Conformations of trans,trans-cycloundecadienes: Molecular-Mechanics Calculations for Cycloundeca-1,4-, -1,5- and 1,6-dienes and X-ray Analysis of Conformationally Disordered (4E,8E)-Cycloundeca-4,8-dien-1-ylmethyl p-Toluenesulfonate at 292 and 160 K

Article abstract of DOI:10.1107/S0108768189004507

Conformations for cycloundeca-1,4-, -1,5- and -1,6- dienes with trans double bonds have been derived by molecular-mechanics calculations.Low-energy conformations of the 1,5- and 1,6-dienes match conformations of the eleven-membered rings in various cytochalasans and dolabellane diterpenoids. (4E,8E)-Cycloundeca-4,8-dien-1-ylmethyl p-toluenesulfonate, C19H26O3S, Mr=334.5, monoclinic, P21/c, z=4, λ(MoKα)=0.7107 A.At 292 K, a=8.457(2), B=11.076(4), c=19.552()A, β=96.65(6) deg, V=1819(1) A3, Dx=1.22 Mg/cm3, μ=0.19 1/mm, R=0.087 for 1638 reflections with I>2.5?(I).At 160 K, a=8.347(3), b=10.967(4), c=19.408(9)A, β=96.03(9) deg, V=1767(1)A3, Dx=1.26 Mg/m3, μ=0.20 1/mm, R=0.049 for 2921 reflections vith I>2.5 ?(I).The eleven-membered ring is conformationally disordered in the crystal at 292 and 160 K.The X-ray results at the lower temperature are compared with the molecular mechanics calculations for cycloundeca-1,5-diene and interpreted in terms of a conformational mixture in which the predominant species are derived from te two lowest-energy conformations of cycloundeca-1,5-diene.The C(sp3)-C(sp3)-C(sp3) angles in the eleven-membered ring are larger than tetraedral, 113.3-116.1(3) deg.