Abstract: The invention concerns a method for preparing compounds of formula (I) wherein R represents a hydrogen atom or an allyl radical containing up to 8 carbon atoms, characterised in that it consists in subjecting a compound of formula (II) wherein alc represents the residue of an alkyl radical containing up to 4 carbon atoms to the action of a compound of formula (III): RCONH2, wherein R retains its previous meaning, to obtain the compound of formula (IV) wherein R retains its previous meaning which is subjected to cyclization to obtain the desired product of formula (I).

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.sub.2 is OH or O-acyl, or an O-alkyl or NH.sub.2 radical; R.sub.1 is a hydrogen atom or a methyl radical; Z is hydrogen or an acyl radical; and R is a hydrogen atom, an NH.sub.2 radical or a (CH.sub.2).sub.n Ar, NH(CH.sub.2).sub.n Ar or N.dbd.CH(CH.sub.2).sub.n Ar radical, in the form of a 10.alpha. isomer or a mixture of 10.alpha. and 10.beta. isomers, is exposed to a basic agent to give the corresponding compound of formula I in which the 10-methyl radical is in the .beta. position.

Abstract: A process for the preparation of a compound of the formula ##STR1## comprising reacting 1R, cis 2,2-dimethyl 3-(2-oxopropyl)-cyclopropane-1-carboxylic acid with an alkali metal, alkaline-earth metal or magnesium hypohalite, and oxidizing the 1R, cis 2,2-dimethyl 3-(hydroxy-carboxy-methyl)-cyclopropane-1-carboxylic acid or its salt or lactonic form thereof thus obtained with an oxidizing agent to obtain the compound of formula I and novel intermediates.