RUTHENIUM-CATALYZED SYNTHESIS OF PIPERAZINES

An alternate approach to the synthesis of the piperazine ring would be to consider the simple condensation of a 1,2-diol with a 1,2-diamine. In view of the potential pharmaceutical interest of piperazines, we decided to study this reaction in more detail. In a first stage, the catalyst effect on the synthesis of piperazine (R//1 equals R//2 equals R//3 minus R//4 equals H) from the condensation of ethylene glycol and ethylenediamine was established. It is clear that ruthenium catalysis is essential to the reaction. The best catalyst is Ru//3(CO)//1//2. The presence of a suitable phosphine helps the reaction, the basic uncrowded tri-n-butylphosphine being the most efficient.