IBX/n-Bu4NBr/CH2Cl2-H2O: A new mild system for selective oxidation of secondary alcohols

Article abstract of DOI:10.1016/j.tet.2005.07.051

A new alternative system for the chemoselective oxidation of secondary hydroxyl group to ketone with IBX/n-Bu₄NBr in CH₂Cl ₂-H₂O has been developed. Under the reaction conditions, the secondary hydroxyl group was highly chemoselectively oxidized to the corresponding ketone, in moderate to good yields at rt, in the presence of primary hydroxyl group within the same molecule.

Full text of DOI:10.1016/j.tet.2005.07.051

Tetrahedron 61 (2005) 8995–9000
IBX/n-Bu4NBr/CH2Cl2–H2O: a new mild system for selective
oxidation of secondary alcohols
*
Chutima Kuhakarn, Krisada Kittigowittana, Manat Pohmakotr and Vichai Reutrakul
Department of Chemistry, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand
Received 27 May 2005; revised 4 July 2005; accepted 15 July 2005
Available online 9 August 2005
Abstract—A new alternative system for the chemoselective oxidation of secondary hydroxyl group to ketone with IBX/n-Bu4NBr in
CH2Cl2–H2O has been developed. Under the reaction conditions, the secondary hydroxyl group was highly chemoselectively oxidized to the
corresponding ketone, in moderate to good yields at rt, in the presence of primary hydroxyl group within the same molecule.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
As part of our ongoing efforts in the development of newer
applications of hypervalent iodine (V) compounds, we wish
to report a new application of 2-iodoxybenzoic acid (IBX)
with catalytic amount of tetrabutylammonium bromide
(n-Bu4NBr) for selective oxidation of secondary hydroxyl
group. Chemoselective oxidation of sulfides to sulfoxides in
the presence of an alcohol functional group using IBX/
tetraethylammonium bromide (Et4NBr) has been documen-
ted in the literature.14 To our knowledge, there is no
previous study that was directed toward selective oxidation
of secondary hydroxyl group in the presence of primary
hydroxyl within the same molecule using IBX as an
oxidizing reagent.
The oxidation of alcohols to carbonyl compounds is a
fundamental reaction in organic chemistry and several
methods covering a wide variety of reagents have been
developed for this important synthetic transformation.1
Desired experimental conditions include high yields, mild
conditions, high chemoselectivity, readily available non-
toxic reagent, and compatibility with functional groups
present in the substrates. In the synthesis of naturally
occurring compounds, one usually faces the manipulation of
compounds containing several types of hydroxyl functional
groups, and it is necessary to selectively oxidize a single
hydroxyl group (primary or secondary alcohol) within the
same molecules. Thus, selective transformation of hydroxyl
group has been a challenging target for synthetic chemists
since it offers an alternative to synthesis via selective
protection and deprotection. Many oxidizing reagents are
known to promote selective oxidation of secondary alcohols
in the presence of primary alcohols, including halogen-
based oxidants, for example, N-bromoacetamide,2 N-chloro/
bromosuccinimide,3 Cl2/pyridine,4 Br2/HMPA/NaHCO3,5
(Bu3Sn)2O/Br2,6 NOCl/CH3CO2H,7 NaBrO3/NaHSO3,8 and
Ce(SO4)2/NaBrO3.9 The other important oxidizing agents
are peroxides/metal system,10 dimethyldioxiranes,11
DMSO-based reagents,12 and Oppenauer oxidation
variations.13 Despite these readily available procedures,
development of a better selective oxidation system is still
desirable.
2. Results and discussion
To begin with, a monofunctional alcohol, benzyl alcohol,
was chosen as a substrate for investigating reaction
conditions. Thus, it was subjected to the oxidation by IBX
in the presence of a collection of phase transfer catalysts,
that is n-Bu4NBr, Et4NCl, Et4NBr, Et4NI, BnMe3NBr, and
BnEt3NCl (Table 1). It should be noted that the type of
halide anion of the catalyst has considerable effect on the
oxidation reaction (Table 1, entries 2–4). The tetraethyl-
ammonium bromide (Et4NBr) catalyzed the reaction more
effectively than the corresponding iodide and chloride,
respectively. The n-Bu4NBr gave the best conversion of
89% (Table 1, entry 1). Tetrabutylammonium bromide was
therefore, chosen as a catalyst of choice for further
investigating optimum reaction conditions (Table 2).
