1556
T. Takemoto et al.
LETTER
(3) Preparation of PB-SiO2-KMnO4: To a solution of KMnO4
(6.32 g), KH2PO4 (3.63 g), K2HPO4·3H2O (3.04 g) in water
(300 mL) was added silica gel (20.0 g). The mixture was
evaporated in vacuo and the weight was adjusted to 40.0 g
by adding an adequate amount of water.
Table Oxidations of Aldehydes to Carboxylic Acidswith Solid-
Supported Oxidants
Entry
Aldehyde
Conditionsa and yield
of corresponding acidb
(4) There is a report of silica gel-supported permanganate, but in
this case the reagent was only used for the oxidation of
alcohols to aldehydes: Jazzaa, A. A.; Clark, J. H.; Robertson,
M. Chem. Lett. 1982, 405.
(5) It was reported that oxidation of aldehydes with potassium
permanganate in the presence of potassium dihydrogen
phosphate gave carboxylic acids in excellent yields. The
buffering agent was used to accelerate the reaction rate by
making the system slightly acidic: Abiko, A.; Roberts, J. C.;
Takemasa, T.; Masamune, S. Tetrahedron Lett. 1986, 27,
4537.
(6) Typical procedure for oxidation of an aldehyde with PB-
SiO2-KMnO4; Procedure A: To a solution of an aldehyde
(0.50 mmol) in cyclohexane (10 mL) was added PB-SiO2-
KMnO4 (0.75 g, 0.75 mmol). The mixture was stirred at
65°C for 20 h. After cooling, Na2S2O3 (0.50 mmol) was
added. The mixture was stirred at r.t. overnight and filtered
through a short pad of silica gel. The precipitate was washed
with hexane-ether (5:1), and suspended again in 10%
MeOH-CHCl3 (5.0 mL). 2 M HCl–ether (2.0 mL) was
added. After stirring for 1 h at r.t., the mixture was filtered
and extracted with 10% MeOH–CHCl3 (20 mL). The filtrate
and the extracts were combined and concentrated in vacuo to
give the product. Procedure B: To a solution of an aldehyde
(0.25 mmol) in cyclohexane (5.0 mL) was added PB-SiO2-
KMnO4 (0.38 g, 0.38 mmol). The mixture was stirred at r.t.
for 3–16 h. Na2S2O3 (0.5 mmol) was added. The mixture was
stirred at r.t. for 1 h, and filtered through a short pad of silica
gel (0.5 g). The precipitate was washed with hexane (5.0
mL), and suspended in 10% MeOH–CHCl3 (5.0 mL).
NH4Cl (1.0 mmol) was added. The mixture was stirred for
0.5 h at r.t., filtered and the precipitate was extracted with
10% MeOH–CHCl3 (20 mL). Removal of the solvent gave
the product.
1
2
3
4
5
6
7
8
9
PhCHO
A: 99%, D: 89%
A: quant, D: 90%
A: 96%, D: 92%
A: 68%, D: 98%
A: 61%, D: 93%
A: quant, C: 89%
A: quant, C: 84%
A: quant, C: 90%
4-Me-PhCHO
4-Me-PhCHO
4-allyloxy-PhCHO
4-BnO-PhCHO
4-NO2-PhCHO
4-NC-PhCHO
4-MeO2C-PhCHO
Bd,
D: 93%
CHO
Ph
10
11
12
13
14
15
B: 84%c, C: 84%
B: 92%, C: 88%
B: 58%, C: 83%
B: 90%, C: 86%
B: 90%, C: 89%
B: 96%, C: 87%
CHO
Ph
CHO
CHO
TBSO
BnO
THPO
BocHN
CHO
CHO
CHO
CbzHN
16
B: 77%, C: 89%
O
O
CHO
CHO
17
18
B: 99%, C: 91%
AcO
AcO
O
(7) (a) Lindgren, B. O. T.; Nilsson, T. Acta Chem. Scand. 1973,
27, 888. (b) Kraus, G. A.; Taschner, M. J. J. Org. Chem.
1980, 45, 1175. (c) Bal, B. S.; Childers-Jr, W. E.; Pinnick,
H. W. Tetrahedron 1981, 37, 2091. (d) Isobe, M.; Ichikawa,
Y.; Goto, T. Tetrahedron Lett. 1986, 27, 963. (e) Isobe, M.;
Ichikawa, Y.; Bai, D.-L.; Masaki, H.; Goto, T. Tetrahedron
1987, 43, 4767.
Be,
C: 89%
CHO
a A: PB-SiO2-KMnO4 in cyclohexane at 65 °C; B: PB-SiO2-KMnO4
in cyclohexane at r.t.; C: PS-chlorite, KH2PO4, 2-methyl-but-2-ene in
t-BuOH-H2O (5:1); D: PS-chlorite, AcOH, 2-methyl-but-2-ene in t-
BuOH.
(8) Preparation of PS-chlorite: Polymer-supported chloride
(Fluka, <4mmol/g, 10 g) was washed with water (500 mL).
The resin was added to sodium chlorite solution (2.0 M, 100
mL) and shaken at 25°C for 24 h. The resin was collected by
filtration, and washed with water (50 mL 2), THF (50 mL
2) and Et2O (50 mL 2)to obtain 18.6 g of PS-chlorite.
(9) Typical procedure for oxidation of an aldehyde with PS-
chlorite; Procedure C: To a solution of an aldehyde (0.5
mmol) in t-BuOH (2.5 mL) and H2O (0.5 mL) were added
KH2PO4 (1.0 mmol), 2-methyl-but-2-ene (2.5 mmol), and
then PS-chlorite (1.0 mmol). The mixture was stirred at
25°C for 10 h, and filtered through a short pad of silica gel.
The residual resin was washed with ethyl acetate. The
combined filtrate was evaporated in vacuo and the product
was directly analysed by 1H NMR spectroscopy. Procedure
D: To a solution of an aldehyde (0.5 mmol)in t-BuOH (3.0
mL) were added AcOH (1.0 mmol), 2-methyl-but-2-ene (2.5
mmol), and then PS-chlorite (1.0 mmol). The mixture was
stirred at 25°C for 10 h, and filtered through a short pad of
silica gel and the residual resin was washed with ethyl
acetate. The combined filtrate was evaporated in vacuo and
the product was directly analysed by 1H NMR spectroscopy.
b Isolated yield.
c Benzylic oxidation products were obtained.
d Target molecule was not observed.
e Product decomposed during work-up.
Acknowledgement
We are grateful to the BP endowment and the Novartis Research
Fellowship for their financial support (to SVL).
References and Notes
(1) Ley, S. V.; Baxendale, I. R.; Bream, R. N.; Jackson, P. S.;
Leach, A. G.; Longbottom, D. A.; Nesi, M.; Scott, J. S.;
Storer, R. I.; Taylor, S. J. J. Chem. Soc., Perkin Trans 1
2000, 3815; and references therein.
(2) (a) Deshmukh, J. G.; Jagdale, M. H.; Mane, R. B.; Salunkhe,
M. M.; Wadgaonkar, P. P. Eur. Polym. J. 1987, 23, 577.
(b) Tamami, B.; Zarchi, M. A. K. Eur. Polym. J. 1995, 31,
715.
Synlett 2001, No. 10, 1555–1556 ISSN 0936-5214 © Thieme Stuttgart · New York