol (2a) in
Water Using the N-Oxyl-Immobilized Silica Gel; 4-Chloroace-
tophenone (3a); Typical Procedure
In a beaker-type undivided cell were placed 1-(4-chlorophenyl)eth-
yl alcohol (2a; 156 mg, 1.0 mmol), N-oxyl-immobilized silica gel 1
CH2OH
10
12
11
OH
O
C
O
C
H
O
cyclization
EO
(488 mg), and acetone (2 mL). The mixture was stirred for 3 min be-
C
H
H
C
H
fore most of the solvent was evaporated under reduced pressure. To
the residual solid was added aq sat. NaHCO containing NaBr (20
H
13
3
wt%, 6.0 mL). To this suspension were immersed two platinum
electrodes (1.5 × 1.0 cm ). The reaction mixture was electrolyzed
Scheme 4 A plausible mechanism for the formation of lactone 11
2
under a constant current (30 mA, 2.23 h, 2.5 F/mol) at 0 °C under
vigorous stirring. At the end of the electrolysis, the disperse media
turned into red brown. After completion of electrolysis, the mixture
was stirred for further 30 min, and the disperse media turned color-
less or into pale yellow. The mixture was filtered, and neither the
product 3a nor the starting material 2a was detected in the aqueous
In conclusion, electrooxidation of alcohols using N-oxyl-
immobilized silica gel in aqueous NaHCO /NaBr pro-
3
ceeded smoothly to give the corresponding carbonyl com-
pounds: secondary and primary alcohols gave the
corresponding ketones and aldehydes, respectively, and filtrate. The solids were rinsed with acetone (20 mL). The washings
1
,4- and 1,5-diols afforded the corresponding g- and d- were combined and most of the acetone was evaporated. The resi-
due was diluted with EtOAc (10 mL), dried (Na SO ), and concen-
lactones. The characteristic features of the N-oxyl-immo-
bilized silica gel disperse electrolysis system are summa-
rized as follows:
2
4
trated in vacuo. The residue was chromatographed (SiO , hexane–
EtOAc, 5:1) to afford 4-chloroacetophenone (3a); yield: 128 mg
2
Synthesis 2009, No. 6, 903–908 © Thieme Stuttgart · New York

PAPER
0.83 mmol, 83%) as a colorless liquid; R = 0.53 (hexane–EtOAc,
Electrooxidation of Alcohols
907
1
(
H NMR (200 MHz, CDCl ): d = 2.69 (t, J = 7.7 Hz, 2 H, ArCH ),
f
3
2
3
:1).
2.97 (t, J = 7.7 Hz, 2 H, CH ), 7.15–7.38 (m, 5 H, C H ), 9.00–11.0
2 6 5
–
1
(br, 1 H, CO H).
2
IR (neat): 3064, 3006, 1687, 1590, 1488, 1358, 1176, 762 cm .
1
H NMR (200 MHz, CDCl ): d = 2.59 (s, 3 H, CH ), 7.44 (d, J = 8.6
3
3
cis-8-Oxabicyclo[4.3.0]nonan-7-one (11a)
Hz, 2 H, Ar), 7.90 (d, J = 8.6 Hz, 2 H, Ar).
Colorless liquid; R = 0.50 (hexane–EtOAc, 1:1).
f
–
1
IR (neat): 3064, 3006, 1687, 1590, 1358, 1176, 762 cm .
Acetophenone (3b)
1
Colorless liquid; R = 0.47 (hexane–EtOAc, 3:1)
H NMR (200 MHz, CDCl ): d = 1.12–1.34 (m, 3 H) 1.52–1.73 (m,
f
3
3
H), 1.74–1.88 (m, 1 H), 2.03–2.18 (m, 1 H), 2.37–2.54 (m, 1 H,
IR (neat): 3063, 3005, 1687, 1599, 1583, 1450, 1360, 1181, 761
–
1
CH), 2.59–2.69 [m, 1 H, CHC(O)], 3.95 [d, J = 8.8 Hz, 1 H,
C(O)OCH ], 4.19 [dd, J = 8.8, 5.1 Hz, 1 H, C(O)OCH ].
cm .
