Palladium(II)-catalyzed oxidation of terminal alkenes to methyl ketones using molecular oxygen

Article abstract of DOI:10.1039/b001854f

Palladium(II) acetate catalyzes the aerobic oxidation of terminal alkenes in toluene into the corresponding methyl ketones in the presence of a catalytic amount of pyridine using propan-2-ol as a reductant and molecular oxygen as an oxidant. Two catalytic cycles sharing a Pd(II)-OOH species are proposed. One is the formation of a Pd(II)-H species in the oxidation of propan-2-ol to acetone, followed by reaction with molecular oxygen to give a Pd(II)-OOH species, and the other is peroxypalladation of an alkene with the Pd(II)-OOH species produced to afford a methyl ketone in the presence of H₂O₂ produced by the former catalytic cycle. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b001854f

View Article Online / Journal Homepage / Table of Contents for this issue
Palladium(II)-catalyzed oxidation of terminal alkenes to methyl
ketones using molecular oxygen
Takahiro Nishimura, Nobuyuki Kakiuchi, Tomoaki Onoue, Kouichi Ohe and Sakae Uemura*
1
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering,
Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
Received (in Cambridge, UK) 7th March 2000, Accepted 18th April 2000
Published on the Web 31st May 2000
Palladium() acetate catalyzes the aerobic oxidation of terminal alkenes in toluene into the corresponding methyl
ketones in the presence of a catalytic amount of pyridine using propan-2-ol as a reductant and molecular oxygen
as an oxidant. Two catalytic cycles sharing a Pd()–OOH species are proposed. One is the formation of a Pd()–H
species in the oxidation of propan-2-ol to acetone, followed by reaction with molecular oxygen to give a Pd()–
OOH species, and the other is peroxypalladation of an alkene with the Pd()–OOH species produced to afford
a methyl ketone in the presence of H2O2 produced by the former catalytic cycle.
Table 1 Pd()-catalyzed oxidation of dodec-1-ene to dodecan-2-one
by molecular oxygen
Introduction
Palladium-catalyzed oxidation of alkenes to methyl ketones
has been developed in synthetic organic chemistry as well as in
industrial processes, and is well-known in the Wacker process
using PdCl2 and CuCl2 or Cu2Cl2 as catalysts in acidic water
under an oxygen atmosphere.1 However, this catalytic system is
highly corrosive because of its acidic conditions and may cause
the formation of chlorinated by-products. To overcome such
drawbacks, halide-free catalytic systems have also been widely
investigated;2–5 e.g. the combination of benzoquinone and
iron() phthalocyanine2 or molybdovanadophosphate,3 the
Pd()salt–heteropolyacid system,4 and the Pd() salt–
polyanilines or polypyrrole system.5 Furthermore, a recent
report of aerobic oxidation in water using a water soluble
palladium complex and a base showed very high selectivity of
the product as well as effective catalyst recycling.6
Conversion
(%)
GLC yield
(%)a
Entry
Solvent
Alcohol
1
2
3
4
5
Toluene
Toluene
Toluene
THF
Methanol
Ethanol
Propan-2-ol
Propan-2-ol
Propan-2-ol
6
26
84
18
22
2
14
70
11
14
1,4-Dioxane
a Based on the amount of dodec-1-ene employed.
