text: The C1, C2 and C4 functional groups were put in place next and starting from oxetane 5.1 (scheme 5) the MOM protecting group is removed in 5.2 (PPTS) and replaced by a TES group TESCl) in 5.3. The acetal group was removed in 5.4 (hydrogenation PdOH, H) and replaced by a carbonate ester group in 5.5 (triphosgene, pyridine). The tertiary alcohol group was acetylated in 5.6 and in the final step the carbonate group was opened by reaction with phenyllithium to the hydroxyester 5.7.
  Prior to tail addition the TES protective group was removed in 5.8 (hydrogen fluoride pyridine) and replaced by a TROC (trichloroethyl carbonate, TROCCl ) group in 5.9. The C13 alcohol protective group was removed in 5.10 (TASF) enabling the tail addition of Ojima lactam 5.11 (this step is common with all total synthetic efforts to date) to 5.12 with Lithium bis(trimethylsilyl)amide. The synthesis was completed with TROC removal (zinc, acetic acid) to taxol 5.13.