Method for preparing taxane derivatives

A process for preparing a taxane derivative of formula I:

• ##STR18## in which:
• Ar represents an aryl radical;
• R represents a phenyl radical or a radical R.sub.5 --O-- in which R.sub.5 represents:
• a straight or branched alkyl radical containing 1 to 8 carbon atoms, an alkenyl radical containing 2 to 8 carbon atoms, an alkynyl radical containing 3 to 8 carbon atoms, a cycloalkyl radical containing 3 to 6 carbon atoms, a cycloalkenyl radical containing 4 to 6 carbon atoms, or a bicycloalkyl radical containing 7 to 11 carbon atoms, these radicals being unsubstituted or substituted by at least one substituent selected from a halogen atom and a hydroxyl radical, an alkoxy radical containing 1 to 4 carbon atoms, a dialkylamino radical in which each alkyl portion contains 1 to 4 carbon atoms, a piperidino radical, a morpholino radical, a 1-piperazinyl radical (unsubstituted or substituted in the 4-position by an alkyl radical containing 1 to 4 carbon atoms or by a phenylalkyl radical in which the alkyl portion contains 1 to 4 carbon atoms), a cycloalkyl radical containing 3 to 6 carbon atoms, a cycloalkenyl radical containing 4 to 6 carbon atoms, a phenyl radical, a cyano radical, a carboxyl radical, and an alkoxycarbonyl radical in which the alkyl portion contains 1 to 4 carbon atoms, wherein the cycloalkyl, cycloalkenyl or bicycloalkyl radicals are unsubstituted or substituted by at least one alkyl radical comprising 1 to 4 carbon atoms;
• a phenyl radical unsubstituted or substituted by at least one substituent selected from a halogen atom, an alkyl radical containing 1 to 4 carbon atoms, and an alkoxy radical containing 1 to 4 carbon atoms;
• or
• a saturated or unsaturated nitrogen containing heterocyclic radical containing 4 to 6 members and unsubstituted or substituted by one alkyl radical containing 1 to 4 carbon atoms;
• R.sub.1 and R.sub.2, which are identical or different, represent a hydrogen atom or an alkyl, phenylalkyl, phenyl, alkoxyphenyl, or dialkoxyphenyl radical, or else R.sub.1 and R.sub.2 form, together with the carbon atom to which they are bonded, a ring having from 4 to 7 members;
• R.sub.3 represents an acetyl radical or a protecting group of the hydroxyl functional group;
• and
• R.sub.4 represents a protecting group of the hydroxyl functional group;
• the process comprising esterifying a protected baccatin III or protected 10-deacetylbaccatin III of formula (II):
• ##STR19## in which R.sub.3 and R.sub.4 are defined as above, with an acid of formula (VI):
• ##STR20## in which Ar, R, R.sub.1 and R.sub.2 are defined as above, or with an anhydride or with an activated derivative of this acid.