Constructing quaternary stereogenic centers using tertiary organocuprates and tertiary radicals. Total synthesis of trans-clerodane natural products.

A new concise construction of trans-clerodane diterpenoids is reported in which oxacyclic and trans-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 (4), (-)-16-hydroxycleroda-3,13-dien-15,16-olide (5, PL3), and (-)-annonene (6).