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Silica-Supported Palladium-Catalyzed Synthesis of Indole Derivatives
H. Sakai, K. Tsutsumi*, T. Morimoto, K. Kakiuchi
Nara Institute of Science and Technology, Japan
22 January 2009 (online)
One-pot, four-step syntheses of indole derivatives using a supported palladium catalyst are reported. Thus, a silica-supported palladium catalyst (PdCl2DPP-Si) was prepared by mixing PdCl2(Ph3P)2 and a commercially available silica-supported phosphine (silicaBond Diphenylphosphine, SILICYCLE Inc.) in refluxing benzene for 24 h. The Sonogashira coupling of 2-iodoanilines 1a with trimethylsilylacetylene (2-TMS) followed by desilylation gave 3-H. The Sonogashira coupling of 3-H with aryl iodides 4a-g gave 3a-k in situ which underwent the successive cyclization to afford the corresponding indoles 5a-k in 11-60% yield (11 examples).