Sesquiterpenoids. Part XXII. X-Ray crystallographic determination of the stereochemistry and conformation of deacetylneotenulin

Abstract

The stereochemistry of deacetylneotenulin (2) has been defined by X-ray crystal-structure analysis. The hydrogen atom at C(5) is shown to be α- and the hydroxy-group at C(6)β-oriented. The c.d. spectrum has a positive Cotton effect associated with the unsaturated ketone and the C:C·C:O chromophore has right-hand chirality (ω 175°). The cycloheptylidene ring adopts a twist-chair conformation. The crystals are monoclinic, space group P2₁. with a= 7.475(2). b= 7.905(1), c= 12.022(2)Å, β= 93° 26(1)′, and Z= 2. X-Ray data were obtained by diffractometer, and the structure determined by direct phasing methods; least-squares adjustment of the atomic parameters converged to R 4.9% over 1 020 reflections.