Azines, which are six-membered aromatic compounds containing one or more nitrogen atoms, serve as ubiquitous structural cores of aromatic species with important applications in biological and materials sciences. Among a variety of synthetic approaches toward azines, C–H functionalization represents the most rapid and atom-economical transformation, and it is advantageous for the late-stage functionalization of azine-containing functional molecules. Since azines have several C–H bonds with different reactivities, the development of new reactions that allow for the functionalization of azines in a regioselective fashion has comprised a central issue. This review describes recent advances in the C–H functionalization of azines categorized as follows: (1) SNAr reactions, (2) radical reactions, (3) deprotonation/functionalization, and (4) metal-catalyzed reactions.

•Direct and equimolar coupling of arenes and imides•Step-/atom-economical and straightforward access to privileged arylamine structures•Photoredox ruthenium catalysis under blue-light irradiation•Electrochemistry-based kinetic analysis uncovers details of the reaction mechanismIt is important to develop new strategies to confer functionality on aromatic molecules. A representative example is installation of the amino group into arenes to form arylamines, which are found ubiquitously in various functional molecules such as materials, pharmaceuticals, and natural products. The ideal transformation is a dehydrogenative-type coupling because no pre-functionalization of both arenes and amines is required. Our methodology enables direct installation of sulfonimide into a variety of arenes through photoredox catalysis. Electrochemical analysis uncovers a detailed reaction mechanism that will be the next standard protocol for the mechanistic study of photoredox-mediated reactions. In addition, this methodology provides an additional route not only to aromatic sulfonimides with unknown properties but also to key intermediates for functional arylamines, which will accelerate the study of material and biological science.In light of the importance of arylamine derivatives in organic materials, pharmaceuticals, and agrochemicals, the development of efficient aromatic C–H amination has long been sought after. Although many attempts have been made to achieve dehydrogenative C–H amination, the low reactivity of simple arenes renders equimolar coupling with amine derivatives a formidable task in synthetic chemistry. Herein, we report equimolar C–H/N–H coupling of arenes and sulfonimides through dehydrogenative aromatic imidation. This was accomplished by means of a ruthenium-based photoredox mediator that employed the arene as the limiting reagent. A wide range of arenes, such as polycyclic aromatic hydrocarbons and heteroarenes, as well as a variety of sulfonimides, were applicable to the reaction. This electrochemistry-based mechanistic study has uncovered that the coupling reaction is initiated by the oxidation of sulfonimides by the ruthenium catalyst.Download high-res image (162KB)Download full-size image

C–H amination is the most powerful method to directly add nitrogen functionalities into a variety of arenes including biology- and materials-oriented molecules. Recent developments in aromatic C–H amination chemistry have enabled the conversion of unactivated arenes into a range of arylamine derivatives without using directing groups or excess amounts of arenes. The key for such successful transformations is the catalytic generation of nitrogen or arene radical intermediates. In this perspective, we discuss recent developments in the radical C–H amination of aromatic molecules. We believe the resulting arylamines, which are hitherto difficult to access, will exhibit unexplored functions for biological and materials application.

C–H amination is the most powerful method to directly add nitrogen functionalities into a variety of arenes including biology- and materials-oriented molecules. Recent developments in aromatic C–H amination chemistry have enabled the conversion of unactivated arenes into a range of arylamine derivatives without using directing groups or excess amounts of arenes. The key for such successful transformations is the catalytic generation of nitrogen or arene radical intermediates. In this perspective, we discuss recent developments in the radical C–H amination of aromatic molecules. We believe the resulting arylamines, which are hitherto difficult to access, will exhibit unexplored functions for biological and materials application.