Keywords: Selective oxidation; IBX oxidation.
*
From the results as shown in Table 2, for the oxidation using
IBX alone in dichloromethane, moderate conversion of
Corresponding author. Tel.: C66 2 201 5155; fax: C66 2 354 7151;
e-mail: scckk@mahidol.ac.th
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.07.051

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C. Kuhakarn et al. / Tetrahedron 61 (2005) 8995–9000
Table 1. Phase transfer catalyst optimization
mechanisms previously reported for the phase transfer
catalyzed IBX oxidation of sulfides to sulfoxides.14
Comparative studies of our method (Method A) with those
reported in the literature for IBX oxidation of alcohols
(Methods B15 and C16) were conducted. The selectivity and
efficiency of our method are clearly demonstrated as shown
in Table 4. A control experiment was also carried out with
the 2,2,4-trimethyl-1,3-pentanediol substrate using the
conditions described in Table 4 (Method A) without the
n-Bu4NBr. The oxidation gave all the possible products, that
is the corresponding hydroxyketone (31%), hydroxyalde-
hyde (4%), dicarbonyl (2%), and recovered starting material
(37%). The results seem to suggest that the origin of
Entry
Phase transfer catalyst
Conversion (%)a
1
2
3
4
5
6
n-Bu4NBr
Et4NCl
Et4NBr
Et4NI
BnMe3NBr
BnEt3NCl
89
22
62
37
18
30
a Conversion (%) was calculated from 1H NMR (300 MHz) integration.
Table 2. Optimization of reaction conditions
Entry
H2O:CH2Cl2 (v/v)
IBX (equiv)
n-Bu4NBr (equiv)
Time (h)
Conversion (%)a
1
2
3
4
5
6
7
0:100
1:1
0:100
1:3
1:1
1.5
1.5
1.5
1.5
1.5
1.5
1.5
—
—
4
7
2
4
4
4
4
45
31
88
92
89
70
60
0.5
0.5
0.5
0.1
1.0
1:1
1:1
a Conversion (%) was calculated from 1H NMR (300 MHz) integration.
benzyl alcohol to benzaldehyde was obtained (Table 2,
entry 1). A similar result was obtained when water was used
as a co-solvent, even with prolonged reaction time (Table 2,
entry 2). Reaction in the presence of 0.5 equiv of n-Bu4NBr
proceeded with shorter reaction time and provided better
conversion (Table 2, entries 3–5). The v/v ratio of
CH2Cl2:H2O employed can be as low as 1:1. When either
a lesser or stoichiometric amount of n-Bu4NBr was
employed, lower conversions were obtained (Table 2,
entries 6–7). Therefore, the 1:1 v/v of H2O:CH2Cl2 solvent
system will be used in the standard conditions.
chemoselectivity of IBX oxidation of diols under a bi-phasic
solvent system in our study stems from the choice of
solvent. The role of the bromide anion was believed to
follow the previously suggested mechanism for Et4NBr
catalyzed IBX oxidation of sulfides to sulfoxides by causing
a polarization of the I]O bond and leading to a reaction rate
acceleration.14
3. Conclusion
In conclusion, a selective and efficient new alternative
method has been developed for the oxidation of secondary
hydroxyl groups to ketones, in moderate to good yields, in
the presence of primary hydroxyl groups within the same
molecule. The reaction conditions do not involve moisture
sensitive and environmentally unfriendly agents. We
anticipate that this protocol will, to some extent, be of
broad interest and use to the chemistry community.
According to Tables 1 and 2, even though the oxidation
reaction of monofunctional alcohols proceeded efficiently
with as few as 1.5 equiv of IBX, an increased reaction rate
was observed with excess oxidant. For the oxidation of
diols, it was found that the use of 3 equiv of IBX afforded
the best results; very small amounts of dicarbonyls or
lactones were obtained. Based on this observation, 3 equiv
of IBX were selected to examine the chemoselective
oxidation of a variety of diols. The results are summarized
in Table 3.
