Synthesis of 6,7-Dihydropyrrolo[2,1-c][1,3]thiazino[3,2-a]pyrazine-4(11bH)-(thi)ones from 1,2-Dithiolo-3-(thi)ones

An efficient synthesis of 6,7-dihydropyrrolo[2,1-c][1,3]thi-azino[3,2-a]pyrazine-4(11bH)-(thi)ones from readily available 1,2-di-thiolo-3-(thi)ones and 3,4-dihydropyrrolo[1,2-a]pyrazine is reported. The S2 atom in both monocyclic and fused 1,2-dithioles is selectively replaced by aminomethylene to afford fused, rigid six-membered 1,3-thiazines. The scope of this two-step one-pot reaction was investigated: 1,2-dithiolo-3-ones were more reactive than the corresponding 1,2-dithiole-3-thiones. Optimized reaction conditions and a mechanistic rationale for the ring transformation are presented.