Process for the preparation of piperazine derivatives

A process for the preparation of a compound of general formula (I)

• wherein
• R1 and R2 represent independently
• C1-6 alkyl with straight or branched chain optionally substituted with aryl group, or
• C2-7 alkenyl group containing 1-3 double bonds, or
• monocyclic, bicyclic or tricyclic aryl group optionally substituted with one or more C1-6 alkoxy, trifluoro-C1-6 alkoxy, C1-6 alkoxycarbonyl, C1-6 alkanoyl, aryl, C1-6 alkylthio, halogen or cyano groups, or
• a monocyclic, bicyclic or tricyclic cycloalkyl group, or
• R1 and R2 together with the adjacent nitrogen atom may form a saturated or unsaturated, monocyclic or bicyclic heterocyclic ring which may contain further heteroatoms selected from oxygen, nitrogen or sulphur atoms comprising reacting the compound of formula (III)
• with a carbamoylchloride of general formula (II)
• wherein R1 and R2 are as described above which comprises carrying out the reaction in a mixture of a solvent and concentrated aqueous solution of an alkali hydroxide at a temperature between 40-100° C. in the presence of a phase transfer catalyst, separating the phases and washing the organic layer then removing the solvent and drying the compound of formula (I) obtained until its weight is constant.