Efficient Benzimidazolidinone Synthesis via Rhodium-Catalyzed Double-Decarbonylative C-C Activation/Cycloaddition between Isatins and Isocyanates

The first decarbonylative cycloaddition of less-strained cyclic ketones (isatins) with isocyanates is reported. Initiated by C-C activation, this distinct [5 - 2 + 2] transformation provides a rapid entry to access various benzimidazolidinone derivatives, and a wide range of isocyanates can be efficiently coupled with broad functional group tolerance. A modified one-pot process combining a Curtius rearrangement and C-C activation was also achieved by using acyl azides as the starting materials. A detailed mechanistic study revealed a surprising double-decarbonylative reaction pathway. The novel reactivity discovered in this basic research is expected to shed light on the development of new heterocycle formation methods through C-C/isocyanate coupling.