ABSTRACT - 593342 The disclosure relates to a process for preparing morphine-6-glucuronide or a derivative thereof, comprising the steps of: (i) reacting a compound corresponding to formula (I) wherein the variables are as defined in the specification, with a glucuronic acid derivative corresponding to formula (II), in the presence: - of an aromatic solvent that is unsubstituted or substituted with one or more substituents chosen from the group formed by a halogen atom, a group (C1-C4)alkyl and a group (C1-C4)alkyloxy, said solvent having a melting point of less than or equal to -20°C, and - of trimethylsilyl trifluoromethanesulfonate； (ii) reacting the product obtained in step (i) with a strong basic agent, and then (iii) recovering the product obtained in step (ii).
