Synthesis of Six‐Membered N‐Heterocycle Frameworks Based on Intramolecular Metal‐Free N‐Centered Radical Chemistry

Abstract

The formation of intramolecular CÀ N bond represents a powerful strategy in organic transformation as the great importance of N-heterocycles in the fields of natural products and bioactive molecules. This personal account describes the synthesis of cyclic phosphinamidation, benzosultam, benzosulfoximine, phenanthridine and their halogenated compounds through transition-metal-free intramolecular oxidative CÀ N bond formation. Mechanism study reveals that NÀ X bond is initially formed under the effect of hypervalent halogen, which is very unstable and easily undergoes thermal or light homolytic cleavage to generate nitrogen radical. Then the nitrogen radical is trapped by the arene to give aryl radical. Rearomatization of aryl radical under the oxidant to provide corresponding N-heterocycle. Under suitable conditions, the Nheterocycles can be further transformed to halogenated N-heterocycles.

Copper-Catalyzed Intramolecular Olefinic C(sp2)–H Amidation for the Synthesis of γ-Alkylidene-γ-lactams

“…The nitrogen-centered, radical-mediated reaction is considered a powerful strategy for dehydrogenative C(sp 2 )–N bond formation, which proceeds via the addition of N-radical species to the π-system of arenes or alkenes, following recovery of the π-system by oxidation or elimination, because it can preclude the use of precious transition-metals or the introduction and removal of directing groups. Over the past few decades, various such processes have been developed [ 20 , 21 , 22 , 23 , 24 ]; however, most of them have been applied to aryl C–H bonds, whereas olefinic C–H aminations are less explored [ 25 ].…”