Configurational assignment by 13C NMR of stereoisomeric 3-bromo-3-acyl derivatives of 5α- and 5β- androstane

The configurational assignment of stereoisomeric 3-bromo-3-acyl derivatives of steroids in both the 5α and 5β series has been carried out by comparing the ¹³C chemical shifts of C-3. A downfield shift is observed for C-3, bearing a bromine and an acyl group, on going from the isomer with an equatorial bromine to that with an axial bromine. This rule has been established by comparison of the ¹³C chemical shifts of model compounds in 4-tert-butylcyclohexanes of known configuration.