complexation.6 Previously Yamada and co-workers reported
preliminary studies on a convoluted polymeric tungstate
catalyst, (isopropylacrylamide)polymer-supported phospho-
tungstate 1, for the oxidation of alcohols; however, the
catalytic activity was insufficient7 and the heterogeneous
catalyst became emulsive during the reaction, presumably
due to its physical fragility, resulting in low recyclability.8
To overcome these drawbacks, we recently developed a
tightly convoluted polymeric catalyst 2 of main-chain poly-
pyridinium and phosphotungstate that exhibited high catalytic
activity and recyclability for the oxidative cyclization of
alkenols and alkenoic acids and sulfide oxidation.9 As part
of our effort to demonstrate the wide utility of the catalyst
system, we decided to examine alcohol oxidation with H2O2
with the polypyridinium-phosphotungstate catalyst system.3,4
Here we report our results, namely that aliphatic alcohols
were readily oxidized with aqueous H2O2 in the presence of
a catalytic amount of a convoluted polypyridinium-phos-
photungstate composite bearing an appropriate length of
oxyethylene units to exhibit high catalytic performance,
recyclability, and chemoselectivity with respect to secondary
alcohols.10
Scheme 1
.
H2O2-Oxidation of 2-Decanol with Polymeric
Phosphotungstates
The catalytic ability of the polypyridinium-phosphotung-
states 2-4 was examined for H2O2-oxidation of 2-decanol
(5) (Scheme 1). The polymeric composites 3 and 4 having
three and twelve units of oxyethylene, respectively, were
designed and prepared with a view toward using them in
aqueous reaction media.11,12 The oxidation of 2-decanol was
carried out with 6 mol equiv of H2O2 (30% aqueous H2O2
was used) in t-BuOH at 80 °C for 24 h in the presence of 2
mol % W of the polymeric phosphotungstate catalysts. After
being cooled to ambient temperature, the reaction mixture
was filtered and the filtrate cake was rinsed with EtOAc.
The combined filtrate was dried and concentrated in vacuo
to give the crude residue, which was chromatographed on
silica gel to give 2-decanone.
As can be seen from Scheme 1, where the result obtained
with (isopropylacrylamide)polymer-supported phosphotung-
state 1 is included for comparison, polypyridinium-phos-
photungstate 3 bearing three oxyethylene units was identified
to be the best catalyst in the alcohol oxidation.13 Thus, of
the polypyridinium-phosphotungstates, composite 3 gave
96% isolated yield of 2-decanone (6) while the alkyl-tethered
2 and the deca(oxyethylene)-tethered 4 afforded 6 in 66%
and 56% yield, respectively. Poly(acrylamide)-based com-
posite 1 gave only 6% yield of 6 under similar conditions.
Though it is difficult to rationalize the appropriate length of
the alkyl and oxyethylene tethering units between the
pyridinium groups, fine-tuning of the hydrophobicity/hydro-
philicity of the main chain cationic polymer should be
essential to achieve high performance in the H2O2-oxidation
catalysis.
(6) (a) For a review, see: Yamada, Y. M. A. Chem. Pharm. Bull. 2005,
53, 723. (b) Yamada, Y. M. A.; Watanabe, T.; Torii, K.; Uozumi, Y. Chem.
Commun. 2009, 5594. (c) Yamada, Y. M. A.; Guo, H.; Uozumi, Y. Org.
Lett. 2007, 9, 1501. (d) Yamada, Y. M. A.; Uozumi, Y. Tetrahedron 2007,
63, 8492. (e) Uozumi, Y.; Yamada, Y. M. A.; Beppu, T.; Fukuyama, N.;
Ueno, M.; Kitamori, T. J. Am. Chem. Soc. 2006, 128, 15994. (f) Yamada,
Y. M. A.; Maeda, Y.; Uozumi, Y. Org. Lett. 2006, 8, 4259. (g) Yamada,
Y. M. A.; Uozumi, Y. Org. Lett. 2006, 8, 1375.
(7) Hamamoto, H.; Suzuki, H.; Yamada, Y. M. A.; Tabata, H.;
Takahashi, H.; Ikegami, S. Angew. Chem., Int. Ed. 2005, 44, 4536.