4. Experimental
4.1. General
The observed transformations were chemoselective when
both the primary and the secondary hydroxyl functional
groups were present within the same molecules (Table 3).
The ketones with the primary alcohol untouched were
obtained in moderate to good yields. The dicarbonyl
compounds as well as some lactones in cases leading to
five- or six-membered ring lactones were also formed as
minor products. The exact mechanism of selective oxidation
is still unclear, but we propose that it should follow those
Melting points (uncorrected) were determined on an
Electrothermal 9100 Apparatus. Reagents were obtained
from commercial sources and used as received. Column
chromatography was performed using silica gel 60 (70–230
mesh). Analytical TLC was performed with silica gel 60
PF254 aluminium sheet with 0.2 mm layer of silica gel. H
NMR spectra were recorded at 300 MHz in CDCl3 solution
with tetramethylsilane as an internal standard. 13C NMR
1

C. Kuhakarn et al. / Tetrahedron 61 (2005) 8995–9000
8997
Table 3. Selective oxidation of secondary hydroxyls using IBX/n-Bu4NBr in 1:1 v/v of H2O:CH2Cl2
Entry
1
Substrate
Product (% yield)a
1a 81% (74%)b
1b 88% (70%)b
2a 10%
3a 3%
3b 5%
2
3
4
2b 2%
2c 3%
1c 72% (70%)b
1d 62% (56%)b
1e 67% (58%)b
1f 84% (71%)b
5
6
2f 8%
7
1g 80% (72%)b
1h 46% (38%)b
2g 7%
2h 8%
8
a GC yields.
b Yields (%) given in parentheses are isolated yields after purification by column chromatography.
Table 4. Comparison of the oxidation of diols by IBX under other conditions
Substrate
Methoda
Product (% yield)b
Ac
B
81
10
83
76
3
16
23
d
d
C
Ae
B
72
d
3
77
86
d
C
a Method A: 3 equiv IBX, 0.5 equiv n-Bu4NBr, CH2Cl2:H2O (1:1), rt, 4 h; Method B: 3 equiv IBX, DMSO, rt, 4 h; Method C: 3 equiv IBX, EtOAc, 80 8C, 4 h.
b GC yields.
c Starting material was recovered (6%).
d Not detected by GC.
e Starting material was recovered (21%).

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C. Kuhakarn et al. / Tetrahedron 61 (2005) 8995–9000
spectra were recorded at 75 MHz with residual non-
deuterated solvent peak as an internal standard. IR spectra
were recorded on a GX FT-IR system (Perkin Elmer)
spectrometer. Elemental analyses were determined on a
Perkin Elmer Elemental Analyzer 2400 CHN. High
resolution mass spectra were obtained on a Micromass
model VQ-TOF2 mass spectrometer.
(6H, s) 1.06 (6H, d, JZ6.8 Hz). 13C NMR (75 MHz, CDCl3,
ppm) d 221.5, 69.3, 49.6, 34.5, 21.0, 19.8.
4.2.4. Preparation of 3-hydroxymethyl-4-heptanone
(1d). According to the general procedure, oxidation of
2-ethyl-1,3-hexanediol (185 mg, 1.27 mmol) gave
3-hydroxymethyl-4-heptanone, after column chromato-
graphy on silica gel (18!1.5 cm, 7:3 n-hexane/diethyl
ether as eluent), 103 mg (isolated yield; 56%) as colorless
liquid:10c analytical TLC on silica gel, 7:3 n-hexane/diethyl
ether, RfZ0.05. IR (neat, cmK1) 3422, O–H; 1705, C]O.
