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Synlett 2009(2): 245-248  
DOI: 10.1055/s-0028-1087674
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Aerobic Oxygenation of Benzylic Ketones Promoted by a Gold Nanocluster Catalyst

Hidehiro Sakurai*a-c, Ikuyo Kamiyaa, Hiroaki Kitaharab, Hironori Tsunoyamad, Tatsuya Tsukudad,e
a Research Center for Molecular Scale Nanoscience, Institute for Molecular Science, Myodaiji, Okazaki 444-8787, Japan
Fax: +81(564)595527; e-Mail: hsakurai@ims.ac.jp;
b Department of Functional Molecular Science, The Graduate University for Advanced Studies, Myodaiji, Okazaki 444-8787, Japan
c PRESTO, Japan Science and Technology Agency, Tokyo 102-0075, Japan
d Catalysis Research Center, Hokkaido Univsersity, Nishi 10, Kita 21, Kita-ku, Sapporo 001-0021, Japan
e CREST, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan
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Publication History

Received 27 September 2008
Publication Date:
15 January 2009 (online)

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Abstract

Gold nanoclusters stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP) promote the oxidation of benzylic ketones, including auto-oxidation-type bond-cleavage reactions and α-hydroxylation, under ambient conditions. The catalyst accelerates the formation of an α-peroxide intermediate, from which bond cleavage spontaneously proceeds in aqueous solvent to give the auto-oxidation products. In contrast, the α-hydroxylation product is obtained predominantly in DMSO solvent.

Key words

gold nanocluster - auto-oxidation - α-hydroxylation

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9

General Procedure for Auto-Oxidation-Type Reaction of Compound 1 Catalyzed by Au:PVP under DBU/H 2 O-MeCN Conditions
A test tube (ϕ = 30 mm) was placed with 1 (0.10 mmol), DBU (30 µL, 0.20 mmol), and MeCN (3 mL). The aq soln of Au:PVP (0.5 mM, 6 mL = 3 atom%) was added and the reaction mixture was stirred vigorously (1300 rpm) at 27 ˚C or 50 ˚C for the time specified. The reaction mixture was quenched with 1 M HCl (2 mL) solution, extracted with MTBE (3 × 10 mL), and then the combined organic layers were washed with brine, dried over Na2SO4, and concentrated in vacuo. The crude products were separated by PTLC (Wakogel BF-5) or GPC, giving 2 and 3.

12

General Procedure for α-Hydroxylation of Compound 1 Catalyzed by Au:PVP under NaOAc/DMSO Conditions
A test tube (ϕ = 30 mm) was placed with 1 (0.1 mmol), NaOAc (8.2 mg, 0.10 mmol), and dried Au:PVP (22.9 mg, 3 atom%). DMSO (6 mL) was added, and the reaction mixture was stirred vigorously (1300 rpm) at 27 ˚C or 50 ˚C for the time specified. The reaction mixture was extracted with EtOAc and then the combined organic layers were washed with brine, dried over Na2SO4, and concentrated in vacuo. Purification of the product was carried out by PTLC or GPC.
Compound 3b: colorless oil. IR (neat): ν = 3445, 1710, 1608, 1509, 1254 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 2.25 (s, 3 H), 3.81 (s, 3 H), 4.79 (s, 1 H), 6.88-6.90 (m, 2 H), 7.25-7.28 (m, 2 H), 7.35-7.38 (m, 5 H) ppm. ¹³C NMR (100 MHz, CDCl3): δ = 208.76, 159.40, 141.41, 133.32, 129.35, 128.43, 128.16, 128.03, 113.80, 85.33, 55.29, 26.07 ppm. Anal. Calcd for C16H16O3: C, 74.98; H, 6.29; Found: C, 74.71; H, 6.37.