title: Regio- and stereocontrolled synthesis of novel steroidal isoxazolines: a new route to the formation of selectively modified steroid side chains.
abstract: 1,3-Dipolar cycloaddition reaction of acetonitrile oxide to cis- and trans-22-hydroxy-24-alkoxycarbonyl-Δ(23)-steroids is investigated. An unusual stereochemical course of the cycloaddition, leading to the same set of the isoxazoline adducts for both (Z)- and (E)-disubstituted olefins is revealed. It is shown, the reaction is regioselective and all possible 4',5'-diastereoisomers of resulting isoxazolines can be prepared as major products by cycloaddition to the suitable alkene. The structure of the key compounds is confirmed by X-ray and 2D NMR analysis.
authors.affiliation: Institute of Bioorganic Chemistry, Laboratory of Steroid Chemistry, National Academy of Sciences of Belarus, BY-220141 Minsk, Belarus.
authors.forename: Halina
authors.initials: H
authors.lastname: Zhylitskaya
authors.forename: Raisa
authors.initials: R
authors.lastname: Litvinovskaya
authors.forename: Alexander
authors.initials: A
authors.lastname: Baranovsky
authors.forename: Václav
authors.initials: V
authors.lastname: Eigner
authors.forename: Bohumil
authors.initials: B
authors.lastname: Kratochvíl
authors.forename: Pavel
authors.initials: P
authors.lastname: Drašar
authors.forename: Vladimir
authors.initials: V
authors.lastname: Khripach
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D060406:Brassinosteroids / Q000138:chemical synthesis*; D061565:Cycloaddition Reaction; D007555:Isoxazoles / Q000138:chemical synthesis*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D013237:Stereoisomerism
chemical_list: D000097:Acetonitriles; D060406:Brassinosteroids; D007555:Isoxazoles; C544154:acetonitrile oxide
keywords: Brassinosteroids; Isoxazolines; Nitrile oxides