Typical Wacker-type catalysis has been extensively studied
and it is believed that Pd() is reduced to Pd(0) and the use of
a reoxidant such as the combination of a copper salt and O2
is indispensable for the catalysis by palladium.1 On the other
hand, an alternative mechanism has also been proposed, in
which a formal oxidation state of Pd() remains throughout
the reaction via the formation of a Pd()–OOH species by O2
insertion to an initially produced Pd()–H species.7
co-workers in 1985. They also proposed the formation of a
Pd()–OOH species from palladium, ethanol and oxygen.9
Recently, we reported the aerobic oxidation of alcohols in
toluene to the corresponding aldehydes and ketones using a
catalytic amount of Pd(OAc)2 and pyridine under an oxygen
atmosphere, in which we proposed that a Pd()–OOH species
was produced in situ by the reaction of a Pd()–H species with
O2.10 We have now applied our Pd(OAc)2–pyridine–O2 catalytic
system to the oxidation of alkenes. We report herein the
palladium-catalyzed aerobic oxidation of alkenes to the corre-
sponding methyl ketones using a suitable alcohol as a reductant
for the formation of a Pd()–H species.11
Mimoun and co-workers have reported that the Pd()–OOH
species undergoes an oxygen transfer to terminal alkenes
through
a five-membered pseudocyclic peroxypalladation
mechanism [eqn. (1)].8 They also investigated this reaction
Results and discussion
Dodec-1-ene (1a) was chosen first as a substrate to determine
the optimum conditions. At first, the reaction was attempted
in different solvents using three alcohols as reductants. The
reaction procedure was as follows: to a mixture of 5 mol%
Pd(OAc)2, 20 mol% pyridine, solvent (5 mL) and alcohol
(1 mL) was added 1a (1 mmol) in alcohol (4 mL) at 60 ЊC and
the mixture was stirred for 6 h under an oxygen atmosphere.
The results are summarized in Table 1. Among the three
alcohols examined in toluene as solvent, propan-2-ol was found
to be most effective for the formation of the expected dodecan-
2-one (2a) (70% GLC yield; Table 1, entry 3), and solvents other
than toluene, such as tetrahydrofuran (THF) and 1,4-dioxane,
(1)
systematically to develop an efficient catalytic procedure for
the oxidation of terminal alkenes to methyl ketones using a
palladium catalyst and 30% aqueous H2O2 as a stoichiometric
oxidant.8b
An example of the palladium-catalyzed oxidation of
cyclopentene to cyclopentanone in ethanol using molecular
oxygen as the sole reoxidant was reported by Takehira and
DOI: 10.1039/b001854f
J. Chem. Soc., Perkin Trans. 1, 2000, 1915–1918
This journal is © The Royal Society of Chemistry 2000
1915

View Article Online
Fig. 1 The effect of the amount of propan-2-ol. Reagents and condi-
tions: Pd(OAc)2 (0.05 mmol), dodec-1-ene (1.0 mmol), pyridine (0.2
mmol), toluene (5 mL), propan-2-ol, O2, 60 ЊC, 6 h.
Table 2 The effect of the amount of pyridine on the oxidation of
dodec-1-enea
Entry
Pyridine/mmol
Conversion (%)
GLC yield (%)b
1
2
3
4
0.1
0.2
0.3
0.4
85
84
53
51
58
70
43
40
Scheme 1
a Reagents and conditions: Pd(OAc)2 (0.05 mmol), dodec-1-ene (1.0
mmol), pyridine, toluene (5 mL), propan-2-ol (5 mL), O2, 60 ЊC, 6 h.
b Based on the amount of dodec-1-ene employed.
yield showing that terminal alkenes are oxidized much faster
than hydroxy groups.15 It is noteworthy that this oxidation sys-
tem was applicable to terminal alkenes, but not to internal ones
(entries 13–15, Table 3): i.e., the terminal alkene group of 1i was
selectively oxidized to give cylohex-3-en-1-yl methyl ketone
(2i) in 75% yield.16 Unfortunately, in the oxidation of 2-
allylcyclohexan-1-one (1j), the corresponding 1,4-diketone 2j
(which is a useful precursor for the synthesis of cyclopent-
anones17) was obtained only in low yield with other unidenti-
fied by-products (entries 16 and 17). Cyclic internal alkenes
such as cyclohexene (1k), cycloheptene (1l), and cyclooctene
(1m) were not oxidized and neither was (E)-tetradec-7-ene (1n).
When the oxidation of styrene (1o) or terminal alkynes (1p and
1q) was attempted, the reaction mixture turned black and
afforded many unidentified products.
