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Synlett 2011(10): 1381-1384  
DOI: 10.1055/s-0030-1260585
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Direct Synthesis of α-Keto Esters from Ethylbenzenes Using 48% Aqueous HBr by Aerobic Visible Light Photooxidation

Norihiro Tada, Kazunori Ban, Tomoya Nobuta, Shin-ichi Hirashima, 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;
Further Information

Publication History

Received 7 February 2011
Publication Date:
26 May 2011 (online)

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Abstract

We report that ethylbenzenes can be directly oxidized to the corresponding α-keto esters with molecular oxygen in the presence of 48% aqueous HBr under visible light irradiation. This synthetic procedure is the first example for direct preparation of the corresponding α-keto esters from ethylbenzenes.

Key words

photooxidation - HBr - aerobic - ethylbenzene - α-keto ester

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15

When 48% aq HBr (1.2 equiv) and H2O (100 µL) were used as additive, ethylbenzene 1d was converted into α-bromo-acetophenone (3d) in 68% yield.¹4

16

Typical Procedure: An anhyd EtOAc solution (5 mL) of ethylbenzenes (0.3 mmol) and 48% aq HBr (0.75 mmol) in a pyrex test tube equipped with an O2 balloon was stirred and irradiated with four 22-W fluorescent lamps, which were set up at a distance of 65 mm, for 20 h. The temperature of the final stage of this reaction was about 40 ˚C. The reaction mixture was concentrated under reduced pressure, and the pure product was obtained by purification with preparative TLC.