Rapid conversion of spirostans into furostan skeletons at room temperature

We report a facile protocol to obtain 22-substituted furostans and pseudosapogenins in high yields from (25R)- and (25S)-sapogenins. This method involves the treatment of the sapogenin with acetic–trifluoroacetic mixed anhydride and BF3·OEt2 at room temperature, followed by the addition of a nucleophile (H2O, MeOH or KSeCN). In the case of 22-hydroxyfurostans, they can be transformed to pseudosapogenins by treatment with p-toluensulfonic acid.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis of 22-substituted-furostane steroids at room temperature. ► One pot synthesis of (25R)- and (25S)-22-substituted-furostans. ► Fast synthesis of pseudosapogenins using soft conditions. ► New application of the acetic–trifluoroacetic mixed anhydride.