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

Satoshi Kikuchi; Yukihiko Hashimoto

doi:10.1055/s-2004-825581

LETTER

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;

Abstract

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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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References

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

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.

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).