Collect. Czech. Chem. Commun. 1983, 48, 937-955

Hydrogenolytic opening of 4,4-dimethyl-4a,5-epoxy-a-homocholestane derivatives and mass spectra of some reaction products

Helena Velgová and Antonín Trka

Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague 6


The hydrogenolytic opening of the epoxide ring of all four stereoisomeric 3-acetoxy-4,4-dimethyl-4a,5-epoxy-A-homocholestanes was investigated. The reaction proceeds at the more substituted carbon atom C(5), giving rise to 4a-hydroxy-5,6-unsaturated derivatives. The hydrogenation of the 5,6-double bond of these allylic alcohols affords 4,4-dimethyl-A-homo-5β-cholestane derivatives. The mass spectra of 3,4a-diketones XI and XVII and 4a-ketones XVI and XXVIII to XXX were also studied. In the case of the saturated diketone XVII it was observed that the most abundant metastable peak corresponds to a two-step fragmentation process. The decomposition of the molecular ion of the unsaturated diketone XI is associated with ring A expansion. The mass spectra of 3-acetoxy ketones XVI and XXVIII are characterized by an elimination of a C4H8 molecule from the contracted ring A of the ion [M-CH3COOH]+. The unexpected elimination of the species C6H11, C6H12, and C6H13 from the ring A of the molecular ions of 3-hydroxy ketones XXIX and XXX is shown to be preceded by hydroxyl migration and ring A rearrangement.