Copper-Catalyzed Borylative and Silylative Cyclization of Isocyanides to Indoles

Significance

A method for the synthesis of 2-borylindoles via copper(I)-catalyzed borylative cyclization of 2-alkenylphenyl isocyanides with B₂pin₂ is presented. The reaction is tolerant of functional groups, such as Br, CN and CO₂R; however, the resulting pinacolboranes are sensitive to column chromatography (yields after NMR analysis are given). After filtration and evaporation of the solvent, the borylated products were subjected to Pd-catalyzed cross-coupling reactions. The method was further extended to the synthesis of 2-hydride indole and 2-silyl indoles (2-SiMe₂Ph) by using appropriate reagents (HBpin and pinB-SiMe₂Ph, respectively). The yields from all the above-mentioned reactions range from moderate to excellent. Substrate scope was well studied.