Pirrung MC.
* University of California, Berkeley, USA
Total Synthesis of (±)-Isocomene.
J. Am. Chem. Soc. 1979;
101: 7130-7131
Key words
(±)-isocomene - Stork–Danheiser transposition - [2+2] photocycloaddition - Wittig
olefination - Wagner–Meerwein rearrangement
Significance
Isolated from rayless goldenrod (Isocoma wrightii) in 1977, (±)-isocomene possesses an intriguing tricyclic carbon skeleton containing
four adjacent stereocenters, three of which are quaternary. These structural features
render the natural product a challenging target for synthesis. Pirrung was able to
access isocomene in seven steps starting from commercially available 2-methylcyclohexa-1,3-dione.
His strategy features an intramolecular [2+2] photocycloaddition to install three
contiguous quaternary stereocenters and a Wagner–Meerwein rearrangement to furnish
the tricyclic core.
Comment
Starting from commercially available 2-methylcyclohexa-1,3-dione (A), cyclohexenone E was accessed using a Stork–Danheiser transposition. Irradiation of the enone effected
intramolecular [2+2] photocycloaddition to furnish cyclobutane F containing three adjacent quaternary stereocenters. Treatment of intermediate G with acid effected a Wagner–Meerwein rearrangement to give (±)-isocomene in excellent
yield.
