The stereochemistry of the 1,3-dipolar cycloadditions of diazomethane to pseudoguaianolides
作者:Adriana Ortiz-León、J. Martín Torres-Valencia、J. Jesús Manríquez-Torres、José G. Alvarado-Rodríguez、Carlos M. Cerda-García-Rojas、Pedro Joseph-Nathan
DOI:10.1016/j.tetasy.2017.01.009
日期:2017.2
The 1,3-dipolar cycloaddition of diazomethane to the sesquiterpene lactones, parthenin, coronopilin, and psilostachyin, gave their respective spiropyrazolines with complete chemoselectivity, while the diastere-oselectivity 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% diastere-oselectivity 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. (C) 2017 Elsevier Ltd. All rights reserved.