Process for the preparation of an oxazolidinecarboxylic acid which is useful for preparing therapeutically active taxoids

A process for preparing an oxazolidinecarboxylic acid of formula I:

• in which:
• R′ represents a hydrogen atom, an alkali metal or alkaline-earth metal atom, or an alkyl radical having 1 to 4 carbon atoms,
• R1 represents a benzoyl radical or a R2—O—CO— radical in which R2 represents:
• a straight or branched alkyl radical having 1 to 8 carbon atoms, an alkenyl radical having 3 to 6 carbon atoms, a cycloalkyl radical having 3 to 6 carbon atoms, or a cycloalkenyl radical having 4 to 6 carbon atoms, these radicals being unsubstituted or substituted with one or more substituents selected from halogen atoms, hydroxyl radicals, alkyloxy radicals having 1 to 4 carbon atoms, dialkylamino radicals in which each alkyl portion has 1 to 4 carbon atoms, piperidino, morpholino and 1-piperazinyl (unsubstituted or substituted at position 4 with an alkyl radical having 1 to 4 carbon atoms radicals, cycloalkyl radicals having 4 to 6 carbon atoms, alkenyl radicals having 4 to 6 carbon atoms, cyano, carboxyl or alkyloxycarbonyl radicals in which the alkyl portion has 1 to 4 carbon atoms;
• or
• alkyl radicals having 1 to 4 carbon atoms, or alkyloxy radicals having 1 to 4 carbon atoms;
• or
• a saturated or unsaturated nitrogen-containing 5- or 6-membered heterocyclic radical unsubstituted or substituted with one or more alkyl radicals having 1 to 4 carbon atoms;
• R3 and R4, which may be identical or different, represent:
• a hydrogen atom, an alkyl radical having 1 to 4 carbon atoms, an aralkyl radical in which the alkyl portion has 1 to 4 carbon atoms and the aryl portion is substituted with one or more alkoxy radicals having 1 to 4 carbon atoms, or an aryl radical substituted with one or more alkoxy radicals having 1 to 4 carbon atoms;
• or
• R3 represents an alkoxy radical having 1 to 4 carbon atoms, a trihalomethyl radical, or a phenyl radical substituted with a trihalomethyl radical and R4 represents a hydrogen atom;
• or
• R3 and R4 form, together with the carbon atom to which they are attached, a 4- to 7-membered ring;
• wherein the process comprises a selective iodination carried out on a oxazolidinecarboxylic acid ester of formula II:
• in which R′ represents an alkyl radical having 1 to 4 carbon atoms and R1, R3 and R4 are defined as above.