Radical C−H Bond Oxidation Initiated Intramolecular Cyclization of Glycine Esters: Construction of Dihydroquinoline Skeletons

Abstract

An efficient construction of dihydroquinoline derivatives was realized through radical cation salt-initiated CÀ H bond oxidation of unsaturated glycine esters. In the presence of dioxygen, the sp 3 CÀ H bond adjacent to nitrogen was oxidized, followed by cascade cyclization, affording the desired dihydroquinoline products. The mechanistic investigation revealed that a radical intermediate was involved in this reaction.

2,5-Diketopiperazine Catalysts as Activators of Dioxygen in Oxidative Processes

“…Interestingly, whereas a couple of oligopeptides have been reported for their ability to perform epoxidations, these cases were solely relying on the use of hydrogen peroxide as the single oxygen donor of the process (Scheme B) . On the other hand, amino acid derivatives such as 2,5-diketopiperazines (DKPs) and glycine derivatives (Scheme B) have been reported to react in the presence of dioxygen to produce the corresponding hydroperoxides in a number of cases. These hydroperoxides can act as stoichiometric oxidants for sulfides or alkenes. , DKPs were also reported to act as radical mediators for the cross-coupling of arenes (Scheme C) .…”