text: In 2006 the group of E.J. Corey published a novel route bypassing shikimic acid starting from butadiene and acrylic acid. The inventors chose not to patent this procedure which is described below.
  Butadiene 1 reacts in an asymmetric Diels-Alder reaction with the esterification product of acrylic acid and 2,2,2-trifluoroethanol 2 catalysed by the CBS catalyst. The ester 3 is converted into an amide in 4 by reaction with ammonia and the next step to lactam 5 is an iodolactamization with iodine initiated by trimethylsilyltriflate. The amide group is fitted with a BOC protecting group by reaction with Boc anhydride in 6 and the iodine substituent is removed in an  elimination reaction with DBU to the alkene 7. Bromine is introduced in 8 by an allylic bromination with NBS and the amide group is cleaved with ethanol and caesium carbonate accompanied by elimination of bromide to the diene ethyl ester 9. The newly formed double bond is functionalized with N-bromoacetamide 10 catalyzed with
  tin(IV) bromide with complete control of stereochemistry. In the next step the bromine atom in 11 is displaced by the nitrogen atom in the amide group with the strong base KHMDS to the aziridine 12 which in turn is opened by reaction with 3-pentanol 13 to the ether 14. In the final step the BOC group is removed with phosphoric acid and the oseltamivir phosphate 15 is formed.