Ag-Catalyzed Intramolecular Sequential Vicinal Diamination of Alkynes with Isocyanates: Synthesis of Fused Indole-Cyclic Urea Derivatives.

A formal intramolecular vicinal 1,2-diamination of alkynes is achieved for the synthesis of indole-cyclic urea fused derivatives through a double cyclization process from readily available aminophenyl propargyl alcohols. This sequential triple C-N bond construction event was possible using isocyanate as urea precursor and Ag(I) catalyst as alkyne activating agent. Control experiments reveal that the cyclization, followed by 1,3-allylic amino dehydroxylation, is preceded by urea formation.