Short and Stereoselective Total Synthesis of A-11,13-Didehydroguaianes and-guaianolides: Synthesis of (±)-Achalensolide and (±)-Pechueloic Acid;Revision of the Structure of (+)-Rupestonic Acid

摘要

(±)-Pechueloic acid (1), (±)-rupestonic acid (3), and (±)-achalensolide (5) (guaian-8-12-olide class) were preparedstereoselectively in only nine steps from the commerciallyavailable tropylium cation via central intermediate 6, whichis used as a general and efficient precursor to bicyclo[5.3.0]-decane sesquiterpenes. The method does not require func-tion protection. It is highly regio- and stereoselective thanks to an efficient C-1 epimerization, a selective C-8,9 hydrogen-ation, and a stereocontrolled 1,6 conjugate addition of an ac-rylate equivalent. These 4-11,13-didehydroguaianes and-guaianolides are good Michael acceptors and hence biolo-gically active.