US Patent 7687658 Process for oseltamivir phosphate

The present invention provides an improved and commercially viable process for the preparation of oseltamivir phosphate. Thus, for example, ethyl (3R,4R,5S)-4-amino-5-azido-3-(1-ethylpropoxy)-1-cyclohexene-1-carboxylate is acetylated with acetic anhydride in methylene chloride in the presence of triethyl amine in the absence of water to give ethyl (3R,4R,5S)-4-(acetylamino)-5-azido-3-(1-ethylpropoxy)-1-cyclohexene-1-carboxylate.