Adriana Ortiz-León, J. Martín Torres-Valencia, J. Jesús Manríquez-Torres, José G. Alvarado-Rodríguez, Carlos M. Cerda-García-Rojas, Pedro Joseph-Nathan, Tetrahedron: Asymmetry, 2017, 28 (2), 367?373https://doi.org/10.1016/j.tetasy.2017.01.009
The 1,3-dipolar cycloaddition of diazomethane to the sesquiterpene lactones, parthenin, coronopilin, and psilostachyin, gave their respective spiropyrazolines with complete chemoselectivity, while the diastereoselectivity in favour of the (11S)-stereoisomer was 86?98%. Similarly, mexicanin I acetate, helenalin, and helenalin acetate provided the (11R)-diastereoisomer. When helenalin and its acetate were treated with a large excess of diazomethane, they afforded their respective dipyrazolines with 98% diastereoselectivity in favour of the (2R,3S,11R)-diastereoisomer. All compounds were characterized by their physical and spectroscopic properties and their absolute configuration was established by X-ray diffraction analysis calculating the Flack and Hooft parameters.