Cobalt(II)-Catalyzed Proficient Synthesis of Enaminones from Aryl Alkenes and Amines

Abstract

A simple, cost-effective, and modular strategy has been developed to synthesize synthetically and pharmaceutically active enaminones by oxidative amination of aryl alkenes with amines and CHCl₃, using tert-butyl hydroperoxide as an oxidant. We describe the synthesis of enaminones from vinyl arenes and sterically hindered N,N-diisopropylethylamine (DIPEA) by employing an Earth-abundant cobalt salt as a catalyst within a very short reaction period for the first time. Furthermore, nitrogen- and oxygen-containing heterocyclic compounds have been synthesized from these highly functionalized enaminones. Moreover, various control experiments, such as radical trapping reaction, along with a Hammett analysis with various types of substituents on the styrene ring unraveled the detailed mechanism of this reaction pathway.