Ruthenium(II)‐Catalyzed C−H Difluoromethylation of Ketoximes: Tuning the Regioselectivity from the <italic>meta</italic> to the <italic>para</italic> Position.

Abstract: A highly <italic>para</italic>‐selective C_Ar−H difluoromethylation of ketoxime ethers under ruthenium catalysis has been developed. A wide variety of ketoxime ethers are compatible with the reaction, which leads to the corresponding <italic>para</italic>‐difluoromethylated products in moderate to good yield. A mechanistic study clearly showed that chelation‐assisted cycloruthenation is the key factor in the <italic>para</italic> selectivity of the difluoromethylation of ketoxime ethers. Density functional theory was used to gain a theoretical understanding of the <italic>para</italic> selectivity.# [ABSTRACT FROM AUTHOR]