Scheme 3.

Reagents and conditions: (a) lipase (CAL), vinyl acetate, MS4A, THF, 60 °C, 89%; (b) TBSCl, DMAP, pyr–DMF, rt, 94%; (c) PvCl, Et₃N, CH₂Cl₂, rt, and then DMAP, MeOH, rt; (d) K₂CO₃, MeOH, 0 °C, 98% from 34; (e) BnBr, ^tBuOK, THF, 0 °C, 97%: (f) K₂CO₃, MeOH, rt, 76%, (g) ^tBuONO, Et₄NCl, CCl₄–CH₂Cl₂, 0–50 °C (h) TBAF, AcOH, THF, rt, 34% from 38; (i) allyl bromide, ^tBuOK, THF, 0 °C; (j) K₂CO₃, MeOH, rt, 73% from 36; (k) ^tBuONO, Et₄NCl, CCl₄–CH₂Cl₂, 0–50 °C (l) TBAF, AcOH, THF, rt, 28% from 41.