The structure and conformation of umbellifolide, a 4,5-secoeudesmane derivative

Abstract

Umbellifolide (3) is the first 4,5-secoeudesmane derivative discovered in nature. Its structure and conformation have been determined by physical methods, including X-ray analysis. Umbellifolide, both in solution and in the solid state, exists as a θ= 60° boat cyclohexanone rotamer. The exo-methylene γ-lactone group, cis-closed at C(8), is almost planar and belongs to the pseudo-rotational P-type. The X-ray determination was based on 1 047 diffractometer intensities and the least-squares refinement converged to R= 0.046. A possible biogenesis of umbellifolide from a Δ^4,5-eudesmane precursor (5)via fragmentation of 4-hydroxy-5-hydroperoxyeudesmane intermediates is proposed.