300 MHz 1H NMR (CDCl3, ppm) d 3.80 (1H, dd, ABX, JZ
11.0, 7.4 Hz) 3.70 (1H, dd, ABX, JZ11.0, 4.1 Hz) 2.70–
2.57 (1H, m) 2.48 (2H, t, JZ7.3 Hz) 2.14 (1H, br s) 1.75–
1.39 (4H, m) 0.93 (3H, t, JZ7.5 Hz) 0.92 (3H, t, JZ
7.4 Hz). 13C NMR (75 MHz, CDCl3, ppm) d 215.1, 62.4,
54.9, 44.8, 21.2, 16.8, 13.7, 11.8.
4.2. General procedure for the oxidation
To a stirred suspension of IBX (3.0 equiv) in H2O:CH2Cl2
(v/vZ1:1, 0.25 M based on starting alcohol) was added
n-Bu4NBr (0.5 equiv) followed by the addition of alcohol
(1.0 equiv) in one portion. The mixture was stirred at rt for
4 h. The residual solids were filtered off and washed
thoroughly with diethyl ether. The combined filtrate was
washed successively with 8% sodium thiosulfate (15 mL),
water (2!15 mL) and brine (1!15 mL). The organic layer
was dried over anhydrous sodium sulfate, filtered, and
evaporated (aspirator). The crude product was subsequently
examined by gas chromatography for determining product
conversion. Purification of the crude product by column
chromatography (SiO2) provided the isolated yield of the
ketone.
4.2.5. Preparation of 3-hydroxy-1-phenyl-1-propanone
(1e). According to the general procedure, oxidation of
3-hydroxy-1-phenyl-1-propanol (152 mg, 1 mmol) gave
3-hydroxy-1-phenyl-1-propanone, after column chromato-
graphy on silica gel (18!1.5 cm, 8.5:1.5 n-hexane/ethyl
acetate as eluent), 86.9 mg (isolated yield; 58%) as a
colorless liquid:18 analytical TLC on silica gel, 7:3
n-hexane/ethyl acetate, RfZ0.29. IR (neat, cmK1) 3412,
O–H; 1681, C]O. 300 MHz 1H NMR (CDCl3, ppm) d 7.97
(2H, d, JZ7.3 Hz) 7.59 (1H, t, JZ7.4 Hz) 7.48 (2H, t, JZ
7.5 Hz) 4.05 (2H, t, JZ5.4 Hz) 3.24 (2H, t, JZ5.4 Hz) 2.85
(1H, br s). 13C NMR (75 MHz, CDCl3, ppm) d 200.4, 136.6,
133.4, 128.6, 128.0, 58.0, 40.3.
4.2.1. Preparation of 1-hydroxy-5-decanone (1a).
According to the general procedure, oxidation of 1,5-
decanediol (174 mg, 1 mmol) gave 1-hydroxy-5-decanone,
after column chromatography on silica gel (18!1.5 cm, 8:2
n-hexane/ethyl acetate as eluent), 127 mg (isolated yield;
74%) as colorless liquid: analytical TLC on silica gel, 7:3
n-hexane/ethyl acetate, RfZ0.17. IR (neat, cmK1) 3423,
O–H; 1712, C]O. 300 MHz 1H NMR (CDCl3, ppm) d 3.57
(2H, br s) 2.55–2.10 (4H, m) 1.70–1.10 (11H, m) 0.82 (3H,
t, JZ6.9 Hz). 13C NMR (75 MHz, CDCl3, ppm) d 211.6,
62.1, 42.7, 42.1, 32.0, 31.3, 23.5, 22.4, 19.6, 13.8. Molecular
ion (MCH) calcd for C10H21O2: 173.1542; found (ESI-
TOF) m/eZ173.1536, errorZ3 ppm.
4.2.6. Preparation of 2-butyl-2-hydroxymethylcyclo-
pentanone (1f). According to the general procedure,
oxidation of 2-butyl-2-hydroxymethylcyclopentanol
(221 mg, 1.28 mmol) gave 2-butyl-2-hydroxymethylcyclo-
pentanone, after column chromatography on silica gel (18!
