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Synlett 2004(7): 1267-1269  
DOI: 10.1055/s-2004-825581
LETTER
© Georg Thieme Verlag Stuttgart · New York

Reduction of 1,2-Dicarbonyl Compounds Mediated by the Combination of Phosphine and Lewis Acid

Satoshi Kikuchi, Yukihiko Hashimoto*
Department of Chemistry and Biotechnology, School of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
Fax: +81(3)58417281; e-Mail: hashimoto@chiral.t.u-tokyo.ac.jp;
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Publikationsverlauf

Received 3 February 2004
Publikationsdatum:
10. Mai 2004 (online)

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Abstract

The combination of Ph3P/AlBr3 effectively promoted the reduction of several 1,2-dicarbonyl compounds in the presence of water (1.0 equiv) and the corresponding α-hydroxy carbonyl compounds were obtained in good yields.

Key words

phosphorus - phosphine - Lewis acid - reduction - 1,2-dicarbonyl compounds

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4

Other phosphines, such as n-Bu3P, (o-tolyl)3P, were also examined, but Ph3P gave the best result.

5

Although the generation of HBr was assumed under these conditions, it seemed that it was not involved in the reaction because the reduction did not proceed when Ph3P and HBr were used instead of Ph3P and AlBr3.

6

Typical Procedure for Reduction of Benzil (Table [2] , Entry 1) : Under an argon atmosphere to a solution of AlBr3 (183.2 mg, 0.69 mmol) and benzil (103.6 mg, 0.49 mmol) in CH3CN (1 mL), which was stirred for 15 min, was added water (9 µL, 0.55 mmol). After 1 h, a solution of Ph3P (180.5 mg, 0.69 mmol) in CH3CN (2 mL) was added and stirred for 24 h. The reaction was quenched with 1 N aq HCl and the mixture was extracted with Et2O (5 × 10 mL). The combined organic layer was dried over MgSO4. This organic layer was filtered and evaporated under reduced pressure, and then the crude product was purified by preparative TLC (SiO2, CH2Cl2) to give benzoin (101.5 mg, 98% yield).