Abstract
The effects of 5-substituents on sodium borohydride reduction of flavanonols have been examined. The bulk of substituents governs the stereochemistry of reduction, and particularly, the acetoxy group gives an interesting result accompanied by over-reduction. In addition, the 5-acetoxy group plays an improtant role in the stereochemistry of the newly introduced 4-oxygen functions in hydrolysis of (±)-fistacacidin acetates.