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.

Automated summary

Herein, we describe a t-BuONa-promoted method for the site-selective silylation of 2H-indazoles. Control over the silylation site is achieved through substituents. Using SEM as a protecting group, the N-SEM 2H-indazoles can be easily deprotected and converted to silylated 1H-indazoles. This protocol shows broad substrate scope and excellent functional group tolerance, with preliminary experimental studies suggesting the involvement of silyl radicals in the reaction.