1.5 cm, 8:2 n-hexane/ethyl acetate as eluent), 156 mg
(isolated yield; 71%) as a pale yellow liquid: analytical
TLC on silica gel, 7:3 n-hexane/ethyl acetate, RfZ0.32. IR
1
(neat, cmK1) 3448, O–H; 1731, C]O. 300 MHz H NMR
4.2.2. Preparation of 1-hydroxy-4-decanone (1b).
According to the general procedure, oxidation of 1,4-
decanediol (174 mg, 1 mmol) gave 1-hydroxy-4-decanone,
after column chromatography on silica gel (18!1.5 cm, 8:2
n-hexane/ethyl acetate as eluent), 120 mg (isolated yield;
70%) as colorless liquid:17 analytical TLC on silica gel, 7:3
n-hexane/ethyl acetate, RfZ0.16. IR (neat, cmK1) 3422,
O–H; 1707, C]O. 300 MHz 1H NMR (CDCl3, ppm) d 3.64
(2H, t, JZ6.1 Hz) 2.55–2.30 (4H, m) 2.00–1.66 (2H, m)
1.65–1.44 (2H, m) 1.40–1.17 (7H, m) 0.88 (3H, t, JZ
6.6 Hz). 13C NMR (75 MHz, CDCl3, ppm) d 212.1, 62.1,
42.9, 39.4, 31.5, 28.8, 26.4, 23.8, 22.4, 14.0.
(CDCl3, ppm) d 3.62 (1H, d, JZ11.0 Hz) 3.47 (1H, d, JZ
11.0 Hz) 2.36 (1H, br s) 2.31–2.17 (2H, m) 2.01–1.80 (4H,
m) 1.55–1.01 (6H, m) 0.88 (3H, t, JZ7.0 Hz). 13C NMR
(75 MHz, CDCl3, ppm) d 224.7, 65.7, 53.4, 38.8, 32.2, 30.5,
26.2, 23.2, 19.1, 13.8. Anal. Calcd for C10H18O2: C, 70.55;
H, 10.66. Found: C, 70.29; H, 10.45.
4.2.7. Preparation of 2-hydroxymethylcyclohexanone
(1g). According to the general procedure, oxidation of
2-hydroxymethylcyclohexanol (130 mg, 1 mmol) gave
2-hydroxymethylcyclohexanone, after column chromato-
graphy on silica gel (18!1.5 cm, 8:2 n-hexane/ethyl acetate
as eluent), 91.8 mg (isolated yield; 72%) as a colorless
liquid:19 analytical TLC on silica gel, 6:4 n-hexane/ethyl
acetate, RfZ0.25. IR (neat, cmK1) 3421, O–H; 1702, C]O.
300 MHz 1H NMR (CDCl3, ppm) d 3.81–3.68 (1H, m)
3.68–3.54 (1H, m) 2.79 (1H, br s) 2.61–1.36 (9H, m). 13C
NMR (75 MHz, CDCl3, ppm) d 214.6, 62.5, 52.1, 42.1,
30.0, 27.4, 24.6.
4.2.3. Preparation of 1-hydroxy-2,2,4-trimethyl-3-penta-
none (1c). According to the general procedure, oxidation of
2,2,4-trimethyl-1,3-pentanediol (146 mg, 1 mmol) gave
1-hydroxy-2,2,4-trimethyl-3-pentanone, after column
chromatography on silica gel (18!1.5 cm, 8:2 n-hexane/
diethyl ether as eluent), 101 mg (isolated yield; 70%) as
colorless liquid:12a analytical TLC on silica gel, 8:2
n-hexane/diethyl ether, RfZ0.12. IR (neat, cmK1) 3479,
O–H; 1699, C]O. 300 MHz 1H NMR (CDCl3, ppm) d 3.56
(2H, s) 3.18–3.02 (1H, m) 2.85 (1H, br d, JZ7.4 Hz) 1.18
4.2.8. Preparation of 2-hydroxy-1-phenylethanone (1h).
According to the general procedure, oxidation of 1-phenyl-

C. Kuhakarn et al. / Tetrahedron 61 (2005) 8995–9000
8999
1,2-ethanediol (138 mg, 1 mmol) gave 2-hydroxy-1-phenyl-
ethanone, after column chromatography on silica gel (18!
