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

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

References

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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).