The iridoid glycoside asperuloside has been converted by both oxidative and reductive routes to optically active prostanoid intermediates. The enol ether group was oxidized to a lactone by I2/PDC followed by in situ reduction of the iodo lactone with thiosulfate. Hydrolysis and decarboxylation then gave the 11-homologue of the Corey lactone aldehyde. Wadsworth-Emmons reaction of this added the lower side chain as expected. Alternatively, tetrahydroasperuloside was converted to a tetracyclic acetal by acid treatment. This was selectively cleaved by acetyl chloride/TiCl4 to a hemiacetal which underwent Wadsworth-Emmons reaction, followed by oxidation and decarboxylation to give the same intermediate prepared by the lactone route.
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