Iodine-catalyzed aerobic oxidation of o-alkylazoarenes to 2H-indazoles

Efficient synthesis of 2-aryl-2H-indazoles by base-catalyzed benzyl C-H deprotonation and cyclization

A straightforward and efficient method for the preparation of 2-aryl-2H-indazoles from ortho-alkyl substituted azoxybenzenes is presented. The reaction proceeds through base-catalyzed benzyl C-H deprotonation and cyclization to afford 2-aryl-2H-indazoles in good yields. This synthetic strategy can be applied to the construction of several fluorescent and bioactive molecules.

Access to 2-substituted-2H-indazoles via a copper-catalyzed regioselective cross-coupling reaction

A CuCl catalyzed C-N cross-coupling reaction using commercially available 1H-indazoles with diaryliodonium salts is described. The methodology features ample structural versatility, affording 2-substituted-2H-indazole in good yields and complete N(2)-regiocontrol. Furthermore, the utility of the reaction was demonstrated in the synthesis of a known estrogen receptor β agonist. Mechanistic studies using density functional theory calculations suggested that the complete regioselectivity can be attributed to the only weak base TfO^- in our system which could not deprotonate indazoles, and the catalyst oxidation process would be the rate-determining step.