SYNTHESIS, CRYSTAL AND MOLECULAR STRUCTURE, AND HYPERCONJUGATION OF THE ISOMERIC 17,20-EPOXY-17-PICOLYL DERIVATIVES OF 5-ANDROSTENE AND 5α-ANDROSTANE

Article abstract of DOI:10.1016/S0040-4020(01)89997-X

Three pairs of isomeric 17,20-epoxy-17-picolyl-derivatives of 5-androstene and 5α-androstane (3 - 8) have been prepared by an oxidation of 3β-acetoxy-17-picolinylidene-androst-5-ene (2) and 3β-acetoxy-17-picolinylidene-5α-androstane (2) with in situ prepared Cr(VI) oxide-pyridine-complex in methylene chloride at room temperature.X-Ray structural analysis of the suitably crystalline epoxides 5 and 6 revealed the structure of 5 being 17α,20α-epoxide, while structure of 6 corresponded to 17β,20β-epoxide.It was proved that in both cases E-geometrical isomers were formed.Based on the deduced absolute stereochemistry of 5 and 6, the structures of other two pairs (3-4, 7-8) were readily worked out by NMR-spectroscopy.A mechanism of the oxidation reaction was proposed, and some other relevant chemical experiments were described.Finally, an explanation was offered for the observed differences of the relevant bond lenghts and dihedral angles in 5 and 6 which indicated a slight ? - ? conjugation between the epoxide and the pyridine rings, which might be coupled with long range effect of the C-7 carbonyl group.