Pyrazine chemistry. II. Reduction of 3,6-Dibenzylidenepiperazine-2,5-diones

A reinvestigation of the reduction of 3,6-dibenzylidenepiperazine-2,5-dione (1) with zinc and acetic acid established that this reaction gave (Z)-6-benzyl-3-benzylidenepiperazine-2,5-dione (10). When a mixture of acetic acid and hydrochloric acid was used in the reduction, a mixture of trans- (12) and cis-3,6-dibenzylpiperazine-2,5-dione (5) was obtained. Direct catalytic reduction of 3,6-di(2-chloro- benzy1idene)piperazine-2,5-dione (2) to (�)-cis-3,6-di(2-chlorobenzyl)piperazine-2,5-dione (6) was also accomplished.