title: Ionic liquid-promoted Wagner-Meerwein rearrangement of 16α,17α-epoxyandrostanes and 16α,17α-epoxyestranes.
abstract: Ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim](+)[PF(6)](-)) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim](+)[BF(4)](-)) were found to promote an unusual Wagner-Meerwein rearrangement of steroidal 16α,17α-epoxides leading to unnatural 13-epi-18-nor-16-one derivatives as the main products. These compounds were isolated in good to excellent yields. 16α-Hydroxy-Δ(13)-18-norsteroids, the results of the usual rearrangement, were obtained as minor components of the reaction mixtures. The ionic liquid [bmim](+)[PF(6)](-) was shown to induce C-ring aromatization of 16α,17α-epoxyestranes due to the formation of HF, the hydrolysis product of [PF(6)](-). Increasing amounts of HF and [PO(2)F(2)](-) were detected by (19)F and (31)P NMR when the ionic liquid was reused. The structures of the steroidal products, 16-oxo-18-nor-13α-steroid derivatives, 16α-hydroxy-Δ(13)-18-norsteroids, and C-aromatic compounds were determined by two-dimensional NMR techniques and high-resolution mass spectrometry (HRMS). The ionic liquids were recirculated efficiently.
authors.affiliation: Department of Organic Chemistry, Institute of Chemistry, University of Pannonia, Post Office Box 158, H-8201 Veszprém, Hungary.
authors.forename: Anita
authors.initials: A
authors.lastname: Horváth
authors.forename: Ágota
authors.initials: Á
authors.lastname: Szájli
authors.forename: Róbert
authors.initials: R
authors.lastname: Kiss
authors.forename: János
authors.initials: J
authors.lastname: Kóti
authors.forename: Sándor
authors.initials: S
authors.lastname: Mahó
authors.forename: Rita
authors.initials: R
authors.lastname: Skoda-Földes
mesh_terms: D000732:Androstanols / Q000737:chemistry*; D004962:Estranes / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D015394:Molecular Structure; D013237:Stereoisomerism
chemical_list: C412621:1-butyl-3-methylimidazolium hexafluorophosphate; C419324:1-butyl-3-methylimidazolium tetrafluoroborate; D000732:Androstanols; D004962:Estranes; D007093:Imidazoles; D052578:Ionic Liquids