US9522922: Stereospecific and proficient synthesis of seven membered sulfide: its application for tamiflu synthesis

The invention discloses an economic, simple, azide and aziridine complexity free process for the synthesis of osletamivir phosphate (Tamiflu) by stereospecific amidoalkylation of imidazothiazolone from easily available L-cysteine via Ramberg-Backlund reaction and Sharpless-Reich protocol.