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Synlett 2011(19): 2896-2900  
DOI: 10.1055/s-0031-1289891
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Catalytic Oxidative Cleavage of 1,3-Diketones to Carboxylic Acids by Aerobic Photooxidation with Iodine

Norihiro Tada, Motoki Shomura, Lei Cui, Tomoya Nobuta, Tsuyoshi Miura, Akichika Itoh*
Gifu Pharmaceutical University, 1-25-4, Daigaku-nishi, Gifu 501-1196, Japan
Fax: +81(58)2308105; e-Mail: itoha@gifu-pu.ac.jp;
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Publication History

Received 29 August 2011
Publication Date:
11 November 2011 (online)

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Abstract

We report the catalytic oxidative cleavage of 1,3-diketones to the corresponding carboxylic acids by aerobic photooxidation with iodine under irradiation with a high-pressure mercury lamp.

Key words

photooxidation - aerobic - iodine - 1,3-diketone - carboxylic acid

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Typical Procedure
A solution of benzoylacetone (1, 0.3 mmol) and I2 (0.03 mmol) in dry EtOAc (5 mL) in a Pyrex test tube, purged with an O2 balloon, was stirred and irradiated externally with 400 W high-pressure mercury lamp for 10 h. The reaction mixture was concentrated under reduced pressure. The pure product 2 was obtained by preparative TLC.

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These compounds were identified by comparison with authentic samples, and yields were determined by ¹H NMR with internal standard.

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Benzil(27) was obtained as major product in the presence of 0.5 equiv of Ca(OH)2 under visible-light irradiation. See ref. 3f.

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Since the reaction did not proceed when using methylene blue, a singlet-state molecular oxygen generator, instead of iodine, singlet-state molecular oxygen is probably not an active species for this reaction.