A proposed total synthesis of a clerodane-type diterpenoid Scaparin C

Abstract

A theoretically feasible synthetic route for Scaparin C, a clerodane-type diterpenoid new-ly discovered in nature is depicted. A Diels-Alder reaction followed by oxidative cleavage of the olefin generates a 1,3,6-tricarbonyl compound as the substrate. Based on the rela-tive reactivities of the three carbonyl groups, the primary aldehyde group is protected as the acetal. It is expected that the right aldol and alkylation reactions take place for the remaining carbonyl groups, collaboratively giving a bi-fused ring system which is the most important constituent of Scaparin C. After deprotection, the primary aldehyde group is connected with the 3-bromofuran through a Friedel-Crafts reaction. Finally, reactions including sequential reduction of the carbonyl groups, selective protection, acylation and oxidation of the alcohols can preserve the diol and the ketone groups needed, intramolec-ularly forming the cyclic acetal and epoxidation of alkene with the m-CPBA completing the synthesis.