A plausible pathway for this oxidation using a Pd(OAc)2–
pyridine–propan-2-ol–O2 catalytic system is shown in Scheme
2. In this mechanism, two catalytic cycles operate. One cycle is
the oxidation of propan-2-ol (cycle A) to give acetone and a
Pd()–H species, the latter of which is transformed to a Pd()–
OOH species by the reaction with oxygen. The Pd()–OOH
species reacts with an alcohol to give the alkoxypalladium(II)
species as well as H2O2.10b This Pd()–OOH species also reacts
with alkenes via a pseudocyclic intermediate [eqn. (1), peroxy-
palladation] in another catalytic cycle (cycle B) to produce
methyl ketones and a Pd()–OH species which reacts with H2O2
to give again the Pd()–OOH species.8b In order to obtain the
best result, it was important to add the alkene ca. 5 min after
the addition of propan-2-ol (see Experimental section). This is
because the low concentration of H2O2 may retard the repro-
duction of the Pd()–OOH species from the Pd()–OH species,
which could react with an alkene to give a stable π-allyl-
palladium complex and thus reduce the ketone yield. The
production of H2O2 was detected by a KI/starch test of the
reaction mixture after oxidation of dodec-1-ene for 6 h, and
therefore supports our plausible pathway. Fig. 2 shows the
relationship between O2 uptake and dodecan-2-one produced in
the oxidation of dodec-1-ene. O2 uptake in the oxidation of
propan-2-ol (15 mL, 196 mmol) to acetone in toluene (15 mL)
without dodec-1-ene using 5 mol% Pd(OAc)2 and 20 mol%
pyridine under oxygen was revealed to be ca. 9 mmol after 6 h,
while an O2 uptake of ca. 11 mmol was observed in the presence
of dodec-1-ene (3 mmol). This result shows that the oxidation
of propan-2-ol is accelerated by the presence of dodec-1-ene
because of the increase in consumption of the Pd()–OOH
were revealed to be ineffective even when using propan-2-ol
(entries 4 and 5). Next, we examined the effect of the amount of
pyridine, because its presence was revealed to be an essential
factor for the oxidation of alcohols in our previous studies.10b
When 0.1 mmol of pyridine (2 equiv. to Pd(OAc)2) were used,
the conversion of 1a was fast, but in this case the precipitation
of metallic palladium was observed, resulting in a reduction in
product selectivity, probably due to the isomerization of 1a to
internal alkenes12 (Table 2, entry 1). The use of 4 equiv. of
pyridine gave 2b in good yield (70%) and selectivity (83%)
(entry 2). On the other hand, the presence of a greater excess of
pyridine decreased the reaction rate (entries 3 and 4). The
amount of propan-2-ol is another crucial factor for this
reaction. When the reaction was performed with less than 65
mmol (5 mL) of propan-2-ol, the reaction rate decreased, while
a large excess of propan-2-ol did not affect the product yield or
its selectivity (Fig. 1). Although various kinds of dehydrating
reagents, such as Na2SO4, CaSO4, CaO, MgSO4, Al2O3,
NaOAc, Na2CO3, SiO2, and K2CO3, were added to the reaction
mixture in the hope of increasing the yield and selectivity, all of
them were revealed to be ineffective.
The results of the application of this optimized procedure to
a variety of terminal alkenes (1a–1j; Scheme 1) are shown in
Table 3. At higher temperatures such as at 80 ЊC using
propan-2-ol as a reductant, the reaction became sluggish and
the product yield decreased.13 However, butan-2-ol could be
used for this oxidation at 75 or 80 ЊC and slightly better yields
were obtained in a shorter reaction time (Table 3, entries 2, 10,
15 and 17). The amount of Pd(OAc)2 could also be reduced to
2.5 mol%, but a longer reaction time was required (entry 3).
