Abstract
(- )-Silphiperfol-6-ene (10) and (-)-methyl cantabradienate (11) have been prepared in seven steps from (i?)-3-methyl-l-cyclopentenecarboxaldehyde in 13 and 9% overall yield, respectively. Addition of isopentenylmagnesium bromide to imine 22 afforded 65% of aldehyde 14. Oxidation provided acid 15, which was converted to ketene 20, which underwent an intramolecular [2 + 2] cycloaddition
to afford cyclobutanone 13. Mn(III)-based oxidative fragmentation—cyclization of ethynyl cyclobu- tanol 25 provided an efficient route to the key methylenecyclopentanone 12. Addition of
methyllithium and Birch reduction completed the synthesis of (—)-silphiperfol-6-ene 10. Formation of dienyl triflate 29 and palladium-catalyzed carbonylation concluded the first synthesis of (—)- methyl cantabradienate (11).