Structure and Absolute Configuration of Cyperotundone

Abstract

Cyperotundone, the constituent of nutgrass (Cyperus rotundus (Cyperaceae)), has been shown to have the stereostructure I as follows : Spectral determinations of it and its derivatives revealed the presence of a 2-methyl-3-substituted cyclopent-2-enone system with a methylene αto the carbonyl. The carbon skeleton was established by transformation to the isopatchoulane (VI) derived from patchouli alcohol (VII). The absolute configuration of the C-11 bridge was deduced from the above transformation and a positive Cotton effect of the optical rotatory dispersion of the ketone (X) and that of the C-10 methyl from examination of the NMR methyl signals.