| abstract |
An isomerization method wherein a compound of formula ##STR1## wherein X and y together form a 3-oxo radical, or X is a hydrogen atom and Y is either a radical a ##STR2## where R 2 is OH or O-acyl, or an O-alkyl or NH 2 radical; R 1 is a hydrogen atom or a methyl radical; Z is hydrogen or an acyl radical; and R is a hydrogen atom, an NH 2 radical or a (CH 2 ) n Ar, NH(CH 2 ) n Ar or N═CH(CH 2 ) n Ar radical, in the form of a 10α isomer or a mixture of 10α and 10β isomers, is exposed to a basic agent to give the corresponding compound of formula I in which the 10-methyl radical is in the β position. |