The Thia-Michael Reactivity of Zerumbone and Related Cross-Conjugated Dienones: Disentangling Stoichiometry, Regiochemistry, and Addition Mode with an NMR-Spectroscopy-Based Cysteamine Assay
The cross-conjugated and electrophilic dienonesystem of the humulane sesquiterpene zerumbone (1a) was modified by E/Z photochemical isomerization and/or by removal of homoconjugation with the isolated endocyclic double bond of the medium-sized ring. The site (C-6/C-9), mode (transient or irreversible), stoichiometry (single or twofold), and comparative rates of thiol addition were evaluated using
in terms of the isoprenoid rule, were obtained by modulating the Lewis acid catalyst. In the course of these studies, the surprising formation of a strained E‐cyclooctene motif was observed in a cyclization reaction.