Total Syntheses of (+)-Thyrsiferol, (+)-Thyrsiferyl 23-Acetate, and (+)-Venustatriol

Article abstract of DOI:10.1021/jo00304a022

The first total syntheses of (+)-thyrsiferol (1), (+)-thyrsiferyl 23-acetate (3), and (+)-venustatriol (5) have been accomplished in a stereoselective manner.An effective synthetic scheme to construct the BC ring system, which adopts a chair/twist-boat conformation, was first developed by means of a model study.This method involves stereoselective formation of the strained C ring by intramolecular attack of the C7-hydroxyl group at the C3-postion of the 2,3-epoxy alcohol, employing titanium tetraisopropoxide as an acidic activator.Based on the information accumulated in the model study and retrosynthetic considerations, the total syntheses of 1,3, and 5 were performed in the sequence of (1) construction of the BC ring system equipped with a C1-C6 carbon unit, (2) elongation of the C17-C24 carbon chain, (3) formation of a D ring through the stereoselective epoxidation of the 4-en-1-ol system and successive cyclization, and (4) construction of the A ring by bromonium ion induced cyclization of the 4-en-1-ol system.