Method for the preparation of β-phenylisoserine derivatives of general formula (I) involving the action of an anhydride and hydrogen with a product of general formula (II). The products of general formula (I) are especially useful in the preparation of taxoids having outstanding antitumour properties. In general formulae (I) and (II), Ar is an aryl radical, Ph is a phenyl radical or an optionally substituted α or β-naphtyl, R is a hydrogen atom or an alkyl radical optionally substituted by a phenyl radical and R1 is an optionally substituted phenyl radical or a R2-O radical wherein R2 is an alkyl, alkenyl, cycloalkyl, phenyl or heterocyclyl.