Synthesis of pyrrolo[1,2-a]pyrazine-1,6,7-triones from 3- methylidenepiperazin-2-ones and oxalyl chloride

We previously reported on reactions of heterocyclic enamino ketones with oxalyl chloride, which produced hetareno[e]pyrrole-2,3-diones [1–4] or 4-hetarylfuran2,3-diones [4, 5]. With a view to accumulate more data allowing a priori prediction of one or another path in the above reaction to be made, we have synthesized 1-aryl-3-phenacylidenepiperazin-2-ones Ia and Ib and examined their reaction with oxalyl chloride. The structure of substituted piperazinones seems to be intermediate from the viewpoint of their reaction with oxalyl chloride along one of the two possible pathways.