Pyrazine chemistry. Part VIII. Oxidations involving 3-arylmethylene-piperazine-2,5-diones

Abstract

Oxidations of 3-benzylidenepiperazine-2,5-diones with singlet oxygen, lead(IV) acetate, and t-butyl hypochlorite have been studied. Cleavage of the benzylidene group occurs with singlet oxygen, via formation of a dioxetan. Diacetoxylation is effected by lead(IV) acetate; the 3-acetoxy-group is particularly labile under acidic conditions, and can be substituted by hydroxy-, alkoxy-, mercapto-, and hydroperoxy-groups. Evidence for acylimine formation during oxidation is presented. For example, with t-butyl hypochlorite chlorination of the α-position occurred with formation of the reactive acylimine (29); reactions of such species and its precursors included an acid- or base-catalysed rearrangement into 6-substituted pyrazines.