Other simple terminal alkenes, such as oct-1-ene (1b) and
tetradec-1-ene (1c), were oxidized to octan-2-one (2b) and
tetradecan-2-one (2c) in good yields, respectively (entries 5 and
6). Pent-4-en-1-ol (1d) yielded 5-hydroxypentan-2-one (2d) in
21% isolated yield in spite of the high conversion of 1d, prob-
ably due to the formation of the product by an intramolecular
Wacker-type reaction (entry 7).14 However, this catalyst system
showed compatibility with a hydroxy protecting group, such as
tert-butyldimethylsilyl (1e), benzoyl (1f), and tetrahydropyranyl
(1g) (entries 8–11). Interestingly, undec-10-en-1-ol (1h) was
mainly transformed into 11-hydroxyundecan-2-one (2h) in 71%
1916
J. Chem. Soc., Perkin Trans. 1, 2000, 1915–1918

View Article Online
Table 3 Pd()-catalyzed oxidation of terminal alkenes to methyl ketones by molecular oxygena
Entry
Substrate
Alcohol
Reaction temp/ЊC
Reaction time/h
Product
Conversion (%)
Isolated yield (%)b
1
2
1a
1a
1a
1a
1b
1c
1d
1e
1f
1f
1g
1h
1i
Propan-2-ol
Butan-2-ol
Propan-2-ol
Propan-2-ol
Propan-2-ol
Propan-2-ol
Propan-2-ol
Propan-2-ol
Propan-2-ol
Butan-2-ol
Propan-2-ol
Propan-2-ol
Propan-2-ol
Propan-2-ol
Butan-2-ol
Propan-2-ol
Butan-2-ol
60
80
60
60
60
60
60
60
60
75
60
60
60
60
75
60
80
6
6
16
24
6
16
6
16
16
8
16
27
6
48
12
6
2a
2a
2a
2a
2b
2c
2d
2e
2f
2f
2g
2h
2i
84
92
88
71
—
100
88
89
60
89
88
70c
72c
71c
53c
80c
74
21
71
56
78
3d
4e
5
f
6
7
8
9
10
11
12
13
14
15
16
17
70
100
71
f
—
—
—
46c
61c
75c
22
f
1i
2i
f
1i
2i
1j
2j
64
95
1j
6
2j
26
a Reagents and conditions: Pd(OAc)2 (0.05 mmol), alkene (1.0 mmol), pyridine (0.2 mmol), toluene (5 mL), alcohol (5 mL), O2. b Based on the amount
of alkene employed. c GLC yield. d 2.5 mol% Pd(OAc)2 and 10 mol% pyridine were used. e 1.0 mol% Pd(OAc)2 and 4.0 mol% pyridine were used.
f Not determined.
Scheme 2 Plausible reaction pathway.
oxidation of terminal alkenes to methyl ketones. The in situ
formation of H2O2 in the oxidation of the alcohol is a key
reaction. Although our system has some limitations as a
synthetic method, these results present a new and mild catalytic
cycle for the aerobic oxidation of terminal alkenes and strongly
support the idea that a Pd()–OOH species is produced in the
aerobic oxidation of alcohols as previously proposed.10b
Experimental
General
NMR spectra were recorded on JEOL EX-400 (1H NMR, 400
MHz; 13C NMR, 100 MHz) and JNM-AL-300 (1H NMR, 300
Fig. 2 Time profile of the oxidation of dodec-1-ene: the relationship
between O2 uptake and product yield. The reaction was carried out on a
MHz; 13C NMR, 75.5 MHz) instruments for solutions in
3 fold scale using propan-2-ol. O2 uptake (ᮀ), produced dodecan-2-one
CDCl3 with Me4Si as an internal standard: the following
abbreviations are used; s: singlet, d: doublet, t: triplet, q: quar-
tet, qui: quintet, m: multiplet. GLC analyses were performed on
a Shimadzu GC-14A instrument (25 m × 0.33 mm, 5.0 mm film
thickness, Shimadzu fused silica capillary column HiCap
CBP10-S25-050) with flame-ionization detectors and helium as
carrier gas. GLC yields were determined using bibenzyl as an
internal standard. Analytical thin layer chromatography (TLC)
was performed with Merck silica gel 60 F-254 plates. Column
chromatography was performed with Merck silica gel 60.
