Piperazines as Model Substrate for Oxidations. -A high tendency of polymerization is observed when piperazine derivatives are oxidized by mercury-EDTA. This unusual behavior is caused by means of the reactive cyclic enediamine intermediates as aza-analogous reductones and to the carbonyl compounds resulting from dehydrogenation in the side chain. Monosubstituted piperazines (I) give rise to the formation of piperazinediones (II) in medium yields. Surprisingly, benzhydryl derivative (IV) on oxidation yields a mixture of piperazinedione (V) and monolactam (VI) in addition to a small amount of benzophenone (VII). The bis-substituted piperazines (VIII) and (X) react more differently due to the symmetry and the preferred direction of the dehydrogenation into the cycle. -(MOEHRLE*, H.; AZODI, K.; Pharmazie 61 (2006) 10, 815-822; Inst. Pharm. Chem., Heinrich-Heine-Univ.,
Hg(II)-EDTA-dehydrogenation of benzylpiperazine (5) in 50% ethanol with addition of diethyl acetylenedicarboxylate (2) to a minor extent gives rise to (piperazine-1,4-diyl)-bis(maleate) (9), which is inert to Hg(II)-EDTA and results in quantitative yield when Hg(II)-EDTA is omitted. 4-Benzylpiperazin-1-yl)-monomaleate (8) reacts with 2 in various solvents by addition of water with dealkylation and formation of 9. CH-acidic compounds may also be used as proton donors. Analogous reactions, although with minor yields, occur with the propiolates 11 and 12. 1-Substituted piperazines with benzyl, methine or allylic groups (5 -5c, 27d -g, and 27h) react readily with acetylenedicarboxylic acid esters to give compounds of type 9, whereas benzhydryl, aromatic and most of the unbranched aliphatic substituents are not replaced. The reactivity of 1,4-disubstituted piperazines corresponds largely to the behaviour of the substituents in the monosubstituted derivatives.
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