TOTAL SYNTHESES OF (+)-THYRSIFEROL, (+)-THYRSIFERYL 2O-ACETATE, AND (+)-VENUSTATRIOL

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 ringby intramolecular attack of the C7-hydroxyl group at the exposition of the 2,3-epoxy alcohol, employing titanium tetraisopropoxide as an acidic activator. Based on the information accumulated in themodel 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-Cm carbon chain, (3) formation of a D ring through the stereoselective epoxidation of the 4-en-l-ol system and successive cyclization, and (4) construction of the A ring by bromoniumion induced cyclization of the 4-en-l-ol system. © 1990, American Chemical Society. All rights reserved.