Pd- and Cu-catalyzed C–H arylation of indazoles

The palladium- and copper-catalyzed C–H arylation reactions of 1H- and 2H-indazoles with haloarenes are described. A PdCl₂/phen/Ag₂CO₃/K₃PO₄ catalytic system is effective for the C–H arylation of 1H- and 2H-indazoles with haloarenes, whereas a less expensive CuI/phen/LiOt-Bu catalytic system is applicable to the C–H coupling of substituted 2H-indazoles and iodoarenes. The utility of newly developed catalyst was demonstrated in the rapid synthesis of YC-1 (an antitumor agent) and YD-3 (platelet anti-aggregating agent). These new reactions represent important direct functionalization tools of indazoles, well-known bioisosteres of pharmaceutically important indole core.