First diastereoselective synthesis of (-)-methyl thyrsiflorin A, (-)-methyl thyrsiflorin B acetate, and (-)-thyrsiflorin C

An efficient procedure for the synthesis of scopadulan diterpenes, using (+)-podocarp-8(14)-en-13-one 13 as starting material, is reported. This procedure has been used for the diastereoselective synthesis of (-)-methyl thyrsiflorin A (8), (-)-methyl thyrsiflorin B acetate (9), and (-)-thyrsiflorin C (7). Key steps in our strategy are the intramolecular cyclopropanation of diazoketone 19 and the regioselective cleavage of the cyclopropane ring.