Total Syntheses of (+)-Stemarin and the Proposed Structures of Stemara-13(14)-en-18-ol and Stemara-13(14)-en-17-acetoxy-18-ol.

An asymmetric and efficient approach for the total syntheses of (+)-stemarin and the proposed structures of stemara-13(14)-en-18-ol and stemara-13(14)-en-17-acetoxy-18-ol are described. The key features of the strategy include a Lewis acid-induced cationic polyene cyclization and an ODI-[5+2] cycloaddition/pinacol-type 1,2-acyl migration cascade.