A Stereoselective Synthesis of (+)-Piscidic Acid and Cimicifugic Acid L

Alkylation of the lithium enolate of (2S,3S,5S,6S)-dimethoxy-2,3-dimethyl-1,4-dioxane-5,6-dithiocarboxylate using 4-benzyloxybenzyl bromide stereoselectively gave two new stereogenic centres with the carboxylate groups in a cis relationship. Hydrolytic deprotection of this intermediate produced the natural product (+)-piscidic acid. Installation of a cinnamic acid ester at the secondary hydroxy group was followed by selective deprotection to give a mixture of cis/trans cinnamates in a 3:1 ratio. Finally, the natural product cimicifugic acid L was obtained.