BIS(CARBODIFLUORO) DERIVATIVE OF ANHYDROPARTHENIN

(3S,6S,6aS,9aR)-6,6a-Difluoromethano-2',2'-difluoro-6,7-dimethyl-2,3,3a,4,5,6,6a,7,8,9,9a,9b-dodecahydrospiro[azuleno[4,5-b]furan-3,1'-cyclopropane]-2,9-dione, C17H16F4O3, M(r) = 344.31, monoclinic, C2, a = 19.271 (7), b = 6.430 (2), c = 12.456 (4) angstrom, beta = 91.70 (3)-degrees, V = 1542.6 (1) angstrom 3, Z = 4, D(x) = 1.48 g cm-3, lambda(Cu K-alpha) = 1.54178 angstrom, mu = 11.23 cm-1, F(000) = 712, T = 296 K, R = 0.046 for 1020 observed reflections [F(o) > 3-sigma(F(o))]. The X-ray analysis enabled us to correct the configuration of the difluorocyclopropane attached to C(1), C(10) previously assigned on the basis of NMR studies. The configuration is 1S,5R,10S,11S relative to 7S as has been found in most of the pseudoguaianolides isolated so far. Cyclopentenone, cycloheptane and gamma-lactone rings adopt envelope, twist-boat and half-chair conformations, respectively. Average bond length asymmetry in cyclopropane: distal bond 1.570 (6), vicinal bonds 1.474 (5) and 1.441 (6) angstrom. Packing entirely due to van der Waals forces.