The stereochemistry and solid state conformation of 1,10β-epoxyachillin

Ass-rum.-The stereochemistry and solid state conformation of the natural guaianolide 1, lO-epoxyachillin [l], isolated from Artemisia ussoana, has been definitively established on the basis of an X-ray analysis. The epoxide ring is oriented and the seven-membered ring shows a chair conformation with the pseudo plane of symmetry through C-7 (guaiane numbering). The lactone ring adopts an envelope conformation with pseudo symmetry plane through C-7, and the qclopentenone ring is almost flat. This geometry is practically identical to that predicted by a computer program for conformational analysis.