Journal
TETRAHEDRON-ASYMMETRY
Volume 28, Issue 2, Pages 367-373Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.tetasy.2017.01.009
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Funding
- CONACYT-Mexico [238206, 389269]
- PRODEP-Mexico
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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.
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