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

摘要

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). (C) 1997 Elsevier Science Ltd. [References: 23]