1.5 cm, 8:2 n-hexane/ethyl acetate as eluent), 52.4 mg
(isolated yield; 38%) as a white solid:20 mp 84.6–85.2 8C
(Aldrich chemicals 86–89 8C); analytical TLC on silica gel,
7:3 n-hexane/ethyl acetate, RfZ0.31. IR (neat, cmK1) 3428,
O–H; 1682, C]O. 300 MHz 1H NMR (CDCl3, ppm) d 7.93
(2H, d, JZ7.6 Hz) 7.63 (1H, t, JZ7.4 Hz) 7.51 (2H, t, JZ
7.7 Hz) 4.89 (2H, s) 2.98 (1H, br s). 13C NMR (75 MHz,
CDCl3, ppm) d 198.4, 134.3, 133.4, 128.9, 127.7, 65.4.
acknowledge Chulabhorn Research Institute for high-
resolution mass spectrometry analysis.
References and notes
1. (a) Hudlicky, M. Oxidation in Organic Chemistry; American
Chemical Society: Washington, DC, 1990. (b) Comprehensive
Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon:
Oxford, 1991. (c) Luzzio, F. A. Org. React. 1990, 53, 1–221.
2. Kritchevzky, T. H.; Garmaise, D. L.; Gallagher, T. F. J. Am.
Chem. Soc. 1952, 74, 483–486.
4.3. Characterization data for dicarbonyl compounds 2
4.3.1. 5-Oxodecanal (2a). Colorless liquid:21 analytical
TLC on silica gel, 6:4 n-hexane/ethyl acetate, RfZ0.52. IR
(neat, cmK1) 1709, C]O. 300 MHz 1H NMR (CDCl3,
ppm) d 9.75 (1H, s) 2.55–2.43 (4H, m) 2.39 (2H, t, JZ
7.4 Hz) 1.97–1.80 (2H, m) 1.65–1.47 (2H, m) 1.40–1.16
(4H, m) 0.89 (3H, t, JZ6.8 Hz). 13C NMR (75 MHz,
CDCl3, ppm) d 210.3, 201.8, 42.8, 42.6, 41.1, 31.2, 23.3,
22.2, 15.8, 13.7.
3. (a) Kim, K. S.; Cho, I. H.; Yoo, B. K.; Song, Y. H.; Hahn, C. S.
J. Chem. Soc., Chem. Commun. 1984, 762–763. (b) Sugimura,
T.; Paquette, L. A. J. Am. Chem. Soc. 1987, 109, 3017–3024.
4. Wicha, J.; Zarecki, A. Tetrahedron Lett. 1974, 15, 3059–3062.
5. (a) Al Neirabeyeh, M.; Ziegler, J. C.; Gross, B.; Caubere, P.
Synthesis 1976, 811–813. (b) Tanaka, T.; Murakami, K.;
Okuda, O.; Kuroda, T.; Inoue, T.; Kamei, K.; Murata, T.;
Yoshino, H.; Imanishi, T.; Iwata, C. Chem. Pharm. Bull. 1994,
42, 1756–1759.
4.3.2. 4-Oxodecanal (2b). Colorless liquid:22 analytical
TLC on silica gel, 6:4 n-hexane/ethyl acetate, RfZ0.47. IR
(neat, cmK1) 1712, C]O. 300 MHz 1H NMR (CDCl3,
ppm) d 9.80 (1H, s) 2.80–2.67 (4H, m) 2.47 (2H, t, JZ
7.5 Hz) 1.65–1.50 (2H, m) 1.40–1.18 (6H, m) 0.88 (3H, t,
JZ6.4 Hz). 13C NMR (75 MHz, CDCl3, ppm) d 208.8,
200.4, 42.6, 37.3, 34.5, 31.4, 28.7, 23.7, 22.3, 13.9.
6. Ueno, Y.; Okawara, M. Tetrahedron Lett. 1976, 17,
4597–4600.
7. (a) Stevens, R. V.; Chapman, K. T.; Weller, H. N. J. Org.
