On heating with alkynes, the readily prepared 1,3-dithioles 3 undergo a new cycloaddition reaction and an unprecedented molecular rearrangement with loss of chlorine to give the first 7H-thieno[2,3-c]thiopyran-7-thiones 4 and 4H-thieno[3,2-c]thiopyran-4-thiones 5 whose structures were confirmed by X-ray diffraction. Unexpectedly, the different alkynes used to form 3 and to convert it into 4 and 5 were incorporated regiospecifically into the thiophene and thiopyran rings, respectively. [reaction: see text]
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.
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