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Synlett 2002(12): 2031-2034
DOI: 10.1055/s-2002-35596
LETTER
© Georg Thieme Verlag Stuttgart · New York

Oxidation of Amines and Sulfides Catalyzed by an Assembled Complex of Phosphotungstate and Non-Cross-Linked Amphiphilic Polymer

Yoichi M. A. Yamada, Hidetsugu Tabata, Hideyo Takahashi, Shiro Ikegami*
Faculty of Pharmaceutical Sciences, Teikyo University, Sagamiko, Kanagawa 199-0195, Japan
Fax: +81(42)6853728; e-Mail: shi-ike@pharm.teikyo-u.ac.jp;
Further Information

Publication History

Received 24 September 2002
Publication Date:
20 November 2002 (online)

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Abstract

Oxidation of sulfides and amines was performed with an assembled catalyst of phosphotungstate and non-cross-linked amphiphilic polymer. The reactions proceeded with hydrogen peroxide under organic solvent-free conditions. This insoluble catalyst was reused five times with the turnover number up to 500.

Key word

polymers - tungsten - oxidation - amines - sulfides

6

General Procedure for the oxidation of amines catalyzed by catalyst 1: To a suspension of 1 [5a] (40 mg; 5 mmol) and 2 (2.52 mmol) was added 2.5% H2O2 aqueous solution (7.56 mmol) dropwise for 50 min at 0 °C (entry 3: added dropwise at r.t.; entry 5: added one portion at r.t.). The mixture was stirred at room temperature (entry 5: 40 °C; entry 7: 0 °C) for 3-24 h, before it was diluted with EtOAc and filtered through a glass filter. Brine was added to the filtrate, and it was extracted with EtOAc (× 3). The extract was washed with brine, dried over Na2SO4, filtered, dried in vacuo, and purified by column chromatography to give 3.

9

The reaction of 2c was performed in CH2Cl2 (0.25 M) at room temperature for 95 h, providing 3c and 3c′ in 95% yield (3c/3c′ = 1.76:1). Even in the reaction of 3c or 3c′ with CH2Cl2, isomerizations were hardly observed.

10

General procedure for the oxidation of sulfides to sulfones catalyzed by catalyst 1: The mixture of 1, 4 and 35-40% H2O2 aqueous solution was shaken by PetiSyther ® (Shimadzu Scientific Research Inc. Japan) at 700 rpm at 50 °C for 4-7 h, it was diluted with EtOAc and filtered. To the filtrate was added saturated Na2S2O3 and brine, and it was extracted with EtOAc (× 3), dried over Na2SO4, filtered, dried in vacuo, and purified by column chromatography to give the products. While the shaker (PetiSyther ®) for solid-phase syntheses was used in these reactions, the glassware vessel equipped with a magnetic stirrer can be also used.

12

The reaction with 2.5% H2O2 proceeded slower (55 h) than that with 35-40% H2O2, providing sulfone 6a in 95% yield.

13

Noyori et al. reported that the oxidation of sulfides to sulfoxides proceeded efficiently in hydrogen peroxide without catalysts, so that we have not examined the selective oxidation to sulfoxide. See ref. [11h]