Nie et al. have reported both a 13-step synthesis (DOI) they were not happy about and then a shorter 7-step synthesis (DOI) both starting from shikimic acid (harvested from Chinese star anise 3.6% yield). The synthetic plans are very similar both using sodium azide (use discouraged due to hazardous nature). The 7-step plan starts from the ethyl ester of shikimic acid with all hydroxyl groups mesylated in step one. First substitution by NaN3 is followed by ring-closure to the aziridine. Acylation, ring re-opening by 3-pentanol and seconds azide attack take place next, concluded by Lindlar catalyst reduction. The authors claim 45% yield based on shikimic acid.
Oshitari & Mandai produced a double-header with synthetic schemes for oseltamivir, one starting from L-Methionine (DOI) and another from D-mannitol (DOI). Too bad the journal they elected to have their work published in (Synlett) is utterly inaccessible.