Total synthesis of (±)-villosin C and (±)-teuvincenone B

Abstract

Herein, we report the first total synthesis of 17(15 → 16)-abeo-abietane diterpenoids (±)-villosin C (5) and (±)-teuvincenone B (4) in 11 steps. The A/B/C ring system was assembled via a modified three-step sequence on gram-scale, while the D ring was constructed by intramolecular iodoetherification. This synthesis relied largely on the rational design of the order for oxidation state escalation (C6/11/14 → C7 → C12 → C17), which was realized through sequential benzylic iodination/Kornblum oxidation, Siegel–Tomkinson C–H oxidation and iodoetherification. In addition, villosin C (5) and its epimer (5a) were found to have indistinguishable NMR data and the correct configuration for villosin C was elucidated by comparing HPLC trace with a natural sample.