A Metathesis Route to (+)-Orientalol F, a Guaiane Sesquiterpene from Alisma Orientalis

The synthesis of (+)-orientalol F (1) started with aldehyde 6, which is available from (R)-limonene in two steps. Wittig reaction of 6 with unsaturated ylide 7 to give a tetraene, and subsequent ring-closing metathesis yielded hydroazulene 4, selective epoxidation of which gave epoxy ester 3. After generation of the requisite isopropyl unit and regioselective reductive epoxide opening, the derived dienol 2 was used for the installation of the oxygen bridge through intramolecular oxymercuration followed by oxidative demercuration. The resulting allylic alcohol epimers 15 and 16 were readily converted into the target natural product 1 by oxidation/reduction sequences.