2
2
1
H NMR (200 MHz, CDCl ): d = 2.61 (s, 3 H, CH ), 7.42–7.63 (m,
3
3
3
H, Ar), 7.96 (d, J = 8.0 Hz, 2 H, Ar).
Phthalide (11b)
Colorless solid; R = 0.50 (hexane–EtOAc, 1:1).
f
4
-Methylacetophenone (3c)
–
1
IR (KBr) 3060, 2947, 1754, 1370, 1189, 800, 764 cm .
Colorless liquid; R = 0.47 (hexane–EtOAc, 3:1).
f
1H NMR (200 MHz, CDCl
H, Ar), 7.70 (t, J = 7.3 Hz, 1 H, Ar), 7.94 (d, J = 7.3 Hz, 1 H, Ar).
): d = 5.34 (s, 2 H, CH ), 7.48–7.58 (m,
3 2
–
1
IR (neat): 2923, 1683, 1607, 1574, 1406, 1358, 1183, 712 cm .
2
1
H NMR (200 MHz, CDCl ): d = 2.41 (s, 3 H, CH ), 2.58 (s, 3 H,
3
3
COCH ), 7.25 (d, J = 8.0 Hz, 2 H, Ar), 7.86 (d, J = 8.0 Hz, 2 H, Ar).
3
d-Valerolactone (11c)
Colorless liquid; R = 0.30 (hexane–EtOAc, 1:1).
f
4
-Methoxyacetophenone (3d)
–
1
IR (neat): 2954, 2875, 1733, 1396, 1171 cm .
Colorless solid; R = 0.33 (hexane–EtOAc, 3:1).
f
1
H NMR (200 MHz, CDCl ): d = 1.65–1.95 (m, 4 H, CH CH ), 2.52
3
2
2
IR (KBr): 3318, 3081, 3001, 2965, 2844, 1669, 1607, 1575, 1508,
1
–
1
[t, J = 6.9 Hz, 2 H, CH C(O)], 4.31 [t, J = 5.6 Hz, 2 H, C(O)OCH ].
2
2
360, 1177, 806 cm .
1
H NMR (200 MHz, CDCl ): d = 2.56 (s, 3 H, CH ), 3.88 (s, 3 H,
3
3
g-Butyrolactone (11d)
Colorless liquid; R = 0.33 (hexane–EtOAc, 1:1).
OCH ), 6.94 (d, J = 8.9 Hz, 2 H, Ar), 7.95 (d, J = 8.9 Hz, 2 H, Ar).
3
f
–
1
IR (neat): 2992, 2919, 1771, 1378, 1171, 802 cm .
3
-Bromo-4-methoxyacetophenone (3d¢)
1
Colorless solid; R = 0.27 (hexane–EtOAc, 3:1)
H NMR (200 MHz, CDCl ): d = 2.16–2.36 (m, 2 H, CH ), 2.49 [t,
f
3
2
J = 7.2 Hz, 2 H, CH C(O)], 4.34 [t, J = 7.2 Hz, 2 H, C(O)OCH ].
2
2
IR (KBr): 3065, 2992, 2925, 2851, 1672, 1592, 1498, 1357, 1168,
6
–
1
59 cm .
1
H NMR (200 MHz, CDCl ): d = 2.56 (s, 3 H, CH ), 3.97 (s, 3 H, References
3
3
OCH ), 6.94 (d, J = 8.4 Hz, 1 H, Ar), 7.92 (d, J = 8.4 Hz, 1 H, Ar),
8
3
(
1) (a) Fieser, L. F.; Fieser, M. Reagents for Organic Synthesis,
Vol. 1; Wiley: New York, 1967, 142–147. (b) Fieser, L. F.;
Fieser, M. Reagents for Organic Synthesis, Vol. 1; Wiley:
New York, 1967, 1059–1064.
.17 (s, 1 H, Ar).
4
-Phenylbutan-2-one (3e)
Colorless liquid; R = 0.43 (hexane–EtOAc, 3:1).
f
(
2) (a) Corey, E. J.; Sugs, J. M. Tetrahedron Lett. 1975, 2647.
IR (neat): 3063, 3028, 2929, 1716, 1603, 1497, 1358, 1162, 750
cm .
