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.
Synthesis of Polycyclic Frameworks through Iron-Catalyzed Intramolecular [5+2] Cycloaddition
作者:Shaomin Fu、Bo Liu、Yongjiang Liu、Yanhui Zhang、Xiao Wang
DOI:10.1055/s-0037-1610258
日期:2018.9
A concise and efficient approach to the core of the C18/C19 diterpenoid alkaloids and phomopsterone B is reported. Both syntheses share the same iron-catalyzed intramolecular [5+2] cycloaddition to assemble the tricyclo[6.3.1.01,6]]dodecane skeleton. The following approach to the 6/5/6/7 tetracyclic core scaffold of C18/C19 diterpenoid alkaloids features a regioselective Grignard addition/thermal