Communication
Table 3. α-Alkylation of ketones with benzyl alcohols.[a]
Although syntheses using homogeneous asymmetric cata-
lysts have become significant in industry, recyclable heteroge-
neous asymmetric catalysts have not yet been used. We believe
that any reaction involving a catalyst in which metallic nanopar-
ticles are loaded onto natural asymmetric ligands (e.g., chitin,
chitosan) is possible. Indeed, asymmetric reactions in the pres-
ence of homogeneous ruthenium–chitosan catalysts have been
reported.[17]
Experimental Section
Typical Procedure for the Preparation of the Palladium/Chitin
Catalyst: A suspension of Pd(OAc)2 (63.5 mg, 0.28 mmol) and chitin
powder (0.52 g) in methanol (25 mL) was stirred at room tempera-
ture under nitrogen for 3 d. The product was collected by filtration,
washed with methanol and ethyl acetate, and then dried to obtain
the 5 % Pd/chitin catalyst in quantitative yield.
Typical Procedure for the Palladium-Catalyzed α-Alkylation Re-
action of Ketones with Alcohols: 2-Pentanone (1.14 g, 10 mmol)
was added to a suspension of 5 % Pd/chitin (106 mg, 0.05 mmol),
(3,4-dimethoxyphenyl)methanol (0.42 g, 2.5 mmol), and K3PO4
(7.5 mmol) in toluene (5.0 mL) in a 50 mL reaction tube. The suspen-
sion was heated at 80 °C under nitrogen for 24 h. The reaction
mixture was cooled to room temperature, and the resulting mixture
was concentrated. The residue was purified by silica gel column
chromatography (hexane/ethyl acetate, 8:1) to afford 1-(3,4-di-
methoxyphenyl)octan-3-one (8d) in 90 % yield (0.59 g).
Acknowledgments
The authors are grateful to Mr. S. Tokuda for his help in install-
ing and operating the TEM system. We would like to thank Edit-
Keywords: Chitin · Phytochemistry · Raspberry ketone ·
Paradol · Heterogeneous catalysis · Hydrogen borrowing ·
C–C coupling
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chitin and Pd/chitosan catalysts were prepared from Pd(OAc)2 using
chitin and chitosan, respectively, in a manner similar to that reported for
Pd/Fib (see above).
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[8] A classical method for the preparation of raspberry ketone through the
reaction of phenol with either 4-hydroxy-2-butanone or 3-butene-2-one
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[a] The coupling reaction between each benzyl alcohol (2.5 mmol) and ket-
one (10 mmol) was performed in the presence of 5 % Pd/chitin catalyst
(2 mol-%) and K3PO4 (7.5 mmol) in xylene (10 mL) under N2 at the indicated
temperature for 24 h. [b] Determined by GLC analysis based on benzyl alco-
hols [product/(alcohol + product) × 100]. Isolated yields are shown in paren-
theses. [c] The coupling reaction was performed in a 100 mL autoclave for
5 d. Since the Pd/chitin activity was low (12 % yield of 13, 43 % yield of
unknown byproduct), Pd/C (1 mol-%) was used as a catalyst. [d] 5 % Ir/chitin
(2 mol-%) was used instead of 5 % Pd/chitin.
Eur. J. Org. Chem. 2017, 7295–7299
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