Transition‐Metal‐Free Dehydrogenative N–N Coupling of Secondary Amines with KI/KIO₄

Abstract

A transition‐metal‐free method for the dehydrogenative N–N coupling of secondary amines has been accomplished. This oxidative KI/KIO4 protocol is mild and operationally simple. A diverse range of diphenylamines, carbazoles, and N‐alkylanilines readily undergo N–N homo‐coupling effectively. Notably, the N–N cross‐coupling of two different arylamines is also demonstrated, which provides a straightforward approach to the complex N–N structures.

Cross-dehydrogenative N–N couplings

“…Using metal-free conditions as previously described for the oxidative N–N homocoupling reaction, Jin and co-workers also explored the hetero-coupling scenario. 25 In contrast to Stahl's conditions, the hetero-coupling reaction performed well with equimolar amounts of the two coupling partners, and no homocoupling products seem to have been observed. They described the cross-coupling reaction between carbazoles bearing electron-withdrawing groups and electron-donating groups and bis(4-bromophenyl)amine in good yields ( Scheme 19A ).…”

“…The same year, Yin and Jin also reported a transition-metal-free dehydrogenative N–N bond formation method utilizing a KI/KIO 4 system for the formation of di- and tetra-phenylhydrazines and 9,9-bicarbazoles ( Scheme 11 ). 25 Moreover, under these metal-free conditions, they demonstrated the feasibility of the dehydrogenative N–N hetero-coupling between arylamines and carbazoles (see Section 3). Generally, good yields were obtained, mostly for the electron-rich substrates.…”

Cross-Dehydrogenative N–N Coupling of Aromatic and Aliphatic Methoxyamides with Benzotriazoles

“…Our investigation began with N -methoxybenzamide 1a and benzotriazole 2a as model substrates. Previous literature conditions , utilizing either Cu/O 2 or KI/KIO 4 did not deliver the desired product 3aa (Table , entries 1 and 2). Instead, the starting materials remained completely unreacted, showing no conversion.…”

“…To the best of our knowledge, the only methods that demonstrate some intermolecular hetero-cross-dehydrogenative N–N coupling were reported by Stahl and independently by Jin (2018 and 2019, Scheme ). , These methods however are strictly limited to carbazoles and diarylamines, thereby leaving the N–N dehydrogenative bond forming toolbox almost empty. Hence, there remains a great demand for novel dehydrogenative reactions that allow hetero N–H/N–H coupling of other ubiquitous nitrogen motifs, besides carbazoles and diarylamines.…”

Intramolecular Aromatic C–H Acyloxylation Enabled by Iron Photocatalysis

“…In light of these facts, we think 2-arylbenzoic acids would be ideal substrates to test the photoreactivity of aryl carboxylate–iron­(III) complexes and to develop a new synthetic protocol for the preparation of benzo-3,4-coumarin derivatives. As part of our long-term interest in oxygen- and nitrogen-centered radicals, herein, we describe a radical intramolecular aromatic C–H oxygenation enabled by iron photocatalysis. The advantages of our current method should include room temperature reaction conditions, much lower price of iron than palladium, copper, and ruthenium, and high tolerance to halogen substitutes which would be left untouched.…”