Intramolecular cationic [5 + 2] cycloaddition reactions promoted by trimethylsilyl triflate in 3.0 M lithium perchlorate-ethyl acetate: Application to a formal total synthesis of (±)-isocomene

Abstract

Trimethylsilyl triflate is an effective reagent in 3.0 M lithium perchlorate-ethyl acetate for promoting intramolecular cationic [5 + 2] cycloaddition reactions. A formal total synthesis of the angular triquinane isocomene ( 10) is detailed. Cationic [5 + 2] cycloaddition of quinone monoketal 40 gives rise to tricyclic diketone 35 which is subsequently converted into the known tricyclic ketone 33. Addition of methyl lithium followed by acid-catalyzed rearrangement employing the Pirrung protocol affords (±)-isocomene ( 10).