(
(
b) Corey, E. J.; Schmidt, G. Tetrahedron Lett. 1979, 399.
c) Piancatelli, G.; Scettri, A.; D’Auria, M. Synthesis 1982,
–
1
1
H NMR (200 MHz, CDCl ): d = 2.14 (s, 3 H, CH ), 2.71–2.95 (m,
245.
(3) (a) Berkowitz, L. M.; Rylander, P. N. J. Am. Chem. Soc.
958, 80, 6682. (b) Griffith, W. P.; Ley, S. V.; Whitcombe,
3
3
4
H, CH CH ), 7.16–7.35 (m, 5 H, C H ).
2
2
6
5
1
4
-Chlorobenzaldehyde (3f)
G. P.; White, A. D. J. Chem. Soc., Chem. Commun. 1987,
1625. (c) Ley, S. V.; Norman, J.; Griffith, W. P.; Marsden,
S. P. Synthesis 1994, 639.
Colorless solid; R = 0.60 (hexane–EtOAc, 3:1).
f
–
1
IR (KBr): 3089, 2861, 1694, 1589, 1484, 1209, 1154, 700 cm .
(
4) Fieser, L. F.; Fieser, M. Reagents for Organic Synthesis,
1
H NMR (200 MHz, CDCl ): d = 7.51 (d, J = 8.4 Hz, 2 H, Ar), 7.82
d, J = 8.4 Hz, 2 H, Ar), 9.99 (s, 2 H, CHO).
Vol. 1; Wiley: New York, 1967, 942–952.
3
(
(5) (a) Dess, D. B.; Martin, J. C. J. Org. Chem. 1983, 48, 4155.
b) Dess, D. B.; Martin, J. C. J. Am. Chem. Soc. 1991, 113,
(
3
-Phenylpropanal (3g)
7277.
Colorless liquid; R = 0.53 (hexane–EtOAc, 3:1).
(6) (a) Fieser, L. F.; Fieser, M. Reagents for Organic Synthesis,
Vol. 1; Wiley: New York, 1967, 296–310. (b) Mancuso,
A. J.; Swern, D. Synthesis 1981, 165.
7) Fieser, L. F.; Fieser, M. Reagents for Organic Synthesis,
Vol. 1; Wiley: New York, 1967, 78–81.
f
IR (neat): 3086, 3063, 3029, 2928, 2826, 2726, 1725, 1604, 1496,
1
–1
180, 856 cm .
(
1
H NMR (200 MHz, CDCl ): d = 2.78 (t, J = 7.4 Hz, 2 H, ArCH ),
3
2
2
.96 (t, J = 7.4 Hz, 2 H, CH ), 7.12–7.44 (m, 5 H, C H ), 9.82 (s, 1
2
6
5
(8) Semmelhack, M. F.; Schmid, C. R. J. Am. Chem. Soc. 1983,
H, CHO).
105, 4492.
(
9) (a) Yanagisawa, Y.; Kashiwagi, Y.; Kurashima, F.; Anzai,
3
-Phenylpropanoic Acid (9g)
J.; Osa, T.; Bobbitt, J. M. Chem. Lett. 1996, 1043.
(b) Kashiwagi, Y.; Yanagisawa, Y.; Kurashima, F.; Anzai,
J.; Osa, T.; Bobbitt, J. M. Chem. Commun. 1996, 2745.
Colorless solid; R = 0.00 (hexane–EtOAc, 3:1).
f
–
1
IR (KBr): 2935, 1697, 1602,1497, 1220, 786 cm .
(
c) Kashiwagi, Y.; Kurashima, F.; Kikuchi, C.; Anzai, J.;
Osa, T.; Bobbitt, J. M. Tetrahedron Lett. 1999, 40, 6469.
d) Barhdadi, R.; Comminges, C.; Doherty, A. P.; Nedelec,
(
Synthesis 2009, No. 6, 903–908 © Thieme Stuttgart · New York

9
08
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(a) Geneste, F.; Moinet, C.; Ababou-Girard, S.; Solal, F.
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(
(
5
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(
(
(
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Synthesis 2009, No. 6, 903–908 © Thieme Stuttgart · New York