Palladium (II) catalyzed regioselective lactonization of steroids. Chemoselective construction of novel estrone derivatives

Tetrahedron Letters

Volumn 40, Issue 9, 1999, Pages 1771-1774

  Troisi, L ^a   Vasapollo, G ^a   El Ali, B ^b   Mele, G ^a   Florio, S ^c   Capriati, V ^c  

^a UNIVERSITY OF SALENTO   (Italy)

^b KING FAHD UNIVERSITY OF PETROLEUM AND MINERALS   (Saudi Arabia)

^c UNIVERSITY OF BARI   (Italy)

Author keywords

Epoxides; Lactones; Palladium; Steroids

Indexed keywords

EPOXIDE; ESTRONE DERIVATIVE; PALLADIUM; STEROID;

ARTICLE; CATALYSIS; EPOXIDATION; REACTION ANALYSIS; STEROIDOGENESIS; STEROL ANALYSIS;

EID: 0033605407     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0040-4039(99)00094-5     Document Type: Article

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16. 2) and then heated (110-120 °C). After 24 h the reaction was cooled to room temperature, filtered through Celite and concentrated by rotary evaporation. The separation and the purification of the lactones was achieved by silica gel chromatography and by HPLC. The epoxidation reagent 1 was prepared in situ by literature procedure described in the Ref. 10a. Reagents 2 and 3 were prepared as reported: 2 (Ref. 10b); 3 (Abbotto A., Bradamante S., Florio S., Capriati V. J. Org. Chem. 1997, 62, 8937). The typical experimental procedure for the epoxidation reaction is described in Ref. 10b. The estrone derivatives were identified by elemental analysis, by IR, NMR and MS techniques, and showed satisfactory spectral data [3,8,10].
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18. 13. Patton T. L. J. Org. Chem. 1962, 27, 910. It's worth noting that only for the less polar isomer 8a a NOE was observed between the H-C(19) and the C-18 angular methyl group (Scheme 1). Therefore, this epoxide should be an α-epoxide (i.e. the oxygen of the epoxide ring was α-oriented according to the commonly accepted α- and β-nomenclature in steroids) with the above mentioned groups at the least distance (1.94 Å by molecular modelling). On the other hand, for the more polar isomer 8b, NOEs were observed between the H-C(19) and undefined methylene groups, but no NOEs between these groups and benzothiazolyl hydrogens. For both isomers, the chemical shift range of the methylene hydrogens was always the same with no particular shielding effect. We have also looked at chemical shift evidence. A downfield shift was noticed for the H-C(19) (4.5 vs. 4.3 δ) on going from one isomer to the other. This trend was analogous (4.2 vs. 4.0 δ) to that noticed in similar E configured epoxy picolyl derivatives of 5-androstene on going from a β-to an α-epoxide probably owing to the anisotropy of the C-18 angular methyl group shielding methine epoxy hydrogen when this lies on its same side. Based on this evidence, we believe that our epoxides, belong to the E-series and have opposite configuration at the C-17 and C-19 atoms as depicted in Scheme 1.
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