(᭺), and O2 uptake (᭝) in the reaction without dodec-1-ene.
species for the alkene oxidation in catalytic cycle B of
Scheme 2.
Conclusions
A novel system of the combination of Pd(OAc)2–pyridine–
propan-2-ol–O2 showed high catalytic activity in the selective
J. Chem. Soc., Perkin Trans. 1, 2000, 1915–1918
1917

View Article Online
Materials
2.47 (2H, t, J = 7.2 Hz), 3.33 (1H, dt, J = 9.7, 6.1 Hz), 3.37–3.46
(1H, m), 3.67 (1H, dt, J = 9.7, 6.1 Hz), 3.70–3.83 (1H, m), 4.48
(1H, br s); δC(75.5 MHz, CDCl3, Me4Si) 19.7, 24.0, 25.5, 29.9,
30.7, 40.6, 62.4, 66.5, 98.9, 208.6.
Commercially available organic and inorganic compounds were
used without further purification except for the solvent, which
was distilled by the known method before use. 5-tert-Butyldi-
methylsilyloxypent-1-ene (1e) was prepared by the reaction of
pent-4-en-1-ol with tert-butyldimethylchlorosilane in the pres-
ence of imidazole in N,N-dimethylformamide. 5-Benzoyloxy-
pent-1-ene (1f) was prepared by the reaction of pent-4-en-1-ol
with benzoyl chloride in pyridine. 5-(Tetrahydropyran-2-yl)-
pent-1-ene (1g) was prepared by the reaction of pent-4-en-1-ol
with 3,4-dihydro-2H-pyran in the presence of K10 montmoril-
lonite in CH2Cl2. 2-Allylcyclohexan-1-one (1j) was prepared by
the enamine method.18
11-Hydroxyundecan-2-one (2h). White solid, mp 38.5–
39.7 ЊC; δH(400 MHz, CDCl3, Me4Si) 1.25–1.58 (15H, m), 2.14
(3H, s), 2.42 (2H, t, J = 7.3 Hz), 3.64 (2H, t, J = 6.6 Hz); δC(100
MHz, CDCl3, Me4Si) 23.8, 25.7, 29.2, 29.3, 29.4, 29.4, 29.9,
32.8, 43.8, 63.0, 209.5.
Acknowledgements
The author T. N. is grateful for the award of a Fellowship of the
Japan Society for the Promotion of Science for Young
Scientists.
5-tert-Butyldimethylsilyloxypent-1-ene (1e). Colorless oil;
δH(300 MHz, CDCl3, CHCl3) 0.05 (6H, s), 0.90 (9H, s),
1.57–1.66 (2H, m), 2.07–2.14 (2H, m), 3.62 (2H, t, J = 6.4 Hz),
4.93–5.05 (2H, m), 5.83 (1H, ddt, J = 17.1, 10.3, 6.6 Hz); δC(75.5
MHz, CDCl3, CHCl3) Ϫ5.3, 18.3, 26.0, 30.0, 32.0, 62.5, 114.5,
138.6.
References
1 For recent reviews, see: (a) J. Tsuji, in Palladium Reagents and
Catalysis, John Wiley, New York, 1995, pp. 19–30; (b) R. Jira, in
Applied Homogeneous Catalysis with Organometallic Compounds,
ed. B. Cornils and W. A. Herrmann, VCH, Weinheim, 1996,
pp. 374–393; (c) E. Monflier and A. Mortreux, in Aqueous Phase
Organometallic Catalysis, ed. B. Cornils and W. A. Herrmann,
VCH, Weinheim, 1997, pp. 513–518.
2 (a) J.-E. Bäckvall and R. B. Hopkins, Tetrahedron Lett., 1988, 29,
2885; (b) J.-E. Bäckvall, R. B. Hopkins, H. Grennberg, M. M.
Mader and A. K. Awasthi, J. Am. Chem. Soc., 1990, 112, 5160.