(8) (a) Yamada, Y. M. A.; Ichinohe, M.; Takahashi, H.; Ikegami, S.
Org. Lett. 2001, 3, 1837. (b) Yamada, Y. M. A.; Tabata, H.; Takahashi,
H.; Ikegami, S. Synlett 2002, 2031. (c) Yamada, Y. M. A.; Tabata, H.;
Ichinohe, M.; Takahashi, H.; Ikegami, S. Tetrahedron 2004, 60, 4097.
(9) (a) Yamada, Y. M. A.; Guo, H.; Uozumi, Y. Org. Lett. 2007, 9,
1501. (b) Yamada, Y. M. A.; Guo, H.; Uozumi, Y. Heterocycles 2008, 76,
645. (c) Jin, C. K.; Yamada, Y. M. A.; Uozumi, Y. Bull. Korean Chem.
Soc. 2010, 31, 547.
(10) For a review, see: (a) Arerburn, J. B. Tetrahedron 2001, 57, 9765.
For selected pioneering works, see: (b) Kaneda, K.; Kawanishi, Y.;
Jitaukawa, K.; Teranishi, S. Tetrahedron Lett. 1983, 24, 5009. (c) Tomioka,
H.; Oshima, K.; Nozaki, H. Tetrahedron Lett. 1982, 23, 539. (d) Steven,
R. V.; Chapman, K. T.; Stubbs, C. A.; Tam, W. W.; Albizani, K. F.
Tetrahedron Lett. 1982, 23, 4647. (e) Jung, M. E.; Spelts, M. L. J. Am.
Chem. Soc. 1976, 98, 7882.
(12) For recent typical examples, see: (a) Hirai, Y.; Uozumi, Y. Chem.
Commun. 2010, 46, 1103. (b) Suzuka, T.; Okada, Y.; Ooshiro, K.; Uozumi,
Y. Tetrahedron 2010, 66, 1064. (c) Uozumi, Y.; Matsu-ura, A. T.; Yamada,
Y. M. A. Angew. Chem., Int. Ed. 2009, 48, 2708. (d) Oe, Y.; Uozumi, Y.
AdV. Synth. Catal. 2008, 350, 18771. (e) Uozumi, Y.; Suzuka, T. Synthesis
2008, 1960. (f) Uozumi, Y.; Takenaka, H.; Suzuka, T. Synlett 2008, 1557.
(g) Uozumi, Y.; Suzuka, T. J. Org. Chem. 2006, 71, 8644. (h) Nakai, Y.;
Kimura, T.; Uozumi, Y. Synlett 2006, 3065. (i) Uozumi, Y.; Suzuka, T. J.
Org. Chem. 2006, 71, 8644, and references cited therein. Also see ref 5.
(13) Catalyst 3 (W 60.5 wt %; ICP-AES analysis) was readily prepared
starting with 1,3-di(4-pyridyl)propane and tetraethylene glycol dichloride
(below). Details are provided in the Supporting Information.
(11) We have been aware of the importance of equipping poly(ethylene
oxide) units with polymer-immobilized catalysts to gain high catalytic
activity in aqueous reaction media through our research on polystyrene-
poly(ethylene oxide) (PS-PEG) resin-supported metal catalysts. For reviews,
see: (a) Uozumi, Y. Top. Curr. Chem. 2004, 242, 77. (b) Uozumi, Y.
Heterogeneous Asymmetric Catalysis in Aqueous Media, In the Handbook
of Asymmetric Heterogeneous Catalysis; Ding, K., Uozumi, Y., Eds.; Wiley-
VCH: Weinheim, Germany, 2008; p 209. (c) Uozumi, Y. Bull. Chem. Soc.
Jpn. 2008, 81, 1183. (d) Uozumi, Y.; Yamada, Y. M. A. Chem. Rec. 2009,
9, 51
.
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