Constructing Quaternary Stereogenic Centers Using Tertiary Organocuprates and Tertiary Radicals. Total Synthesis of <i>trans</i>-Clerodane Natural Products

A new concise construction of <i>trans</i>-clerodane diterpenoids is reported in which oxacyclic and <i>trans</i>-hydronaphthalene fragments are coupled, and the critical C9-quaternary carbon stereocenter formed stereoselectively, by 1,6-addition of a tertiary cuprate or a tertiary carbon radical to β-vinylbutenolide. This strategy is specifically illustrated by total syntheses of (−)-solidagolactone (<b>4</b>), (−)-16-hydroxycleroda-3,13-dien-15,16-olide (<b>5</b>, PL3), and (−)-annonene (<b>6</b>)