[Piperazines as model substrate for oxidations]

Piperazines as model substrate for oxidations Piperazine derivatives when being oxidized by mercury-EDTA behave unusually. Due to the reactive cyclic enediamine intermediates as aza-analogous reductones and to the carbonyl compounds resulting from dehydrogenation in the side chain, there exists a high tendency of polymerization. 1-Benzylpiperazines 5a-d generate the piperazine-2,3-diones 8a-d in medium yields. From 1-benzhydrylpiperazine 11 results a mixture of piperazine-2,3-dione 12 and piperazine-3-on 13. The 1,4-bis-substituted piperazines react more differently because of the symmetry and the preferred direction of the dehydrogenation into the cycle. Thus, from 15 and 19 the diones 16 and 20, respectively, were available in very good yields. A mechanism for the reactions is proposed.