Substituent-controlled site-selective silylation of 2H-indazoles to access silylated 1H-indazoles and 2H-indazoles under transition metal-free conditions

Herein, we report a t-BuONa-promoted method for the site-selective silylation of 2H-indazoles. In our system, the selective silylation of 2H-indazoles to access silylated 1H-indazoles and 2H-indazoles is controlled by substituents. Using SEM ((2-(trimethylsilyl)ethoxy)methyl) as a protecting group, N-SEM 2H-indazoles can be readily deprotected by the base and converted to silylated 1H-indazoles, thus controlling the site-selective silylation. Moreover, this protocol shows broad substrate scope and excellent functional group tolerance. Preliminary experimental studies suggest that silyl radicals are involved in the reaction.