Cyclometalated Ruthenium Catalyst Enables Selective Oxidation of N -Substituted Tetrahydroquinolines to Lactams.

Herein, we report an unusual α-methylene oxidation of N -substituted tetrahydroquinoline to lactams using the cyclometalated Ru(II)-complex as a catalyst. Cyclic-α-methylene C-H bonds are selectively oxidized under the reaction conditions even in the presence of α-methyl or reactive α-methylene C-H bonds. This methodology is also useful in the late-stage functionalization of pharmaceuticals. Mechanistic study demonstrates that the high-valent Ru(VI)- cis -dioxo species plays an important role in controlling selectivity.