Stereoselective total synthesis of obolactones and 7′,8′-dihydroobolactones

Abstract

A concise stereoselective total synthesis of two diastereomeric obolactones and 7′,8′-dihydroobolactones has been achieved using a metal-free catalytic δ-hydroxyalkynone rearrangement, which could provide the required dihydro-γ-pyrone moiety. The desired first stereogenic center was installed through the chiral pool material, L-aspartic acid. Next, the allylation reaction was strategically utilized to provide the requisite olefin bond for the intended ring-closing metathesis, allowing the installation of the remaining dihydro-α-pyrone moiety in the natural products. It also enabled the targeting of both dihydro-α-pyrone diastereomers. Thus, the first stereoselective total synthesis of (+)-7′,8′-dihydroobolactone was accomplished, establishing its structure and absolute configuration.