Cu-Catalyzed Oxidative Synthesis of Tetrahydroquinolines from N-Methylanilines

Significance

Miura has previously reported the oxidative coupling of N,N-dimethylanilines with maleimides under manganese catalysis to give tetrahydroquinolines (S. Murata, K. Teramoto, M. Miura, M. Nomura Heterocycles 1993, 36, 2147). Almost two decades later and to the credit of the researchers, the final entry in the table in the 1993 publication describing the utilized CuCl₂ catalyst has been expanded to a full publication. CuCl₂ as catalyst and air as oxidant constitute the optimized conditions. With one exception (benzylidene malononitrile), 1 atm of oxygen led to lower yields of products. The yields range from poor to good, but are generally better than those reported for reactions with the manganese catalyst. The study of the substrate scope was somewhat lacking, for example, reactivity (or non-reactivity) of other electron-deficient alkenes could have been reported.