Ni-Catalyzed Reductive Ring Contraction via Desulfurative Cross-Coupling.

The construction of C-C bonds by contractive "deletion" of the sulfur atom from a C-S-C motif is a useful transformation for the synthesis of complex heterocycles. The transformation allows a user to take advantage of the nucleophilic reactivity of sulfur (e.g., for SNAr reactions) and remove that temporary atom at a late stage. A few homogeneous metal systems have been reported to mediate such desulfurizations, but under harsh conditions and, due to the formation of stable oligomeric sulfido complexes, without catalytic turnover. Here, we report a catalytic solution using an accessible Ni precatalyst, inexpensive additives, and mild conditions. The method provides rapid access to a broad scope of fused heterocycles. Preliminary mechanistic studies provide insight into key aspects of the transformation, including the order of C-S bond activations, the synergistic effects of the unusual combination of additives, and the fate of the excised sulfur atom.