Regio‐ and Chemoselective Palladium‐Catalyzed Additive‐Free Direct C─H Functionalization of Heterocycles with Chloroaryl Triflates Using Pyrazole‐Alkyl Phosphine Ligands

Abstract

A series of new pyrazole‐alkyl phosphine ligands with varying cycloalkyl ring sizes that enable additive‐free regio‐ and chemoselective C─H arylation of heterocycles are reported. Excellent α/β selectivity of various heterocycles such as benzo[ b]thiophene, thiophene, furan, benzofuran, and thiazole can be achieved using these ligands, along with excellent chemoselectivity of C─Cl over C─OTf of chloroaryl triflates. Mechanistic studies supported by both experimental findings and density functional theory calculations indicate that the pyrazole phosphine ligands with optimal ring sizes allow the reaction to proceed with a lower energy barrier via a concerted metalation–deprotonation pathway.

Abstract

The Authors report new pyrazole‐alkyl phosphine ligands enabling additive‐free, regio‐, and chemoselective C─H arylation of heterocycles, showing excellent α/β selectivity and unprecedented C─Cl over C─OTf chemoselectivity. Mechanistic studies, supported by experiments and density functional theory calculations, reveal that pyrazole phosphine ligands with optimal ring sizes lower the energy barrier of the reaction proceeding via a concerted metalation‐deprotonation pathway.