3 T. Yokota, S. Fujibayashi, Y. Nishiyama, S. Sakaguchi and Y. Ishii,
J. Mol. Catal. A: Chem., 1996, 114, 113.
5-Benzoyloxypent-1-ene (1f). Colorless oil; δH(300 MHz,
CDCl3, Me4Si) 1.81–1.92 (2H, m), 2.16–2.26 (2H, m), 4.33 (2H,
t, J = 6.6 Hz), 4.97–5.05 (1H, m), 5.07 (1H, dq, J = 17.1, 1.7
Hz), 5.85 (1H, ddt, J = 17.1, 10.3, 6.6 Hz), 7.38–7.46 (2H, m),
7.50–7.58 (1H, m), 8.01–8.08 (2H, m); δC(100 MHz, CDCl3,
Me4Si) 27.9, 30.2, 64.3, 115.4, 128.3, 129.6, 130.5, 132.8, 137.5,
166.6.
4 (a) E. Monflier, E. Blouet, Y. Barbaux and A. Mortreux,
Angew. Chem., Int. Ed. Engl., 1994, 33, 2100; (b) E. Monflier,
S. Tilloy, G. Fremy, Y. Barbaux and A. Mortreux, Tetrahedron Lett.,
1995, 36, 387; (c) E. Monflier, S. Tilloy, E. Blouet, Y. Barbaux and
A. Mortreux, J. Mol. Catal. A: Chem., 1996, 109, 27; (d) A. Kishi,
T. Higashino, S. Sakaguchi and Y. Ishii, Tetrahedron Lett., 2000, 41,
99.
5 (a) T. Hirao, M. Higuchi, B. Hatano and I. Ikeda, Tetrahedron Lett.,
1995, 36, 5925; (b) M. Higuchi, S. Yamaguchi and T. Hirao, Synlett,
1996, 1213.
5-(Tetrahydropyran-2-yl)pent-1-ene (1g). Colorless oil; δH(300
MHz, CDCl3, Me4Si) 1.46–1.90 (8H, m), 2.09–2.18 (2H, m),
3.40 (1H, dt, J = 9.7, 6.6 Hz), 3.45–3.55 (1H, m), 3.75 (1H, dt,
J = 9.7, 6.6 Hz), 3.82–3.92 (1H, m), 4.58 (1H, dd, J = 4.2, 2.8
Hz), 4.90–5.01 (1H, m), 5.03 (1H, dq, J = 17.1, 1.7 Hz), 5.83
(1H, ddt, J = 17.1, 10.3, 6.6 Hz); δC(100 MHz, CDCl3, Me4Si)
19.7, 25.6, 29.1, 30.5, 30.8, 62.2, 66.9, 98.8, 114.7, 138.4.
General procedure for palladium(II)-catalyzed oxidation of alk-1-
ene to alkan-2-one using molecular oxygen
6 G.-J. ten Brink, I. W. C. E. Arends, G. Papadogianakis and R. A.
Sheldon, Chem. Commun., 1998, 2359.
7 (a) T. Hosokawa and S.-I. Murahashi, Acc. Chem. Res., 1990, 23, 49;
(b) T. Hosokawa, M. Takano and S.-I. Murahashi, J. Am. Chem.
Soc., 1996, 118, 3990 and references therein.
8 (a) H. Mimoun, R. Charpentier, A. Mitschler, J. Fischer and
R. Weiss, J. Am. Chem. Soc., 1980, 102, 1047; (b) M. Roussel and
H. Mimoun, J. Org. Chem., 1980, 45, 5387; (c) H. Mimoun, Angew.
Chem., Int. Ed. Engl., 1982, 21, 734.
9 (a) K. Takehira, T. Hayakawa and H. Orita, Chem. Lett., 1985,
1835; (b) K. Takehira, T. Hayakawa, H. Orita and M. Shimizu,
J. Mol. Catal., 1989, 53, 15.
10 (a) T. Nishimura, T. Onoue, K. Ohe and S. Uemura, Tetrahedron
Lett., 1998, 39, 6011; (b) T. Nishimura, T. Onoue, K. Ohe and
S. Uemura, J. Org. Chem., 1999, 64, 6750.
11 For cobalt()-complex catalyzed aerobic oxidation of alkenes using
an alcohol as reductant, see: T. Mukaiyama and T. Yamada, Bull.
