(E)-13-(4-Aminophenyl)parthenolide

The title compound, C₂₁H₂₅NO₃ [systematic name: (3aS,9aR,10aR,10bS,E)-3-[(E)-4-(4-aminobenzylidene)-6,9a-dimethyl-3a,4,5, 8,9,9a,10a,10b-octahydrooxireno[2′,3′:9,10]cyclodeca[1,2-b] furan-2(3H)-one] was obtained from the reaction of parthenolide [synonym: 4,5-epoxygermacra-1(10),11(13)-dieno-12,6-lactone] with 4-iodoaniline under Heck reaction conditions. It was identified as the E-isomer (conformation about the exocyclic methylidene C=C bond; the conformation about the C=C bond in the ten-membered ring is also E). The molecule is built up from fused ten-, five- (lactone) and three-membered (epoxide) rings with a 4-aminophenyl group as a substituent. The ten-membered ring displays an approximate chair-chair conformation, while the lactone ring has an envelope conformation with the C atom bonded to the ring O atom as the flap. The dihedral angle between the benzene ring of the 4-aminophenyl moiety and the lactone ring mean plane is 23.50(8)°. In the crystal, molecules are linked via N - H⋯O hydrogen bonds, between the amine group and the lactone and epoxide ring O atoms, forming chains propagating along the b-axis direction. Adjacent chains are linked via C - H⋯O interactions, forming an undulating two-dimensional network lying parallel to the plane (001). The absolute structure of the molecule in the crystal was confirmed by resonance scattering [Flack parameter = 0.03(3)].