Synlett 2003(5): 0723-0725
DOI: 10.1055/s-2003-38373
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Facile and Efficient Oxidative Transformation of Primary Alcohols to Methyl Esters in Water Using Hypervalent Iodine(III) Reagents

Hirofumi Tohma, Tomohiro Maegawa, Yasuyuki Kita*
Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamada-oka, Suita, Osaka, 565-0871, Japan
Fax: +81(6)68798229; e-Mail: kita@phs.osaka-u.ac.jp;
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Publikationsverlauf

Received 9 January 2003
Publikationsdatum:
28. März 2003 (online)

Abstract

A facile and direct oxidative esterification of primary alcohols in water using a combination of the hypervalent iodine(III) reagent, iodosobenzene (PhIO), and KBr has been developed. This methodology is expected to be environmentally benign since it uses a recyclable polymer-supported iodine(III) reagent in water.

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Among the typical hypervalent iodine(III or V) reagents, PhIO gave the best yield [75% yield], while other reagents such as phenyliodine diacetate (PIDA) [47% yield], phenyliodine bis(trifluoroacetate) (PIFA) [40% yield], Dess-Martin periodinane [trace], and o-iodoxybenzoic acid [trace], were also examined under the reaction conditions described in Table [1] .

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General Experimental Procedure: Oxidation with PhIO-KBr: To a stirred solution of 1 (1.0 mmol) and KBr (0.5 mmol) in MeOH (1 mL) was added dropwise 0.5 N HCl aq (0.5 mL). PhIO (3.5 mmol) was added to the vigorously stirred solution and stirring was continued for several hours at room temperature while checking the reaction progress by GC or TLC. After completion of the reaction, water (ca. 1.5 mL) was added to the mixture. The mixture was filtrated through BOND ELUT C 18 (Varian), washed with a small amount of water, and extracted with Et2O. The filtrate was dried with MgSO4, and evaporated. The residue was purified by column chromatography (SiO2/n-hexane-Et2O) to give pure 2. Oxidation with PDAIS-KBr: To a stirred solution of 1 (1.0 mmol) and KBr (1.0 mmol) in MeOH (2 mL) was added dropwise 0.5 N HCl aq (1 mL). PDAIS (prepared by the reported procedure [9b] ) (3.0 mmol) was added to the vigorously stirred solution and stirring was continued for several hours at room temperature. After completion of the reaction, water (ca. 3 mL) was added to the mixture. The mixture was filtered through BOND ELUT C 18 (Varian) and washed with a small amount of water to remove KBr. The residue was extracted with Et2O, and the filtrate was dried and evaporated. The residue was purified by column chromatography to give pure 2.