Stereoselective Total Synthesis of Formosanol, Tsugacetal, and Methyl ß-Conidendral.

The first enantioselective total synthesis of aryltetralin lignan acetals, (-)-formosanol, (+)-tsugacetal, (+)-methyl ß-conidendral, and their enantiomers have been accomplished on the basis of the Pd-catalyzed asymmetric allylic cycloaddition as a key step. Six stereoisomers of the lignan acetals have been synthesized via a 7-8 step sequence in up to 14% overall yield. The in vitro cytotoxicity against several cancer cells has preliminarily been examined for the obtained six stereoisomers of lignan acetals.