Second-generation synthesis of a chiral building block for oxygenated terpenoids via a ring-contractive coupling with a secondary alcohol

A much improved second-generation synthesis of a chiral building block, developed for the syntheses of C17-oxygenated steroids/triterpenoids and C9-oxygenated labdane diterpenoids, was accomplished by exploiting a ring-contractive coupling between an α-bromo-δ-valerolactone and (R)-seudenol, wherein the use of t-BuOK as a base allowed clean conversion to the corresponding tetrahydrofuran-2-carboxylate even with a small excess of the alcohol component.