Enediols are formed by treating the sugars with

In carbohydrate chemistry, the Lobry de Bruyn-van Ekenstein transformation also known as the Lobry de Bruyn-Alberda-van Ekenstein transformation is the base or acid catalyzed the transformation of an aldose into the ketose isomer or vice versa, with a tautomeric enediol as a reaction intermediate. Ketoses may be transformed into 3-ketoses, etcetera. The enediol is also an intermediate for the epimerization of an aldose or ketose.Mild alkaline conditions, Aldehyde or keto groups will tautomerize to form enediols.Enediols are highly reactive. So sugars are powerful reducing agents in alkaline condition.Ref: Harper&;s Biochemistry; 30th edition