Formal Synthesis of (-)-Oseltamivir Phosphate

Abstract

The formal synthesis of (-)-oseltamivir phosphate (Tamiflu (TM)) was accomplished starting from (S)-pyroglutamic acid. The synthesis comprised two carbon-carbon bond forming reactions, the first one being a diastereoselective, indium-mediated allylation of a pyroglutamic aldehyde derivative. However, attempts to effect the second carbon-carbon bond formation - cyclohexene ring closure - using an enol-exo aldolization of a dialdehyde resulted in the formation of a product with the opposite regioselectivity. This shortcoming could be overcome by using a reaction sequence of Mannich methylenation/ring-closing metathesis, which provided the desired regioisomer in high yield.