An Improved Synthesis of Methyl Protodioscin: Tautomerization and Direct Access to the 3-O-Substituted Kryptogenin
The acid-catalyzed tautomerization of 3-0-substituted kryptogenin 2 was studied, and the effects of acids such as silica gel, TMSOTf, acetic acid, and CDCl 3 , are discussed. Additionally, a Zn/KI/HOAc reduction based on this tautomerization was adopted, which afforded 2 directly, and provided a facile procedure for the synthesis of methyl protodioscin and other furostanol saponins in a mild way.