Total syntheses of seven stemoamide-type Stemona alkaloids

Six Stemona alkaloids were synthesized racemically using stemoamide, obtained via a cascade cyclization or our reported transannular cyclization of parvistemoamide, as the common intermediate. Thioamides facilitated the separation of isosaxorumamide and saxorumamide, and promoted the first syntheses of other four N-oxide or pyrrolidine bearing Stemona alkaloids via chemoselective reduction and oxidation.