Yeast benzaldehyde reaction with acetaldehyde

A very ingenious direct synthesis of i-ephedrine, avoiding the laborious resolution of the racemic mixture, has been devised by Hildebrandt and Klavehn (271) and described by Kamlet (272). Neuberg and Hirsch (273) in 1921 demonstrated that when equal mols of acetaldehyde and benzaldehyde are added to a carbohydrate solution actively fermenting by yeast, levorotatory l-phenyl-2-ketopropanol-l, C H5-CH(OH)CO-CHi, is formed. This compound on reaction with methylamine and catalytic reduction yields 1-ephedrine directly. 

---