1,2‐Migration of the Thio Group in Allenyl Sulfides: Efficient Synthesis of 3‐Thio‐Substituted Furans and Pyrroles

The copper-catalyzed cycloisomerization of thioalkynyl ketones 1 a and thioalkynyl imines 1 b allows the efficient synthesis of 3-thio-substituted furans 3 a and pyrroles 3 b, an important class of heterocyclic unit previously inaccessible by standard cycloisomerization techniques. A plausible mechanism for this unusual cascade involves a 1,2-migration of the thio group in the intermediate keto- and iminoallenyl sulfides 2. DMA=N,N-dimethylacetamide.