Chem. 1980, 45, 2030–2032. (b) Stevens, R. V.; Chapman,
K. T.; Stubbs, C. A.; Tam, W. W.; Albizati, K. F. Tetrahedron
Lett. 1982, 23, 4647–4650.
8. (a) Sakaguchi, S.; Kikuchi, D.; Ishii, Y. Bull. Chem. Soc. Jpn.
1997, 70, 2561–2566. (b) Tomioka, H.; Oshima, K.; Nozaki,
H. Tetrahedron Lett. 1982, 23, 539–542. (c) Lampe, T. F. J.;
Hoffman, H. M. R.; Bornscheuer, U. T. Tetrahedron:
Asymmetry 1996, 7, 2889–2900. (d) Rydberg, D. B.;
Meinwald, J. Tetrahedron Lett. 1996, 37, 1129–1132.
9. Kanemoto, S.; Tomioka, H.; Oshima, K.; Nozaki, H. Bull.
Chem. Soc. Jpn. 1986, 59, 105–108.
4.3.3. 2,2,4-Trimethyl-3-oxopentanal (2c). Colorless
liquid:23 analytical TLC on silica gel, 8:2 n-hexane/diethyl
ether, RfZ0.45. IR (neat, cmK1) 1736, 1702, C]O;
1
300 MHz H NMR (CDCl3, ppm) d 9.64 (1H, s) 3.03–
2.97 (1H, m) 1.35 (6H, s) 1.06 (6H, d, JZ6.7 Hz). 13C NMR
(75 MHz, CDCl3, ppm) d 213.5, 200.9, 60.7, 36.5, 19.2,
19.0.
10. (a) Trost, B. M.; Masuyama, Y. Tetrahedron Lett. 1984, 25,
173–176. (b) Masuyama, Y.; Takahashi, M.; Kurusu, T.
Tetrahedron Lett. 1984, 25, 4417–4420. (c) Yamawaki, K.;
Yoshida, T.; Nishihara, H.; Ishii, Y.; Ogawa, M. Synth.
Commun. 1986, 16, 537–541. (d) Choudary, B. M.;
Durgaprasad, A.; Valli, V. L. K. Tetrahedron Lett. 1990, 31,
5785–5788. (e) Palombi, L.; Bonadies, F.; Scettri, A.
Tetrahedron 1997, 53, 15867–15876. (f) Krohn, K.; Vinke,
I.; Adam, H. J. Org. Chem. 1998, 61, 1467–1472.
4.3.4. 1-Butyl-2-oxocyclopentanecarbaldehyde (2f).
Colorless liquid: analytical TLC on silica gel, 7:3
n-hexane/diethyl ether, RfZ0.55. IR (neat, cmK1) 1745,
1713, C]O; 300 MHz 1H NMR (CDCl3, ppm) d 9.41 (1H,
s) 2.66–1.07 (12H, m) 0.90 (3H, t, JZ7.2 Hz). 13C NMR
(75 MHz, CDCl3, ppm) d 215.3, 199.0, 67.5, 38.6, 32.7,
27.7, 26.6, 22.9, 19.2, 13.7. Molecular ion (MCH) calcd for
C10H17O2: 169.1229; found (ESI-TOF) m/eZ169.1223,
errorZ3 ppm.
11. (a) Bovicelli, P.; Lupattelli, P.; Sanetti, A.; Mincione, E.
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Orange liquid;24 analytical TLC on silica gel, 8:2
n-hexane/ethyl acetate, RfZ0.48. IR (neat, cmK1) 3421,
O–H; 1715, C]O; 1603, C]C. 300 MHz 1H NMR
(CDCl3, ppm) d 14.40 (1H, br s) 8.64 (1H, s) 2.47–2.25
(4H, m) 1.80–1.59 (4H, m). 13C NMR (75 MHz, CDCl3,
ppm) d 187.5, 184.9, 108.8, 31.2, 23.1, 22.5, 21.2.
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Acknowledgements
We thank the financial contribution from the Thailand
Research Fund (TRF) and the Postgraduate Education and
Research Program in Chemistry (PERCH) for the generous
support of the research program. The authors also
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