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Synthesis of Indazoles by Cycloaddition of Diazo Acetates with Arynes
Z. Liu, F. Shi, P. D. G. Martinez, C. Raminelli, R. C. Larock*
Iowa State University, Ames, USA
19 March 2008 (online)
The [3+2] cycloaddition reaction of arynes, in situ generated from o-(trimethylsilyl)aryltriflates, with diazoacetates to furnish indazoles is reported. Performing the reaction at -78 °C with TBAF leads to the desired indazoles A but executing the reaction at room temperature with CsF leads to further arylation of the indazoles to furnish products B. Using various silyl aryl triflates, the reactions with ethyl or methyl diazoacetate gave products generally in good to excellent yields, except for the electron-poor difluorosubstrate (R3 = 4,5-diF, 45% yield). With disubstituted diazomethanes, of the two possible products, C and D, product D was observed to be predominant. The electron-poor substrate (R3 = 4,5-diF) led only to a complex mixture. The substrate scope was well studied within the limits of available diazoacetates and TMS triflates.