Chem. Soc. Jpn., 1995, 68, 17.
12 Isomerized alkenes were detected by GLC analyses.
13 Similar results were observed in the aerobic oxidation of alcohols
when the reaction was carried out at a temperature close to the
boiling point of the solvent; ref. 10b.
14 Another product was detected by TLC analysis, but it could not be
isolated due to its high volatility. 1H NMR of the crude reaction
mixture did not show any signals due to the aldehyde proton in low
field, suggesting that the oxidation of the hydroxy group in 1d may
be slower than that of a terminal alkene.
Pyridine (0.2 mmol) was added to a mixture of Pd(OAc)2 (11.2
mg, 0.05 mmol) and toluene (5 mL) in a 20 mL two-necked
flask equipped with an O2 balloon. Oxygen gas was introduced
into the flask and propan-2-ol (1 mL) was added at 60 ЊC. The
yellow solution turned to yellowish orange when the propan-2-
ol was added. After the reaction had been left at 60 ЊC for ca. 5
min, the appropriate alk-1-ene (1 mmol) in propan-2-ol (4 mL)
was added and the mixture was stirred for 6 h at 60 ЊC under O2.
The reaction mixture was passed through Florisil, and
the amount of the corresponding product was determined by
GLC analysis (for 2a, 2b and 2i) using bibenzyl as an internal
standard. In the case of compounds 2c–h and 2j the solvent was
first evaporated and the residue was then purified by column
chromatography on silica gel using hexane and ethyl acetate as
eluents.
5-tert-Butyldimethylsilyloxypentan-2-one (2e). Colorless oil;
δH(400 MHz, CDCl3, Me4Si) 0.03 (6H, s), 0.87 (9H, s), 1.77
(2H, qui, J = 6.7 Hz), 2.14 (3H, s), 2.50 (2H, t, J = 6.7 Hz), 3.60
(2H, d, J = 6.7 Hz); δC(100 MHz, CDCl3, Me4Si) Ϫ5.5, 18.2,
25.8, 26.8, 29.8, 40.0, 62.0, 208.7.
15 The oxidation of 1h using Pd(OAc)2–pyridine–3 Å molecular sieve–
O2 catalytic system yielded undec-10-en-1-al in 91% yield after 17 h;
unpublished results.
16 We examined the oxidation of 1i using Mimoun’s method
(Pd(OAc)2 and 30% H2O2), but overoxidation proceeded to give
acetophenone as a major product. In our present system, the
formation of acetophenone was not observed.
17 (a) J. Tsuji, I. Shimizu and K. Yamamoto, Tetrahedron Lett., 1976,
2975; (b) J. Tsuji, Synthesis, 1984, 369.
18 G. Stork, A. Brizzolara, H. Landesman, J. Szmuszkovicz and
R. Terrell, J. Am. Chem. Soc., 1963, 85, 207.
5-Benzoyloxypentan-2-one (2f). White solid, mp 45.2–
47.0 ЊC; δH(300 MHz, CDCl3, Me4Si) 2.06 (2H, qui, J = 6.7 Hz),
2.17 (3H, s), 2.61 (2H, t, J = 6.7 Hz), 4.33 (2H, t, J = 6.7 Hz),
7.38–7.60 (3H, m), 8.03 (2H, d, J = 7.7 Hz); δC(75.5 MHz,
CDCl3, Me4Si) 22.9, 30.0, 39.9, 64.1, 128.4, 129.5, 130.2, 133.0,
166.5, 207.6.
5-(Tetrahydropyran-2-yl)pentan-2-one (2g). Colorless oil;
δH(300 MHz, CDCl3, Me4Si) 1.35–1.85 (8H, m), 2.09 (3H, s),
1918
J. Chem. Soc., Perkin Trans. 1, 2000, 1915–1918