The invention relates to an improved process for the synthesis of 13-(N-Boc-.beta.-isobutylserinyl)-14-.beta.-hydroxybaccatin III-1,14-carbonate (I), wherein carbonation of the 1,14-hydroxy groups of the baccatin skeleton is carried out with bis(trichloromethylcarbonate and the 7-hydroxy group is protected with a trichloroacetyl group.