Scheme 4.

Reagents and conditions: a) EDC⋅HCl, NEt₃, DMAP; b) LiHMDS, NEt₃, PhMe, −78 °C→RT; then 5 % NaOH; then conc. HCl; c) TMSCHN₂, MeOH/PhMe, 0 °C→RT; d) DIBALH, CH₂Cl₂, −78 °C→RT; e) DMP, NaHCO₃, CH₂Cl₂; f) NaHMDS, [Ph₃PCH₂I]I, THF, −78 °C→RT; NaHMDS, −78 °C→RT; g) LiHMDS, THF, −78 °C; BnMe₂SiCl, −78 °C to RT, 88 %; h) DDQ, CH₂Cl₂; i) DMP, NaHCO₃, CH₂Cl₂; j) CBr₄, PPh₃, CH₂Cl₂, 0 °C; then 50, NEt₃, −30 °C→0 °C; k) nBuLi, THF, −78 °C→RT. DDQ=2,3‐Dichloro‐5,6‐dicyano‐1,4‐benzoquinone; DMP=Dess–Martin periodinane; EDC=1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide.