title: Regio- and stereoselective access to novel ring-condensed steroidal isoxazolines.
abstract: Novel 5α-androstanes containing an isoxazoline moiety condensed to ring A or D were efficiently synthetized by 1,3-dipolar cycloadditions of aryl nitrile oxides to steroidal α,β-unsaturated ketones. During the ring closures, regioisomers in which the O terminus of the nitrile oxide dipoles is attached to the β-carbon of the dipolarophile were formed in a stereoselective manner to furnish exclusively 1α,2α- or 15β,16β-condensed heterocycles. The cyclic enone moiety of the six-membered ring A proved to be less reactive than that of the five-membered ring D, but all the reactions were affected significantly by the substitution pattern of the nitrile oxide. 17-Deacetylation of the primary products resulted in aromatization or simultaneous hydroxylation, depending on the base applied for the ring A-fused heterocycles, while retro-Dieckmann-like fragmentation was observed partially or completely for the ring D-fused analogues during 3-deacetylation.
authors.affiliation: Department of Organic Chemistry, University of Szeged, Dóm tér 8, H-6720 Szeged, Hungary.
authors.forename: Gergő
authors.initials: G
authors.lastname: Mótyán
authors.affiliation: Department of Organic Chemistry, University of Szeged, Dóm tér 8, H-6720 Szeged, Hungary.
authors.forename: Zalán
authors.initials: Z
authors.lastname: Kádár
authors.affiliation: Department of Organic Chemistry, University of Szeged, Dóm tér 8, H-6720 Szeged, Hungary.
authors.forename: Dóra
authors.initials: D
authors.lastname: Kovács
authors.affiliation: Department of Organic Chemistry, University of Szeged, Dóm tér 8, H-6720 Szeged, Hungary.
authors.forename: János
authors.initials: J
authors.lastname: Wölfling
authors.affiliation: Department of Organic Chemistry, University of Szeged, Dóm tér 8, H-6720 Szeged, Hungary. Electronic address: frank@chem.u-szeged.hu.
authors.forename: Éva
authors.initials: É
authors.lastname: Frank
mesh_terms: D061565:Cycloaddition Reaction; D007555:Isoxazoles / Q000138:chemical synthesis* / Q000737:chemistry*; D013237:Stereoisomerism; D013256:Steroids / Q000737:chemistry*; D013379:Substrate Specificity
chemical_list: D007555:Isoxazoles; D013256:Steroids
keywords: 5α-Androstanes; Cycloaddition; Isoxazolines; Regioselectivity; Stereocontrol