Photocatalytic transition-metal-free direct 3-alkylation of 2-aryl-2H-indazoles in dimethyl carbonate

Abstract

A general transition-metal-free photocatalytic decarboxylative 3-alkylation reaction of 2-aryl-2H-indazoles was developed under visible-light irradiation under mild conditions. By employing dimethyl carbonate as a green solvent, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) as an inexpensive photocatalyst, and alkyl N-hydroxyphthalimide esters as alkylating reagents, various primary, secondary, and tertiary alkylated 2-aryl-2H-indazoles were synthesized in moderate to good yields. Moreover, the protocol was successfully applied to the late-stage modification of drug molecules.