Sodium-potassium alloy ester reduction

Another important coupling reaction uses esters as the electron-accepting species and leads to a-hydroxy ketones (acyloin coupling). Sodium, potassium (less frequently) or sodium-potassium alloys are commonly used as electron donors in nonpolar solvents such as toluene or xylene. The first detectable reaction intermediate after the primary reductive step is the enediolate which can be trapped with tri-alkylsilyl chloride. This method is widely used to synthesize highly nucleophilic alkenes and/or protected acyloins (Scheme 12) [50, 51]. 

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