Scheme 21.

Synthesis of compound 140 and coupling of fragments to furnish RvT2 (27) [71]. Reagents and conditions: (i) methyl (triphenylphosphoranylidene)acetate, benzoic acid, 1,4-dioxane, reflux; (ii) acetone/2,2-dimethoxypropane (2/1), p-toluenesulfonic acid, rt; (iii) amberlyst^® 15, MeOH/H₂O 9/1, rt; (iv) NaIO₄, CH₃OH/H₂O 10/4, 0 °C to rt; (v) (triphenylphosphoranylidene)acetaldehyde, benzene, rt; (vi) 67, n-BuLi, THF, −78 °C to −20 °C; (vii) DIBAL-H, CH₂Cl₂, −78 °C to −20 °C; (viii) CBr₄, Ph₃P, CH₂Cl₂, 0 °C; (ix) Ph₃P, CH₂Cl₂, 0 °C to rt; (x) 132, KHMDS, THF, −78 °C to −20 °C; (xi) 2 N HCl, MeOH, 0 °C to rt, 76%; (xii) 1 N LiOH, MeOH/H₂O 2/1, 0 °C to rt.